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IJCSIET-ISSUE5-VOLUME3-SERIES-2

IJCSIET--International Journal of Computer Science inf ormation and Engg., Technologies ISSN 2277-4408 || 01102015-005

DESIGN OF CABLE – STAYED

RAILWAY BRIDGE

SARATH BABU J,ROLL NO:137K1D8716

M-TECH STRUCTURAL ENGINEERING DJR COLLEGE OF ENGINEERING &TECHNOLOGY

UNDER THE GUIDENCE OF

L.NAGARAJA (PH.D)

ABSTRACT

A bridge is a structure built to span physical obstacles

such as a body of water, valley, or road, for the purpose

of providing passage over the obstacle. Designs of

bridges vary depending on the function of the bridge, the

nature of the terrain where the bridge is constructed; the

material used to make it and the funds available to build

it. Bridge building is a complex art and science and

involves extensive knowledge, skill and expertise. It is

engineering in itself. Among the various kinds of

bridges existing cable –stayed bridges are found to be

highly economical and have great aesthetic appeal. These

are the preferred bridges for long spans in the recent

days. Cable – stayed bridges are easy to construct and

maintain. The history of bridges, bridge components and

bridge terminology has been clearly discussed. General

steps involved in any bridge construction are mentioned.

A brief literature report of cable – stayed bridges is also

presented.

In this report we designed a cable – stayed railway

bridge on River Gauthami between Yanam and

Yedurlanka. The various survey data has been collected

and thoroughly analyzed before proceeding to the design

of the bridge. A drawing of the alignment is also shown

in this report. The catchment area maps have been

studied before determining the hydrographical

particulars. The bridge is designed as per the IRS code

for MBG two tracks. Two plate girders are used and truss

shaped cross girders are placed at suitable spacing. Steel

pylons and cables are designed to support the deck and

transfer the forces effectively. The scour depth is

calculated in order to calculate the depth of the pile

foundation adopted. The bore – hole log and the soil

characteristics at different depths are studied before

determining the bearing capacity and type of foundation.

A cost estimate is made considering the material costs as

well as the construction costs. Finally the advantages of a

cable – stayed bridge for longer spans over other kinds of

bridges are discussed.

It is found that cable – stayed bridges have the following

advantages:

1) Greater stiffness than the suspension bridge,

so that deformations of the deck under live

loads are reduced.

2) Can be constructed by cantilevering out from

the tower - the cables act both as temporary

and permanent supports to the bridge deck.

3) It is very economical and has a huge aesthetic

appeal especially if very long spans are

involved.

1.1. INTRODUCTION

Bridges are defined as structures, which provide a

connection or passage over a gap without blocking the

opening or passageway beneath. They can be over

streams, canals and rivers, creeks and valleys or roads

and railways passing beneath. These days‟ bridges are

also being constructed over oceans to connect two or

more islands. The structure can be for passage/ carriage



of persons, cattle, vehicles, water or other materials

carried across in pipes or conveyers. Bridges are a civil

engineering creation that holds enormous appeal and

fascination to the people. Bridge building is as old as

civil engineering. The design of bridges depends on

various factors like function of the bridge, the nature of

the terrain where the bridge is constructed, the material

used to make it and the funds available to build it etc…

The concept of bridge building came into existence

with the felling of wooden logs across small streams due

to natural forces. With the growth of civilizations, the

need for travel impelled mankind to find ways and means

of bridging gaps over deep gorges and perennial streams,

for walking across. Owing to the above fact timber can

be considered as the earliest material to be used for

bridging. This has been followed by bridges built with

stone and then of brick, used by themselves or in

combination with timber. Such bridges however have

been possible only for short spans. But with the

development of steel and iron as construction materials

bridge engineering has also expanded its horizons to span

longer distances.

Design of a bridge is an art involving immense

knowledge, skill and experience. It is a highly tedious job

which requires through expertise in all branches of civil

engineering like surveying, transportation, structural

engineering, geotechnical engineering material science

etc… There are three dimensions involved in the

planning of huge structures which are designed for a

period of 50 to 100 years. They are:

1) Scientific dimension

2) Social dimension

3) Technological dimension

Scientific dimension implies that every structure has

to perform in accordance with laws of nature. These laws

of nature are interpreted by scientists as formulas

containing relationships between various basic elements,

and engineers make use of such pre – existing formulas

to design the structures. Though the method of analysis

may differ depending on the structure and practice the

ultimate concept of design remains the same. The

scientific dimension helps the engineer in evolving

efficient structures.

Bridges are built for improving the mobility of people

and enhancing the quality of life of the society. Such man

– made structures may have some adverse effects on the

environment. Therefore bridges should satisfy both the

immediate and future demands of mobility and also be

acceptable to people in terms of visibility, noise and

pollution during and after construction. As construction

of bridges is a public welfare program, the society has to

pay for the cost of the structure in the form of taxes and

tolls. These aspects form the social dimension of any

project.

Technological dimension deals with the major

technological developments in evolution in different

forms of structures, materials of construction, design and

construction techniques and also machinery and plants

used for construction. Technology played a vital role in

finding and refining a number of alternative materials for

use in bridge building, like bricks, cast iron, wrought

iron, steel, cement etc… Because of such technological

research and advances bridges of longer spans at

challenging locations have become possible. A

technological development in the design and manufacture

of vehicles has also led to a need to increase the strength

and geometrical requirements of the bridges being built

as well as their standards of maintenance.

However for a structural engineer, the scientific

dimension is of primary importance, but it is also

necessary to balance the other two dimensions before,

during and after construction of the structure. It is the

responsibility of a structural engineer to evolve a form of

structure which is socially acceptable and at the same

time results in an economic, durable and efficient

product. For this he/she has to make use of the

technological developments in an optimal manner.

Some of the famous bridges in the world are listed

below:

1) Golden Gate Bridge, San Francisco (Fig 1)

2) Millau Bridge, France

3) Tower Bridge, London

4) Akashi-Kaikyo Bridge, Japan (Fig 3)



5) Sydney Harbor Bridge, Australia

6) Brooklyn Bridge, New York

7) Howrah Bridge, India (Fig 2)

8) Chapel Bridge, Switzerland

9) Godavari Bridge, India

10) Antioch Bridge, USA

11) Royal Victoria Dock Bridge, London

Fig. 1 Golden Gate Bridge, San Francisco Fig. 2

Howrah Bridge, Calcutta

Fig. 3 Akashi-Kaikyo Bridge, Japan

1.2. BASIC BRIDGE FORMS

There are six basic forms of bridge structures:

1) Beam bridges

2) Truss bridges

3) Arch bridges

4) Cantilever bridges

5) Suspension bridges

6) Cable stayed bridges

Beam bridges are horizontal beams supported at each end

by abutments, hence their structural name of simply

supported. A beam bridge carries vertical loads by

flexure.

A truss bridge is a bridge composed of connected

elements (typically straight) which may be stressed

from tension, compression, or sometimes both in

response to dynamic loads. The truss bridge of simple

span behaves like a beam because it carries vertical loads

by bending. The top chords are in compression, and the

bottom chords are in tension, while the vertical and

diagonal members are either in tension or compression

depending on their orientation.

Loads are carried primarily in compression by the

arch bridge, with the reactions at the supports (springing)

being both vertical and horizontal forces.

A cantilever bridge generally consists of three spans,

of which the outer spans, known as anchor spans, are

anchored down to the shore, and these cantilever over the

channel. A suspended span is rested at the ends of the

two cantilevers, and acts as a simply supported beam or

truss. The cantilevers carry their loads by tension in the

upper chords and compression in the lower chords.

A suspension bridge carries vertical loads from the

deck through curved cables in tension. These loads are

transferred to the ground through towers and through

anchorages.

In cable stayed bridge, the vertical loads on the deck

are carried by the nearly straight inclined cables which

are in tension. The towers transfer the cable forces to the

foundation through vertical compression. The tensile

forces in the stay cables induce horizontal compression in

the deck.

1.3. BRIDGE COMPONENTS

The main components of a bridge structure are:

1) Decking, consisting of deck slab, girders,

trusses, etc.;

2) Bearings for the decking;



3) Abutments and piers;

4) Foundations for the abutments and the piers:

5) River training works, like revetment for

slopes for embankments at abutments, and

aprons at river bed level;

6) Approaches to the bridge to connect the

bridge proper to the roads on either side; and

7) Handrails, parapets and guard stones.

Some of the components of a typical bridge are shown in

the figure below:

Fig. 4 Components of a typical bridge

The components above the level of bearings are

grouped as superstructure, while the parts below the

bearing level are classed as substructure. The portion

below the bed level of a river bridge is called the

foundation. The components below the bearing and

above the foundation are often referred as substructure.

1.4. BRIDGE TERMINOLOGY

An important first step in understanding the

principles and processes of bridge construction is

learning basic bridge terminology. Although bridges vary

widely in material and design, there are many

components that are common to all bridges. In general,

these components may be classified either as parts of a

bridge superstructure or as parts of a bridge substructure.

Fig. 5 Parts of Bridge

SUPERSTRUCTURE

The superstructure consists of the components that

actually span the obstacle the bridge is intended to cross

and includes the following:

1) Bridge deck

2) Structural members

3) Parapets (bridge railings), handrails,

sidewalk, lighting and some drainage features

The top surface of a bridge which carries the traffic is

called deck. The deck is the roadway portion of a bridge,

including shoulders. Most bridge decks are constructed

as reinforced concrete slabs, but timber decks are

occasionally used in rural areas and open-grid steel decks

are used in some movable bridge designs (Bascule

Bridge). As polymers and fibre technologies are

improving in the recent days, Fibre Reinforced Polymer

(FRP) decks are also being used these days. Bridge decks

are required to conform to the grade of the approach

roadway so that there is no bump or dip as a vehicle

crosses onto or off of the bridge.

The most common causes of premature deck failure are:



1) Insufficient concrete strength from an

improper mix design, too much water,

improper amounts of air entraining

admixtures, segregation, or improper curing.

2) Improper concrete placement, such as failure

to consolidate the mix as the concrete is

placed, pouring the concrete so slowly that

the concrete begins the initial set, or not

maintaining a placement rate in accordance.

3) Insufficient concrete cover due to improper

screed settings or incorrect installation of the

deck forms and/or reinforcement

A bridge deck is usually supported by structural

members. The most common types are:

1) Steel I-beams and girders

2) Pre - cast, pre - stressed, reinforced concrete

bulb T beams

3) Pre - cast, pre - stressed, reinforced concrete I

beams

4) Pre - cast, pre - stressed, concrete box beams

5) Reinforced concrete slabs

Fig. 6 Bridge Deck

Secondary members called diaphragms are used as

cross-braces between the main structural members and

are also part of the superstructure. Bracing that spans

between the main beams or girders of a bridge or viaduct

and assists in the distribution of loads is called

diaphragm.

Parapets (bridge railings); handrails, sidewalks,

lighting, and drainage features have little to do with the

structural strength of a bridge, but are important aesthetic

and safety items. The materials and workmanship that go

into the construction of these features require the same

inspection effort as any other phase of the work.

SUBSTRUCTURE

The substructure consists of all of the parts that support

the superstructure. The main components are:

1) Abutments or end-bents,

2) Piers or interior bents,

3) Footings

4) Piling.

Abutments support the extreme ends of the bridge and

confine the approach embankment, allowing the

embankment to be built up to grade with the planned

bridge deck. When a bridge is too long to be supported

by abutments alone, piers or interior bents are built to

provide intermediate support. Although the terms may be

used interchangeably, a pier generally is built as a solid

wall, while bents are usually built with columns.

The top part of abutments, piers, and bents is called

the cap. The structural members rest on raised, pedestal-

like areas on top of the cap called the bridge seats. The

devices that are used to connect the structural members

to the bridge seats are called shoes or bearings.

Abutments, bents, and piers are typically built on spread

footings. Spread footings are large blocks of reinforced

concrete that provide a solid base for the substructure and

anchor the substructure against lateral movements.

Footings also serve to transmit loads borne by the

substructure to the underlying foundation material.

When the soils beneath a footing are not capable of

supporting the weight of the structure above the soil,

bearing failure occurs. The foundation shifts or sinks

under the load, causing structure movement and damage.

In areas where bearing failure is likely, footings are built

on foundation piling. These load bearing members are

driven deep into the ground at footing locations to

stabilize the footing foundation. Piling transmits loads



from the substructure units down to underlying layers of

soil or rock.

Fig. 7 Abutment Types

SPANS AND SPAN LENGTH

The terms bridge and span are used interchangeable;

however, to avoid confusion and misunderstanding,

Technicians and construction personnel draw a

distinction between the two.

A bridge is made up of one or more spans. A span is a

segment of a bridge that crosses from one substructure

unit to the next, from abutment to abutment, from

abutment to pier, from pier to pier, or from pier to

abutment. Span length refers to either the length of any

individual span within the structure or to the total bridge

length. In most cases, span lengths are considered as the

distance between centrelines of bearing from one

substructure unit to the next.

The three basic types of spans are shown below. Any of

these spans may be constructed using beams, girders or

trusses.

Simple Span: A span in which the effective length is the

same as the length of the spanning structure. The

spanning superstructure extends from one vertical

support, abutment or pier, to another, without crossing

over an intermediate support or creating a cantilever.

Continuous Span: A superstructure which extends as

one piece over multiple supports is called a continuous

span.

Cantilever Span: A cantilever span is a span which

projects beyond a supporting column or wall and is

counterbalanced and/or supported at only one end.

