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Untuk contoh jika dari sebuah bawah jembatan diatasnya terdapat pembukaan yang dangkal ,

bentanganya lebih pendek dengan member tabung yang akan melebihi panjang bentang

pada berat pendeknya sebuah dermaga .ratio kedalaman bentangan juga berhubungan dengan

ketinggian Dari sebuah batasan . beton atau bangunan dermaga dngan beton baja campuran

atau RCCT-beam, dan bentuk lemping yang dapat digunakan untuk bentangan yang pendek.Untk lurus panjang atau tikungan bentangan lebih dalam pembukaannya,baja atau kotak jarring

beton menyediakan lebih halus dan bagian luar yang kelihatan simple.untuk kedalaman

lembah dan berakhir dengan sungai kecil anak sungai dan sungai yang membutuhkan

pembukaan yang besar untuk navigasi , besara bentangan dengan kabel tetap atau jenis kabel

gantung membuat suatu pilihan yang bagus. Ketika celah itu mengharuskan menyempit

medim atau bentangan yang pendek, satu baja atau lengkungan beton jenis dari struktur

kenaikan rendah akan menyediakan sebuah kesenangan dan kebebasan economical. Khusus

Beberapa saran untuk dasar balok penopang pada estesisyang diberikan oleh leonhard8

adalah

area ilustrasi

Superstructure

The Superstructure forms the dominant and dynamic member of the bridge carrying the load

directly and passing on to supports. The may deflect under loads. The soffit should preferably

be horizontal even under load or cambered up so as to provide a good view from below. For

single or multiple medium spans, flat graders with slight positive haunch of small depth at

supports are preferred. For longer bridges with multiple spans, haunched box continuous over

the supports can be adopted. The most important factor in design of superstructure is the

continuity of planes and lines and even colour. In case of unequal spans, there will be difficultyin carrying through the continuity in the soffit line. This difficulty can be overcome by varying

depths of interior girders but maintaining constant depth of fascia members. Abrupt changes in

lines at transitions can be avoided by tapering the fascia member at the piers and at abutment

ends.

Shallow segmental arches in concrete can also be used for shorter multiple span bridges

with pleasing appearance. Open spandrel concrete arches provide a good choice for medium

spans across creeks and deep valleys and even as multiple spans where there is no minimum

clearance restriction. They are common in span range 50 to 150 cm, but much longer spans

have been used. Wanxian Yangtze Bridge in china is the longest concrete arch in the world with

a single span of 425 and 45 m rise. Open spandrel steel arches can be used for long spans in

similar setting, with good rock for founding the abutments. Longest true steel arch bridge with

a span of 518 m is at evile, west Virginia, USA. Some of these shapes are shown in fig. 1.4 (a)

Tied arches, Otherwise known as bow string arches, in concrete have been popular

across streams for low heights (vide Fig.1.4.(b). hybrid tied arches with steel arches and


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concrete decks with slender prestressed steel cable suspenders are becoming popular also. A

recent example is a railway bridge on thee Qinghai-Tibet line, worlds highest railway which was

opened in july,20069. Railways in India have built perhaps one of the longest multi-span (26

numbers of 90 m spans) railway bridge with tied is across River Godavari near Rajahmundry.

Plate 1.12 shows a part of this bridge while under construction.

Pier

The function of piers and abutments is to transfer loads and forces from the

superstructure to the foundation and the design of the shaft, caps, bearings and pedestals ,if

any, should be expressive of this function. Short piers can be in masonry, where good stones

are available, or of mass concrete. Brick is masonry is rarely used in bridge building now as they

are labor intensive and call for more maintenance effort. Piers and medium height piers are

made of solid or hollow RRC section. RRC framers made of braced columns or bents are also

used for medium heights. Pier from can be made responsive to the material used specially ingrade separators, e.g., by textural treatment on concrete. Steel trestles have bee in

conjunction with steel girder superstructure for tall viaducts over deep valleys in hilly tracts for

railway bridges resulting in efficient structures with good aesthetic blending with surroundings.

They are quick to be erected also. Such trestles will have to be erected over concrete bases

taken above normal water level to avoid frequent wetting and drying, steel trestles for regular

scraping and painting to prevent corrosion.

