Road Structures Design Manual - Abu Dhabi - Jawdah

ROAD STRUCTURES DESIGN MANUAL

DOCUMENT NO: TR-516

SECOND EDITION

AUGUST- 2021

Document No: TR-516

Second Edition, August-2021

Department of Municipalities and Transport

PO Box 20

Abu Dhabi, United Arab Emirates

© Copyright 2021, by the Department of Municipalities and Transport. All Rights Reserved. This

document, or parts thereof, may not be reproduced in any form without written permission of the

publisher


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TOC SECOND EDITION – AUGUST 2021

TABLE OF CONTENTS

Table of Contents .......................................................................................................................... i

List of Figures .............................................................................................................................. xi

List of Tables............................................................................................................................... xii

Abbreviations and Acronyms ................................................................................................... xiii

1 INTRODUCTION ................................................................................................................. 1

1.1 Overview .......................................................................................................................... 1

1.2 Purpose and Scope .......................................................................................................... 1

1.2.1 General ...................................................................................................................... 1

1.2.2 AASHTO LRFD Bridge Design Specifications ............................................................ 2

1.3 Application of this Manual ................................................................................................. 3

1.3.1 Definition of Road Structures ..................................................................................... 3

1.3.2 Hierarchy of Priority ................................................................................................... 3

1.4 Design Objectives ............................................................................................................. 3

1.4.1 Serviceability ............................................................................................................. 3

1.4.2 Constructability .......................................................................................................... 4

1.4.3 Maintenance of Traffic ............................................................................................... 4

1.4.4 Sustainability ............................................................................................................. 4

1.4.5 Aesthetics .................................................................................................................. 4

1.5 Design Approval Procedures ............................................................................................ 4

1.5.1 Objectives .................................................................................................................. 4

1.5.2 Reference .................................................................................................................. 5

1.6 Structure Design Checklists .............................................................................................. 5

2 LOADS AND LOAD FACTORS .......................................................................................... 6

2.1 General ............................................................................................................................. 6

2.1.1 Limit States ................................................................................................................ 6

2.1.2 Load Factors and Combinations ................................................................................ 7

2.2 Permanent Loads ........................................................................................................... 11

2.2.1 General .................................................................................................................... 11

2.2.2 Down drag (DD) on Deep Foundations .................................................................... 11

2.2.3 Support Settlement (SE) .......................................................................................... 11

2.3 Transient Loads .............................................................................................................. 12

2.3.1 General .................................................................................................................... 12


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2.3.2 Abu Dhabi Vehicular Load (ADVL) ........................................................................... 12

2.3.3 Wind Loads (WS and WL) ....................................................................................... 14

2.3.4 Earthquake Effects (EQ) .......................................................................................... 14

2.3.5 Uniform Temperature (TU) ....................................................................................... 17

2.3.6 Temperature Gradient (TG) ..................................................................................... 17

2.3.7 Live-Load Surcharge (LS) ........................................................................................ 18

2.3.8 Ground Water Levels ............................................................................................... 18

3 STRUCTURAL ANALYSIS ............................................................................................... 19

3.1 Acceptable Methods ....................................................................................................... 19

3.1.1 General .................................................................................................................... 19

3.1.2 Exceptions ............................................................................................................... 19

3.2 Static Analysis ................................................................................................................ 19

3.2.1 Refined Analysis ...................................................................................................... 19

3.2.2 Approximate Analysis .............................................................................................. 20

3.2.3 Lateral Wind-Load Distribution in Multi-Beam Bridges ............................................. 22

3.3 Dynamic Analysis ........................................................................................................... 23

3.3.1 Seismic Analysis ...................................................................................................... 23

3.3.2 Wind-Induced Vibration ........................................................................................... 23

3.4 Transverse Deck Loading, Analysis, and Design ............................................................ 23

4 CONCRETE STRUCTURES ............................................................................................. 24

4.1 Structural Concrete Design ............................................................................................. 24

4.1.1 Member Design Models ........................................................................................... 24

4.1.2 Flexural Resistance ................................................................................................. 24

4.1.3 Shear Resistance .................................................................................................... 26

4.1.4 Strut-and-Tie Model ................................................................................................. 26

4.1.5 Torsion .................................................................................................................... 27

4.1.6 Fatigue .................................................................................................................... 28

4.1.7 Lateral Confinement Reinforcement ........................................................................ 28

4.2 Environmental Classification ........................................................................................... 28

4.2.1 General .................................................................................................................... 28

4.2.2 Classification Criteria ............................................................................................... 29

4.2.3 Chloride Content ...................................................................................................... 31

4.3 Materials ......................................................................................................................... 32

4.3.1 Concrete Strength ................................................................................................... 32


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4.3.2 Reinforcing Steel ..................................................................................................... 32

4.3.3 Prestressing Strand ................................................................................................. 32

4.3.4 Prestressing Bars .................................................................................................... 32

4.4 Reinforced Concrete Structures ...................................................................................... 33

4.4.1 Durability Measures ................................................................................................. 33

4.4.2 Reinforcing-Steel Details ......................................................................................... 33

4.5 Prestressed Concrete Superstructures ........................................................................... 37

4.5.1 Basic Criteria ........................................................................................................... 37

4.5.2 Post-Tensioned Bridges .......................................................................................... 37

4.5.3 Precast, Prestressed Concrete Girders.................................................................... 50

4.5.4 Pretensioned/Post-Tensioned Beams ...................................................................... 57

4.5.5 Camber Diagram ..................................................................................................... 57

4.5.6 Responsibilities ........................................................................................................ 57

5 STEEL STRUCTURES ..................................................................................................... 59

5.1 General ........................................................................................................................... 59

5.1.1 Economical Steel Superstructure Design ................................................................. 59

5.1.2 Rolled Beams vs Welded Plate Girders ................................................................... 60

5.1.3 Economical Plate Girder Proportioning .................................................................... 61

5.1.4 Falsework ................................................................................................................ 64

5.2 Materials ......................................................................................................................... 64

5.2.1 Structural Steel ........................................................................................................ 64

5.2.2 Bolts ........................................................................................................................ 67

5.2.3 Splice Plates ............................................................................................................ 67

5.3 Horizontally Curved Members ......................................................................................... 67

5.3.1 General .................................................................................................................... 67

5.3.2 Diaphragms, Bearings, and Field Splices ................................................................ 67

5.4 Fatigue Considerations ................................................................................................... 68

5.4.1 Load-Induced Fatigue .............................................................................................. 68

5.4.2 Other Fatigue Considerations .................................................................................. 69

5.5 General Dimension and Detail Requirements ................................................................. 69

5.5.1 Deck Haunches ....................................................................................................... 69

5.5.2 Sacrificial Metal Thickness ....................................................................................... 69

5.5.3 Minimum Thickness of Steel Plates ......................................................................... 69

5.5.4 Camber .................................................................................................................... 70


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5.5.5 Diaphragms and Cross Frames ............................................................................... 70

5.5.6 Jacking .................................................................................................................... 74

5.5.7 Lateral Bracing ........................................................................................................ 74

5.5.8 Inspection Access (Tub Girders) .............................................................................. 75

5.6 I-Sections in Flexure ....................................................................................................... 75

5.6.1 General .................................................................................................................... 75

5.6.2 Shear Connectors .................................................................................................... 76

5.6.3 Stiffeners ................................................................................................................. 76

5.6.4 Deck-Overhang Cantilever Brackets ........................................................................ 78

5.7 Connections and Splices ................................................................................................ 78

5.7.1 Bolted Connections.................................................................................................. 78

5.7.2 Welded Connections ................................................................................................ 79

5.7.3 Splices ..................................................................................................................... 80

6 DECKS AND DECK SYSTEMS ........................................................................................ 82

6.1 Concrete Decks .............................................................................................................. 82

6.1.1 Protection of Reinforcing Steel ................................................................................ 82

6.1.2 Empirical Design ...................................................................................................... 82

6.1.3 Traditional Design Using the “Strip Method” ............................................................ 82

6.1.4 Precast Concrete Deck Panels ................................................................................ 83

6.2 Metal Decks .................................................................................................................... 83

6.2.1 Grid Decks ............................................................................................................... 83

6.2.2 Orthotropic Steel Decks ........................................................................................... 83

6.3 Design Details for Concrete Bridge Decks ...................................................................... 84

6.3.1 General .................................................................................................................... 84

6.3.2 Detailing Requirements for Concrete-Deck Haunches ............................................. 85

6.3.3 Reinforcing Steel Over Intermediate Piers or Bents ................................................. 88

6.3.4 Minimum Negative Flexure Slab Reinforcement ...................................................... 88

6.3.5 Crack Control in Continuous Decks ......................................................................... 88

6.3.6 Skewed Decks ......................................................................................................... 89

6.3.7 Temperature and Shrinkage Reinforcement ............................................................ 91

6.3.8 Thickened Slab End Requirements .......................................................................... 91

6.3.9 Phase Constructed Decks ....................................................................................... 91

6.3.10 Stay-in-Place Forms ................................................................................................ 91


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6.3.11 Concrete Deck Pouring Sequence for Decks Constructed Compositely in Conjunction

with Concrete and Steel Girders .............................................................................. 91

6.3.12 Longitudinal Construction Joints .............................................................................. 94

6.3.13 Longitudinal Concrete Deck Joints ........................................................................... 96

6.3.14 Transverse Edge Beam for Steel Girder Bridges ..................................................... 96

6.3.15 Concrete Deck Overhang/Bridge Rail ...................................................................... 96

6.4 Approach Slabs .............................................................................................................. 98

6.4.1 Usage ...................................................................................................................... 98

6.4.2 Design Criteria ......................................................................................................... 98

7 FOUNDATIONS ................................................................................................................ 99

7.1 General ........................................................................................................................... 99

7.1.1 Scope ...................................................................................................................... 99

7.1.2 Design Methodology ................................................................................................ 99

7.1.3 Bridge Foundation Design Process .......................................................................... 99

7.1.4 Bridge Design/Geotechnical Design Interaction ..................................................... 100

7.2 Spread Footings and Pile Caps .................................................................................... 103

7.2.1 Usage .................................................................................................................... 103

7.2.2 Dynamic Load Allowance (Impact Modifier, IM) ..................................................... 104

7.2.3 Thickness .............................................................................................................. 104

7.2.4 Depth ..................................................................................................................... 104

7.2.5 Bearing Resistance and Eccentricity ...................................................................... 104

7.2.6 Sliding Resistance ................................................................................................. 104

7.2.7 Differential Settlement ........................................................................................... 105

7.2.8 Reinforcement ....................................................................................................... 106

7.2.9 Miscellaneous ........................................................................................................ 106

7.3 Deep Foundations ........................................................................................................ 107

7.3.1 General .................................................................................................................. 107

7.3.2 Component Spacing .............................................................................................. 107

7.3.3 Drilled Shafts ......................................................................................................... 107

7.3.4 Driven Piles ........................................................................................................... 112

7.3.5 Pile/Shaft Testing .................................................................................................. 115

7.4 Modelling for Lateral Loading ........................................................................................ 117

7.4.1 Horizontal Movement ............................................................................................. 118

7.5 Mass Concrete ............................................................................................................. 118


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8 ABUTMENTS, PIERS, AND WALLS .............................................................................. 119

8.1 Abutments/Wingwalls ................................................................................................... 119

8.1.1 General .................................................................................................................. 119

8.1.2 General Abutment/Wing wall Design and Detailing Criteria .................................... 120

8.1.3 Seat Abutments ..................................................................................................... 120

8.1.4 Integral Abutments................................................................................................. 121

8.1.5 Semi-Integral Abutments ....................................................................................... 121

8.1.6 MSE Wall Abutments ............................................................................................. 122

8.1.7 Wingwalls .............................................................................................................. 122

8.1.8 Abutment Construction Joints ................................................................................ 123

8.2 Piers ............................................................................................................................. 123

8.2.1 Pier Caps ............................................................................................................... 123

8.2.2 Column Cross Sections ......................................................................................... 124

8.2.3 Column Reinforcement .......................................................................................... 125

8.2.4 Column Construction Joints ................................................................................... 126

8.2.5 Multi-Column Piers ................................................................................................ 126

8.2.6 Single-Column Piers .............................................................................................. 126

8.2.7 Pier Walls .............................................................................................................. 127

8.2.8 Dynamic Load Allowance (DLA) ............................................................................ 127

8.2.9 Moment-Magnification ........................................................................................... 127

8.2.10 Pier, Column, and Footing Design ......................................................................... 127

8.3 Walls (Earth Retaining Systems) .................................................................................. 129

8.3.1 General .................................................................................................................. 129

8.3.2 Responsibilities ...................................................................................................... 130

8.3.3 Types of Earth Retaining Systems ......................................................................... 132

8.3.4 Mechanically-Stabilized Earth (MSE) Walls ........................................................... 134

8.4 Geosynthetic Reinforced Soil (GRS) Walls and Abutments .......................................... 143

9 EXPANSION JOINTS ..................................................................................................... 144

9.1 Design Requirements: Movement and Loads ............................................................... 144

9.1.1 General .................................................................................................................. 144

9.1.2 Estimation of General Design Thermal Movement, T ........................................... 145

9.1.3 Estimation of Design Movement ............................................................................ 145

9.1.4 Setting Temperature .............................................................................................. 146

9.2 Expansion Joint Selection and Design .......................................................................... 146


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9.2.1 General .................................................................................................................. 146

9.2.2 Sheet and Strip Seals ............................................................................................ 146

9.2.3 Modular Expansion Joint ....................................................................................... 147

9.2.4 Steel Finger Joints ................................................................................................. 147

9.2.5 Reinforced Elastomeric .......................................................................................... 147

9.2.6 Silicone Joint Sealant ............................................................................................ 147

9.2.7 Compression and Cellular Seals ............................................................................ 148

9.2.8 Asphaltic Plug Joint (Poured Seals) ....................................................................... 148

9.2.9 Expansion Joints for Asphaltic Overlays ................................................................ 148

9.3 Expansion Joints for Post-Tensioned Bridges ............................................................... 148

9.4 Expansion Joint Design ................................................................................................ 149

10 BEARINGS ..................................................................................................................... 150

10.1 General ......................................................................................................................... 150

10.1.1 Movements and Loads .......................................................................................... 150

10.1.2 Effect of Camber and Construction Procedures ..................................................... 150

10.1.3 Design Thermal Movements .................................................................................. 150

10.1.4 Estimation of Total Design Movement.................................................................... 151

10.1.5 Serviceability, Maintenance, and Protection Requirements .................................... 151

10.1.6 Anchor Bolts .......................................................................................................... 151

10.1.7 Bearing Plate Details ............................................................................................. 152

10.1.8 Levelling Pad at Integral Abutments ...................................................................... 152

10.1.9 Lateral Restraint .................................................................................................... 153

10.2 Bearing Types and Selection ........................................................................................ 153

10.2.1 General .................................................................................................................. 153

10.2.2 Steel-Reinforced Elastomeric Bearings .................................................................. 154

10.2.3 Plain Elastomeric Bearing Pads ............................................................................. 154

10.2.4 High-Load, Multi-Rotational (HLMR) Bearings ....................................................... 155

10.2.5 Polytetrafluoroethylene (PTFE) Sliding Surfaces ................................................... 155

10.2.6 Seismic Isolation Bearings ..................................................................................... 155

10.3 Plain Elastomeric Bearing Pads and Steel-Reinforced Elastomeric Bearings ............... 155

10.3.1 General .................................................................................................................. 156

10.3.2 Holes in Elastomer................................................................................................. 156

10.3.3 Edge Distance ....................................................................................................... 156

10.3.4 Steel-Reinforced Elastomeric Bearings .................................................................. 156


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10.3.5 Design of Plain Elastomeric Bearing Pads ............................................................. 156

10.3.6 Design of Steel-Reinforced Elastomeric Bearings .................................................. 156

11 PEDESTRIAN BRIDGES ................................................................................................ 158

11.1 General ......................................................................................................................... 158

11.2 Live Load ...................................................................................................................... 158

11.2.1 Pedestrian Load (PL) ............................................................................................. 158

11.2.2 Vehicle Load (LL) .................................................................................................. 158

11.3 Wind Load (WS) ........................................................................................................... 158

11.4 Vibrations ..................................................................................................................... 159

11.5 Design .......................................................................................................................... 159

11.5.1 Geometrics ............................................................................................................ 159

11.5.2 Structure Type ....................................................................................................... 159

11.5.3 Seismic .................................................................................................................. 159

11.5.4 Fatigue .................................................................................................................. 159

11.5.5 Detailed Design Requirements .............................................................................. 159

11.5.6 Deflections ............................................................................................................. 160

11.5.7 Steel Connections ................................................................................................. 160

11.5.8 Charpy V-Notch Testing ........................................................................................ 161

11.5.9 Painting/Galvanizing .............................................................................................. 161

11.5.10 Erection ................................................................................................................. 161

11.5.11 Railings/Enclosures ............................................................................................... 162

11.5.12 Drainage ................................................................................................................ 162

11.5.13 Corrosion Resistant Details ................................................................................... 162

11.5.14 Lighting/Attachments ............................................................................................. 162

11.5.15 Maintenance and Inspection Attachments ............................................................. 162

12 CULVERTS ..................................................................................................................... 163

12.1 Reinforced Concrete Boxes .......................................................................................... 163

12.1.1 General .................................................................................................................. 163

12.1.2 Analysis ................................................................................................................. 163

12.1.3 Span-to-Rise Ratios ............................................................................................... 163

12.1.4 Deformations ......................................................................................................... 164

12.1.5 Design Method ...................................................................................................... 164

12.1.6 Dead Loads and Earth Pressure ............................................................................ 164

12.1.7 Live Load ............................................................................................................... 164


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12.1.8 Wall Thickness Requirements ............................................................................... 164

12.1.9 Reinforcement Details ........................................................................................... 165

12.1.10 Skewed Culverts .................................................................................................... 165

12.2 Concrete Arch Culverts ................................................................................................. 165

12.3 Concrete Pipe Culverts ................................................................................................. 166

12.3.1 General .................................................................................................................. 166

12.3.2 Materials ................................................................................................................ 166

12.3.3 Design ................................................................................................................... 166

13 SOUND BARRIERS ........................................................................................................ 167

13.1 Sound Barrier Design ................................................................................................... 167

13.1.1 General Features – Panel Height and Post Spacing .............................................. 167

13.1.2 Wind Loads ........................................................................................................... 167

13.1.3 Lateral Earth Pressure ........................................................................................... 167

14 SIGN AND LUMINAIRE SUPPORTS .............................................................................. 168

14.1 General ......................................................................................................................... 168

14.2 Deformations ................................................................................................................ 168

14.3 Basic Wind Speed ........................................................................................................ 168

14.4 Steel Design ................................................................................................................. 168

14.4.1 Base-Plate Thickness ............................................................................................ 168

14.4.2 Welded Connections .............................................................................................. 168

14.4.3 Bolted Connections................................................................................................ 169

14.4.4 Anchor Bolt Connections ....................................................................................... 169

14.4.5 Bolt Types ............................................................................................................. 169

14.5 Aluminium Design ......................................................................................................... 169

14.6 Prestressed-Concrete Poles ......................................................................................... 170

14.7 Foundation Design........................................................................................................ 170

14.7.1 Geotechnical Design of Drilled Shaft Foundations ................................................. 170

14.7.2 Structural Design of Drilled Shaft Foundations ....................................................... 170

14.8 Design Loads for Vertical Supports ............................................................................... 170

15 ROAD TUNNELS ............................................................................................................ 171

15.1 General ......................................................................................................................... 171

15.2 Definition of Road Tunnels ............................................................................................ 171

15.3 Geotechnical Site Investigations ................................................................................... 172

15.4 Fire Protection .............................................................................................................. 172


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15.5 Constructability ............................................................................................................. 172

15.6 Design Life ................................................................................................................... 172

15.7 Design Considerations .................................................................................................. 173

15.7.1 Design Elements ................................................................................................... 173

15.7.2 Live Load ............................................................................................................... 174

15.7.3 Seismic Considerations ......................................................................................... 174

15.8 Tunnel Types ................................................................................................................ 174

15.8.1 Cut-and-Cover Tunnels ......................................................................................... 174

15.8.2 Mined or Bored Tunnels ........................................................................................ 175

15.8.3 Immersed Tunnels ................................................................................................. 176

15.9 Tunnel Lining ................................................................................................................ 176

16 BRIDGE EVALUATION .................................................................................................. 177

16.1 Load Rating .................................................................................................................. 177

16.1.1 General .................................................................................................................. 177

16.1.2 Importance of Load Rating ..................................................................................... 177

16.1.3 Methodology .......................................................................................................... 177

16.1.4 Thresholds for Re-Rating Existing Bridges ............................................................ 177

16.1.5 Limit States for Load Rating ................................................................................... 177

16.1.6 Dimensions ............................................................................................................ 178

16.1.7 The LRFR Load-Rating Equation ........................................................................... 178

16.1.8 Analytical Methods for the Load Rating of Post-Tensioned Box Girder Bridges ..... 179

16.2 Design Load Rating ...................................................................................................... 179

16.3 Legal-Load Rating and Load Posting ............................................................................ 179

16.3.1 Legal-Load Rating ................................................................................................. 179

16.3.2 Load Posting.......................................................................................................... 180

16.4 Permitting and Permit-Load Rating ............................................................................... 180

16.4.1 Permitting .............................................................................................................. 180

16.4.2 Permit-Load Rating ................................................................................................ 180

16.5 Load Testing of Bridges ................................................................................................ 180

16.5.1 General .................................................................................................................. 180

16.5.2 Load Testing Calculations...................................................................................... 181

16.5.3 Load Testing Method Statement ............................................................................ 181

16.5.4 Load Testing Analysis Report ................................................................................ 183

CITED REFERENCES ................................................................................................................ 184


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INDEX 187

APPENDIX A .............................................................................................................................. 193

LIST OF FIGURES

Figure 2.1: Characteristics of the Design Truck ............................................................................. 12

Figure 2.2: Permit Design Live Loads (for P-13 Vehicle) ............................................................... 13

Figure 2.3: Design Response Spectrum ....................................................................................... 15

Figure 2.4: Positive Vertical Temperature Gradient in Concrete and Steel Superstructures .......... 18

Figure 3.1: Common Deck Superstructures Covered .................................................................... 21

Figure 4.1: Flowchart for Environmental Classification of Structures ............................................. 30

Figure 4.2: Deviator Diaphragm Detail .......................................................................................... 45

Figure 4.3: Inside Corner Detail at Pier ......................................................................................... 45

Figure 4.4: Details at Expansion Joints ......................................................................................... 46

Figure 5.1: Grouping Flanges for Efficient Fabrication (from the AASHTO/NSBA Steel Bridge

Collaboration (15)) ........................................................................................................................ 62

Figure 5.2: Flange Width Transition (Plan View) ........................................................................... 62

Figure 5.3: Drip Plate Detail .......................................................................................................... 66

Figure 5.4: Typical Pier and Intermediate Diaphragm Connection (Rolled Beams) ....................... 72

Figure 5.5: Typical Abutment Diaphragm Connection (Skewed Diaphragm with Rolled Beams) .. 72

Figure 5.6: Typical Pier and Intermediate Cross Frames (Plate Girder Web > 1200 mm) ............ 73

Figure 5.7: Typical Abutment Cross Frames (Plate Girder Web > 1200 mm) ................................ 73

Figure 5.8: Schematic of Location for Deck Overhang Bracket ..................................................... 78

Figure 5.9: Typical Welded Splice Details ..................................................................................... 81

Figure 6.1: Haunch Dimension for Steel Plate Girders .................................................................. 86

Figure 6.2: Haunch Dimension for Steel Rolled Beams ................................................................. 86

Figure 6.3: Haunch Dimension for Concrete ................................................................................. 87

Figure 6.4: Haunch Reinforcement for Deep Haunches (> 100 mm) ............................................. 87

Figure 6.5: Skew Angle and Length/Bridge Width Ratios .............................................................. 90

Figure 6.6: Typical Pour Diagram (Continuous Steel and Precast Girders) ................................... 93

Figure 6.7: Support for Finishing Machine ..................................................................................... 95

Figure 6.8: Transverse Edge Beam .............................................................................................. 97

Figure 7.1: Concrete Backfill Under Stepped Footing.................................................................. 107

Figure 7.2: Drilled Shaft Detail (For Shafts Larger Than Columns) ............................................. 110

Figure 7.3: Drilled Shaft Detail (With Equal Diameter Shaft and Column) .................................. 111

Figure 7.4: Method of Modelling Deep Foundation Stiffness ....................................................... 118


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Figure 8.1: Tops of Drop Caps .................................................................................................... 124

Figure 8.2: Design Criteria for Acute Corners of MSE Bin Walls ................................................. 135

Figure 8.3: MSE Wall Minimum Front Face Embedment ............................................................. 136

Figure 8.4: Broken Backfill with Traffic Surcharge ....................................................................... 138

Figure 8.5: Broken Backfill without Traffic Surcharge .................................................................. 139

Figure 8.6: Proprietary Retaining Walls ....................................................................................... 140

Figure 11.1: Tubular Truss Splice Detail ..................................................................................... 161

LIST OF TABLES

Table 2.1: Load Combinations and Load Factors ............................................................................ 7

Table 2.2: Load Factors for Permanent Loads, p ......................................................................... 10

Table 2.3: Spectral Response Accelerations for the Abu Dhabi Emirate ....................................... 14

Table 2.4: Acceleration Coefficients .............................................................................................. 16

Table 2.5: Site-Class Definitions ................................................................................................... 16

Table 2.6: BDS Procedure “A” Temperature Ranges .................................................................... 17

Table 4.1: Criteria for Substructure Environmental Classifications ................................................ 31

Table 4.2: Chloride Intrusion Rate/Environmental Classifications.................................................. 31

Table 4.3: Compressive Strength of Concrete .............................................................................. 32

Table 4.4: Concrete Cover ............................................................................................................ 34

Table 4.5: Tensile Stress Limits .................................................................................................... 37

Table 4.6: Minimum Centre-to-Centre Duct Spacing (Straight Ducts) ........................................... 39

Table 4.7: Minimum Tendons Required for Critical Post-Tensioned Sections .............................. 42

Table 4.8: Recommended Minimum Duct Radius (for Steel Ducts) ............................................... 43

Table 6.1: Orthotropic-Deck Panel Proportions ............................................................................ 84

Table 7.1: Resistance Factors for Drilled Shafts ......................................................................... 112

Table 7.2: Driven Pile Selection Guide ........................................................................................ 113

Table 7.3: Table of Additional Sacrificial Steel Thickness Required (mm) ................................... 116

Table 8.1: Required Tendons for Post-Tensioned Substructure Elements .................................. 128

Table 8.2: Minimum Centre-to-Centre Duct Spacing ................................................................... 128

Table 9.1: BDS Procedure “A” Temperature Changes ................................................................ 144

Table 9.2: Expansion Joint Selection ......................................................................................... 146

Table 10.1: Summary of Bearing Capabilities ............................................................................. 154


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ABBREVIATIONS AND ACRONYMS

AASHTO American Association of State Highway and Transportation Officials

ACI American Concrete Institute

AD Police Abu Dhabi Traffic Police

ADSC International Association of Foundation Drilling

ADVL Abu Dhabi Vehicular Load

AHT Astronomic High Tide

AISI American Iron and Steel Institute

ASCE American Society of Civil Engineers

ASTM American Society for Testing and Materials

AWS American Welding Society

BCS AASHTO LRFD Bridge Construction Specifications

BDS AASHTO LRFD Bridge Design Specifications

BR Braking Force

Caltrans California Department of Transportation

CANDE Culvert Analysis and Design

CE Centrifugal Force

CIS Cast-in-Situ

CR Creep

CT Truck Collision

CV Vessel Collision

DC Component Dead Load

DCDT Deflected Cantilever Displacement Transducers

DD Down Drag

DL Dead Load

DLA Dynamic Load Allowance

DMA Department of Municipalities and Transport

DMAT Department of Municipal Affairs and Transport

DPB AASHTO Guide Specifications for Design of Pedestrian Bridges

DTI Direct Tension Indicator

DW Wearing Surface Dead Load

EH Horizontal Earth Pressure

EL Locked-In Forces


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EQ Earthquake Effects

ES Earth Surcharge

EV Vertical Earth Pressure

FCM Fracture Critical Member

FHWA Federal Highway Administration

FR Friction

GGBFS Ground Granulated Blast Furnace Slag

GRS Geosynthetic Reinforced Soil

GSBD AASHTO Guide Specifications for LRFD Seismic Bridge Design

HDPE High-Density Polyethylene

HLMR High-Load, Multi-Rotational

HPS High-Performance Steel

IM Impact Modifier

ITS Intelligent Transportation Systems

LL Live Load

LS Live-Load Surcharge

LRFD Load-and-Resistance Factor Design

LRFR Load and Resistance Factor Rating

LVDT Linear Variable Displacement Transducers

MBE AASHTO Manual for Bridge Evaluation

MCFT Modified Compression Field Theory

MHW Mean High-Water Level

MLL Minimum Low-Water Level

MLW Mean Low-Water Level

MRT AASTHO Technical Manual for Design and Construction of Road Tunnels – Civil

Elements

MSE Mechanically Stabilized Earth

NATM New Austrian Tunnelling Method

NCHRP National Cooperative Highway Research Program

NFPA National Fire Protection Association

NHW Normal High-Water Level

NJDOT New Jersey Department of Transportation

NLW Normal Low- Water Level

NSBA National Steel Bridge Alliance


PAGE xv


PCA Portland Cement Association

PCI Prestressed/Precast Concrete Institute

PGA Peak Ground Acceleration

PI Point of Intersection

PL Pedestrian Load

ppm Parts per Million

PS Secondary Forces from Post-Tensioning

PT Post-Tensioned

PTFE Polytetrafluoroethylene

PVC Polyvinyl Chloride

RF Rating Factor

RF Reduction Factor

RSDM Abu Dhabi Road Structures Design Manual

RSF Reinforced Soil Foundations

SE Differential Settlement

SEM Sequential Excavation Method

SH Shrinkage

SSS AASHTO Standard Specifications for Structural Supports for Highways Signs,

Luminaires, and Traffic Signals

T Period

TBM Tunnel Boring Machine

TG Temperature Gradient

TU Uniform Temperature

UPC Urban Planning Council

UV Ultra Violet

WA Water Load

WS Wind Load on Structure

WL Wind on Live-Load


Page 1

01-INTRODUCTION SECOND EDITION – AUGUST 2021

1 INTRODUCTION

1.1 Overview

In 2010, DMAT-DOT (former Abu Dhabi Department of Transport) commenced with the “Unifying

and Standardizing of Road Engineering Practices” Project. The objective of the project was to

enhance the management, planning, design, construction, maintenance, and operation of all roads

and related infrastructures in the Emirate and to ensure a safe and uniform operational and structural

capacity throughout the road network.

To achieve this objective, a set of standards, specifications, guidelines, and manuals were

developed in consultation with all relevant authorities in the Abu Dhabi Emirate including the

Department of Municipal Affairs (DMA) and Urban Planning Council (UPC). In the future, all

authorities or agencies involved in roads and road infrastructures in the Emirate shall exercise their

functions and responsibilities in accordance with these documents. The purpose, scope, and

applicability of each document are clearly indicated in each document.

It is recognized that there are already published documents with similar objectives and contents

prepared by other authorities. Such related publications are mentioned in each new document and

are being superseded by the publication of the new document, except where previously published

documents are recognized and referenced in the new document.

The Executive Council issued amendments to some of the Structural Design Criteria, detailed in

previous edition of this Manual. The key objective of the amendments was primarily to reduce the

initial cost of the highway structures that corresponds to reduction in the service life of highway

structures (bridges, underpasses, and tunnels). The service life of the structure and associated cost

is fundamentally controlled by many factors some of these key factors considered revisions are

reducing the clear concrete cover, concrete compressive strength, revising crack width parameters

etc.

1.2 Purpose and Scope

1.2.1 General

The basic purpose and scope for the Road Structures Design Manual (RSDM, the Manual) is as

follows:

1. Purpose. The Manual is an application-oriented document for design of road structures.

2. Scope. The Manual provides design specifications for road structures in the Abu Dhabi

Emirate as a supplement to the AASHTO Bridge Design Specifications. In some instances,

background information is provided on design specifications. The Manual is not a structural

design theory resource or a research document. Where beneficial, the Manual provides

design details for various structural elements.

3. Audience. The primary audience for the Manual is the owner’s employees, other relevant

authorities, consultants and contractors for the design and construction of road structures in

the Abu Dhabi Emirate.


Page 2


The Manual is based on the AASHTO LRFD Bridge Design Specifications, 6th Edition, 2012 (1)

(BDS) and:

• in general, does not duplicate information in the BDS, unless necessary for clarity;

• elaborates on specific articles of the BDS;

• presents interpretative information and commentary on some provisions, where required;

these texts are highlighted throughout the document;

• modifies sections from the BDS where required due to local conditions or because the bridge

owner has adopted a different practice;

• indicates owner’s preference where the BDS presents multiple options; and

• indicates bridge design applications presented in the BDS that are not typically used in the

Abu Dhabi Emirate.

In addition, the Manual discusses, for selected applications, the intent of the BDS to assist the bridge

designer in proper application.

The Manual will be revised periodically as newer editions of the BDS are published. If newer editions

of the BDS (and any Interims) become available before the Manual is revised, then the more recent

editions of the BDS shall govern.

1.2.2 AASHTO LRFD Bridge Design Specifications

1.2.2.1 General

The BDS establishes minimum requirements that apply to common road bridges and other structures

such as retaining walls and culverts. Long-span or unique structures may require design provisions

in addition to those presented in the BDS. AASHTO issues interim revisions annually and,

periodically, publishes a completely updated edition. The BDS serves as a standard for use by bridge

designers. Many agencies also have used the BDS as a basis for the development of their own

structural specifications.

All calculations and drawings should be provided in the metric (SI) system, as far as possible.

However, the Consultant may refer to AASHTO LRFD (2007) for the conversion of formulae where

applicable. US customary units may be used if conversion is not possible, or if loss of accuracy

would result.

1.2.2.2 LRFD Methodology

The BDS presents a Load-and-Resistance-Factor Design (LRFD) methodology for the structural

design of bridges. Basically, the LRFD methodology requires that bridge components be designed

to satisfy four sets of limit states: Strength, Service, Fatigue-and-Fracture, and Extreme-Event.

Through the use of reliability indices derived through statistical analyses, the Strength limit-state

provisions of the BDS reflect a uniform level of safety for all structural elements, components, and

systems.


Page 3


1.3 Application of this Manual

1.3.1 Definition of Road Structures

Road structures are part of the roadway infrastructure including bridges, viaducts, utility bridges,

culverts, underpasses, tunnels, and retaining walls. Road structures also include pedestrian bridges,

sound barriers, and structural supports for traffic signs and luminaires.

1.3.2 Hierarchy of Priority

Where conflicts are observed in publications and documents for structural design, the following

hierarchy of priority applies to determine the appropriate application:

• Structural Design Memoranda issued by the owner,

• This Manual,

• BDS, and

• All other generally recognised structure-related publications (e.g. research studies).

1.4 Design Objectives

Reference: BDS Article 2.5

In addition to the design objectives outlined in the BDS, the following emphasizes objectives of

special importance to the Abu Dhabi Emirate.

1.4.1 Serviceability

1.4.1.1 Durability

Reference: BDS Article 2.5.2.1

Provide special attention to durability issues during design and construction. In consideration of local

conditions, this Manual specifies material and protective measures to enhance the durability

provisions already included in the BDS.

1.4.1.2 Inspectability and Maintainability

Reference: BDS Articles 2.5.2.2 and 2.5.2.3

Provide access to different parts of structures for inspection, maintenance, rehabilitation, and

replacement where necessary (e.g. bearings, expansion joints, future post-tensioning tendons).

Provide all required jacking points.

1.4.1.3 Adjacent Structures

As practical, the bridge design shall not affect nor have any negative impact, on adjacent existing

buildings and structures (if any) or any planned construction in the area. Therefore, consideration

shall be given to existing structures during the design process.

1.4.1.4 Utilities and Intelligent Transportation Systems (ITS)



Page 4


Provide service provisions as required by the interested authorities. Design protection culverts for

oil, water, sewer, gas and electricity in consideration of the service authorities’ requirements.

Design bridges and tunnels to accommodate necessary ITS infrastructure, as identified in the project

ITS documents.

Provide pull boxes at appropriate spacing for ease of maintenance and for pulling cables.

1.4.2 Constructability

Reference: BDS Article 2.5.3

1.4.3 Maintenance of Traffic

Minimize the disturbance to traffic flow on the existing roads during construction. (Refer to the “Abu

Dhabi Work Zone Traffic Management Manual”).

1.4.4 Sustainability

A sustainable bridge project must satisfy transportation requirements and improve the economy,

environment, and social aspects. Although the concept of sustainable bridge design is still in

development, and clear standards have not been formalized, all bridges in the Abu Dhabi Emirate

shall be designed with sustainability as a major design objective.

1.4.5 Aesthetics


Every effort shall be made in the treatment of structures to respect the local aesthetic design and

culture. Design concepts would be easily implementable. Also, construction issues shall be

considered in the architectural treatment concepts. Architectural elements must be functional,

durable, and easily maintainable. Desirably, each structure will have individuality; however, a

completely different aesthetic treatment is not required for every structure. Desirably, maintain a

sense of continuity throughout the entire highway corridor.

Design the architectural treatment to be continuous throughout an interchange. Underpasses

spanning a given roadway would have a similar treatment to establish continuity. Decorative and

median lighting would be similar on overpasses along a given route, unless special lighting is

requested by the client over the structure. For more details on the aesthetics and landscape works,

refer to PR-401 Public Realm Design Manual (PRDM).

1.5 Design Approval Procedures

1.5.1 Objectives

The fundamental objectives of the design approval procedures are to ensure that the project’s

required construction, rehabilitation, or demolition are safe to implement. The procedures also

ensure that any new structures are:

• safely serviceable in use,

• constructible,

• durable,


Page 5


• economic to build and maintain,

• comply with the objectives of sustainability,

• have due regard for the environment, and

• satisfactorily perform their intended functions.

The design check shall also ensure that the road users, and others who may be affected, are

protected from any adverse effects resulting from any work to the structure, and that there is always

adequate provision for safety.

1.5.2 Reference

The design approval procedures for different types of structures shall be according to CG 300

(Revision-0) “Technical Approval of Highway Structures” (2).

When independent checking (Category 2 & 3) is required, the Checker must perform their own

calculations (to be submitted, any disagreement arising between Designer or Assessor and Checker

that they cannot resolve must be notified immediately to the client and the approving authority.

1.6 Structure Design Checklists

The bridge design documents (calculations, specifications, and drawings) shall be checked for

completeness, at all design stages, according to the Bridge Design Checklists presented in Appendix

A.


PAGE 6

02-LOADS AND LOAD FACTORS SECOND EDITION – AUGUST 2021

2 LOADS AND LOAD FACTORS

Sections 1 and 3 of the BDS discuss various aspects of loads and load factors. Unless noted

otherwise in Chapter 2, the BDS loads and load factors shall be followed.

2.1 General

2.1.1 Limit States

Reference: BDS Articles 1.3.2 and 3.4.1

All of the limit-state load combinations as specified in BDS Table 3.4.1-1 shall be followed, except

as modified herein.

The BDS groups the design criteria together within groups termed as “limit states” to which different

load combinations are assigned.

2.1.1.1 BDS “Total Factored Force Effect” Equation

All structure components and connections shall be designed to satisfy the basic BDS equation for

the total factored force effects for all limit states:

Equation 2.1

where: ɣi = load factor

Qi = load or force effect

ɸ = resistance factor

Rn = nominal resistance

ɳi = load modifier as defined in BDS Equations 1.3.2.1-2 and 1.3.2.1-3

The left-hand side of BDS Equation 1.3.2.1-1 (Equation 2.1 above) is the sum of the factored load

(force) effects acting on a component; the right-hand side is the factored nominal resistance of the

component. Consider the equation for all applicable limit state load combinations. Similarly, the

equation is applicable to superstructures, substructures, and foundations.

For the Strength limit states, the BDS is basically a hybrid design code. The force effect on the left-

hand side of the BDS equation is based upon elastic structural response, while resistance on the

right-hand side of the equation is determined predominantly by applying inelastic response

principles. The hybrid nature of strength design assumes that the inelastic component of structural

performance will always remain relatively small because of non-critical redistribution of force effects.

This non-criticality is assured by providing adequate redundancy and ductility of structures.

2.1.1.2 Load Modifier

Use ɳi values of 1.00 for all limit states, because bridges designed in accordance with this Manual

will demonstrate traditional levels of redundancy and ductility. Rather than penalize less redundant

niii RQ


PAGE 7


or less ductile bridges, such bridges are not encouraged. The designer may on a case-by-case basis

designate a bridge to be of special operational importance and specify an appropriate value of ɳi.

The load modifier ɳi relates to ductility, redundancy, operational importance, and is a function of the

factors ɳD, ɳR, and ɳI. The location of ɳi on the load side of Equation 2.1 may appear counterintuitive

because it appears to be more related to resistance than to load. ɳi is on the load side for a logistical

reason. When ɳi modifies a maximum load factor, it is the product of the factors as indicated in BDS

Equation 1.3.2.1-2; when ɳi modifies a minimum load factor, it is the reciprocal of the product as

indicated in BDS Equation 1.3.2.1-3. These factors are somewhat arbitrary; their significance is in

their presence in the BDS and not necessarily in the accuracy of their magnitude. The BDS factors

reflect the desire to promote redundant and ductile bridges.

Do not confuse the load modifier accounting for importance of BDS Article 1.3.5, ηI, with the

importance categories for seismic design of BDS Articles 3.10.3 and 4.7.4.3. The importance load

modifier is used in the basic BDS Equation, but the importance categories are used to determine the

minimum seismic analysis requirements.

2.1.2 Load Factors and Combinations


Table 2.1 (BDS Table 3.4.1-1) provides the load factors for all load combinations of the BDS.

Table 2.1: Load Combinations and Load Factors

Load Combination Limit State

DC DD DW EH EV ES EL PS CR SH

LL IM CE BR PL LS WA WS WL FR TU TG SE

Use One of These at a Time

EQ IC CT CV

Strength I (unless noted) p 1.75 1.00 — — 1.00 0.50/1.20 TG SE — — — —

Strength II p 1.35 1.00 — — 1.00 0.50/1.20 TG SE — — — —

Strength III p — 1.00 1.40 — 1.00 0.50/1.20 TG SE — — — —

Strength IV p — 1.00 — — 1.00 0.50/1.20 — — — — — —

Strength V p 1.35 1.00 0.40 1.0 1.00 0.50/1.20 TG SE — — — —

Extreme Event I p EQ 1.00 — — 1.00 — — — 1.00 — — —

Extreme Event II p 0.50 1.00 — — 1.00 — — — — 1.00 1.00 1.00

Service I 1.00 1.00 1.00 0.30 1.0 1.00 1.00/1.20 TG SE — — — —

Service II 1.00 1.30 1.00 — — 1.00 1.00/1.20 — — — — — —

Service III 1.00 0.80 1.00 — — 1.00 1.00/1.20 TG SE — — — —

Service IV 1.00 — 1.00 0.70 — 1.00 1.00/1.20 — 1.0 — — — —

Fatigue I – LL, IM & CE only — 1.50 — — — — — — — — — — —

Fatigue II – LL, IM & CE only

— 0.75 — — — — — — — — — — —


PAGE 8


2.1.2.1 Strength Load Combinations

The load factors for the Strength load combinations are calibrated based upon structural reliability

theory and represent the uncertainty of their associated loads. The significance of the Strength load

combinations can be simplified as follows:

1. Strength I Load Combination. This load combination represents random traffic and the

heaviest truck to cross the bridge in its design life. During this live-load event, a significant

wind is not considered probable.

2. Strength II Load Combination. In the BDS, this load combination represents an owner-

specified permit load model. This live-load event has less uncertainty than random traffic

and, thus, a lower live-load load factor. Use this load combination for design in conjunction

with the permit live load design vehicle (P-13 load) discussed in Section 2.3.2.2.

3. Strength III Load Combination. This load combination represents the most severe wind

during the bridge’s design life. During this severe wind event, no significant live load is

assumed to cross the bridge.

4. Strength IV Load Combination. This load combination represents an extra safeguard for

bridge superstructures where the unfactored dead load exceeds seven times the unfactored

live load. Thus, the only significant load factor is the 1.25 dead-load maximum load factor.

For additional safety, and based solely on engineering judgment, the BDS has arbitrarily

increased the load factor for DC to 1.5. Do not consider this load combination for any

component except a superstructure component, and never where the unfactored dead-load

force effect is less than seven times the unfactored live-load force effect. This load

combination typically governs only for longer spans, approximately greater than 60 m in

length. Thus, this load combination is only necessary in relatively rare cases.

5. Strength V Load Combination. This load combination represents the simultaneous

occurrence of a “normal” live-load event and a wind event with load factors of 1.35 and 0.4,

respectively.

For components not traditionally governed by wind force effects, the Strength III and Strength V load

combinations usually do not govern. Generally, the Strength I and Strength II load combinations will

govern for a typical multi-girder highway bridge.

2.1.2.2 Service Load Combinations

Unlike the strength load combinations, the service load combinations are material dependent. The

following applies:

1. Service I Load Combination. Apply this load combination to control cracking in reinforced

concrete components and compressive stresses in prestressed concrete components. Also,

use this load combination to calculate deflections and settlements of superstructure and

substructure components.

2. Service II Load Combination. Apply this load combination to control permanent deformations

of compact steel sections and the “slip” of slip-critical (i.e. friction-type) bolted steel

connections.


PAGE 9


3. Service III Load Combination. Apply this load combination to control tensile stresses in

prestressed concrete superstructure components under vehicular traffic loads. The Service

III load combination does not apply to the design permit live load design vehicle.

4. Service IV Load Combination. Apply this load combination to control tensile stresses in

prestressed concrete substructure components under wind loads. For components not

traditionally governed by wind effects, this load combination usually does not govern.

2.1.2.3 Extreme-Event Load Combinations

The extreme-event limit states differ from the strength limit states, because the event for which the

bridge and its components are designed has a greater return period than the design life of the bridge

(or a much lower frequency of occurrence than the loads of the strength limit state). The following

applies:

1. Extreme-Event I Load Combination. This load combination is applied to earthquakes. Use a

load factor of 0.5 for γEQ for all live-load related forces in BDS Table 3.4.1-1. Earthquakes in

conjunction with scour (which is considered a change in foundation condition, not a load) can

result in a very costly design solution if severe scour is anticipated. In this case, typical

practice is to combine one-half of the total design scour (sum of contraction, local, and long-

term scour) with the seismic loading.

2. Extreme-Event II Load Combination. This load combination is applied to various types of

collisions (vessel or vehicular) applied individually.

2.1.2.4 Fatigue-and-Fracture Load Combination

The Fatigue-and-Fracture load combination, although strictly applicable to all types of

superstructures, only affects the steel elements, components, and connections of a limited number

of steel superstructures. Chapter 5 discusses fatigue and fracture for steel structures.

2.1.2.5 Application of Multiple-Valued Load Factors

Maximum and Minimum Permanent-Load Load Factors

In Table 2.1, the variable P represents load factors for all of the permanent loads, shown in the first

column of load factors. This variable reflects that the Strength and Extreme-Event limit state load

factors for the various permanent loads are not single constants, but they can have two extreme

values. Table 2.2 (BDS Table 3.4.1-2) provides these two extreme values for the various permanent

load factors, maximum and minimum. Permanent loads are always present on the bridge, but the

nature of uncertainty is that the actual loads may be more or less than the nominal specified design

values. Therefore, maximum and minimum load factors reflect this uncertainty.

Select the appropriate maximum or minimum permanent-load load factors to produce the more

critical load effect. For example, in continuous superstructures with relatively short end spans,

transient live load in the end span causes the bearing to be more compressed, while transient live

load in the second span causes the bearing to be less compressed and perhaps lift up. To check

the maximum compression force in the bearing, place the live load in the end span and use the

maximum DC load factor of 1.25 for all spans. To check possible uplift of the bearing, place the live

load in the second span and use the minimum DC load factor of 0.90 for all spans.


PAGE 10


Table 2.2: Load Factors for Permanent Loads, p

Type of Load, Foundation Type, and Method Used to Calculate Downdrag

Load Factor

Maximum Minimum

DC: Component and attachments

DC: Strength IV only

1.25

1.50

0.90

0.90

DD: Downdrag Piles, Tomlinson method

Piles, method

Drilled shafts, O’Neill and Reese (1999) Method

1.40

1.05

1.25

0.25

0.30

0.35

DW: Wearing surfaces and utilities 1.50 0.65

EH: Horizontal earth pressure

• Active

• At-Rest

• AEP for anchored walls

1.50

1.35

1.35

0.90

0.90

N/A

EL: Locked-in construction stresses 1.00 1.00

EV: Vertical earth pressure

• Overall stability

• Retaining walls and abutments

• Rigid buried structure

• Rigid frames

• Flexible buried structures other than metal box culverts

• Flexible metal box culverts and structural plate culverts

with deep corrugations

1.00

1.35

1.30

1.35

1.95

1.50

N/A

1.00

0.90

0.90

0.90

0.90

ES: Earth surcharge 1.50 0.75

Superstructure design uses the maximum permanent-load load factors almost exclusively. The most

common exception is uplift of a bearing as discussed above. The BDS has generalized load

situations such as uplift where a permanent load (in this case a dead load) reduces the overall force

effect (in this case a reaction). Select permanent load factors, either maximum or minimum, for each

load combination to produce extreme force effects.