Fig. 8 Types of Spans

2. THERITICAL ASPECTS

2.1. HISTORY OF BRIDGES

The history of development of bridge construction is

closely linked with the history of human civilization. The

efficiency and sophistication of design and the ingenious

construction procedures kept pace with the advances in

science, materials and technology. Since ancient times,

bridges have been the most visible testimony to the

contribution of engineers. Bridges have always figured

prominently in human history . Nature fashioned the first



bridges. The tree fallen accidentally across a stream was

the earliest example of a beam type bridge. Similarly, the

natural rock arch formed by erosion of the loose soil

below and the creepers hanging from tree to tree

allowing monkeys to cross from one bank to the other

were the earliest forebears of the arch and the suspension

bridges, respectively. The primitive man imitated nature

and learnt to build beam and suspension bridges.

The earliest reference to a man made bridge goes as far

as 3306 BC, an 1100 – m – long wooden bridge built in

England. The oldest bridge still standing is a stone slab

pedestrian bridge across river Meles in Smyrna, Turkey

said to be 2500 years old. Swiss were the pioneers of

timber bridges, specially using trestle form. In known

history, the Chinese appear to be the earliest to build

stone bridges. Romans are believed to have built bridges

and aqueducts for carriage of water before even the start

of the first millennium. Romans are also credited to have

used timber pile bents for foundation and piers as early as

95 BC. Queen Nitocrin built a bridge in stone piers and

wooden deck in about 780 BC. Iron and lead were used

in this bridge to bind the stones together. Gordon River

Bridge built in 13 BC in France was a masonry aqueduct

49 m high, with three rows of superposed arches.

Etruscans are believed to have used vaults for bridge

construction as early as 600 BC. Europe is considered to

be one of the birthplaces of bridge design and

technology. Therefore it may also be said that they must

have been the earliest to develop bridge building as a

technique.

Gradually the Roman Bridge building art spread to

Middle East as far as India. Macro Polo is said to have

remarked „Indian cultures adopted their own tools under

this influence for bridge building and further developed

suspension bridges‟. Indians have built suspension

bridges with use of ropes for suspension and bamboo and

timber planks for decks in the hilly regions from early

days. They are also credited to have built cantilever type

of bridges laying stone slabs one over the other in a

progressive manner to bridge gaps, but have kept no

records. Russians used timber as main bridge building

material until the end of 15th century. China has built

some notable bridges using tied arch form and cable

stayed bridges. Two elegant examples are Dagu Bridge at

Tianjin and a railway bridge at high altitude on their

recently opened rail link to Tibet.

In the medieval times church has greatly influenced

bridge building. All the bridges in this age have been

built with stone, brick masonry and timber using

empirical methods for design. A typical example is the

first London Bridge built by Peter of Colechurch in 1176

– 1209 AD. This was masonry with 19 pointed masonry

arches on piers, none of them with same dimensions.

Wittengen Bridge built in 1758 in Germany was the

longest timber bridge in Europe with a span of 119 m in

those days.

It was during Renaissance period that the concept of

bridge building based on scientific basis came into

existence. The truss system based on the principle of

triangles, which cannot be deformed, was developed.

Andrea Pallaido (1508 – 1580 AD), evolved several truss

forms, including the king post type. Verrazino (1615)

had written about roads, machines, water wheels, bridges

including masonry arches with use of pre - stressing rods,

as well as suspension bridges and the use of iron bars for

suspension bridges. First metal bridge was

Coalbrookdale Bridge built in cast iron in the year 1776.

James was the person who patented suspension bridge

form and built some with steel chains. French Engineer

Vicat invented the aerial spun cables for suspension. This

type has become the major form for building longer and

longer spans today.

The industrial revolution ushered in the use of iron in

bridges in place of stone and timber. The first iron bridge

was built at Coalbrookdale in 1779 over the Severn in

England by Abraham Darby and John Wilkinson. It

consisted of five semicircular arch ribs in cast iron,

joined together side by side to form a single arch span of

30 m. The construction details of Iron Bridge followed

the spirit of timber and masonry construction practices.

Wrought iron replaced cast iron in bridge construction

during the period 1880 – 90. Wrought iron was ductile,

malleable and strong in tension. In 1808, James Finley in

Pennsylvania patented a design for suspension bridge

with wrought iron chain cables and level floor. Wrought

iron chains were used for a suspension bridge built by

Thomas Telford across the Menai Straits in Wales in



1826 with a record – breaking span of 177 m. The Menai

Straits Bridge was the world‟s first iron suspension

bridge for vehicles and also the world‟s first iron

suspension bridge over sea water. Japanese also built iron

bridges in the same period. The longest cable suspension

bridge, Akashi Kaikyo Bridge, with a record span of

1991 m was built by them. Germany was the first to

introduce the concept of cantilever construction in the

modern days and incremental launching of concrete

decks, as well as the modern form of cable stayed

bridges.

Though steel is said to have been known in China by 200

BC and in India by 500 BC, its widespread use

materialized only in the latter half of nineteenth century

after the discovery of the Bessemer process in 1856. Eads

Bridge at St. Louis was the first bridge to be built with

extensive use of steel, as early as 1874. Firth of Forth

Railway Bridge in Scotland followed suit, with use of

tubular steel sections for main girders and columns. This

design had been appreciated for the bold attempt made to

span such lengths and shaping the structure so as to

follow clearly the force lines and giving an elegant look

for a viewer. Trend in 18 th and 19 th centuries for longer

span bridges especially in USA tended towards cable

stayed suspension bridges. The Golden Gate Bridge in

San Francisco, built in 1973 is the most famous of this

type. Use of wrought iron and steel as basic materials

instead of masonry and timber has revolutionized bridge

building for many centuries till the arrival of pre -

stressed concrete. The first Portland cement concrete

bridge to be built was the Grand Maitre Aqueduct across

River Vane in France built in 1867 – 1874. France is also

the birthplace of pre - stressed concrete, which is the

major form of bridge superstructures all over the world

today either by itself or in combination with steel.

The world‟s first modern cantilever bridge was built in

1867 by Heinrich Gerber across the river Main at

Hassfurt, Germany, with a main span of 129 m. The

world‟s most famous cantilever bridge is the Firth of

Forth Bridge in Scotland. The world‟s longest span

cantilever bridge was built in 1917 at Quebec, over St.

Lawrence River, with a main span of 549 m. The first

attempt to construct this bridge ended in failure due to

miscalculation of the dead load and buckling of the web

plates of the structure was rebuilt. The Howrah Bridge

over the Hooghly River at Kolkata, built in 1943 with a

main span of 457 m, has elegant aesthetics and possesses

pleasing proportions among the suspended span,

cantilever arms and anchor spans. It was a notable

achievement at the time of construction. Developments in

welding technology and precision gas cutting techniques

in the post Second World War period facilitated the

economical fabrication of monolithic structural steel box

girders characterized by the use of thin stiffened plates

and the closed form of cross section.

Franklin D. Roosevelt once said „there can be little

doubt that in many ways the story of bridge building is

the story of civilization. By it, we can readily measure a

progress I each particular country‟. Based on this saying,

the Indian civilization being one of the oldest, must have

built bridges well before Christian era. According to

records of Chinese travelers on Indian history, India

appears to have had a number of bridges. Firoze Shah

who ruled in Delhi is said to have built canals and

bridges. One can still see some old masonry arch bridges

built by the Portuguese in 16th or 17 th century in Goa.

One old bridge still in use is the stone slab bridge across

River Cauvery at Srirangapatnam built by Tipu Sultan.

India also has a number of old masonry and stone arch

bridges built in the middle of the 19th century on the

Railways, which bear testimony to the skill of the local

people in bridge construction. The British who built the

railways have brought the steel bridge girders and their

designs form UK, but they depended on the local skills

and expertise to build the others. Structural forms and

designs for longer spans also appear to have come from

the British. The technical knowledge within the country

has since kept pace with the developments abroad. The

use of reinforced concrete for road bridges has become

popular in India since the beginning of the twentieth

century. The bridge types adopted include simply

supported slabs, simply supported T – beam span,

balanced cantilever with suspended spans, arch and bow

string girder and continuous or framed structures. The

Third Godavari Railway Bridge built in 1996 with 28

spans of 97.5 m is a recent example of elegant concrete

bowstring girder bridges.



A number of cable stayed bridges have been built in

India in the past two decades, the major one being the

VidhyasagarSethu across Hooghly at Kolkata and the

Naini Bridge on River Jamuna at Allahabad. The

railways are building a number of major bridges

including a large steel arch bridge in Jammu and

Kashmir. The Border Roads Organization has erected a

cable stayed bridge using Bailey bridge girders in early

part of this millennium, which bridge is claimed to be

only bridge of the type at highest altitude in the world at

the time of construction.

Fig. 9 Millennium Bridge, London (Steel Suspension

Bridge)

Fig. 10 Godavari Bridge, India (Steel Arch Bridge)

2.2. CLASSIFICATION OF BRIDGES

Bridge may be classified into different types depending

on various factors as listed below:

Function: Based on the purpose for which a

bridge is constructed it may be classified as

follows

Foot

Road

Railway

Road – cum – rail

Pipe line

Water conveying

(aqueduct)

Jetty

Material: Based on the material used for

construction bridges may be divided into the

following type

Stone

Brick

Timber

Steel

Concrete

Composite

Aluminium

Fibre



Form: Based on the form of the superstructure

bridges may be classified as

Beam

Arch

Truss

Suspension

Cable stayed

Cantilever

Type of support: Bridges are also classified

based on the type of the structure it is

supported with

Simply supported

Continuous

Cantilever

Position of floor/ deck: The deck plays an

important role in classification of bridges.

Deck

Through

Semi – through

Usage: The time period for which a particular

bridge is used also aids in division of bridges

into different types.

Temporary

Permanent

Service (Army)

With respect to water level: They are

classified as follows

Causeway

Submersible

High level (normal case)

Grade separators: The purpose of separation

classifies bridges as

Road – over

Road under (subway)

Flyover (road over road)

With respect to connections: The joints used

in the bridge greatly affect the functioning and

analysis of bridge and based on this they may

be classified as

Pin jointed

Riveted/ bolted

Welded

Temporary Bridges: There are also many

types of temporary bridges.

Pontoon

Bailey

Callender – Hamilton

Fig. 11 Through Type Bridge



Fig. 12 Simply Supported Bridge

Fig. 13 Temporary Bridge

2.3 CABLE STAYED BRIDGES

A cable stayed bridge is a bridge whose deck is

suspended by multiple cables that run down to the main

girder from one or more towers .The cable stayed bridge

is specially suited in the span range of 200 to 900 m and

thus provides a transition between the continuous box

girder bridge and the stiffened suspension bridge .It was

developed in Germany in the post war years in an effort

to save steel which was then in short supply. Since then

many cable stayed bridges have been built all over the

world, chiefly because they are economical over a wide

range of span lengths and they are aesthetically attractive

.The wide application of the cable stayed bridge has been

greatly facilitated in recent years by the availability of

high strength steels, the adoption of orthotropic decks

using advanced welding techniques and the use of

electronic computers in conjunction with rigorous

structural analysis of highly indeterminate structures. The

beauty and visibility of a cable stayed bridge at night can

be enhanced by innovative lighting schemes .The early

cable stayed bridges were mainly constructed using steel

for stay cables, Deck and towers. In some of the recent

constructions, the deck and towers have been constructed

in structural concrete or a combination of steel and

concrete.



The Stromsund Bridge in Sweden, built in 1957 with

a main span of 183 m, and the Dusseldorf North Bridge

built in 1958 with a span of 260 m are early examples of

cable – stayed bridges. Another well known bridge in

this category is the Maracaibo Lake Bridge in Venezuela

designed by Ricardo Morandi of Italy and built in 1963.

The Sunshine Skyway Bridge (1987) designed by

Eugene Figg and Jean Muller over Tampa Bay in Florida,

has a main span of 360 m with pre – stressed concrete

deck and single – plane cables. The Dames Pont Bridge

at Jacksonville, Florida, built in 1987 with a span of 390

m is the longest cable stayed bridge in USA. Designed by

Howard Needles and Finsterwalder, the bridge features H

– shaped Reinforced Concrete towers and two – plane

cables supporting R.C deck girders. Currently, the Tatara

Bridge in Japan (1999) with a span of 890 m is the

longest cable – stayed bridge in the world. The Millau

Viaduct, completed in 2005, with six spans of 350 m and

two spans of 240 m, supported on towers up to 235 m

height is a unique cable – stayed bridge.

India‟s first cable – stayed vehicular bridge is the

Akkar Bridge in Sikkim completed in 1988 with two

spans of 76.2 m each. The Second Hooghly Bridge

(VidyasagarSetu), completed in 1992, with a central span

of 457.2 m and two side spans of 182.9 m each, is a

notable engineering achievement in India. The various

cable – stayed bridges are shown in the following table.

Basic concepts of the application and design of the cable

stayed bridges are presented here.