Abutments and wing walls

Abutment have two function, viz., transmitting the loads and forces from thesuperstructure and containing the pressure exerted by the embankment behind. With the wing

walls, it provides the transition between the bridge and the embankment. The objective in their

design is to make positive and expressive composition out of the disparate elements.

Parapets and railings

Though the parapets are secondary members on bridges, they have dual function of

being a safety barrier for the road user and at the same time making a major visual impact on

the user and surroundings. The safety requirement calls for a heavy design while the visual

requirement calls for a lighter structure, with minimum visual obstruction. This will have to be

solved by designing them with directness, simplicity and quality of forms. Modern technological

developments in from steel crash barriers and railings have much to offer in this respect.


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1.6.4. Aesthetic Design Of bridges

Aesthetic design of any structure touches emotion and defies rational analysis. still home

broad guide lines are advantage to the designer. Leonhardt8

, who has designed a large number

of modern bridges, has done a study and formulated some guides lines illustrated with some

example in paper 8 developing Guidelines for Aesthetic Design. A few salient ones are covered

in this section. For more details, the reader is referred to the original paper. Issues involved are:

function of structure ; proportions ; order; refining the form; integration into environment;

surface texture; color; character; color; character; stimulation by variety and incorporating

nature.

Function

The structure should by its form, impose a feeling of confidence and stability to the user and

viewer about is performing is primary function. Incase of a bridge one should while looking at it,

feel confident that it will carry the anticipated load and forces safely down to the supporting

soil, be stable and provide safety to the user. The function and from will depend on the

materials used and their inherent qualities in respect of strength, ductility etc. brick or stone

masonry and timber forms different from those for steel or reinforced concrete. It should

provide adequate protection against vagaries of weather and limitation of deformation and

oscillation. It should be of good quality and be durable.

Good in Harmonious proportioning of the various elements in three-dimensional space is

important to achieve a structure of acceptable aesthetic value. Good proportions are required

in the total structure to convey an impression of balance between different parts of thestructure . such relationship on a bridge structure have to be considered between the spans

and supporting columns)piers; between spent length and depth of girder; and among height,

length and width of openings. The proportion of overhangs has to be decided based on their

influence on the light and shade effect on girder. It will be good to adopt same proportion in

the entire structure and maintain symmetry on the entire length. For example a golden mean in

proportioning adjacent openings is 2:3:2,e.g in at three span bridge the end span length should

be about two thirds that of middle span ( fig.1.3)

Order

Principle of order applies to lines and edges of a structure and placing of adjoining

opening. The directions of the lines and edges of structure should be limited. Similarly good

order should exist between adjacent objects, like proportions in adjacent units or even opening

by avoiding placing a stout rectangle or square object by side of a lean rectangle one. On the

order hand repetition of equally proportioned object can provide rhythm. In some cases,

uniformly varying proportions like increasing span lengths of a multi span bridge while


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providing an ascending gradient or increasing span length of an arch bridge tower the centre

with a hump in centre can give a pleasing elevation. Unnecessary accessories should avoid.

Refining the form

Refining of the basic form may become necessary, when structural form parallel straightlines horizontal and vertical may create an uncomfortable feeling of static and stiffness. The

soffit of girders on long spans can look as though they are sagging. Giving a pre-camber to the

soffit can remedy this situation. Continuous spans can be used with larger depth at ends with

the depth reducing toward the centre, by proving well proportioned haunches in soffit of girder

et ends. The soffit can be given a shallow convex curvature also to achieve more pleasing look.

Similarly parallel surface of tall piers on a viaduct will given an illusion of being wider on top at

bottom. This is remedied by providing a taper to the pier toward top, which is functionally and

structurally also more desirable. Skew angles on piers can also cause a disturbing of overlapping

in elevation. In such cases, it is desirable to study the light and shade effect on scale models andrefine the form.

Integration into environment

The need for integrating a structure into environment has already been emphasized. One

should avoid longspan bridges with deep beams over a lovely valley or over a river in a town

old row rise houses lining the bank. Alternative like provision of short slander arches or cable

supported structure or large tied arch with slender wire suspended decks is preferable. On

narrow deep valleys and gorges, open spandrel arch bridges provide an efficient and pleasing

solution.