Substructure design routinely uses the maximum and minimum permanent-load load factors from

Table 2.2. An illustrative yet simple example is a spread footing supporting a cantilever retaining

wall. When checking bearing, the weight of the soil (EV) over the heel is factored up by the maximum

load factor, 1.35. This increase is because greater EV increases the bearing pressure, qult, making

the limit state more critical. When checking sliding, EV is factored by the minimum load factor, 1.00,

because lesser EV decreases the resistance to sliding, Q, again making the limit state more critical.

The application of these maximum and minimum load factors is required for foundation and

substructure design; see Chapters 7 and 8.

Load Factors for Superimposed Deformations

The load factors for the superimposed deformations (TU, CR, SH) for the strength limit states also

have two specified values — a load factor of 0.5 for the calculation of stress, and a load factor of 1.2

for the calculation of deformation. Use the greater value of 1.2 to calculate unrestrained deformations

(e.g. a simple span expanding freely with rising temperature). The lower value of 0.5 for the elastic

calculation of stress reflects the inelastic response of the structure due to restrained deformations.


PAGE 11


For example, use one-half of the temperature rise to elastically calculate the stresses in a

constrained structure. Using 1.2 times the temperature rise in an elastic calculation overestimates

the stresses in the structure. The structure resists the temperature inelastically through redistribution

of the elastic stresses.

2.2 Permanent Loads

2.2.1 General


The BDS specifies seven components of permanent loads, which are either direct gravity loads or

caused by gravity loads. The primary forces from prestressing are considered as part of the

resistance of a component and has been omitted from the list of permanent loads in Section 3 of the

BDS. However, when designing anchorages for prestressing tendons, the prestressing force is the

only load effect, and it will appear on the load side of Equation 2.1. The permanent load EL includes

secondary forces from pre-tensioning or post-tensioning.

As discussed in Section 2.1.2.5, the permanent force effects in superstructure design are factored

by the maximum permanent-load load factors almost exclusively. The most common exception is

the check for uplift of a bearing. In substructure design, the permanent force effects are routinely

factored by the maximum or minimum permanent-load load factors from BDS Table 3.4.1-2.

The following lists additional minimum loads that are usually applicable to Abu Dhabi structures:

• Unit weight of reinforced and prestressed concrete: 25 kN/m3.

• 110 mm of asphalt wearing course shall be considered. Unit weight of wearing course: 23

kN/m3.

• The actual weight and position of all known utilities; otherwise, an additional dead load (curb

to curb) of 1.0 kN/m2 shall be considered.

2.2.2 Down drag (DD) on Deep Foundations


Deep foundations (i.e. drilled shafts and driven piles) through unconsolidated soil layers may be

subject to downdrag, DD. Downdrag is a load developed along the vertical sides of a deep-

foundation element tending to drag it downward typically due to consolidation of soft soils underneath

embankments reducing its resistance. Calculate this additional load as a skin-friction effect. If

possible, detail the deep foundation to mitigate the effects of downdrag; otherwise, design the

foundation considering downdrag. Chapter 7 discusses mitigation methods.

2.2.3 Support Settlement (SE)

Differential settlement between adjacent substructure units or transversely across a single

substructure unit induces stresses in continuous structures and deflections in simple supported

structures. Although some bridges can easily resist these stresses and deflections, consider the

potential effects of differential settlement in the longitudinal and transverse direction on a case-by-

case basis.

.


PAGE 12


A minimum value of differential settlement of 20 mm with short-term concrete modulus OR 10 mm with long-term concrete modulus shall be considered in the design. In the event of bridge jacking for bearing’s replacement, the live load shall be closed partially (50%) or totally (100%) (if required).

The location of jacking points and area of jack for replacing the bearings shall also be specified on the design drawings.

2.3 Transient Loads

2.3.1 General

The BDS recognizes 19 transient loads. Static water pressure, stream pressure, buoyancy, and

wave action are integrated as water load, WA. Creep, settlement, shrinkage, and temperature (CR,

SE, SH, TU, and TG), are superimposed deformations. If restrained, these result in force effects,

and are elevated in importance to “loads.” For example, restrained strains due to an increase in

uniform-temperature induce compression forces.

2.3.2 Abu Dhabi Vehicular Load (ADVL)

Reference: BDS Articles 3.6.1, 3.6.3, 3.6.4, and 3.11.6.4

Design all bridges and their components for the ADVL notional live-load model. The ADVL replaces

the HL-93 notional live-load model of the BDS. It consists of the HL-93 notional live-load components

— the design truck, the design tandem and the design lane loads — each multiplied by 1.5. The

dimensions of the vehicles and the lanes remain the same as the HL-93. See Figure 2.1.

Figure 2.1: Characteristics of the Design Truck

Multiply all other transient loads associated with vehicular load as defined in the BDS (e.g. CE, BR,

LS, and the fatigue load) by 1.5.

For short and medium span bridges, vehicular live load is the most significant component of load.

Dead loads become more significant for long-span bridges. Long-span bridges are defined as those


PAGE 13


governed by the Strength IV load combination where the dead load is seven times or more greater

than the live load.

2.3.2.1 Multiple Presence Factors

The multiple presence factor of 1.0 for two loaded lanes, as given in BDS Table 3.6.1.1.2-1, is the

result of the BDS calibration for the notional load, which has been normalized relative to the

occurrence of two side by side, fully correlated, or identical, vehicles. Use the multiple presence

factor of 1.2 for one loaded lane where a single design tandem or single design truck governs, such

as in overhangs, decks, etc. The multiple presence factors of 0.85 and 0.65 for three lanes and more

than three lanes loaded, respectively, may govern for wider bridges.

Do not apply the multiple-presence factors to fatigue loads.

2.3.2.2 Permit Loads for Design (P Load)

Use the Caltrans P-13 “Standard Permit Design Vehicle” for the design of structures to provide a

minimum permit-load capacity on all highway structures. This accounts for vehicles that exceed the

legal limits and that operate on highways and structures under special transportation permits. See

Error! Reference source not found.. Design all bridges for the Strength II, Service I, and Service II l

oad combinations with the P load in the exterior right lane and the ADVL in all other lanes.

Figure 2.2: Permit Design Live Loads (for P-13 Vehicle)


PAGE 14


2.3.3 Wind Loads (WS and WL)


Use a wind velocity, VB, of 160 km/h at 10 m above low ground or above design water level. Use a

gust factor of 1.14 for signs, luminaire supports, and pedestrian bridges only. For some Pedestrian

Bridges, an increased Gust factor value may be required depending upon the structure flexibility and

exposure conditions. The increased factor shall be subjected to client approval

The wind velocity used in the BDS is often referred to as a “3-second gust,” which is the highest

sustained gust over a 3-second period having a probability of being exceeded per year of 1 in 50

(ASCE 7-10) (3).

2.3.4 Earthquake Effects (EQ)

Reference: AASHTO LRFD Specifications for Bridge Design (BDS)

Apply the provisions of the BDS (1) to bridges in the Abu Dhabi Emirate. Use the spectral response

accelerations given in Table 2.3 in conjunction with the provisions of the BDS.

Design bridges and road tunnels to withstand the spectral response accelerations given in Table 2.3 for return periods of 475,1000 and 2475 years. The return period of 2475 years shall be used for “Critical Bridges” and the return period of 1000 years for the “Essential Bridges” and the return period of 475 years for other bridges, or as specified by owner. After the event characterized by these spectral response accelerations, the structure may sustain significant damage, and a possible disruption of service; however, the structure will have a low probability of collapse

Table 2.3: Spectral Response Accelerations for the Abu Dhabi Emirate

Return Period in Years

Peak Horizontal Ground Acceleration

Coefficient, PGA

Short-Period (0.2 sec) Value of

Spectral Acceleration Coefficient, Ss

Longer-Period (1 sec) Value of

Spectral Acceleration Coefficient, S1

475 0.060 0.150 0.067

1000 0.075 0.185 0.083

2475 0.090 0.225 0.100

Although most of the Emirate, based on available information, falls in zone 1, the owner may

require higher level of performance and may select zone 2 for some areas.

The design response spectrum, illustrated in Figure 2.3 is variable and constructed using the

spectral response accelerations specified in Table 2.3 and other characteristics of the structure

as defined below.


PAGE 15


AS = FpgaPGA

SD1 = FvS1

SDS = FaSs

Figure 2.3: Design Response Spectrum

Determine the design earthquake response spectral acceleration coefficients for the acceleration

coefficient, As, the short period acceleration coefficient, SDS, and at the 1-sec period acceleration

coefficient, SD1, from the following equations:

Equation 2.2

Equation 2.3

Equation 2.4

where: Fpga = site coefficient for peak ground acceleration, specified in Table 2.4.

PGA = peak horizontal ground acceleration coefficient

Fa = site coefficient for 0.2-sec period spectral acceleration, specified in Table 2.4

Ss = 0.2-sec period spectral acceleration coefficient

Fv = site coefficient for 1.0-sec period spectral acceleration, specified in Table 2.4.

S1 = 1.0-sec period spectral acceleration coefficient


PAGE 16


Table 2.4: Acceleration Coefficients

Site Class Fpga Fa Fv

A 0.8 0.8 0.8

B 1.0 1.0 1.0

C 1.2 1.2 1.7

D 1.6 1.6 2.4

E 2.5 2.5 3.5

F Consider the site-specific response geotechnical investigation and dynamic-site response analysis

Table 2.5 provides site-class definitions by soil type and profile.

Table 2.5: Site-Class Definitions

Site Class Soil Type and Profile

A Hard rock with measured shear wave velocity, sv > 1500 m/sec

B Rock with 750 m/sec < sv < 1500 m/sec

C Very dense soil and soil rock with 350 m/sec < sv < 750 m/sec, or with either N > 150

blows/m or us > 100 kPa

D Stiff soil with 175 m/sec < sv < 350 m/sec, or with either 50 m blows < N < 50 blows/m or

50 kPa < us < 100 kPa

E Soil profile with sv < 175 m/sec, or with either N < 50 blows/m or us < 50 kPa, or any profile

with more than 3 m of soft clay defined as soil with PI > 20, w > 40%, and us < 25 kPa

F

Soils requiring site-specific ground motion response evaluations, such as:

• Peats or highly organic clays (H > 3 m of peat or highly organic clay, where H = thickness of soil)

• Very high plasticity clays (H > 7.5 m with PI > 75)

• Very thick soft/medium stiff clays (H > 35 m)

Exceptions:

Where the soil properties are not known in sufficient detail to determine the site class, a site investigation shall be undertaken sufficient to determine the site class. Do not use Site Class E or F unless the owner determines that Site Class E or F could be present at the site or if Site Class E or F is established by geotechnical data.

where: sv = average shear wave velocity for the upper 30 m of the soil profile

N = average standard penetration test (SPT) blow count (blows/m) (ASTM D 1586) for the upper 30 m of the soil profile

us = average undrained shear strength in kPa (ASTM D 2166) for the upper 30 m of the soil

profile

PI = plasticity index (ASTM D 4318)

w = moisture content (ASTM D 2216)

H = thickness of soil layer


PAGE 17


2.3.5 Uniform Temperature (TU)


Use Procedure A of BDS Article 3.12.2.1 to determine the appropriate design thermal range. Use

the minimum and maximum temperatures specified in Table 2.6 as TMinDesign and TMaxDesign,

respectively, in BDS Equation 3.12.2.3-1.

Assume a construction temperature of 30°C.

Table 2.6: BDS Procedure “A” Temperature Ranges

Concrete Bridges Steel Bridges

0°C - 60°C 0°C - 70°C

2.3.6 Temperature Gradient (TG)


Include the effects of TG in the design of all superstructures. The vertical TG is from


PAGE 18


Figure 2.4.

Dimension A in


PAGE 19


Figure 2.4 shall be:

• For concrete superstructures that are 400 mm or more in depth: 300 mm

• For concrete sections shallower than 400 mm: 100 mm less than the actual depth

• For steel superstructures: 300 mm and the distance t shall be the depth of the concrete deck

Temperature values T1 and T2 shall be 30°C and 8°C, respectively. Temperature value T3 shall be

0°C, unless a site-specific study is made to determine an appropriate value. Positive vertical

temperature gradient in concrete and steel structures is shown in


PAGE 20


Figure 2.4. Other provisions shall be the same as BDS Article 3.12.3.


PAGE 21


Figure 2.4: Positive Vertical Temperature Gradient in Concrete and Steel Superstructures

2.3.7 Live-Load Surcharge (LS)


Multiply equivalent heights of soil for vehicular loading on abutments and retaining walls specified in

BDS Tables 3.11.6.4-1 and 3.11.6.4-2, respectively, by 1.5 for use in the Abu Dhabi Emirate.

Retaining walls that retain soil supporting a roadway must resist the lateral pressure due to the live-

load surcharge. See Chapter 8 for retaining walls.

2.3.8 Ground Water Levels

Ensure that false water table measurements, resulting from a temporary depression of the water

table, because of construction activities, are not used in the design. Estimate the water table

conservatively considering the effects of tidal and seasonal fluctuations.


PAGE 22

03-STRUCTURE ANALYSIS SECOND EDITION – AUGUST 2021

3 STRUCTURAL ANALYSIS

Section 4 of the BDS (1) discusses the methods of structural analysis for the design and evaluation

of bridge superstructures, but it does not address analysis procedures for substructures. Section 5

of the AASHTO Guide Specifications for LRFD Seismic Bridge Design (4) (GSBD) discusses the

methods of analysis for seismic design and evaluation of bridges. Chapter 3 of this Manual provides

an elaboration on the provisions of BDS Section 4 and GSBD Section 5 to discuss specific practices

on structural analysis. Chapter 7 provides provisions on structural analysis procedures for

foundations. Chapter 8 provides provisions on piers, abutments, and walls.

3.1 Acceptable Methods

3.1.1 General

All bridge superstructures shall be designed based upon refined analysis employing two-dimensional

(2-D) or three-dimensional (3-D) models (see Section 3.2.1 below).

See Section 3.2.2 for the use of approximate analyses.

3.1.2 Exceptions

Reference: BDS Articles 4.6.1.1, 4.6.1.2.2, and 4.6.1.2.3

With approval of the owner, one-dimensional single-spline beam analysis (i.e. where the single

dimension explicitly modelled represents the span lengths) may be applied to bridges where the

span length of a superstructure with torsionally stiff closed cross sections exceeds 3 times its width.

For multi-cell boxes, the width is assumed to be the distance between the outside faces of the

exterior webs.

A single-spline beam is sometimes termed a beam deck.

3.2 Static Analysis

3.2.1 Refined Analysis


See Hambly (6) and O’Brien & Keogh (7) for detailed information on 2-D and 3-D modelling of

structures. The term “bridge deck” in these references refers to the term “bridge superstructure” in

this Manual.

When a refined method of analysis is used, the name, version, and date of the software used shall

be indicated in the design documents.

Refined analyses include both 2-D and 3-D modelling. 2-D models consist of elements essentially

lying in a single plane with the third dimension represented only through the stiffness properties of

the elements (such as a grillage). 3-D models consist of elements in all three dimensions (space

truss) or of elements with three dimensions (such as solid elements). BDS Article 4.6.3 provides

general guidance for 2-D and 3-D models for the number of elements and aspect ratios.


PAGE 23


3.2.2 Approximate Analysis


3.2.2.1 General

The bridge designer may use the approximate methods of BDS Article 4.6.2 for preliminary design

and single-spline beam analysis.

3.2.2.2 Live Load Distribution Factors In BDS Article 4.6.2.2.2, extend the Range of Applicability for the referenced bridge types of Figure

3.1 as follows:

1. BDS Table 4.6.2.2.2.b-1. For open prestressed concrete box beam bridges (Type “c” cross-

section), change the depth parameter range to 450 mm < d < 1800 mm, and the span length

parameter range to 6 m < L < 50 m. For prestressed flat slab bridges (Type “f” cross-section),

change the width parameter to 750 mm < b < 1550 mm. For prestressed concrete I-beam

bridges (Type “k” cross-section), change the longitudinal stiffness parameter range to 4.0

109 mm4 < Kg < 3.324 1012 mm4.

2. BDS Table 4.6.2.2.3.a-1. For open prestressed concrete box beam bridges (Type “c” cross-

section), change the depth parameter range to 450 mm < d < 1800 mm, and the span length


change the moment of inertia range to 4.0 109 mm4 < I < 2.4 1011 mm4, and the width

parameter to 750 mm < b < 1550 mm.

3. BDS Table 4.6.2.2.3.b-1. For prestressed flat slab bridges (Type “f” cross-section), change

the width parameter to 750 mm < b < 1550 mm.

4. BDS Table 4.6.2.2.3.c-1. For open prestressed concrete box bridges (Type “c” cross-

section), change the depth parameter range to 450 mm < d < 1800 mm and the span length


change the width parameter to 750 mm < b < 1550 mm.

The BDS distribution factor equations are based on work conducted in NCHRP Project 12-26. When

one or more of the parameters are outside the listed range of applicability, the equation could still

remain valid, particularly when the value or values are only slightly outside the range. The extended

values given herein are considered slightly outside of the BDS range of applicability. If one or more

of the parameters greatly exceeds the range of applicability, engineering judgment needs to be

exercised.

The BDS approximate method produces distribution factors that are conservative when compared

to refined analyses, although the beam stiffness and spacings vary significantly.


PAGE 24


Figure 3.1: Common Deck Superstructures Covered

Supporting Components Type of Deck Typical Cross Section

Steel beam

Cast-in-situ concrete slab, precast concrete slab, steel grid, glued/spiked panels, stressed wood

Closed steel or precast concrete boxes

Cast-in-situ concrete slab

Open steel or precast concrete boxes

Cast-in-situ concrete slab, precast concrete deck slab

Cast-in-situ concrete multicell box

Monolithic concrete

Cast-in-situ concrete tee beam

Monolithic concrete

Precast solid, voided or cellular concrete boxes with shear keys

Cast-in-situ concrete overlay

Precast solid, voided or cellular concrete box with shear keys and with or without transverse post-tensioning

Integral concrete

Precast concrete channel sections with shear keys

Cast-in-situ concrete overlay


PAGE 25


Figure 3.1: Common Deck Superstructures Covered

(Continued)

Supporting Components Type of Deck Typical Cross Section

Precast concrete double tee section with shear keys and with or without transverse post-tensioning

Integral concrete

Precast concrete tee section with shear keys and with or without transverse post-tensioning

Integral concrete

Precast concrete I or bulb-tee sections

Cast-in-situ concrete, precast concrete

Wood beams Cast-in-situ concrete or plank, glued/spiked panels or stressed wood

3.2.2.3 Distribution of Superimposed Load on Beam-Slab Bridges


Distribute barrier and railing permanent loads in accordance with BDS Article 4.6.2.2.

3.2.2.4 Consideration of Railing in Limit State Checks


Do not include traffic and pedestrian railings and raised sidewalks in the stiffness of the bridge when

determining deflections or for service or fatigue limit state checks.

3.2.3 Lateral Wind-Load Distribution in Multi-Beam Bridges

Reference: BDS Articles 3.8.1 and 4.6.2.7.1

Assume that typical concrete fascia girders satisfactorily resist transverse wind loads.

BDS Article 4.6.2.7.1 discusses load paths for transferring wind loads transversely applied to the

fascia girder to the bridge’s bearings. The Commentary provides guidelines on how girders resist

the wind loads. The provisions are directly applicable to steel girder bridges. In typical concrete girder

bridges, the distribution of wind load becomes insignificant due to their greater out-of-plane stiffness

in comparison with steel girders.


PAGE 26


3.3 Dynamic Analysis

3.3.1 Seismic Analysis

Reference: BDS Article 4.7.4, GSBD Articles 4.5 and 5.4

BDS Article 4.7.4 shall be followed with consideration of provisions in Chapter 2 of this Manual.

3.3.1.1 Structural Global Analysis

Use structural global analysis when it is necessary to capture the response of the entire bridge

system.

Bridge systems with irregular geometry (especially those with horizontal curvature, skews, multiple

transverse expansion joints, massive substructure components, and foundations supported by soft

soil) can exhibit dynamic response characteristics that are not obvious and may not be captured in

a separate subsystem analysis.

3.3.2 Wind-Induced Vibration


Special attention shall be given to wind-sensitive structures. These structures shall be analysed for

dynamic effects, such as buffeting by turbulent or gusting winds, and unstable wind-structure

interaction, such as galloping and flutter.

3.4 Transverse Deck Loading, Analysis, and Design

Reference: BDS Articles 3.6.1.2.2 and 3.6.1.2.3

Axle loads are usually those that produce the maximum effect from either the ADVL (i.e. 1.5 HL-93)

design truck or the design tandem axles (BDS Articles 3.6.1.2.2 and 3.6.1.2.3, respectively). Also

include the Multiple Presence Factors (BDS Article 3.6.1.1.2) in the transverse design. Do not

include the Tire Contact Area (BDS Article 3.6.1.2.5) in the transverse design of new bridges when

using influence surface analysis methods to calculate fixed-end moments. Consider lane loading

also in design of transverse deck.

Design the prestressed concrete deck for Strength I and Service I Load Combination excluding all

wind effects. Perform all analyses assuming no benefit from the stiffening effects of any traffic railing

barrier.

The Tire Contact Area (BDS Article 3.6.1.2.5) may be used when evaluating the transverse operating

rating of existing prestressed concrete box girder decks.


Page 27

04-CONCRETE STRUCTURE SECOND EDITION – AUGUST 2021

4 CONCRETE STRUCTURES

Section 5 of the BDS presents unified design requirements for reinforced and prestressed concrete

in all structural elements. This Chapter presents supplementary information specifically on the

properties of concrete and reinforcing steel and the design of structural concrete members.

The American Concrete Institute (ACI) uses unified provisions in ACI 318 (8).

4.1 Structural Concrete Design

4.1.1 Member Design Models

Reference: BDS Articles 5.6.3, 5.8.1, 5.8.3, and 5.13.2

Where planar sections remain planar after loading, the BDS allows two approaches to the design for

concrete members ⎯ the strut-and-tie model and the traditional sectional design model. For

members where planar sections do not remain planar after loading, use the strut-and-tie model. The

basic application of these models is as follows:

1. Sectional Design Model. Use the sectional design model for the design of typical bridge

girders, slabs, and other regions of components where the assumptions of traditional girder

theory are valid.

The sectional design model assumes that the response at a particular section depends only

on the calculated values of the sectional force effects such as moment, shear, axial load, and

torsion. The model does not consider the specific details of how the force effects are

introduced into the member. BDS Article 5.8.3 discusses the sectional design model.

Subarticles 1 and 2 describe the applicable geometry to use the technique to design for

shear.

2. Strut-and-Tie Model. Use the strut-and-tie model in regions near discontinuities (e.g. abrupt

changes in cross section, openings, coped (dapped) ends, deep girders, corbels). See BDS

Articles 5.6.3 and 5.13.2.

The strut-and-tie model discusses how the load is introduced into the member as a part of

the analysis.

The following Sections discuss each member design approach.

4.1.2 Flexural Resistance


4.1.2.1 Sectional Design Model

The flexural resistance of a section is typically obtained using the rectangular stress distribution of

BDS Article 5.7.2.2. In lieu of using this simplified approach, use a strain compatibility approach as

outlined in BDS Article 5.7.3.2.5.

The general equation for structural concrete flexural resistance in BDS Article 5.7.3.2.1 is based

upon the rectangular stress block, commonly called the Whitney stress block.


Page 28


4.1.2.2 Limits for Flexural Steel Reinforcement

Maximum Reinforcement

Reference: BDS Articles 5.7.3.3.1 and 5.5.4.2.1

The current BDS provisions eliminate the former maximum limit of reinforcement. Instead, a

resistance factor varying linearly between the traditional values for flexure and compression

members (see BDS Equations 5.5.4.2.1-1 or 5.5.4.2.1-2) is applied to differentiate between tension-

and compression-controlled sections. Compression-controlled sections use a lower resistance factor

to achieve safety comparable to tension-controlled sections.

Minimum Reinforcement

Reference: BDS Articles 5.7.3.3.2 and 5.4.2.6

Provide flexural resistance equal to the lesser of:

• 1.2 times the cracking moment of the concrete section, defined by BDS Equation 5.7.3.3.2-1

and assuming that cracking occurs at the modulus of rupture, which is 1.0

for normal-weight concrete; or

• 1.33 times the factored moment required by the governing load combination.

4.1.2.3 Distribution of Reinforcement


In addition to the provisions of BDS Article 5.7.3.4, use the following:

1. Negative Moments. For the distribution of negative moment tensile reinforcement continuous

over a support, compute the deck’s effective tension width separately on each side of the

support based on BDS Article 5.7.3.4. Use the larger of the two effective widths for the

uniform distribution of the reinforcement into both spans.

2. Girders. Within the negative moment regions of continuous cast-in-situ structures, use a T25

for the top side face bar (skin reinforcement) on each face of the girder web.

3. Integral Pier Caps. For integral pier caps, place reinforcement approximately 75 mm below

the construction joint between the deck and the rest of the cap beneath it, or lower if

necessary to clear prestressing ducts. Design the reinforcement by taking Mu as 1.3 times

the negative moment of the dead load for that portion of the cap and superstructure located

beneath the construction joint and within 3 m of each side face of the cap; i.e. the cap width

plus 6 m. Service limit-state checks and shear design are not required for this condition. Only

include this reinforcement in computing the flexural resistance of the cap if a strain-

compatibility analysis is made to determine the stress in the bars.

4.1.2.4 Crack Control Reinforcement


Non-structural concrete, such as a levelling course, 100 mm or greater in thickness requires

reinforcement.

c

f


Page 29


Distribute the reinforcing bars in all reinforced concrete members in tension to control cracking in

accordance with BDS Article 5.7.3.4. When designing for crack control, use γe = 0.65 in all cases.

Exceptions are buried structures and bridges in extremely aggressive environments, as discussed

in Section 4.2, in which case use γe = 0.50.

The thickness of clear cover used to compute dc shall not be taken to be greater than 50mm. Any

concrete cover thickness greater than the minimum required by Table 4.4 in Section 4.4.2.2 may be

neglected when calculating dc and h. See Section 7.5 for mass concrete requirements.

Provide additional consideration in the design to limit cracks due to intrinsic (including early thermal)

effects.

Several smaller reinforcing bars at moderate spacing are more effective in controlling crack widths

than fewer larger bars. The application of exposure conditions lower than those of the BDS provide

additional durability.

4.1.3 Shear Resistance


4.1.3.1 Sectional Design Models

For the sectional design model, use the general procedure of BDS Article 5.8.3.4.2 to determine the

shear resistance. When calculating the shear resistance, use the area of stirrup reinforcement

intersected by the distance 0.5dv cot on each side of the design section, as shown in BDS

Figure C5.8.3.2-3.

The simplified procedure for non-prestressed sections of BDS Article 5.8.3.4.1 and the simplified

procedure for prestressed and non-prestressed sections of BDS Article 5.8.3.4.3 are less accurate

methodologies. The general procedure mandated herein is the most accurate determination of shear

resistance.

4.1.3.2 Shear Friction


The steel required to comply with the provisions of BDS Article 5.8.4 is additive to the steel required

from other analyses, except as provided in BDS Article 5.10.11.

4.1.4 Strut-and-Tie Model


The strut-and-tie model is only applicable to the Strength and Extreme-Event limit states because

significant cracking must be present for the model to be valid.

Members, when loaded, indicate the presence of definite stress fields that can individually be

represented by tensile or compressive resultant forces as their vectorial sums. The “load paths”

taken by the resultants form a truss-like pattern that is optimum for the given loading. The resultants

are in reasonable equilibrium, especially after cracking. The designer’s objective is to conceive the

optimum pattern in developing the strut-and-tie model. The closer the designer’s assumption is to

the optimum pattern, the more efficient the use of materials. For poorly conceived strut-and-tie


Page 30


models, the materials are used less efficiently, but the structure will be safe. The compressive

concrete paths are the struts, and the reinforcing steel groups are the ties. The model does not

involve shear or moment because the stresses are modelled as axial loads alone.

The application of the strut-and-tie model includes several simple steps:

1. Identify the truss model that carries the applied loads to the reactions and, subsequently,

establishes the truss geometry.

2. Proportion the struts according to the provisions of BDS Article 5.6.3.3, and the ties according

to BDS Article 5.6.3.4.

3. Proportion the nodal regions connecting the truss members based on BDS Article 5.6.3.5,

wherein concrete compression stresses are limited.

4. Provide crack control reinforcement according to BDS Article 5.6.3.6 to control the significant

cracking necessary to facilitate the strut-and-tie model.

The strut-and-tie model applies to bridge components such as pier caps, girder ends, post-tensioning

anchorage zones, etc. A thorough presentation of the model can be found in:

• NCHRP 20-7, Task 217 Verification and Implementation of Strut-and-Tie Model in BDS

Bridge Design Specifications, November 2007 (9);

• D. Mitchell, M. Collins, S. Bhidé and B. Rabbat, AASHTO “BDS Strut-and-Tie Model Design

Examples,” EB231, Portland Cement Association (PCA) (10);

• Chapter 8 of the PCI Precast Prestressed Concrete Bridge Design Manual (11); and

• J. Schlaich, et al, “Towards a Consistent Design of Structural Concrete,” PCI Journal, Vol.

32, No. 3, 1987 (12).

Cracking is associated with at least partial debonding and, thus, the bonding capacity of cracked

concrete cannot be considered completely reliable. The BDS generally requires that reinforcing steel

not be anchored in cracked zones of concrete. Improperly anchored reinforcing steel is commonly

overlooked.

4.1.5 Torsion


Where torsion effects are present, design the member in accordance with BDS Articles 5.8.2 and

5.8.3.6.

Torsion is not normally a major consideration in highway bridges. Examples that may require a

torsion design include:

• Cantilever brackets connected perpendicular to a concrete girder, especially if a diaphragm

is not located opposite the bracket;

• Concrete diaphragms used to make precast girders continuous for live load where girder

spacing varies in adjacent spans; and

• Abutment caps, if they are unsymmetrically loaded.


Page 31


4.1.6 Fatigue

Reference: BDS Articles 3.4.1, 3.6.1.4, and 5.5.3

Do not consider fatigue for concrete decks or where the permanent stress fmin is compressive and

exceeds twice the maximum tensile live load stress. Also, do not consider fatigue for strands in fully

prestressed concrete members.

The fatigue limit state is not normally a critical issue for concrete structures.

4.1.7 Lateral Confinement Reinforcement

4.1.7.1 Columns


Lateral reinforcement for compression members consists of either spiral reinforcement, welded

hoops, or a combination of lateral ties and cross ties. Only use ties when it is not practical to provide

spiral or hoop reinforcement. Where longitudinal bars are required outside the spiral or hoop

reinforcement, provide lateral support with bars spaced and hooked as required for cross ties.

Extend the hooked bars into the core of the spiral or hoop one full development length.

4.1.7.2 Drilled Shafts

Extend the reinforcing steel cage for drilled shafts the full length of the pile.

Maximize the size of longitudinal and transverse reinforcement to increase the openings between all

reinforcement. This allows concrete to pass through the cage during placement. Maintain the

maximum spacing requirements of BDS Article 5.13.6.3d.

4.1.7.3 Headed Reinforcement

Consider headed reinforcement as an alternative to lateral reinforcing steel when conflicts make the

use of tie reinforcement impractical. Headed reinforcement consisting of friction welded or internally

forged heads conforms to ASTM A970M.

4.2 Environmental Classification

4.2.1 General

In the bridge drawing “General Notes,” include the environmental classification for both the

superstructure and substructure according to the following classifications:

1. Slightly aggressive

2. Moderately aggressive

3. Extremely aggressive

For the substructure, additional descriptive data is required for the environmental classification. After

the classification, provide the source and magnitude of the environmental classification parameters

for the classification in parentheses.


Page 32


As an example, where the substructure is in an Extremely Aggressive environment due to low soil

pH of 4.5 and the superstructure is in a Slightly Aggressive environment, the format on the bridge

plans is:

ENVIRONMENTAL CLASSIFICATION:

Substructure: Extremely Aggressive (Soil pH = 4.5)

Superstructure: Slightly Aggressive

The substructure is not classified less severely than the superstructure.

4.2.2 Classification Criteria

Bridge substructure and superstructure environments are classified as Slightly Aggressive,

Moderately Aggressive, or Extremely Aggressive environments according to Figure 4.1. The

superstructure is defined as all components from the bearings upward. Every element below the

bearings is classified as substructure.

4.2.2.1 Marine Structures

Marine structures are structures located 1 km or less from a body of water containing chloride above

2000 ppm. All other structures are considered non-marine structures. Use chloride test results to

determine if a structure is classified as marine.

Classify superstructure and substructure as follows:

1. For structures 1 km or more from a body of water with chloride concentrations in excess of

6000 ppm, both superstructure and substructure are classified as extremely aggressive.

2. For structures over water with chloride concentrations of 2000 to 6000 ppm, the substructure

is classified as Extremely Aggressive. Superstructures located at 3.5 m or less above the

mean high water elevation are classified as extremely aggressive. Superstructures located

at an elevation greater than 3.5 m above the mean high water elevation are classified as

Moderately Aggressive.

3. For structures within 1 km of a body of water with a chloride concentration of 2000 to 6000

ppm, but not directly over the body of water, the superstructure is classified as Moderately

Aggressive. The non-marine criteria in

4. Table 4.1 applies to the substructure.

4.2.2.2 Non-Marine Structures

All structures that do not meet the criteria above are considered non-marine structures.

1. Substructure. Use

2. Table 4.1 to classify all non-marine substructures in contact with water and/or soil.

3. Superstructure. For any superstructure located within 1 km of any carbon burning industrial

facility, fertilizer plant, or any other similar industry, classify as Moderately Aggressive. For

all others, classify as Slightly Aggressive.


Page 33


Figure 4.1: Flowchart for Environmental Classification of Structures

Start

Is thestructure over

Or within 1 km of a body of water with CL > 2000

ppm?

Non-Marine Structure

Marine Structure

Is the structure over or

within 1 km of a bodyof water with CL > 6000

ppm?

Is the superstructure within 1 km of

industrial facility?

Is the structure over

water?

Is the structure higher

than 3.5 m aboveMHW?

SuperstructureModerately

Aggressive and go to Table 4.1

for substructure classification

SuperstructureSlightly

Aggressive and go to Table 4.1

for substructure classification

SuperstructureExtremely

Aggressive and substructure

Extremely Aggressive

SuperstructureModerately

Aggressive and substructure


NoYes

Yes

No

No

No

Yes

No

Yes

Yes

Abbreviations:

CL = Chlorideppm = parts per million


Page 34


Table 4.1: Criteria for Substructure Environmental Classifications

Classification Environmental

Condition Units

Steel Concrete

Water Soil Water Soil

Extremely Aggressive (if any of these conditions exist)

pH < 6.0 < 5.0

CI ppm > 2000 > 2000

SO4 ppm N/A > 1500 > 2000

Resistivity Ohm-cm < 1000 < 500

Slightly Aggressive (if all of these conditions exist)

pH > 7.0 > 6.0

CI ppm < 500 < 500

SO4 ppm N/A < 150 < 1000

Resistivity Ohm-cm > 5000 > 3000

Moderately Aggressive

This classification must be used at all sites not meeting requirements for either Slightly Aggressive or Extremely Aggressive environments.

pH = acidity (-log10H+; potential of hydrogen) CI = chloride content SO4 = sulphate content

4.2.3 Chloride Content

To optimize the materials selection process, the designer and/or materials engineer can obtain

representative cores to determine chloride intrusion rates for a superstructure within 1 km of a major

body of water containing more than 6000-ppm chlorides. The materials engineer takes core samples

from bridge superstructures in the immediate area of the proposed superstructure. The materials

laboratory tests core samples for chloride content and intrusion rates.

Generally, all superstructures within the line-of-sight and within 1 km of the Gulf are subject to

increased chloride intrusion rates of 0.027 kg/m3/year at a 50-mm concrete depth. The intrusion rate

decreases rapidly with distance from open waters and/or when obstacles such as rising terrain,

foliage, or buildings alter wind patterns.

After representative samples are taken and tested, use Table 4.2 to correlate the core results (the

chloride intrusion rate in kg/m3/year at a depth of 50 mm) with the classification.

Table 4.2: Chloride Intrusion Rate/Environmental Classifications

Chloride Intrusion Rate Classification

≥ 0.027 kg/m3/year Extremely Aggressive

< 0.027 kg/m3/year Moderately Aggressive

See Figure 4.1 for determining environmental classification.


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4.3 Materials

4.3.1 Concrete Strength


Comply with all structural concrete requirements of the Abu Dhabi Standard Specifications: Volume

1: Road Works, Chapter 4, and Volume 2: Road Structures, Chapter 21 (Document Reference

Number TR-542-1 and TR-542-2).

Table 4.3 presents criteria for the minimum compressive strength of concrete in structural elements

in the Abu Dhabi Emirate.

Table 4.3: Compressive Strength of Concrete

Structural Element

Minimum 28-Day Compressive Strength

Cube Strength (Fcu)

Cylinder Strength

( cf )

Cast-in-situ post-tensioned concrete 45 MPa 36 MPa

Prestressed, precast concrete in bridge superstructure

50 MPa 40 MPa

Cast-in-situ reinforced concrete in bridge superstructure, barriers, and precast panels

45 MPa 36 MPa

Pier shafts, abutments, walls, drilled shafts, and their caps, approach slab

40 MPa 32 MPa

Non-reinforced concrete 25 MPa 20 MPa

4.3.2 Reinforcing Steel


Comply with all reinforcement requirements of the Abu Dhabi Standard Specifications: Volume 1:

Road Works, Chapter 5 (Document Reference Number TR-542-1). Black steel shall be used for all

structural elements.

4.3.3 Prestressing Strand


Comply with prestressing strand requirements of the Abu Dhabi Standard Specifications: Volume 2:

Road Structures, Chapter 22 (Document Reference Number TR-542-2).

4.3.4 Prestressing Bars


Comply with prestressing bar requirements of the Abu Dhabi Standard Specifications: Volume 2:

Road Structures, Chapter 22 (Document Reference Number TR-542-2).


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4.4 Reinforced Concrete Structures

4.4.1 Durability Measures

Design the bridges and underpasses structures for a design life of 75 years.

Use the following measures as specified in the Abu Dhabi Standard Specifications: Volume 1: Road

Structures, Chapter 4 (Document Reference Number TR-542-1) to enhance the durability of

concrete structures:

• Addition of cementitious materials such as GGBFS, fly ash, and microsilica;

• Special proportioning of aggregates and selection of sources;

• Reduced water-to-cement ratio;

• Increased concrete cover;

• Use of corrosion inhibitor in some cases;

• Painting (protection coating) of concrete surfaces;

• Use of stainless steel reinforcement in difficult to access areas;

• Providing possible future connection to a cathodic protection system (where black steel is

used).

Protection of the bridge deck top surface against chloride ingress by a system of spray applied

waterproofing membrane (minimum 2mm thickness) shall be used for bridges located at

maximum 10km from coastal area.

Protection of the bridge deck top surface against chloride ingress by a system of spray applied

waterproofing membrane (minimum 1mm thickness) shall be used for bridges located at a

distance between 10-20km from coastal area and/or areas surrounded by sabkha salt.

For other locations, no need to use waterproofing membrane to protect the bridge deck top

surface.

An additional 20mm sand asphalt layer (or equivalent) shall be applied immediately above the

bridge deck spray applied waterproofing to those areas shown on the drawings and shall comply

with the specifications and the thickness should be deducted from wearing course thickness.

4.4.2 Reinforcing-Steel Details

4.4.2.1 Fabrication Lengths

Use a maximum length of 12 m for detailing reinforcing steel. Longer lengths up to 24 m are available

by special order (check with suppliers).

4.4.2.2 Concrete Cover


Table 4.4 presents the requirements for concrete cover over steel.


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When deformed reinforcing bars are in contact with other embedded items (e.g., post-tensioning

ducts), consider the actual bar diameter, including deformations, in determining the design

dimensions of concrete members and cover.

4.4.2.3 Spacing of Reinforcing Bars


Use a maximum size of coarse aggregate of 20 mm to determine minimum spacing between

reinforcement bars based upon BDS Articles 5.10.3.1.1 and 5.10.3.1.2 for cast-in-situ and precast

members, respectively. In addition, use a clear distance between bars of 40 mm and 30 mm for cast-

in-situ and precast members, respectively.

Check the fit and clearance of reinforcing by calculations and large-scale drawings.

Table 4.4: Concrete Cover

Structural Elements or Conditions Concrete Cover (mm)

S or M E

Superstructure (cast-in-situ)

All external surface 50

All internal surfaces 40

Superstructure (precast)

Internal and external surfaces of segmental concrete boxes 40

Outside surface of superstructure box elements 40

Inside surface of superstructure box elements 40

External surfaces of prestressed beams 40

Substructure (cast-in-situ)

Piles & bottom surface of pile cap 100

External surfaces cast against earth and in contact with water 80

Exterior formed surfaces, columns, and top of footings not in contact with water/soil

60 80

Internal surfaces 70

Pierheads 60

Substructure (precast)

Substructure not in contact with water/soil 50 70

Prestressed piles 60 80

S = Slightly Aggressive

M = Moderately Aggressive

E = Extremely Aggressive

Skews tend to complicate problems with reinforcing fit.


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Consider the tolerances normally allowed for cutting, bending, and locating reinforcing. Refer to ACI

315 (13) for allowed tolerances.

Some of the common areas of interference are:

• Anchor bolts in abutment caps;

• Between slab reinforcing and reinforcing in monolithic abutments or piers;

• Vertical column bars projecting through main reinforcing in pier caps;

• The areas near expansion devices;

• Embedded plates for prestressed concrete girders;

• Anchor plates for steel girders;

• At anchorages for a post-tensioned system; and

• Between prestressing (pretensioned or post-tensioned) steel and reinforcing steel stirrups,

ties, etc.

4.4.2.4 Development Length of Reinforcement

Develop reinforcement on both sides of a point of maximum stress at any section of a reinforced

concrete member. This requirement is based on development length, ld.

Development Length in Tension


The development length, ld (including all applicable modification factors), must not be less than 300

mm.

The development of bars in tension involves calculating the basic development length, ldb. The

length is modified by factors for bar spacing, cover, enclosing transverse reinforcement, top bar

effect, type of aggregate, and the ratio of required area to the area of reinforcement to be developed.

Development Length in Compression

Do not consider columns as compression members for development length computations. When

designing column bars with hooks to develop the tension, ensure that the straight length is also

adequate to develop the bar in compression because hooks are not effective in developing bars in

compression.

This practice ensures that columns in bending have adequate development in both tension and

compression.

Standard End Hook Development Length in Tension


The figure in the commentary of BDS Article C5.11.2.4.1 for hooked-bar details presents the

development of standard hooks. Use the same figure for both uncoated and coated bars, modified

as appropriate by the factors above.


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Standard hooks use a 90 and 180 bend to develop bars in tension where space limitations restrict

the use of straight bars. End hooks on compression bars are not effective for development length

purposes.

4.4.2.5 Splices


Types/Usage

The following presents preferred practices on the types of splices and usage:

1. Lap Splices. Use conventional lap splices whenever practical. Use a minimum Class C splice

for T12 through T25 bars and a Class B splice for T32 bars. Where feasible, stagger lap

splices for main-member reinforcement such that a maximum of 50% are lapped in any one

location. Use a minimum stagger of 60 bar diameters between adjacent centrelines of splices

for individual and bundled bars.

If transverse reinforcing steel in a bridge deck is lapped near a longitudinal construction joint,

place the entire lap splice on the side of the construction joint that is poured last.

2. Mechanical Splices. (Reference: BDS Articles 5.11.5.2.2, 5.11.5.3.2, and 5.11.5.5.2). A

second method of splicing is by mechanical splices, which use proprietary splicing

mechanisms. Mechanical splices are appropriate away from plastic hinges and where

interference problems preclude the use of conventional lap splices, and in staged

construction. Even with mechanical splices, staggered splices are frequently necessary. The

designer must check clearances. In addition, consider fatigue. Mechanical splices must

develop 125% of the bar yield strength for reinforcing steel in non-yielding areas. Mechanical

splices must develop 160% of the bar yield strength for reinforcing steel in yielding areas not

subject to plastic hinging.

3. Welded Splices. Splicing of reinforcing bars by welding, although allowed by the BDS, is

prohibited.

4. Full Mechanical/Welded Splices. See BDS Article 5.11.5.3.2.

Plastic Hinge Regions

In columns and drilled shafts, do not use splices in the longitudinal reinforcing or splicing of spiral

reinforcing within the plastic hinge regions. Clearly identify the regions in the contract documents.

4.4.2.6 Bundled Bars

Reference: BDS Articles 5.11.2.3 and 5.11.5.2.1

Use two-bundled or three-bundled bars; do not use four-bundled bars.

For the development length of bars within a bundle, use an individual bar as specified in Section

4.4.2.4, increased by 20% for a three-bar bundle.

Determine lap splices of bundled bars based on development lengths as specified above. Do not

lap-splice entire bundles at the same location. Individual bars within a bundle may be lap spliced,


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but do not overlap the splices. Check fit and clearance of reinforcing by calculations and large-scale

drawings.

4.5 Prestressed Concrete Superstructures

4.5.1 Basic Criteria

This discussion applies to both pretensioned and post-tensioned concrete members.

4.5.1.1 Concrete Stress Limits


The tensile stress limits in Table 4.5 shall apply under the Service III limit state for main members

that are prestressed. Limit the tensile stress limit at transfer to 0.35c

f MPa.

Table 4.5: Tensile Stress Limits

Environment Stress Limit (MPa)

Extremely Aggressive 0

Moderately Aggressive 0.175c

f

Slightly Aggressive 0.35 c

f

Non-Aggressive 0.5 c

f

4.5.1.2 Concrete Strength at Release


At release of the prestressing force, the minimum compressive concrete strength shall be 60% of

the specified 28-day strength.

4.5.2 Post-Tensioned Bridges


Post-tensioned box-girder bridges are inherently complex to design and build. They require a

coordinated effort between designers and detailers to develop integrated plans that address all

design, detailing, and constructability issues. This Section presents only a portion of the

requirements necessary to accomplish this task.

4.5.2.1 Design

Shear Resistance

Strength Limit State


Determine the shear resistance of CIS, P/T bridges using the modified compression field theory

(MCFT) sectional model of BDS Article 5.8.3.4.2.


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Service Limit State


The principal stress-limit requirements of BDS Article 5.8.5 apply to CIS, P/T bridges at the Service

limit state.

Flexural Resistance


Determine flexural resistance for CIS, P/T concrete bridges using the combined effects of bonded

prestressing and mild reinforcing steel based on BDS Article 5.7.3.2.

Principal Tensile Stresses

Reference: BDS Articles 5.8.5, 5.9.4.2.2 and 5.14.2.3.3

Use segmental construction without the use of vertical PT bars in the webs. First, reduce high

principal stresses by extending the section depth and/or thickening the web. When vertical PT bars

are required, limit the placement to the lesser of (1) the first two segments from the pier

segment/table or (2) ten percent of the span length.

Occasionally in cast-in-situ balanced cantilever construction, vertical PT bars supplying a nominal

vertical compression are used at select locations to control web cracking.

Anchor Set

Assume a typical post-tensioning anchor set of 6 mm (to be verified during construction).

Creep and Shrinkage

Calculate creep and shrinkage strains and effects using a relative humidity of 60%.

4.5.2.2 Detailing

Post-Tensioning Tendons

Strand Size

The preferred diameter of the prestressing strand for post-tensioning is 15.24 mm or 15.7 mm.

Tendon Components

Use ducts made of HDPE. However, if the tendon profile radius is less than 9 m, corrugated steel

ducts shall be used.

Tendons are proprietary systems that consist of an anchorage, duct, grout injection pipes, and

prestressing strand. Smaller tendons used in decks contain up to four strands. Consult specific post-

tensioning system brochures for the actual size of ducts. Two to five tendons are usually needed for

each girder web to satisfy design requirements. The centre of gravity specified at anchorages must

be consistent with tendon anchorage requirements (e.g. anticipated size(s) of bearing plates).

For cast-in-situ, post-tensioned box girder bridges, tendons are internal to the girder webs.

Segmental precast bridges can have tendons either external or internal to the girder web.


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Tendon Profile

Show offset dimensions to post-tensioning duct profiles from fixed surfaces or clearly defined

reference lines. In regions of tight reverse curvature of short sections of tendons, show offsets at

sufficiently frequent intervals to clearly define the reverse curve.

Encase curved ducts that run parallel to each other, ducts in curved girders, ducts in chorded girders

where angle changes occur between segments, or ducts placed around a void or re-entrant corner

in concrete and reinforced as necessary to avoid radial failure (pull-out into the other duct or void).

For the tendon profile, use the following:

1. Secondary Effects.

• During design of continuous straight and curved structures, account for secondary

effects due to post-tensioning.

• Design curved structures for the lateral forces due to the plan curvature of the

tendons.

2. Tendon Geometry. When coordinating design calculations with detail drawings, consider that

the centre of gravity of the duct and the centre of gravity of the prestressing steel are not

necessarily coincidental. See Table 4.6.

3. Required Prestress. On the drawings, show prestress force values for tendon ends at

anchorages.

4. Internal/External Tendons. External tendons must remain external to the section without

entering the top or bottom slab.

