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International Journal of Civil Engineering and Technology (IJCIET)

Volume 8, Issue 4, April 2017, pp. 431–440 Article ID: IJCIET_08_04_050

Available online at http://iaeme.com/Home/issue/IJCIET?Volume=8&Issue=4

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

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A PARAMETRIC STUDY OF INTEGRAL

BRIDGES SUBJECTED TO THERMAL

LOADING

Surana Samyak

Student, Master of Technology, Structural Engineering,

VIT University, Vellore-632014, Tamil Nadu, India

TP Manoj

Senior Design Consultant, Bridges and Metros Department,

L&T Infrastructure Engineering Ltd. Mumbai-400031,

Maharashtra, India

Santhi A.S

Professor, Department of Structural and Geotechnical Engineering,

VIT University, Vellore-632014, Tamil Nadu, India

ABSTRACT

Bridge construction has maintained a worldwide level of importance in the

construction industry. Bridges are the key elements in any road network. An industrial

8 span integral bridge structure having dimensions 261m*12.5m along with open

foundation is modelled using STAAD. Pro software as a 3D grillage model and all the

required loads were applied to the integral bridge structure as per IRC 6:2014 and IRC

5:2015. Only 4 span model is created due to the presence of an expansion joint after 4

spans with another similar 4 span structure in mirror. After extracting the bending

moments and shear forces for the various sections taken along the longitudinal and

transverse direction, the load combinations were formed as per IRC: 6-2014 and design

is performed in accordance with IRC: 112-2011 for Ultimate Limit State and

Serviceability Limit State. The design changes as per the change in parameters viz.

structural stiffness, pier geometry, concrete grade etc. and the behavior of integral

bridge was then studied specifically for thermal loading in accordance to the changing

parameters, as they are dominant in integral bridges. Results helps us in understanding

how the parameters on change, affects the bridge superstructure and substructure and

how they respond structurally.

Key words: Bridge, Integral, Limit State, Parameters, Span, Thermal Loading, Etc.

A Parametric Study of Integral Bridges Subjected To Thermal Loading


Cite this Article: Surana Samyak, TP Manoj and Santhi A.S, A Parametric Study of

Integral Bridges Subjected To Thermal Loading. International Journal of Civil

Engineering and Technology, 8(4), 2017, pp. 431–440.

http://iaeme.com/Home/issue/IJCIET?Volume=8&Issue=4

1. INTRODUCTION

Since ancient times, bridges have been the most visible testimony to the contribution of

engineers. Bridge is a structure providing passage over an obstacle without closing the way

beneath which may be for roads, railways, pedestrians, a canal or a pipeline. Bridges are a

crucial part of the overall transportation system as they play very important role in evacuation

and emergency routes for rescues, first-aid and transport. A bridge section is selected

exclusively on the basis of the building location, topography, loading conditions, expected

vehicle passing and various other parameters.

Integral bridges can be defined as bridges with monolithic joints between the

superstructure and substructure. They are basically portal frames with a single span or multiple

spans. Integral bridges have gained importance due to the following advantages: More material

efficient structurally viz., continuity of superstructure, flexibility of substructure, better

optimisation in design is; Less maintenance as the elements like bearings and expansion joints

are avoided/reduced. The expansion joints and bearings, by virtue of their functions are sources

of weakness in the bridge and there are many examples of distress in bridges, primarily due to

poor performance of these elements which includes: leaking of expansion joints and seals

permit the surface run-off water from roadway; continual wear and heavy impact from repeated

live loads as well as continual stages of movement from expansion and contraction; impact

loadings from heavy commercial vehicles; elastomeric bearings can split and rupture due to

unanticipated movements, or ratchet out of position; malfunctioning of bearings can lead to

unanticipated structural damage; joints and bearings are expensive.

During the lifetime, it is unavoidable that bridges are subjected to daily, seasonal and yearly

repeated cycles of heating and cooling induced by solar radiations and surrounding atmosphere.

The up and down temperatures in structural components may lead to nonlinear thermal loads

that influence the performance of integral bridges significantly. In actuality, the variation of

temperatures affects the integral bridge structure in a complex manner. In view of the global

response, uniform temperature changes cause massive expansion and contraction in bridge

components and the deformation induces shift of structural dynamics characteristics as well.