Table 1. List of Cable – Stayed Bridges

The main components of a cable stayed bridge are:

1) Inclined Cables

2) Towers (also referred as pylons)

3) Deck

In a simple form, the cables provided above the deck

and connected to the towers would permit elimination of

intermediate piers facilitating a larger width for purposes

of navigation. When the number of stay cables in the

main span is between 2 and 6 the spans between the stay

supports tend to be large (between 30 and 60 m)

Year Bridge Location Main

Span

(m)

Deck

Material

1999 Tatara Kamiura,

Japan

890 Steel

1994 Normandie Seine,

France

856 Steel

2001 Nanjing – 2 Nanjing,

China

628 Steel

1993 Yangpu Shanghai,

China

602 Composite

1997 Maiko Chuo Nagoya,

Japan

590 Steel

1999 Oresund Sweden 490 Steel

1992 VidyasagarSetu Kolkata 457 Composite

1996 Second Severn Bristol,

UK

456 Composite

1987 Rama IX Bangkok 450 Steel

1983 Luna Spain 440 Concrete

1975 St. Nazaire France 404 Steel

1978 Stretto di

Rande

Vigo,

Spain

400 Steel

1982 Luling Mississippi 372 Steel

1978 Dusseldorf

Flehe

Germany 367 Steel

1987 Sunshine

Skyway

Florida,

USA

366 Concrete

1970 Duisburg

Neuekam

Germany 350 Steel

1990 Tempozan Japan 350 Steel

1990 Glebe Island Australia 345 Concrete

2004 Millau Viaduct Millau,

France

342 Steel

1974 West Gate Australia 336 Steel

1978 Zarate - Brazo Argentina 330 Steel

1993 Karnali Nepal 325 Composite

1972 Kohlbrand Germany 325 Steel

1969 Kniebrucke Germany 320 Steel

1977 Brotonne France 320 Concrete

1971 Erskine Scotland 305 Steel

1959 Severins Cologne 302 Steel

1987 Dongying China 288 Steel

1976 WadiKuf Beida,

Libya

282 Concrete



requiring large bending stiffness. The stay forces are

large and the anchorages of cables become complicated.

The erection of such bridges involves use of auxiliary

structures. On the other hand , the use of multiple stay

cables would facilitate smaller distances between points

of supports (between 6 and 10 m) for the deck girders ,

resulting in reduced structural depth and facilitating

erection by free cantilever method without auxiliary

supports .

The multiple stay cable system also permits easy

replacement of cables if needed and enhances

aerodynamics stability through increased damping

capacity. The deck can be supported by a number of

cables in a fan form (meeting in a bunch at the tower) or

in a harp form (joining at different levels on the tower) as

shown in the figure. The figure shows a typical fan-

shaped cable arrangement with the anchorages at the

tower distributed vertically down a certain length

(modified fan form). This arrangement facilitates easy

replacement of cables at a later date in case of accidents.

The fan type configuration results in minimum axial

force in deck girders. The harp form requires larger

quantity of steel for the cables. Includes the fan shape is

superior from a structural and economical view. The harp

shape possesses enhanced aesthetics. The harp

configuration cables also permits erection of the tower

and the deck to progress at the same time. Because of the

damping effect of inclined cables of varying lengths, the

cables stayed decks are less prone to wind –induced

oscillation than suspension bridges.

Fig. 14 Types of Cable Systems

Based on the span arrangement, the cable stayed bridge

can be one of four types:

1) Bridge with an eccentric tower, e.g. Hoescht

Bridge on main river

2) Symmetrical two – span bridge, e.g.

Ottmarshein Bridge in France

3) Three – span bridge, e.g. Brotonne Bridge,

France

4) Multi – span Bridge, e.g. Millau Viaduct,

France

TYPICAL CABLE STAYED BRIDGES

The first modern cable stayed bridge was the

Stromsund bridge in Sweden, built in 1956 with a main

span of 183m and two side span of 75m each .This

bridge consist of continuous plate girders supported by

two plane radial cables anchored to the tops of towers of

portal shape. The deck is of reinforced concrete slab

supported on strings and cross beams. The Dusseldorf

north bridge (1958) has harp type cables in two vertical

planes attached to single towers. The decking is of

orthotropic steel deck with box shaped main girders

stiffened by cross beams. The bridge has spans of 108-

260-108 m. The Severins Bridge (1959) in cologne has a



single A-frame tower with fan type cables, converging at

the apex of the A- frame. The decking is of orthotropic

steel deck with two main girders of box section as in fig.

The Norderelbe Bridge (1962) in Hamburg was the first

bridge with cables arranged in star type in single plane.

The bridge has a box section at centre with one single

web girder on either side as in fig. The cable

configuration is justified more from aesthetic

considerations than on economic grounds. The Brotonne

Bridge built in 1977 with a main span of 320 m has a

single plane of cable stays and uses a precast pre -

stressed concrete box girder deck. The Yangpu Bridge in

Shanghai, china built in 1994 with a main span of 620 m

marked a significant development. This was surpassed in

the same year by the Normandie Bridge in France with a

main span of 856 m. The Sunniberg Bridge in

Switzerland built in 1999 with main spans of 140 m and

the Millau viaduct in France completed in 2005 with

main spans of 342 m are outstanding applications of

multi-span cable stayed bridges.

Akkar Bridge (2 spans of 79.0 m) and Hardwar bridge (2

spans of 65.0 m) are early examples of Indian cable

stayed bridges, essentially evolved as forerunners for

longer spans to follow .The second Hooghly bridge

(Vidyasagarsethu) completed in 1992 with a main span

of 457 m and side spans of 182.9 m each, using fan type

cable arrangement, is a land mark of bridge construction

in India. The Tatara Bridge on the Onomichi –Lmabari

highway route of the Honshu-shikoku bridge project in

Japan is the longest span cable stayed bridge in the world

with a main span of 890 m. The steel towers are 176 m

high above the bridge deck, corresponding to 0.2 of the

main span. The towers are shaped like an inverted Y after

examining the wind resistance, structural efficiency and

aesthetics. The stay cables have two-plane multi-fan

shape. The cables are anchored at spacing of 20 m at

deck level and at 3 m spacing at the tower. Based on

wind tunnel tests, the surface of the polyethylene cover

of the stay cables was provided with indentations, with a

view to prevent the turbulence that results from wind

blowing on rain water running on the surface of the long

stay cables. This innovation provides sufficient damping

and avoids the need for ties between the cables. The deck

is of streamlined steel box girder. The deck width is 28.1

m corresponding to width-to-span ratio of 1:31.7. The

center span was erected by the cantilever method. The

aesthetic appeal, the economic advantage and the ease of

construction make the cable stayed bridge the preferred

option in the span range of 200 to 900 m.

Fig. 15 Tatara Bridge, Japan

Fig. 16 Millau Viaduct Bridge, France

ARRANGEMENT OF CABLES

The cables may be arranged in one central plane (axial

suspension) as in Norderelbe bridge, in two vertical

planes with twin-leg tower as in Stromsund or



Dusseldorf North bridges, or in two inclined planes as in

Severins bridge (lateral suspension) .The single-plane

system has the advantage that the anchorage at deck level

can be accommodated in the traffic median resulting in

the least value of required total width of deck. With the

two -planes system, additional widths are needed to

accommodate the towers and deck anchorages.

Aesthetically, the single-plane system is more attractive

as this affords an unobstructed view on one side for the

motorist. Other notable examples of single-plane system

are the Rama IX Bridge (1987) in Bangkok, Thailand,

the Sunshine Skyway Bridge (1987) in Florida, USA and

the Normandie Bridge (1994) in France. In the case of a

two-plane system of cables, a side view of the bridge

would give the impression of intersection of the cables.

The choice of the cable arrangement should be done with

care and diligence, so as to ensure an enhanced aesthetic

quality of the bridge through a system in harmony with

the environment.

The two inclined plane system of cables with the

cables radiating from the apex of an A-frame as in

Severins bridge facilitates the three-dimensional

structural performance of the superstructure and reduces

the torsional oscillations of the deck due to wind, thus

enhancing the aerodynamic stability of the bridge. The

torque due to eccentric concentrated loads would

necessitate the use of box section orthotropic deck for the

single-plane system. The decking is generally of

orthotropic plate system with box girders for the two-

plane system also, but can be of pre stressed concrete

girders as in Maracaibo bridge in Venezuela and Hoescht

bridge over main river in Germany. The Rama VIII

Bridge in Bangkok uses a combination of two-plane and

single plane systems. Using an inverted-Y pylon, the 300

m main span is supported with twin inclined stays while

the back span has a single plane system of stays.

DECK STRUCTURE

While the deck is merely supported by the cables in

suspension bridge, the deck of a cable stayed is an

integral part of the structure resisting the axial force and

bending induced by the stay cables. For bridge width

greater than 15 m and spans in excess of 500 m, the need

to reduce dead weight prompts the use of all-steel

orthotropic plate deck, as adopted for the Normandie

Bridge and the Tatara Bridge. Torsion box deck sections

in pre stressed concrete have been used with single-plane

system, as in Brotonne Bridge and the sunshine bridge.

Composite deck section have been employed in the

second Hooghly bridge at Kolkata, India and the Second

Severn crossing, U K. Special attention should be

devoted to the anchorage of cables to the deck. The

superstructure of the main span is normally constructed

using the segmental cantilever method.

The ratio of the side span (Ls) to the main span (Lm)

for the case of a bridge with towers on both sides of the

main span usually lies between 0.3 and 0.45.The ratio

Ls\Lm can be 0.42 for concrete highway bridge decks

and not more than 0.34 for Railway Bridge. This ratio

influences the changes in stress in the back stay cables

due to variation of live load. It further influences the

magnitude of vertical forces at the anchor pier, the

anchor force decreasing with increasing Ls\Lm. The

choice of Ls\Lm depends also on the local conditions of

water depth and foundation.

TOWERS

Towers carry the forces imposed on the bridges on the

bridge to the ground. They are not replaceable during the

life of the bridge. Hence they should be designed to be

structurally strong, constructible, durable and

economical.

The tower may take any one of the following forms:

1) Single free standing tower, as in Norderelbe

Bridge

2) Pair of free standing tower shafts, as in

Dusseldorf North Bridge

3) Portal frame, as in Severins Bridge and

Second Hooghly Bridge

4) A – frame, as in Severins Bridge or inverted

Y – shape as in Yangpu Bridge

5) Diamond configuration, as in Globe Island

Bridge, sydney

When the stay cables are in one plane, a single free

standing tower may be adopted. In this case, the pier

below the box girder should be sufficiently wide for



bearings to resist the torsional moments of the

superstructure. For bridges with cables in two planes, the

towers can be a free standing pair, or a portal frame with

a slender bracing. An additional bracing may be

introduced below the deck. The A-shaped tower and the

inverted Y-shaped tower have been favoured for long

bridges having shallow box girder decks in regions of

strong wind forces. The land take at the base can be

reduced by adopting a diamond configuration, as used in

the Tatara Bridge. Typical arrangements of towers are

shown in figure.

Fig. 17 Types of Pylons

Since the tower is the most conspicuous component in

a cable stayed bridge, besides structural considerations,

aesthetics plays a prominent part in the selection of the

particular shape of the tower. For example, the proximity

of cologne cathedral influenced the adoption of the A-

frame for the Severins Bridge. Sometimes, an additional

height is provided for the tower above the point of

connection of the cable for architectural reasons, as in

Norderelbe Bridge. Anchorage of cables at the tower

should follow good order. Since the cables at the deck

level are anchored along a line along the edges or at the

middle of the deck, it is natural that these should end

along a vertical line at the tower head. In the case of A-

shaped tower, the anchorage line can be parallel to the

tower leg it is not desirable to spread the anchorages

transversely in one layer at the tower.

The single tower or towers consisting of a pair of

separate columns will be stable in the lateral direction

due to the restoring force provided by the cables in case

of lateral displacement due to wind forces, as long as the

cable anchorages are situated at a level above the base of

the tower. The towers may be designed to be hinged or

fixed at the base, depending on the magnitude of the

vertical loads and distribution of the cable forces. While

a tower with a fixed base induces a large moment, the

increased rigidity of the total structure resulting from a

fixed base at the towers and the relative ease in erection

as compared with a hinged base may be advantageous.

On the other hand, the hinged base results in reduced

bending moments in the towers and may be advantageous

with weak soil conditions. The towers should be slender

and should have a low bending stiffness in the

longitudinal direction so that back stay cables will be

functional in partially catering to live loads in the main

span. Towers should normally be vertical.

The height of the tower should be preferably being in

the range of 0.2 to 0.25 Lm. The higher the tower, the

smaller will be the quantity of steel required for the

cables and the compressive forces. But it is not

advantageous to increase the height beyond 0.25 Lm.

CABLES

The stay cables constitute critical components of a

cable stayed bridge, as they carry the load of the deck

and transfer it to the tower and the back stay cable

anchorage. The main requirements of stay cables are:

1) High load carrying capacity

2) High and stable Young‟s Modulus of

elasticity

3) Compact cross – section

4) High fatigue resistance

5) Ease in corrosion protection

6) Handling convenience

7) Low cost

The ultimate tensile strength of wire is of the order of

1600 MPa. A typical section of a stay cable is shown in

figure 18 (Fig.18). While locked coil strands have been

used in early bridges, the recent preference is towards the

use of cables with bundles of parallel wires or parallel



long lay strands. The sizes of cables are selected to

facilitate a reasonable spacing at the deck anchorages.

Parallel wires cables using 7mm wires of high tensile

steel have been adopted in Second Hooghly Bridge.

Corrosion protection of the cables is of paramount

importance. For this purpose, the steel may be housed

inside a polyethylene (PE) tube which is tightly

connected to the anchorage. The cables are anchored at

the deck and at the tower. The anchorage at the deck is

fixed and has a provision for a neoprene pad damper to

damp oscillations. The length adjustment is done at the

tower end.

The cables are pre - stressed by introducing additional

tensile force is the cables in order to improve the stress in

the main girder and tower at the completion stage, to

prevent the lowering of rigidity due to sagging of cable,

and to optimize the cable condition for the erection. The

magnitude of the pre - stress is determined by taking into

consideration the following factors: I) the horizontal

component of each cable tension in balanced such that

there is no in-plane bending of the tower due to balanced

horizontal force due to dead load at the completion stage:

and ii) the net force on the main girder member at the

connection of the cable at the completion stage be zero.

Currently the steel used for cables have ultimate

tensile of the order of 1600Mpa. Carbon fibre cables

having UTS of about 3300Mpa are under development.