5. Strand Couplers. Do not use strand couplers as described in BDS Article 5.4.5.

The geometry of a typical tendon profile is predominantly second-degree parabolic curved segments.

The tendons are essentially straight segments near the anchorages. The tendon group centre of

gravity and the bridge’s neutral axis coincide at the following locations ⎯ at the centrelines of

abutments, hinges, and points of dead-load contraflexure.

Table 4.6: Minimum Centre-to-Centre Duct Spacing (Straight Ducts)

Post Tensioned Bridge Type Minimum Centre-to-Centre Longitudinal Duct Spacing1

Precast segmental balanced cantilever 200 mm, two times outer duct diameter, whichever is greater.

Spliced I-girder bridges 100 mm, outer duct diameter plus 1.5 times maximum aggregate size or outer duct diameter plus 50 mm, whichever is greater.

Cast-in-situ voided slab bridges

Cast-in-situ multi-cell bridges

Cast-in-situ balanced cantilever

Duct diameter plus 75 mm or 1.7 times duct diameter, whichever is greater

1 Bundled tendons are not allowed. Note: For curved ducts, the BDS provisions shall be followed.


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Post-Tensioning Systems

Specify tendon duct radius and dimensions to duct PI points on the design plans. For parabolically

curved ducts, show offset dimensions to post-tensioning duct trajectories from fixed surfaces or

clearly defined reference lines at intervals not exceeding 1.0 m. For curved ducts that run parallel to

each other or around a void or re-entrant corner, encase the ducts in concrete and reinforce as

necessary to avoid radial failure (pull-out into another duct or void). For approximately parallel ducts,

consider the arrangement, installation, stressing sequence, and grouting to avoid potential problems

with cross grouting of ducts.

Detail post-tensioned precast I-girders to utilize round ducts only.

Size ducts for all post-tensioning bars 13 mm larger than the diameter of the bar coupler.

Post-tensioned bridges can be constructed segmentally, consisting of many relatively short

components, or non-segmentally or span-by-span, consisting of long span-length components. In

segmental construction, no more than 50% of the number of tendons shall be coupled at a segmental

joint. In non-segmental construction, up to 100% of the tendons may be coupled at a joint on a case-

by-case basis.

Internal post-tensioning ducts must be positively sealed with a segmental duct coupler or O-ring at

all segment joints. Design and detail all internal tendon segmental duct couplers with a maximum

deflection of 9 degrees at the segment joint as shown in the following sketch.

Mount segmental duct couplers or O-ring hardware perpendicular to the bulkhead at the segment

joints. Use only approved PT systems that contain segmental duct couplers. See tendon alignment

schematic on the next page. Cast-in-situ closure joints are a minimum 450-mm wide.

Make segmental duct couplers normal to joints to allow stripping of the bulkhead forms.

Theoretically, the tendon must pass through the coupler without touching the duct or coupler. Over-

sizing couplers allows for standardized bulkheads and avoids curved tendons. The BDS limits the

number of coupled tendons to 50% of the total number.

To allow room for the installation of duct couplers, detail all external tendons with an additional cover

of 10 mm above that specified based upon environmental exposure.

Where external tendons pass through deviation saddles, design the tendons to be contained in

grouted steel pipes, cast into the deviation saddle concrete.

All anchorages must be accessible but protected after construction. Do not use strand anchorages

cast into concrete structures.

“Diablos” are preferred at deviation saddles as they are less susceptible to installation errors.


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Instead of using steel pipes at the deviators, continuously curved voids (diablos) are cast into the

deviation diaphragm to allow larger deviations from the theoretical tendon profile.

For external tendons, use steel pipe ducts for curved portions of the tendon profile in the diaphragm.

Plastic duct is permissible for straight portions of tendon profile in the diaphragm.


Page 45


See Table 4.7 for the minimum tendons required. All balanced cantilever bridges must utilize a

minimum of four, positive moment, external draped, continuity tendons (two per web) that extend to

adjacent pier diaphragms.

Table 4.7: Minimum Tendons Required for Critical Post-Tensioned Sections

Post-Tensioned Bridge Element Minimum Number of Tendons

Mid span closure pour

Cast-in-situ and precast balanced cantilever bridges

Bottom slab – two tendons per web

Top slab – one tendon per web

(15.24-mm dia. min)

Span by span segmental bridges Four tendons per web

Cast-in-situ multi-cell bridges Three tendons per web

Spliced I-girder bridges1 Three tendons per girder

Unit end spans

Cast-in-situ and precast balanced cantilever bridges

Three tendons per web

Diaphragms – vertically post-tensioned

Six tendons; if strength is provided by P.T. only

Four tendons; if strength is provided by combination of P.T. and mild reinforcing

Diaphragms – Vertically post-tensioned Four bars per face per cell

Segment – Vertically post-tensioned Two bars per web

1 4 girders minimum per span.

Ducts

In post-tensioned construction, ducts are cast into the concrete to permit placement and stressing

of the tendons. Always use high-density polyethylene ducts at all locations in the deck section. Girder

ducts are typically galvanized corrugated steel (semi-rigid). For external tendons on segmental

bridges, use smooth polyethylene. The contract documents must designate the type of duct material.

The duct-wall thickness must be no less than 0.40 mm. Use prebending of ducts for bend radii less

than 9 m. Avoid radii that require prebending whenever possible. Use


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Table 4.8 to tabulate the minimum bend radius of ducts for steel ducts. Do not use a bending radius

of less than 9 m for polyethylene or polypropylene ducts. For a radius less than 9 m, use galvanized

corrugated steel ducts.


Page 47


Table 4.8: Recommended Minimum Duct Radius (for Steel Ducts)

Tendon Size Minimum Radius

12 15.24-mm dia 3.0 m

19 15.24-mm dia 4.0 m

27 15.24-mm dia 5.0 m

37 15.24-mm dia 6.0 m

A bridge can be constructed by post-tensioning precast components together longitudinally and/or

transversely by use of a cast-in-situ concrete joint. For this type, extend the end of the duct beyond

the concrete interface by at least 75 mm and not more than 150 mm to facilitate joining the ducts. If

necessary, the extension could be in a local blockout at the concrete interface. Joints between

sections of ducts must be positive metallic connections, which do not result in angle changes at the

joints. Use waterproof tape at all connections.

For multiple-strand tendons, the outside diameter of the duct must be no more than 40% of the least

gross concrete thickness at the location of the duct. During design, the bridge designer must lay out

an acceptable duct arrangement that matches the post-tensioning centre of gravity to determine the

need for a wider web. The internal free area of the duct must be at least 2.5 times the net area of

the prestressing steel. See BDS Article 5.4.6.2.

Grouting

Detail all post-tensioned bridges with the following corrosion protection strategies:

• Enhanced post-tensioned systems,

• Fully grouted tendons,

• Multi-level anchor protection,

• Bridges with no deck joints or watertight deck joints, and

• Multiple tendon paths.

Enhanced post-tensioning systems require three levels of protection for strand and four levels for

anchorages. (Deck overlays are not considered a level of protection for strands or anchorages):

1. Within the segment or concrete element:

a. Internal Tendons

• Concrete cover

• Plastic duct

• Complete filling of the duct with approved grout

b. External Tendons

• Hollow box structure itself

• Plastic duct

• Complete filling of the duct with approved grout


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2. At the segment face or construction joint (internal and external tendons):

a. Epoxy seal (precast construction) or wet cast joint (cast-in-situ construction)

b. Continuity of the plastic duct

c. Complete filling of the duct with approved grout

The required four levels of protection for anchorages on interior surfaces (e.g. interior diaphragms)

are:

1. Grout

2. Permanent grout cap

3. Elastomeric seal coat

4. Concrete box structure

The required four levels of protection for anchorages on exterior surfaces (e.g. pier caps, expansion

joints, diaphragms) are:

1. Grout

2. Permanent grout cap

3. Encapsulating pour-back

4. Seal coat (elastomeric/methyl methacrylate on riding surface)

Internal post-tensioning bars used for erection with acceptable ducts, grout, and cover may remain

in the structure with no additional protection. Do not incorporate the force from these bars in the

service stress or strength calculations for the structure.

The strength of the grout should be comparable to that of the girder concrete; however, the strength

is not specified due to the high strengths that typically result from tendon grouts.

Use pre-approved bagged grout for tendon grouting. Use multiple injection and bleed ports at the

ends of the tendons and at all low and high points. The flushing of tendons due to blockage is

discouraged but allowed using vacuum grouting as a consideration for repairs.

Anchorage Details

Temporary or permanent post-tensioning anchorages may be required in the top or bottom slab of

box girders. If so, design and detail interior blisters, face anchors, or other approved means. Do not

use block-outs that extend to either the interior or exterior surfaces of the slabs.

Provide continuous longitudinal mild reinforcing through all segment joints for cast-in-situ segmental

construction.

Design and detail so that any future post-tensioning for strengthening utilizes external tendons (bars

or strands). Design future post tensioning so that any one span can be strengthened independently

of adjacent spans. For each future tendon, provide one duct/anchorage location for expansion joint

diaphragms and two duct/anchorage locations for internal pier segment diaphragms.

Detail anchor blisters so that tendons terminate no closer than 300 mm to a joint between segments.

Do not use transverse bottom slab ribs. Design full height diaphragms directing the deviation forces

directly into the web and slab. See Figure 4.2.


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Do not use raised corner recesses in the top corner of pier segments at closure joints. Continue the

typical cross section to the face of the diaphragm. See Figure 4.3. Locate tendon anchorages to

permit jack placement.

Detail all interior blisters set back a minimum of 300 mm from the joint. Provide a “V”-groove around

the top slab blisters to isolate the anchorage from any free water. See the “V”-groove detail of


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Figure 4.4.

Figure 4.2: Deviator Diaphragm Detail

Figure 4.3: Inside Corner Detail at Pier


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Figure 4.4: Details at Expansion Joints

Deck Slabs

The following applies:

• Where draped post-tensioning is used in deck slabs, consider the final location of the centre

of gravity of the prestressing steel within the duct.

• Reduce critical eccentricities over the webs and at the centreline of the box by 5 mm from

theoretical to account for construction tolerances.

Intermediate Diaphragms

Intermediate diaphragms are not necessary for straight CIS concrete box girder bridges and curved

CIS concrete box girder bridges with an inside radius of 250 m. For curved box girder bridges having

an inside radius less than 250 m, intermediate diaphragms are required unless shown otherwise by

tests or structural analysis. For such curved box girders, the maximum diaphragm spacing shall be

12 m for a radius 20 m or less and 25 m for a radius between 135 m and 250 m.

Expansion Joint Details

At expansion joints, provide a recess and continuous expansion joint device seat to receive the

assembly, anchor bolts, and frames of the expansion joint; i.e. a finger or modular type joint. Lower

the upper tendon anchors and re-arrange the anchor layout as necessary to provide access for the

stressing jacks.

At all expansion joints, protect anchors from dripping water by means of skirts, baffles, V-grooves,

or drip flanges. Ensure that drip flanges are of adequate size and shape to maintain structural

integrity during form removal and erection.


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4.5.2.3 Tendon Jacking

If the distance between anchorages exceeds 60 m, consider jacking at both ends. Determine one-

end or two-end stressing by design and specify in the contract documents.

Show the values of the wobble and curvature friction coefficients and the anchor set loss assumed

for the design in the contract documents.

There are several types of commercially available anchorages. The anchorages normally consist of

a steel block with holes in which the strands are individually anchored by wedges. Near the anchor

block (or coupler), the strands are fanned out to accommodate the anchorage hardware. The fanned

out portion of the tendon is housed in a transition shield. This is often called a trumpet, which could

be either steel or polyethylene, regardless of the duct material. Trumpets must have a smooth,

tangential transition to the ducts.

4.5.2.4 Erection Schedule and Construction System

Include a description of the construction method upon which the design is based.

Include in the design documents in outlined, schematic form, a typical erection schedule and

anticipated construction system.

State in the plans the assumed erection loads, and the times of application and removal of each

erection load.

Temporary load conditions often control the design and detailing of segmental and spliced girder

structures. Size the structure components for the temporary and final condition and loadings of the

bridge.

For large projects, more than one method of construction may be necessary based on project

specific site constraints.

4.5.2.5 Falsework

Cast-in-situ, post-tensioned bridges must be supported during construction. The bridge cannot

support even the dead load until post-tensioning is complete. The temporary supports used are

either earth fills, if traffic does not have to be maintained, or falsework. Earth fills must be compacted

sufficiently to keep settlement to a minimum. Falsework usually consists of a combination of timber

and steel structural components. Design the falsework to carry the entire dead load of the bridge

and construction loads. The falsework shall be checked and approved by a specialized engineer

with adequate related experience, as approved by the client.

4.5.2.6 Access and Maintenance


During preliminary engineering and when determining structure configuration, emphasize

accessibility and the safety of bridge inspectors and maintenance:

1. Height. For maintenance and inspection, the minimum interior, clear height of box girders

shall be 1.4 m.

2. Electrical. Show interior lighting and electrical outlets at the following locations:


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• all ingress/egress access openings,

• both sides of diaphragms where girder is continuous,

• at the inside face of diaphragms where the girder is discontinuous; e.g. at end bents

and expansion joints, and

• spaced between the above locations at approximately equal intervals not to exceed

15 m.

3. Access. The following applies:

• Design box sections with ingress/egress access openings located at maximum 60 m

spacing. Space ingress/egress access openings such that the distance from any

location within the box to the nearest opening is 30 m or less. Provide a minimum of

two ingress/egress access openings per box girder line. Locate one ingress/egress

access opening near each end bent. Provide additional ingress/egress access doors

along the length of the box girder as required to meet the maximum spacing

requirement.

• Design doors in diaphragms with in-swinging, hinged, 6-mm mesh, steel screen

doors. Equip all doors at abutments and entrances with a lock and hasp.

• Provide an access opening through all interior diaphragms. If the bottom of the

diaphragm access opening is not flush with the bottom flange, provide concrete

ramps to facilitate equipment movement.

• The minimum diaphragm access opening is 800 mm wide 1050 mm, or 900 mm

diameter. Indicate on the plans that diaphragm access openings must remain clear

and must not be used for utilities, drain pipes, conduits, or other attachments. If these

items are required, provide additional areas or openings. In all other areas of the box,

provide a minimum continuous maintenance/inspection access envelope of 2-m high

1-m along the length of the box. Measure the 2-m height dimension of the envelope

from the bottom slab of the box. The height should clear all tendon ducts, anchorages,

blisters, deviation saddles, etc.

• Analyse access opening sizes and bottom flange locations for structural effects on

the girder. Generally, do not place ingress/egress access openings in zones of high

compression.

• Avoid ingress/egress access opening locations over traffic lanes that will require

extensive maintenance of traffic operations, and avoid other locations such as over

sloped embankments, over water or locations that could otherwise impact the safety

of inspectors or the travelling public. Where vagrant access is not a problem, place

an access opening near the abutment where no additional equipment will be required

for access.

4. Other Exterior Openings. Design each box girder with minimum 50-mm diameter ventilation

or drain holes located in the bottom flange on both sides of the box. Space the holes at

approximately 15-m or as needed to provide proper drainage. Place additional drains at all

low points against internal barriers. Locate drains to accommodate bridge grade.


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Provide drains to prevent water (including condensation) from ponding near post-tensioning

components, face of diaphragms, blisters, ribs, and other obstructions. Show details in the

plans. Include the following:

• Specify a 50-mm diameter permanent plastic pipe (PVC with UV inhibitor) set flush

with the top of the bottom slab.

• A drip recess, 13 mm by 13 mm around bottom of pipe insert.

• Drains at all low points against internal barriers, blisters, etc.

• Drains on both sides of the box, regardless of cross slope (to avoid confusion).

• Vermin guards for all drains and holes.

• A note stating, “Install similar drains at all low spots made by barriers introduced to

accommodate means and methods of construction, including additional blocks or

blisters.”

Require a 6-mm screen on all exterior openings not covered by a door. This includes holes

in webs through which drain pipes pass, ventilation holes, drain holes, etc.

Design flexible barriers to seal openings between expansion joint segments of adjacent end

units to prevent birds from roosting on the box end ledges. Barriers are typically UV and

weather resistant and easily replaceable.

5. Other Box Sections. Provide accessibility to box sections (e.g. precast hollow pier segments)

similar to that for box girders, particularly concerning the safety of bridge inspectors and

maintenance personnel. During preliminary engineering and when determining structure

configuration, consider box girder accessibility and the safety of bridge inspectors and

maintenance personnel.

4.5.2.7 Integrated Drawings

Show congested areas of post-tensioned concrete structures on integrated drawings with an

assumed post-tensioning system. Such areas include anchorage zones, areas containing

embedded items for the assumed post-tensioning system, areas where post-tensioning ducts

deviate, both in the vertical and transverse directions, and other highly congested areas.

For all post-tensioned structures, accommodate possible conflicts between webs and external

tendons. Check for conflicts between future post-tensioning tendons and permanent tendons.

Select the assumed post-tensioning system, embedded items, etc., so that they accommodate

competitive systems using standard anchorages of 12, 19, 22, 25, 27, 31 or 37 15.24-mm dia.

strands. Detail integrated drawings utilizing the assumed system to a scale and quality required to

show double-line reinforcing and post-tensioning steel in two-dimension (2-D) and, when necessary,

in complete three-dimension (3-D) drawings and details.

Verify that the post tensioning in the structure can be accommodated by the anchorages listed in the

specifications and has been sized according to the approved post-tensioning systems.


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Space post tensioning anchorages to accommodate spirals based on the anchorage size and not

on the number of strands in that anchorage.

Check required clearances for stressing jacks. Do not detail structures or provide construction

sequences that require curved stressing noses for jacks.

4.5.3 Precast, Prestressed Concrete Girders

4.5.3.1 Design


General

This Section addresses the general design theory and procedure for precast, prestressed (pre-

tensioned) concrete girders. For design examples, consult the PCI Bridge Design Manual, Chapter

9 (11).

Design bridges consisting of simple-span precast concrete girders and cast-in-situ concrete slabs to

be continuous for live load and superimposed dead loads by using a cast-in-situ closure diaphragm

at piers whenever possible. Other design options, including providing a compressible spacer at

debonded strand ends, are permissible.

The design of the girders for continuous structures is similar to the design for simple spans with the

following exception. In the area of negative moments, the member is treated as an ordinary

reinforced concrete section, and the bottom flanges of adjoining girders are connected at the interior

supports by reinforcement projecting from girder ends into a common diaphragm. The members are

typically fully continuous with a constant moment of inertia when determining both the positive and

negative moments due to loads applied after continuity is established.

The resistance factor (BDS Article 5.5.4) for flexure is 1.0, except for the design of the negative-

moment steel in the deck for structures made continuous for composite loads only. See the Abu

Dhabi Standard Drawings for Road Projects (Document Reference Number TR-541-2) for

continuous details. For this case, the resistance factor is the 0.90 value for reinforced concrete

members in flexure.

Use ASTM A416 (A416M), Grade 1860, low-relaxation, prestressing strands for the design of

prestressed beams. Do not use stress-relieved strands. Use straight-strand configurations (where

feasible) instead of draped strand configurations. The following requirements apply to simply

supported, fully pretensioned beams, whether of straight or depressed (draped) strand profile,

except where specifically noted otherwise.

Bridges with varying span lengths, skew angles, beam spacing, beam loads, or other design criteria

may result in very similar individual designs. Consider the individual beam designs as a first trial

subject to modifications by combining similar designs into groups of common materials and stranding

based upon the following priorities:

1. 28-day compressive concrete strength ( cf )

2. Strands (size, number, location)

3. Compressive concrete strength at release ( cif )

4. Do not use full length shielding (debonding) of prestressing strands


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Grouping beam designs in accordance with the priority list maximizes casting bed usage and

minimizes variations in materials and stranding.

To achieve uniformity and consistency in designing beams, the following parameters apply:

1. Provide a strand pattern that is symmetrical about the centreline of the beam.

2. Distribute debonded strands evenly throughout the strand pattern. Whenever possible,

separate debonded strands in all directions by at least one fully bonded strand.

3. When analysing stresses of simple span beams, limit stresses based on BDS Table

5.9.4.1.2-1 with the following exception: For the outer 15 percent of the design span, tensile

stress at the top of beam may not exceed 1.05 cif at release. For transient loads during

construction, the tensile stress limit may be taken as 0.525 cf .

4. The minimum compressive concrete strength at release is the greater of 28 MPa or 0.6 cf .

Higher release strengths may be used on a case-by-case basis but must not exceed the

lesser of 0.8 cf or 42 MPa.

5. For precast, pretensioned, normal weight concrete members designed as simply supported

beams, use BDS Article 5.9.5.3, Approximate Estimate of Time-Dependent Losses. For all

other members, use BDS Article 5.9.5.4 with a 180-day differential between girder concrete

casting and placement of the deck concrete.

Controlling the Contractor’s construction sequence and materials for simple span precast,

prestressed beams is challenging. To benefit from the use of refined time-dependent analysis,

literally every prestressed beam design would have to be re-analysed using the proper construction

times, temperature, humidity, material properties, etc., of both the beam and the yet-to-be-cast

composite slab.

1. Base the stress and camber calculations for the design of simple span, pretensioned

components on the use of transformed section properties.

2. When wide-top beams such as I- and bulb-tees are used in conjunction with stay-in-place

metal forms, evaluate the edges of flanges of the beams to safely support the weight of the

forms, concrete, and construction load.

3. Provide the design thickness of the composite slab from the top of the stay-in-place metal

form to the finished slab surface. The superstructure concrete quantity does not include the

concrete required to fill the form flutes.

For non-standard single web prestressed beam designs, modify the requirements of BDS Article

5.10.10.1 to provide vertical reinforcement in the ends of pretensioned beams with the following

splitting resistance:

• 3% Pu from the end of the beam to h/8, but not less than 250 mm;

• 5% Pu from the end of the beam to h/4, but not less than 250 mm;

• 6% Pu from the end of the beam to 3h/8, but not less than 250 mm.

Do not apply losses to the calculated prestressing force (Pu). The minimum length of debonding from

the ends of the beams is one half of the depth of beam.


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Provide embedded bearing plates in all prestressed I-girder beams deeper than 1500 mm. Provide

embedded bearing plates for all I beams. For all beam designs where the beam grade exceeds 2%,

include bevelled bearing plates.

Bearing plates add strength to the ends of the concrete beams to resist the temporary loadings

created in the bearing area by the release of prestressing forces and subsequent camber and elastic

shortening.

Analyse spans subject to significant lateral loads to determine the need for diaphragms.

When investigating the effect of significant lateral loads such as vessel collision or wave loads, check

the stresses at the interface of the beam top flange and the beam web, from each end of the beam

to a longitudinal distance approximately equivalent to the beam height.

Precast I-Girder Sections

Select the type of girder used in the superstructure based upon geometric restraints, economy, and

appearance. This Manual has not adopted standard precast concrete I-girder sections. AASHTO

and PCI have developed standard sections that are used in most locations throughout the world;

however, the sections and the associated design aids are not appropriate for the Abu Dhabi Emirate

because they do not have the required increased concrete cover.

To ensure that the structural system has an adequate level of redundancy, use a minimum of four

girder lines on new bridges.

Stage Loading

There are four loading conditions that must be considered in the design of a precast, prestressed

girder:

1. The first loading condition is when the strands are tensioned in the bed prior to placement of

the concrete. Seating losses, relaxation of the strand, and temperature changes affect the

stress in the strand prior to placement of the concrete. The fabricator must consider these

factors during girder fabrication and adjust the initial strand tension to ensure that the tension

prior to release meets the design requirements for the project. The prestressing shop

drawings must present a discussion on the fabricator’s proposed methods to compensate for

seating losses, relaxation, and temperature changes.

2. The second loading condition is when the strands are released and the force is transferred

to the concrete. After release, the girder will camber up and be supported at the girder ends

only. Therefore, the region near the end of the member is not subject to bending stresses

due to the dead load of the girder. This region may develop tensile stresses in the top of the

girder large enough to crack the concrete. The critical sections for computing the critical

temporary stresses in the top of the girder are near the end and at all debonding points. If

the designer considers the transfer length of the strands at the end of the girder and at the

debonding points, then assume that the stress in the strands is zero at the end of the girder

or debonding point. Also, assume that the stress varies linearly to the full transfer of force to

the concrete at the end of the strand transfer length.

Use the level of effective prestress immediately after release of the strands, which includes

the effects of elastic shortening and the initial strand relaxation loss, to compute the concrete

stresses at this stage.


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There are several methods to relieve excessive tensile stresses near the ends of the girder:

• Debonding, where the strands remain straight but wrapped in plastic over a

predetermined distance to prevent the transfer of prestress to the concrete through

bonding;

• Adding additional strands in the top of the girder that are bonded at the ends but are

debonded in the centre portion of the girder. These strands are typically detensioned

after the girder is erected; or

• Deviating some of the strands to reduce the strand eccentricity at the end of the

girder.

3. The third loading condition occurs several weeks to several months after strand release when

the girder is erected, and the composite deck is cast. Camber growth and prestress losses

are design factors at this stage. If a cast-in-situ composite deck is placed, field adjustments

to the haunch thickness are usually needed to provide the proper vertical grade on the top of

deck and to keep the deck thickness uniform. Use reliable estimates of deflection and camber

to prevent excessive haunch thickness or to avoid significant encroachment of the top of

girder into the bottom of the concrete deck. Stresses at this stage are usually not critical.

See Section 8.7 of the PCI Bridge Design Manual (11) for determining the girder camber at

erection.

4. The fourth loading condition is after an extended period of time during which all prestress

losses have occurred and loads are at their maximum. This is often referred to as the

“maximum service load, minimum prestress” stage. The tensile stress in the bottom fibres of

the girder at mid-span generally controls the design.

Flexural Resistance

The design of prestressed concrete members in flexure normally begins with the determination of

the required prestressing level to satisfy service conditions. Consider all load stages that may be

critical during the life of the structure from the time prestressing is first applied. This is then followed

by a strength check of the entire member under the influence of factored loads. The strength check

seldom requires additional strands or other design changes.

For checking the stresses in the girder at the Service limit state, use the following basic assumptions:

1. Planar sections remain plane, and strains vary linearly over the entire member depth.

Therefore, adequately connect composite members consisting of precast concrete girders

and cast-in-situ decks so that this assumption is valid and all elements respond to

superimposed loads as one unit. Transform deck concrete to girder concrete when

computing section properties. Accomplish this by multiplying the effective deck width by the

ratio of the deck concrete modulus of elasticity to the girder concrete modulus of elasticity.

Use the gross concrete section properties (i.e. do not transform the area of prestressing

strands and reinforcing steel).

2. Assume that the girder is uncracked at the Service limit state.

3. Do not check stress limits for the deck concrete in the negative-moment region because the

deck concrete is not prestressed.


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Vui = 12 Vu1/dv

Minimum Reinforcement Requirements

Reference: BDS Article 5.7.3.3.2

Apply the minimum reinforcement requirements of BDS Article 5.7.3.3.2 to all sections being

analysed, except at the ends of simply supported bridge girders.

The following defines the girder length from the simply supported end where the minimum

reinforcement does not need to be checked:

1. For prestressing concrete girders for a distance equal to the bonded development length.

For example, for a 1900 MPa strand with fpe = 1100 MPa, a 13-mm dia. strand yields 4 m

and a 15-mm dia. yields 4 m from the ends of the simply supported girder.

2. For reinforced concrete girders for a distance equal to 2.5 times the superstructure depth

from the centreline of bearing of the simply supported end.

For span lengths less than 8 m for simple span bridges, check the minimum reinforcement at mid-

span.

The use of a minimum reinforcement check was developed to ensure a ductile failure mode for lightly

reinforced deep beams. Bridge girders are slender and do not generally meet the definition of a deep

beam. Deep beams are members having a clear span less than 4 times the overall depth (as defined

by ACI 318). The use of the minimum reinforcing check has evolved in the specifications from

checking the critical section to checking every section. This evaluation at every section is justified in

buildings where heavy concentrated loads may be present near supports. In bridges, this condition

does not exist, and the critical section for bending is not near the support for simply supported bridge

beams. The ends of simply supported bridge girders are dominated by shear, not bending moment.

At these locations, it is unnecessary to check minimum reinforcing.

Interface Shear


Cast-in-situ concrete decks acting compositely with precast concrete girders must be able to resist

the interface shearing forces between the two elements. Use the following formula, substituting BDS

Equation 5.8.4.2-2 into BDS Equation 5.8.4.2-1, to determine the factored interface shear stress, Vui

:

Equation 4.1

The factored interface shear force must be less than or equal to the factored nominal interface shear

resistance; i.e.:

Equation 4.2

where: Vni = cAcv μ(Avf fy + Pc) (BDS Eq. 5.8.4.1-3)

Vui Vni


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Neglect the permanent net force normal to the interface, Pc, if it is compressive.

4.5.3.2 Detailing

Prestressing Strands

Strand Size

Use 15.24 mm or 15.7 mm diameter seven-wire strand.

Strand Spacing

For the minimum spacing of strands, do not use less than 50 mm centre to centre.

Strand Profile

It is acceptable to use either a straight or draped strand profile for precast members. However, where

possible, use “draped” strand (i.e. deviated, harped, deflected) instead of “debonded,” because of

the greater shear capacity and reduced number of strands. However, the designer can use a

combination of debonded and draped strands when necessary to satisfy design requirements.

The advantages of straight trajectories include their simplicity of fabrication and greater safety.

Debonded or draped strands are used to control stresses and camber. Debonded strands are easier

to fabricate because a hold-down point is not required in the stressing bed.

Draped Strand

The following applies to draped strands in precast, pretensioned girders:

• At ends of girders, maintain a minimum of 100 mm between the top draped strands and any

straight strands that are located directly above the draped strands.

• At each hold-down point, limit the vertical force to a maximum of 215 kN for all draped strands

and 18 kN for each individual draped strand.

• The slope of the draped strands would not exceed 9.

• Where practical, locate hold-down points 1.5 m on each side of the centreline of the girder

(3 m apart).

Debonded Strands

Debond strands at the ends of precast, pretensioned concrete girders with the following restrictions:

1. Debond a maximum of 25% of the total number of prestressing strands to satisfy the

allowable stress limits. In any row, do not allow debonded strands to exceed 40% of the total

strands in that row.

2. Terminate not more than 40% of the debonded strands or four strands, whichever is greater,

at any section.

3. Debond strands in a pattern that is symmetrical about the vertical axis of the girder.

4. Round off the theoretical number of debonded strands to the closest even number (pairs) of

strands, except do not allow debonded strands in rows containing three strands or less.


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5. Fully bond all exterior strands (including the entire bottom row).

6. At each end of a girder, the maximum length for debonding is 15% of the entire girder length.

In analysing stresses and/or determining the required length of debonding, limit stresses to the

values in BDS Article 5.9.4, except that tension is limited to 0.0948 cf for all exposure conditions.

Strand Patterns

Detail the strand pattern showing the total number of strands, layout and spacing, edge clearances,

which strands will be draped and/or debonded, and the layout of all mild reinforcing steel.

Frequently, precast, pretensioned girders of the same size and similar length in the same bridge or

within bridges on the same project may be designed with a slightly different number of strands. In

this case, consider using the same number and pattern of strands (including height of draping) for

these girders to facilitate fabrication.

Strand Splicing

Do not splice prestressing strand.

Diaphragms


For precast, prestressed girder spans, use cast-in-situ concrete diaphragms at all supports with the

girders embedded a minimum of 200 mm into the diaphragm.

For continuous precast, prestressed girder spans, ensure that the closure diaphragms at the piers

are cast with a horizontal construction joint between the diaphragm and the deck slab. For integral

abutments, also ensure that the end diaphragms are similarly cast.

Sole Plates

For an instantaneous slope at the bottom of the girder greater than or equal to 2%, use bevelled sole

plates to allow for level girder seats.

4.5.3.3 Girder Transportation

The bridge designer must investigate the feasibility of transporting heavy, long and/or deep girders.

In general, consider the following during the design phase:

• whether or not multiple routes exist between the bridge site and a major transportation facility,

and

• shorter and/or lighter girders may be required if access to the bridge site is limited by

roadway(s) with sharp horizontal curvature or weight restrictions.

Investigate routes for obstructions for girder depths exceeding 3 m, or if posted height restrictions

exist on the route.

Length of travel significantly increases the difficulty to transport girders. Consider alternative

transportation for heavy, long and/or deep girders. The transportation of girders weighing more than

72,500 kg may require analysis by a specialist, bridge strengthening, or other unique measures.


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When the use of heavy, long and/or deep girders is being evaluated and transportation of the girders

over land is required, contact at least one prestressed girder manufacturer and request their input

regarding girder transportation. At least one combination of viable casting location and transportation

route is required.

4.5.4 Pretensioned/Post-Tensioned Beams

In the design of pretensioned beams made continuous by field-applied post-tensioning, design the

pretensioning such that, as a minimum, the following conditions are satisfied:

1. The pretensioning meets the minimum steel provisions of BDS Article 5.7.3.3.2.

2. The pretensioning is capable of resisting all loads applied prior to post-tensioning, including

a superimposed dead load equal to 50% of the uniform weight of the beam, without

exceeding the stress limitations for pretensioned concrete construction.

3. The pretensioning force is of such magnitude that the initial midspan camber at release,

including the effect of the dead load of the beam, is at least 13 mm.

4. Anchorage zones of post-tensioning ducts, and beam lengths in which ducts deviate both

horizontally and vertically, require integrated drawings in accordance with the minimum

reinforcement requirements in Section 4.5.3.1.

5. The limitation on the percentage of debonded strands of the pretensioned strand group at

the ends of beams may be increased to 37.5%. This limitation is assuming that post-

tensioning is applied to the beams prior to casting the deck concrete and that the total number

of debonded strands is equal to or less than 25% of the total area of pretensioned and post-

tensioned strands at the time of placement of the deck concrete (14).

Full depth diaphragms are required at all splice (closure pour) and anchorage locations. At closure

pour locations, cast intermediate diaphragms with the closure pours. Design diaphragms for out-of-

plane loads for chorded girders on a horizontal curve.

4.5.5 Camber Diagram

The designer must prepare a camber diagram that shows the amount of camber needed to

counteract the dead load and superimposed dead-load (if any) deflection. Determine the calculation

of the dead-load camber based on the gross section properties and BDS Article 5.7.3.6.

4.5.6 Responsibilities

4.5.6.1 Designer

The bridge designer is responsible for ensuring that the proposed design serves the purpose. The

designer chooses a cross section with a centre of gravity (force and location) and provides a

strand/tendon size and pattern to achieve the required allowable Service limit state stresses and

factored flexural resistance. The contract documents will specify the exact value with respect to

cf that the contractor must reach at release and at 28-days. The designer is also responsible for a

preliminary investigation of shipping and handling issues where larger or long precast girders are

used or where unusual site access conditions are encountered.


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4.5.6.2 Contractor

In general, the contractor is responsible for implementing the prestressed concrete design according

to the bridge designer’s specifications. The contractor provides shop drawings showing all

calculations. In addition, for precast girders, the contractor is responsible for investigating stresses

in the components during proposed handling, transportation, and erection. The contractor may

propose changes to the cross-sectional shape of the girder. In these cases, the contractor must

redesign the girder to meet all requirements of the project. The contractor shall also prepare the “As

Built” drawings.

Contractor shall not commence the erection of installation of precast elements until the temporary

works design is approved by the Engineer. Contractor shall be responsible for design of temporary

works and supporting gantries and shall be in compliance with TA requirements specified in CG300.

All the temporary supporting members shall be rigid enough to sustain the anticipated loading and

shall be supported on firm & adequately compacted ground in accordance with the relevant

specifications. Contractor shall submit in advance a detailed Method Statement and Shop Drawings

with construction sequence for the approval of the Engineer.


PAGE 64

05-STEEL STRUCTURE SECOND EDITION – AUGUST 2021

5 STEEL STRUCTURES

This Chapter discusses structural steel provisions in Section 6 of the BDS that require amplification

or clarification for users of this Manual.

5.1 General

5.1.1 Economical Steel Superstructure Design

5.1.1.1 General

Factors that influence the initial cost of a steel bridge include detailing practices, the number of

girders (for a girder bridge), the grade of steel, type and number of substructure units (i.e. span

lengths), steel weight, fabrication, transportation, and erection. The cost for these factors changes

periodically based upon economic issues and the cost relationship among them.

Based upon market factors, the availability of steel may be an issue in meeting the construction

schedule. The bridge designer must verify the availability of the specified steel plates and rolled

beams. Producers and fabricators shall be contacted to ensure the availability of plates and rolled

beams. For more detailed information on availability, see Section 1.4 of the AASHTO/NSBA Steel

Bridge Collaboration’s Guidelines for Design for Constructability, G12.1-2003 (15).

5.1.1.2 Exterior Girders

The location of the exterior girder with respect to the overhang is controlled by these factors:

• Locate the exterior girder to limit the dead load and live load on the exterior girder such that

the exterior girder does not control the design (i.e. the interior and exterior girders are as

identical as possible).

• Consider the minimum and maximum overhang widths specified in Chapter 6.

• The space required for deck drains may affect the location of the exterior girder lines.

5.1.1.3 Fracture-Critical Members (FCMs)

Avoid bridges with fracture-critical members, which are members without a redundant load path

whose failure in tension would result in the collapse of the bridge.

5.1.1.4 Span Arrangements

Where pier locations are flexible, optimize the span arrangement. Consider the cost of the

superstructure, substructure, foundations, and approaches together as a total system.

To provide a balanced span arrangement for continuous steel bridges, select the end spans to be

approximately 80% of the length of interior spans. Avoid end spans less than 50% of the interior

span lengths to mitigate uplift.

End spans approximately 80% of the length of interior spans result in the largest possible negative

moments at the piers and smaller resulting positive moments and girder deflections. As a result, the

optimum proportions of the girders in all spans are nearly the same, resulting in an efficient design.


PAGE 65


5.1.2 Rolled Beams vs Welded Plate Girders

5.1.2.1 General

Use rolled beams for spans up to approximately 25 m. Use welded plate girders for spans from

approximately 25 m to 120 m. When rolled beams are specified, ensure that the selected sections

are available consistent with the construction schedule.

For more information, see Section 1.1 of the AASHTO/NSBA Steel Bridge Collaboration’s Guidelines

for Design for Constructability, G12.1-2003 (15).

5.1.2.2 Welded Plate Girders

Design welded steel plate girders to optimize total cost including material costs also considering

fabrication, transportation, and erection costs. Top flanges of composite plate girders are typically

smaller than the bottom flanges. Vary the flange section along the length of the bridge generally

following the moment envelope to save cost by offsetting the increased fabrication costs of welded

flange transitions with larger savings in material costs. Typically, vary only flange thicknesses, not

widths, within a field section to reduce fabrication costs. The webs of plate girders are typically

deeper and thinner than the webs of rolled beams. To save in total costs, increase minimum web

thicknesses to minimize the use of stiffeners.

Due to buckling considerations, address the stability of the compression flange (i.e. the top flange in

positive-moment regions and the bottom flange in negative-moment regions) by providing lateral-

brace locations based upon BDS Equation 6.10.8.2.3 instead of the traditional 7.5 m maximum

diaphragm spacing.

On straight bridges (skewed or non-skewed), detail diaphragms as secondary members. On

horizontally curved bridges, design diaphragms as primary members.

The traditional 7.5 m maximum diaphragm spacing provides a good average preliminary value.

Horizontally curved girders transfer a significant amount of load between girders through the

diaphragms.

5.1.2.3 Rolled Beams

Rolled steel beams are available in depths up to 900 mm, with beams 600 mm and greater rolled

less frequently. Before beginning final design, verify with one or more potential fabricators and/or

producers that the section size is available. Most rolled beams used in the Abu Dhabi Emirate are

imported from Europe.

Rolled steel beams are characterized by doubly symmetrical, as-rolled cross sections with equal-

dimensioned top and bottom flanges and relatively thick webs. Thus, rolled steel beams are not

optimized cross sections for weight savings (as is a plate girder), but they are cost effective due to

lower fabrication and erection costs. The relatively thick webs preclude the need for web stiffeners.

Unless difficult geometrics or limited vertical clearances control, rolled steel beam superstructures

are more cost effective in relatively shorter spans.


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5.1.3 Economical Plate Girder Proportioning

The AASHTO/NSBA Steel Bridge Collaboration has published the Guidelines for Design for

Constructability, G12.1-2003 (15). This document presents cost-effective details for steel bridges

from the perspective of the steel fabricator. The following Section presents information from the

AASHTO/NSBA Guidelines that is of particular interest.

5.1.3.1 General

Design plate girders and rolled beams composite with the concrete bridge deck through shear studs

and continuous over interior supports where possible. To achieve economy in the fabrication shop,

design all girders in a multi-girder bridge to be identical where possible. When using plate girders,

use a minimum number of plate sizes.

5.1.3.2 Haunched Girders

When practical, use girders with constant web depths. Haunched girders are generally uneconomical

for spans less than 90 m. Use parabolic haunched girders for aesthetics or other special

circumstances, but constant-depth girders are generally more cost effective.

5.1.3.3 Flange Plate Sizes

The minimum flange plate size for plate girders is 300 mm 25 mm to avoid cupping of the flanges

due to distortion from welding. Use as wide a flange plate as practical, consistent with stress and b/t

(flange width/thickness ratio) requirements. As a guide, flange width is approximately 20% to 25%

of web depth. Do not size flange widths in any set increments; base the width on mill plate widths

minus the waste from torch cutting. Limit the maximum flange thickness to 75 mm to ensure more

uniform through-thickness properties.

A wider flange contributes to girder stability during handling and in-service, and it reduces the

number of passes and weld volume at flange butt welds. Thicker plates demonstrate relatively poor

material properties near mid-thickness.

Within a single field section (i.e. an individual shipping piece), design the flanges with constant width.

A design using multiple identical girders with constant-width flanges minimizes fabrication costs.

Proportion flanges so that the fabricator can economically cut them from steel plates between 1500

mm and 3000 mm wide. The most economical mill widths are 1800 mm, 2100 mm, 2400 mm, and

3000 mm. Allow 6 mm for internal torch cutting lines and 13 mm for exterior torch cutting lines; see

Figure 5.1. Group flanges to provide an efficient use of the plates.

Because structural steel plate is more economical in these widths, it is advantageous to repeat plate

thicknesses as much as practical. Many of the plates of like width can be grouped by thickness to

meet the minimum width purchasing requirement, but this economical purchasing strategy may not

be possible for thicker, less-used plates.

The most efficient method to fabricate flanges is to groove-weld together several wide plates of

varying thicknesses from the mill. After welding and non-destructive testing, the individual flanges

are “stripped” from the full plate. This method of fabrication reduces the number of welds,


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Figure 5.1: Grouping Flanges for Efficient Fabrication (from the AASHTO/NSBA Steel Bridge Collaboration (15))

individual runoff tabs for both start and stop welds, the amount of material waste, and the number of

X-rays for non-destructive testing. The objective, therefore, is for flange widths to remain constant

within an individual shipping length by varying material thickness as required. Figure 5.1 illustrates

one example of an efficient fabrication for girders.

A constant flange width within a field section may not always be practical in girder spans over 90 m

where a flange width transition may be required in the negative bending regions. Though not

preferred, if a transition is necessary, shift the butt splice a minimum of 75 mm from the transition

into the narrower flange plate. See Figure 5.2.

This 75-mm shift makes it simpler to fit run-off tabs, weld and test the splice, and then grind off the

run-off tabs. For additional information on sizing flange plates, see Section 1.5 of the AASHTO/NSBA

Steel Bridge Collaboration’s Guidelines for Design for Constructability, G12.1-2003 (15).

Figure 5.2: Flange Width Transition (Plan View)


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5.1.3.4 Field Splices

Use bolted field splices to reduce shipping lengths, but minimize the number. The preferred

maximum length of a field section is 35 m. However, the bridge designer may use lengths up to 45

m, but do not use field sections greater than 35 m without considering shipping, erection, and site

constraints. Welded field splices are prohibited.

As a general rule, the unsupported length in compression of the shipping piece divided by the

minimum width of the flange in compression in that piece is less than approximately 85. Good design

practice is to reduce the flange cross sectional area by no more than approximately 25% of the area

of the heavier flange plate at field splices to reduce the build-up of stress at the transition. For

continuous spans, the field sections over a pier are usually a constant length to simplify erection.

5.1.3.5 Shop Splices

Include no more than two shop flange splices in the top or bottom flange within a single field section.

Maintain constant flange widths within a field section for economy of fabrication as specified in

Section 5.1.3.3. In determining where changes in plate thickness occur within a field section,

compare the cost of groove-welded splices to the extra plate area.

Table 1.5.2.A of the AASHTO/NSBA Steel Bridge Collaboration’s Guidelines for Design for

Constructability, G12.1-2003 (15), provides guidelines for weight savings for Grade 345 steel

required to justify a flange shop splice. In many cases, it may be advantageous to continue the

thicker plate beyond the theoretical step-down point to avoid the cost of the groove-welded splice.

To facilitate testing of the weld, locate flange shop splices at least 600 mm away from web splices,

and locate flange and web shop splices at least 150 mm from transverse stiffeners.

Section 1.5 of the AASHTO/NSBA Steel Bridge Collaboration’s Guidelines for Design for

Constructability, G12.1-2003 (15), provides additional guidance on shop splices.

5.1.3.6 Web Plates

Where there are no depth restrictions, optimize the web depth. The minimum web thickness is 14

mm. Do not change the web thickness at any splice less than 3 mm. Maintain symmetry by aligning

the centrelines of the webs at splices.

Web design can have a significant impact on the overall cost of a plate girder. Considering material

costs alone, it is desirable to make girder webs as thin as design considerations permit. However,

this practice will not always produce the greatest economy because fabricating and installing

transverse stiffeners is one of the most labour-intensive of shop operations.

The following guidelines apply to the use of transverse stiffeners:

1. Unstiffened webs are generally more economical for web depths approximately 1200 mm or

less.

2. Between 1200-mm and 1800-mm depths, consider options for a partially stiffened and

unstiffened web, with unstiffened webs preferred.


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A partially stiffened web is one whose thickness is 1.5 mm less than that allowed by

specification for an unstiffened web at a given depth and where stiffeners are required only

in areas of higher shear.

3. Above 1800 mm, consider options for partially stiffened or fully stiffened webs, with partially

stiffened webs preferred.

A fully stiffened web is one where stiffeners are present throughout the span.

5.1.3.7 Transverse Stiffeners

Proportion stiffeners that will be fabricated from flat bars in 6-mm increments in width and 3-mm

increments in thickness. Consult a fabricator for available flat sizes.

Flat bars (i.e. bar stock rolled to widths up to 200 mm at the mill) are typically more economical than

plates for stiffeners. The stiffeners can be fabricated by shearing flat bars of the specified width to

length.

5.1.3.8 Longitudinally Stiffened Webs

Do not use longitudinally stiffened webs.

In addition to being uneconomical, the ends of longitudinal stiffeners are fatigue sensitive if subject

to applied tensile stresses. Therefore, where used, terminate the ends in zones of little or no applied

tensile stresses.

5.1.4 Falsework

Design steel superstructures without intermediate falsework during the placing and curing of the

concrete deck slab.

5.2 Materials


5.2.1 Structural Steel


The following presents typical practices for the material type selection for structural steel members.

Typically, steel for bridge construction in the Abu Dhabi Emirate is imported from Europe.

5.2.1.1 Grade 250

Use Grade 250 steel only for the following structural members:

• transverse stiffeners,

• diaphragms, and

• bearing plates.

Grade 250 steel is becoming less used and, thus, less available. Generally, there is little or no cost

difference between Grade 345 and Grade 250 steel.


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5.2.1.2 Grade 345

Use Grade 345 steel for the following structural members:

• rolled beams,

• plate girders,

• splice plates,

• diaphragms,

• stiffeners,

• steel piles, and

• bearing plates.

5.2.1.3 High-Performance Steel

Grade HPS485W

For some plate-girder bridges, a good choice of steel may be Grade HPS485W. In addition to

increased strength, the high-performance steels exhibit enhanced weathering, toughness, and

welding properties. A savings in weight offsets the premium on material costs. The most cost-

effective design solutions tend to be hybrid girders with Grade 345 webs with HPS485W tension and

compression flanges in the negative-moment regions and tension flanges only in the positive-

moment regions.

HPS485W may be painted for aesthetic reasons.

Grade HPS700W

Do not use Grade HPS700W except for special applications.

High-performance steel with a minimum specified yield strength of 700 MPa is available. It has yet

to be proven cost-effective for girder bridge applications.

5.2.1.4 Unpainted Weathering Steel

General

Unpainted weathering steel is the more cost-effective choice for structural steel superstructures. Do

not use weathering steel where the following conditions exist:

1. Environment. Do not use unpainted weathering steel in industrial areas where concentrated

chemical fumes may drift onto the structure or where the nature of the environment is

questionable. Do not use weathering steel in coastal regions where airborne salt may drift

onto the structure.

2. Water Crossings. Do not use unpainted weathering steel over bodies of water where the

clearance over the ordinary high water is 3.5 m or less.

The initial cost advantage of unpainted weathering steel when compared to painted steel can range

up to 15%. When future repainting costs are considered, the cost advantage is more substantial.

This reflects, for example, environmental considerations in the removal of paint, which significantly

increases the life-cycle cost of painted steel. FHWA Technical Advisory T5140.22 “Uncoated

Weathering Steel in Structures,” October 3, 1989 (16) discusses in-depth the application of


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weathering steel and its potential problems. In addition, the proceedings of the “Weathering Steel

Forum,” July 1989 (17), are available from the FHWA Office of Implementation, HRT-10.