Surface texture

Surface finishes can provided good appearances in certain cases , but they have to be chosen

so hat they not wheatear badly,, do not lose their color and can be maintained well offer the

life of the structure. On bridges, rough finishes are suitable for piers and abutments and

smooth surfaces for superstructure elements and slender columns. Stone rough finished can be

used in conjunction with stone masonry columns for small and medium span arches, with

pleasing effect. Concrete piers on interchanges and elevated roads are beneficially given

special texturing apart from giving different plan shape. Typical example can be seen in recentlycompleted flyovers in Delhi, Mumbai, Bangalore and Chennai. Figure 1.6 shows an example.

Views of piers on two major flyovers are shown in Annexure 21.1.

Color


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Color is play a major role in the overall aesthetic effect of the structure, especially in urban

areas. There should be harmonious combination of color schemes on various parts of the

structure. Urge to finish with sensational or aggressive effects should be avoided. Too dark

colors tend to give an opposite effect.

Character

Each major structure should have a unique effect on the people. The effect will depend

on the type of society and their tastes in the immediate surroundings. Translation of too much

individualism and egoism of the designer on to the stricture should be avoided.

Incorporating nature

Even while building a bridge, one can give more room to nature in its built environment.

This can be done by introducing green areas on and around a structure. It is learnt that this had

been done on the first autobahns in Germany. Singapore planner have given such an effect ontheir bridges on the expressways and elevated metro rail lines by growing of creepers and

letting them fall over the parapets.

Foot bridges

In the past decade, a large number of elevated pedestrian walkways and bridges have

built all over. Trend has been to go aesthetically pleasing and light structure. The light structure

are mostly cable supported either from light towers or elegant arches on inclined planes. While

going in for light structure, care has to be taken in the design on the vibration aspect. The panic

caused by excessive vibration by the millennium bridge in London and their redesign is anexample. Solid structure mostly use arch forms blending with surroundings

Detailed design

Loading standards

Loading standards for design for bridges are specified by various countries through

either their standardization organization or recognized professional bodies. They may very

considerably country to country, depending on the type of vehicles in use or proposed for use

in their country. In UK , BSI has been issuing loading standard which cover road bridges in termsof struck axle loads and axle spacing; and for railways in terms of locomotive axle loads and

spacing and trailing loads following. Britain also has drawing available for standard lengths of

bridge beams for RCC and PSC formulated and issued by their department of transportation.

Russians have their own common standard of loading for highway bridges and specific

enhanced loading standard for some areas like Moskow metropolitan area. Russians railways

have also developed standard plans/drawing for steel girder spans of common use.


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The European countries has different specifications for each country before the

formation on the European Union. In order to have a common basis for bids emanating from

different country for the same job, they intended to have a common set of calculation rules.

The Structural (Euro) codes have been drafted as an alternative set of codes and standards for

their use by individual member countries and ultimately these standards will replace thestandards of individual countries. Part 3 of Structural Code covers loads common for all

structures and part 4 covers live loads on bridges. The codes specifies that design of bridge

should be for withstanding the cumulative effect of loads on the pass through the structure

and forces arising out of natural actions for a return period of 100 years. With regard to traffic

loads, they constitute a completely new document, which gives the required elaboration as

scientifically as possible.

The wide variation in highway bridge loading adopted by different countries, are they

were some time back in different countries in the world, can be judged from the comparative

graph evolved by Thomas [1975] and reproduced in Fig.7.10. it will be seen, as at the time, up

to 100 meter spans, the German Codes specified the heaviest loads and the AASHTO the

lightest.

The developing countries, which were under different European powers during the

industrial revolution and after followed the practice of the respective masters and most of

them are continuing to do so even after independence, as a matter of convenience. The Middle

countries appear to have been adopting the AASHTO practice. The countries like Malaysia,

Myanmar and Sri Lanka fallow the British Standards. It will therefore be necessary for those

who want to take up design jobs in these countries to be conversant with at least Euro Codesfor structures, BS 5400 and AASHTO and ACI (American Concrete institute)

The concept of design has also undergone changes. Earlier practice was to use working

stress or allowable stress concept for design of bridge structures. Most countries now follow

Limit State design concept in design of bridge structures also. The load factors assumed may

vary from standard to standard. AASHTO specifies use of LRFFD (Load and Resistance Factor

Design ) for design of highway bridges.