The latter cables are claimed to have negligible corrosion

and to possess high fatigue resistance. However, carbon

fibber cables are presently very expensive.

Fig. 18 Typical cross section of Stay Cable

ANALYSIS

The cable stayed bridge with multi – stay

configuration is a statically indeterminate structure with a

high order of indeterminacy. The deck acts as a

continuous beam on elastic supports of varying stiffness.

Bending moments in the deck and pylons increase due to

second order effects due to deflection of the structure.

The effects of creep and shrinkage during construction

and service life should be considered for concrete and

composite decks. The internal force distribution in the

deck and tower can be managed to be compression with

minimum bending, by adjustment of the forces in the

stay cables. A rigorous analysis considering three –

dimensional space action is quiet complex. Approximate

designs can be made using a two – dimensional

approach. Though the cable stays show a non – linear

behaviour due to large displacements, sag in cables and

moment – axial force interactions in stays, girders and

towers, an approximate analysis assuming linear

behaviour leads to satisfactory results in most cases.

However, a non – linear analysis is essential for very

long span bridges.

CONSTRUCTION BY CANTILEVER METHOD



The cantilever method is normally adopted for the

construction of long span cable stayed bridges. Here the

towers are built first. Each new segment is built at site or

installed with precast segment, and then supported by

one new cable or a pair of new cables which balance its

weight. The stresses in the girder and the towers are

related to the cable tensions. Since the geometric profile

of the girder or elevation of the bridge segments is

mainly controlled by the cable lengths, the cable length

should be set appropriately at the erection of each

segment. During construction, monitoring and

adjustment of the cable tension and geometric profile

require special attention.

A notable example of construction of a major cable

stayed bridge by cantilever method is the Yangpu Bridge

in Shanghai, China, built in 1994 with a main span of

602 m. The composite girders of this bridge consisted of

prefabricated, wholly welded steel girders and precast

reinforced conceret deck slab.

Depending on the bridge site, cable stayed bridges can

have any one of four general layouts of spans:

1) Cable stayed bridges with one eccentric

tower, eccentric with respect to the gap to be

bridged, e.g. Severins Bridge

2) Symmetrical two – span cable stayed bridges

e.g. Akkar Bridge

3) Three – span cable stayed bridges, e.g.

Second Hooghly Bridge

4) Multi – span cable stayed bridge e.g. Millau

Viaduct.

Of these the most common type is the three – span

cable stayed bridge, consisting of the central main span

and the two side spans. Temporary stability during

construction is a major problem, particularly just prior to

closure at mid span. The structure must be able to

withstand the effects due to wind and accidental loads

due to mishaps during erection. When intermediate piers

are provided in the side spans, the stability is very much

enhanced. In this case, the side spans are built first on the

intermediate supports, and later the long cantilevers in

the main span.

2.4 GENERAL STEPS IN BRIDGE DESIGN

The sequence of planning for bridges forming part of

a new highway or railway project will form part of that

particular project planning. But, in case of a major

crossing across a large or important river or a major road

intersection, a more detailed planning for the particular

bridge itself will be required.

Different steps involved in planning for such a bridge

and for major links are:

1) Study the need for a bridge

2) Assess the traffic requirement

3) Location study

4) Study of alternatives

5) Short listing feasible alternatives

6) Developing concept plans for alternatives

including choice of form, materials, span

arrangements etc...

7) Preliminary design and costing

8) Evaluation of alternatives, risk analysis and

final choice

9) Finding resources, detailed survey and design

10) Implementation including final preparation of

bid documents, fixing agency, construction

and commissioning

A new highway or railway line may need to be

provided as part of development of an area; linking two

or more places of commercial or tourist interest and

strategic importance; as a link to a port, mines, industrial

area and/or a large thermal power plant. Their need is

usually established by evaluating their socio – economic

and/or financial viability.

Once the need for the project is established the

various details have to be worked out. Any highway or

rail line will be crossing a number of small and large

streams, canals, rivers and lakes, over which culverts or

bridges will have to be provided. Need for a culvert or

bridges become automatically established in such cases

during preparation of project sheets. When a bridge

forming part of such new road or rail projects has to be

provided over a large river, a more detailed initial

planning is required involving various steps listed above.

Apart from this, need may arise to provide additional

bridges across major rivers, for linking two major



highways or rail lines or a network of roads in an urban

area, including grade separators at busy road

intersections in urban areas. Similar planning approach is

required in such projects.

LOCATION OF BRIDGE

Cross drainage works on alternative alignments of a

road or rail alignment can differ considerably and since

they tend to form 15 to 20 % of the cost of the total

project, it is essential to analyze and consider the effect

of all the CD works on the alignment, before choosing

the alignment. While fixing the horizontal alignment of

the line/road, it is desirable to select a bridge site such

that the bridge/culvert is:

On a straight reach of the stream avoiding any

bends or meanders

Clear of the confluence of any tributaries or

branches

Confined within well defined banks

With the road approach on either side straight

to maximum extent and

With the crossing normal to the road alignment

and if skew is unavoidable, limit the skew

angle

In addition, major river crossings should satisfy

following conditions to the maximum extent.

River Regime

The upstream reach of the river, should be

straight, and any sharp bend downstream

should be avoided.

The river in the reach should have a regime

flow free of whirls, eddies and excess current.

It should preferably not have any confluence of

streams immediately upstream.

The channel in the reach should be well

defined and as narrow as possible.

It should have firm high banks which are fairly

inerodable (the ideal site is at a gorge).

In a meandering river, it should be at a nodal

point

Where artificial gorging is necessary due to absence of

firm inerodable high banks, it should be possible to build

protection works like guide bunds on a dry location or in

shallow water if unavoidable.

Approaches

The approach bank should be secure, and not

be liable to flash flood attacks or major spills

during floods.

It should not be too high or too expensive to

build; it should not pass through high hills or

major drainage basins or built up areas or

religious structures.

It should have reasonable proximity to the

main road or railway to be served without need

for long or costly connecting links.

It should be such as to avoid excessive

construction works under water or over marshy

lands.

Approaches and protection works should be

such as to involve minimum recurring

maintenance expenditure and be reasonably

safe from flood damages which would

otherwise put the bridge out of use for long

periods.

INVESTIGATIONS FOR MAJOR BRIDGES

Planning and design of major bridges call for more

detailed survey and collection of data. Such requirements

are detailed in ensuing paragraphs:

TOPOGRAPHIC DETAILS `

The survey of the river course should extend up to the

firm banks or up to the HEL line, if it over-tops the banks

and water spreads out. It should cover a distance of about

2 km upstream and 2 km downstream of the alignment in

the case of smaller streams and 5 km upstream and 2 km

downstream for larger rivers. This is necessary for

locating a straight reach of river where a good normal

crossing can be provided. The extent of water course at

flood time (excluding, of course, spill) will give an idea

of` the minimum width of waterway that will be required

for providing a bridge with minimum obstruction to the

natural flow.



The plan of the water course should be drawn to a

scale of l : 2000 for smaller rivers and l : 5000 for larger

ones. Cross sections should be taken at the proposed

crossing, one upstream and one downstream, each about

2 km apart. They should be drawn to the same horizontal

scale as that of the plan. In case it is fairly flat, the cross

section can be plotted to different vertical and horizontal

scales (the latter being the same as that of the plan), with

the proportion between the two not less than 1:10 this

will give a better idea of the area of section of flow for

working out the observed discharge and also correctly,

determining the position of the bridge so as to cover the

deeper and perennially flowing channels.

The plan should cover the details of all streams

joining the main stream river within the reach surveyed,

the location and value of any benchmark, and the closest

inhabited locality; it should also provide sufficient spot-

levels for drawing contours, and indicate clearly the

alignment and position of the proposed bridge with its

change marked. The low water level, highest flood level

(HFL) and ordinary flood level (OFL) should be marked

on the cross section. The position of any borings and trial

pits should be indicated on the plan while the details of ̀

bore data should be indicated on the section. The position

of GTS benchmarks with their values and also any

survey reference pillars left by the survey party should be

marked, indicating, by the side, benchmark values. Such

detailing will give an idea of all related data governing

the siting of the bridge at a glance. If any checking

becomes necessary later, referencing will be easy and

quick, without any need to refer to a number of detailed

drawings.

The survey can be conducted by triangulation in the

case of a small stream or by a closed traverse in the case

of larger streams. (For detailed procedure for

triangulation and other detailed surveys, in order to

achieve a good accuracy of the plan, suitable cross

checks in the case of running open traverses along the

bank should be established. Some spot-levels should be

taken so that the contours can be plotted on the plan also.

This plotting of contours will help in proper location of

the axis of bridge with respect to the stream and

determining the sew angle, if any. Any marginal bunds,

other flood protection works, and any tanks, lakes and

irrigation works in the vicinity should be clearly

indicated. The direction of flow of the stream and the

north line are the most important markings that are

sometimes omitted by oversight.

CATCHMENTS AREA MAP

The catchments area map for major bridges can be

prepared from the available topographic sheets of the

most recent survey made in the area. The Survey of India

has prepared maps for the entire country to scale 1” to a

mile or 1: 50,000. They are now preparing maps to scale

1: 25,000 and such maps for some areas are available.

The map available to the largest scale should be obtained

from them. All these maps contain contours for areas

covered. Hence, the ridge line bounding the watershed

contributing to the flow to a particular stream/river can

be easily traced on such maps. A tracing showing the

river, tributaries and the ridge or catchments boundary

line prepared will form the catchments area map. The

area bounded can be worked out either by a planimeter or

using squared paper to proper scale. Where the

catchments is small, close enough contours may not be

available on these topographical sheets and a tracing of

the ridge line may be difficult.

Additional details to be marked on the catchments area

map are:

1) All irrigation tanks and reservoirs in the

catchment area intercepting the contributing

streams and which are likely to affect the

bridge if any of them is damaged

2) Rain gauge stations

3) Discharge observations

4) River bed levels along the river up to the

source, as may be available

5) Levels of peaks on ridges and peaks of

isolated hillocks falling within

If possible, the heaviest intensity of rainfall recorded

at the rain gauge stations can be indicated on the

catchments plan. The work of preparation of this map can



be done in the office itself and supplementary

information obtained from enquiries from other

departmental officers.

HYDROLOGIC PARTICULARS

Some particulars which come under this heading have

been covered under `topographic details‟ and catchments

area‟. The hydrographical, i.e., gauging and discharge

details available for the bridge site or the nearest

available site should be collected for the longest periods

available, either from irrigation or flood control

engineers. If not available, some short – term

observations for velocity and discharge can be made by

the survey team. Enquiries should be made regarding the

data, formulae and coefficients adopted for working out

the design discharge for the same or similar

streams/rivers in the same area by other engineers. The

size of the openings which have been provided for

existing bridges on the same river upstream and

downstream should be ascertained along with

information on past experience regarding their adequacy

or otherwise. Hydrographical details available for such

bridges can be of much help.

GEO-TECHNICAL DETAILS

The scope of geo-technical investigations should be

such as to enable the designer determine or comprehend

the following:

1) Location and extent of soft layers and gas

pockets, if any, especially in apparent hard

founding strata

2) The type of rock, dips, faults and fissures

3) Possibility of subsidence due to mining in the

neighbourhood

4) Sub – soil water level and artesian conditions

5) Quality of ground water

6) Particle size and classification of the soils at

various levels

7) Physical properties of the soil to determine

the bearing capacity

8) Settlement characteristics of the soil for

determining the settlement and differential

settlement

9) Frictional and porosity properties for

determining sinking or driving effort

10) Any possible constructional difficulties

SEISMOLOGY OF THE AREA

India is divided into five seismic zones based on the

likely intensity and frequency of earthquakes. The

coefficients to be used for arriving at horizontal and

vertical seismic forces induced on the structure in

different zones are covered in IS: 1893. It may be

necessary to modify the coefficients in specific cases or

carry out model studies to determine these coefficients in

the case of very long spans in highly earthquake-prone

areas, particularly for the sub – Himalayan zone, the

entire north eastern India and in some areas like Koyna

where there is a past history of occurrence of disastrous

earthquakes. Detailed information can be obtained from

the Geological Survey and Meteorological Departments

regarding the seismic history and intensity as well as of ̀

damages caused by past earthquakes in the area. This

information can be used for modifying the coefficient of

design of structures or Carry out model studies. In case

there is any geological fault along the river course, the

Meteorological Department should be consulted

regarding the likelihood of its buffing action.

NAVIGATIONAL REQUIREMENTS

There may be some plans by the Inland Navigation

Department of the State or Union Government for

introducing navigation in the water course to be bridged

in the foreseeable fixture. Provision should be made for

adequate headroom above the OFL (or normal HFL) in

such cases. The general standards suggested for different

types of craft (boats and barges) used in inland

navigation are indicated in table 2.



Table 2 Navigational Clearance for Bridges

Tonnag

e of

Vessel

Lengt

h (m)

Bea

m

(m)

Draf

t

(m)

Minimu

m clear

span (m)

Minimu

m

headroo

m over

mean

HFL (m)

50 18 5.0 1.5 15 2.0

100 24 5.0 1.5 17 3.0

300 35 6.5 2.0 25 3.9

600 60 7.0 2.0 30 6.0

900 and

more

75 10.0 2.0 90 to

110

10 to 12

CONSTRUCTION RESOURCES

During the field survey, sufficient information should

be collected to have an idea of the type of labour that will

be available locally and if they will have to be

supplemented by bringing people, particularly skilled,

from outside. If all the required labour is locally

available, they should be able to come to the site, from

their homes; they will not need much of site

accommodation and may only need some transport

arrangement. If any type of skilled and other labour has

to be brought from outside, residential and! Or camp

accommodation will have to be provided for them as

close to the site as possible. Such people will have to be

paid higher rates of wages and given additional leave and

also travel expenses from and to i - their homes.