In one of the previous researches after a number of calculations, it was found that thermal

loads are the highest under following conditions, as in extreme diurnal variation of the ambient

temperature, snow or ice on top of the bridge, high solar radiation intensity in areas of moderate

or no air pollution and high sea levels, winter spring and summer conditions and for which

finite difference and finite element method can be used for analysis [1]. The three important

issues related to integral bridge and its behaviour that need to be considered in design were

found to be bridge displacement at the deck level, strains that develop in the substructure due

to integral abutment construction, and additional stresses that develop in the girders. Girder

stresses that develop in integral bridges due to thermal loads can be significant, particularly for

bridge with large EEL and large pile sizes or open foundations; also increased bridge skew was

seen to decrease girder strong-axis demands but increase girder weak-axis bending [2]. Also

increasing the span length by a factor of 2, an approximate 60% increase in weak-axis bending

moment in the bridge abutments was observed in a research. The temperature gradients, in

combination with uniform temperature changes, influence the stresses in the bridge abutments.

A 20° F increase in temperature difference between the girders and deck of the bridge can cause

an increase in the stresses in abutments [3].

Surana Samyak, TP Manoj and Santhi A.S


For bridges with an even number of spans, the middle support is translationally fixed, and

the rest of pier supports are rollers. For bridges with an odd number of spans, and therefore no

middle support, all the pier supports are rollers [4]. Also one of the researches shows that the

movement of abutment into the approach fill develops passive earth pressure which is

displacement-dependent. Using full passive pressure regardless of displacement is not

conservative because it reduces the flexural effects of dead and live load in the bridge girders

[5]. One of important performance reviews suggested that dead load, live load, shrinkage, and

temperature gradient induce positive stringer moments at the centre span of a continuous

structure and should be considered in the design of integral bridges. The extreme load

combination should be considered in design, which causes tension at the bottom of the mid-

span of a stringer combining all of the above loads. Also the major contributor to the total

stresses is the temperature gradient. When the total stresses are taken in account, the mid-span

section is subjected to moderate compressive stresses at the top and larger tensile stress at the

bottom. A reverse gradient in winter would induce opposite nature of stress, which decreases

high bottom tensile stresses. The top of the concrete deck over the pier gets subjected to high

tensile stresses. Additional reinforcement to accommodate these tensile stresses in concrete

over the pier or pre stressing the slab over the pier may have to be adopted to counteract high

tensile stresses [6].

Due to the integrity of the integral bridge and complex soil-structure-footing interactions,

thermal and seismic loads massively affect the design of an integral bridge, hence many

researches have studied the behaviour of integral bridges with pile foundations under seismic

or thermal loads, separately but there was no research about the coupling effect of the two [7].

Mostly while focusing on the substructure, the foundation system taken into consideration is a

pile system and not an open foundation system hence, research for the same should be carried

out and is focused on in this study as well.

Also while designing any integral or simple bridge structure the following points play an

important role during design and construction process viz., length of the structure, climatic

conditions, seismic zone, type of superstructure, type of abutment, type of foundations and sub-

soil conditions, geometry of the structure, complexity in analysis and design etc.

2. PURPOSE OF STUDY

• To study the design of an integral bridge in accordance with IRC:112-2011.

• To understand the behavior and structural response of an integral bridge subjected to thermal

loading under various chosen parameters.

3. PARAMETERS OF STUDY

Following were the chosen parameters for study:

(a) Height of substructure

The height of the substructure is of primary importance in an integral bridge structure and the

design of the same is very much dependent on the shape and size of the pier. While the shape

of the pier depends on the hydrological and flow data of the water body, its size is determined

and fixed as per the stress retention and the load bearing capacity of the same which is getting

transferred from the super structure. The Abutment of the integral bridge is a wall type

abutment considering clause 7.6.4.1 of IRC:112-2011 [11]. The foundation system of the

integral bridge structure is open type and sloped footings were provided for the same. Height

of the substructure in this particular study is referred as the total of the pier height and the



foundation depth up to the top level of PCC. Following were the heights of the substructure

taken under consideration: 11.5m, 13.5m, 15.56m.

Figure 1: Grillage models depicting different heights of substructure

(b) Load transfer component

The load transfer component is basically the structural component which connects the

superstructure with the substructure and is the medium of load transfer as well. In an integral

bridge structure this component can either be a straight and stepped type or Y type. The

selection of the type of component for load transfer is very crucial as the distribution and

transfer of moments depends on it and hence the complete design of substructure relies on the

same. The pier size taken was 3m*1m and the straight type component goes with the same

dimension till it connects with the superstructure whereas, the Y type component is 1.5 m deep

and 6m wide with thickness of 1m. For the study the straight type and the Y shaped type load

transfer component was chosen.

Figure 2 3D solid models showing the shape of load transfer component

(c) Grade of concrete

In practical use, the minimum grade of concrete used for an integral bridge construction is M35

but the IRC codes provides provision for construction with lesser grades as well. Here the

grades of concrete which were used for study purposes are M50 and M60. The grade of concrete

does not drastically affect the strength and durability of the substructure but it does have a

worth in stress limitations and cracking.