Despite its cost advantage, the use of unpainted weathering steel is not appropriate in all

environments and at all locations. For additional guidance on the appropriate application of

unpainted weathering steel, see the AISI publication Performance of Weathering Steel in Highway

Bridges: A Third Phase Report (18).

5.2.1.4.1 Design Details for Weathering Steel

Where weathering steel girders are used, use the same steel for the bearing plates as the girders.

Use Type 3 for the bolts, nuts, washers, and Direct Tension Indicators (DTIs), as specified in ASTM

A325M/ASTM A563M and ASTM F959M.

Paint weathering steel at the ends of girders, at expansion joints, and over piers for a distance of

3 m or for 1.5 times the web depth, whichever is greater. Use only the prime coat of the approved

bridge paint systems.

When using unpainted weathering steel, incorporate the following drainage treatments:

1. Minimize the number of bridge deck drains and extend the drainage outlets below the steel

bottom flange.

2. Eliminate details that serve as water and debris “traps.” Seal or paint overlapping surfaces

exposed to water. This sealing or painting applies to non-slip-critical bolted joints. Slip-critical

bolted joints or splices do not produce “rust-pack” when the bolts are spaced according to

the BDS and, therefore, do not require special protection.

3. Place a drip plate or other material transverse across the top of the bottom flange in front of

the substructure elements to prevent water from running off the flange onto the concrete.

Ensure that these attachments meet all fatigue requirements. Figure 5.3 shows a typical drip

plate detail.

Figure 5.3: Drip Plate Detail


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5.2.1.1 Charpy V-Notch Fracture Toughness


The temperature zone appropriate for using BDS Table 6.6.2-1 for Abu Dhabi is Temperature

Zone 1.

5.2.2 Bolts


5.2.2.1 Type

For normal construction, high-strength bolts are:

1. Painted Steel: Use 22-mm A325M (Type 1).

2. Weathering Steel: Use 22-mm A325M (Type 3).

5.2.2.2 Hole Size

Do not use oversized or slotted holes; use these only in unusual circumstances with approval.

5.2.3 Splice Plates

In all cases, use the same material for the steel for all splice and filler plates as used in the web and

flanges of plate girders.

5.3 Horizontally Curved Members

Reference: BDS Articles 6.10 and 6.11

5.3.1 General

Use a curved girder on curved alignments, unless otherwise approved.

The BDS includes horizontally curved girders as a part of the provisions for proportioning I-shaped

and tub girders at both the Strength and Service limit states. In addition, the BDS specifies analysis

methodologies that detail various required levels of analysis.

5.3.2 Diaphragms, Bearings, and Field Splices

Use diaphragms for all curved steel simple-span and continuous-span bridges directed radially

except end diaphragms, which are parallel to the centreline of bearings.

Cross frames and diaphragms are primary members. However, due to the difficulty of obtaining a

Charpy specimen from a rolled shape such as an angle, Charpy V-notch impact-energy testing of

the cross frames is not required.

Design all diaphragms, including the connections to the girders, to carry the total load transferred at

each diaphragm location. Place cross frames and diaphragms as close as practical to the full depth

of the girders. Design cross frame and diaphragm connections for the 75% and average load

provisions of BDS Article 6.13.1, unless actual forces in the connections are determined from an

appropriate structural model.


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Using the provisions of BDS Article 6.13.1 may result in very large connections that are difficult to

detail.

For typical bridges that are long in relationship to their width, ignore the transverse expansion. For

ordinary geometric configurations where the bridge length is long relative to the bridge width (say,

2½ times the width) and the rate of curvature is moderate (those satisfying the requirements of BDS

Article 4.6.1.2.4b), it is not necessary to consider the unique expansion characteristics of horizontally

curved structures. Wide, sharply curved or long-span structures may require the use of high-load

multi-rotational bearings. See Chapter 10. Consider providing restraint either radially and/or

tangentially to accommodate the transfer of seismic forces and the thermal movement of the

structure because the bridge tries to expand in all directions.

Design the splices in flanges of curved girders to carry flange bending or lateral bending stresses

and vertical bending stresses in the flanges.

5.4 Fatigue Considerations


BDS Article 6.6.1 categorizes fatigue as either “load induced” or “distortion induced.” Load induced

is a “direct” cause of loading. Distortion induced is an “indirect” cause in which the force effect,

normally transmitted by a secondary member, may change the shape of or distort the cross section

of a primary member.

5.4.1 Load-Induced Fatigue


5.4.1.1 General

For new steel bridges, design for infinite life. In addition, for all details, provide a fatigue resistance

greater than or equal to Detail Category C (i.e. Detail Categories A, B, B, C, and C).

5.4.1.2 Fatigue Stress Range


1. Range. If a refined analysis method is used, position the fatigue design truck to maximize

the stress in the detail under consideration. The fatigue design truck has a constant 9-m

spacing between the rear (1.5 140)-kN axles. The dynamic load allowance is 0.15. See

Chapter 2 for the definition of the fatigue design truck for the ADVL.

The fatigue stress range is the difference between the maximum and minimum stresses at a

structural detail subject to a net tensile stress. The stress range is caused by a single design truck

that can be placed anywhere on the deck within the boundaries of a design lane.

2. Analysis. Unless a refined analysis method is used, use the load distribution factor for a

single design lane in BDS Article 4.6.2.2 to determine fatigue stresses.

These tabularized distribution-factor equations incorporate a multiple presence factor of 1.2

that is removed by dividing either the distribution factor or the resulting fatigue stresses by

1.2. This division does not apply to distribution factors determined using the lever rule.


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5.4.1.3 Fatigue Resistance

Fatigue resistance is independent of the steel strength. The application of higher-grade steels

causes the fatigue stress range to increase, but the fatigue resistance remains the same. This

independence implies that fatigue may become more of a controlling factor where higher strength

steels are used.

5.4.2 Other Fatigue Considerations

Reference: Various BDS Articles

Ensure compliance with fatigue requirements for all structural details (e.g. stiffeners, connection

plates, lateral bracing) shown in the contract documents. In addition to the considerations in Section

5.4.1, investigate the fatigue provisions in other Articles of Chapter 6 of the BDS. These include:

• Fatigue due to out-of-plane flexing in webs of plate girders — BDS Article 6.10.6.

• Fatigue at shear connectors — BDS Articles 6.10.10.1.2 and 6.10.10.2.

• Bolts subject to axial-tensile fatigue — BDS Article 6.13.2.10.3.

5.5 General Dimension and Detail Requirements


5.5.1 Deck Haunches

Detail the haunch at the centreline of bearing. It can vary in the span, if necessary, to accommodate

variations in camber, super-elevation ordinate, and vertical curve ordinate. The maximum positive

camber allowed in excess of that specified at mid-span is as follows: 20 mm for spans less than 30

m and 40 mm for spans more than 30 m. Use a 50-mm haunch for spans of less than 30 m and a

75-mm haunch for spans of more than 30 m. Neglect the haunch when determining the resistance

of the section.

A deck haunch is an additional thickness of concrete between the top of the girder and the bottom

of the deck to provide adjustability between the top of the cambered girder and the roadway profile.

5.5.2 Sacrificial Metal Thickness

Add a sacrificial metal thickness of 4 mm to 6 mm to the calculated thicknesses (round to practical

total thicknesses) to compensate for members subject to future corrosion.

5.5.3 Minimum Thickness of Steel Plates


For welded plate girder fabrication, minimum thickness requirements reduce deformations and

defects due to welding. Use the following for the minimum thickness of steel elements:

• Plate girder webs: 14 mm

• Stiffeners, connection plates: 12 mm; 14 mm preferred

• Plate girder flanges: 25 mm


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• Bearing stiffener plates: 25 mm

• Gusset plates: 12 mm

• Angles/channels: 10 mm

For more detailed information, see Section 1.3 of the AASHTO/NSBA Steel Bridge Collaboration’s

Guidelines for Design for Constructability, G12.1-2003 (15).

5.5.4 Camber

Camber the entire girder length as required by the loading and profile grade. The loading includes

the shrinkage of the concrete deck. In addition, where dead load deflection and vertical curve offset

are greater than 6 mm, provide a compensating camber. Calculate camber to the nearest 3 mm,

with ordinates at 0.1 points throughout the length of the girder. Show the required camber values

from a chord line that extends from point of support to point of support. The camber is typically

parabolic.

Provide a camber diagram in all contract documents with structural steel girders.

5.5.5 Diaphragms and Cross Frames

Reference: BDS Articles 6.7.4 and 6.6.1.3.1

Determine the spacing of diaphragms and cross frames based upon the provisions of BDS Article

6.7.4.1. The design of the spacing is iterative. A good starting point is the traditional maximum

diaphragm and cross frame spacing of 7.5 m.

Most economical steel girder designs are spaced typically greater than 7.5 m in the positive-moment

regions. Diaphragms on rolled-beam bridges and cross frames on plate-girder bridges are vitally

important in steel girder superstructures. They stabilize the girders in the positive-moment regions

during construction and in the negative-moment regions after construction. Cross frames also serve

to distribute gravitational, centrifugal, and wind loads.

5.5.5.1 General

The following applies to diaphragms and cross frames:

1. Location. Place diaphragms or cross frames at each support and throughout the span at an

appropriate spacing. Plan the location of the field splices to avoid conflict between the

connection plates of the diaphragms or cross frames and any part of the splice material.

2. Skew. Regardless of the angle of skew, place all intermediate diaphragms and cross frames

perpendicular to the girders.

Locating cross frames near girder supports on bridges with high skews requires careful

consideration. When locating a cross frame between two girders, the relative stiffness of the

two girders must be similar. Otherwise, the cross frame acts as a primary member supporting

the more flexible girder. This may be unavoidable on bridges with exceptionally high skews

where a rational analysis of the structural system is required to determine actual forces.

3. End Diaphragms and Cross Frames. Locate end diaphragms and cross frames along the

centreline of bearing. Set the top of the diaphragm below the top of the girder to

accommodate the joint detail and the thickened slab at the end of the superstructure deck,


PAGE 76


where applicable. Design the end diaphragms to support the edge of the slab including live

load plus impact.

4. Interior Support Diaphragms and Cross Frames. Generally, locate interior support

diaphragms and cross frames along the centreline of bearing. They provide lateral stability

for the bottom flange and bearings.

5. Curved-Girder Structures. Consider diaphragms or cross frames connecting horizontally

curved girders as primary members and orient radially.

6. Detailing. Detail diaphragms and cross frames to follow the cross slope of the deck; i.e. the

diaphragm or cross frame is parallel to the bottom of the deck. In the contract documents,

allow the contractor to use diaphragms or cross frames fabricated as a rectangle (as opposed

to a skewed parallelogram). In this case, the drops vary across the bridge.

Detailing diaphragms and cross frames to follow the cross slope allows the fabricator to use

a constant drop on each connection plate (i.e. the distance from the bottom of the flange to

the first bolt hole on the connection plate is constant).

The following identifies typical practices on the selection of diaphragms and cross frames:

1. Solid Diaphragms. These are preferred for rolled beams. For rolled-beam bridges with seat

abutments, design the end diaphragms as full depth to provide sufficient lateral restraint.

2. K-Frames. These are preferred for plate girder bridges.

3. X-Frames. In the case of relatively narrow girder spacings relative to the girder depth, an X-

frame may be more appropriate than a K-frame.

5.5.5.2 Diaphragm Details

On spans composed of rolled beams, detail diaphragms at interior span points as illustrated in Figure

5-4.

Figure 5.5 illustrates the typical diaphragm connection details at abutment supports for rolled beams.

Plate girders with web depths of 1200 mm or less have similar diaphragm details. For plate girder

webs more than 1200 mm deep, use cross frames as detailed in Figure 5.6 and Figure 5.7.

Detail pier and intermediate diaphragms for rolled-beam spans with a 75-mm minimum clearance

between the top of the diaphragm and the bottom of the top beam flange. For bridges having a

normal roadway crown, make the diaphragms level. For bridges having a super-elevated roadway,

place the diaphragms parallel to the slab.

Design and detail intermediate diaphragms as non-load bearing in the final position. Design

diaphragms at points of support as a jacking frame as specified in Section 5.5.6.


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Figure 5.4: Typical Pier and Intermediate Diaphragm Connection (Rolled Beams)

Note: Select a channel depth approximately ½ of the girder depth.

Figure 5.5: Typical Abutment Diaphragm Connection (Skewed Diaphragm with Rolled Beams)


PAGE 78


Figure 5.6: Typical Pier and Intermediate Cross Frames (Plate Girder Web > 1200 mm)

Figure 5.7: Typical Abutment Cross Frames (Plate Girder Web > 1200 mm)

5.5.5.3 Cross Frame Details

Figure 5.6 illustrates typical pier and intermediate cross frame details for plate girder webs more

than 1200 mm deep. The K-frame is the preferred cross frame configuration. Use the X-frame

instead of the K-frame where the girder spacing is less than approximately 1.75 of the girder depth.

A solid bent-plate diaphragm with a depth equal to 75% of the girder depth is a good option for plate

girders less than 1200 mm deep.

In general, an X-frame is more cost effective than a K-frame; however, with a typical girder spacing,

the X-frame is shallow and less effective.


PAGE 79


Figure 5.7 illustrates the typical abutment cross frame connection details for plate girder webs more

than 1200 mm deep.

The rolled angles that comprise the cross frames are minimum sizes based upon the limiting

slenderness ratios of BDS Articles 6.8.4 and 6.9.3.

Weld the cross-frame transverse connection plates to the compression flange and the tension flange.

Design the welded connections to the flanges to transfer the cross-frame forces into the flanges.

Size the width of connection plates to use bar stock and to be not less than 125 mm. When the

connection plate also acts as a transverse stiffener, meet the requirements of BDS Article 6.10.8.1.

5.5.6 Jacking


Include a jacking plan in the contract drawings for all bearing-supported structures. Include live load

in the jacking plan for bridges with moderate to high traffic volumes or those with no readily available

detour. The bearing type determines the level of detail shown for the jacking plan.

Include only bearing stiffeners at all points of jacking for plain or reinforced elastomeric bearings.

Provide a conceptual jacking plan showing the jack location and clearances, required factored

reactions, and modifications to cross frames and diaphragms. Also, show conceptual requirements

for falsework and jacking frames if required.

Include a complete jacking plan for high-load multi-rotational, isolation, or other specialty bearings.

The jacking plan must include necessary bearing stiffeners, jack locations and clearances, factored

reactions, and additional modifications to cross frames and diaphragms. Also, include a detailed

design of the jacking frame if required, but do not include its fabrication as part of the contract

documents. Provide only conceptual falsework requirements.

In general, jacking frames will not be required at the supports unless there is insufficient clearance

between the bottom of girder and top of cap to place a jack. If less than 175 mm of clearance for the

jack, determine if the jack can be supported by temporary falsework. If temporary falsework is not

feasible, provide details for a jacking frame or widen the cap and place the bearings on pedestals to

provide sufficient space for a jack placed under the girder.

Other locations where jacking may be required are:

• At supports under expansion joints where joint leakage could deteriorate the bearing areas

of the girders; and

• At expansion bearings with large displacements where deformation-induced wear-and-tear

is possible.

If no jacking frame is provided, design the cross frame at the support to transfer lateral wind and

seismic forces to the bearings.

5.5.7 Lateral Bracing



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The BDS requires the evaluation of lateral bracing for all stages of assumed construction

procedures. If the bracing is included in the structural model used to determine force effects, then

design it for all applicable limit states.

Provide temporary lateral bracing between adjacent boxes at ¼ points of spans. Remove after deck

placement.

In general, lateral bracing is not required in the vast majority of steel I-girder bridges (short through

medium spans); however, the bridge designer must check for this. Typical diaphragms and cross

frames transfer lateral loads adequately to eliminate the need for lateral bracing. For tub girders,

internal top lateral bracing is more typical. Tub girders can rack as much as 150 mm in one day due

to the thermal effects of the sun.

BDS Article 4.6.2.7 provides various alternatives relative to lateral wind distribution in multi-girder

bridges.

5.5.8 Inspection Access (Tub Girders)

Detail all steel tub girder bridges with access openings to allow inspection of the girder interior. Do

not locate access openings over travel lanes or railroad tracks and, preferably, not over shoulders

or maintenance roads. Locate the openings such that the general public cannot gain easy entrance.

Provide access openings in the bottom flange plate of all steel tub girders. Provide one access

opening at each end of the bridge when the total span length is 30 m or more.

Connect access plates to the bottom flange with high-strength bolts. If the general public has access

to the openings, provide bolts with special head configurations. The dimensions of the access

opening is a minimum 800 mm 800 mm square.

5.6 I-Sections in Flexure


5.6.1 General


5.6.1.1 Positive-Moment Region Maximum-Moment Section

For a compositely designed girder, consider the positive-moment region maximum-moment section

as compact in the final condition.

The cured concrete deck in the positive-moment region provides a large compression flange, and it

laterally braces the top flange. Very little, if any, of the web is in compression.

Top Flange

The Strength limit state during construction when the concrete is not fully cured governs the design

of the top flange in the positive-moment region as specified in BDS Article 6.10.3.4.

In the final condition after the deck has cured, the top flange adds little to the resistance of the cross

section. During curing of the concrete deck, however, the top flange is very important.


PAGE 81


Bottom Flange (Tension Flange)

The Service II load combination permanent deformation provisions of BDS Article 6.10.4.2 govern.

The bottom flange, if properly proportioned, is not governed by the construction phase. The bottom

flange is governed by the final condition.

5.6.1.2 Negative-Moment Region Pier Section

Both top and bottom flanges in the negative moment region are governed by the Strength limit state

in the final condition. Furthermore, the bottom flange in compression is governed by the location of

the first intermediate diaphragm off the pier because it provides the discrete bracing for the flange.

The negative-moment region pier section is likely a non-compact section during all conditions. The

concrete deck over the pier is in tension in the negative-moment region and, thus, considered

cracked and ineffective at the nominal resistance (i.e. ultimate). Thus, a good portion of the steel

cross section is in compression. To qualify as compact, the web usually needs to be too thick to be

cost effective. Thus, the cost-effective section is typically a non-compact section.

5.6.1.3 Rigidity in Negative-Moment Regions


BDS Article 6.10.1.5 permits the assumption of uncracked concrete in the negative-moment regions

for member stiffness. Use this stiffness to obtain continuity moments due to live load, future wearing

surface, and barrier weights placed on the composite section.

For the Service limit state control of permanent deflections under BDS Article 6.10.4.2 and the

Fatigue limit state under BDS Article 6.6.1.2, consider the concrete slab fully effective for both

positive and negative moments for members with shear connectors throughout the full lengths and

satisfying BDS Article 6.10.1.7.

5.6.2 Shear Connectors


The preferred size for shear studs for use on the flanges of girders and girders is a 22-mm diameter

by 125 mm; the minimum is a 20-mm diameter by 125 mm. The minimum number of studs in a group

is three in a single transverse row. Skew the studs parallel to the bottom slab reinforcing steel.

Increase the stud length in 25 mm increments when necessary to maintain a 50-mm minimum

penetration of the stud into the deck slab. Detail studs placed on relatively thin elements (e.g. girder

webs) as 19 mm diameter.

5.6.3 Stiffeners


5.6.3.1 Transverse Intermediate Stiffeners



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Design straight girders without intermediate transverse stiffeners, if economical, or with intermediate

transverse stiffeners placed on one side of the web plate. If stiffeners are required, fascia girders

typically only have stiffeners on the inside face of the web for aesthetics.

Due to the labour intensity of welding stiffeners to the web, the unit cost of stiffener by weight is

approximately nine times that of the unit cost of the web by weight. It is seldom economical to use

the thinnest web plate permitted; therefore, investigate the use of a thicker web and fewer

intermediate transverse stiffeners or no intermediate stiffeners. If the bridge designer uses a design

that requires stiffeners, the preferred width of the stiffener is one that can be cut from commercially

produced bar stock.

Weld intermediate transverse stiffeners near side and far side to the compression flange. Do not

weld transverse stiffeners to tension flanges. The distance between the end of the web-to-stiffener

weld and the near toe of the web-to-flange fillet weld is between 4tw and 6tw.

Place transverse stiffeners, except when used as diaphragm or cross frame connections, on only

one side of the web.

Orient transverse intermediate stiffeners normal to the web. However, where the angle of crossing

is between 70 and 90, skew the stiffeners so that the diaphragms of cross frames may be

connected directly to the stiffeners.

Avoid longitudinal stiffeners. If used in conjunction with transverse stiffeners on spans with deeper

webs, place these preferably on the opposite side of the web from the transverse stiffener. Where

this is not practical (e.g. at intersections with cross frame connection plates), make the longitudinal

stiffener continuous. Do not interrupt the longitudinal stiffener for the transverse stiffener.

5.6.3.2 Bearing Stiffeners


Provide bearing stiffeners for all plate girders to prevent the possibility of web buckling at temporary

supports. They only require placement on one side and, for fascia girders, place on the inside.

Provide bearing stiffeners at the bearing points of rolled beams and plate girders. Design bearing

stiffeners at integral abutments for dead and construction loads only.

Design the bearing stiffeners as columns and extend the stiffeners to the outer edges of the bottom

flange plates. Use an effective column length of ¾ of the web depth.

The BDS does not specify an effective column length for the design of bearing stiffeners. The

reaction load applied at one end of the stiffener pair is resisted by forces distributed to the web

instead of by a force concentrated at the opposite end, as in columns. Therefore, it is not necessary

to consider the stiffeners as an end-hinged column even where the flanges are free to rotate.

Design the weld connecting the bearing stiffener to the web to transmit the full bearing force from

the stiffener to the web due to the factored loads.

Detail bearing stiffeners with the stiffener ends bearing on the loaded flange being milled to bear, or

weld with a full-penetration butt weld. The opposite end is tight fit only to the flange. Where bearing


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stiffeners are also used as diaphragm or cross frame connection plates, fillet weld the stiffeners to

the girder flanges if they are milled to bear or tight fit.

5.6.4 Deck-Overhang Cantilever Brackets


During construction, the deck overhang brackets may induce twist in the exterior girder. Include in

the contract documents the requirement for the contractor to check the twist of the exterior girder

and bearing of the overhang bracket on the web. See Figure 5.8.

Figure 5.8: Schematic of Location for Deck Overhang Bracket

5.7 Connections and Splices


5.7.1 Bolted Connections


The following applies to bolted connections:

1. Type. For painted steel, use 22 mm A325M (Type 1) bolts. For unpainted weathering steel,

use A325M (Type 3) bolts.

2. Design. Design all bolted connections as slip-critical at the Service II limit state, except for

secondary bracing members.

3. Slip Resistance. BDS Table 6.13.2.8-3 provides values for the surface condition. Use Class

B surface condition for the design of slip-critical connections. Class B is applicable to

unpainted, blast-cleaned surfaces and to blast-cleaned surfaces with a Class B coating. Test

all specified coatings to ensure a slip resistance equal to or exceeding Class B. Paint the

faying surfaces of all slip-critical connections with the prime coat of the approved paint

systems.


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5.7.2 Welded Connections


5.7.2.1 Welding Process

The governing specification for welding is the ANSI/AASHTO/AWS Bridge Welding Code D1.5 (19).

However, this specification does not provide control over all of the welding issues that may arise on

a project. As needed, consult additional reference specifications:

• AWS D1.1 (20) for welding of tubular members and strengthening or repair of existing

structures, and

• AWS D1.4 (21) if the welding of reinforcing steel must be covered by a specification.

5.7.2.2 Field Welding

Do not permit field welding except for all but a few special applications. The permissible applications

are welded splices for piles, connecting pile tips to piles, bearing plates to bottom flange plates, and

connector plates between new and existing portions of widened bridges at ends of simply supported

spans (though bolted connections are preferred for this application).

5.7.2.3 Design of Welds

The maximum weld size for a single-pass fillet weld applicable to all weld types is 8 mm. The AWS

D1.1 Structural Welding Code (20), Table 3.7, provides more specific maximum single-pass fillet-

weld sizes for various welding processes and positions of welding. Design the weld economically,

but its size is not typically less than 6 mm and, in no case, less than the requirements of BDS Article

6.13.3.4 for the thicker of the two parts joined. Show the weld terminations.

The following types of welds are prohibited:

• field-welded splices,

• intersecting welds,

• intermittent fillet welds (except for the connection of stop bars at expansion joints), and

• partial penetration groove welds (except for the connection of tubular members in hand rails).

Provide careful attention to the accessibility of welded joints. Provide sufficient clearance to place a

welding rod at the joint. Often, a large-scale sketch or an isometric drawing of the joint will reveal

difficulties in welding or where critical weld stresses must be investigated.

The design of fillet welds is integral to BDS Section 6 on steel design. The BDS addresses topics

such as resistance factors for welds, minimum weld size, and weld details to reduce fatigue

susceptibility.

The weld-strength calculations of the BDS assume that the strength of a welded connection is

dependent only on the weld metal strength and the area of the weld. Weld metal strength is a self-

defining term. The area of the weld that resists load is a product of the theoretical throat multiplied

by the length. The theoretical weld throat is the minimum distance from the root of the weld to its


PAGE 85


theoretical face. Fillet welds resist load through shear on the throat, while groove welds resist load

through tension, compression, or shear depending upon the application.

Preferably, only show the type and sizes of the weld required and leave the details to the fabricator.

When considering design options, note that the most significant factor in the cost of a weld is the

volume of the weld material deposited. Over specifying a welded joint is unnecessary and

uneconomical. A single-pass weld is one made by laying a single weld bead in a single move of the

welder along the joint. A multiple-pass weld is one in which several beads are laid one upon the

other in multiple moves along the joint. Welds sized for a single pass are preferred because these

are more economical and least susceptible to resultant flaws.

5.7.3 Splices


5.7.3.1 Shop Splices

In addition to the provisions of BDS Article 6.13.6, the following applies to splices:

1. Location. Numerous groove welds and/or groove welds located in high stress regions are not

desirable. Locate flange shop splices away from high moment regions and web splices away

from high shear regions.

This is simple for flange splices in negative moment regions but more difficult with positive

moment regions. In positive moment areas, the magnitude of moment does not change

quickly along the girder compared to the negative moment. As such, locate shop splices on

longer span bridges in high positive moment regions.

The location of shop groove splices is normally dependent upon the length of plate available

to the fabricator. This length varies depending upon the rolling process. Fifteen meters is the

maximum length of plates that are normalized, quenched, and tempered (485 HPS). Other

plates (e.g. Grades 250 and 345) can be obtained in lengths greater than 25 m depending

on thickness. Consider the cost of adding a shop-welded splice instead of extending a thicker

plate when designing members.

2. Welded Shop Splice.

3. Figure 5-9 illustrates a welded flange splice. At flange splices, the thinner plate is not less

than one-half the thickness of the thicker plate.


PAGE 86


Figure 5.9: Typical Welded Splice Details

See BDS Article 6.13.6.2 for more information on splicing different thicknesses of material

using butt welds.

5.7.3.2 Field Splices

In addition to the provisions of BDS Article 6.13.6, the following applies to field splices:

1. Type. Use bolted field splices only. In exceptional cases, welded splices may be used subject

to client’s approval.

2. Location. In general, locate field splices in main girders at low-stress areas and near the

points of dead-load contraflexure for continuous spans. Long spans may require that field

splices be located in high moment areas.

3. Bolts. Calculate design loads for bolts by an elastic method of analysis. Provide at least two

lines of bolts on each side of the web splice.

4. Design. Design bolted splices to satisfy both the slip-critical criteria under Service II loads

and the bearing-type connection criteria under the appropriate Strength limit states.

5. Swept Width (or Shipping Width) for Curved Girders. Locate field splices such that the

maximum swept width for a horizontally curved girder is 3 m within a single field section.

The swept width is the horizontal sweep in a curved girder plus its flange width.


PAGE 87

06-DECK AND DECK SYSTEM SECOND EDITION – AUGUST 2021

6 DECKS AND DECK SYSTEMS

Sections 3, 4, 5, 6, and 9 of the BDS present the AASHTO criteria for the structural design of bridge

decks. Section 3 specifies loads for decks and deck systems, Section 4 specifies their analyses, and

Section 9 specifies their resistance. Unless noted otherwise in this Chapter, BDS applies to the

design of decks.

This Chapter documents criteria on the design of concrete bridge decks constructed compositely in

conjunction with concrete and steel girders and top slabs of cast-in-situ, post-tensioned box girders.

The - Drainage Manual presents the requirements for bridge deck drainage.

6.1 Concrete Decks

6.1.1 Protection of Reinforcing Steel

Reference: BDS Articles 2.5.2.1 and 5.12

Protect the concrete bridge deck top surface against chloride ingress by a waterproofing as specified

in Section 4.4.1. Provide access for a possible future connection to a cathodic protection system. In

addition, for all concrete for deck slabs, approach slabs, and barrier rails, use a high-performance

concrete having a low water/cement ratio and low permeability.

Other methods are available to protect the reinforcing steel in concrete decks and to retard the rate

of corrosion. The bridge designer may occasionally use some of these methods to protect reinforcing

steel in concrete decks.

6.1.2 Empirical Design


Design all concrete decks that satisfy the requirements of BDS Article 9.7.2.2 in accordance with the

empirical-deck design provisions of BDS Article 9.7.2. Detail the reinforcement as specified in BDS

Article 9.7.2.5, except that the minimum amount of reinforcement is 860 mm2/m of steel for each

bottom layer and 573 mm2/m of steel for each top layer in lieu of the amounts of steel reinforcement

specified in the BDS.

The minimum amount of reinforcement specified in the BDS is increased to reflect the heavier

design live loads specified for the UAE.

6.1.3 Traditional Design Using the “Strip Method”

Reference: BDS Articles 9.7.3, 4.6.2.1.1, 4.6.2.1.3, and Appendix A4

Use BDS Table A4-1 to design the concrete deck reinforcement where the provisions of BDS Article

9.7.2.2 are not satisfied. Use a 215-kN axle instead of the 142-kN axle specified in the BDS.

Therefore, multiply the design moments shown in BDS Table A4-1 by 1.5.

BDS Table A4-1 tabulates the resultant live-load moments per unit width for slab steel design as a

function of the girder or web spacing, S. The Table distinguishes between negative moments and

positive moments and tabulates these for various design sections as a function of the distance from


PAGE 88


the girder or web centreline to the design section. BDS Article 4.6.2.1.6 specifies the design sections

for use.

6.1.4 Precast Concrete Deck Panels

The bridge designer may use precast bridge deck panels in lieu of a cast-in-situ concrete deck to

reduce bridge closure times for deck replacements or new bridge construction. Use grout to fill the

haunch between the top of the girder and the bottom of the deck panel, plus the horizontal shear

connector pockets and the panel-to-panel joints.

Design horizontal shear connectors for precast deck panels using the cohesion and friction factors

for a clean concrete surface, free of laitance, as specified in BDS Article 5.8.4.3 when extended

reinforcing bars are used as shear connectors. If a welded shear stud detail is used, design the

connections for strength using the cohesion and friction factors for concrete anchored to as-rolled

structural steel by headed studs, or use reinforcing bars where all steel in contact with concrete is

clean and free of paint. Also, check the studs for fatigue in accordance with Section 5 of the BDS.

Specify a smooth bottom surface on precast deck panels along the girder lines.

Based on research, no significant increase in strength is observed when the aggregate on the bottom

slab surface is exposed.

6.2 Metal Decks

6.2.1 Grid Decks


Use partially filled steel grid decks for redecking where the dead load of a concrete deck cannot be

tolerated due to deterioration of the girders and where an orthotropic deck is not cost effective.

Partially filled steel grid decks are also an alternative for moveable bridges where the deck weight is

an issue.

Do not use unfilled steel grid decks or fully-filled steel grid decks.

Unfilled grid decks exhibit poor fatigue resistance. The additional fill of a fully filled grid decks offers

no additional benefit.

6.2.2 Orthotropic Steel Decks


Investigate the fatigue limit state using the Level 3 design of BDS Article 9.8.3.4.

Three design levels are available in BDS Article 9.8.3.4. The preferred method is the more rigorous

Level 3 design of BDS Article 9.8.3.4.4 employing refined three-dimensional analysis.

Table 6.1 summarizes the limits for panel detailing proportions.


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Table 6.1: Orthotropic-Deck Panel Proportions

Detailing Dimension Limit

Deck Plate Thickness > 14 mm

Rib Thickness 8 mm < tr < 12 mm

Rib Spacing – direct wheel load 600 mm < s < 760 mm

Rib Spacing – no direct wheel load 600 mm < s < 1000 mm

Floor Beam Spacing < 6000 mm

Ratio of Rib to Floor beam Depth < 0.4

Floor Beam Web thickness 10 mm < tFB < 20 mm

For additional guidance on proportioning and detailing orthotropic decks, see the US Department of

Transportation, Federal Highway Administration Manual for Design, Construction, and Maintenance

of Orthotropic Steel Bridges (22).

6.3 Design Details for Concrete Bridge Decks

6.3.1 General

The following general criteria apply to concrete bridge decks constructed compositely in conjunction

with concrete girders, steel girders, and the top slabs of cast-in-situ, post-tensioned box girders:

1. Minimum Thickness. The minimum thickness of reinforced concrete decks is 250 mm.

2. Reinforcing Steel Strength. The specified yield strength of reinforcing steel is in the Abu

Dhabi Standard Specifications: Volume 2: Road Structures.

3. Exposure Factor. Take the exposure factor in BDS Equation 5.7.3.4-1 as 0.75 in general for

concrete bridge decks. For decks within an extremely aggressive environment, the exposure

factor is 0.50.

4. Reinforcement Cover. See Section 4.4.2.2 for specified concrete covers. The primary

reinforcement in the top and bottom mats must be the reinforcement closer to the concrete

face.

5. Placement of Top and Bottom Transverse Reinforcing Steel. Offset the top and bottom

transverse reinforcing steel, preferably at half the spacing, so that the top mat is not directly

above the bottom mat.

6. Reinforcing Steel Spacing. Maintain a minimum of 40-mm vertical separation between the

top and bottom reinforcing mats. Where conduits are present between mats, increase this

separation. Maintain a minimum horizontal spacing of 125 mm c/c between adjacent bars

within each mat. The maximum horizontal reinforcing steel spacing is 200 mm for primary

(transverse) steel bars.

7. Reinforcing Bar Size. The minimum reinforcing steel size used for concrete bridge deck

reinforcement is a T12 bar.


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8. Asphaltic Wearing Surface. Consider 110 mm of asphaltic wearing surface with a unit weight

of 23 kN/m3.

9. Length of Reinforcement Steel. For detailing, the maximum length of reinforcing steel in the

concrete deck is 12 m.

10. Placement of Transverse Reinforcing Steel on Skewed Bridges. The following applies:

a. Skews 25°: Place the transverse reinforcing steel parallel to the skew.

b. Skews > 25°: Place the transverse reinforcing steel perpendicular to the longitudinal

reinforcement.

See Section 6.3.4 for a definition of skew angle and for structural considerations related to

skewed reinforcing steel placement.

11. Splices/Connectors. Use lap splices for concrete deck reinforcement unless special

circumstances exist. Use mechanical connectors where clearance problems exist or on a

phased-construction project that precludes the use of lap splices. See Chapter 4 for more

discussion on splices.

Lap transverse slab reinforcement, if necessary, as follows: Negative moment steel in the

positive-moment region between the slab supports and positive moment steel in the

negative-moment region over the slab supports.

12. Shear Connectors for Concrete Girder Bridges. Extend stirrups from the girders into the

concrete slab to provide a composite section. Detail bars to hook around longitudinal

concrete deck reinforcement.

6.3.2 Detailing Requirements for Concrete-Deck Haunches

6.3.2.1 General

Provide haunches (i.e. concrete between the top of a steel flange or concrete girder and the bottom

of the concrete bridge deck) to account for construction variations and tolerances. The haunch varies

across the width of the flange due to cross slope, the length of the girder due to flange thickness,

camber variation, and profile. In all cases, however, use a minimum of a 15-mm haunch.

Include the girder haunch in the load calculations as dead load by applying the maximum haunch

dimension throughout the span. Ignore the haunch, however, in the calculation of the section’s

resistance.

Measure the control dimension “Y” at the centreline of bearing.

The control dimension varies along the span to compensate for variations in camber and super

elevation ordinate. In some cases where vertical curve corrections are small, the vertical curve

ordinate can be accommodated in the haunch without including it in the girder.

Detail the haunch flush with the vertical edge of the top flange.


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6.3.2.2 Haunch Dimensions for Steel Girders

Figure 6.1 illustrates the controlling factors used to determine the haunch dimension for steel plate

girders. Figure 6.2 illustrates a steel rolled beam. For plate girders, the control dimension “Y” is the

deck thickness “T” plus a dimension “X”. “X” is the greater of 50 mm plus the thickest top flange, or

75 mm.

Figure 6.1: Haunch Dimension for Steel Plate Girders

Figure 6.2: Haunch Dimension for Steel Rolled Beams


PAGE 92


The 50-mm dimension represents the maximum positive camber fabrication tolerance allowed by

AWS D-1.5 of 40 mm plus a moderate deck cross slope.

For rolled beams, the control dimension “Y” includes the deck thickness “T” plus 50 mm.

6.3.2.3 Haunch Dimensions for Precast Concrete Girders

Figure 6.3 illustrates the controlling factors used to determine the haunch dimension for precast

concrete girders. Control dimension “Y” is the deck thickness “T” plus 75 mm.

Figure 6.3: Haunch Dimension for Concrete

The 75-mm dimension is used to account for camber growth in the girder at the centre of span. The

amount of camber growth can vary even between girders cast at the same time.

6.3.2.4 Reinforcement for Deep Haunches

Provide additional reinforcement in haunches greater than 100 mm deep. For the additional

reinforcement, use a minimum of T16 U-shaped reinforcing bars spaced at a maximum of 300 mm.

Properly develop these reinforcing bars into the concrete bridge deck. See Figure 6.4

Figure 6.4: Haunch Reinforcement for Deep Haunches (> 100 mm)


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6.3.3 Reinforcing Steel Over Intermediate Piers or Bents

When cast-in-situ slabs are composite with simple span concrete beams, and are cast continuous

over intermediate piers or bents, provide supplemental longitudinal reinforcing in the tops of slabs.

Size, space, and place reinforcing bars in accordance with the following criteria:

1. T16 bars placed between the continuous, longitudinal reinforcing bars.

2. A minimum of 12 m in length or ⅔ of the average span length, whichever is less.

3. Placed symmetrically about the centreline of the pier or bent, with alternating bars staggered

1.5 m.

6.3.4 Minimum Negative Flexure Slab Reinforcement


Any location where the top of the slab is in tension under any combination of dead load and live load

is considered a negative flexural region.

6.3.5 Crack Control in Continuous Decks


To minimize shrinkage and deflection cracking in cast-in-situ decks, develop a designated deck

casting sequence for continuous flat slab and beam/girder superstructures and simple span

beam/girder superstructures with continuous decks. Indicate on the plans the sequence and

direction of each deck pour to minimize cracking in the freshly poured concrete and previously cast

sections of deck. Provide construction joints as required to limit the volume of concrete cast in a

given pour to between 153 m3 and 305 m3.

For simple span and continuous steel beam/girder superstructures, develop camber diagrams

considering the deck casting sequence and the effect on the changing cross section characteristics

of the superstructure. For continuous superstructures, the sequence results in construction joints

spaced approximately at locations of the points of dead load moment contraflexure. On continuous

superstructures, check longitudinal tension stresses in previously cast sections of the deck during

deck casting sequence per BDS Article 6.10.3.2.4. On the plans, state that a minimum of 72 hours

is required between pours in a given continuous unit. When developing casting sequences and

camber diagrams, use the appropriate concrete strength based on the day the structure is being

analysed.

Generally, for continuous steel girder superstructures, all of the positive moment sections of the deck

are cast first, followed by the negative moment sections.

For continuous concrete beam/girder superstructures, develop build-up diagrams considering the

deck casting sequence, time dependent effects, and the effect on the changing cross section

characteristics of the superstructure. The sequence results in construction joints spaced

approximately at locations of the points of dead load moment contraflexure. On the plans, state that

a minimum of 72 hours is required between pours in a given continuous unit

.


PAGE 94


Generally for continuous concrete beam/girder superstructures, all of the positive moment sections

of the deck are cast first, followed by the negative moment sections.

For simple span concrete beam/girders with continuous decks, locate construction joints at the ends

of the spans and at intermediate locations as required. Include the alternate detail showing the deck

continuously cast over intermediate supports with tooled joints in lieu of construction joints. After

placement of the first unit, begin succeeding placements at the end away from and proceed toward

the previously placed unit. On the plans, state that a minimum of 72 hours is required between

adjacent pours in a given continuous unit.

For simple and continuous flat slab superstructures, develop camber diagrams indicating the

deflection of the spans due to self-weight of the deck and railings. For continuous flat slab

superstructures, show construction joints at most one-quarter and/or three-quarter points in the

spans. After placement of the first unit, begin succeeding placements at the end away from and

proceed toward the previously placed unit. On the plans, state that a minimum of 72 hours is required

between adjacent pours in a given continuous unit.

For flat slab superstructures, the Contractor is responsible for determining the deflection of the

formwork due to the weight of the wet deck concrete, screed, and other construction loads.

For all superstructure types listed above, state on the plans that the casting sequence may not be

changed unless the Contractor performs a new structural analysis, and new camber diagrams are

calculated.

Units composed of simple span steel girders with continuous decks are not allowed due to the

flexibility of the girders.

Size the casting sequences and the location of the construction joints so that the concrete can be

placed and finished while the concrete is in a plastic state and within an eight-hour work shift. A

reasonable limit on the size of a superstructure casting is 153 m3 to 305 m3. For small projects, the

153 m3 per day production rate is a reasonable upper casting limit. For larger projects, the 305 m3

per day maximum casting volume may be more reasonable. Plan the location of construction joints

so that the concrete can be placed using a pumping rate of 46 m3/hr for each concrete pumping

machine. Consider site specific constraints (i.e. land closure restrictions) when determining the size

of a deck casting and/or location of construction joints.

6.3.6 Skewed Decks


Skew is the angle between the centreline of support and the normal drawn to the longitudinal

centreline of the bridge at that point. See Figure 6.5. The support skews can be different.

In addition to skew, the behaviour of the superstructure is also affected by the span-length-to-bridge-

width ratio.

Figure 6.5 illustrates four combinations of skew angles 30° and 50° and length-to-width ratios of 3:1

and 1:3. Both the 50° skew and the 1:3 length-to-width ratio are extreme values for bridges, but this

often occurs where the concrete deck constitutes the top slab of a box culvert.

Both combinations with 30° skew may be orthogonally modelled for design with the skew ignored.


PAGE 95


Figure 6.5: Skew Angle and Length/Bridge Width Ratios

The combinations with 50° skew may require additional thought. Consider, for example, the

combination of 50° skew and L/W = 1:3. If the concrete deck is a cast-in-situ concrete slab without

girders, the primary direction of structural action is perpendicular to the span not in the direction of

the span. In this case, consider running the primary reinforcement in that direction and fanning it as

appropriate in the side zone. With this arrangement, the secondary reinforcement could then be run

parallel to the skew, thus regaining the orthogonality of the reinforcement as appropriate for this

layout.

Reinforcing placement when the slab skew is 25 degrees or less:

Place the transverse reinforcement parallel to the skew for the entire length of the slab.

Reinforcing placement when the slab skew is more than 25 degrees:

Place the required transverse reinforcement perpendicular to the centreline of span. Because

the typical required transverse reinforcement cannot be placed full-width in the triangular

shaped portions of the ends of the slab at open joints, the required amount of longitudinal

reinforcing must be doubled for a distance along the span equal to the beam spacing for the

full width of the deck. For all bridges, except those with a thickened slab end as used with I-

beam simple span structures, place three T16 Bars at 150-mm spacing, full-width, parallel to

the end skew in the top mat of each end of the slab.

Regardless of the angle of skew, the traffic railing reinforcement cast into the slab is not skewed.


PAGE 96


6.3.7 Temperature and Shrinkage Reinforcement

For all cast-in-situ decks, design temperature and shrinkage reinforcement per BDS Article 5.10.8,

except do not exceed 300 mm spacing. The minimum bar size is T12.

6.3.8 Thickened Slab End Requirements

For pretensioned simple span I-beam bridges, design the thickened slab end at locations of slab

discontinuity not supported by full depth diaphragms. Do not thicken the slab at intermediate

supports within an I-beam simple span unit where the deck slab is continuous.

6.3.9 Phase Constructed Decks

For decks constructed in phases and on bridge widenings, live load on the existing or previously

constructed portions of the superstructure can induce vibration and deflection into the newly

constructed portion of the superstructure. Evaluate the live load induced effects on deck casting and

curing and minimize these where possible.

Where possible, shift live load away from newly constructed portions of the deck during casting and

curing operations to minimize or eliminate deflection and vibration effects. This can be a significant

issue on long span or flexible superstructures, especially steel superstructures. Coordinate with the

traffic control plans.

6.3.10 Stay-in-Place Forms

Concrete stay-in-place forms can be used with precast concrete girders and steel I-girders. Do not

use stay-in-place forms in bays having longitudinal joints or in concrete deck overhangs.

Apply design loads for stay-in-place forms to all girder bridges.

Clearly state in the “General Notes” for each bridge project, whether or not stay-in-place forms are

permitted for the project and how the design was modified for their use; e.g. dead load allowance.

Composite stay-in-place forms are not permitted.

6.3.11 Concrete Deck Pouring Sequence for Decks Constructed Compositely in Conjunction with Concrete and Steel Girders


6.3.11.1 Typical Practice

The bridge designer determines the need for a concrete bridge deck pouring sequence based on

factors such as size of pour, configuration of the bridge, potential placement restrictions, direction of

placement, concrete deck tensile stresses, and any other special circumstances that might affect

the concrete bridge deck placement. In addition, provide a concrete deck-pouring schedule for

bridges that have any of the following features:

• continuous bridges,

• bridges with curved or non-parallel deck edges, or

• wide or long single span bridges.


PAGE 97


Where required, the bridge designer will present in the contract documents the sequence of placing

concrete in various sections (separated by transverse construction joints) of deck slabs on

continuous spans. Avoid or minimize the dead-load tensile stresses in the slab during concrete

setting to minimize cracking, and arrange the sequence to cause the least disturbance to the portions

placed previously.

For longer span steel girder bridges, the pouring sequence can lock-in stresses far different than

those associated with the instantaneous placement typically assumed in design. Therefore, for these

bridges, consider the pouring sequence in the design of the girders.

Concrete deck placement is uniform and continuous over the full width of the superstructure. The

first pours include the positive-moment regions in all spans. For all deck pours on a longitudinal

gradient of 3% or greater, the direction of pouring is uphill.

Figure 6.6 illustrates a sequence diagram for a sample pour for a continuous girder bridge. For

precast concrete girders, use a minimum of 1 m on each side of the centre of support or 5% of the

span length, whichever is greater.

For precast concrete girders, the cast-in-situ diaphragm over the abutment is cast integrally at the

same time as the concrete deck above it. The negative-moment regions for steel girders extend

between the points of beam dead load contraflexure.

For simple spans, pour the entire concrete deck at once. If this is not practical, pour the deck in a

series of longitudinal strips with closure pours as needed. For steel bridges, investigate potential

differential deflections.

Treat precast concrete girders made continuous for live load and superimposed dead load as a

special case. Pour the concrete deck segment and diaphragm over supports after the mid-span

regions of the deck have been poured as simple-span loads.

End wall concrete in integral abutments is usually cast concurrently with applicable portions of the

superstructure (e.g. bottom slab, web/diaphragm, concrete deck). The contract documents must

indicate the requirements for a special placement sequence.

6.3.11.2 Transverse Construction Joints

Place a transverse construction joint in the end span of concrete bridge decks on steel

superstructures where uplift is a possibility during the deck pour. Where used, place transverse

construction joints parallel to the transverse reinforcing steel. Do not place the joints over field

splices.

A bridge with a relatively short end span (60% or less) when compared to the adjacent interior span

is most likely to produce this form of uplift. Uplift during the deck pour can also occur at the end

supports of curved concrete decks and in superstructures with severe skews.

If analysis using the appropriate permanent load factors of BDS Article 3.4.1 demonstrates that uplift

occurs during concrete deck placement, require a construction joint in the end span and require

placing a portion of the deck first to act as a counterweight.


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Figure 6.6: Typical Pour Diagram (Continuous Steel and Precast Girders)


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6.3.12 Longitudinal Construction Joints

Longitudinal construction joints in concrete bridge decks can create planes of weakness that can

lead to maintenance problems. In general, do not use longitudinal construction joints, although they

cannot be avoided under certain circumstances (e.g. widenings, phased construction). The following

will apply to longitudinal construction joints:

1. Usage. Do not use longitudinal construction joints on concrete decks having a constant cross

section where the width is less than or equal to approximately 35 m. For deck widths greater

than 35 m (i.e. where the finishing machine span width must exceed 35 m), make provisions

to permit placing the deck in practical widths. Detail either a longitudinal joint or a longitudinal

closure pour, preferably not less than 1 m in width. Locate lap splices in the transverse

reinforcing steel within the longitudinal closure pour.

Such a joint should remain open as long as the construction schedule permits to allow

transverse shrinkage of the deck concrete. Consider the deflections of the bridge on either

side of the closure pour to ensure proper transverse fit.