Information collected will give an idea of the extent

which temporary accommodation for such imported

labour will have to be provided and also to arrive at

correct unit rates for the labour component of the

various items of work. The availability of construction

materials, particularly bricks, quarry materials like stone

and aggregate, and good quality sand and timber in the

vicinity will have to be found out to determine the extent

to which transportation will be involved in carrying these

to the site. While doing so, the existing roads, pathways,

the availability of the various types of transport, their

cost, etc. should be considered. This will give a better

idea to work out to the unit cost to be adopted for

material components of various items of work and also

the infra-structure requirement for transporting materials

and equipment.

PARTICULARS OF NEAREST BRIDGES

During the investigations, particulars with regard to

foundation details, clearances and other physical

features of the bridges that might have been constructed

on the same water course on the nearest railway line or

road should be obtained. Enquiries should also be made

of the bridges that have been overtopped or breached

since their construction or any other type of failure to the

structure. In the case of bridges of smaller magnitude, it

should be sufficient if particulars of such bridges within

about l0 km radius are obtained. In the case of larger

bridges, particulars should be gathered for those situated

even 50 to 60 km away.

TRAFFIC FORECAST

If the bridge forms part of an overall project like the

construction of a new railway line or construction of a

new road, the traffic forecast would have been already

made earlier. If not made already, this forecast will have

to be done for purposes of:

1) Determining the size of the bridge, i.e., the

number of lanes or tracks to be provided and

whether a footpath has to be provided.

2) Working out the benefits that will accrue by

providing such a bridge (if it is a project by

itself).

There may be some traffic across the stream already at

the location, but that may be using some other mode like

a ferry, or a crossing may be made only when the water

level is low. It may also be taking the route over a bridge

already existing over the stream by a detour Hence, an

assessment has to be made first of the diversion of the

existing traffic which will use the bridge after it is

provided. Second, the provision of the bridge itself can

create development opportunities on either side and also

increase the inter- flow, and this will have to be forecast

taking into consideration the economic and social

conditions of the area. The structure to be provided

should be for a volume of traffic that will develop over a

foreseeable future so that no additional work or



reconstruction will be called for in that period. A time

space of 40 to 50 years is generally advisable for this.

REPORT AND DRAWING

The documents to be prepared for the bridge project

will comprise a brief report giving the salient features for

aiding in detailed design and an estimate along with the

under mentioned drawings:

a) An index map to scale, 1; 50,000 in the case of

small rivers and 1: 2, 50,000 in the case of

larger ones. It should show the road/rail

alignment, the position of the proposed bridge

with the chainage, general topography of the

area, existing communication lines. Important

towns and villages, rivers, canals and other

irrigation works.

b) A survey plan showing all topographical

features in the immediate vicinity for sufficient

distance on either side of the proposed bridge

showing the contours at 1 to 2m intervals

should be prepared; All alternative sites should

be marked on this plan. All features that can

influence the design of the bridge should also

be marked on this plan. A longitudinal section

along the proposed alignment to the same

horizontal scale as that of the plan and one-

tenth of the same as the vertical scale should be

drawn. The line showing the top of the

proposed formation should be marked in red on

the same sheet. These distances can be reduced

for artificial (like men-made irrigation and

navigation canals) and in difficult countries by

the engineer to suit site conditions. The Indian

Roads Congress requires this sheet to cover

details for distances on either side and to scales

as indicated below.

Catchment areas less than 3 sq. km:

100 metres and to scale

1:1000

Catchment areas of 3 to 15 sq. km:

300 metres and to scale

1:1000

Catchment areas over 15 sq. km:

1.5 km and to scale

1:5000

c) A site plan to a suitable scale should show the

selected site and ground details for a distance

of 100 m upstream and 100 m downstream for

small bridges and 500 m on either side for

larger bridges. It shall contain the following

details:

1) Name of the channel and road, chainage

and identification mark (number etc...)

allotted to the crossing

2) Direction of flow, maximum and

minimum discharges

3) Existing and proposed alignments, if it

is in replacement

4) Angle and direction of skew

5) Name of the nearest identifiable town at

either end of the road

6) Position of any bench marks and their

values

7) Reference to the value of the bench

marks, the mean sea level taken as

datum

8) Location of cross – section lines

9) Longitudinal section (i.e., alignment

centre) line with reduced levels marked

10) Location of trial pits and bore holes with

identification numbers/ marks

11) Location of any obstruction for road

alignment, such as nullahs, buildings,

wells, outcrops of rocks etc... (the scale

should preferably be to 1:1000) the

alignment line shall be shown in form of

a thick green line.

d) Cross Sections, one along the proposed

alignment and two others, one upstream and

one downstream at a suitable distance to scale

1 : 1000 horizontal and 1 : 100 vertical. It

should contain the following:

1) Bed levels up to tops of banks/ bunds

and ground levels for sufficient distance

beyond, the intervals being such as to



give a clear idea of the uneven features

both in the bed and ground

2) Location and depth of trial pits or

borings and nature of soil in bed, banks

and approaches (in cases of smaller

bridges and shallow bores, the section of

soil profile at each bore/ pit can be given

on this itself).

3) HFL, OFL, LWL on the entire three

cross – sections.

e) In addition, a few more cross sections to the

same horizontal and vertical scales as that of

the site plan-

f) A longitudinal section along the channel,

showing the site of the bridge, to the same

horizontal scale as the survey plan (in the case

of small bridges this can be plotted on the

survey plan itself), the vertical scale not less

than 1: 1000.

g) Typical cross sections along alternative sites

considered, if any, with a brief note giving

reasons for selection of the proposed site to the

same scale as in (d) above.

The purposes of these drawings are given below briefly:

Index map: The index map will indicate the

geographical location of the bridge and the

nature of the area served by the bridge

Survey plan: It will give an idea of the nature

and direction of flow of the river and will help

in choosing a location that will ensure a

straight flow through the bridge. The

catchment area map is required to assess the

catchment areas and the type of terrain to work

out the design discharge using a flood formula

Plan: The plan will show the exact location

and lay out of the bridge for the purpose of

future setting out

Cross – sections: These are required firstly for

working out the area of flow as existing and the

slope of the river with which the volume of

discharge that has passed over the site can be

worked out. It is also used for centring the

bridge opening, and locating abutments and

piers so that the bridge covers the deepest and

perennially flowing channel. The flood levels

are required for the purpose of determining the

deck level of the bridge after allowing for the

necessary clearance. The low water level helps

in fixing the top of the well or pile foundations

taking into consideration the working

conditions.

Collection of data: The collection of data with

reference to construction resources and the

details of the nearest bridge across the same

river are required for obtaining an idea of the

construction problems that are likely to be met

with and working out the unit cost for

preparation of the estimate for the cost of the

bridge and appurtenant works. Forecast of the

traffic is likely to use the bridge is made for

determining the width of the bridge and in the

case of a costly alternative, for working out the

relative cost – benefit ration also.

Report: After the collection of these data and

working out the details, a report has to be made

out bringing the salient features of the bridge,

its estimated cost, cost – benefit ration, etc...

for helping to obtain the sanction. This report

should, as far as possible, be so detailed that

when work is sanctioned, the site work can be

commenced immediately.

3.DESIGN PROCEDURE

3.1 EXISTING BRIDGE DESCRIPTION

A road bridge presently exists across Gauthami River,

a tributary of Godavari between Yanam and Yedurlanka.

It is named as “BalayogiVaradhi”. It is a simply

supported Pre – stressed Concrete (PSC) box girder

bridge with 43 spans @ 40 m and 2 end spans @39.4 m

between centre to centre (c/c) of pier/ face of dirt wall.

The total length of the bridge is 1798.8 m between the

river faces of dirt walls. The bridge was constructed by

M/s. Navayuga Engineering Company Limited,

Visakhapatnam under Build Operate and Transfer (BOT)

vide Government Order (G.O) as a part of construction



works of National Highway (NH) 214. The work was

supervised by Consulting Engineering Services (India)

Private Limited (CES) and PWD, Andhra Pradesh.

Now using the topographical survey data,

hydrographical survey data, sub – soil investigation data

conducted by PWD, Andhra Pradesh for the construction

of this bridge we are designing a Cable – Stayed Railway

Bridge in the same location is proposed in this report in

order to compare the advantages of each bridge.

3.2 AREA DESCRIPTION

The bridge is located between yanam (one of the four

districts of the Union Territory of Pondicherry in India)

and Yedurlanka (East Godavari District of Andhra

Pradesh in India) on Gauthami River, a tributary of the

perennial river Godavari. An extensive survey of the

area was done before deciding on the site for the bridge.

Yanam (Latitude16°42' N – 16°46' N; Longitude:

82°11' E – 82°19' E)is a town in the Indian union

territory of Pondicherry; it is located in Yanam district.

Yanam has about 300 years of history and it was

transferred to India in 1954. It forms a 30 km² enclave in

the district of East Godavari in Andhra Pradesh. It

occupies the delta of Godavari River, the town is situated

where the River Coringa(Atreya) branches off from

Gauthami into two parts, 9 km from the Bay of Bengal in

the Coromandel Coast. It has a population of about

32,000. Due to some relaxation in Tax and other

exemptions, lots of Business activities go on in Yanam.

Many people are getting employment in these

industries/firms. The major business areas in this region

are Coconut Dwelling, Rice Mills, Fishing and Other

Traditional Occupations. According to the 1995–2005

Development Records it was the first best constituency

in Pondicherry, which is moving forward in the

development sector, and also one of the best

constituencies in India.

Yedurlanka (Latitude 160 42‟ N; Longitude 820 12‟ E) a

village in East Godavari district of Andhra Pradesh is

situated on the banks of Gauthami River. It is located

28.7 km from the district main City Kakinada in

I.Polavarammandal. The District is known as rice bowl

of Andhra Pradesh with lush paddy fields and coconut

groves. The village is located in the Godavari Delta

region. The main soils in the area are alluvial red soil,

sandy loam and sandy clay.

3.3 NEED FOR BRIDGE

During the time of bridge construction there was no

bridge existing across the river Gauthami, branch of

Godavari River, connecting Yanam to Yedurlanka in

East Godavari District in Andhra Pradesh. Ferry service

was being operated for crossing the river. However, since

the width of the river is very large between the banks, it

was a huge inconvenience to the large crowds who had to

cross the river daily. It was therefore felt necessary to

construct a high level bridge at this location for smooth

flow of daily traffic. Before finalizing the project bridge

expert from CES along with representatives of PWD,

visited the site to have firsthand information about the

work and local conditions.

This stretch from Yanam – Yedurlanka is now a part of

NH 214. At the time of survey the people in Konaseema

area covering Yedurlanka, Muramalla, Polavaram,

Pallamkurru and other villages up to Amalapuram of East

Godavari District had to cross the Gauthami, Branch of

Godavari River by ferry service from Yedurlanka in

Konaseema area to Yanam in Pondicherry Union

Territory and then proceed by road to Kakinada, the

District Head Quarters of East Godavari District. When

the river is in floods, there is much inconvenience in

transportation of their agricultural produce to the markets

of Yanam and Kakinada and vice – versa. Yanam is fast

growing Industrial center and several Gas Based

Industries are now coming up around Yanam and

Kakinada. Kakinada port is fast developing and two

Major fertilizer Companies i.e., Godavari and Nagarjuna

fertilizers are located at Kakinada.

If a high level bridge is constructed across Gauthami

branch of river Godavari between Yanam and

Yedurlanka, it will help in development of 2 regions i.e.,

Yanam of Pondicherry State and Konaseema area

(Central Delta) of Andhra Pradesh. As the O.N.G.C

activities in Godavari basin are in full swing it will



facilitate government and transportation of their vehicles

and also supply of Natural Gas to Yanam and other

industrially developing centers in East Godavari District.

Also several raw materials particularly, that required for

coir industries and edible oil units can be easily

transported from Konaseema area to Yanam. Further the

construction of the bridge reduces the distance between

Amalapuram and Kakinada by 40 km, by road. Apart

from the above mentioned facts, the fact that both Yanam

and East Godavari Districts are centers of tourism is well

known. Therefore providing a bridge in this region will

enable the development of tourism in this area.

Railway track always leads to improvement in

the economy of any area. The provision of this railway

link between Yanam and Yedurlanka will prove

advantageous both to the industries in the area as well as

tourism.

3.4 TOPOGRAPHICAL SURVEY

A detailed survey has been carried out in the area in

order to decide the alignment of the bridge. Due to lack

of resources and permissions we could not conduct the

survey, but as a part of the project we have collected the

data from R&B, Andhra Pradesh and made a detailed

study of the same. The method used in surveying and the

various facts observed thereby in the finalization of the

alignment are briefly described below.

The survey of the river course was done up to the

High Flood Level (HFL) line covering a distance of

about 5 km upstream and 2 km downstream for locating a

straight reach of river where a normal crossing can be

provided. Hydrographic surveying was used for

surveying over the body of water and determining the

levels at various points across the stream. A contour

survey i.e., triangulation by closed traverse was also

carried out to determine the levels at various points near

the river. Before deciding the alignment the soil profile at

all the suitable sites was taken into account. A

reconnaissance survey team has carried out the on field

survey to assess the site and determine the final

alignment. The alignment of the bridge was proposed

along the ridge line in order to reduce the Cross Drainage

(CD) works. The skew angle is also taken into

consideration. Skew angle is the angle between the major

axis of the substructure and a perpendicular to the

longitudinal axis of the superstructure. The

representatives of CES, with assistance from PWD,

examined the site. The site was inspected from both

Yedurlanka and Kakinada sides.