4. ANALYSIS AND DESIGN

(a) Methodology

1. The integral bridge structure was designed by modelling a grillage model with an aspect ratio

of 1:1.55 as an 8 span bridge of 261m*12.5m. For ease of understanding only first 4 spans were

taken into consideration for study purposes as post the fourth span there is a presence of an

expansion joint of 80 mm and the remaining 4 spans are replica of the previous as shown in

Fig. 3

Figure 3 Eight span actual model of the integral bridge

2. The 4 span model spanning 130.5 m was taken into consideration with following precast rcc

composite girder sections:

Figure 4 Four span model of the bridge Figure 5 Inner & outer girder sections

3. Material and Section properties were assigned as per the dimension considerations.

4. Loads were applied on the bridge structure as per IRC: 6-2014 [9] and further investigations

and design was done in accordance with IRC: 112-2011 [11] and substructure and foundation

design were as per IRC: 78-2014 [10].

5. After considering all the forces acting on the structure, the magnitude of maximum shear forces

and bending moments of various components were summarized from the model.

6. The sections with the chosen dimensions were checked under Ultimate Limit State (ULS) and

under Serviceability Limit State (SLS) in accordance with IRC: 112-2011 [11].

(b) Loads Applied

All the applied loads were in accordance with IRC: 6-2014 [9] and load combinations has been

formed using IRC: 6-2014 Annex B, Table 3.2 and 3.4 [9].



Table 1 Type and Direction of Loads Applied

Loads Type / Direction

1. Gravity Loads Self weight, Loads due to Crash barrier and Bearing

coat surface Load

2. Lateral Loads Earth Pressure, Live load Surcharge, Braking load

3. Wind Loads With and Without Live loads in Longitudinal and

Transverse directions

4. Temperature Loads (Strain based Loads) Uniform Rise and Fall, Gradient Rise and Fall,

Shrinkage

5. Seismic Loads Longitudinal and Transverse directions

6. Live Loads 70R, 1 Class A, 70R+Class A, 3 Class A

7. Water Current Forces Lateral Direction only

8. Settlement Direction of gravity

Thermal / Temperature Loads

Since thermal loads vary from region to region, the temperature range of the State of Rajasthan

was taken into consideration as it is one of the places in India which is subjected to high

temperatures and radiations. Following were the thermal load calculations taken into

consideration;

Uniform temperature loads were calculated as per IRC: 6-2014 clause 215.2 [9].

Temperature Rise = 36.25 οC Temperature Fall = -36.25 οC

Temperature Gradient Rise and Fall were calculated as per IRC: 6-2014 clause 215.3 [9].

Figure 6 Design temperature difference for concrete bridge decks

For applying temperature gradient loads in STAAD. Pro temperatures were assigned as

follows:

For uniform temperature across depth for gradient rise = -2.34 οC

For linear temperature across depth for gradient rise = 10.79 οC

For uniform temperature across depth for gradient fall = 0.12 οC

For linear temperature across depth for gradient fall = -5.68 οC

Applied Shrinkage Strain = 0.0002



5. RESULTS AND OBSERVATIONS

After the modelling, analysis was performed and design was done. As mostly the combination

of thermal loads and gravity loads dominate the design of an integral bridge, they were mainly

focused upon. Following were the results obtained:

Table 2 Bending Moments at Abutment bottom

Substructure Height 11.5m 13.5m 15.56m

Loads Bending Moment (kN-m) Bending Moment (kN-m) Bending Moment (kN-m)

Gravity Loads

Self Weight -872.014 -1108.585 -1663.292

Load due to Crash Barrier -88.178 -103.998 -170.800

Surfacing Load -112.143 -143.774 -224.218

Thermal Loads

Uniform Temp Rise -20132.064 -16414.131 -13316.846

Uniform Temp Fall 20132.064 16414.131 13316.846

Temp Gradient Rise 1704.630 1520.670 1551.030

Temp Gradient Fall -325.428 -293.116 -391.365

Shrinkage 7412.435 6575.948 5270.563

Table 3 Bending Moments at Pier bottom near Expansion Joint



Gravity Loads

Self Weight 982.395 1131.190 1638.50

Load due to Crash Barrier 95.238 97.993 164.867

Surfacing Load 126.070 146.734 222.327

Thermal Loads

Uniform Temp Rise 6634.490 5473.835 4867.579

Uniform Temp Fall -6634.490 -5473.835 -4867.579

Temp Gradient Rise -888.247 -820.114 -799.597

Temp Gradient Fall 277.885 259.772 230.339

Shrinkage -2498.356 -2174.935 -1958.50

Table 4 Bending Moments at Other Pier Bottoms



Gravity Loads

Self Weight 271.531 300.209 317.745

Load due to Crash Barrier 50.914 51.579 52.754

Surfacing Load 33.078 37.283 41.897

Thermal Loads

Uniform Temp Rise 8166.108 6703.464 4472.795

Uniform Temp Fall -8166.108 -6703.464 -4472.795

Temp Gradient Rise -622.865 -531.832 -322.779

Temp Gradient Fall 94.470 67.338 26.832

Shrinkage -2963.091 -2670.59 -1770.590

Bending Moments for the above applied loads were only taken at the nodes as per

mentioned in Table 2, 3 and 4 as they are componential regions critical in nature for designing



an integral bridge structure. With an increase in height of the substructure a decrease in

magnitude of thermal loads and increase in magnitude of gravity loads can be observed.