2. Location. If a longitudinal construction joint is necessary, do not locate it underneath a wheel

line. Preferably, locate construction joints outside the girder flange and in a shoulder or

median area.

3. Closure Pours. For staged construction projects, use a closure pour to connect the slab

between stages. When used, the following apply:

• Do not use stay-in-place forms under the closure pour.

• Do not rigidly connect diaphragms/cross frames in the staging bay of structural steel

girders until after the adjacent stages of the concrete deck have been poured.

Construct concrete diaphragms in the staging bay of prestressed concrete girders

after adjacent portions of the bridge are complete. The diaphragms may be poured

as part of the closure.

• Do not tie or couple reinforcing steel between different stages until after the adjacent

stages of the concrete deck have been poured.

• Support the finishing machine on an overhang jack that is connected to the girder

loaded by the concrete deck pour. Do not place the finishing machine on a previously

poured deck. Indicate in the contract documents that this method of constructing the

closure pour is not allowed. See Figure 6.7.

A closure pour serves two useful purposes: It defers final connection of the stages until after

the deflection from concrete deck slab weight has occurred, and it provides the width needed

to make a smooth transition between differences in final grades that result from construction

tolerances. The closure width relates to the amount of relative dead-load deflection that is

expected to occur across the pour after the closure is placed. Use a minimum closure width

of 1 m.

Greater closure widths may be required when larger relative dead-load deflections are

anticipated. Estimate the required width by considering the closure pour to be a fixed-fixed

beam and by limiting the stresses in the concrete to the cracking stress.


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Figure 6.7: Support for Finishing Machine


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6.3.13 Longitudinal Concrete Deck Joints


There is not a specified maximum bridge width that can be used without a longitudinal open joint. As

an approximate guide, widths up to 35 m without a joint are usually acceptable. Open longitudinal

joints may be needed where the width of the bridge exceeds 35 m or on multiple-span bridges with

large skews.

Open longitudinal joints, used on slab-on-girder bridges, are not typically needed except on the

widest bridges. The requirement for open longitudinal joints in bridges is based on the bridge width,

skew, and span configuration.


1. Column Design. Use a longitudinal open joint where transverse temperature controls the

column design.

Desirably, the column design is controlled by seismic loads and not other load combinations.

2. Location. Do not place longitudinal open joints over a girder flange. If a longitudinal joint is

used, place the joint in both the superstructure and substructure.

6.3.14 Transverse Edge Beam for Steel Girder Bridges


Provide a transverse edge beam to support wheel loads near the transverse edge of the concrete

deck in conjunction with an end diaphragm for steel girder bridges. See Figure 6.8.

6.3.15 Concrete Deck Overhang/Bridge Rail


6.3.15.1 Overhang Width and Thickness

Concrete bridge deck overhang is the distance between the centreline of the exterior girder to the

outside edge of the deck. The overhang width must not be more than 40% of the girder spacing. The

thickness of the overhang at the outside edge of deck is the same as the interior deck thickness.

The thickness of the overhang at outside edge of girder is the deck thickness plus the haunch depth.

6.3.15.2 Structural/Performance Design

Reference: BDS Articles 13.6.1, 13.6.2, and 13.7.2

Design all combination bridge rail/concrete deck overhang designs to meet the structural design

requirements to sustain rail collision forces in BDS Article A13.2. Use a Class 2 exposure factor in

BDS Equation 5.7.3.4-1 for all bridge rails and deck overhang designs.


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Figure 6.8: Transverse Edge Beam


PAGE 103


When designing the deck overhang for Extreme Event II, include a vertical wheel load located 300

mm from the face of bridge rail in conjunction with transverse and longitudinal bridge rail loads; do

not apply the wheel load in combination with vertical rail loads. Design the deck overhang using the

rail resistance instead of the rail load. This ensures failure in the rail before the concrete deck

overhang.

Place sidewalks, when used, on the outside edge of bridge decks adjacent to rails. Assume the point

of fixity for the design of the rail at the deck level and not the top of sidewalk.

6.3.15.3 Bridge Barriers

See Chapter 7 “Bridge Rails” of the Abu Dhabi Roadside Design Guide (Document Reference No.

TR-518) for a discussion on bridge rails and transitions to bridge rails.

The following applies to bridge barrier joints:

1. Concrete Bridge Barrier Joints. Provide joints on concrete bridge rails at all locations of

expansion in the bridge; i.e. the joints on the bridge deck and barrier will match. In addition,

provide 50-mm open joints in the barrier, extending from the top of the barrier downward 600

mm, at the mid-span of each span and over supports. Consider additional open joints on

longer spans. Design open joints as discontinuities.

2. Barrier Rail Connection. Extend the expansion joint up into the barrier rail at least 150 mm.

6.4 Approach Slabs

6.4.1 Usage

Provide approach slabs on all bridges. See the Abu Dhabi Standard Drawings for Road Projects

(Document Reference No. TR-541-2).

6.4.2 Design Criteria

Design the roadway ends of approach slabs parallel to the bridge ends. The following design criteria

apply to approach slabs:

1. Analysis. If a special design is used, model the approach slab as a simple span with a span

of L/2.

2. Bridge Approach Joints. Provide a terminal joint or pavement relief joint at the end of the

roadway at the bridge approach slab, if the approaching roadway is concrete.

3. For the purpose of analysis of at-grade approach slab, it may be either partially suspended

or preferably fully supported on equivalent springs to achieve overall economy in design.

4. For approach slab that are buried less than 300mm, provide a flexible joint at the interface of

approach slab edge and fill. Flexible joint in the form of saw-cut filled with approved joint filler

or asphaltic plug joint to absorb any cracks on asphalt surface due to any differential

settlements.


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07-FOUNDATIONS SECOND EDITION – AUGUST 2021

7 FOUNDATIONS

7.1 General

7.1.1 Scope

A critical consideration for the satisfactory performance of any structure is the proper selection and

design of a foundation that will provide adequate support and addresses constructability

considerations. This Chapter presents criteria that are supplementary to Section 10 of the BDS for

the design of drilled shafts, spread footings, and driven piles. The Chapter is intended for use by the

bridge designer and as a reference for the geotechnical engineer. The Abu Dhabi Geotechnical

Investigation and Design: Part 2: Ground Investigation and Geotechnical Design (Document

Reference No. TR-509) discusses the geotechnical considerations for the design of bridge

foundations.

The structural engineer, with input from the geotechnical and hydraulic engineers, must determine

the structure loads and the pile/shaft section or spread footing configuration. The structural engineer

and the geotechnical engineer must consider constructability in the selection of the foundation

system. Consider issues such as existing underground and overhead utilities, pile-type availability,

availability of construction equipment, phase construction, conflicts with existing piles and structures,

effects on adjacent structures, etc., in evaluating foundation design.

Design all substructures to incorporate bearings or provide fixed connections to the superstructure.

Determine pile and drilled shaft loads and design footings and bent caps using plan pile and drilled

shaft locations. Detail footings and bent caps considering pile driving and drilled shaft placement

tolerances.

7.1.2 Design Methodology

Use the load and resistance factor design (LRFD) methodology for foundations.

The BDS distinguishes between the strength of the in-situ materials (soils and rock strata) supporting

the bridge and the strength of the structural components transmitting force effects to these materials.

Section 10 “Foundations” addresses in-situ materials, and Section 11 “Abutments, Piers, and Walls”

addresses structural components, which is necessitated by the substantial difference in the reliability

of in-situ materials and man-made structures. The foundation provisions of the BDS are essentially

strength design provisions with a primary objective to ensure equal, or close to equal, safety levels

in all similar components against structural failure.

Sections 5 and 6 of the BDS specify requirements for concrete and steel components. Apply the

appropriate provisions from these Sections in the structural design of drilled shafts, footings, and

driven piles.

7.1.3 Bridge Foundation Design Process

To select a foundation type, evaluate the load/structural considerations for the superstructure and

substructure, the geotechnical factors pertaining to the native soils, and site conditions. The following

summarizes the procedure for selecting and designing a bridge foundation type:


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1. Preliminary Structure Layout. The bridge designer obtains preliminary soils information from

the geotechnical engineer to assist with the selection of support locations and span lengths.

Provide preliminary foundation loads to the geotechnical engineer.

2. Scour Potential. For bridges over waterways, the hydraulics engineer evaluates the proposed

bridge site and preliminary structure layout to identify the predicted hydraulic scour based on

material properties provided by the geotechnical engineer. This analysis is provided to both

the bridge designer and the geotechnical engineer.

As part of the subsurface site investigation, the geotechnical engineer provides a geologic or

historic elevation for scour. The hydraulics engineer calculates an anticipated hydraulic scour

depth. The bridge designer in conjunction with the geotechnical engineer and hydraulics

engineer determines a “design” scour for the design of the foundation.

3. Geotechnical Data. For all sites, the geotechnical engineer conducts a site-specific

subsurface investigation and prepares a Geotechnical Report. The geotechnical engineer

provides this Report to the bridge designer.

4. Foundation Type Selection. Based on information provided by the bridge designer (e.g.

structure layout, vertical and lateral loads, settlement criteria), the geotechnical engineer

provides the foundation-type to the bridge designer in the Geotechnical Report.

5. Detailed Structural Design. The bridge designer performs the detailed structural design of

the foundation based on Section 10 of the BDS as modified by Chapter 7 of this Manual in

conjunction with the structural requirements of Sections 5 and 6 of the BDS.

6. Soil Structure Interaction shall be considered according to AASHTO LRFD requirements.

7. The design of MSE walls shall satisfy AASHTO LRFD Section 11.

7.1.4 Bridge Design/Geotechnical Design Interaction

7.1.4.1 Overview

The geotechnical engineer is responsible for developing a subsurface exploration program and

preparing the preliminary geotechnical design and a Geotechnical Report. The bridge designer uses

the information to design bridge foundations and other structures. The successful integration of the

geotechnical design into the bridge design requires close coordination between the geotechnical

engineer and the bridge designer.

Prior to the design of the foundation, the bridge designer must have knowledge of the environmental,

climatic, and loading conditions expected during the life of the proposed unit. The primary function

of the foundation is to spread concentrated loads over a sufficient zone, to provide adequate bearing

resistance and limitation of movement and, when necessary, to transfer loads through unsuitable

foundation strata to suitable strata. Therefore, knowledge of the subsurface soil conditions, ground

water conditions, and scour is necessary.

7.1.4.2 Preliminary Geotechnical Design Data

The geotechnical engineer provides the preliminary geotechnical design data based on existing soil

information and any preliminary subsurface investigation. These general geotechnical data are used

to select the bridge foundation and initiate the preliminary structure design. Use the geotechnical


PAGE 106


information in conjunction with the input of the hydraulics engineer (as applicable) to establish

support locations. Prior to beginning work on preliminary bridge design, the bridge designer reviews

the preliminary geotechnical design information to gain knowledge of the anticipated soil conditions

at the bridge site and the potential general foundation types. The preliminary geotechnical design

data provide a preliminary footing elevation and an expected allowable bearing pressure when

spread footings are used. For deep foundations, the selection will be driven piles or drilled shafts.

Driven piles will include pile capacity and type. Use the preliminary geotechnical information to

estimate sizes of foundation members.

7.1.4.3 Geotechnical Report

Subsurface Exploration

The geotechnical engineer performs a detailed subsurface exploration based on the bridge abutment

and pier locations and anticipated foundation type. The geotechnical engineer determines the

proposed boring locations. Typically, the structural modelling and analysis of the bridge proceed

based on the preliminary geotechnical design while the geotechnical subsurface exploration is

conducted. During this time, the bridge designer assumes a preliminary point-of-fixity or preliminary

footing elevation to model the substructure. The bridge designer determines, verifies, and provides

foundation loads or calculated bearing pressures to the geotechnical engineer. The bridge designer

provides the design loads (vertical and horizontal) at the bottom of substructure units. The bridge

designer also provides the elevation at which the loads or bearing pressures are applied. When the

geotechnical subsurface exploration has been completed, the geotechnical engineer will perform

laboratory testing and geotechnical design. The geotechnical engineer issues a Geotechnical Report

based on the field exploration, laboratory testing, geotechnical design, the preliminary bridge design,

and the loads provided by the bridge designer.

Foundation Design

The bridge designer uses the information provided in the Geotechnical Report to design foundations

for bridges and bridge-related structures. For deep foundations, the Geotechnical Report provides

tip elevations and p-y soil models of the subsurface that are used to perform foundation lateral soil-

structure interaction analyses. The bridge designer then performs the lateral soil-structure interaction

analysis with computer programs such as DFSAP, LPile Plus, or COM624. The bridge designer uses

the information to compute lateral displacements and to analyse the structural adequacy of the

columns and foundations. Use the lateral soil-structure interaction analysis to select the appropriate

method (point-of-fixity, stiffness matrix, linear stiffness springs, or p-y nonlinear springs) to model

the bridge foundation in the structural design software. For spread footings, the Geotechnical Report

provides the estimated footing elevation, allowable bearing pressure, and estimates on settlements

and lateral displacements. The bridge designer uses the information to finalize the design of the

footing and verify that members are not overstressed. Computer programs for lateral soil-structure

interaction analysis require reputable well-tested software.

Seismic Design

For bridges on deep foundations requiring seismic analysis, the bridge designer performs lateral

soil-structure interaction analyses using Extreme Event I loadings. If soil liquefaction is anticipated,

the geotechnical engineer provides the bridge designer with foundation downdrag loads due to

liquefaction for use in developing the Extreme Event I load combination. The geotechnical engineer

also provides any lateral soil forces that act on the foundation as a result of seismically induced


PAGE 107


stability movements of earth retaining structures (e.g. embankments, retaining walls) or lateral soil

movements attributable to lateral spread. Include these additional lateral loads in the Extreme Event

I load combinations when evaluating lateral soil-structure interaction. The geotechnical engineer

generates the p-y soil model of the subsurface that accounts for cyclic loadings and any liquefied

soil conditions. The bridge designer then performs the lateral soil-structure interaction analysis with

computer programs such as DFSAP, LPILE Plus, or COM624. The bridge designer uses this

information to calibrate the seismic model of the structure.

The geotechnical engineer or the contracted geotechnical firm will issue a Geotechnical Report for

most projects. This report will include:

1. detailed soil conditions,

2. foundation type,

3. design parameters,

4. constructability considerations,

5. background information that may assist the structural engineer in determining appropriate

pile lengths,

6. input data for COM624, FBPier, and other design programs when lateral loads are a major

concern,

7. completed FHWA Report Checklist and Guidelines for Review of Geotechnical Reports and

Preliminary Plans and Specifications,

8. core boring drawings reflecting the foundation data acquired from field investigations, and

9. Required load tests.

The geotechnical engineer will obtain local, site-specific foundation construction history.

Geotechnical Reports shall conform to the Abu Dhabi Geotechnical Investigation and Design: Part

2: Ground Investigation and Geotechnical Design (Document Reference No. TR-509) and the FHWA

Report Checklist and Guidelines for Review of Geotechnical Reports and Preliminary Plans and

Specifications prepared by the Geotechnical and Materials Branch, FHWA, Washington, D.C.,

October 1985. Contact the Geotechnical Engineer to receive a copy of this document.

Verify the scope of services, as well as the proposed field and laboratory investigations before

beginning any operations.

7.1.4.4 Foundation Scour Design

This is a multi-discipline effort involving geotechnical, structures, and hydraulics engineers. The

process described below often requires several iterations. The foundation design must satisfactorily

address the various scour conditions, and furnish sufficient information for the Contractor to provide

adequate equipment and construction procedures. These three engineering disciplines have specific

responsibilities in considering scour as a step in the foundation design process.

1. The structures engineer determines the preliminary design configuration of a bridge structure

utilizing all available geotechnical and hydraulic data and performs lateral stability


PAGE 108


evaluations for the applicable loadings (do not impose arbitrary deflection limits except on

movable bridges). A preliminary lateral stability analysis generally occurs during the

predesign phase of the project, and a final evaluation occurs subsequent to the selection of

the final configurations. The structures engineer must apply sound engineering judgment in

comparing results obtained from scour computations with available hydrological, hydraulic,

and geotechnical data to achieve a reasonable and prudent design.

2. The hydraulics engineer provides the worst case scour elevation through a 100-year flood

event (100-Year Scour), a 500-year flood event (500-Year Scour), and for “Long-Term

Scour.”

3. The geotechnical engineer provides the nominal axial (compression and tension)

capacity curves, mechanical properties of the soil, and foundation type based on

construction methods, pile availability, similar nearby projects, site access, etc.

It is not necessary to consider the scour effects on temporary structures.

7.2 Spread Footings and Pile Caps


This discussion applies to spread footings supported on soil and to pile caps.

Pile caps distribute loads among two or more drilled shafts or driven piles that support a single

column, group of columns, or walls.

7.2.1 Usage

Spread footings supported on soil are an appropriate foundation type if soils and estimated

settlements allow their use. They are typically only used in the Abu Dhabi Emirate to sometimes

support walls. Spread footings are prohibited:

• at stream crossings where they may be susceptible to scour, and

• on MSE fills.

Spread footings are thick, reinforced concrete members sized to meet the structural and

geotechnical loading requirements for the proposed structural system. A factor affecting the size of

the footing is the structural loading versus the ability of the soil to resist the applied loads.

The Geotechnical Report provides the maximum soil pressures, the minimum footing widths, and

the minimum footing embedment. BDS Table 10.5.5.2.2-1 shall be used for Resistance Factors ().

Determine the factored design load and proportion the footings to provide the most cost effective

design without exceeding the maximum soil pressures. Communicate with the geotechnical engineer

to ensure that the corresponding settlements do not exceed the tolerable limits.

Require dewatering with a note on the plans when in the Geotechnical Report. Dewatering is

required if the seasonal high ground water elevation is higher than 600 mm below the bottom of the

footing.

Verify sliding, overturning, and rotational stability of the footings.


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7.2.2 Dynamic Load Allowance (Impact Modifier, IM)

If a significant portion of the footing is above ground, apply the dynamic load allowance, traditionally

termed Impact Modifier (IM), to the proportioning of footings.

7.2.3 Thickness


Use a minimum footing thickness of 600 mm for bridge abutments and piers. Thinner footing

thicknesses may be used to support walls.

The footing or pile cap thickness may be governed by the development length of the column or wall

reinforcement, or by shear requirements. Avoid shear reinforcement in footings or pile caps. If shear

governs the thickness, it is usually more economical to use a thicker footing or pile cap without shear

reinforcement instead of a thinner footing or pile cap with shear reinforcement.

7.2.4 Depth

Reference: BDS Articles 5.8.3, 5.13.3.6, and 5.13.3.8

The following will apply:

1. In Waterways. On soil, locate the top of the spread footing below the design scour depth. On

rock, locate the bottom of the footing 300 mm below the surface of the scour-resistant rock.

2. Minimum Embedment and Bench Depth. Embed spread footings a sufficient depth to provide

the greatest of the following:

• adequate bearing and scour,

• 900 mm to the bottom of footing, or

• 600 mm of cover over the footing.

Locate pile caps above the lowest anticipated scour level if the piles are designed for this condition.

Construct footings to neither pose an obstacle to water traffic nor expose the footing to view during

low flow. Construct footings to pose minimum obstruction to water and debris flow if exposed during

high flows. In all cases, allowance to scour potential must be taken into consideration.

7.2.5 Bearing Resistance and Eccentricity


Present the required nominal bearing and the geotechnical resistance factor in the Contract

Documents.

7.2.6 Sliding Resistance


Use the coefficients of friction in the BDS for sliding resistance.

Keys in footings to develop passive pressure against sliding are not commonly used for bridges.

When it becomes necessary to use a key, the bridge designer will consult with the geotechnical

engineer.


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7.2.7 Differential Settlement

Reference: Section 2.2.3

7.2.7.1 Typical Practice

Angular distortion is the differential settlement divided by the distance between the adjacent

foundations. The following presents general practices on the acceptable limits for angular distortion:

1. Limiting Angular Distortion. BDS Article C10.5.2.2 states that angular distortions between

adjacent foundations greater than 0.008 radians in simple spans and 0.004 radians in

continuous spans not be ordinarily permitted (Moulton et al., 1985 (23)); DiMillio, 1982 (24);

and Barker et al., 1991 (25).

2. Piers. Consider continuous footings or deep foundations where differential settlement is a

concern between columns within a pier.

Differential settlement (SE) is considered a superstructure load in the BDS. Differential settlement is

the difference between the settlements of two adjacent foundations. Generally, due to the methods

used to proportion foundations, settlements are within a tolerable range and, therefore, force effects

due to differential settlement are not investigated.

7.2.7.2 Effects of Foundation Settlement

If varying conditions exist, the Geotechnical Report will address settlement. Consider the following

effects:

1. Structural. Consider differential settlement in design if deemed significant, especially those

negative movements that may either cause or enlarge existing cracking in concrete deck

slabs.

The differential settlement of substructures causes the development of force effects in

continuous superstructures. The force effects are directly proportional to structural depth and

inversely proportional to span length, indicating a preference for shallow, long-span

structures. They are normally smaller than expected and tend to be reduced in the inelastic

phase.

2. Joint Movements. Consider any change in bridge geometry due to settlement that causes

movement in deck joints in detailing, especially for deep superstructures.

3. Profile Distortion. Excessive differential settlement may cause a distortion of the roadway

profile that may be undesirable for vehicles travelling at high speed.

4. Appearance. Viewing excessive differential settlement may create a feeling of lack of safety.

5. Mitigation. Where necessary, use ground modification techniques to improve the soil to

address differential settlement concerns. The techniques include but are not limited to:

• chemical grouting,

• over-excavation and replacement,

• surcharging,

• the construction of stone columns, and


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• compaction grouting.

7.2.8 Reinforcement


Chapter 4 discusses practices for the reinforcement of structural concrete. In addition, unless other

design considerations govern, use the following for reinforcement in footings:

1. Steel in Top of Footing. Use the minimum reinforcement in the top of pile caps and spread

footings as required by design.

For pile caps, the anchorage of piles or drilled shafts into footings requires tension

reinforcement in the top of the footing to resist the potential negative bending under seismic

action.

2. Embedment Length. Extend the vertical steel of the footing down to the bottom pile cap or

spread footing steel and hook onto the bottom end regardless of the footing thickness.

3. Spacing. The recommended minimum spacing of reinforcing steel in either direction is 125

mm centre to centre; the recommended maximum spacing is 300 mm centre to centre.

4. Blinding. Where blinding is used, extend the piles through the blinding and 100 mm into the

footing and locate the reinforcement above the top of piling.

5. Other Reinforcement Considerations. BDS Article 5.13.3 specifically addresses concrete

footings. For items not included, the other relevant provisions of Section 5 will govern. For

narrow footings, to which the load is transmitted by walls or wall-like abutments, the critical

moment section is at the face of the wall or abutment stem. The critical shear section is a

distance equal to the larger of “dv” (dv is the effective shear depth of the footing) or “0.5dv cot

“ ( is the angle of inclination of diagonal compressive stresses as defined in BDS Article

5.8.3.4) from the face of the wall or bent stem where the load introduces compression in the

top of the footing section. For other cases, either use BDS Article 5.13.3, or use a two-

dimensional analysis for greater economy of the footing.

7.2.9 Miscellaneous

7.2.9.1 Joints

Footings do not generally require construction joints. Where used, offset footing construction joints

600 mm from expansion joints or construction joints in walls and construct them with 75-mm deep

keyways.

7.2.9.2 Stepped Footings

Stepped footings may be used occasionally. Where used, the difference in elevation of adjacent

stepped footings is not be less than 600 mm. Extend the lower footing at least 600 mm under the

adjacent higher footing.

If high bearing pressures under a spread footing are present, use concrete backfill instead of

granular backfill for support under the upper step. See Figure 7.1. The two footings could be placed

monolithically, if the bearing pressure allows.


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Figure 7.1: Concrete Backfill Under Stepped Footing

7.3 Deep Foundations

7.3.1 General

Attempt to use only one type and size of deep-foundation component (i.e. drilled shaft or driven pile)

throughout a structure.

7.3.2 Component Spacing


To determine the minimum spacing of deep-foundation components in a group, obtain the maximum

resistance of the individual components; that is, select the spacing such that the efficiency factor, η,

equals 1.0.

Unless otherwise specified, determine the maximum spacing of deep-foundation components in a

group based upon the stiffness of the cap.

7.3.3 Drilled Shafts


7.3.3.1 Usage

Drilled shafts are the most common foundation for road structures. Typical shaft diameters range

from 900 mm to 1500 mm. In general, use drilled shafts to resist large lateral or uplift loads where

deformation tolerances are relatively small.

Drilled shafts derive load resistance either as end-bearing shafts transferring load by tip resistance

or as friction shafts transferring load by side resistance or a combination of both. Friction-only shafts

are the most desirable but may not be the most economical. Drilled shafts are typically good for

seismic applications.

7.3.3.2 Drilled Shaft Axial Compressive Resistance at the Strength

Limit State

Reference: BDS Articles 10.8.3.5.1, 10.8.3.5.2, and 10.8.3.5.4


PAGE 113


The BDS provides procedures to estimate the axial resistance of drilled shafts in cohesive soils and

cohesionless soils in BDS Articles 10.8.3.5.1 and 10.8.3.5.2. In both cases, the resistance is the

sum of the shaft and tip resistances. BDS Article 10.8.3.5.4 discusses the determination of axial

resistance of drilled shafts in rock.

7.3.3.3 Structural Design

Use the following for the design of drilled shafts:

1. Column Design. Even soft soils provide sufficient support to prevent lateral buckling of the

shaft. Therefore, design drilled shafts surrounded by soil according to the criteria for short

columns in BDS Article 5.7.4.4 when soil liquefaction is not anticipated. If the drilled shaft is

extended above ground to form a pier, analyse and design the shaft as a column. Similarly,

consider the effects of scour around the shafts in the analysis.

2. Casing. Consider using a casing to maintain the excavation, especially when placing a shaft

within the water table. Do not consider this casing, if left in place after construction, in the

determination of the structural resistance of the shaft. However, consider the casing when

evaluating the seismic response of the foundation because the casing provides additional

resistance.

3. Lateral Loading. Section 7.3.3.8 discusses the analysis of drilled shafts for lateral loading

and resistance.

7.3.3.4 Design Details

Use the following when designing drilled shafts:

1. Location of Top of Shaft. Terminate drilled shafts 300 mm to 600 mm above the highest

anticipated groundwater table.

2. Edge Distance and Spacing. Locate shafts used in groups such that the distance from the

side of any shaft to the nearest edge of the cap is not less than 400 mm. Shaft spacing can

not exceed four shaft diameters.

3. Reinforcement. Chapter 5 discusses practices for the reinforcement of structural concrete.

Additional reinforcement criteria include:

• The shaft reinforcement is a minimum of 1% of the gross concrete area, and the

reinforcement extends over the entire length of the shaft and into the footing.

• For confinement reinforcement, use spirals (up to T16). For seismic applications,

consider butt-welded hoops.

• Detail drilled shafts and columns to accommodate concrete placement considering the

multiple layers of reinforcing steel including lap splices. Maximize lateral reinforcement

spacing. Use information from “The International Association of Foundation Drilling”

(26).

Figure 7.2 and Figure 7.3 (not recommended) illustrate typical drilled shaft and column

longitudinal and transverse reinforcement for the alternative of a single drill shaft supporting


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a single column. Typically, groups of drilled shafts are preferred due to redundancy

considerations.

4. Construction Joints. Do not use keys in the design of construction joints for drilled shafts.

5. Diameter. The minimum diameter of a drilled shaft supporting a single column is 500 mm

greater than the greatest dimension of the column cross section.

6. Constructability. Detail drilled shafts and columns to accommodate concrete placement

through the layers of reinforcing steel. Limit lap splices in the drilled shaft locations and

provide adequate openings.

7.3.3.5 Minimum Sizes

The recommended minimum diameter size for drilled shaft bridge foundations is 900 mm. Shafts for

bridge widening or under miscellaneous structures (i.e. sign structures, mast arms, high-mast light

poles, sound barriers) are exempt from this requirement.

The recommended minimum drilled shaft diameter for bridges is 900 mm to alleviate construction

difficulties. Rebar cages for 900 mm shafts have fewer flexibility issues during installation, pose less

congestion and consolidation issues during concreting and permit more tremie options than cages

for smaller shafts.

7.3.3.6 Downdrag

Show the downdrag load on the plans.

For drilled shaft foundations, “downdrag” is the ultimate skin friction above the neutral point (the

loading added to the drilled shaft due to settlement of the surrounding soils) minus the live load.

Do not discount scourable soil layers to reduce the predicted downdrag.

Scour may or may not occur as predicted; therefore, the presence of scourable soil layers must be

accounted for.

7.3.3.7 Group Effect

Minimum spacing requirements are based upon group effect. BDS Articles 10.8.3.6 and 10.8.3.7.3

specify group effects.


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Figure 7.2: Drilled Shaft Detail (For Shafts Larger Than Columns)


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Figure 7.3: Drilled Shaft Detail (With Equal Diameter Shaft and Column)


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7.3.3.8 Laterally Loaded Shafts

Estimate the resistance of laterally loaded shafts according to approved methods. Several methods

exist for including the effects of shafts and surrounding soil in the structural model for lateral loadings

including seismic loads. Section 7.4 discusses the preferred method.

7.3.3.9 Resistance Factors

Use Table 7.1 to determine the resistance factors for drilled shafts.

Table 7.1: Resistance Factors for Drilled Shafts

Loading Design Method Construction QC

Method

Resistance

Factor,

Compression

For soil: FHWA alpha or beta method1 Specifications 0.6

For rock socket: McVay’s method2 neglecting end bearing

Specifications 0.6

For rock socket: McVay’s method3 including 1/3 end bearing

Specifications 0.55

For rock socket: McVay’s method2 Statnamic Load

Testing 0.7

For rock socket: McVay’s method2 Static Load Testing 0.75

Uplift

For clay: FHWA alpha method1 Specifications 0.35

For sand: FHWA beta method1 Specifications 0.45

For rock socket: McVay’s method2 Specifications 0.5

Lateral4 FBPier4 Specifications or lateral load test5

1.00

1 Refer to FHWA-IF-99-025, soils with N<15 correction suggested by O’Neill. 2 Refer to FDOT Soils and Foundation Handbook. 3 Extreme event. 4 Or comparable lateral analysis program. 5 When uncertain conditions are encountered.

Refer to BDS relevant section 10 and Manual TR-509 part-2, table 26 for further details on the

methods to determine the resistance factors.

7.3.4 Driven Piles


Driven piles are not typically used in the Abu Dhabi Emirate. Only consider driven piles if they prove

more economical than drilled shafts for deep foundations. Driven piles may become necessary

where other foundation solutions have an undesirable impact on marine ecology, result in soil-

contamination issues with regard to workers, etc.


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Piles transfer loads to deeper suitable strata. Piles may function through skin friction and/or through

end bearing.

7.3.4.1 Pile Types/Selection

Pile Selection

The geotechnical engineer ultimately determines the selected type of pile. Table 7.2 provides

guidance in selecting pile types based on potential usage.

Table 7.2: Driven Pile Selection Guide

Pile Type Soil Conditions and Structural Requirements

Steel Pipe Pile

(closed or open end)

Loose to medium dense soils or clays where skin friction is the primary

resistance, and lateral stiffness in both directions is desirable, especially

in rivers where deep scour is anticipated and high lateral stiffness is

needed. Primarily used as a friction pile.

Steel H-Pile Rock or dense soil where end bearing is desirable and lateral flexibility in

one direction is not critical. Primarily used for end bearing.

Prestressed

Concrete Pile

Loose to medium dense soils or clays where skin friction is the primary

resistance.

7.3.4.2 Design Details


Pile Length

Reference: BDS Articles 10.7.1.10, 10.7.1.11, and 10.7.1.12

Determine pile length on a project-by-project basis. Use the same length for all piles for a specific

pier or abutment where practical. Show pile lengths in whole-meter increments.

Present the design and minimum pile tip elevations on the drawing of the structural element in the

contract documents.

Design pile tip elevations to reflect the elevation where the required ultimate pile capacity is

anticipated. Minimum pile tip elevations reflect the penetration required, considering scour and

liquefaction, to support both axial and lateral loads.

Predrill for piles placed at abutment embankments that are more than 1.5 m in depth. The size of

the pre-drilled hole is 50 mm larger than the diameter or largest dimension of the pile.

The Geotechnical Report provides project-specific requirements for the pile embedment, socketing,

and special construction requirements.

Reinforced Pile Tips

Where hard layers are anticipated, use reinforced pile tips to minimize damage for all steel piles.

Where rock is anticipated, equip the pile tips with teeth designed to penetrate into the rock.


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The geotechnical engineer selects the type of pile tip. The bridge designer shows this in the contract

documents.

Battered Piles

Preferably, use vertical piles. Consider battered piles, typically 3V:1H, where there is inadequate

horizontal resistance. If battered piles are used, use a refined analysis; a two-dimensional analysis

is a minimum.

Edge Distance and Spacing

The distance from the side of any pile to the nearest edge of pile cap is not less than 250 mm. Pile

spacing cannot exceed 4.0 pile diameters.

Orientation

The orientation of steel H-piles (strong versus weak axis) is a design consideration, and it is

preferable that all piles be oriented the same. For diaphragm-with-pile integral abutments, use a

single row of piles driven vertically, with the strong axis parallel to the diaphragm centreline. See

Chapter 8 for a discussion on integral abutments.

7.3.4.3 Force Effects

Downdrag (DD) Loads

Mitigate downdrag forces by the following methods:

• provide friction-reducing material around the piles;

• construct embankments a sufficient amount of time in advance of the pile driving for the fill

to settle; or

• prebore and backfill the space around the installed pile with pea gravel (may be less effective

if the adjacent soil continues to settle).

When a pile penetrates a soft layer subject to settlement, evaluate the force effects of downdrag or

negative loading on the foundations. Downdrag acts as an additional permanent axial load on the

pile and may cause additional settlement. If the force is of sufficient magnitude, structural failure of

the pile or a bearing failure at the tip is possible. For piles that derive their resistance mostly from

end bearing, the structural resistance of the pile must be adequate to resist the factored loads

including downdrag.

Uplift Forces

Avoid tensile piles resisting uplift forces where practical due to the Abu Dhabi Emirate’s high water

table. Mass concrete is a potential alternative.

Uplift forces can be caused by lateral loads, buoyancy, or expansive soils. Check piles intended to

resist uplift forces for resistance to pullout and structural resistance to tensile loads. Check the

connection of the pile to the cap or footing.

Laterally Loaded Piles

Estimate the resistance of laterally loaded piles according to approved methods. Several methods

exist for including the effects of piles and surrounding soil into the structural model for lateral loadings

including seismic loads. Section 7.4 discusses the preferred method.


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Group Effect

Minimum spacing requirements are based upon group effect. BDS Articles 10.7.3.9 and 10.7.3.11

specify group effects.

7.3.5 Pile/Shaft Testing

7.3.5.1 Pile Loads

Contract Documents

Present the applicable pile loads in the contract documents.

This information helps ensure that pile driving efforts during construction result in a foundation

adequate to support the design loads.

Static Load Tests


The geotechnical engineer determines the number and location of the static load tests. Present the

test locations and sizes in the contract documents. Pile tests shall be performed as specified in Abu

Dhabi Standard Specifications: Volume 2: Road Structures (Document Reference Number TR-542-

2).

Dynamic Pile Monitoring


Data obtained during pile-driving monitoring is used to verify pile resistance with CAPWAP.

During the installation of production piles, dynamic pile monitoring ensures that driving occurs in

accordance with the established criterion. It provides information on soil resistance at the time of

monitoring and on driving performance. Dynamic pile monitoring also reveals driving stresses, which

helps prevent pile damage. If damage is imminent, the monitoring provides an alert early enough to

save the pile from complete destruction.

7.3.5.2 Additional Steel Thickness

To account for future corrosion, add an additional sacrificial steel thickness to all permanent steel

substructure and wall components as shown in

Table 7.3.

The following criteria were used to determine the additional steel thickness required:

Environmental classification versus corrosion rate per side for partially buried piles and wall anchor

bars:

Non aggressive 0.01 mm/year

Slightly aggressive: 0.03 mm/year

Moderately aggressive: 0.05 mm/year

Extremely aggressive: 0.07 mm/year


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Table 7.3: Table of Additional Sacrificial Steel Thickness Required (mm)

Steel Component

Substructure Environmental Classification

Slightly

Aggressive

Moderately

Aggressive


Case 11 Case 22

Pipe and H-Piles completely buried in

ground without corrosion protection

measures

2 4 Do not use 6

Pipe and H-Piles on land, partially buried in

ground with corrosion protection measures 2 5 Do not use 7

Pipe and H-Piles in water, partially buried in

ground without corrosion protection

measures

4 8 Do not use N/A

Pipe and H-Piles in water, partially buried in

ground with corrosion protection measures 2 5 Do not use N/A

Anchored Sheet Piles 0 0 0 0

Cantilevered Sheet Piles 1 2 3 3

Wall Anchor Bars with corrosion protection

measures 2 5 7 7

1 Case 1: Water > 2000 ppm chlorides or resistivity < 1000 ohm/cm or pH < 6.0; except for special case. 2 Case 2: Special case for land applications: where ground water < 2000 ppm chlorides and resistivity > 5000

ohm-cm and 4.9 < pH < 6.0

Environmental classification versus corrosion rate per side for completely buried piles:

Slightly aggressive: 0.01 mm/year

Moderately aggressive: 0.03 mm/year

Extremely aggressive: 0.04 mm/year

Design Life:

Pipe and H-piles without corrosion protection measures:

100 years (additional sacrificial thickness required)

Pipe and H-piles, sheet piles and wall anchor bars with corrosion protection measures:

100 years (coating system 30 years and sacrificial thickness 70 years). Corrosion

rates for anchored sheet pile walls beyond the coating system life are neglected due

to structural redundancy.

Application:

Partially buried pipe piles and H-piles: Two-sided attack at soil and/or water line.


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Completely buried pipe piles and H-piles: Two-sided attack below ground line as shown in table

above; single sided attack if pipe piles are concrete filled.

Sheet Piles: Single-sided attack at soil and/or water line.

7.3.5.3 Test Piles


Test piles are constructed to determine soil capacity, pile-driving system, pile drivability, production

pile lengths, and driving criteria.

Depending on the bridge site and local conditions, a few test piles, as indicated in the contract

documents, are tested to 200% of service load or to failure. A number of working piles, as indicated

in tender documents, are tested to 150% of service load. All piles are tested with integrity testing.

Locate at least one test pile approximately at a recommended maximum of every 60 m of bridge

length with a minimum of two test piles per bridge structure. These requirements apply for each size

and pile type in the bridge except at end bents. For bascule piers and high-level crossings that

require large footings or cofferdam-type foundations, specify at least one test pile at each pier.

Consider maintenance of traffic requirements, required sequence of construction, geological

conditions, and pile spacing when determining the location of test piles. For phased construction,

locate test piles in the first phase of construction. The geotechnical engineer must verify the

suitability of the test pile locations.

The structural engineer must coordinate the test pile lengths and locations with the geotechnical

engineer and geotechnical consultant, before finalization of the plans.

Determination of pile capacity based on soil parameters from trial pile load testing shall not be

considered.

7.3.5.4 Load Tests

Reference: BDS Articles 10.7.3.8 and 10.8.3.5.6

See the Abu Dhabi Standard Specifications: Volume 2: Road Structures (Document Reference

Number TR-542-2), for load testing of drilled shafts and driven piles.

7.4 Modelling for Lateral Loading

When modelling deep foundations for lateral loading, ignore the first one meter of soil below

undisturbed grade. Use a structural model with site-specific p-y curves to represent the soil and

determine the lateral resistance of shafts or piles. Model the soil surrounding the shaft as a set of

equivalent non-linear soil “springs,” as represented in Figure 7.4. A discussion on modelling of the

soil strata as equivalent non-linear soil springs is given in Priestley, et al, “Seismic Design and

Retrofit of Bridges,” Wiley-Interscience, 1996.

The soil resistance “p” is a non-linear function of the corresponding horizontal shaft or pile deflection

“y.” The solution’s accuracy is a function of the spacing between nodes used to attach the soil

springs to the shaft or pile (the closer the spacing, the better the accuracy), and the shaft or pile

itself. Simple girder column elements are usually adequate for modelling behaviour.


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The node placement for springs models the soil layers. Generally, the upper ⅓ of the shaft or pile in

stiff soils has the most significant contribution to the lateral soil reaction. Space springs in this region

at no more than 1 m apart. Springs for the lower ⅔ of the shaft or pile may transition to a much larger

spacing. Stiff foundations in weak soils will transfer loads much deeper in the soil, and the use of

more springs is necessary.

Figure 7.4: Method of Modelling Deep Foundation Stiffness

Use computer software (e.g. DFSAP, LPILE Plus, COM624) or similar to model soil-structure

interaction. Section 7.1.4 discusses the interaction between the bridge designer and the

geotechnical engineer.

7.4.1 Horizontal Movement

Horizontal displacement at top of pile shall be assessed in accordance with BDS clause 10.5.2.2. However, for service load combination, a value of 25mm at top of pile is acceptable. For abutments with single row of piles, a maximum value up to 38mm at ground level is acceptable.

7.5 Mass Concrete

Consider mass concrete requirements in selecting member sizes and avoid mass concrete if

practical; however, when its use is unavoidable, indicate which portions are mass concrete. See the

Abu Dhabi Standard Specifications: Volume 2: Road Structures (Document Reference Number TR-

542-1) for thermal control of mass concrete.


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08-ABUTMENTS, PIERS AND WALLS SECOND EDITION – AUGUST 2021

8 ABUTMENTS, PIERS, AND WALLS

Section 11 of the BDS discusses design and detailing requirements for abutments, piers, and walls.

This Chapter presents supplementary information on the design of these structural elements.

8.1 Abutments/Wingwalls

8.1.1 General

An abutment includes an end diaphragm, a stem wall, and wingwalls. A stem wall or diaphragm

functions as a wall providing lateral support for fill material on which the roadway rests immediately

adjacent to the bridge.

Abutments can be generally classified as rigid or flexible. This refers to the abutment’s fixity to the

foundation. Do not confuse this classification with the fixity of the beams or girders to the

substructure.

Rigid abutments incorporate expansion joints at the end of the bridge between the deck and the

backwall to accommodate thermal and other movements.

Flexible abutments (integral abutments) eliminate expansion joints at the end of the superstructure

by integrating the bridge deck and encased beam ends with the “backwall” to form an end wall.

Flexible abutments must accommodate the movements through elastic behaviour of the bridge and

the surrounding soil because the deck and beams are integral with the end bent.

An abutment may be one of the following three types:

1. Seat Abutment. Rigid abutment with a joint between the bridge deck and the backwall.

2. Integral Abutment. Flexible abutment without an expansion joint between the abutment and

the bridge deck (in cross section, the end wall and cap may appear as a monolithic rectangle

with no apparent division between them).

3. Semi-Integral Abutment. Flexible abutment with the bridge deck cast monolithically with the

end wall but with a bearing under the beam and a bond-breaker between the end wall and

cap to facilitate construction and subsequent maintenance.

Abutments may consist of a cast-in-situ, reinforced concrete cap founded on drilled shafts, piles, or

spread footings. The seat abutment supported on drilled shafts is the most common abutment

configuration in the Abu Dhabi Emirate. When practical, consider a jointless bridge in design.

Abutments on shafts or piles may use MSE walls to retain the approach fill.

Jointless bridges in service have demonstrated the ability to perform well within certain parameters.

Therefore, in the absence of in-depth analyses, design a jointless bridge under the following

parameters. Exceeding one or more of these parameters requires a more detailed analysis:

• 15 mm of total movement at each abutment,

• 30 degree skew or less, and

• abutment types that are supported on a single row of shafts or piles.


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Where required, a detailed analysis must consider the zone of soil/structure interaction behind the

abutments, specifically the lateral soil pressure build-up and settlements that occur in this zone as a

result of thermal cycling. Conduct the design based upon the detailed analysis in published design

criteria from a recognized source applicable to the type of jointless bridge under consideration. One

suitable design guide is Section 15, Integral Abutment Bridges, of the NJDOT Design Manual for

Bridges and Structures (27).

8.1.2 General Abutment/Wing wall Design and Detailing Criteria

Use the following:

1. Expansion Joints. Consider vertical expansion joints for wall lengths exceeding 40 m. Water

proofing of expansion joints varies depending on whether the structure is submerged

(underpasses) or not (flyovers). See the Abu Dhabi Standard Specifications: Volume 2: Road

Structures (Document Reference Number TR-542-2).

2. Abutment Top Surfaces. Abutment seats at bearing locations are level. For seat abutments,

slope the remaining exposed top surfaces transversely to provide adequate drainage.

3. Approach Slab Support. Assume that the end of the approach slab at the bridge is supported

on the abutment and that the other end of the approach slab away from the bridge is

supported over half of its length by springs, which represent the soil under the approach slab.

4. Live-Load Surcharge (LS). Apply the live-load surcharge (LS) to the abutment assuming no

mitigating effect from the approach slab.

5. Dead Load. Include one-half of the dead load of the approach slab as an abutment dead

load.

6. Skewed Bridges. For skew angles greater than 30°, detail a 75-mm minimum chamfer at

acute corners.

7. Soil Reinforcements. Do not use soil reinforcements (such as steel strips and bar mats

commonly used in MSE wall construction) as attachments to abutment diaphragms or stem

walls to resist lateral loads applied to these components.

8. Reinforcement. Chapter 4 discusses practices for the reinforcement of structural concrete

(e.g. concrete cover, bar spacing). The design of abutments and wingwalls must meet all

applicable requirements in Chapter 4.

8.1.3 Seat Abutments

Use the following:

1. Seat Width. Typically, seismic design requirements govern the seat width.

2. Stem Width. The minimum stem width is 600 mm. Increase as required by design.

3. Minimum Size and Spacing of Bars. Determine the size and spacing of bars with a minimum

of T16 bars @ 200 mm unless noted otherwise.


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8.1.4 Integral Abutments


Design integral abutment details to meet the following requirements:

1. Joints. The use of integral abutments allows joints to be placed away from the superstructure.

Thus, the potential leaking of joints does not result in deterioration of the bridge.

2. Foundation Components. Use a single row of drilled shafts or driven piles to support integral

abutments.

3. Shaft or Pile Embedment. To provide fixity, embed the shafts or piles a minimum of 100 mm

into the capping beam or pile cap.

4. Top and Bottom Deck Reinforcing. Extend the top and bottom slab reinforcing bars through

the abutment diaphragm.

5. Settlement of Fill. Investigate settlement of the fill in and around integral abutments.

See the Standard Drawings Manual for integral abutment details (TR 541)

Typically, integral abutments around the world have been supported on driven piles. Several

successful designs have used drilled shafts instead of piles. Shafts would have a lateral stiffness

comparable to typical driven piles.

8.1.5 Semi-Integral Abutments

For this type of abutment, cast the integral end diaphragm around the girder ends, attached to the

slab but separated from the cap. Attach wingwalls to the cap with only the diaphragm remaining free

to move. The usage of semi-integral abutments is limited for the Abu Dhabi Emirate.

Allow diaphragm movement and rotation through the detailing of the bearing or connection of the

girder and the cap as either:

• a pinned connection through a fixed (in terms of translation) bearing, or

• a floating abutment with an expansion bearing with the end of the bridge free to translate.

Usually in a single-span bridge, one end (typically, the downhill end) is fixed and the other end is

free to translate. In a multi-span bridge, both abutments are usually free with fixity provided at the

pier(s).

The following applies to the design of semi-integral abutments:

1. Pinned End. Assume a pinned (in terms of rotation) end for the structural design of the

superstructure.

2. Diaphragm Width. Typically, the end diaphragm width is the same as the pile cap beam but

will be a minimum of 750 mm.

3. Batter. Design walls to be a constant thickness; do not use battered walls except for high

cantilever abutments.

See the AD QCC Standard Drawings Manual for semi-integral abutment details (TR-541).


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Semi-integral abutments allow for better detailing of abutments. At least two rows of piles are

required to support the abutment seat. It shares all of the benefits of an integral abutment and does

not have the problem of ensuring a flexible abutment support. The stiffer abutment seat may now be

used if necessary to fix the bridge superstructure. Supporting the deck on bearings also allows for

future jacking if required to overcome settlement, which is not possible for integral abutments.

8.1.6 MSE Wall Abutments

Two basic types of abutments with MSE walls exist:

1. “True” Abutment. An abutment supported by an MSE wall, in which the wall rests on a spread

footing atop the reinforced earth. Design the load from the spread footing as an earth

surcharge load (ES).

2. “False” Abutment. A shaft-supported abutment, in which the MSE wall wraps around an

otherwise open abutment. Isolate the shafts from the MSE backfill through sleeves to

eliminate down drag, and found the shafts in the soils below the MSE wall.

The typical MSE wall abutment in the Abu Dhabi Emirates is the “false” abutment type.

Piles placed within the mechanically stabilized earth backfill require special consideration. Place the

piles before the construction of the wall. To reduce the friction on the piles and to mitigate the down

drag forces, place a prefabricated jacketed pile sleeve on the plies, or place a slightly larger

corrugated pipe over the pile prior to backfilling. The piles must resist any horizontal each pressures

present.

As the wall is constructed, the subsoils beneath the wall and the MSE wall itself may compress. The

piles, however, are rigid. The compression of the soils induces a load into the piles due to friction.

Depending on site materials, the down drag forces can be substantial.