The alignment proposed after analyzing all the

contributing factors is shown in “Drawings”. The

proposed alignment is shown in green. The reasons for

selecting this particular alignment are as listed below:

1) This gives shorter bridge length

2) This is at a smaller skew angle

3) This lies beyond the territory of pondicherry

The alignment starts at km. 22/2 +175 of Kakinada –

Yanam road (now part of NH214) goes round of Yanam

town and crosses the river Gauthami in a normal

direction (1 km upstream side of the existing ferry point)

and then turns right and runs parallel to flood bank before

joining the Amalapuram – Yedurlanka road at km 24/6.

The total width of the river at site of crossing is 2.331 km

form flood bank to flood bank. The approach length of

Yanam side is 5.285 km and on Yedurlanka side is 4.115

km.

3.5 HYDROGRAPHIC PARTICULARS

The terms necessary for the hydrologic design of a

structure are as follows:

AFFLUX (h) is the rise in water level upstream

of a bridge as a result of obstruction to natural

flow caused by the construction of the bridge

and its approaches.

CAUSEWAY or Irish bridge in a dip in the

railway track which allows floods to pass over

it.

CLEARANCE(C) is the vertical distance

between the water level of the design discharge

(Q) including afflux and the point on the bridge



super-structure where the clearance is required

to be measured.

DEPTH OF SCOUR (D) is the depth of the

eroded bed of the river, measured from the

water level for the discharge considered.

DESIGN DISCHARGE (Q) is the estimated

discharge for the design of the bridge and its

appurtenances.

DESIGN DISCHARGE FOR FOUNDATIONS

(Qf) is the estimated discharge for design of

foundations and training/protection work.

FREE BOARD (F) is the vertical distance

between the water level corresponding to the

Design Discharge (Q) including afflux and the

formation level of the approach banks or the

top level of guide banks.

FULL SUPPLY LEVEL (FSL) in the case of

canals is the water level corresponding to the

full supply as designed by canal authorities.

HIGHEST FLOOD LEVEL (HFL) is the

highest water level known to have occurred.

LOW WATER LEVEL (LWL) is the water level

generally obtained during dry weather.

The department has also carried out the

hydrographical survey and has provided the hydraulic

details such as HFL, Design Discharge, HTL, LTL, and

Water Current Velocity etc… The catchment area maps

of the region have been collected and studied carefully

before determining the hydrographical details. The

discharge data has been collected as per the specification

in Indian Railway Standard Code of Practice for Design

of the Substructures and Foundations of Bridges (Bridge

Sub-structure and Foundation Code). The particulars are

as shown below:

Deepest Bed Level =

14.860 m

Maximum flood level =

+4.58 m

T.B.L =

+4.94 m (on Yedurlanka side)

+5.060 m (on Yanam side)

Free board

= 3.66 m for central spans for

navigational purpose and

varying

from 3.66 m to 1.5 m

LTL

= -0.60 m

HTL

= +1.20 m

Width of river at gorge portion

= 520 m

Scour level : Normal

condition = -29.00

Seismic condition

= -25.62

Width of river in at M.F.L

= 2331 m

Flood discharge

= 56,700

cumecs

Water current velocity

= 3.5 m/s

On Yanam side, there is a flood bank approximately

600 m form the water line. From this bank about 600 m

length of the river bed is generally dry except for the

HFL condition which occurs once in 10 years or so. This

600 m stretch of bank is cultivated and there are a large

number of coconut and other trees. It shows scouring

does not take place in this portion. The average bed level

in this stretch is little above Reduced Level (RL) 3.00 m.

There after the waterline starts and well demarcated bank

line have been noticed, where ferry has been operated.

This bank of the river has been protected by stone

pitching at number of stretches and to prevent further

erosion, spurs also exist.

In the middle portion of the river there is an island

which separates the shallow channel from the deep

channel. The river on Yedurlanka side channel is much

deeper (about 18 to 19 m in depth), whereas on

Yanamside channel is shallower (about 4 to 6 m in

depth). The total waterway width under HTL condition



will be approximately 1700 m whereas only during HFL

condition the waterway spreads further and waterway

width becomes about 2300 m.

The proposed bridge site is located near the sea and is

subject to tidal variation. Under HTL condition, the

waterway is restricted between the banks which are about

1700 m apart.

Because of close proximity to the sea, during the rainy

season when the high flood occurs, the river cannot

generate a very high velocity with the result the water

spreads on the banks and the highest flood known is only

1.5 m above the ground. There are lots of trees and

cultivation is going on in all the seasons and there is no

visible sign of any scour that has taken place in this

stretch.

Under HFL condition Lacey‟s waterway comes out to

1370 m which is less than 1700 m. Therefore, the bridge

length of 2150 m as suggested by the survey team is not

necessary. It is proposed to have 1798.8 m length of

bridge between river faces of dirtwalls, which is more

than Lacey‟s waterway, thus excluding the 600 m

shallow depth stretch towards Yanam side from the

existing bund up to the Ferryghat, over which approach

embankment of suitable height may be provided, to

minimize the cost.

On Yanam side well demarcated bank line starts at

chainage 580. This bank is being pitched by the Irrigation

Department to protect it. Hence, we propose the

abutment A1 at chainage 560.3 (19.7 m beyond the bank

line). Pitching around the abutment is proposed to be

done after construction.

On Yedurlanka side flood bank (bund) is at chainage

2320 with top of bund at RL + 4.94. We propose the

abutment A2 at chainage 2359.7 i.e., 40 m away from the

bund.

It is suggested that vertical clearance for navigational

purposes i.e., 3.66 m above the exceptional HFL of +4.58

may be provided at the center of the bridge and towards

the ends the bridge may be sloped on either side with a

gradient of 1 in 50 with introduction of vertical curve of

50 m. Minimum abutment clearance of 1.5 m is provided

at the abutment ends thus providing formation level at

abutments as +8.73

3.6 SCOUR DEPTH AND LINEAR WATERWAY

CALCULATION OF SCOUR DEPTH

The scour depth is calculated in accordance with IRS

substructure code.

As per Lacey‟s formula

Where Q = Discharge = 56700 cumecs

f = Lacey‟s silt factor for bed material

D = mean scour depth

“f” shall be determined for representative samples of bed

material collected from scour zone.

Where m = weighted mean diameter of the bed material

in mm.

For standard silt

Particle size = 0.32mm

Therefore silt factor (f) =1

The depth calculated has to be increased to obtain

maximum as per clause 4.6.6 of IRS sub-structure.

Hence depth is increased by 1.25D



Therefore

= 18.17 say

18.2 m

Afflux for non – erodiable beds

Where H = afflux

v = velocity in m/s

A = un-obstructed sectional area in sq.m

a = sectional area of river at obstruction

in sq.m

For piers scour level is given by

= H.F.L-2(mean scour depth)

= 4.58-2D

= 4.58-2(18.17)

= -31.8 (RL)

For seismic scour level, it has to be multiplied by a factor

of 0.9.

Seismic scour level = HFL-(2(D) 0.9)

= 4.58-2(18.2) (0.9)

= -2.82 (RL)

Minimum grip length =

=

= 12.13 say 12.2m

Corresponding

founding level =

= - 44.0

(RL)

However in design, considering factor of safety founding

level is kept at

RL - 45.8 m

For abutment, scour level =

= 4.58-1.27(18.17)

= -18.50

However in design of abutment wall, we consider 2

cases.

1) Earth protected by pitching

2) Scour all around

CALCULATION OF EFFECTIVE WATERWAY

As per IRS substructure code the linear waterway is

calculated as below.

Linear waterway,

Where Q = 56700 cumecs.

C = 4.8

=1143 m



Effective width of pier foundation =

= 4.91 m

Effective width of abutment foundation =

= 2.92 m

Total obstruction =

= 222.9 say 222m

Total waterway = 1143 + 222

=1365m say 1370m

The distance between flood banks at site of crossing is

2331 m but water spread under HTL condition is about

1700 m only. On Yanam side there is a flood bank

approximately 600 m form the water line. From this bank

about 600 m length of the riverbed is generally dry

except for the H.F.L. condition, which of course occurs

once in 10 years or so. This 600 m stretch of bank is

being cultivated. Thus it shows clearly that scouring does

not take place in this portion. The total length of the

bridge proposed by contractors is 1800 m (leaving 530 m

for approaches) which is more than the water spread

under HTL condition. The lacey‟s regime width for the

discharge was worked out to be 1143 m. The clear water

way proposed was (1800 – 224) m = 1576 m is therefore

more than the lacey‟s regime width. The additional water

will cater for the flow in the portion of the river, which is

proposed to be blocked by the approach embankment

under HTL condition.

The proposed bridge site is located near the sea and

subject to tidal variation. Under HTL condition, the

waterway is restricted between the banks which are about

1700 m apart. Because of close proximity to the sea,

during the rainy season when the high flood occurs, the

river cannot generate very high velocity with the result

the water spreads on the banks and the highest flood is

only 1.5 m above the ground. There is cultivation is

going on in all the seasons and there is no visible sign of

any scour that has taken place in this stretch. Under HFL,

condition Lacey‟s waterway comes out to 1370 m which

is less than 1700 m.

Therefore it is felt that as proposed earlier a bridge

span of 2150 m is not really required. It is proposed to

have 1798.8 m length of bridge between river faces of

dirtwalls, which is more than Lacey‟s waterway, thus

including 600 m shallow depth stretch towards Yanam

side from the existing bund up to the Ferryghat, over

which approach embankment of suitable height may be

provided, to minimize the cost.

3.7 SOIL PARTICULARS

The scope of this soil investigation includes

exploration of subsoil using 150 mm diameter bore holes

form ground surface to hard rock or 1m below refusal

resistance. It includes conducting various field tests,

collection of samples from the field and conducting

various laboratory tests analyzing the results and

preparation of soil investigation report and

recommendations. The field tests conducted include SPT

at all depths where change of strata occurs and VST for

soft marine clay in bore holes at specified depths in

enclosed bore logs.

The field tests also include collection of US form bore

holes, and DS were collected at every meter depth

intervals or where the strata changes. The samples

collected from the field are subjected to various

laboratory tests including atterberg limits, NMC, dry

density, bulk density, void ratio and specific gravity tests

at each bore. The laboratory test program also includes

grain size analysis tests, undrainedtriaxial tests and

consolidation tests in each bore. The results of laboratory

and field investigations are used for classification of soil,

determination of shear parameters and appropriate

recommendations for foundation.

FIELD INVESTIGATIONS

Actual field investigations were carried out with 14

bore holes using power driven mechanical auger and



wash water. In this method, water was forced under

pressure through an inner tube which is rotated inside a

casing pipe. The slurry flowing out gives an indication of

the soil type. Whenever a change in strata is indicated by

the slurry flowing out, washing was stopped and a tube

sampler was attached to the end of the drill rod. Soil

samples were obtained by driving the sampler into the

soil. The entire boring operation was conducted in

accordance with the provisions laid in IS: 1892 – 1962

The diameter of the bore hole was 150 mm and casing

was used to support the walls of the bore hole. US

samples were collected using seamless thin walled

sampling tubes at all bore holes. The thin walled sampler

is 100 mm in diameter and 1.7 mm in wall thickness. The

inside and outside clearances as well as the area ratio of

the sampling tube are within the permissible limit. The

collection of UD samples was done as per provisions laid

in IS: 2132 – 1963.

SPT were conducted at change of strata in each bore

hole, depending on the soil strata, throughout the depth

of exploration, the SPT was conducted by driving a split

spoon sampler under the blows of 65 kg weight with a 75

cm free fall. The initial 15 cm penetration was taken as

the seating drive. The number of blows required to drive

the sampler 30 cm beyond the seating drive is taken as

the SPT „N‟ value. Refusal is considered to have been

reached when the rate of advance is less than 2.5 cm for

50 blows. All standard penetration tests are carried out as

per provisions in IS: 2131 – 1963. DS samples were

collected at required intervals to assess the nature of soil

and to evaluate geo – technical properties in the

laboratory.

Field VST is conducted as per IS: 4434 – 1978 code

to determine inplace shearing resistance in saturated soft

marine clay. The test was conducted at various depths.

For conducting tests, the shear – vane is pushed into the

ground up to a depth of 4 times the diameter of the bore

hole or 50 mm whichever is more below the bottom of

the bore hole. It was ensured that no torque is applied to

the torque rods during the thrust. No hammering was

permitted. A minimum period of 5 minutes was allowed

after insertion of the vane. The gear handle is turned so

that the vane is rotated at the rate of 0.1 /sec. the

maximum dial reading attained is noted. From initial and

final dial gauge readings the deflection may be found out.

Torque may be obtained from the calibration chart. By

the torque value shear strength of the soil may be

computed from the height diameter ratio is 2 for the

apparatus using in the field.

SOIL PROFILE

At bore hole number LB – 3, the soil profile consists

of yellowish clay with sand from + 2.632 m to + 2.032 m

followed by soft clay from + 2.032 to – 1.268. Medium

sand from -1.268 to – 3.618, soft clay from – 3.618 to –

6.868, medium sand from – 6.868 to – 12.268, soft clay

from – 12.268 to – 17.268, stiff clay from – 17.268 to –

26.468, coarse sand from – 26.468 to – 30.368, stiff clay

from – 30.368 to – 36.868, yellowish very stiff clay from

– 36.868 to – 47.088, yellowish very stiff clay with

pebbles from – 47.088 to – 55.368, very stiff clay from –

55.368 to – 57.768. Where the bore was terminated the

water table was met with at a depth of 2.5 m below the

EGL.