For the load transfer component parameter, the middle pier of the 4 span model was taken

into consideration and bending moments were extracted at a depth of 1.5 from the top of the

substructure for all the models with different substructure heights chosen for the study.

Following were the results obtained:

Table 5 Bending Moments at 1.5m depth with 2 type of Load transfer components



Type of load transfer

component

Straight type Y type Straight type Y type Straight type Y type

Gravity Loads

Self Weight 373.89 434.59 469.85 529.62 348.28 589.46

Load due to Crash Barrier 47.27 64.42 53.51 71.04 68.11 71.12

Surfacing Load 41.47 54.18 47.85 67.09 56.40 78.79

Thermal Loads

Uniform Temp Rise 1861 2430 1560 2120 1350 1850

Uniform Temp Fall -1861 -2430 -1560 -2120 -1350 -1850

Temp Gradient Rise -304.22 -345.35 -263.31 -300.24 -197.90 -265.89

Temp Gradient Fall 97.15 113.34 103.52 106.24 61.09 83.24

Shrinkage -781.65 -925.94 -681.85 -856.27 -538.29 -781.56

The grade of concrete plays an important role while checking the design of an integral

bridge or rather say any bridge for Serviceability Limit State as it ensures whether the section

is cracked or un-cracked and is also used to determine the permissible stress limits in

compression and tension for concrete and steel reinforcement provided in the design. As per

IRC:112-2011 clause 12.2.1 and 12.2.2 and A-2 [11], following are the limits:

Table 6 Grade of Concrete with Permissible stress limits as per IRC 112:2011

Grade of Concrete M50 (fck) M60 (fck)

Calculation MPa Calculation MPa

Rare Combination

Permissible Compressive stress in

Concrete

0.48*50 24 0.48*60 28.8

Permissible Tensile Stress in Concrete 0.259 ∗ 500.666 3.51 0.259 ∗ 600.666 3.97

Permissible tensile stress in Steel 0.6*500 300 0.6*500 300

Quasi Permanent Combination

Permissible Compressive stress in

Concrete

0.36*50 18 0.36*60 21.6

Permissible Tensile Stress in Concrete 0.259 ∗ 500.666 3.51 0.259 ∗ 600.666 3.97

Permissible tensile stress in Steel 0.6*500 300 0.6*500 300

As per Table 6 it can be observed that lower grade of concrete gives lesser stress

permissibility than the higher grade which directly affects the quantity of steel provided in the

design of integral bridge structure.

The girders in the superstructure are the members who primarily get subjected to thermal

loads and were checked for stresses limitations due to temperature gradient rise and fall at mid

and end sections (as per IRC 112:2011) and following were the obtained results:



Figure 7 Stress Check for Mid Section of Girder

Figure 8 Stress check for End Girder Section

The value of 0.5fck can be taken as 0.5*50= 25 MPa or 0.5*60=30 MPa for any of which

the girders were safe and the stresses were well within the limits and therefore were considered

safe when subjected to the aforementioned thermal loads.

6. CONCLUSIONS

1. Construction of Integral bridge is favourable when one has to reduce the maintenance costs.

2. As the substructure height increases the temperature loads decreases along the depth and

increases if the case is vice versa.

3. Due to the increment of temperature loads for lesser height of the substructure, construction of

integral bridges for lesser heights should be avoided as it would make the structure

uneconomical.

4. As Integral Bridges are dominated by frame action, expansion joints in the structure cannot be

avoided altogether as it releases the moments due to thermal loads acting on the pier and the

substructure due to its presence, as seen in Table 3.

5. Though Y type load transfer component attracts more moments as seen in Table 5, the

distribution mechanism of the same is more efficient along the depth of the substructure and it

ensures that maximum moments reach the foundation system accordingly.

6. Usage of higher grade of concrete is advisable while construction of the integral bridge

superstructure and substructure is it gives a larger window for stress permissibility which is in

relation with the percentage of steel used and economy of construction.

ACKNOWLEDGEMENT

The authors would like to thank L&T Infrastructure Engineering Ltd. Mumbai and VIT

University, Vellore for the extensive help and guidance provided by them.



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