Modify the soil reinforcement when piles are located within the wall. The soil reinforcement cannot

be bent around the piles; they must remain linear to develop their strength. Also, do not attach the

soil reinforcement to the piles. Consider a skew of up to 15 from a line perpendicular to the wall

face, provided that the design accounts for this.

Bar mats can be cut and skewed, but they must conform to the following:

• Do not allow single longitudinal wires.

• Bar mats develop their strength from the cross wires. Use at least two longitudinal wires to

make the cross wire effective.

• Cut segments must meet minimum pull-out capacity factors of safety. Testing of cut

segments is required to show that their full strength is developed.

Ensure that all cutting of reinforcement occurs prior to the application of corrosion protection.

Section 8.3 discusses the use and design of MSE walls in more detail. The owner must approve the

use of MSE walls.

8.1.7 Wingwalls



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Wingwalls must have sufficient length to retain the roadway embankment and to furnish protection

against erosion. With respect to abutments, the following applies to wingwalls:

1. Orientation. Orient wingwalls perpendicular to the direction of traffic on the bridge.

2. Thickness. The minimum thickness of any wingwall is 300 mm.

3. Wingwall/Abutment Connection. The junction of the abutment and wingwall is a critical design

element, requiring special considerations. Use a 600-mm triangular fillet at the junction of the

back of the abutment and wingwall. Use fillet reinforcement with a minimum of T20 reinforcing

bars at 300-mm spacing properly anchored into the wingwall and abutment.

4. Design Forces. The design forces for wingwalls are earth-pressure forces only. Also consider

seismic forces from the soil behind the wingwall in their design.

8.1.8 Abutment Construction Joints

To accommodate normal construction practices, detail the following horizontal construction joints in

the contract documents:

1. Seat Abutments. Detail a horizontal construction joint between the top of the abutment seat

and the bottom of the backwall. Some expansion joint types may require another construction

joint at the approach slab seat.

2. Integral Abutments. Detail a horizontal construction joint at the top of the end diaphragm at

the joint with the soffit.

3. Wingwalls. Detail a permissible horizontal construction joint at an elevation that is the same

as the top of the abutment seat.

Planned vertical construction joints are normally associated with staged construction. Make

provisions for splicing or mechanical reinforcing couplers on horizontal reinforcing steel. Place the

vertical reinforcing steel at least 75 mm from the construction joint.

8.2 Piers


8.2.1 Pier Caps

8.2.1.1 Usage

In general, use pier caps supported by a single column, multiple columns, or a solid pier wall.

Integral pier caps are preferred for aesthetics.

For outrigger caps, consider the torsional effects resulting from longitudinal seismic displacements.

Use a pin connection at the interface between the column top and bottom of the outrigger cap to

minimize torsion in the cap.

An outrigger cap is an integral cap that extends beyond the edge of the bridge superstructure. They

are used where columns cannot be placed within the width of the bridge superstructure.


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8.2.1.2 Cap Width

Extend the width of pier caps beyond the sides of columns. The added width of the cap is a minimum

of 100 mm on each side of the column for a total of 200 mm by which the cap is larger than the

column. This width reduces the reinforcement interference between the column and cap. The cap

also has short cantilevered ends, when practical, to balance positive and negative moments in the

cap. Design the caps to meet the deflection requirements of BDS Article 2.5.2.6.2.

Seismic requirements for girder-seat widths may control cap width.

8.2.1.3 Superstructure Diaphragms

The dimension of diaphragm shall satisfy the requirements of BDS clause 5.12.3.5 & 5.12.4 and

relevant section of this manual.

The width of diaphragm should be evaluated taking into consideration of several factors that widely

vary from project to project e.g. the bridge span length, bearing arrangement, spacing and no. of

web or girders, congestion of reinforcement etc. and the design shall be supported with structural

calculations.

For preliminary assessment, the total width of box girder diaphragm at abutment shall not be less

than 1.5m or 5% of the span length, whichever is greater. For voided deck slab it shall be a minimum

5% of the span length. At pier location, the total width of diaphragm for box girder (at continuous

span) should be 2.0m for preliminary assessment. However, for voided deck slabs, total width of

diaphragm can be estimated as 10% of the span length.

.

8.2.1.4 Drop Caps

Step down the tops of drop caps as shown in Figure 8.1 to account for elevation differences between

girders:

Figure 8.1: Tops of Drop Caps

The drop cap steps are vertical, and the bearing surfaces are level. For planar (super-elevated) cross

sections, slope the bottom of the cap at the same rate as the cross slope of the top of the bridge

deck. For crowned sections, the bottom of the cap is level.

8.2.2 Column Cross Sections

Where a pier wall is used, the wall is solid for its entire height. The minimum thickness is 600 mm

and may be widened at the top to accommodate the bridge seat where required.

Caps are at least 200 mm wider than the column’s greatest dimension.


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Where columns are supported on isolated drilled shafts, enlarge the shaft diameter relative to the

column to force plastic hinging in the column and protect the drilled shaft from inelastic action. The

drilled shaft diameter is typically 500 mm larger than the column diameter. Confirm that the diameters

selected for the column and shaft accommodate the overlapping reinforcing steel cages and cover

requirements in both the column and drilled shaft.

8.2.3 Column Reinforcement

8.2.3.1 General

Chapter 4 discusses practices for the reinforcement of structural concrete. This includes:

• concrete cover,

• bar spacing,

• lateral confinement reinforcement,

• development of reinforcement, and

• splices.

Design all concrete pier columns to meet all applicable requirements in Chapter 4.

8.2.3.2 Transverse Reinforcement


General

Use spirals or butt-welded spliced hoops as transverse reinforcing steel in octagonal or round

columns. Use ties in rectangular columns or for shapes where spirals or hoops cannot be used.

Reinforce columns with oblong cross sections and interlocking hoops with a centre-to-centre spacing

not to exceed ¾ times the diameter of the cage. Interlock the overlaps by a minimum of four bars.

Spiral Splices

Almost all spiral reinforcement requires a splice. BDS Article 5.10.11 provides requirements for

splices in spiral reinforcement. The contract documents must indicate plastic hinge regions where a

spiral splice is not allowed.

A lapped splice, where permitted, consists of an overlap distance of 60 bar diameters or 1½ column

diameters whichever is more. Terminate the ends of both spirals in a 135° hook, wrapped around a

longitudinal bar, and with a tail length of at least 150 mm. Provide a detail or description of the lapped

splice in the contract documents.

Where the spiral reinforcement extends into a footing or cap, the spiral reinforcement can be

discontinuous. This allows easier placement of the top mat of footing or bottom mat of cap

reinforcement. Provide a detail or note in the plans that shows an allowed discontinuity in the spiral

with a splice.

8.2.3.3 Longitudinal Reinforcement


For longitudinal column reinforcing bars, use T25 or larger, with T32 bars being the preferred

maximum. Detail the longitudinal reinforcing steel continuous with a maximum spacing of 200 mm


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centre-to-centre. Fully develop the longitudinal column reinforcing bars where the bars enter into the

pier cap and the drilled shaft, spread footing, or pile cap.

The preferred detail for longitudinal reinforcement is continuous, unspliced reinforcement. In such

cases, include a note on the plans stating that splices are not allowed in the longitudinal

reinforcement.

If column heights require splices, use the provisions in BDS Article 5.10.11. Use mechanical couplers

or lap splices for splicing the longitudinal reinforcing steel. Do not locate splices within the plastic-

hinge regions of the column. Use a minimum stagger of 600 mm between adjacent splices and show

the locations in the plans. Stagger splices in bundled bars at a minimum of 600 mm.

Proposals by contractors to change the location or type of splice from those in the contract

documents are not allowed unless approved by the bridge designer. The resolution of conflicts or

errors requires special consideration.

8.2.3.4 Compression Member Connection to Caps

Terminate longitudinal bars at a point below the top cap reinforcement or prestressing ducts. If a

hook is required, extend the hook toward the compression member core. Maintain minimum

clearances for the placement of cap concrete through tremies.

8.2.4 Column Construction Joints

Use construction joints at the top and bottom of the column. Where columns exceed 8 m in height,

show construction joints such that concrete pours do not exceed 8 m in height. Where applicable,

locate all construction joints at least 300 mm above the water elevation expected during construction.

8.2.5 Multi-Column Piers

Support the columns by drilled shafts, individual caps/footings, or a combined cap/footing. The

following applies to the design and detailing of multi-column piers:

1. Column Spacing. In general, column spacing does not exceed approximately 8 m centre to

centre of columns.

2. Compressive Reinforcing Steel in Cap or Footing. If the initial design indicates the need for

compressive steel, redesign the pier to eliminate the need.

Compressive reinforcing steel tends to buckle when the cover is gone or when the concrete

around the steel is weakened by compression.

8.2.6 Single-Column Piers

The following applies to the design of single-column piers:

1. Cantilevers. The design of the cantilever is affected by the cantilever depth-versus-length

geometry. Where the distance between the centreline of the bearing and the column is less

than approximately twice the depth of the cantilever, consider using the strut-and-tie model

in BDS Article 5.6.3 for the design of the cantilever.


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2. Cantilever Reinforcement. Extend all calculated cantilever reinforcement throughout the

entire length of the cap. Place cap stirrups in the cap within the limits of the shaft at a spacing

not exceeding 200 mm.

8.2.7 Pier Walls

Pier walls are solid full height. The dimensions of the wall in the transverse direction may be reduced

by providing cantilevers to form a hammerhead pier.

8.2.8 Dynamic Load Allowance (DLA)


Consider the Dynamic Load Allowance or Impact Modifier (IM) in the structural design of pier caps

and pier columns.

8.2.9 Moment-Magnification


For exceptionally tall or slender columns/shafts where the slenderness ratio (Kl/r) is greater than

100, use a refined analysis, as outlined in BDS Article 5.7.4.1. Where P-Delta design procedures

are used, consider the initial out-of-straightness of columns and the sustained dead load in the

design.

Ignore moment magnification in seismic design.

Piers, pier columns, and piles are referred to as compressive members, although their design is

normally controlled by flexure. In most cases, the use of the moment-magnification approach in BDS

Article 5.7.4.3 is necessary.

8.2.10 Pier, Column, and Footing Design

For tall piers or columns, detail construction joints to limit concrete lifts to 7.5 m. A maximum lift of 9

m may be allowed to avoid successive small lifts (less than approximately 5 m), which could result

in vertical bar splice conflicts or unnecessary splice length penalties.

Detail splices for vertical reinforcing at every horizontal construction joint, except that the splice

requirement may be disregarded for any lift of 3 m or less.

Avoid construction joints in tidal zones.

Coordinate the lift heights and construction joint locations with the concrete placement requirements

of the specifications.

On structures over water, vertical post-tensioning strand (except in cylinder piles) cannot extend

below an elevation that is 3.6 m above Mean High Water Level (MHW) or Normal High Water Level

(NHW), regardless of the Environmental Classification. Post-tensioning bars are excluded from this

restriction.

Precast pier sections with spliced sleeve connections for mild reinforcing are acceptable.


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The minimum wall thickness for segmental piers is 250 mm if external post-tensioning is used and

300 mm if internal post-tensioning is used.

Locate post-tensioning applied to piers within a voided or hollow cross section and not external to

the pier. Where tendons extend from the underside of pier caps into hollow sections, provide a

13 mm 13 mm drip recess around the tendon duct. See Table 8.1 and Table 8.2.

Table 8.1: Required Tendons for Post-Tensioned Substructure Elements

Post-Tensioned Bridge Element Minimum Number of Tendons

Hammerhead pier cap

6

Straddle beam cap

Framed straddle pier column

C-pier column

C-pier cap

All other pier types and components not

listed

C-pier footing 8

Hollow cast pier column

Table 8.2: Minimum Centre-to-Centre Duct Spacing

Substructure Element Duct Spacing

Hammerhead pier cap Vertical Spacing. 100 mm, outer duct

diameter plus 1.5 times maximum aggregate

size or outer duct diameter plus 50 mm,

whichever is greater.

Horizontal Spacing. Outer duct diameter

plus 75 mm.

Straddle beam cap

C-pier cap

Pile/drilled shaft cap

Solid vertical column Outer duct diameter plus 75 mm.

Hollow cast pier column

Size footings such that the effective depth of concrete is sufficient to resist shear without the

requirement for shear reinforcement per BDS Article 5.13.3.6.

For bridges designed for vessel collision, design pier columns to be solid concrete from 5 m above

MHW or NHW to 600 mm below Mean Low Water Level (MLW) or Normal Low Water Level (NLW).

Voided sections that are filled after the column is constructed may be used.


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The above requirement is sufficient for barge collision. Evaluate ship collision on a case-by-case

basis.

For all land projects, voided substructure piers and columns located within the clear zone (regardless

of the presence of guardrail or barriers) must be filled with concrete to 5 m above the finished grade.

For voided piers, the fill section may be accommodated with a secondary pour. Mass concrete fill

sections are cast against two layers of roofing paper.

For water crossings:

1. Locate the bottom of all pile caps a minimum of 300 mm below Minimum Low-Water Level

(MLL).

2. Locate the top of pile caps a minimum of 300 mm above Astronomic High Tide (AHT).

3. For submerged piers, provide fenders for protection.

A minimum height of 100 mm is required for all bearing pedestals (plinths) not poured monolithically.

The recommended maximum pedestal height is 375 mm. If taller pedestals are required, use

transversely sloping caps to minimize pedestal heights.

For precast struts set into, cast into or placed against cast-in-situ concrete within the splash zone,

maintain concrete cover over the entire interfacing surfaces of both the precast strut and the cast-

in-situ concrete. Connect precast struts to cast-in-situ concrete using only stainless steel or non-

metallic reinforcement.

Cast-in-situ concrete pulls away from a precast strut at the interface allowing water and/or chlorides

to enter and initiate corrosion.

Connect stay-in-place precast “bathtub” forms to cast-in-situ footings using stainless steel or non-

metallic reinforcement, or provide a mechanical connection across the interface between the form

and the footing (e.g. shear keys).

8.3 Walls (Earth Retaining Systems)

Reference: BDS Section 11

8.3.1 General

Use earth retaining systems to provide lateral support for a variety of applications:

• cuts in slopes for roadway alignments;

• roadway widening where right-of-way is limited;

• grade separations;

• proximate live-load surcharge from buildings, highways, etc., that must remain in place;

• stabilization of slopes where instabilities have occurred;

• protection of environmentally sensitive areas; and

• excavation support.

Earth retaining systems are classified according to the construction method and the mechanism

used to develop lateral support:

1. Construction Method. This may be either a “fill-wall” construction or “cut-wall” construction.

Fill-wall construction is where the wall is constructed from the base of the wall to the top (i.e.


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“bottom-up” construction) such as an MSE wall. Cut-wall construction is where the wall is

constructed from the top of the wall to the base (i.e. “top-down” construction) such as a

soldier-pile wall.

2. Lateral Load Support. The basic mechanism of lateral load support may be either “externally

stabilized” or “internally stabilized.” Externally stabilized wall systems use an external

structural wall, against which stabilizing forces are mobilized. Internally stabilized wall

systems employ reinforcement that extends within and beyond the potential failure mass.

Rankin earth pressure may be used in lieu of Coulomb earth pressure. If Rankin earth pressure is

used, the resultant lateral earth load is considered located at the centroid of the earth pressure

diagram.

During the design process, review wall locations for conflicts with existing or proposed utilities and

drain pipes located beneath or adjacent to the proposed wall and/or reinforced soil zone. Analyse

for constructability, settlement effects, wall stability, maintenance repair access, potential for

relocation of the utility or drain pipe, etc. Coordinate wall and utility locations and designs with the

utilities engineer.

Do not place utilities or longitudinal drainage conveyances in the soil-reinforced zone behind

Mechanically Stabilized Earth (MSE) or tie-back walls.

It is undesirable and, in some cases, impossible to incorporate drain pipes and utilities within the

layered structural elements in the reinforced soil zone of an MSE wall, considering special design

and construction difficulties resulting from obstructions. Drain pipes and utilities placed below the

wall or in the reinforced soil zone cannot be maintained, because excavation in this zone can

undermine stability of the wall. In addition, leaking pipes can generate soil wash out and compromise

the structural integrity of the wall. Special design constraints may be imposed when a pressurized

utility carrier is placed within, through, under, or immediately adjacent to an MSE wall. This assures

that the design of structural elements considers support limitations that may be created by the

presence of utilities and potential damage or failure if a pressurized utility carrier leaks.

8.3.2 Responsibilities

The type selection for an earth retaining system is a collaborative effort between the bridge designer

and geotechnical engineer. The following identifies the basic responsibilities of each for the design

of earth retaining systems, except MSE walls.

8.3.2.1 Geotechnical Engineer

For permanent earth retaining systems, the geotechnical engineer:

• performs the geotechnical investigations;

• provides the wall type;

• provides the allowable soil bearing and lateral earth design coefficients for gravity, surcharge,

and seismic loading;

• performs the global and external stability checks;


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• determines if there is a need for special drainage features due to the selected wall type and/or

site conditions; and

• determines the size and spacing of soil nails and tie-back anchors.

The geotechnical engineer also provides the following information to the bridge designer:

• earth pressure coefficients (ka, ko, kp) and an estimate of the amount of deformation to

develop the active and passive earth pressures and the factors of safety;

• unit weight of the backfill material;

• allowable interface friction between cast-in-situ concrete footing and soil;

• allowable bearing capacity;

• expected settlement;

• requirements for drainage control;

• testing requirements for anchored and soil nail walls; and

• special construction requirements for all walls.

8.3.2.2 Bridge Designer

The bridge designer performs the following for the design of earth retaining systems:

1. Design. For cast-in-situ concrete cantilever walls, non-gravity cantilever (sheet pile) walls,

and anchored walls, perform the internal stability design for the wall (e.g. wall dimensions

and reinforcing configurations). Perform the overturning, sliding, and bearing checks using

the geotechnical parameters provided by the geotechnical engineer. For soil nail and tie-

back anchor walls, design the reinforcing for the structural facing of the wall.

2. Detailing. Provide all construction details for the earth retaining system, including:

• Plan views to indicate the layout of the walls. Provide the station and offset to the wall

layout line (usually the front face) at all locations needed for locating the wall.

• Elevation views to show the length and design height of wall segments, and top and

bottom elevations of the wall. Provide top-of-wall elevations at intervals necessary to

build the walls. Provide elevations every 5 m when the top of wall is not on a straight

line. Footings are almost always level with the bottom and top of footing elevation

shown for each step.

• Typical sections to show all additional information on the wall. This includes the

dimensions of the footing and wall, approximate original ground line, finished ground

line at the bottom and top of wall, bench at bottom of wall, slopes at the bottom and

top of wall, drainage requirements, and reinforcing steel.

The Cited References provides additional references (28) (29) (30) (31) (32) (33) for the design of

earth retaining systems.


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For determining the preliminary sizes, the stability of walls and footings shall be checked for a

minimum factor of safety of 1.5 against sliding and 2.0 against overturning for service limit state.

However, design approach recommended in LRFD bridge design specifications for stability checks

in strength limit state shall be adopted in the final design.”

8.3.3 Types of Earth Retaining Systems

8.3.3.1 Fill Walls

MSE Walls

MSE walls are constructed using reinforced layers of earth fill with extensible (polymeric or

geosynthetic) reinforcing. The facing for the walls can be concrete panels, geotextile fabrics, or

exposed welded wire. The heights of the walls can extend to over 30 m.

Advantages of MSE walls include:

• They tolerate larger settlements than a cast-in-situ concrete cantilever wall.

• They are relatively fast to build.

• They are relatively low in cost.

Cast-in-Situ Concrete Cantilever Walls

Cast-in-situ concrete cantilever walls are best-suited for sites with good bearing material and small

long-term settlement. In soft soils or when settlement may be a problem, the semi-gravity walls can

be pile supported. This adds to the cost, especially relative to a MSE wall. However, for short wall

lengths, the cast-in-situ concrete cantilever wall may be the most cost-effective selection.

Cast-in-situ concrete cantilever walls do not require special construction equipment, wall

components, or specialty contractors. They can be up to 10 m in height, although most are less than

6 m in height. The footing width for the walls is normally ½ to ⅔ the wall height.

Cast-in-situ concrete cantilever walls can be used in cut slope locations. In this case, the slope

behind the face of the wall requires excavation to provide clearance for the construction of the wall

footing. Do not use excavation slopes steeper than 1V:1.5H, which can result in significant

excavations in sloped areas.

8.3.3.2 Cut Walls

Soldier Pile Walls

For soldier pile walls, install H-piles every 2.5 m to 3 m and span the space between the H-piles with

lagging. Install the H-piles by grouting the H-pile into a drilled hole; however, they can also be

installed by driving.

The advantage of installing the H-pile by drilling is to avoid vibrations and the potential for driving

refusal.

The depth of the soldier pile is similar to the sheet pile wall; i.e. approximately two times the exposed

height. Use either timber or concrete panels for lagging.


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For most soldier pile walls, a concrete facing is cast in front of the soldier piles and lagging after the

wall is at full height. Various architectural finishes can be used for the facing.

Anchored Walls

Ground-anchored wall systems (often called tie-back walls) typically consist of tensioned ground

anchors connected to a concrete wall facing. Ground anchors consist of a high-strength steel bar or

prestressing strand or FRP or GFRP shall be used. These are grouted into an inclined borehole and

then tensioned to provide a reaction force at the wall face. As a guidance, locate the anchors at 2.5-

m to 3-m horizontal and vertical spacing, depending on the required anchor capacity. Each anchor

is proof tested to confirm its capacity. The upper row of anchors can extend a distance equal to the

wall height plus up to 12 m behind the face of the wall.

Detailed design shall be carried out as per relevant international standards such as BS 8081:2015”.

For Proof Testing, relevant codes such as BS EN 1997-1:2004+A1:2013 shall be referred. Testing

at each anchor may not be required.

Specialized equipment is required to install and test the anchors, resulting in a higher cost relative

to conventional walls. An important consideration for this wall type can be the subsurface easement

requirements for the anchoring system.

Soil Nail Walls

A soil nail wall uses top-down construction. The typical construction methodology includes:

• a vertical cut of approximately 1.2 m;

• drill, insert, and grout soil nails;

• shotcrete exposed cut surface;

• repeat operation until total height of wall is complete; and

• for permanent applications, a reinforced concrete wall is cast over the entire surface.

A soil nail wall involves grouting large diameter rebar (e.g. T32 or larger) or strand into the soil at

1.2-m to 1.8-m spacing vertically and horizontally. For the length of the rebar or strand, use from 0.7

times the wall height to 1.0 times the wall height.

Specialty contractors are required when constructing this wall type. Soil nail walls can be difficult to

construct in certain soil and groundwater conditions. For example, where seeps occur within the wall

profile or in relatively clean sands and gravels, the soil may not stand at an exposed height for a

sufficient time to install nails and apply shotcrete.

Nongravity Cantilever (Sheet Pile) Walls

Sheet pile walls are normally driven or vibrated into the ground with a pile-driving hammer and are

most suitable at sites where driving conditions are amenable to pile driving. Therefore, part of the

design process requires performing a driveability analysis. Sites with shallow rock or consisting of

significant amounts of cobbles and boulders are not suitable for sheet pile driving.

Generally, the sheet pile must be driven to a depth of at least the exposed height to meet stability

requirements. Most sheet pile walls are 3 m to 4.5 m or less in height.


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Although higher walls are possible, the structural design and installation requirements increase

significantly. Taller sheet pile walls require ground anchors that are typically attached to a horizontal

whaler beam installed across the face of the sheet piles.

8.3.4 Mechanically-Stabilized Earth (MSE) Walls

8.3.4.1 Design

FHWA Publication No. FHWA-NHI-00-043, “Mechanically Stabilized Earth Walls and Reinforced Soil

Slopes Design & Construction Guidelines,” contains background information on the initial

development of MSE wall design and is referenced in BDS Article 11.10.1 as the design guidelines

for geometrically complex MSE walls.

MSE walls are proprietary systems. The suppliers of the system design and supply all of the

elements that compose the wall, such as the precast concrete facing panels, tension straps, precast

barriers with their counterbalancing slabs, and copings. The supplier is responsible for the total

design of the MSE retaining wall system, including its internal and external stability, considering the

existing site/ground conditions and any required improvement to the existing soils.

For concrete cover requirements, see Table 4.4.

Only non-metallic soil reinforcement and fixings shall be utilized.

Construction of MSE walls shall be according to Abu Dhabi Standard Specifications: Volume 2: Road

Structures (Document Reference Number TR-542-2).

Minimum Service Life

1. Design permanent walls for a service life of 75 years.

2. Design temporary walls for the length of construction contract or a service life of three years,

whichever is greater.

Concrete Levelling Course

1. All permanent walls have a non-structural concrete levelling course as a minimum.

2. The entire bottom of the wall panel has bearing on the concrete levelling course.

Bin Walls

1. When two walls intersect forming an internal angle of less than 70 degrees, design the nose

section as a bin wall. Submit calculations for this special design with the plans for review and

approval.

2. Design structural connections between wall facings within the nose section to create an at-

rest bin effect without eliminating flexibility of the wall facings to allow tolerance for differential

settlements.

3. For wall facings without continuous vertical open joints, such as square or rectangular panels,

design the nose section to settle differentially from the remainder of the structure with a slip

joint. Facing panel overlap, interlock, or rigid connection across vertical joints is not permitted.

For aesthetic and differential settlement concerns, erect the panels in a pattern where the


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horizontal panel joint line is discontinuous at every other panel. Use alternating standard

height and half height panel placement along the levelling pad.

4. Design soil reinforcements to restrain the nose section by connecting directly to each of the

facing elements in the nose section. Run soil reinforcement into the backfill of the main

reinforced soil volume to a plane at least 900 mm beyond the Coulomb (or Rankine) failure

surface. See Figure 8.2.

5. The design of facing connections, pullout, and strength of reinforcing elements and

obstructions must conform to the general requirements of the wall design.

Figure 8.2: Design Criteria for Acute Corners of MSE Bin Walls

Minimum Length of Soil Reinforcement

In lieu of the requirements for minimum soil reinforcement lengths in BDS Article C11.10.2.1, use

the following:

The minimum soil reinforcement length “L” is measured from the back of the facing element. The

length must be the maximum of the following:

• Walls in front of abutments on piling L 2.4 m and L 0.7H.

• Walls supporting abutments on spread footings L 7 m and L 0.6 (H+d) + 2 m, (d = fill

height about wall) and L 0.7H.


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where: H = height of wall, in meters, and measured from the top of the levelling pad to the top of

the wall coping

L = length in meters, required for external stability design

For a MSE wall with reinforcement lengths equal to 70% of the wall height, estimate the anticipated

factored bearing pressure (quniform) to be about 200% of the overburden weight of soil and surcharge.

It may be necessary to increase the reinforcement length for external stability to assure that the

factored bearing pressure does not exceed the factored bearing resistance (qr) of the foundation

soil.

Minimum Front Face Wall Embedment

1. Consider scour and bearing capacity when determining front face embedment depth.

2. Consult with the hydraulic and geotechnical engineers to determine the elevation of the top

of levelling pad.

3. In addition to the requirements for minimum front face embedment in BDS Article 11.10.2.2,

the minimum front face embedment for permanent walls must comply with both a minimum

of 600 mm to the top of the levelling pad and Figure 8.3. Also, consider normal construction

practices.

Figure 8.3: MSE Wall Minimum Front Face Embedment

Facing

1. The typical panel size must be square and not exceed 2.75 sq m in area, nominal.

2. The typical non-square (i.e. diamond-shaped, not rectangular) panel size must not exceed

3.5 sq m in area.

3. Special panels (top out, etc.) must not exceed 4.5 sq m in area.

4. Full height facing panels must not exceed 2.4 m in height.

5. Consider the use of larger panels on a case-by-case basis. The reinforcing steel concrete

cover must comply with the design standard for the wall type as determined using Figure 8.3.

External Stability

The reinforced backfill soil parameters for analysis are (if detailed information is not available):

1. Sand backfill:


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Moist unit weight: 1682 kg/m3

Friction angle: 30 degrees

2. Limerock backfill:

Moist unit weight: 1842 kg/m3

Friction angle: 34 degrees

3. Flowable fill backfill:

Moist unit weight: 721 to 2003 kg/m3

cf : Minimum 0.52 MPa

4. In addition to the horizontal back slope with traffic surcharge figure in BDS.

5.

6.

7.

8. Figure 8.4 illustrates a broken back slope condition with a traffic surcharge. If a traffic

surcharge is present and located within 0.5 H of the back of the reinforced soil volume, then

it must be included in the analysis.

9. Figure 8.5 illustrates a broken back slope condition without a traffic surcharge.

10. The geotechnical engineer is responsible for designing the reinforcement lengths for the

external conditions shown in Figure 8.6 and any other conditions that are appropriate for the

site.


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Apparent Coefficient of Friction

When the angle of internal friction is determined for saturated conditions, do not modify the pullout

friction factor (F*) and the resistance factor for pullout (Ø) for the design of soil reinforcement below

the design flood elevation.

Soil Reinforcement Strength

1. For geosynthetic reinforcement, supplement BDS Table 11.10.6.4.3b-1 with the following

default value:

Application Total Reduction

Factor, RF

Critical temporary wall applications with non-aggressive soils

and polymers meeting the requirements listed in BDS Table

11-10.6.4.2b-1.

7.0

2. Do not design soil reinforcement to be skewed more than 15 degrees from a position normal

to the wall panel unless necessary and clearly detailed for acute corners.

3. Sometimes, the 15-degree criteria cannot be met due to vertical obstructions such as piling,

drainage structures, or bridge obstructions with angles. In these cases, clearly detail the soil

reinforcement skew details in the Shop Drawings.

4. Do not design soil reinforcement to be skewed more than 15 degrees from a horizontal

position in elevation view to clear horizontal obstructions.

5. Do not attach soil reinforcement to piling, and do not attach abutment piles to any retaining

wall system.

Reinforcement/Facing Connection

Design the soil reinforcement to facing panel connection to assure full contact of the connection

elements. The connection must be visible during construction for inspection.

Normally, mesh and bar mats are connected to the facing panel by a pin passing through loops at

the end of the reinforcement and loops inserted into the panels. If these loops are not aligned, then

some reinforcement will not be in contact with the pins, causing the remaining reinforcement to be

unevenly stressed and/or overstressed. If the quality of the connection cannot be assured through

pullout testing and quality control during installation, then reduce the strength of the soil

reinforcement and its connections accordingly.


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Figure 8.4: Broken Backfill with Traffic Surcharge

Figure 8.5: Broken Backfill without Traffic Surcharge


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Figure 8.6: Proprietary Retaining Walls


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Reinforcement/Facing Connection

Design the soil reinforcement to facing panel connection to assure full contact of the connection

elements. The connection must be visible during construction for inspection.

Normally, mesh and bar mats are connected to the facing panel by a pin passing through loops at

the end of the reinforcement and loops inserted into the panels. If these loops are not aligned, then

some reinforcement will not be in contact with the pins, causing the remaining reinforcement to be

unevenly stressed and/or overstressed. If the quality of the connection cannot be assured through

pullout testing and quality control during installation, then reduce the strength of the soil

reinforcement and its connections accordingly.

Flowable Fill Backfill

1. Flowable fill backfill will prevent the MSE wall from adapting to differential settlements and

sand or limerock backfilled MSE walls; however, the use of flowable fill may speed wall

construction. Flowable fill backfill is permitted only with written approval.

2. Prior to requesting approval, verify external stability, the accommodation of anticipated

settlements, and the cost-effectiveness of flowable fill backfill.

3. Provide 300 mm flowable fill cover in all directions between metallic soil reinforcement and

adjacent sand or limerock backfill. Provide 900 mm of sand or limerock backfill between the

top of the flowable fill and the bottom of the roadway base.

4. Indicate the minimum and maximum flowable fill unit weights that satisfy all external stability

requirements with a range of at least 160 kg/m3.

5. Provide for drainage of water between the flowable fill and the MSE wall panels.

End Bents on Piling or Drilled Shafts Behind MSE Walls

1. Locate MSE walls adjacent to end bents to avoid any conflicts with the end bent foundation

elements.

2. The minimum clear distance is 600 mm for the following:

Between the front face of the end bent cap or footing and the back face of wall panel.

For battered piles, at the base of the wall between the face of piling and the levelling pad.

Note: The 600-mm dimension is based on the use of 450 mm piles. For larger piles and

drilled shafts, increase the clear distance between the wall and pile or drilled shaft such that

no soil reinforcement is skewed more than 15 degrees.

3. Attach soil reinforcement to resist the overturning produced by the earth load, friction, and

temperature to end bents, unless the total settlement of the soil above the bottom of the end

bent cap exceeds 100 mm. In this case, do not attach the reinforcement to the end bent, and

design a special wall behind the backwall to accommodate the earth load.

End Bents on Spread Footings Behind MSE Walls

Size the spread footing so that the factored bearing pressure does not exceed 282 kN/m2.


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1. The edge of the footing must be a minimum of 300 mm behind the back of the wall panel.

2. The minimum distance between the centreline of bearing on the end bent and the back of

the wall panel must be 1200 mm.

Back-to-Back MSE Walls

Design back-to-back MSE walls in accordance with Section 6.4 of FHWA-NHI-10-024 Design and

Construction of Mechanically Stabilized Earth Walls and Reinforced Slopes – Volume I.

GRS Walls and Abutments

FHWA Publication No. FHWA-HRT-11-026 “Geosynthetic Reinforced Soil Integrated Bridge System

Interim Implementation Guide” (GRS Guide) contains background information and design steps for

GRS walls and abutments. (Refer to this guide for figures referenced below.)

1. GRS abutments may be used to support single-span bridges that are not at risk of movement

due to sliding, uplift, etc.

2. Design the GRS abutment in accordance with the LRFD methodology contained in Appendix

C of the GRS Guide, except as otherwise described in this section.

3. Coordinate with the hydraulics engineer to determine the design scour depth at the abutment

with respect to the distance between abutments.

4. Utilize a reinforced soil foundation (RSF) in lieu of the concrete levelling course utilized for

MSE walls. (See Figure 30 and Section 7.4 of the GRS Guide.)

5. Detail the bottom layer of reinforcement for the GRS abutment to bear on top of the RSF at

the design scour elevation or 150 mm below the finished ground surface, whichever is

deeper.

6. Ensure that the minimum length of reinforcement, B (bottom layer of reinforcement) is not

less than 1800 mm.

7. Ensure that the thickness of the RSF is 450 mm or 0.25B, whichever is greater.

8. Extend the RSF a distance of at least 450 mm or 0.25B, whichever is greater, in front of the

wall facing.

9. Use a maximum vertical reinforcement spacing of 200 mm. (In the bearing reinforcement

zone, the reinforcement spacing is reduced by 50 percent.)

10. GRS walls are designed as GRS abutments, but without a “bearing reinforcement zone.”

8.3.4.2 External Stability and Internal Stability

The approved wall suppliers are responsible for the internal and external stability of the wall.

The external stability calculation includes a check for sliding, overturning, rotational failure, and

bearing pressure. Establish the wall geometry (including the width of reinforcement and height)

based on these items for each height of wall. Verify increases over that required for external stability

by the geotechnical engineer to ensure that the increase is justified.


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8.3.4.3 Loads from Other Structures

Design MSE walls that support structures, such as soundwalls, for the lateral and vertical loads

imposed on the MSE wall. Document the magnitude of the force and where the force is applied on

the MSE wall in the contract documents or provide a drawing.

8.3.4.4 Barrier Rails

MSE walls that incorporate a roadside barrier or bridge rail at the top of wall require special attention.

The top of MSE walls are not strong enough to resist traffic impacts. Ensure that traffic impacts are

transferred from the barrier into a reinforced concrete slab that is part of or located just below the

roadway pavement. The concrete slab is sufficiently massive to keep vehicle impact forces from

being transferred into the MSE wall. Size the concrete slab to resist sliding and overturning forces

due to vehicle impacts, wind, or seismic loading as appropriate.

8.3.4.5 Copings

Cast-in-situ all copings at the top of MSE walls. Project the top of the walls 300 mm to 600 mm above

the top layer of soil reinforcement. The coping must be sufficiently large to hold together the

unbraced section. Extend reinforcing steel from the top wall panels into the coping.

8.4 Geosynthetic Reinforced Soil (GRS) Walls and

Abutments

GRS abutments are a shallow foundation and retaining wall option that may significantly reduce the

construction time and cost of single span bridges.

GRS walls and abutments, like MSE walls, are very adaptable to both cut and fill conditions and can

tolerate a greater degree of differential settlement than cast-in-situ walls. GRS walls, however, are

not appropriate for all sites.

GRS walls and abutments are constructed with coarse aggregate or GAB backfill and geosynthetic

soil reinforcement. However, site space limitations may preclude the use of GRS walls and

abutments because of the inability to place the soil reinforcement.

When excessive scour or settlements are anticipated, countermeasures, deep foundations, and/or

other wall types may be required.


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09-EXPANSION JOINTS SECOND EDITION – AUGUST 2021

9 EXPANSION JOINTS

BDS Article 14.4 discusses bridge joint movements and loads, and BDS Article 14.5 provides

requirements for joints and considerations for specific joint types. This Chapter presents criteria for

the design and selection of expansion joints in bridges.

9.1 Design Requirements: Movement and Loads

Reference: BDS Articles 14.4 and 14.5

9.1.1 General

Expansion joints in bridges accommodate the expansion and contraction of bridges due to

temperature variations, creep, and shrinkage. The following general criteria apply:

1. Minimize Number. Minimize the number of expansion joints because of the inherent

operational and maintenance problems. Abutment seats tend to deteriorate due to leaky

joints, collect debris, and provide locations for animal and human habitation. The use of

continuous structures minimizes the number of joints. When conditions permit, eliminate the

expansion joints on the bridge, and tie the approach slab into the superstructure. However,

always provide joints at the roadway end of approach slabs.

2. Tributary Expansion Length. The location of the point of zero movement is a function of the

longitudinal stiffness of the substructure elements and fixed bearings.

The tributary expansion length equals the distance from the expansion joint to the point of

assumed zero movement, which is the point along the bridge that is assumed to remain

stationary when expansion or contraction of the bridge occurs.

3. Consistency. When possible, use the same type of joint and construction details throughout

the bridge.

4. Maintenance. The selection, design, and detailing of expansion joints are of critical

importance to minimize maintenance problems.

Many of the maintenance problems on bridges are the result of failed joints.

5. Temperature Range. Use Procedure A of BDS Article 3.12.2.1 to determine the appropriate

design thermal range. Use the minimum and maximum temperatures specified in Table 9.1

as TMinDesign and TMaxDesign, respectively, in BDS Equation 3.12.2.3-1 (Equation 9.1).

Table 9.1: BDS Procedure “A” Temperature Changes

Concrete Bridges Steel Bridges

0°C to 60°C 0°C to 70°C

6. Recess Detail. Recess embedded steel elements, such as approach slab protection angles

and strip seal expansion joint restrainers, 6 mm from the finished grade.

This recess accommodates milling of the concrete adjacent to the joints.


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7. Effects of Skew. Limit racking to 20% of the rated movement of the joint.

The thermal movements of skewed bridges are such that asymmetrical movements

(“racking”) can occur along the length of the expansion joints. The movement is not solely in

the longitudinal direction. The acute corners of a bridge with parallel skewed supports tend

to expand and contract more than the obtuse corners, causing the joint to rack.

8. Other Geometric Considerations.

Horizontally curved bridges and bridges with other special geometric elements (e.g. splayed

girders) do not necessarily expand and contract in the longitudinal direction of the girders.

The effect of thermal movements on the joints of complex bridges could be more pronounced

compared to bridges with simple geometrics.

9. Block-outs. Provide block-outs in decks at expansion joints to allow for joint placement.

The expansion joint assembly is installed and the block-out concrete placed after profile

grinding has been completed.

10. Cover Plates Over Expansion Joints. Use cover plates over expansion joints at sidewalks.

Where bicycles are anticipated in the roadway, consider using cover plates in the shoulder

area.

9.1.2 Estimation of General Design Thermal Movement, T


Estimate the design thermal movement, in millimetres, by the following equation:

Equation 9.1: (BDS Equation 3.12.2.3-1)

where: α = coefficient of thermal expansion, 1.08 x 10-5 for concrete bridges and 1.17 x

10-5 for steel girder bridges, mm/mm/C

L = tributary expansion length, mm

TMaxDesign = maximum design temperature from Table 9.1

TMinDesign = minimum design temperature from Table 9.1

9.1.3 Estimation of Design Movement

In addition to the thermal movement determined in Section 9.1.2, include the effects of creep (CR)

and shrinkage (SH) in the total movement for prestressed concrete bridges.

For steel girder structures, neglect creep and shrinkage effects in expansion-joint design because

they are minimal.

( )MinDesignMaxDesignT

TTLαΔ −=


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9.1.4 Setting Temperature

Determine gap widths at setting (ambient) temperatures of 20°C, 25°C, 30°C, 35°C, and 40°C,

consistent with the minimum and maximum temperatures at the bridge site. Use gap widths

considering minimum gap widths and, for cast-in-situ post-tensioned boxes, elastic shortening when

appropriate.

9.2 Expansion Joint Selection and Design

9.2.1 General

Table 9.2 presents the typical application for several types of expansion joints based upon joint

movement.

Select the type of expansion joint and its required movement rating based on the expansion and

racking demands, skew, and gap widths. Gap width does not directly apply to asphaltic plug joints.

Do not use a minimum gap less than 30 mm on any bridge. Use a maximum gap width of 75 mm for

strip seals and 75 mm for individual components of modular joints.

Gap width is the perpendicular distance between the faces of the joint at the road surface.

Table 9.2: Expansion Joint Selection

Joint Type Total Joint Movement

One-Directional Movement Only (mm)

Sheet and strip seals 45

Modular expansion joint > 150

Steel finger joints > 125

Reinforced elastomeric joints 150

Silicone joint sealant 15

Compression and cellular seals 40

Asphaltic plug 50

9.2.2 Sheet and Strip Seals


The strip seal expansion joint is the preferred deck expansion joint system for new bridges with

estimated total design thermal movements ranging from 25 mm to 125 mm.

Where practical and where additional protection for bearing assemblies and hinges is necessary,

provide a secondary sealing system below the expansion joint assembly.

A strip seal consists of a neoprene membrane (gland) rigidly attached to a steel restrainer on both

sides of the joint. The material is remoulded into a “V” shape that opens as the joint width increases

and closes as the joint width decreases. Strip seal joints are usually protected by a steel cover plate.


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Strip seal joints are watertight when properly installed. Under typical conditions, the life of a strip

seal tends to be longer than that of other joint seals. However, these seals are difficult to replace,

and avoid splices in the membrane.

9.2.3 Modular Expansion Joint


Modular joints are expensive and may require significant maintenance; therefore, limit their use to

where thermal movements are greater than 125 mm. When selecting a modular joint system, use

only those that are designed to facilitate the repair and replacement of components and that have

been verified by long-term in-service performance. The contract documents must include a detailed

description of the requirements for a modular joint system.

The following applies to the design of modular-type expansion joints:

1. Joint Support. The block-outs and supports needed for modular joint systems are large and

require special attention when detailing. For modular joints supported from the top of the

girder, present a detail of the supporting device in the contract documents.

2. Splices. Where practical, provide full-length modular joints with no field splices across the

roadway width. If a field splice is required for staged construction on a slab-on-girder bridge,

space the support girders at a maximum of 600 mm from the splice location, outside of the

wheel path. The splice must be constructed according to the manufacturer’s requirements.

3. Neoprene Seal. Ensure that the neoprene seal, which is a strip seal gland in a modular joint,

is one piece across the roadway width, regardless of construction staging considerations.

9.2.4 Steel Finger Joints

Design steel fingers joints to support traffic loads with sufficient stiffness to preclude excessive

vibration. In addition to longitudinal movement, finger joints must also accommodate any rotations

or differential vertical deflection across the joint.

Steel finger joints have been successfully used to accommodate medium and large movement

ranges. They are generally fabricated from steel plates and are installed in cantilevered

configurations. Unfortunately, finger joints do not provide an effective seal against water infiltration.

Elastomeric and metal troughs have been installed beneath steel finger joints to catch and redirect

runoff water. However, in the absence of routine maintenance, the troughs clog and become

ineffective.

9.2.5 Reinforced Elastomeric

These joints are prefabricated units which span the deck joint gap and are either an elastomer or

elastomer reinforced with metal plates. Different sizes are available to suit various movement

ranges.

9.2.6 Silicone Joint Sealant


Use this system where anticipated movements are small and where the strip seal joint is impractical.


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The movement capacity of this type of joint is dictated by the joint width at the time of installation,

which is a function of the installation width plus or minus some percent of original gap size. The

silicone joint sealant is relatively easy to maintain because local joint failures can be repaired. This

system can be bonded to concrete or steel surfaces.

9.2.7 Compression and Cellular Seals


Low-density, closed-cell foam products consist of pre-formed shapes compressed into the joint. The

sizes of the material and movement capacity follow the manufacturer’s requirements. Larger joints

may also require a cover plate for protection of the compression seal.

9.2.8 Asphaltic Plug Joint (Poured Seals)


Only use an asphaltic plug for retrofit applications for total movements of up to 50 mm.

This joint system consists of a metal flashing installed over the existing joint and covered with

concrete containing an asphaltic or other elastomeric binder. Its advantages include the elimination

of any mechanical anchorage system, ease of placement, low maintenance, and rideability. Its

disadvantages include the tendency to rut under heavy traffic and turning movements in hot weather.

9.2.9 Expansion Joints for Asphaltic Overlays

If a bridge deck will have an asphalt overlay, expansion joints that move less than 50 mm can be

retrofitted with plug joints. See Section 9.2.8.

These systems have the flexibility to accommodate joint movement and the strength to carry traffic.

Plug joints work well with asphalt overlays because they have similar flexibility.

For movement greater than 50 mm, place concrete headers within an asphalt overlay to facilitate

installation of the appropriate expansion joint from Table 9.2.

These concrete headers are often damaged by traffic impacting the edge, but are required for greater

movements.

9.3 Expansion Joints for Post-Tensioned Bridges

At expansion joints, provide a recess and continuous expansion joint device seat to receive the

assembly, anchor bolts, and frames of the expansion joint; i.e. a finger or modular type joint. In the

past, block-outs have been installed in the seats to provide access for stressing jacks to the upper

longitudinal tendon anchors and set as high as possible in the anchor block. Lower the upper tendon

anchors and re-arrange the anchor layout as necessary to provide access for the stressing jacks.

At all expansion joints, protect anchors from dripping water by means of skirts, baffles, v-grooves,

or drip flanges. Ensure that drip flanges are of adequate size and shape to maintain structural

integrity during form removal and erection.

See the Standard Drawings Manual for typical expansion joint details (TR-541)


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9.4 Expansion Joint Design

Do not design superstructures utilizing expansion joints within the span (i.e. ¼ point hinges).

Identify the setting of expansion joint recesses and expansion joint devices, including any

precompression, on the drawings. Size and set expansion joints at time of construction for the

following conditions:

1. Allowance for opening movements based on the total anticipated movement resulting from

the combined effects of creep, shrinkage, and temperature rise and fall. For box girder

structures, compute creep and shrinkage from the time the expansion joints are installed

through day 4000.

2. To account for the larger amount of opening movement, set expansion devices

precompressed to the maximum extent possible. In calculations, allow for an assumed

setting temperature of 30 degrees C. Provide a table on the plans giving precompression

settings according to the prevailing conditions. Size expansion devices and set to remain

precompressed through the full range of design temperature from their initial installation until

a time of 4000 days.


PAGE 155

10-BEARINGS SECOND EDITION – AUGUST 2021

10 BEARINGS

BDS Article 14.4 discusses the force effects of bearings, and BDS Article 14.7 discusses types of

bearings. This Chapter presents criteria for the selection, design, and detailing of bearings for

bridges.

10.1 General

Select bridge bearings to accommodate the anticipated movements of the superstructure and

transmit the anticipated loads to the substructure.

The type of bearing selected depends upon the magnitude and type of movement and the magnitude

of the load.

10.1.1 Movements and Loads

Include both translations and rotations in the selection, design, and detailing of bearings.

The sources of movement include initial camber or curvature, construction loads, misalignment,

construction tolerances, settlement of supports, thermal effects, elastic shortening due to post-

tensioning, creep, shrinkage, and seismic and traffic loading.

10.1.2 Effect of Camber and Construction Procedures

Evaluate both the initial rotation and its short duration. At intermediate stages of construction, add

deflections and rotations due to the progressive weight of the bridge elements and to the construction

equipment to the effects of live load and temperature.

Consider the direction of loads, movements, and rotations. Do not simply add the absolute maximum

magnitudes of the design requirements. Anticipate the worst possible condition, but do not consider

combinations of absolute maximums that cannot realistically occur. In special cases, it may be

economical to install the bearing with an initial offset, or to adjust the position of the bearing after

construction has started, to minimize the adverse effect of the temporary initial conditions.

The initial camber of bridge girders induces bearing rotation. Initial camber may cause a larger initial

rotation on the bearing, but this rotation may decrease as the construction of the bridge progresses.

Rotation due to camber and the initial construction tolerances are sometimes the largest component

of the total bearing rotation.

10.1.3 Design Thermal Movements


Estimate the design thermal movement in accordance with Section 9.1.2.

Assume setting temperatures for the installation of the bearings of 20°C, 25°C, 30°C, 35°C, 40°C,

and 45°C, consistent with the minimum and maximum temperatures at the bridge site. At the time of

construction, the appropriate setting conditions may be chosen based upon the ambient

temperature.