At bore hole number LB – 4, the soil profile consists

of yellowish silty sand from + 3.076 to + 0.576 followed

by soft clay from + 0.576 to – 6.424, sandy clay from –

6.424 to – 9.674, stiff clay from – 9.674 to – 16.424, stiff

clay with pebbles from – 16.424 to – 23.424, coarse sand

from – 23.424 to – 26.674, yellowish stiff clay from –

26.674 to – 39.174, yellowish very stiff clay with pebbles

from – 39.174 to – 46.124, yellowish very stiff clay with

pebbles and traces of mica from – 46.124 to – 50.924,

very stiff clay with pebbles from – 50.924 to – 57.374.

At bore hole number MB – 1, the soil profile consists

of sandy clay from – 2.268 to – 3.268, medium sand –

3.268 to – 6.768, coarse sand with pebbles sand shells

from – 6.768 to – 17.268, soft clay from – 17.268 to –

27.268, sandy clay from – 27.268 to -29.268, yellowish

very stiff clay from – 29.268 to – 51.968, yellowish very

stiff clay with pebbles from – 51.968 to – 63.018 where

the bore was terminated.



At bore hole number MB – 2, the soil profile consists

of sandy clay from – 4.297 to – 4.797, medium sand with

traces of silt from – 4.797 to – 10.297, medium sand with

traces of silt and clay from – 10.297 to – 15.047, medium

sand from – 15.047 to – 21.797, soft clay – 21.797 to -

32.297, yellowish stiff clay from – 32.297 to -65.247,

where the bore was terminated.

At bore hole MB – 3, the soil profile consists of sandy

clay from – 1.496 to – 2.246 followed by medium sand

with traces of silt from – 2.246 to – 7.746, medium sand

with traces of silt and clay from – 7.746 to – 13.246,

medium sand – 13.246 to – 17.596, soft clay from –

17.596 to -17.796, medium sand from – 17.796 to –

20.996, soft clay from – 20.996 to – 26.996, yellowish

very stiff clay from – 26.996 to -62.996, where the bore

was terminated.


clay from – 1.413 to – 2.163 followed by medium sand –

2.163 to -20.913, coarse sand with shells from – 20.913

to – 23.913, soft clay – 23.913 to – 30.413, yellowish

very stiff clay with pebbles from – 30.413 to – 62.563



clay from – 1.768 to – 3.768 followed by medium sand -

3.768 to – 20.768, soft clay from – 20.768 to – 25.768,

soft clay with pebbles from – 25.768 to – 28.768,

yellowish stiff clay with pebbles from – 28.768 to –

62.718 where the bore was terminated.


clay from – 3.925 to – 4.825 followed by medium sand

from – 4.825 to – 24.925, coarse sand with shells –

24.925 to -26.925, soft clay from – 26.925 to – 30.925,

yellowish very stiff clay with pebbles from – 30.925 to -

64.875 where the bore was terminated.

At bore hole MB – 7, the soil profile consists of sand

clay with silt from – 5.168 to – 6.918 followed by

medium sand – 6.918 to – 9.268, sandy clay – 9.628 to –

9.668, medium sand with traces of silt from – 9.668 to -

24.168, soft clay with pebbles from – 24.168 to – 27.168,

yellowish clay with pebbles from – 27.168 to -66.318



clay from – 4.113 to – 5.613, medium sand with traces of

silt from – 5.613 to – 22.613, soft clay with pebbles from

– 22.613 to – 28.113, yellowish very stiff clay with

pebbles from – 28.113 to – 64. 963, where the bore was

terminated.

At bore hole MB – 9, the soil profile consists of

medium sand from – 10.250 to – 17.45 followed by soft

clay with pebbles from – 17.45 to – 31.05, yellowish

very stiff clay with pebbles from – 31.05 to – 72.20


At bore hole LB – 5, the soil profile consists of

brownish stiff clay from + 2.892 to – 1.908 followed by

medium sand with traces of silt from – 1.908 to -13.108,

soft clay from – 13.108 to – 25.608, yellowish very stiff

clay with pebbles from – 25.608 to – 57.858 where the

bore was terminated.

LABORATORY TEST RESULTS

The various soil samples namely the US samples, the

DS samples and SPT samples were used to determine the

following soil properties.

1) Grain size distribution by wet mechanical

analysis and hydrometer

2) The Atterberg limits i.e., liquid limit, plastic

limit and plasticity index

3) The specific gravity of soil solids

The US samples collected from the field are testes for the

following soil properties

1) Natural moisture content, bulk density and

dry density hence void ratio

2) Shear parameters using triaxial tests in

undrained conditions

3) Consolidation characteristics using

consolidation tests.



All the soil properties in laboratory are determined as

per the provision in relevant Indian Standards IS: 2720 –

part I through VIII. Using the test results of the soil

sample, the soil at the site at different bores and at

different depths has been classified as per IS: 1498 –

1970.

SILT FACTOR:

Most of the bore holes have medium sand / sandy clay in

the upper region. The mean particle diameter is obtained

from the average grain size distribution curve as shown

in the figure.

Mean particle size

Silt factor

=

1.27

SCOUR DEPTH:

As per Lacey‟s formula

Where Q = Discharge = 56700 cumecs

f = Lacey‟s silt factor for bed material = 1.27

D = mean scour depth

= 16.78 m

Pier scour level

= 4.58 – 2

Dsm

= 4.58 – (2)

16.78

= - 28.98 m

(RL) say – 29 m

Seismic scour level

= 4.58 – (2

* 16.78 * 0.9)

= - 25.62 m

Abutment scour level

= 4.58 –

(1.27 * 16.78)

= - 16. 73

say – 16.75 m

After critical review of field conditions, laboratory

test results and probable foundation systems for bridge

sub – structures, Bored cast – in – situ piles are selected

for bridge abutments and pylons. All piles should be

designed as friction cum end bearing piles

The depth of pile foundation is taken from

consideration of scour, settlement and overall stability.

The depth of foundation is generally governed by scour

depth. All the piles shall be taken up to at least – 29 m

(RL) at all the bore holes investigated for major bridges.

As soft clay layers of large thickness are encountered

in most of the bore holes, considerable amount of

negative drag is expected on piles. However the negative

drag need not be considered under scour conditions. It is

advised to use larger diameter piles which would increase

the negative friction linearly but would also improve the

vertical load carrying capacity at a higher rate that the

negative drag. A factor of safety of 2.5 shall be used on

the ultimate capacity estimated by static formula. In stiff



clay layer the „C‟ values to be adopted for the pile

capacity are shown in the table 3.

Table 3 „C‟ values for stiff clay layer

Depth (RL) „C‟ value (t/m2)

-30 to -35 m 63.0

-35 to -40 m 54.0

-40 to -45 m 43.5

-45 to -50 m 48.0

-50 to -55 m 48.0

-55 to -60 m 75.0

-60 to -65 m 95.0

3.8 LOAD COMPUTATIONS

The loads to be considered on the bridge are taken as

specified in IRS Bridge rules. The track is a BG-main

line. The width of the track is taken as 1676 mm. The

various load considered to compute stress in the bridge

members as follows:-

1) Dead load

2) Live load

3) Dynamic effects

4) Temperature effect

5) Frictional resistance of expansion bearings.

6) Longitudinal forces

7) Racking force

8) Wind pressure effect

9) Forces on parapets

10) Erection forces and effects.

DEAD LOAD: The dead load is the weight of the

structure and any permanent load fixed thereon. The dead

load is initially assumed and checked after design is

completed.

In this case

=47539.2*1000/400

=118848 kN/m

LIVE LOAD: The actual loads i.e., live loads consist of

axle loads from engine and (i.e., cable stayed bridge of

span 1000m) bogies. In this case it is necessary to

proceed from the basic wheel loads. The EUDLS for

bending moment and shear force for BG main line

loading are obtained by regression analysis

For bending moment

For shear force

Where L is the effective span for bending moment and

loaded length for the maximum effect in the member

under consideration of shear.”L” is expressed in „m‟

In this case the wheel loads are considered as shown in

fig.20.

The train length is taken as 910metres in level grade.

From the entire length of the train the segment of loading

producing worst effect in the constituent members of the

bridge is taken as shown in the fig 20 by trial and error.

It is clearly evident that the load is moving load and the

shear force and bending moments at various sections are

computed by ILDs.

SHEAR FORCE AND BENDING MOMENT

It is evident that the maximum shear force will occur

at the centre of the span. Maximum shear force will

occur when the entire moving load of span 910m is on

the deck.



In order that maximum positive shear force is

produced the leading load should be at section X which is

at a distance of „x‟ as shown in the figure

Positive shear = 33701.42 kN

In order that maximum negative shear force is

produced the trailing load should be at section „X‟

Negative shear = - 3095.42 kN

As the load crosses the centre of the span „c‟ the negative

shear produced at „c‟ is

F = - 931.814 kN

Now in order to find the absolute bending moment we

should find the centre of gravity of load system.

C.G of load system = 364.53m from first train load as

shown in the figure

It is also known that the absolute maximum bending

moment will occur when the heaviest load is close to the

centre of span.

Assume maximum bending moment will occur under

245.2kN load.

For maximum bending moment to occur the load

should occupy such a position on the beam, that the

centre of the span is midway between the centre of

gravity of the load and 245.2kN load.

Therefore 245.2kN load should be at a distance

= 461m from A as shown in the

figure

The ordinate at the centre is

The absolute maximum bending moment

M = 4536767.218kN-m

The distribution of wheel loads on steel troughing or

steel or wooden beams spanning transversely to the track

and supporting the rails directly shall be designed in

accordance with the constant elastic support theory.

DYNAMIC EFFECTS

When a train moves over a bridge an additional impact

load is caused due to factors such as fast travel of load,

uneven track, rough joints, imperfectly balanced driving

wheels and lateral sway. The increase in load due to

dynamic effects should be considered by adding a load

equivalent to a CDA multiplied by the LL giving the

maximum stress in the member under consideration. The

speeds up to 160 km/h are taken for BG.

For main girders of double track spans with 2 girders

Where „L‟ is loaded length of span in meters for the

position of the train giving the maximum stress in the

member under consideration

L = 910 m

= 0.114

Increase in load due to dynamic effect = 0.114 (47539.2)

= 4519.468 kN/m

TEMPERATURE EFFECT

Where any portion of the structure is not free to

expand (or) contract under variation of temp., allowance

should be made for stresses arising from this condition.

In computing these stresses, the co-efficient of expansion

is assumed as 11.7*10-6 per degree centigrade for steel.

Increase in load due to temperature effects =



= 0.556 kN/m

FRICTIONAL RESISTANCE OF EXPANSION

BEARINGS

Frictional resistance of expansion bearings has to be

taken into account; the co-efficient of friction for steel

bearings of steel on steel (or) cast iron is 0.25.

For expansion (or) contraction of the structure, due to

variation of temperature under dead load, the friction on

the expansion bearing shall be considered as an

additional load throughout the chord to which the bearing

plates are attached.

Load increase due to frictional resistance of expansion

bearings

=

11884.8 kN/m

LONGITUDINAL FORCES

Longitudinal loads are caused due to one (or) more of the

following Causes:

1) The tractive effort of the driving wheels of

locomotives = 490.3kN/m

2) The braking force due to application of the

brakes to all braked vehicles.

Braking force per locomotive =

0.25*axle load

= 0.25*245.2

= 61.3kN/m

Braking force per train load =

0.25*train load

= 0.25*80*150

= 3000kN/m

3) Resistance due to the movement of bearings

due to change in temperature. These forces are

considered as acting horizontally through the

grider seat where the girders have sliding

bearings. For spans supported on sliding

bearings, the horizontal loads are d ivided

equally between the two ends.

The loaded length „L‟ is taken as follows:

1) The length of one span, when

considering the effect of the

longitudinal loads on

The girders

The stability of abutments

The stability of piers under

the condition of span

loaded, or when piers carry

one fixed and one roller

bearing.

2) The length of two spans, when

considering the stability of piers

carrying fixed or sliding bearing for

the condition of both spans loaded. In

this latter case, the total longitudinal

force is to be divided between the 2

spans in proportion to their lengths.

3) For determining the value of tractive

effort, L should not be taken to

exceed 29m for BG. Where the

structure carries more than one track,

the longitudinal loads shall be

considered to act simultaneously on

all tracks. The maximum effect on

any girder with 2 tracks so occupied

should be allowed for, but with more

than 2 tracks a suitable reduction

may be made on the loads for the

additional tracks.

Total longitudinal loads =

3551.6 + 887.9

=

4439.5kN/m

RACKING FORCES

Lateral bracings of the loaded deck of railway spans

should be designed to resist, in addition to the wind and



centrifugal forces, a lateral load due to racking forces of

5.9KN/m is treated as a moving load. This lateral load

need not be considered for computing the stresses in

chords or flanges of main members.

FORCES ON PARAPETS

Railings or parapets should have a minimum height

above the adjacent roadway or footway surface of 1m

less one half of the horizontal width of the top rail (or)

top of the parapet. They are to be designed to resist a

horizontal force and the vertical force each of 1.5 kN/m

applied simultaneously at the top of the railing (or)

parapet.

WIND PREESURE EFFECT

The basic wind pressure is obtained from IS: 875. No

live load on the bridge need to be considered when the

basic wind pressure at deck level exceeds for BG bridges

1.5kN/m2.

a) For unloaded spans:

One and half times the horizontal

projected area of the spans for decks

other than plate girders.

For plate girders, the area of the

windward girder plus a fraction as

below of the area of the leeward

girder.

For spacing of leeward girder.

Less than half its depth 0

Half depth to full depth 0.25

Full depth to 1.5 depth 0.50

1.5 depth to 2.0 depth 1.00

b) For loaded spans:

The area as above for the unloaded portion, plus the area

of the windward girder above and below the moving load

plus the horizontal projected area of the moving load. For

railway bridges, the height of the moving load is the

distance between the top of the highest stack for which

the bridge is designed and the rail level, less than

600mm. In case of foot bridges, the height of moving

load is to be taken as 2m throughout the span.