1.7.2 Practice in India

In India, during the early days of structured bridge building, i.e.. during the British period, the

Public Works Departments of different providences appear to have followed loading standards

to suit expected truck loadings in their respective areas. Many of the presidencies like Madras,

Bombay and Bengal had their, Specification ( like MDSS, Bombay PWD/Manuals), which

covered not only material and construction specification, but also axle loads and their spacing

to be used for bridge designs on different types of roads. Major inter-state highway had to take


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into consideration movement of army vehicles including armored ones on their major roads.

Madras Presidency, which was the forerunner in forming a separate department for highway,

had formulated a Highways Manuals, which covered loading standards and design and

construction specification for roads and bridges. With the advent of the Indian Roads Congress (

since middle of last century ), the loading requirement for bridges on different types of roadshave been standardized. Different IRC codes exits for design and construction of bridges in

steel, concrete and for foundation including soil investigation Separate codes have been formed

for design and testing of Elastomeric bearings and expansion joints. These codes have been

drown up modeled on international codes, though some of the provision in them are

considered too conservative. IRC have also issued a detailed Standard Specifications for Roads

and Bridges, which have become mandatory for all National Highway works. In order to assists

the departments, IRC has also issued standard drawings for box culverts, RRC culverts slabs for

small spans; also beam and slab designs with RRC girders for 12 to 18 m spans with PSC girders

for some longer span for use on State and National Highway.

The Indian Railway in early days followed either provision in different parts of old BS 153

( codes for bridges ) or loadings to suit the axle loads of heaviest locomotives used or likely to

be used on respective individual railway systems. For example, the axle load adopted was 12

towns in 1875, which was progressively increased to 18 tons 1903 standard. It was increased by

25% in 1908. It was in 1926 that the concept of Heavy Mineral load HM (28i) axle load, Main

Line MBG (22.5t axle load) and Branch line BGBL ( 17 t axle load ) was introduced. They had also

issued similar standard for MGML, MGBL and NG tracks also. Tractive force be used in design

for longitudinal effect was also specified then.

Each railway company or unit had its own standard specifications for civil engineering

works and even type drawings for different spans with steel girders. Structure for important

bridges were designed by reputed consultants from UK. With more and more railway system

being taken over by the government, the Indian Railway Board constituted a Central Standard

Organization ( CSO ) for laying down common standard to be followed by all railway systems in

India. This organization later became the Railways Research Design and standards Organization

(RSDO). The former organization ( CSO ) had brought out in 1937 Bridge Rules, Which

specified the loading arrangements to be used in design of bridges for thee three different

gauges and separately for Branch, Main and Heavy Mineral Lines. They were based on the

steam locomotive wheel arrangements. This has since undergone a number of revisions to take

car of heavier load locomotive and change of traction as well as increased speeds. CSO also

brought out Codes of Practice and Standard Specifications for design and construction of

bridges and structures in steel and steel and concrete and for design and construction of

foundation and substructures for bridges and for road-cum-rail bridges. Later the RSDO issued

standard drawing for steel girder spans up to 61 meter and steel-composite girder bridges for


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shorter spans. They have issue also issued standard drawing for RCC/PSC bridges slabs and PSC

Box girders for standard spans. The available IRS parameters have been found to be deficient

for design of long span steel arch bridges in respect of additional parameters like fatigue,

global stability, seconds order column effects, composite action etc. while design two such

bridges on Udhampur-Srinagar-Baramulla rail link. Their provisions have had to besupplemented with the provisions in BS 5400, AASTHO and Euro Codes

9

Anyone familiar with these codes and specification for road and railway bridges can

easily understand the requirements of codes and standards of other countries, especially

developing countries. A list of codes and standards applicable for design of bridges for roads

and railways in India is given under References at end of Chapter 14.