PAGE 156


A given temperature change causes thermal movement in all directions. Because the thermal

movement is a function of the expansion length as shown in BDS Equation 3.12.2.3-1, a short, wide

bridge may experience greater transverse movement than longitudinal movement.

10.1.4 Estimation of Total Design Movement

In addition to the thermal movement determined in Section 10.1.3, consider the effects of creep (CR)

and shrinkage (SH) in the total movement for bridges in accordance with Section 9.1.3.

10.1.5 Serviceability, Maintenance, and Protection Requirements


Design and detail bearings under deck joints to minimize environmental damage and to allow easy

access for inspection. Design and detail bearing locations for potential bearing replacement.

Bearings under deck joints may be exposed to dirt, debris, and moisture that promote corrosion and

deterioration. The service demands on bridge bearings are very severe and result in a service life

that is typically shorter than that of other bridge elements.

The following provisions apply to all bridges with the exception of flat slab superstructures (cast-in-

situ or precast):

1. Design and detail the superstructure using bridge bearings that are reasonably accessible

for inspection and maintenance.

2. On all new designs, make provisions for the replacement of bearings without causing undue

damage to the structure and without having to remove anchorages or other devices

permanently attached to the structure.

3. Design and detail provisions for the removal of bearings, such as jacking locations, jacking

sequence, jack load, etc. Size the substructure width to accommodate the jacks and any

other required provisions.

4. When widening a bridge that does not already include provisions for replacing bearings,

consult the maintenance engineer who will decide if bearing replacement provisions must be

made on the plans.

Certain non-conventional structures, such as steel girders or segmental concrete box girders, require

separate details and notes describing jacking procedures. For steel I-girder bridges, design so that

jacks are placed directly under girder lines. For steel box girder bridges, design so that jacks are

placed directly under diaphragms. Always include a plan note stating that the jacking equipment is

not part of the bridge contract.

Few concrete I-beam bridges require elastomeric bearing pad replacement. Occasional replacement

of the pads does not justify requiring these provisions for every bridge.

10.1.6 Anchor Bolts



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Use anchor bolts to transfer horizontal forces through bearing assemblies when external devices

such as shear keys are not present. In addition, use anchor bolts as hold downs for bearings.

Use holes for anchor bolts in steel elements of bearing assemblies that are 6 mm larger in diameter

than the diameter of the anchor bolt. Locate the centrelines of anchor bolts a minimum of 50 mm

from the edge of the girder. A larger offset may be necessary to facilitate installation. Consider the

space necessary for nuts, washers, base plate welds, and construction tolerances and establish

anchor bolt locations accordingly. Maintain a 13-mm clearance from the edge of the elastomeric

bearing to the edge of the anchor bolt.

Provide sufficient reinforcement around the anchor bolts to develop the horizontal forces and anchor

them into the mass of the substructure unit. Identify potential concrete crack surfaces next to the

bearing anchorage and evaluate the shear friction capacity.

Conflicts between anchor bolt assemblies and substructure reinforcement are common, especially

for skewed bridges. Therefore, ensure that all reinforcing steel can fit around the bearing assemblies.

10.1.7 Bearing Plate Details

Use a bearing plate that is at least 25 mm wider than the elastomeric bearing on which the plate

rests. Use a minimum bearing plate thickness of 40 mm. When the instantaneous slope of the grade

plus the final in-place camber exceeds 1%, bevel the bearing plate to match the grade plus final

camber. For bevelled bearing plates, maintain a minimum of 40 mm thickness at the edge of the

bearing plate.

At expansion bearings, provide slotted bearing plates. Determine the minimum slot size according

to the amount of movement and end rotation calculated. The slot length, L, is:

L = (diameter of anchor bolt) + 1.2 (total movement) + 25 mm

The multiplier of 1.2 represents the load factor from BDS Table 3.4.1-1 for TU, CR, and SH.

The total movement should include an effect of girder end rotation at the level of the bearing plate.

Round the slot length to the next higher 6 mm. To account for possible different setting temperatures

at each stage, provide offset dimensions in the contract documents for stage-constructed projects.

For all other projects, consider the need to provide offset dimensions.

Top and bottom adapter plates shall be provided to allow for simple mechanical bearing

replacement. The fixing arrangement of the bearing to the top and bottom adapter plates shall be

such as to enable bearing replacement without the need for cutting into the bridge superstructure or

substructure. The bearing may be attached to the masonry plate by seating it in a machined recess

and bolting it down. To replace the bearing, the bridge will need to be lifted a height equal to the

depth of the recess.

10.1.8 Levelling Pad at Integral Abutments

Detail a plain elastomeric pad under the bearing plate of girders at integral abutments to provide a

level and uniform bearing surface. Structural grout is not an acceptable substitute.


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10.1.9 Lateral Restraint

Determine if lateral restraint of the superstructure of a bridge is required and make necessary

provisions to assure that the bridge will function as intended. The provisions include considerations

for the effects of geometry, creep, shrinkage, temperature, and/or seismic on the structure. When

lateral restraint of the superstructure is required, develop the appropriate method of restraint as

described hereinafter.

10.1.9.1 Elastomeric Bearings

When the required restraint exceeds the capacity of the bearing pad, provide the following

appropriate restraint:

1. For concrete girder superstructures, provide concrete blocks cast on the substructure and

positioned to avoid interference with bearing pad replacement.

2. For steel girder superstructures, provide extended sole plates and anchor bolts.

10.1.9.2 Mechanically Restrained Bearings

Design bearings that provide restraint through guide bars or pintles (e.g. pot bearings) to provide the

required lateral restraint. When unidirectional restraints are required, avoid multiple permanent

unidirectional restraints at a given pier location to eliminate binding. Where multiple unidirectional

restraints are necessary at a given pier, require bearings with external guide bars that are adjustable

and include a detailed installation procedure in the plans or specifications to ensure that the guide

bars are installed parallel to each other.

10.2 Bearing Types and Selection

10.2.1 General

Use steel-reinforced elastomeric bearings or plain elastomeric bearing pads for all girder bridges

where possible. Bridges with large bearing loads and/or multi-directional movement may require

other bearing devices such as high-load, multi-rotational (HLMR) bearings.

Distribute the loads among the bearings according to the superstructure analysis.

See Table 10.1 for a general summary of bearing capabilities. Use the values shown in the table for

preliminary guidance only. Complete the final design of the bearing according to the BDS. Provide

the geometry and other pertinent specifications for the bearing. If the load falls outside of the optimal

ranges, contact the bearing manufacturer.

Use bearing plates and anchor bolts for precast concrete and steel girder superstructures. Use

concrete shear keys with elastomeric bearings to transfer horizontal forces from a concrete box

girder superstructure to the substructure.

Bearing selection is influenced by many factors including loads, geometry, maintenance, available

clearance, displacement, rotation, deflection, availability, policy, designer preference, construction

tolerances, and cost. In general, vertical displacements are restrained, rotations are allowed to occur

as freely as possible, and horizontal displacements may be either accommodated or restrained.


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Table 10.1: Summary of Bearing Capabilities

Type

Load (kN) Absolute

Max. Load Limits

(kN)

Translation (mm)

Rotation

Limit

(Rad)

Cost

Typical Design Range1

Min Max Initial Maintenance

Steel-reinforced elastomeric bearing

450 to 6000 10,000 0 100 0.04 low high

High-load, multi-rotational (HLMR) bearings

Pot bearing

4000 to 30,000 50,000 02 02 0.04 - 0.05 high low

Disc bearing

4000 to 30,000 50,000 02 02 0.03 high low

Spherical bearing

4000 to 30,000 50,000 02 02 > 0.05 high low

Plain elastomeric pad 0 to 670 1000 0 20 0.0175 low high

1 Higher or lower values may be applicable if necessary.

2 High-load, multi-rotational (HLMR) bearings have no inherent translational capability. Expansion bearings

are achieved by using them in conjunction with flat PTFE sliding surfaces.

10.2.2 Steel-Reinforced Elastomeric Bearings


Use steel-reinforced elastomeric bearings for all typical girder bridges. Section 10.3 discusses the

design of these bearings in more detail.

Provide elastomeric expansion bearings with adequate seismic-resistant anchorages to resist the

horizontal forces in excess of those accommodated by shear in the pad. Provide a wider sole plate

and base plate to accommodate the anchor bolts.

Provide elastomeric fixed bearings with a horizontal restraint adequate for the full horizontal load.

Steel-reinforced elastomeric bearings are usually a low-cost option but require high maintenance.

10.2.3 Plain Elastomeric Bearing Pads


Use plain elastomeric bearing pads where bearing loads are light, up to 670 kN, and as levelling

pads at integral abutments for girder bridges.

Plain elastomeric bearing pads are usually a low-cost option and require minimal maintenance.

However, their use is restricted to lighter bearing loads for practical reasons. Plain elastomeric

bearing pads can support modest gravity loads, but they can only accommodate limited rotation or

translation. Hence, they are best suited for bridges with small expansion lengths or specialty

situations.


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10.2.4 High-Load, Multi-Rotational (HLMR) Bearings

Reference: BDS 14.7.4, 14.7.3 and 14.7.8

High-load, multi-rotational (HLMR) bearings include pot bearings, spherical bearings (termed

“Bearings with Curved Sliding Surfaces” in the BDS), and disc bearings. Only use these bearings

where bearing loads exceed the capabilities of steel-reinforced elastomeric bearings greater than

2900 kN. Select among HLMR bearings based upon the rotational capabilities presented in Table

10.1.

Only show schematic bearing details, combined with the specified loads, movements, and rotations,

in the contract documents. The manufacturer designs the bearing; this advantageously uses the

cost-effective fabrication procedures that are available in the shop.

HLMR bearings are generally avoided due to their cost.

Pot bearings are able to support large compressive loads, but their elastomer can leak and their

sealing rings can suffer wear or damage.

Modelling of a bridge supported on spherical bearings must recognize that the centre of rotation of

the bearing is not coincident with the neutral axis of the girder above.

Disc bearings are susceptible to uplift during rotation, which may limit their use to bearings with

polytetrafluoroethylene (PTFE) sliding surfaces.

10.2.5 Polytetrafluoroethylene (PTFE) Sliding Surfaces


Consider using PTFE sliding surfaces with expansion HLMR bearings and where the maximum

movements exceed the allowable for elastomeric bearings.

The following design information applies to PTFE sliding surfaces:

• Optimal design range for loads: 0 to 30,000 kN

• Translation: 25 mm to > 100 mm

10.2.6 Seismic Isolation Bearings

The AASHTO Guide Specifications for Seismic Isolation Design (34) and the FHWA Seismic

Retrofitting Manual for Highway Structures: Part 1 – Bridges (35) discuss the use of seismic isolation

bearings.

There are various types of seismic isolation bearings, most of which are proprietary.

10.3 Plain Elastomeric Bearing Pads and Steel-Reinforced Elastomeric Bearings



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10.3.1 General

Plain elastomeric bearing pads and steel-reinforced elastomeric bearings have fundamentally

different behaviours and, therefore, are discussed separately.

Orient elastomeric pads and bearings so that the long side is parallel to the principal axis of rotation,

because this orientation better accommodates rotation.

10.3.2 Holes in Elastomer

Do not use holes in steel-reinforced elastomeric bearings or plain elastomeric bearing pads.

10.3.3 Edge Distance

For elastomeric pads and bearings resting directly on a concrete bridge seat, the minimum edge

distance is 75 mm.

The minimum low-temperature elastomer is Grade 3. Indicate the elastomer grade in the contract

documents.

10.3.4 Steel-Reinforced Elastomeric Bearings

Preferably, use steel-reinforced elastomeric bearings in combination with steel bearing plates for

slab-on-girder bridges. Use a 25-mm minimum clearance between the edge of the elastomeric

bearing and the edge of the bearing plate in the direction parallel to the beam or girder. Use a 13-

mm minimum clearance between the edge of the elastomeric bearing pad and the anchor bolt in the

direction perpendicular to the girder.

10.3.5 Design of Plain Elastomeric Bearing Pads

Design and detail plain elastomeric bearing pads according to Method A of BDS Article 14.7.6.

Use a maximum friction coefficient of 0.20 for the design of elastomeric pads that are in contact with

clean concrete or steel surfaces (1). If the shear force is greater than 0.20 of the simultaneously

occurring compressive force, then secure the bearing against horizontal movement. Use a friction

coefficient of 0.40 when checking the maximum seismic forces that can be transferred to the

substructure through the pad.

Plain elastomeric bearing pads rely on friction at the top and bottom surfaces to restrain bulging due

to the Poisson effect. Friction is unreliable, and local slip results in a larger elastomer strain than that

which occurs in steel-reinforced elastomeric pads and bearings. The increased elastomer strain

limits its load capacity, and the pad must be relatively thin if it will carry the maximum allowable

compressive load.

10.3.6 Design of Steel-Reinforced Elastomeric Bearings


Typically, use the Method A procedure in BDS Article 14.7.6 for steel-reinforced elastomeric

bearings. The Method B procedure in BDS Article 14.7.5 may be used for high-capacity bearings.


PAGE 162


Use high-capacity elastomeric bearings only where very tight geometric constraints, extremely high

loads, or special conditions or circumstances require the use of higher grade material.

If a high-capacity elastomeric bearing is used, prepare a unique Special Provision for inclusion in

the contract documents.

Use a minimum elastomeric bearing length or width of 150 mm. Provide a minimum of 6 mm of cover

at the edges of the steel shims.

For bearing design, classify all bridge sites as being in Temperature Zone A, for which BDS Table

14.7.5.2-1 presents the design data.

Use a setting temperature of 20°C for the installation of the bearings unless the time of construction

is known. In this case, modify the setting temperature accordingly. Use 80% of the total movement

range for design. This value assumes that the bearing is installed within 30% of the average of the

maximum and minimum design temperatures.

BDS Article C14.7.5.3.4 recommends using 65% of the total movement range for design but, due to

the wide variation in temperatures across the Abu Dhabi Emirate and variations within a single day,

the design value is increased.

Account for creep (CR) and shrinkage (SH) according to the assumed construction schedule for

determining elastomeric thickness. If the construction schedule differs significantly, the contractor

must reconsider the required thickness.

Base the design thermal movement (ΔT) upon TMaxDesign and TMinDesign from Table 9.1.

For the minimum total elastomer thickness, use 2 (ΔT + ΔSH + ΔCR + ΔEL) with the appropriate

values of ΔT, ΔSH, ΔCR, and ΔEL for the bridge type and construction.

Ensure that the bearing details are consistent with the design assumptions used in the seismic

analysis of the bridge.

The Method B design procedure allows significantly higher average compressive stresses than

Method A. The higher allowable stress levels are justified by an additional acceptance test,

specifically a long-duration compression test. Design criteria for both methods are based upon

satisfying fatigue, stability, delamination, steel reinforcement yield/rupture, and elastomer stiffness

requirements.


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11-PEDESTRIAN BRIDGE SECOND EDITION – AUGUST 2021

11 PEDESTRIAN BRIDGES

A pedestrian bridge is defined as a bridge intended to carry primarily pedestrians and bicyclists and

light maintenance vehicles and not intended for use by typical highway traffic.

11.1 General

Use the AASHTO BDS and Guide Specifications for Design of Pedestrian Bridges (36) (DPB) for

the design and construction of typical pedestrian bridges with any modifications presented herein.

The DPB provides additional guidance on the design and construction of pedestrian bridges when

compared to the BDS, and for wind and fatigue provisions, when compared to the AASHTO Standard

Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals (37) (SSS).

In addition, the AASHTO Guide for the Planning, Design, and Operation of Pedestrian Facilities may

be useful in the planning, access facilities (i.e. stairs, lifts), and design of pedestrian bridges.

The preliminary design for a pedestrian bridge is intended to determine the most appropriate

structure type and configuration for a given site considering the design objectives of BDS Article 2.5

and Section 1.4 of this Manual.

11.2 Live Load

11.2.1 Pedestrian Load (PL)

Reference: DPB Article 3.1

Use a uniform pedestrian loading of 5.0 kN/m2 as specified in DPB Article 3.1.

The commentary of the DPB suggests that 7.18 kN/m2 represents the maximum credible pedestrian

load. This may be used for special cases where heavy pedestrian traffic can be expected.

11.2.2 Vehicle Load (LL)

Reference: DPB Article 3.2

Where maintenance vehicles can reach the superstructure, apply the vehicle configuration specified

in DPB Article 3.2 for the design of pedestrian bridges in the Abu Dhabi Emirate.

11.3 Wind Load (WS)

Reference: DPB Article 3.4 and SSS Articles 3.8 and 3.9

Use 160 km/h for the basic wind speed with a gust factor of 1.14 for the Abu Dhabi Emirate.

An increased Gust factor value may be required depending upon the structure flexibility and

exposure conditions. The increased factor shall be subjected to client approval.

The DPB specifies that wind loading is taken from the SSS instead of the BDS due to the potentially

flexible nature of pedestrian bridges and also due to the potential for traffic signs to be mounted on

them.


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11.4 Vibrations

Reference: DPB Section 6

The bridge owner must not waive the vibration control provisions of DPB Section 6.

This provision mandates that the owner control vibrations whereas the DPB allows the owner to

waive this control.

11.5 Design

11.5.1 Geometrics

Design the geometrics of the bridge and the approach transitions to meet the requirements of the

DPB. For pedestrian bridges over waterways, the hydraulics engineer determines the necessary

hydraulic opening. Clearances over other facilities are determined on a project-by-project basis.

11.5.2 Structure Type

Select structure types as deemed appropriate for the given site. For an evaluation of structure type,

consider constructability, aesthetics, use of falsework, construction costs, etc.

11.5.3 Seismic

Apply the AASHTO seismic provisions to pedestrian bridges, as modified by this Manual. See

Chapter 2 and Section 3.3.1.

11.5.4 Fatigue

For fatigue load, use Section 11 of the SSS as specified in the DPB; for fatigue resistance, use

Section 6 of the BDS, Section 11 of the SSS, or Figure 2.13 of the AWS D1.1 – Structural Welding

Code – Steel (20), as appropriate, also as specified in the DPB.

11.5.5 Detailed Design Requirements

Design and detail pedestrian bridges as follows:

1. Fully design and detail foundation and substructure in the plans.

2. Fully design and detail all approach structures including non-truss approach spans, ramps,

steps/stairways, approach slabs, retaining walls, etc., in the plans.

3. Include general plan and elevation indicating minimum aesthetic requirements for the

prefabricated bridge in the plans.

4. In case of “Design and Build” contract, the Contractor designs and details a prefabricated

superstructure after award of the contract and submits the design calculations, technical

specifications, and fully detailed shop drawing to the Engineer for review and approval prior

to fabrication. Components in the shop drawings must include trusses, floor system, lateral

bracing, deck, railing/fencing, deck joints, bearing assemblies, etc. In conventional contracts,

these services (except shop drawings) will be provided by the Design Consultant and the

design will go through an appropriate checking in accordance with section 1.5 of this manual.


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Desirably, limit the maximum overall width of prefabricated bridges to 3.6 m. This eliminates the

need for a spliced section.

Design all pedestrian bridges for a 75-year design life.

Clearance criteria for pedestrian bridges are as follows:

1. Provide a minimum of 3.0 m vertical clearance above the bridge deck, except for pedestrian

bridges that can be accessed by camels, where the vertical clearance above the deck is 4.5

m.

2. Consider future widening of the roadway below when determining horizontal clearances.

11.5.6 Deflections

Use the following to determine maximum allowable deflections for pedestrian bridges:

1. Pedestrian Load .................................................................. Span/500

2. Maintenance Vehicle Load .................................................. Span/500

3. Cantilever Arms Due to Service Pedestrian Live Load ....... Cantilever Length/300

4. Horizontal Deflection Due to Lateral Wind Load ................. Span/500

5. Design the pedestrian bridge to match the plan profile grade after all permanent dead load

has been applied.

11.5.7 Steel Connections

Field welding is allowed only by prior written approval and then only when bolting is impractical or

impossible.

11.5.7.1 Bolting Criteria

Design bolted connections per Chapter 5 with the exception of bearing type connections permitted

only for bracing members.

11.5.7.2 Tubular Steel Connections

Open-ended tubing is not acceptable.

Prior to bolting of field sections, tubular members are capped and fully sealed with the following

exception. Provide weep holes at the low point of all members to allow for drainage of water

accumulated inside the members during transport and erection. After erection is complete and prior

to painting, the weep holes are sealed with silicone plugs.

Require that all field splices be shop fit. Specify or show field sections bolted together using splice

plates. Direct Tension Indicators (DTI) are prohibited in bolted connections. When through bolting is

necessary, stiffen the tubular section to ensure the shape of the tubular section is retained after final

bolting. See Figure 11.1.

11.5.7.3 Vibrations

Pedestrian bridges are highly susceptible to vibrations. Limits on vibration are specified in the DPB.

Check vibration frequency under temporary construction conditions.


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11.5.8 Charpy V-Notch Testing

Require ASTM A709M Charpy V-notch testing for all structural steel tension members.

Figure 11.1: Tubular Truss Splice Detail

Require impact testing requirements as follows:

1. Test non-fracture critical tension members in accordance with ASTM A709M (latest version).

2. Primary tension chords in a two truss bridge may be considered non-fracture critical due to

frame action.

3. Test fracture critical tension members according to ASTM A709M (latest version).

4. Test tubular tension members according to ASTM A500M.

5. Cross frames, transverse stiffeners, and bearing stiffeners not having bolted attachments

and expansion joints do not require testing.

11.5.9 Painting/Galvanizing

Coatings are not required for the interior of tubular components. Consider the suitability of the

fabricated component for galvanizing. Hot-dip galvanizing may be used where entire steel

components can be galvanized after fabrication and where project specific aesthetic requirements

allow. Welding components together after galvanizing is not acceptable.

11.5.10 Erection

Design and detail pedestrian bridge plans to minimize the disruption of traffic during bridge erection.

Include the following notes on the plans:

• erection over traffic is prohibited, and


PAGE 167


• the Contractor is responsible for designing a falsework system capable of supporting portions

of the superstructure during erection.

11.5.11 Railings/Enclosures

Occasional use of the bridge by maintenance or emergency vehicles generally does not warrant the

use of a crash tested combination pedestrian/traffic railing.

Provide railing options as follows:

1. 1.3 m pedestrian/bicycle railing (minimum)

2. 1.5 m special height bicycle railing

3. Open top fence/railing combination

4. Full enclosure fence/railing combination

5. Open top cladding/railing combination (e.g. glass, steel panel, concrete panel)

6. Full enclosure cladding/railing combination

Utilize standard fence designs or connection details, where applicable.

In addition, structural review and approval, the railing shall also require approval by the Road Safety

Specialist from the relevant authorities.

11.5.12 Drainage

Design and detail drainage systems as required. Provide curbs, drains, pipes, or other means to

drain the superstructure pedestrian deck. Do not allow drainage of the superstructure onto the

roadway underneath.

11.5.13 Corrosion Resistant Details

Provide designs so that water and debris will quickly dissipate from all surfaces of the structure and

will not cause corrosion of members and connections.

11.5.14 Lighting/Attachments

For tubular structures, design any attachment, including electrical wiring, signs, signals, etc.,

strapped to the bridge. Do not allow the tapping of holes into the structural tubular members.

Design lighting attachments for wind loads as per the SSS.

11.5.15 Maintenance and Inspection Attachments

Inspections will be performed in accordance with current procedures and criteria and maintenance

guidelines. The inspection and maintenance criteria of private permitted bridges that cross Abu

Dhabi Emirate roadway facilities are the same as for public bridges.


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12-CULVERTS SECOND EDITION – AUGUST 2021

12 CULVERTS


Use only reinforced concrete boxes, concrete arch culverts, and concrete pipe culverts. Other culvert

options in the BDS offer less durability.

12.1 Reinforced Concrete Boxes

12.1.1 General

The structural design of reinforced concrete boxes is based on Section 12 of the BDS. The hydraulics

engineer is responsible for drainage appurtenances, and standard drawings apply in most cases.

Use a special design other than those represented by the standard drawings when:

• The box geometry or height of soil above the reinforced concrete box exceeds the limits

indicated on the standard drawings.

• Other structures impose loads on the reinforced concrete box.

• The sequence of backfilling the sides of the reinforced concrete box will not allow equal

loading.

• The design requires a special inlet, outlet, confluence, or other special hydraulic structure for

which a standard drawing does not exist.

12.1.2 Analysis

Analyse culverts using elastic methods and model the cross section as a plane frame (2D) using

gross section properties. Restrain the bottom slab by any of the following methods:

• Fully pinned support at one corner and pin-roller support at the opposite corner.

• Vertical springs (linear-elastic or non-linear soil springs) at a minimum of tenth points and a

horizontal restraint at one corner.

• Beam on elastic foundation and a horizontal restraint at one corner.

• Detail up-stand beams at the edges of the box with discontinuity joints so that they do not

contribute to the load distribution from the top slab (deck).

Obtain the modulus of subgrade reaction from the geotechnical engineer when performing the more

refined analyses in the second and third bullet items above.

12.1.3 Span-to-Rise Ratios

Do not use span-to-rise ratios exceeding 4:1.

As span-to-rise ratios approach 4:1, frame moment distribution is more sensitive to support

conditions, and positive moments at midspan can significantly exceed computed values even with a

relatively small horizontal displacement of frame leg supports.


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12.1.4 Deformations

Ensure that top slab deflection due to the live load plus impact does not exceed 1/800 of the design

span. For culverts located in urban areas used in part by pedestrians, ensure that this deflection

does not exceed 1/1000 of the design span.

Determine live-load deflections in accordance with BDS Article 2.5.2.6.2.

12.1.5 Design Method

Design new reinforced concrete culverts and extensions to existing culverts (precast or cast-in-situ,

four-sided, or three-sided) subjected to either earth fill and/or highway vehicle loading in accordance

with the BDS.

Investigate the need for culvert barrel weep holes to relieve uplift pressure. When culvert barrel weep

holes are necessary, show the requirement in the plans.

12.1.6 Dead Loads and Earth Pressure

Reference: BDS Articles 3.5, 3.11.5, and 3.11.7

The dead load on the top slab consists of the pavement, soil, and concrete slab. For simplicity in

design, the pavement may be assumed to be soil.

Use the following design criteria in determining dead load and earth pressures:

Soil = 1900 kg/m3 at = 30° to 2000 kg/m3 at = 32°

Reinforced concrete = 2500 kg/m3 horizontal earth pressure (at-rest) for:

Maximum horizontal load effects = 960 kg/m3, (assumes soil internal friction angle = 30°)

Minimum horizontal load effects = 480 kg/m3, (50% of maximum load effects)

Modify vertical earth pressures in accordance with BDS Article 12.11.2.2.1, Modification of Earth

Loads for Soil Structure Interaction (Embankment Installations), for both box and three-sided

culverts.

Verify final designs for materials used on site.

12.1.7 Live Load

Lane loading is required for the design of culverts with spans greater than 5 m in lieu of the exemption

in BDS Article 3.6.1.3.3.

12.1.8 Wall Thickness Requirements

Determine the exterior wall thickness for concrete culverts based on the design requirements, except

use the following minimum thickness requirements to allow for a better distribution of negative

moments and corner reinforcement:

Clear Span Minimum Exterior Wall Thickness

< 2.4 m 250 mm (precast); 300 mm (cast-in-situ)

2.4 m to < 4 m 300 mm

4 m to < 6 m 350 mm

6 m 400 mm


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The interior wall thickness in multi-cell culverts must not be less than 250 mm for precast culverts

and 300 mm for cast-in-situ culverts.

Increase the minimum wall thickness by 50 mm for concrete culverts in extremely aggressive

environments (100 mm concrete cover)

12.1.9 Reinforcement Details

Design the main reinforcement in the top and bottom slabs perpendicular to the sidewalls in cast-in-

situ culverts and non-skewed units of precast culverts. For reinforcement requirements of skewed

precast culverts, see Section 12.1.10.

The minimum inside bend diameter for negative moment reinforcement (outside corners of top and

bottom slabs) must satisfy the requirements of BDS Article 5.10.2.3 and must not be less than 4.0db

for welded wire reinforcement.

Top and bottom slab transverse reinforcement must be full-length bars, unless spliced to top and

bottom corner reinforcement.

12.1.10 Skewed Culverts

Design and detail skewed precast concrete culverts with non-skewed interior units designed for the

clear span perpendicular to the sidewalls and skewed end units designed for the skewed clear span.

For a cast-in-situ concrete box culvert with a skewed end, the top and bottom slab reinforcement is

“cut” to length to fit the skewed ends. The “cut” transverse bars have the support of only one culvert

sidewall and must be supported at the other end by edge beams (headwall or cutoff wall).

Precast concrete culverts with skewed ends usually cannot use edge beams as stiffening members

because of forming restrictions. The transverse reinforcement must be splayed to fit the geometry

of the skew. This splaying of the reinforcement increases the length of the transverse bars and, more

importantly, the design span of the end unit. For small skews, the splayed reinforcement is usually

more than adequate. However, large skews require more reinforcement and may require an

increased slab thickness or integral headwalls.

12.2 Concrete Arch Culverts

The following applies to concrete arch culverts:

• The design must meet the requirements of Section 12 of the BDS.

• Provide double reinforcement meeting BDS requirements for minimum reinforcing and

service limit state (crack control) criteria.

• Use the CANDE or similar computer program to verify the design.

• Provide design verification for a potential future condition that would require excavation of

backfill material along one edge of the arch.

• Design the arch culvert with a concrete invert.

• Ignore creep and shrinkage at mid-span of arch culverts with a CIS top and integral joint to

precast components.

• Design the “saddle” area of multiple-cell arch structures with a waterproofing system and a

suitable drainage system to control ponding and saturation of backfill soils. Provide


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weepholes in exterior walls at 10-m maximum spacing. All drains and weepholes are a

minimum 75-mm diameter.

• A technical representative of the arch culvert supplier must be on-site and must supply the

necessary technical assistance during the initial completion of major work activities. This

includes the placement of reinforcing, forming, concrete placement, form removal,

waterproofing, and backfilling.

First introduced in 1976 under the sponsorship of US Federal Highway Administration, CANDE

(Culvert ANalysis and DEsign) is a design and analysis tool for all types and sizes of buried

structures. CANDE is a public-domain finite element program that is used worldwide. CANDE

provides an elastic solution (Level 1), automated finite element mesh generation for common

configurations (Level 2), and a user-defined finite element mesh (Level 3).

12.3 Concrete Pipe Culverts

12.3.1 General

Round and elliptical pipes are widely used for roadway drainage. They are standardized structures,

and no structural drawings are necessary in the contract documents.

Elliptical pipes used in the Abu Dhabi Emirate are normally horizontally elliptical.

12.3.2 Materials

Materials for round and elliptical concrete pipe must meet the requirements of the Abu Dhabi

Standard Specifications: Volume 2: Road Structures (Document Reference Number TR-542-2) and

the AASHTO Standard Specifications for Transportation Materials and Methods of Sampling and

Testing (38), M170 (Round RCP) and M207 (Elliptical RCP).

12.3.3 Design

Design round and elliptical concrete pipe culverts according to Section 12 “Buried Structures and

Tunnel Liners” of the BDS.

Determine earth loads and live loads in accordance with Section 3 of the BDS as modified by Chapter

2 of this Manual.

The standard pipe class used in the Abu Dhabi Emirate is Class III. Use Classes IV and V pipe when

higher resistance is required. Base the selection of the required class of pipe on the diameter and

height of fill above the top of the pipe.

Concrete pipes are classified according to their construction and resistance as Class I, II, III, IV, or

class V.


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13-SOUND BARRIERS SECOND EDITION – AUGUST 2021

13 SOUND BARRIERS


The environmental engineer determines the warrants for, locations of, and minimum heights for

sound barrier walls. Use the following for the structural design of sound barriers:

• Section 15 of the BDS.

• Wind pressure from a wind velocity of 160 km/h and a gust factor of 1.14, as specified in

Chapter 2 of this Manual, Loads and Load Factors.

• Seismic load as specified in Chapter 2 of this Manual, Loads and Load Factors.

• For the masonry design, grout all cells and provide minimum reinforcing consisting of T16

bars at 400-mm vertical and 600-mm horizontal spacing.

13.1 Sound Barrier Design

13.1.1 General Features – Panel Height and Post Spacing


Post spacing is a minimum of 3 m and a maximum of 6 m.

All concrete wall panels are a minimum of 2 m high. Bottom panels are a minimum of 2.4 m high

when emergency access is required.

The minimum bottom panel height of 2 m is used to clear required fire hose access holes. The

minimum bottom panel height of 2.4 m for sound barriers requiring emergency access is used to

allow forming and installation of 2 m high doors.

13.1.2 Wind Loads

For sound barriers located on embankments and structures, determine the height zone by using the

elevation of adjoining ground as the approximate elevation of the original ground surface prior to

embankment construction.

13.1.3 Lateral Earth Pressure


For sound barriers supported on discrete vertical wall elements embedded in granular soil, rock, or

cohesive soil, use the simplified lateral earth pressure distributions shown in BDS Figures 3.11.5.10-

1, 3.11.5.10-2, and 3.11.5.10-3, respectively.

For sound barriers supported on continuous vertical elements embedded in granular soil or cohesive

soil, use the simplified earth pressure distributions shown in Figures 3.11.5.10-4 and 3.11.5.10-5,

respectively.


Page 173

14-SIGN AND LUMINAIRE SUPPORTS SECOND EDITION – AUGUST 2021

14 SIGN AND LUMINAIRE SUPPORTS

Reference: AASHTO Standard Specifications for Structural Supports for Highway Signs,

Luminaires, and Traffic Signals

14.1 General

This Section is a supplement to the AASHTO Standard Specifications for Structural Supports for

Highway Signs, Luminaires, and Traffic Signals (SSS) (37), much as the rest of the Manual is a

supplement to the BDS. Standard designs represented by standard drawings in the Abu Dhabi

Standard Drawings for Road Structures (Document Reference Number TR-541-2) apply in most

cases. Occasionally, the bridge designer becomes involved in the design of structural supports for

these roadside appurtenances.

14.2 Deformations

Reference: SSS Article 10.4

Deformations for specific structure types shall be limited as provided in SSS Articles 10.4.1 and

10.4.2. Where the deformations are not specified in SSS Articles, the provisions of BD 51/14 shall

govern.

The limit on deformations serves two purposes — to provide an aesthetically pleasing structure and

to provide adequate structural stiffness that will result in adequate serviceability.

14.3 Basic Wind Speed

Reference: SSS Article 3.8.2

Base the wind loads on the wind speeds of 160 km/h with a gust factor of 1.14.

14.4 Steel Design

14.4.1 Base-Plate Thickness

For base plate connections without stiffeners, the minimum base plate thickness is 50 mm.

Research has proven that full-penetration groove welds combined with thicker base plates increases

the pole-to-base-plate connection fatigue strength.

14.4.2 Welded Connections

14.4.2.1 Circumferential Welded Splices

On steel sign and signal structures, do not use circumferential welds on the uprights, arms, or chords

with the exceptions of the base plate weld, the flange plate connections on tubular truss members,

and the mitred arm-to-upright angle weld on monotube.

The intent is to avoid any unnecessary welds on sign, signal, or lighting structures.


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14.4.2.2 Base Connection Welds

For base plate connections without stiffeners, only use full-penetration groove welds.

Research has proven that full-penetration groove welds combined with thicker base plates increases

the pole-to-base-plate connection fatigue strength.

14.4.3 Bolted Connections


Design all pole-to-arm connections on mast arm structures as “through bolted.” Do not use tapped

connections.

Through-bolted connections provide fully tensioned A325 bolts.

14.4.4 Anchor Bolt Connections


14.4.4.1 Minimum Number of Bolts

Use a minimum of six Grade 380, ASTM F1554 anchor bolts at the pole-to-foundation connection,

in case round base plates, for all sign, signal, and lighting structures that are designed for a minimum

service life of 50 years.

A minimum of six anchor bolts provides redundancy and better distribution of forces through the

base plate.

14.4.4.2 Use of Grout

Grout pads underneath the base plates in double-nut moment joints of miscellaneous highway

structures (i.e. mast arms, overhead sign structures, high mast lights, steel strain poles and

monotube structures) are not required.

Inspections have shown that a poorly functioning grout pad is worse than no grout pad at all. For

poles without a grout pad beneath the base plate, the double-nut moment joint requires adequate

tensioning of the anchor bolts. The nuts beneath the base plate, typically referred to as levelling

nuts, must be firmly tightened and locked to prevent loosening. This locking mechanism is

accomplished through the turn of the nut method or a properly placed grout pad.

14.4.5 Bolt Types

Reference: SSS Article 5.17.1

Do not use adhesive anchors or threaded post-tensioning bars.

Adhesive anchor and threaded post-tensioning bars have undesirable creep and ductility behaviour,

respectively.

14.5 Aluminium Design

Reference: SSS Article 6


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Do not specify aluminium overhead sign structure supports with the exception of the vertical sign

panel hangers, which may be aluminium or steel.

Aluminium overhead sign structures are prone to unacceptable levels of vibration and fatigue

cracking.

14.6 Prestressed-Concrete Poles


The minimum clear concrete cover for all prestressed and non-prestressed poles shall be 40 mm

and 50 mm, respectively.

The minimum 40-mm and 50-mm covers are required on all concrete poles in all environments.

14.7 Foundation Design


Drilled shafts are the standard foundation type on high-mast light poles, span overhead signs, mast

arms, monotube, and steel strain poles. See Chapter 7 of this Manual for detailing requirements for

drilled shafts.

14.7.1 Geotechnical Design of Drilled Shaft Foundations

When calculating the embedment length of the drilled shaft, designer can refer to section 13 of

AASHTO-signs. Experience has established a safety factor of 2 produces conservative designs.

14.7.2 Structural Design of Drilled Shaft Foundations

Longitudinally reinforce drilled shaft foundations with a minimum of 1% steel. At a minimum, place

T16 stirrups at 100 mm spacing in the top 610 mm of shaft. In cantilever structures, design for shear

resulting from the torsion loading on the anchor bolt group.

Using 1% steel is conservative for flexural design in most cases. Additional stirrups in the top of the

shaft provide resistance against shear failure in the top of the shaft. Due to torsion, additional stirrups

may be required in cantilever structures.

14.8 Design Loads for Vertical Supports

When 3 or 4 span wire pole structures are connected, analyse the system with wind directions of 0,

45, and 90 degrees. If other angles are used, document the angles in the analysis report.

More refined analysis is typically not required due to the number of approximate assumptions made

in the analysis. Other angles may be analysed and substituted if program results are not consistent

at the specified angle.


PAGE 176

15-ROAD TUNNELS SECOND EDITION – AUGUST 2021

15 ROAD TUNNELS

Reference: AASHTO Technical Manual for Design and Construction of Road Tunnels - Civil

Elements

15.1 General

The AASHTO Technical Manual for Design and Construction of Road Tunnels - Civil Elements

(MRT) (39) provides recommendations for the planning, design, construction, and structural

rehabilitation and repair of the civil elements of road tunnels. The MRT is not an AASHTO

specification. AASHTO design and construction specifications for highway tunnels are under

development considering safety and operations, maintenance, and inspection for road tunnels.

This Chapter is a supplement to the MRT, much as the rest of the Abu Dhabi Road Structures Design

Manual is a supplement to the BDS. Except as modified herein, apply the MRT to the design of road

tunnels in the Abu Dhabi Emirates.

The MRT includes various types of tunnels, including cut-and-cover tunnels, mined or bored tunnels,

immersed tunnels, and jacked box tunnels.

Although there are no applicable mandatory International Standards, Highways Agency (Highways

Agency 1999) (40), Austroads (Austroads 2010a and 2010b) (41) and other publications provide

considerable reference and guidance material in addition to the MRT.

The type of construction (e.g. cut-and-cover, driven, or bored) may influence the cross-section

decision because the resulting cross-sections are different for each type. Bored tunnels are circular,

driven tunnels have a somewhat flatter roof, and cut-and-cover tunnel roofs are generally flat.

The Sequential Excavation Method (SEM), also commonly known as the New Austrian Tunnelling

Method (NATM), discussed in Chapter 9 of the MRT, is a type of mined tunnel construction. SEM

attempts to mobilize the self-supporting capability of the ground to an optimum, thus achieving

economy in ground support by understanding the behaviour of the ground as it reacts to the creation

of an underground opening.

Jacked box tunnelling, discussed in Chapter 12 of the MRT, is a unique tunnelling method for

constructing shallow, rectangular road tunnels beneath critical facilities such as operating railways,

major highways, and airport runways without the disruption of the services provided by these surface

facilities or having to relocate them temporarily to accommodate open excavations for cut-and-cover

construction.

15.2 Definition of Road Tunnels

Any fully enclosed length of roadway may be called a road tunnel, but there is general agreement

that a structure less than 80 m in length is not a tunnel. Various jurisdictions identify a minimum

length of between 80 m and 150 m as the length above which the structure is considered to be a

tunnel.


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A short tunnel may also be termed an underpass but, in general, treat any covered length of road

over 80 m as a tunnel in terms of fire considerations (NFPA 2008) (42).

The Highways Agency defines a road tunnel as a subsurface highway structure enclosed for a length

of 150 m or more (Highways Agency 1999) (43).

15.3 Geotechnical Site Investigations

The geotechnical site investigation is the most important process in planning, design, and

construction of a road tunnel. The geotechnical investigation and risk assessment shall be according

to the Manual for Geotechnical Investigation and Design: (Parts 1 and 2) (Document Reference

Number TR-509 part 1 and 2).

Tunnels are unique structures in that the surrounding ground material is the structural material that

carries most of the ground load. Therefore, geology has even more importance in tunnel construction

than above-ground bridge structures.

15.4 Fire Protection

For fire protection of road tunnels, use NFPA 502 - Standard for Road Tunnels, Bridges, and Other

Limited Access Highways (NFPA 2008) (42). Generally, due to local conditions, clients consider

variations to this standard. The designer shall identify potential deviations before designing tunnels.

This document, a standard produced by the National Fire Protection Association, uses tunnel length

to dictate minimum fire protection requirements:

• 90 m or less: No fire protection requirements.

• 90 m to 240 m: Minor fire protection requirements.

• 240 m or more: Major fire protection requirements.

15.5 Constructability

Select a type of tunnel construction that considers ground conditions, geometric

constraints/requirements, and other factors. In addition to being constructible, the type of

construction must be safe to construct.

In most cases, the designer must consider the need to obtain specialised equipment to make the

proposed type of tunnel construction achievable.

An essential consideration in the design of road tunnels is the constructability of the tunnel and the

safety of the people performing the construction.

15.6 Design Life

Design the main tunnel structure for a design life of 100 years or more. Select a design life for various

elements in the tunnel structure and the ancillary infrastructure based on the nature of the element

on the ease of maintaining or replacing the element. Replaceable items, such as computerised

operating systems, fans, and pumps, may be designed for a much shorter design life.


PAGE 178


Design the underpass structure for a design life of 75 years, which can be extended to 100 years

using cathodic protection according to specifications.

15.7 Design Considerations

15.7.1 Design Elements

Structural design considerations involve the integrity of the natural ground through which the tunnel

passes and the design of structural components to support the traffic and construction equipment.

The relevant structural design elements include:

• Geotechnical integrity of the surrounding ground;

• Strength of support linings;

• Design of running surface support where required (bridge or pavement design as required);

• Structural integrity of roof structures;

• Consideration of tunnel-induced ground movements and settlement;

• Adjacent infrastructure, excavations, and tunnels;

• Fire resistance of structural elements;

• Structural integrity of supports for equipment (e.g. ventilation, lighting, traffic signage,

communication facilities); and

• Design of ancillary structures (e.g. control centre, plant rooms, services buildings).

The structural design of tunnels requires the evaluation of the following:

• Evaluate the minimum hydraulic head adopted as part of the tunnel design, whether the

tunnel is fully tanked or not.

• Consider symmetric and asymmetric loads.

• Analysis of arching may be required, particularly where the cover is less than the width of the

tunnel.

• Incorporate concrete shrinkage, creep, and temperature effects.

• Consider the long-term concrete modulus (particularly in deflection assessments).

• Consider transverse shear keys under inclined tunnels if necessary to resist longitudinal

movement.

• When considering the leakage of water into the tunnel, ensure that no water leaks or drips

onto the tunnel road surface. Treat all tunnels in Abu Dhabi as submerged because of the

presence of a high water table. Therefore, provide a waterproofing membrane on all surfaces

in contact with the ground.


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Use the available literature for more complex tunnels.

15.7.2 Live Load

Design the structural components of road tunnels carrying traffic loads for the live-load models

specified in Sections 2.3.2 and 2.3.6.

Design tunnels (including the roof) for existing and known future loads (e.g. surface traffic loads,

buildings, earth pressures). Provide easements above, below, and around tunnels to ensure that

unintended loads are not imposed on the tunnel.

15.7.3 Seismic Considerations

Reference: MRT Chapter 13

Design road tunnels to withstand the spectral response accelerations given in Table 2-3 for a return period of 1000 years. After the event characterized by these spectral response accelerations, the tunnel may sustain significant damage and a possible disruption to service; however, the tunnel will have a low probability of collapse.

Although most of the Emirate, based on available information, falls in SDC A, the owner may select

SDC B for some areas.

These provisions are intended to achieve minimal damage to tunnels during moderate earthquake

ground motions and to prevent collapse during rare earthquakes that result in higher levels of ground

shaking.

See Section 2.3.4 for more information.

15.8 Tunnel Types

15.8.1 Cut-and-Cover Tunnels


This type of tunnel is constructed in a trench excavated from the surface and is appropriate for

shallow depths in suitable soils. Special cases include:

• Use of temporary sheet piles, contiguous pile or diaphragm walls. Do not use contiguous

piles or diaphragm walls as the permanent wall of the tunnel. It is not possible to waterproof

these walls. They are used only as temporary walls so that a structure waterproofed on the

outside can be constructed from within the temporary diaphragm-walled tunnel; and

• “Top down” construction.

Design considerations for cut-and-cover tunnels include the:

• Ease with which the soil can be excavated,

• Depth of water table below the natural surface,

• Availability of the surface material being removed for backfilling during the construction,

• Period and the consequences for the subsequent land use,


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• Need to dewater/pump the excavation,

• Stability and earth pressure on the sidewalls and loads and surcharges on the tunnel roof,

• Temporary construction loads,

• Preclude water leakage

• Uplift forces, and

• Access restrictions.

In sections of cut-and-cover tunnel in soft ground conditions, settlement adjacent to the structure

may occur. To account for control over the settlement, limit the deflection of the embedded wall

(contiguous pile wall or diaphragm wall) by propping, tie backs, or similar measures.

15.8.2 Mined or Bored Tunnels

References: MRT Chapters 6 through 9

Construct mined or bored tunnels, sometimes called driven tunnels, where there is sufficient ground

cover.

Typical mined tunnelling approaches use road headers, excavators, or drill-and-blast excavation

techniques.

For mined tunnels, a primary support is often required before the secondary lining is placed. The

lining may comprise cast-in-situ concrete, precast segments, or shotcrete (with or without rock bolts

depending on the material excavated). The cost of liners can vary widely depending on the soil types,

presence of swelling clays, soft rock, and/or water.

Typical bored tunnels use single shield, double shield, earth pressure balance, slurry shield, and

compressed air tunnel boring machines (TBMs).

In tunnels excavated using a tunnel boring machine (TBM), a liner (often precast segmental

concrete) is placed continuously behind the TBM as it advances creating a circular cross-section.

For bored tunnels, the timing of the placement of the liner behind the TBM depends on the integrity

of the material being excavated. The TBM may grip the sides of the tunnel (gripper) or thrust off the

liner (using hydraulic rams) as it advances. There are many different types of TBMs for various

situations.

Where soft ground conditions are common, earth pressure balance machines, slurry shield tunnel

boring machines, and mixed shield TBMs have been used.

In these shielded machines, the cutting head is enclosed within an air/watertight bulkhead that

stabilises the excavation face. Behind the sealed bulkhead, the rest of the tunnelling operations

remain under normal atmospheric pressure.

Tunnelling materials (e.g. earth, rock, clay, water, bentonite, lubricants) are directed through the

TBM cutting head and out the rear end. In addition to the TBM, there is a considerable amount of

material and transportation equipment that removes these products, recycles the bentonite, and

delivers power and hydraulics, water, chemicals, precast segments, or other materials for the lining.


PAGE 181


Air, water, lubricants, and chemicals can be lost through the tunnel face, side, and tail. This requires

continuous monitoring of face pressure, rate of advance, quantity of excavated material, and

chemical usage to maintain face integrity, skin, and tail seal.

15.8.3 Immersed Tunnels


Select the immersed tunnel construction for underwater crossings where conditions are suitable.

This may occur where it is not appropriate to use bored tunnels under the water (depth required,

material properties).

Precast reinforced concrete sections of the tunnel are manufactured in a dry dock, floated and towed

to their location above a dredged channel, sunk into position, and joined to previous sections.

Additional cells are often used to create extra buoyancy during placement, and these cells may then

be used for other functions such as placement of tunnel services and evacuation. Note that a tunnel

of this type with no cell would rarely be acceptable and, then, only for short tunnels.

15.9 Tunnel Lining

Reference: MRT Chapter 10 and BDS Article 12.13

Design steel tunnel liner plates in accordance with BDS Article 12.13. Construction will conform to

Section 25 of the AASHTO LRFD Bridge Construction Specifications (BCS) (44).