3.9 DECK DESIGN

Generally, the main girders require web stiffening

(either transverse or both transverse and longitudinal) to

increase efficiency. Sometimes variations of bending

moments in main girders may require variations in flange

thickness to obtain economical design. This may be

accomplished either by welding additional cover plates

or by using thicker flange plate in the region of larger

moment. In very long continuous spans (span > 50 m)

variable depth plate girders may be more economical.

MAIN GIRDER DESIGN

The main span is taken as 1000 m and the side spans are

399.4 m each. The plate girders for the main span are

designed here and a similar consideration is considered

for the side spans also. The loads are moving loads and

the deck is designed to withstand the worst position of

loading i.e., the maximum bending moment is considered

for the loading which causes maximum stress in the

members.

Total Load = 188731.52 kN/m for 1000 m

As it is not feasible to design a plate girder for the entire

span the span of each plate girder is taken as 200 m.

Effective span (L) = 200m

Maximum Bending Moment is calculated as follow

As the effective span is taken as 200 m the load should

also be considered proportionally in order that the design

is economical

Therefore, for 200 m span length

Total Load = 37746.304 kN/m

L = 200m



=

188731520 kN –

m

=

188731520*106 N – mm

Maximum shear force is calculated as follows

= 3774630.4 kN

Design of Web

Assume

= 372025.690 mm

= 372.025 m

= 101.46 say 110

mm

Provide a web of =

(372025.690*110) mm

=

40922825.9 mm2

=

40.92 m2

Design of Flange Plate

=

307459

2.494

mm2

Assume b=1500 mm

= 2049.7

mm say 2100 mm

Therefore provide 4 plates

Thickness of plates = 525mm

Size of the flange plate = (1500*525) mm2

= 376225.68 mm

= 376.225 m

=188112.84 mm

=

188112.84 +

1050

=189162.845

mm

= 5.283447875*1017 mm4

= 67.19 N/mm2



67.19 < 165 N/mm Hence

it is safe

Curtailment of Flange Plates

X1 = 308.67 mm say 310 mm

X2= 436.525 mm say 440 mm

X3 = 534.632 mm say 535 mm

Design of Stiffeners

It is essential to provide stiffeners at appropriate

distance in order that the plate girder is safe.

Bearing Stiffeners:

The permissible bearing stress is given by

= 187.5 N/mm2

= 20131362.13

mm2

= 20.13 m2

Therefore t = 0.91 m

b = 10.9 m

Hence provide a plate (10.9 * 0.91) m as bearing stiffener

Intermediate Stiffener:

= 92.23 N/mm2

1) = 2107.301 mm

2) = 2225.392 mm

3) = ( ) / 85 = 2225.392 mm

The actual thickness of web 110 mm is less than the

above values hence vertical stiffeners should be

provided.

In case only vertical stiffeners are provided then the

thickness of web required is as follows:

1) = 934.664 mm

2) = 945.814 mm

But the actual web thickness of web is 110 mm,

therefore both vertical and horizontal stiffeners are

necessary. After providing the stiffeners the

values should be as follows:

1) = 747.73 mm

2) = 756.651 mm

Since even now the actual thickness of web is less the

required thickness a horizontal stiffener should be

provided at the Neutral Axis. The stiffeners are steel

plates of (10.9 * 0.91) m size with a spacing of 5 m

between each other. All the connections are butt welds

and the design procedure is done in accordance with IS:

800.

CROSS GIRDER DESIGN

A cross girder is very important as it connects the two

main girders and is also responsible for supporting the

bridge against all the lateral forces. A cross girder is a

beam column acted upon by the lateral forces i.e., the

wind pressure etc... and also a concentrated transverse



load at the centre of the span of the girder. As the bridge

is a double track BG bridge the width of the bridge is 4.5

m.

For a span of 1000 m 100 cross girders placed at a

spacing of 10 m are found necessary to balance the

lateral force and provide bracing of the main girders.

Total Lateral Force is found out to be P = 8900 kN

The concentrated load acting on each cross girder is W =

475.392 kN

The maximum bending moment is found using the

following formula

= 9334869.523

N – mm

= 9.33 kN –m

Steel ISHB sections are provided as cross girders.

3.10 PYLON DESIGN

The towers are the most visible elements of a cable-

stayed bridge. Therefore, aesthetic considerations in

tower design are very important. Generally speaking,

because of the enormous size of the structure, a clean and

simple configuration is preferable. Though concrete is

the best choice for the pylon, in this case a steel tower is

considered as the loads are large and concrete is not

economical. Steel tubular members are therefore

considered in the pylon design. The pylon is subjected

primarily to compressive loads. The forces acting on the

deck are transferred to the cable in the form of tension;

these tensile forces in turn are transferred to the pylon.

Therefore the pylon is designed to withstand the axial

forces to which it is subjected. Tubular sections are an

economical choice especially if the member is designed

to resist axial forces. The round tubular sections have 30

to 40 percent less surface area than that of an equivalent

rolled steel shape. Therefore, the cost of maintenance,

cost of painting reduces considerably. The tubular

sections are used to advantages in structural designed for

material handling equipment like a bridge where weight

savings are a substantial economic consideration. Apart

from these moisture and dirt do not collect on the smooth

external surface of the tubes thereby reducing the

possibility of corrosion. The steel tubes here are taken as

per the specifications in IS: 228 and steel tables.

The direct stress in compression on the cross sectional

area of axially loaded steel tubes should not exceed the

values of 𝞼c as per IS: 806. The maximum shear stress in

a tube is calculated by dividing the total shear by an area

equal to half the net cross – sectional area of tube, and

this should not exceed the 𝞼b values mentioned in IS:

806.

The round tubular sections provide the most efficient

cross – sectional shape for compression members having

lateral restraint in all directions normal to the axis of the

member. The diameter of the member should be as large

as possible with the additional requirement of d/t should

be small enough to assure that pressure failure by local

buckling will not occur.

The local buckling strength of very short perfect tubes

depends primarily on L/d ratio. The local buckling is

obtained using the following equation.

Where C is approximately equal to 0.6

In the design of steel tubular compression members

attention is to be paid against crinkling and heat

treatment. The yield strength of mild steel considerably

reduces by any heat treatment which it receives such as

welding. On this account, the precautions should be taken

to prevent heat treatment or the strength must be taken as

that of the annealed material. The former is the better

option as it is both safe and economical. The effective

length is taken as per the specifications in IS: 800. In

addition to this the member should also satisfy minimum

thickness requirement.

The steel tubes used for construction exposed to the

weather should not be less than 4 mm thick and for

construction not exposed should not be less than 3.2 mm

thick when the structures are not readily accessible for

maintenance, the minimum thickness should be 5 mm.

The thickness can be found out using the following

formula.

= 1.47 m

The crinkling is calculated as follows



Where p is stress causing the collapse

t is thickness of the tube

R is Mean radius of tube

3.11 CABLES DESIGN

The basic element for all cables to be found in modern

cable supported bridges is the steel wire characterized by

a considerably larger tensile strength than that of

ordinary structural steel. In most cases, the steel wire is

of cylindrical shape with a diameter between 3 and 7

mm. typically, a wire with a diameter of 5–5.5mm is

used in the main cables of suspension bridges whereas

wires with diameters up to 7mm are used for parallel

wire strands in cable stayed bridges. In the present cable

– stayed bridge a harp type cable system is adopted.

Cables are the most important elements of a cable-stayed

bridge. They carry the load of the girder and transfer it to

the tower and the back-stay cable anchorage. The actual

stiffness of an inclined cable varies with the inclination

angle, a, the total cable weight, G, and the cable tension

force, T.

EA(eff) = EA {1+ G2 EA cos2 a(12 T3)}

Where E and A are Young‟s modulus and the cross-

sectional area of the cable. And if the cable tension T

changes from T 1 to T 2, the equivalent cable stiffness

will be

EA(eff) = EA {1+ G2 EA cos2 a(T1+ T2) (24 T12 T22 )}

In most cases, the cables are tensioned to about 40%

of their ultimate strength under permanent load

condition. Under this kind of tension, the effective cable

stiffness approaches the actual values, except for very

long cables. However, the tension in the cables may be

quite low during some construction stages so that their

effectiveness must be properly considered.

A safety factor of 2.2 is usually recommended for cables.

This results in an allowable stress of 45% of the

guaranteed ultimate tensile strength (GUTS) under dead

and live loads. It is prudent to note that the allowable

stress of a cable must consider many factors, the most

important being the strength of the anchorage assemblage

that is the weakest point in a cable with respect to

capacity and fatigue behaviour. Therefore consider steel

tables of 7 mm diameter spanning 30 m on the deck.

Hence the number of cables is 17.

3.12 FOUNDATION DESIGN

Taking into consideration the soil characteristics it is

found that pile foundations are the most suitable type of

foundation in this case. The bearing capacity for pylons

and abutments is as under.

For pylon locations, bearing capacity is calculated with c

= 0.8 kg/cm2 and ѳ = 80

Calculation of Bearing Capacity for Pylon Foundation

For C = 0.8 kg/cm2

ѳ = 80

Nc = 7.606

Nq = 2.110

Nr = 0.912

Therefore

Sc = 1.3

Sq = 1.2

Sr = 0.6

Hence

dq = dr = 1 for ѳ = 80

For α = 0

ic = iq = ir = 1

w‟ = 1

= 141.79 t/m2

𝞼all = 141.79 /2.5 = 56.7 t/m2

Addition should be made to the bearing

capacity for skin friction

As per IS: 2911 for cohesive soil,

Skin friction (Qs) = α C

As

Here α = 0.3

C = 8

t/m2

Hence Qs = 0.3 * 8 *λ DH = 636.4



D = 6 m and H =

14 m

𝞼all = 7.1 t/m2

Therefore total all = 7.1 + 56.7 = 63.8 t/m2

Surcharge = 14 * 1 = 14 t/m2

Total gross bearing capacity = 63.8 + 14 = 77.8 t/m2

Under seismic / wind case, bearing capacity = 77.8 *

1.25 = 97.25 t/m2

Calculation for Bearing Capacity for Abutment A1

For C = 0.1 kg/cm2

ѳ = 220

Nc = 17.19

Nq = 8.1

Nr = 7.59

Therefore

Sc = 1.3

Sq = 1.2

Sr = 0.6

Hence

For α = 0

ic = iq = ir = 1

w‟ = 1

= 210.83 t/m2

𝞼all = 210.83 /2.5 = 84.3 t/m2

Surcharge = 14 * 1 = 14 t/m2


Calculation for Bearing Capacity for Abutment A2

For C = 0.45 kg/cm2

ѳ = 190

Nc = 14.060

Nq = 5.908

Nr = 4.842

Therefore

Sc = 1.3

Sq = 1.2

Sr = 0.6

Hence

For α = 0

ic = iq = ir = 1

w‟ = 1

= 246.95 t/m2

𝞼all = 246.95 /2.5 = 98.8 t/m2

Surcharge = 14 * 1 = 14 t/m2


Founding level is at 14 m below scour level and due

to this large embedment, deep seated failure theory

which is nothing but “General shear failure theory” will

be applicable as there is no chance of punching shear

failure. On this basis bearing capacity has been

calculated by “General shear failure theory” as per IS:

6403. The foundation system adopted is group piles at –

45 m reduced level.

CONCLUSION

The main aim of this report is to highlight the advantages

of cable – stayed bridges. The design of a cable – stayed

bridge is presented taking into consideration all the active

forces of nature. The designs have been computed as per

the specifications in the various Indian Standard Codes



and Indian Railway Standards. The cable-stayed bridge is

related to the cantilever bridge. The cables are in tension,

and the deck is in compression. The spans can be

constructed as cantilevers until they are joined at the

centre. A cable stayed-bridge lacks the great rigidity of a

trussed cantilever, and the continuous beam compensates

for this. Indeed, while a long cable-stayed span is under

construction, there can be great concern about possible

oscillations, until the cantilevers are joined.

Advantages of cable-stayed bridges are that the two

halves may be cantilevered out from each side. There is

no need for anchorage's to sustain strong horizontal

forces, because the spans are self-anchoring. They can be

cheaper than suspension bridges for a given span. Many

asymmetrical designs are possible. They can be built

with any number of towers. The number of cables

required is also less and the time taken for construction is

also very less. The aerodynamic design of a cable stayed

bridge is very effective and in spite of very long spans

the lateral sway due to wind pressure can be easily

countered by a cable – stayed bridge. These bridges do

not block the waterway and thereby provide greater

width and height for navigation.

Disadvantages of cable-stayed bridges are that in the

longer sizes, the cantilevered halves are very susceptible

to wind induced oscillation during construction. The

cables require careful treatment to protect them from

corrosion.

REFERENCES

1) Victor Johnson. D., „Essentials of Bridge

Engineering‟, Sixth Edition.

2) Ponnuswamy. S., „Bridge Engineering‟,

Second Edition.

3) Niels J. Gimsing., „Cable Supported Bridges

Concept and Design‟, Third Edition

4) Bridge Engineering Handbook

5) Indian Railway Standard Bridge Rules

6) Indian Railway Standard Bridge Sub –

structure Code

7) Indian Railway Standard Steel Bridge Code

8) Khurmi .R.S, Theory of Sturctures, Revised

Edition

9) Ram Chandra, Design of Steel Structures,

Volume – 1

10) Troitsky, M.S., „Cable stayed bridges –

Theory and Design‟

11) Department of Roads and Building,

Government of Andhra Pradesh

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