1.7.3 Design Practice

The design of various components of bridges is now done is most countries almost invariably

with the use of the computers. Designers are going in for longer and longer spans and adopt

different forms and geometry in alignment. At one time engineers preferred to have straight

alignments in plan and avoided vertical curves on bridges decks. Now such limitation are

looked down upon from the point of view of aesthetics and economy in construction as well as

maintenance, though such requirement call for complicated calculation. Design have to be

competitive and during conceptual and design stage,, this calls for an iterative approach to

arrive at the optimal span, type and structural arrangements. Design by hand calculation for

such cases is very difficult and time consuming, if not impossible, Naturally, this calls for use of

computers and custom made programmers. A number off standard structural packages like

STAAD III/ STAAD Pro, GTSTRUDL and SAP 2000 are used along with power full tools like

ADINA,ANSYS, NASTRAN and ABAQUS for analysis. These are utilized for determining the most

probable response of bridge structure for arrange of applied loads. The output provides the

engineer the design date for evaluating the bridge structure. By trying alternatives, most

efficient configuration can be arrived at and most reliable design alternative arrived at. By

suitable linking with older relevant computer software, plans, specifications and estimate are

drawn up.

Firms in many countries have developed specific sub programmers with in-built graphic

capabilities bridge design. One such is bridge-design-specific programs like LUCAS available inthe market. The extent of development of purpose built software can be judges from the

approach used in China in recent times1

. computer technologies have been used in China for

structural analysis in bridge design since late 1970s and many special purpose programmers

have been developed. Synthetically Bridge Programmers provided the capability of

construction stage transferring, concrete creep and shrinkage analysis, priestess calculation

etc. the first version of BICADS consists of five subsystems including the Design


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Documentation, Pre-Processing of Bridge FEM, and the Preliminary Design of Box Girder

Bridges. A new generation BICADS ( Bridges Cad System )has been developed recently. Several

detailed design subsystems of other commonly used bridges can be included by employing a

good integrating and expanding mechanism in the main system.

But very few locally developed bridge design programmers have been made

commercially available in India. A number of academic institutions including the Indian

Institutes of Technologies have been developing design software as part of academic research

programmers. Railways have developed in house programmers for design of bridge girders and

design of wells. Recently, they have availed of the services of the Indian Institute of Technology

for developing interactive design software for design of steel girders and prestressed concrete

box girder. Similarly, the Indian Roads Congress has been sponsoring development of such

software for road bridge design. Apart from these, practicing engineers develop their own

simple spread sheet programmers for design of some bridge components. Though they are of

limited use on and can not be extended for design of innovative forms of bridge components,

they facilities the engineer to do trial and error calculation for arriving at more cost effective

solutions.


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In some case , it may be necessary to provide a change of gradient on the bridge itself calling

for provision of vertical curves. These provide an opportunity to the engineer to design

structure harmoniously blending with the road alignment and surroundings. the form, span

arrangement, depth of girders and height of the piers have to result in a pleasing structure to

the one who looks at it from below and also while passing over the same. For example, an archfrom chosen for a long bridge with level roadway will look better with equal spans, with the

same with a curved vertical alignment with summit at center can have spans of varied lengths,

increasing in lengths from end towards center. Same bridge with a rising gradient will look

better with span lengths progressively increasing from lower end. This principle can be followed

while using RRC or PSC girders over viaducts across shallow valleys also, but it will be desirable

to keep uniform depths of girders of fascia members so that there is no break in the soft line .

Choice of type of structure

The factors determining the type of structure are : basic geometry of roadway/railway ;dimensions of openings spanned; topography; requirements of clearance ( for navigation or

flood flow for passage of vehicles below ); sub-grade conditions; accessibility and working

conditions (including clear working season for construction) at site. The choice is finally dictated

by other major factors of availability of materials and technologies in the area/region where the

bridge is proposed, likely costs of construction and maintenance and any time limitations.

Visually the structure has to provide a pleasing appearance ,for which the designer has to look

at the forms, lines, planes and proportions of spaces formed by various components of the

bridge like superstructure, piers, abutments, wings and embankments. Ideally objective is

lightness and openness, with least encroachment on thee motorists visual and physical space.There should be easy flow of lines and forms and abrupt changes and transition should be

avoid.

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