Use Chapter 10 of the MRT to design cast-in-situ concrete linings, precast segmental concrete

linings, and shotcrete linings.


PAGE 182

16-BRIDGE EVALUATION SECOND EDITION – AUGUST 2021

16 BRIDGE EVALUATION

16.1 Load Rating

16.1.1 General

The AASHTO Manual for Bridge Evaluation (MBE) (45) serves as a standard for bridge inspection

and rating. This Section is a supplement to the MBE with respect to bridge rating and, in particular,

Section 6A on ratings using the Load and Resistance Factor Rating (LRFR) methodology.

The LRFR methodology includes three levels of load rating:

• design load rating,

• legal load rating, and

• permit load rating.

16.1.2 Importance of Load Rating

The load rating of bridges is an important function in the Abu Dhabi Emirates. It allows the

comparative evaluation of existing structures. Bridges designed to former standards are compared

to contemporary standards, in conjunction with an appraisal of the bridge condition. Load rating is

also used to post bridges with insufficient load-carrying capacity and to evaluate permit overloads

on structures; see Sections 16.3 and 16.4, respectively.

16.1.3 Methodology

Load rate all bridges by the Load and Resistance Factor Rating (LRFR) methodology in Section 6A

of the MBE. The use of this single methodology provides uniformity in ratings.

The LRFR bridge-rating methodology is fully consistent with the BDS bridge-design methodology.

16.1.4 Thresholds for Re-Rating Existing Bridges

Re-rate a bridge to determine the new load-carrying capacities when a bridge inspection reveals a

quantifiable change in the bridge condition from deterioration or damage (e.g. increased metal

section loss). If the load-carrying capacity falls below certain limits, the bridge must be posted; see

Section 16.3.

16.1.5 Limit States for Load Rating

Use all limit states in MBE Table 6A.4.2.2-1 to load rate bridges in the Abu Dhabi Emirate.

The researchers who developed the original draft of the MBE included all appropriate limit states

necessary to operate highway bridges. Upon adoption, AASHTO made several of the limit states

(those shown as shaded cells in MBE Table 6A.4.2.2-1) optional for political reasons.


PAGE 183


( ))IMLL()(

)DW(()DC)(CRF

LL

DWDC

+

−−=

nnsc RC =

85.0sc

RfC =

16.1.6 Dimensions

Show dimensions from the as-built plans unless measured dimensions, as part of a visual inspection,

deviate significantly from the plan dimensions. With reported deterioration, the Evaluator may reduce

the structural dimensions of a deteriorated component based on engineering judgment derived from

a visual inspection of the bridge to discount deteriorated material.

Base the section properties of composite girders on the full depth of the composite deck slab unless

deterioration is noted.

16.1.7 The LRFR Load-Rating Equation

Reference: MBE Article 6A.4.2.1

Use the following general equation for rating factor, RF, to determine the load rating of each

component and connection of the bridge for each force effect (i.e. axial force, flexure, shear). The

equation is used for all three levels of the LRFR methodology:

Equation 16.1

For the strength limit states:

Equation 16.2

Where:

Equation 16.3

For the service limit states:

Equation 16.4

where: RF = rating factor

C = capacity

fR = allowable stress specified in the BDS

Rn = nominal member resistance

DC = dead-load effect due to structural components and attachments


PAGE 184


DW = dead-load effect due to wearing surface and utilities

LL = live-load effect

IM = dynamic load allowance

γDC = dead-load load factor for structural components and attachments

γDW = dead-load load factor for wearing surface and utilities

γLL = evaluation live-load load factor

φc = condition factor

φs = system factor

φn = BDS resistance factor

Use the application of the condition and system factors for load rating in the Abu Dhabi Emirate,

although they are optional in the MBE.

The researchers who developed the original draft of the MBE included the condition and system

factors as appropriate to operate highways bridges. Upon adoption, AASHTO made these factors

optional for political reasons.

16.1.8 Analytical Methods for the Load Rating of Post-Tensioned Box

Girder Bridges

Perform load rating in accordance with AASHTO MBE Article 6A.5.11.

16.2 Design Load Rating

Reference: MBE Articles 6A.1.7.1 and 6A.4.3

Design-load rating is the first level of rating in the LRFR methodology. Rate all bridges at this level.

Specify the design live load (ADVL) as in Chapter 2.

The design-load rating is used to assess the bridge’s adherence to the applicable design standard.

Two levels of reliability are included in the design-load rating level reflected by two different live-load

load factors for application in the general LRFR load-rating equation. Bridges with adequate design-

load capacity (i.e. RF 1) at the inventory level require no further evaluation.

The two levels of design-load rating are analogous to the traditional inventory and operating levels.

16.3 Legal-Load Rating and Load Posting

Reference: MBE Articles 6A.1.7.2, 6A.4.4 and 6A.8

16.3.1 Legal-Load Rating

Legal-load rating is the second level of load rating in the LRFR methodology. Rate bridges that do

not have sufficient design-load capacity (the first level of rating in the LRFR methodology) at the

legal-load level to determine the need to post or strengthen the bridge.

Legal-load rating provides a single safe load capacity for the ADVL model of Chapter 2. Use the

generalized live load factors for routine commercial traffic for the ADVL model.


PAGE 185


The legal-load ratings are used in decision-making for bridge posting or strengthening.

16.3.2 Load Posting

Close the bridge when it is not capable of carrying a minimum gross live-load weight of 5 tons.

Do not post the bridge when the rating factor, RF, calculated for the ADVL is greater than or equal

to 1.0. Otherwise, use the posting load as the rating factor, RF, times 45 tons.

16.4 Permitting and Permit-Load Rating

Reference: MBE Article 6A.1.7.3 and 6A.4.5

16.4.1 Permitting

Permits can be issued for single trips, multiple trips, or on an annual basis. Routine or annual permits

are usually valid for unlimited trips over a specified period of time for vehicles of a given axle

configuration within specified weight limits. Special or limit-crossing permits are usually valid for a

single trip or limited number of trips for a vehicle of a given axle configuration within specified weight

limits. Special permits may be allowed to mix with normal traffic or may be required to be escorted

in a manner that controls the speed, position, and proximity with regard to other traffic. The

Department of Transport has prepared permitting procedures for exceptional vehicles.

16.4.2 Permit-Load Rating

Permit-load rating is the third level of load rating in the LRFR methodology. Only consider bridges

that have sufficient load-carrying capacity for the Abu Dhabi legal load for permit-load rating.

Apply a live-load factor of 1.20 to the specific permit load for permit-load rating.

The calibrated load factors specified in MBE Article 6A.4.5.4.2a for use in the general LRFR load-

rating equation are specified for both types of permits mixing with or without traffic as a function of

ADTT. The load factors are intended to be used in conjunction with the AASHTO approximate

analysis method using distribution factors. Refined analysis is required in the Abu Dhabi Emirate for

load rating. Thus, the specified load factors in MBE Article 6A.4.5.4.2a are not applicable in the Abu

Dhabi Emirate.

16.5 Load Testing of Bridges

Reference: BDS Article 4.8.2 and MBE Section 8

16.5.1 General

The purpose of the load testing is to evaluate the structural performance and functional adequacy of

the bridge tested as an exact full-sized model with an appropriate margin of safety.

16.5.1.1 Classifications

Two basic types of load tests are available for bridge evaluation — diagnostic tests (see MBE Article

8.8.2) and proof tests (see MBE Article 8.8.3). Diagnostic tests determine certain response

characteristics of the bridge, or validate analytical procedures or mathematical models. Proof tests


PAGE 186


establish the maximum safe load-carrying capacity of a bridge, where the bridge behaviour is within

the linear-elastic range.

Load testing may be further classified as static load tests (see MBE Article 8.4.1) and dynamic load

tests (see MBE Articles 8.4.2). A static load test uses stationary loads to avoid bridge vibrations. The

intensity and position of the load may be changed during the test. A dynamic load test uses time-

varying loads or moving loads that excite vibrations in the bridge. Dynamic tests measure modes of

vibration, frequencies, dynamic load allowance, or obtain load history and stress ranges for fatigue

evaluation.

Diagnostic load tests may be either static or dynamic tests. Proof load tests are mostly static tests.

16.5.1.2 Definitions

“Design Live Load” means the ADVL including the corresponding dynamic load allowance (IM) and

multiple presence factors.

“Test Load” means the actual loads used at each stage of testing.

16.5.2 Load Testing Calculations

Predetermine the Test Load patterns and positions on the bridge deck to simulate load effects due

to the Design Live Load. The amount and configuration of the Test Load spectrum increments

applied during the test produces internal forces (bending moments, shear, and axial forces),

reactions, and deflections, at critical sections, equal to the corresponding Design Live Load values

used in the bridge design. Place the Test Load mutually in standard width design traffic lanes, spaced

across the entire bridge roadway width measured between curbs at pre-marked locations. The Test

Load shall be positioned within the lane so that the maximum effect is achieved. Precast concrete

blocks may be used as truck loads to achieve the required axle loads. Lorries loaded with aggregates

may also be used if the required axle loads can be achieved. Concentrated loads can be applied to

the deck by jacking against dead weight. Perform the load testing for all spans.

During the test, increase the Test Load incrementally to achieve the predetermined maximum live

longitudinal and transverse positive and negative (if any) moments in mid-spans; maximum live

longitudinal negative moments and maximum live transverse negative and positive moments at

internal supports; and maximum live-load reactions at supports.

Provide the theoretical bending moment, shear, and deflection diagrams and reactions for each Test

Load increment. Do not allow their values to exceed the corresponding values under Design Live

Loads.

Calculate and check longitudinal flexural stresses along the bridge at critical sections, so that they

do not exceed the maximum stress limits of the bridge at any time during the test.

16.5.3 Load Testing Method Statement

Perform the load testing after the bridge construction is completed and all superimposed dead loads

(pavement layers, parapets, footway, etc.) are applied.


PAGE 187


Apply the Test Load gradually in increments before reaching the final total amount, in a period not

less than five hours. Apply the maximum Test Load for a minimum period of twelve hours, and

perform the unloading gradually for mid spans but immediately for supports.

After each Test Load, measure the incremental deflections accurately and at a sufficient number of

points (at least two points every one fifth of each span) to produce sufficient data to plot the

theoretical and measured deflected shapes of the structure.

Take deflection measurements at piers and abutments for each Test Load increment, and for the

recovery case, to verify that the differential settlements or rotations of the supports do not exceed

the corresponding design values.

Measure elastic deflections, after the removal of each Test Load increment, to check recovery such

that any permanent deflection is minimal and within limits. The ratio of permanent irreversible

deflection to the total deflection will not exceed 0.2.

Provide and plot comparison tables and linear relationships between theoretical and measured

deflections for each Test Load increment to determine the slope of the compatibility line.

The general and structural safety of the bridge during testing is the responsibility of the consultant.

The consultant ensures that the elastic limit of the bridge is not exceeded and no damage is done to

the bridge or its components due to the test. Prestress steel, in case of prestressed concrete, must

not suffer any excessive losses due to faulty overload.

Submit the Load Testing Method Statement of bridge at least two months before the testing date,

including the following:

• the current status (or the status at testing time) of bridge to be tested;

• traffic management;

• load testing procedure;

• bridge deck discretization (measurement reference positions);

• dial gauges locations, sensitivities, etc., Deflected Cantilever Displacement Transducers

(DCDT) gauges, Linear Variable Displacement Transducers (LVDT) gauges and Demec

gauges;

• type of truck to be used in the test, its load capacity, load to be used in the test and wheel

load after each Test Load increment;

• loading test truck configurations in the longitudinal and transverse directions for each Test

Load increment;

• bridge deck moment influence lines for each test node;

• the bending moment, shear force, and theoretical deflection diagrams and support reactions

due to the Test Load;


PAGE 188


• a comparison between Design Live Load moments, shears, reactions, and deflections, and

their corresponding Test Load values at test nodes for each Test Load increment; and

• any additional information the consultant may find useful for the execution of the Load testing.

Conduct performance inspections on bearings to check that no additional restraint is present. Ensure

that the vertical deflections and compression of bearings and differential translations (i.e.

temperature-induced movements at expansion joints) are considerably below the design (or

manufacturer’s) limits. Determine the bridge deck temperature by means of thermocouples.

16.5.4 Load Testing Analysis Report

Submit a comprehensive Load Testing Analysis Report two weeks after the load testing is

completed. This report will include, but not be limited to the following:

• A summary of all items mentioned above in the Method Statement;

• The Interpretation of the test results;

• Loading diagrams for all Test Load increments and the unloading cases;

• A table containing measured vs. theoretical deflections for each Test Load increment;

• Longitudinal measured and theoretical deflection curves along the bridge centerline for each

Test Load increment;

• Graphs showing the measured and the theoretical deflections;

• Any local effects; and

• Final analysis, conclusions, and requirements for the bridge load testing.


PAGE 189

CITED REFERENCES SECOND EDITION – AUGUST 2021

CITED REFERENCES

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Association of State Highway and Transportation Officials, 2012.

2. British Highways Agency. CG-300 Technical Approval of Highway Structures (Revision-0)

(Formerly BD 2/12)

3. ASCE. Minimum Design Loads for Building and Other Structures. Reston, VA : American Society

of Civil Engineers, 2010. ASCE/SEI 7-10.

4. AASHTO. Guide Specifications for LRFD Seismic Bridge Design. Washington, D.C. : American


5. Pascucci, V., M. W. Free and Z. A. Lubkowski. Seismic Hazard and Seismic Design

Requirements for the Arabian Peninsula Region. Beijing, China : Proceedings of the 14th

World Conference on Earthquake Engineering, October 12-17, 2008.

6. Hambly, E.C. Bridge Deck Behaviour. 2nd Edition. London & New York : Taylor & Francis, 1991.

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York : s.n., 1999.

8. ACI. Building Code Requirements for Reinforced Concrete and Commentary. Detroit, MI :

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9. NCHRP. Verification and Implementation of Strut-and-Tie Model in LRFD Bridge Design

Specifications. [ed.] B. T. and D.H. Sanders Martin. Washington, D.C. : NCHRP 20-7, Task

217, Final Report, National Academies, November 2007.

10. Portland Cement Association. AASHTO LRFD Bridge Design Specifications Strut-and-Tie

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(PCA), 2004.

11. PCI. Bridge Design Manual. 3rd Edition. Chicago, IL : Prestressed/Precast Concrete Institute,

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1999. ACI 315-99.

14. DOT, Florida. Structures Design Guidelines. s.l. : Florida Department of Transportation, 2012.

15. AASHTO/NSBA Steel Bridge Collaboration. Guidelines for Design for Constructability. G12.1-

2003.

16. FHWA. Uncoated Weathering Steel in Structures. Washington, D.C. : US Department of

Transportation, Federal Highway Administration, October 1989. Technical Advisory

T5140.22.


PAGE 190


17. —. Forum on Weathering Steel for Highway Structures: Summary Report. Washington, D.C. :

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D.C. : American Iron and Steel Institute, 1995.

19. ANSI/AASHTO/AWS. Bridge Welding Code. Miami, Florida : American Welding Society, 2010.

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22. FHWA. Manual for Design, Construction, and Maintenance of Orthotropic Steel Bridges.

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2012.

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25. NCHRP. Barker, R. M., J. M. Duncan, K. B. Rojiani, P.S.K. Ooi, C. K. Tan and S. G. Kim.

Manual for the Design of Bridge Foundations: Shallow Foundations, Driven Piles, Retaining

Walls and Abutments, Drilled Shafts, Estimating Tolerable Movements, Load Factor Design

Specifications, and Commentary. Washington, D.C. : NCHRP Report 343, National

Academies, 1991.

26. ADSC. Drilled Shafts: Construction Procedures and Design Methods. Irving, TX : ADSC: The

International Association of Foundation Drilling, 1999. TL4.

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28. US Navy. Foundations and Earth Structures. Alexandria, VA : Department of the Navy, Naval

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PAGE 191


32. —. Earth Retaining Structures: Reference Manual. Washington, D.C. : US Department of

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032.

36. AASHTO. LRFD Guide Specifications for Design of Pedestrian Bridges. 2nd Edition.

Washington, D.C. : American Association of State Highway and Transportation Officials,

2009.

37. —. Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic

Signals. 5th Edition. Washington, D.C. : American Association of State Highway and

Transportation Officials, 2009.

38. —. Standard Specifications for Transportation Materials and Methods of Sampling and Testing.

31st Edition. Washington, D.C. : American Association of State Highway and Transportation

Officials, 2011.

39. —. Technical Manual for Design and Construction of Road Tunnels - Civil Elements. 1st Edition.

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40. Highways Agency. Design Manual for Roads and Bridges. London, UK : Highways Agency,

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41. Austroads. Guide to Road Tunnels, Part 1: Introduction to Road Tunnels. Sydney, Australia :

Austroads, Publication No. AGRt01/10, 2010.

42. NFPA. Standard for Road Tunnels, Bridges and Other Limited Access Highways. s.l. : NFPA

502, National Fire Protection Association, 2008.

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Australia : Austroads, Publication No. AGRT02/10, 2010.

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Highway and Transportation Officials, 2010.


PAGE 192

INDEX SECOND EDITION – AUGUST 2021

INDEX

A

AASHTO Guide Specifications for LRFD Seismic Bridge Design

........................................................................................ 19

AASHTO Manual for Bridge Evaluation ............................. 176

AASHTO Standard Specifications for Structural Supports for

Highway Signs, Luminaires, and Traffic Signals ............ 167

AASHTO Technical Manual for Design and Construction of

Road Tunnels - Civil Elements ....................................... 170

AASHTO/NSBA Steel Bridge Collaboration’s Guidelines for

Design for Constructability ............................................. 59

Abu Dhabi Vehicular Load ................................................... 12

Abutments ............................................... 32, 34, 56, 120, 142

Cantilever ..................................................................... 122

Integral ............................................. 77, 92, 121, 123, 153

MSE Walls ..................................................................... 122

Seat ....................................................................... 120, 123

Semi-Integral ................................................................ 121

Wingwalls ..................................................................... 119

Abutments/Wingwalls

Approach Slab Support ................................................. 120

Construction Joints ....................................................... 123

Dead Load ..................................................................... 120

Design and Detailing ..................................................... 120

Expansion Joints ........................................................... 120

Live-Load Surcharge ..................................................... 120

Reinforcement .............................................................. 120

Skewed Bridges ............................................................ 120

Aesthetics ........................................................ 4, 77, 123, 158

American Concrete Institute (ACI) – Analysis and Design of

Reinforced Concrete Bridge Structures .......................... 24

American Concrete Institute (ACI) 318 ................................ 54

Anchor Bolts ...................................34, 46, 147, 152, 153, 168

Anchored Walls ......................................................... 131, 132

ANSI/AASHTO/AWS Bridge Welding Code D1.5 .................. 79

Approach Slabs .............................................. 82, 98, 143, 158

Approximate Analysis .......................................................... 20

Arch Culverts ............................................................. 162, 164

Asphalt Wearing Course ...................................................... 11

Asphaltic Plug Joints .................................................. 145, 146

B

Barrier Rails ......................................................................... 82

Bearing Stiffeners .................................................. 74, 77, 160

Bearings ...................... 3, 22, 29, 67, 71, 74, 99, 122, 143, 149

Anchor Bolts ................................................................. 150

Bearing Plate Details ..................................................... 151

Camber ......................................................................... 151

Effect of Camber and Construction .............................. 149

Integral Abutments ...................................................... 151

Lateral Restraint ........................................................... 152

Movements .......................................................... 149, 150

Movements and Loads ................................................. 149

Serviceability, Maintenance, and Protection

Requirements .......................................................... 150

Thermal Movements ............................................ 149, 156

Types ............................................................. 149, 152, 153

Bents ................................................................................... 88

Bolted Connections ..................................................... 78, 159

Bolted Splices ...................................................................... 81

Bolts ........................................................... 66, 69, 75, 81, 168

Bridge Barriers .................................................................... 98

Bridge Design Checklists ....................................................... 5

Bridge Rails ......................................................................... 96

Buried Structures .............................................................. 165

C

Camber.......... 51, 52, 53, 55, 69, 70, 85, 87, 88, 149, 151, 197

Bearing Rotation .......................................................... 149

Structural Steel Girders .................................................. 70

Camber Diagram ................................................................. 57

Cantilever Walls

Concrete ............................................................... 131, 132

Chloride Content ................................................................. 31

Closed-Cell Compression Seal ........................................... 146

Closure Pour ....................................................... 42, 57, 92, 94

COM624 ............................................................................ 102

Compressive Strength of Concrete ..................................... 32

Concrete Cover ............ 26, 33, 43, 52, 84, 125, 129, 136, 169

Concrete Decks ................................................................... 82

Asphaltic Wearing Surface ............................................. 85

Camber Diagram ............................................................ 89

Closure Pours ................................................................. 94

Construction Joints ................................................... 88, 89

Crack Control .................................................................. 88

Empirical Design ............................................................. 82

Exposure Factor ............................................................. 84

Haunches........................................................................ 85

Length of Reinforcement Steel ...................................... 85

Live-Load Moments ........................................................ 82

Longitudinal Construction Joints .................................... 94

Longitudinal Joints ......................................................... 96

Minimum Negative Flexure Slab Reinforcement ........... 88

Minimum Thickness ....................................................... 84

Phase Constructed Decks ............................................... 91

Pouring Sequence .......................................................... 91

Precast Concrete Deck Panels ........................................ 83


PAGE 193


Protection of Reinforcing Steel ....................................... 82

Reinforcing Bar Size ........................................................ 85

Reinforcing Steel Spacing ............................................... 84

Reinforcing Steel Strength .............................................. 84

Shear Connectors ........................................................... 85

Skews ........................................................................ 85, 89

Splices ............................................................................. 85

Strip Method .................................................................. 82

Transverse Construction Joints ....................................... 92

Transverse Reinforcing Steel .......................................... 84

Concrete Girders

Deck Pours ...................................................................... 91

Concrete Pipe Culverts ...................................................... 165

Concrete Strength at Release .............................................. 37

Concrete Stress Limits ......................................................... 36

Construction Joints .........................92, 94, 106, 109, 126, 127

Creep ............................................................................. 12, 38

Cross Frames ............................ 67, 70, 71, 73, 74, 75, 77, 160

Culverts ................................................................. 3, 162, 165

Concrete Cover ............................................................. 164

Dead Loads ................................................................... 163

Design ................................................................... 162, 164

Live Load ....................................................................... 163

Reinforcement .............................................................. 164

Skewed ......................................................................... 164

Span-to-Rise Ratios ....................................................... 162

Wall Thickness .............................................................. 163

Cut-and-Cover Tunnels ...................................................... 173

D

Dead Load .8, 10, 11, 12, 25, 47, 49, 57, 59, 70, 83, 85, 91, 92,

94, 120, 127, 159, 163, 180

Deck Haunches .................................................................... 69

Deck Overhang .............................................................. 91, 96

Deck Reinforcement ............................................................ 85

Deck Thickness ........................................................ 52, 86, 87

Deck-Overhang .................................................................... 78

Deflection ....... 40, 53, 57, 70, 91, 94, 102, 117, 124, 172, 180

Concrete Decks ............................................................... 88

Department of Municipal Affairs ........................................... 1

Design Load Rating ............................................................ 178

DFSAP ................................................................................ 102

Diaphragms ................................................................... 75, 77

Concrete ............................................................. 27, 56, 57

Steel Structures .................................................. 64, 70, 71

Steel Superstructures ..................................................... 67

Direct Tension Indicators ..................................................... 66

Disc Bearings ..................................................................... 154

Distribution of Superimposed Load on Beam-Slab Bridges . 22

Downdrag .............................................. 10, 11, 101, 114, 122

Drilled Shafts ... 32, 36, 99, 101, 103, 106, 107, 109, 112, 117,

121, 124, 140, 169, 194

Abutments .................................................................... 119

Additional Steel Thickness ............................................ 115

Axial Compressive Resistance at the Strength Limit State

................................................................................ 108

Construction Joints ....................................................... 109

Diameter ...................................................................... 109

Downdrag ..................................................................... 109

Group Effect ................................................................. 109

Laterally Loaded Shafts ................................................ 112

Location of Top of Shaft ............................................... 108

Minimum Sizes ............................................................. 109

Reinforcement ............................................................. 108

Resistance Factors ........................................................ 112

Spacing ......................................................................... 108

Structural Design .......................................................... 108

Testing .......................................................................... 115

Usage ........................................................................... 107

Drip Plate ............................................................................ 66

Ductility ............................................................................. 6, 7

Durability .............................................................................. 3

Concrete Structures ....................................................... 33

Dynamic Analysis ................................................................ 23

E

Earth Retaining Systems ................................................... 129

Earthquakes ............................................................. 9, 14, 173

Elastomeric Bearings ............................................ 74, 152, 153

Environmental Classification ............................................... 28

Marine Structures .......................................................... 29

Non-Marine Structures .................................................. 29

Substructure ................................................................... 31

Superstructure ............................................................... 29

Expansion Joints ... 3, 23, 44, 45, 47, 66, 74, 79, 120, 143, 144,

160

Asphaltic Overlay ......................................................... 147

Cover Plates ................................................................. 144

Design .......................................................................... 147

Design Requirements: Movement and Loads .............. 143

Effects of Skew ............................................................. 144

Estimation of Design Movement .................................. 144

Estimation of General Design Thermal Movement ...... 144

Post-Tensioned Bridges ................................................ 147

Selection and Design .................................................... 145

Temperature Range ..................................................... 143

Tributary Expansion Length.......................................... 143

Extreme Event I

Foundations ................................................................. 101

Extreme Event II

Deck Overhang ............................................................... 98

Extreme-Event Load Combinations ....................................... 9

F

Fatigue

Fatigue Resistance.................................................... 69, 83

Fatigue Load ................................................................ 12, 158


PAGE 194


Fatigue Stress Range ........................................................... 68

FBPier ................................................................................ 102

Field Splices ............................................... 67, 70, 81, 92, 159

Expansion Joints ........................................................... 146

Flange Plates ................................................................. 62, 77

Flexural Resistance ...................................... 24, 25, 37, 53, 57

Flexural Steel Reinforcement .............................................. 25

Foundation Design ...................................................... 99, 101

Foundations ....................................23, 99, 101, 117, 142, 194

Bridge Design/Geotechnical Design Interaction ........... 100

Design ............................................................................. 99

Design Methodology ...................................................... 99

Downdrag ..................................................................... 101

Drilled Shafts ........................................................ 107, 169

Driven Piles ................................................................... 112

Geotechnical Report ............................................. 100, 101

Modelling for Lateral Loading ....................................... 117

Pile Caps ....................................................................... 103

Scour ............................................................................. 102

Scour Potential ............................................................. 100

Seismic Analysis ............................................................ 101

Spread Footings ............................................................ 103

G

Geosynthetic Reinforced Soil (GRS) Walls ......................... 142

Geotechnical Considerations ............................................... 99

Geotechnical Report .......................................... 100, 101, 102

Settlement .................................................................... 105

Girder Spacings .............................................................. 71, 96

Girders

Number of ...................................................................... 42

Grade HPS485W .................................................................. 65

Ground Water ..................................................................... 18

Guide Specifications for Design of Pedestrian Bridges ...... 157

Guide Specifications for Seismic Isolation Design .............. 154

H

Haunches

Reinforcement ................................................................ 87

High-Load, Multi-Rotational Bearings ....................... 153, 154

HL-93 ................................................................................... 23

HL-93 Notional Load ............................................................ 12

Horizontally Curved Bridges ........................................ 60, 144

Horizontally Curved Steel Members .................................... 67

I

Immersed Tunnels ............................................................. 175

Inspection Access (Tub Girders) .......................................... 75

Inspection and Maintenance ................................................. 3

Integral Abutments .. 56, 77, 92, 114, 119, 120, 121, 123, 153

Intelligent Transportation Systems ....................................... 3

I-Sections............................................................................. 75

J

Jacking .................................... 3, 12, 46, 71, 74, 122, 150, 180

Jointless Bridges ................................................................ 119

L

Lateral Bracing ....................................................... 69, 75, 158

Legal-Load Rating .............................................................. 178

Limit States ...................... 2, 6, 9, 10, 26, 67, 75, 81, 176, 177

Live Load .. 8, 9, 12, 14, 49, 59, 71, 74, 76, 82, 88, 91, 92, 109,

149, 163, 165, 173, 178, 195

Pedestrian Bridges ....................................................... 157

Live Load Distribution Factors ............................................. 20

Live-Load Surcharge ............................................. 18, 120, 129

Load Factors .................................................i, xii, 7, 9, 10, 166

Load Factors and Combinations ............................................ 7

Application of Multiple-Valued Load Factors ................... 9

Fatigue-and-Fracture Load Combinations ........................ 9

Service Load Combinations .............................................. 8

Load Modifier ........................................................................ 6

Load Posting ...................................................................... 178

Load Rating ........................................................ 176, 177, 178

Load Rating of Post-Tensioned Box Girder Bridges ........... 178

Load Testing ...................................................................... 179

Load Testing Calculations .................................................. 180

Load-Induced Fatigue.......................................................... 68

LPILE Plus .......................................................................... 102

LRFD Bridge Design Specifications .................................... 1, 2

LRFD Methodology ................................................................ 2

LRFR Load-Rating .............................................................. 177

M

Maintenance of Traffic .......................................................... 3

Mass Concrete .................................................................. 118

Metal Decks ........................................................................ 83

Grid Decks ...................................................................... 83

Orthotropic Steel Decks ................................................. 83

Mined or Bored Tunnels ................................................... 174

Modified Compression Field Theory ................................... 37

Modular Expansion Joint ................................................... 146

MSE Wall Abutments ........................................................ 122

MSE Walls .................. 119, 122, 123, 130, 132, 133, 140, 142

Barrier Rails .................................................................. 142

Copings ......................................................................... 142

Design .......................................................................... 133

End Bents on Piling or Drilled Shafts ............................ 140

End Bents on Spread Footings...................................... 140

External Stability .......................................................... 136

Facing ........................................................................... 136

Flowable Fill Backfill ..................................................... 140


PAGE 195


Minimum Front Face Wall Embedment........................ 135

Minimum Length of Soil Reinforcement ....................... 135

Reinforcement/Facing Connection ....................... 137, 140

Soil Reinforcement Strength ........................................ 137

Multiple Presence Factors ..................................... 13, 23, 180

N

Nongravity Cantilever (Sheet Pile) Walls ........................... 133

O

Operational Importance ........................................................ 7

P

Painting

Pedestrian Bridges ........................................................ 160

Steel Superstructures ............................................. 65, 159

Pedestrian Bridges ........................................... 2, 13, 157, 159

Charpy V-Notch Testing ................................................ 159

Deflections .................................................................... 159

Design ........................................................................... 158

Railings/Enclosures ....................................................... 161

Steel Connections ......................................................... 159

Permanent Loads................................................. 9, 10, 11, 22

Permit Loads ........................................................................ 13

Permit-Load Rating ............................................................ 179

Pier Caps

Cap Width ..................................................................... 124

Diaphragms for Piers Integral with the Superstructure 124

Drop Caps ..................................................................... 124

Usage ............................................................................ 123

Piers ................ 34, 50, 56, 59, 66, 88, 105, 117, 123, 127, 129

Column and Footing Design .......................................... 127

Column Cross Sections ................................................. 124

Columns 34, 35, 36, 77, 101, 103, 105, 106, 109, 110, 123,

124, 126, 127

Construction Joints ............................................... 126, 127

Development of Reinforcement ................................... 125

Drilled Shafts ................................................................ 126

Dynamic Load Allowance .............................................. 127

Lateral Confinement Reinforcement ............................ 125

Longitudinal Reinforcement ......................................... 125

Moment-Magnification ................................................ 127

Multi-Column ............................................................... 126

Pier Caps ........................................25, 27, 34, 44, 123, 127

Pier Walls ...................................................................... 127

Post-Tensioning ............................................................ 128

Reinforcement .............................. 124, 125, 126, 128, 129

Single-Column ............................................................... 126

Splices in Reinforcement .............................................. 125

Transverse Reinforcement ........................................... 125

Pile Caps .................................................................... 106, 129

Bearing Resistance and Eccentricity ............................. 104

Depth ........................................................................... 104

Dynamic Load Allowance ............................................. 104

Joints ............................................................................ 106

Reinforcement ............................................................. 106

Thickness ...................................................................... 104

Piles

Abutments ........................................................... 119, 121

Battered Piles ....................................................... 114, 140

Downdrag Loads........................................................... 114

Driven Piles ........................................... 101, 103, 117, 121

Force Effects ................................................................. 114

Group Effect ................................................................. 115

Laterally Loaded Piles ................................................... 114

Orientation ................................................................... 114

Pile Length .................................................................... 113

Prestressed Concrete Pile ............................................ 113

Reinforced Pile Tips ...................................................... 113

Spacing ......................................................................... 114

Steel H-Pile ................................................................... 113

Steel Pipe Pile ............................................................... 113

Steel Thickness ............................................................. 115

Testing .......................................................................... 115

Types/Selection ............................................................ 113

Uplift Forces ................................................................. 114

Plain Elastomeric Bearing Pads ................................. 153, 155

Polytetrafluoroethyl (PTFE) Sliding Surfaces ..................... 154

Post-Tensioned Box Girders ................................................ 82

Post-Tensioned Bridges....................................................... 37

Post-Tensioning Anchorage ................................................ 27

Post-Tensioning Systems

Access and Maintenance ................................................ 47

Anchorage Details .......................................................... 44

Construction ................................................................... 46

Deck Slabs ...................................................................... 46

Ducts ........................................................................ 39, 42

Expansion Joints ............................................................. 46

Falsework ....................................................................... 47

Grouting ......................................................................... 43

Integrated Drawings ....................................................... 49

Intermediate Diaphragms .............................................. 46

Post-Tensioning Tendons ................................................ 3, 49

Strand Size ...................................................................... 38

Tendon Profile ................................................................ 38

Pot Bearings .............................................................. 152, 154

Precast Concrete Girders

Haunches........................................................................ 87

Precast, Prestressed Concrete Girders ................................ 49

Debonded Strands.......................................................... 55

Design ............................................................................ 49

Detailing ......................................................................... 54

Diaphragms .................................................................... 56

Flexural Resistance ......................................................... 53

Girder Transportation .................................................... 56

Interface Shear ............................................................... 54


PAGE 196


Minimum Reinforcement Requirements ........................ 53

Precast I-Girder Sections ................................................ 51

Sole Plates ...................................................................... 56

Stage Loading ................................................................. 52

Strand Patterns ............................................................... 56

Strand Splicing ................................................................ 56

Prestressing Bars ................................................................. 32

Prestressing Strands ...................................................... 32, 54

Pretensioned/Post-Tensioned Beams ................................. 57

p-y Curves .......................................................................... 117

R

Range of Applicability .......................................................... 20

Redundancy ................................................. 6, 7, 52, 109, 116

Refined Analysis .................................... 19, 68, 114, 127, 169

Reinforced Concrete Boxes ............................................... 162

Reinforcement

Bundled Bars................................................................... 36

Columns .................................................................. 28, 109

Concrete Cover ......................................................... 33, 34

Crack Control Reinforcement ......................................... 25

Deck Reinforcement ................................................. 82, 85

Development Length of Reinforcement ......................... 35

Distribution ..................................................................... 25

Drilled Shafts .................................................................. 28

Fabrication Lengths ........................................................ 33

Flexural Steel .................................................................. 25

Headed Reinforcement .................................................. 28

Lateral Confinement Reinforcement .............................. 28

Spacing ........................................................................... 33

Spread Footings .................................................... 103, 125

Re-Rating Existing Bridges ................................................. 176

S

Seat Abutments ................................................... 71, 119, 120

Sectional Design Model ................................................. 24, 26

Segmental Concrete Box Girders ....................................... 150

Seismic

Acceleration Coefficients ................................................ 16

Soil Type and Profile ....................................................... 16

Seismic Analysis ....................................................... 7, 23, 101

Seismic Isolation Bearings ................................................. 154

Semi-Integral Abutments .......................................... 119, 121

Service Limit State ............................................................... 37

Service Load Combinations ................................................... 8

Settlement ... 8, 11, 12, 47, 100, 101, 103, 105, 109, 120, 121,

122, 131, 132, 134, 140, 142, 149, 174, 194

Shear Connectors ................................................................ 83

Shear Resistance ................................................................. 26

Post-Tensioned Bridges .................................................. 37

Shrinkage12, 38, 70, 88, 91, 94, 143, 144, 148, 149, 150, 152,

156, 164, 172

Sign and Luminaire Supports

Anchor Bolt Connections .............................................. 168

Bolt Types ..................................................................... 168

Bolted Connections ...................................................... 168

Design Loads ................................................................ 169

Foundation Design ....................................................... 169

Silicone Joint Sealant ........................................................ 146

Skews . 23, 34, 50, 60, 70, 71, 72, 76, 77, 90, 92, 96, 120, 122,

140, 144, 145, 197, 198

Soil Nail Walls ............................................................ 131, 133

Soldier Pile Walls ............................................................... 132

Sound Barriers........................................................ 2, 109, 166

Design .......................................................................... 166

Lateral Earth Pressure .................................................. 166

Wind Loads ................................................................... 166

Span Length 13, 19, 20, 38, 50, 54, 59, 75, 100, 105, 124, 194

Spectral Response Acceleration .......................................... 13

Spherical Bearings ............................................................. 154

Spiral Splices ..................................................................... 125

Splices .......................................... 35, 63, 66, 68, 94, 109, 198

Lap Splices ...................................................................... 35

Mechanical Splices ......................................................... 36

Reinforcing Bars ............................................................. 36

Shop Splices ................................................................... 80

Welded ........................................................................... 36

Spread Footings

Bearing Resistance and Eccentricity ............................. 104

Depth ........................................................................... 104

Differential Settlement ................................................ 105

Dynamic Load Allowance ............................................. 104

Joint Movement ........................................................... 105

Joints ............................................................................ 106

Reinforcement ............................................................. 106

Reinforcement Spacing ................................................ 106

Settlement ................................................................... 105

Sliding Resistance ......................................................... 104

Stepped Footings ......................................................... 107

Thickness ...................................................................... 104

Usage ........................................................................... 103

Standard Specifications for Structural Supports for Highway

Signs, Luminaires, and Traffic Signals .................. 157, 167

Static Analysis ..................................................................... 19

Stay-in-Place Forms ....................................................... 91, 94

Steel Finger Joints ............................................................. 147

Steel Girders....................................................... 22, 34, 70, 84

Continuous Decks ........................................................... 89

Deck Pours ..................................................................... 91

Diaphragms/Cross Frames ............................................. 94

Haunches........................................................................ 86

Negative Moment .......................................................... 92

Steel Plates, Minimum Thickness ........................................ 69

Steel Rolled Beams .............................................................. 86

Steel Structures

Diaphragm Spacing ........................................................ 60

Economical Plate Girder Proportioning .......................... 61

Economical Steel Superstructure Design ....................... 59


PAGE 197


Exterior Girders .............................................................. 59

Falsework ....................................................................... 64

Field Splices .................................................................... 63

Flange Plate Sizes ........................................................... 61

Fracture-Critical Members .............................................. 59

Haunched Girders ........................................................... 61

Longitudinally Stiffened Webs ........................................ 64

Rolled Beams .................................................................. 60

Rolled Beams vs Welded Plate Girders ........................... 60

Shop Splices .................................................................... 63

Span Arrangements ........................................................ 59

Transverse Stiffeners ...................................................... 64

Web Plates ...................................................................... 63

Welded Plate Girders...................................................... 60

Steel Superstructures

Camber ........................................................................... 70

Cross Frame Details ........................................................ 73

Fatigue Considerations ................................................... 68

Lateral Bracing ................................................................ 74

Shear Connectors ........................................................... 76

Splices ....................................................................... 78, 80

Stiffeners ........................................................................ 76

Steel Thickness .................................................................. 116

Steel-Reinforced Elastomeric Bearings .............. 153, 154, 155

Stiffeners ........................................................... 60, 63, 69, 77

Strand Splicing ..................................................................... 56

Strength Limit State ............................................................... 6

Strength Load Combinations ................................................. 8

Strip Seal Joint ................................................................... 145

Structural Concrete Design .................................................. 24

Structural Steel

Bolts ................................................................................ 67

Charpy V-Notch Fracture Toughness .............................. 67

Grade 250 ....................................................................... 64

Grade 345 ....................................................................... 65

High-Performance Steel.................................................. 65

Unpainted Weathering Steel .......................................... 65

Structural Supports for Signs and Luminaires ....................... 2

Strut-and-Tie Model .............................................. 24, 26, 126

Substructures ....................... 10, 11, 29, 34, 96, 101, 116, 158

Superimposed Deformations............................................... 10

Superstructure Types .......................................................... 21

Sustainability ......................................................................... 4

T

Temperature Gradient ........................................................ 17

Thermal Movement ............................. 68, 144, 145, 149, 150

Torsion ................................................................................ 27

Total Factored Force Effect ................................................... 6

Transient Loads ............................................................. 12, 50

Earthquake Effects .............................................. 13, 14, 15

Live-Load Surcharge ....................................................... 18

Transverse Construction Joints ........................................... 92

Transverse Deck Loading .................................................... 23

Transverse Edge Beam .................................................. 96, 97

Transverse Intermediate Stiffeners..................................... 76

Transverse Stiffeners ....................................... 63, 64, 77, 160

Tunnels

Design Considerations .................................................. 172

Design Life .................................................................... 171

Fire Protection ............................................................. 171

Geotechnical Site Investigations .................................. 171

Lining ............................................................................ 175

Live Load ...................................................................... 173

Seismic ......................................................................... 173

Types ............................................................................ 173

U

Uniform Temperature ......................................................... 17

Unit Weight of Concrete ..................................................... 11

Unpainted Weathering Steel .............................................. 65

Urban Planning Council ......................................................... 1

Utilities ........................................................... 3, 195, 196, 197

V

Vertical Clearance ....................................................... 60, 159

Vibration ............................................................................. 23

W

Walls ................................................................................. 129

Water Load ......................................................................... 12

Web Plates .......................................................................... 77

Welded Connections .............................................. 74, 79, 167

Welded Wire Reinforcement ............................................ 164

Wind Load

Pedestrian Bridges ....................................................... 157

Wind Loads ................................................................... 13, 22

Wingwalls .......................................................................... 123


PAGE 198

APPENDIX A SECOND EDITION – AUGUST 2021

APPENDIX A

STRUCTURE DESIGN CHECKLIST


❖PROJECT INFORMATION

• Project Name: • Designer:

• Structure Name: • Checker:

• Highway No.: • Drafter:

• Location: • Reviewer:

• NOTE: Each task, when applicable & completed, is Checked (Y, N, N/A), Dated and Initialled by the Designer, Checker and Reviewer.

Items Y N N/A Designer DATE Checker DATE Reviewer DATE

1. CONCEPT DESIGN

Data Collection

Project Scope

Vicinity Map or Data

Geotechnical Report

Hydraulic Report

Grade & Alignment

Location Narrative Concept Design Report (AIP) Title Block with location, Structure Number

General Background: Project Development & Justification

Design Objectives Purpose/Function of the Proposed Structure

Right-of-Way Restrictions

Permits and Restrictions

Utility Conflicts or Restrictions

ITS Strategy

Railroad Clearances & Restrictions

Geometry and Layout: Roadway Width, ADT, Grades & Alignment and Clearance

Sidewalks, Bridge Railings & Protective Screening

Hydraulics: Waterway Openings, High Water Elevation and Clearances

Embankment or Bent Protection Floodway Information, when appropriate

Foundations: Piling, Drilled Shafts, Spread Footings

Fills, Surcharges

Settlement

Lateral Earth, Seismic Loads

Liquefaction Potential

Aesthetic Requirements:



Features on Railing, Piers, walls etc.

Design and Service Life

Selection of Structure Materials

Construction Sequence

Structure Features: Span Length & Span Arrangements

Type of Superstructure

Type of Bents & Location

Articulation of Structure Stage Construction & Detour Requirements

Design Concepts (decision/assumptions):

Building a New Structure vs. Widening Existing One

Use a Bridge vs. Culvert

Foundation Support Assumptions Assumed Pile or Drilled Shaft Bearing Capacity Loads

Assumed Lateral Soil Pressure Against End Bent

Seismic Load Assumptions Environmental Assessment Considerations:

Project Timing and Chronology

In-Water Work Period

Bird Nesting

Proposed Treatment of the Runoff Number & sizes of bents/footings added for new Structure. Discuss construction of new footings, bents & piles.

Type of isolation methods used during construction (i.e., coffer dam)

Extent and duration of in-water work (i.e. heavy machinery in wetted channel)

Amount or extent of fill or riprap

Other Considerations:

Existing Conditions

Constructability

Potential Risks and Hazards Coordination with Stakeholders Authorities

Obtaining NOCs from Service Authorities.

Concept Drawings

General and Structural Notes Alignment Data

Roadway Width

Intersection Stations & Angles

Span Lengths & Numbers

Angles between Bents & Centerline

Existing Structures

Right-of-Way Lines Demolitions

Utilities

ITS North Arrow Location map (w/North Arrow, Project Location Arrow and Nearest Town)



Live Load Loading (sketch and note)

Elevation Datum

Existing Ground Line

High Water Elevation

Proposed Ground Line Hydraulic Data

Roadway Clearances

Footing Elevations & Pile Types

Datum Elevation

Concept Architectural Details Concept Cost Estimate Based on rough approximate calculations per square meter

Using projected quantities for tall abuts

2. PRELIMINARY DESIGN

General

Detours/Traffic Staging

Type of Bridge Railing

Movement (Expansion/ & Fixed) Joints

End Slope & Protection

Typical Bent Section

Guardrail Transitions

Plans

General and Structural Notes General Arrangement Drawings Plan & Elevation Drawings:

Foundation Footing Plan shown

Alignment & Bearing shown

Skew Angles shown

Bent Fixity (free, exp., hinge, etc.) shown

Slope Paving shown

Foundation Elevations

Pile Bearing or min. Tip Elevation shown

Drainage details

Stationing shown

Clearances shown

Railroad

Navigation

Highway

Location Map shown

Existing Structure shown

Utilities shown & located

ITS infrastructure shown and located

Grade Line Diagram shown

Elevation Datum shown

North Arrow shown

Hydraulic Data & High Water Mark shown

Superstructure Details:

Deck Elevation – Shown

Bearing Devices – Shown & Detailed

No. of Bearing Devices – Given



Expansion Allowances – Shown

Joints – Shown & Detailed


Located & Dimensioned

Cross Sections – Shown

Pre-stressing Details – Shown

Interim Bars – Shown

Bar Extensions – Adequate

End Anchorages of Longitudinal Bars – Sufficient

Post-tensioning Data – Included

Pier Details:

Column Steel – properly dim. w/splices

Neg. moment at X-Beam – Reinforced

Footing Elevations – Shown

Skew Angles – Shown

Hinges – Shown & Detailed

Seismic Restraints – Shown & Noted

Other necessary details for Preliminary Design:

3. DETAILED DESIGN

Detailed Drawings General and Structural Notes General Arrangement Drawings Plan & Elevation Drawings:

Footing Plan shown

Alignment & Bearing shown

Skew Angles shown

Bent Fixity (free, exp., hinge, etc.) shown

Slope Paving shown

Foundation Elevations

Pile Bearing or min. Tip Elevation shown

Drainage Details

Station and Layout Coordinates shown

Clearances shown

Railroad

Navigation

Highway

Minimum Construction Clearances shown

Rail Ends shown

Location Map shown

Detour shown

Existing Structure shown

Utilities shown & located

Grade Line Diagram shown

Elevation Datum shown

General Notes complete



Accompanying Drawings shown correctly

North Arrow shown

Hydraulic Data & High Water Mark shown


Deck Elevation – Shown

Bearing Devices – Shown & Detailed

No. of Bearing Devices – Given

Expansion Allowances – Shown

Camber Diagram – Shown

Joints – Shown & Detailed

Stage Construction – Detailed

Pour Schedule – Shown

Concrete Finish Sketch – Shown

Other Details:

Located & Dimensioned

Cross Sections – Shown

Reinforcement Details

Prestressing Details – Shown

Interim Bars – Shown @ Top of Stem

Bar Extensions – Adequate

End Anchorages of Longitudinal Bars – Sufficient

Post-tensioning Details/Data – Included

Pier Details:

Column Reinforcement Steel – properly dim. w/splices

Neg. moment at X-Beam – Reinforced

Foundation Elevations – Shown

Skew Angles – Shown

Utility Holes – Shown & Noted

Hinges – Shown & Detailed

Seismic Restraints – Shown & Noted

Guardrail Connections at End Bents

Concrete Finish – Shown

Miscellaneous Details:

Approach Slab, Railing, Joints, Waterproofing etc.

Specifications

Prepare & Assemble:

Specifications

Supplemental Specifications

Special Provisions

Bid Item Names Check

Bid Item Quantities Check

Specials Verify & Review

Cost Estimates

Calculate Quantities for All Materials



Construction Time Estimate:

Graph Format

Critical Stages Shown

Design Calculations

Analysis & Design of structural Components

Documentation of work with:

Hand calculations, if required

Computer input and output

Detailed Design Calculations Including a brief summary for Design Straining Actions “bending moments, shear forces and bearing loads” for key Structural Elements

Design Verification Report and Design Completion Certificate

Durability Report, if required

Road Structures Design Manual - Abu Dhabi - Jawdah

Documents

Transcript of Road Structures Design Manual - Abu Dhabi - Jawdah