SUBMITED BY- SUBMITED TO-

ANKIT SINGH DR. S.N. SACHDEVA

M.TECH (TRANSPORTATION ENGINEERING) SECTION HEAD (TRANSPORTATION ENGINEERING)

ROLL NUMBER- 3140715 DEPARTMENT OF CIVIL ENGINEERING

NIT KURUKSHETRA NIT KURUKSHETRA

What is bridge?A structure which provides a passage over a gap without closing the opening which is beneath that gap.

The passage may be due to railway , roadway , canal & natural river etc.

Initially the naturally available materials such as stone and timber were extensively used for bridges but now days artificial materials such as cement concrete & steel are utilized more in the construction of bridge.

RIVER BRIDGE CANAL BRIDGE

ROADWAY BRIDGE RAILWAY BRIDGE

History of bridge in india.During the king “harshavardhna” or even before him india appears to have a good highway system & such highways had a number of bridge.

“firoze shah” who ruled the delhi in mid 14th century built a number of canal & bridges.

“portuguese” in 16th and 17th century built many old arch masonary bridges in “goa”.

One of oldest stone slab bridge still in use across the river “cauvery” at “srirangapatnam” bulit by “tippusultan”.

Cauvery bridge

Vidhyasagar setu

CAUVERY BRIDGE

VIDYASAGAR SETHU

A number of cable stayed bridges has been built in india in past two decades. The major one is “vidhyasagar sethu” across “hooghly” at “kolkata” & “nalini bridge” on river “jamuna” at “allahabad”.

Inidian railways build a number of large steel arch bridge in “j & k”.

BRO has erceted a cable stayed bridge in early part of this milleium which is claimed to be only bridge of the type at highest altitude in the world at the time of construction.

ECONOMY IN BRIDGE CONSTRUCTION

Can be achived by using proper materials , effective supervission & economic method of construction etc.

Planning of a bridgeThere are few steps in planning of a bridge

Study the need for the bridge

Assess traffic requirement

Location study

Study of alternatives

Short listing feasible alternatives

Developing plans for alternatives including materials etc

preliminary design and costing

Evaluation of alternative , risk analysis and final choice

Finding resources , detailed survey & design

Implementation of design , fixing agency, construction and commissioning, preparing estimates.

Site selection of bridgeDepends upon

Foundations conditions

Clearance requirements

Length of the bridge

Width of the bridge

Live load on the bridge

Initial cost

Operation and maintenance

appearance

Classification of bridgeA single construction of bridge can be classified in manyways but we have a general classification of bridge.

MASONARY ARCH BRIDGEProbably first category of bridge to be involved.Aesthetically superior to slab bridges.Consist of a arch shape slab supported on two apposite wall & it was adopted earlier for small of 3 to 15m in masonry & extended up to 519m in steel & 305m in concrete has been built in the world.

PIPE CULVERTConsist of a pipe barrel under the embankment with protection works at the entry and exit.It is suitable for cross drainage flow on relatively flat terrain & in this discharge is limited & it has negligible maintenance.

MASANORY ARCH BRIDGE

PIPE CULVERT

SLAB BRIDGESimplest type of construction.Adopted for small bridges and culverts.Span is between 10-20m.Concrete slab cast monolithically over longitudinal girder.No. of longitudinal girders depends upon the width of road.

PLATE GIRDER BRIDGESpan ranges 10 to 60m.Can be extending up to 250m in continuous construction.

TRUSS BRIDGESpan 30 to 375m in simply supported case.Span 30 to 550m in cantilever combination ca

SLAB BRIDGE

PLATE GIRDER BRIDGE

TRUSS BRIDGE

SUSPENSSION BRIDGE

Made up of high tensile steel cables strung in form of a catenary to which the deck is attached by steel suspenders which are made up of steel rods/members/cables.

Deck can be of timber , concrete or steel spanning across the stiffening girders transmitting loads to suspenders.

CABLE STAYED BRIDGE

Similar to suspenssion bridge except that there will be no suspenders in the cable stayed bridges .

A number of cables are streched from support tower directly connected the decking.

OTHER IMPORTANT CLASSIFICATION OF BRIDGE

Based upon type of structural arrangement.

I-girder bridge

Plate girder bridge

SUSPENSION BRIDGE

CABLE STAYED BRIDGE

truss girder bridge

Suspenssion bridge

Based upon structural action or nature of superstructure action

Simply supported span bridge

Continuous span bridge

Cantilever bridge

Arch bridge

Rigid frame bridge

Based upon type of connections

Riveted bridge

Welded bridge

Bolted bridge

Pinned bridge

Based upon floor action

Deck type bridge

Through type bridge

Semi –through type bridge or pony bridge

Double deck bridge-used in rail cum road bridge

Based upon movement of structural parts of the bridge

Fixed(permanent) bridge

Movable bridge

can opened either horizontally or vetically so as allow the river or channel traffic to pass.

Based upon purpose of bridge

Road bridge

Railway bridge

Padestrain bridge

Based upon loading

Irc class aa loading bridge

Irc class a loading bridge

Irc class b bridge

Base upon span length

Culver – up to span length 6m

Minor bridge – up to span length 6 to 30m.

Major bridge – up to span length over 30m.

LOAD FOR DESIGN OF BRIDGE

1. Dead load

Aggregate weight of complete structure elements such as deck, wearing coat, parapets, stiffeners and utilities.

It does not changes its direction and magnitude with respect to the passage of time.

2. LIVE LOAD

Includes vehicle live load That are moving on the bridge.

IRC has categorized standards of vehicle live load as under three following category which is-

(a) IRC CLASS AA LOADING

Treated as heavy loading and all NH & SH and industrial areas’sbridge are designed for only IRC class AA loading.

If a bridge designed for IRC class AA loading then it will automatically satisfied IRC class A & class B loading.

It has two pattern of loading

(i) tracked type (ii) wheeled type

(b) IRC CLASS A LOADING

Generally Treated as standard loading for permanent bridges.

Having eight axles with a total length of 25m.

IRC CLASS AA LOADINGIRC CLASS AA LOADING

IRC CLASS A LOADING

IRC CLASS B LOADING

Used for temporary bridges.

It is a light loading as compard to all other loading.

CLASS 70R LOADING

Not used in our country it is used only in US.

3.Impact load

It is account for the dynamic effects of sudden loading of a vehicle on bridge structure.

It is calculated by multiplying the live load with an impact factor.

The impact factor is calculated as the IRC-6 suggested which are discussed below.

Impact factor for IRC CLASS A loading

If=A/(B+L)

Where If=Impact factor

A=constant( 4.5 for RCC bridge & 9.0 for STEEL bridge)

B=constant (6.0 for RCC bridge & 13.5 for STEEL bridge)

L= effective span

Impact factor IRC CLASS AA loading & CLASS 70R loading

for span < 9m

(a) Tracked vehicle- 25% for span upto 5m & reducing to 10% for span upto 9m.

(b) Wheeled vehicle-25% for span upto 9m.

for span > 9m

(a) Tracked vehicle-for RCC bridge 10% upto 40m & as per graph for span >40m . For steel bridge 10% for all span.

(b) Wheeled vehicle-for RCC bridge 25% upto 12m & as per graph for span >12m. For steel bridges 25% for span upto 23m & as per graph for span > 23m.

4. Centrifugal force

consider for bridge constructed on horizontal curve.

Considered to act at a height of 1.2m above the level of carriage way.

C=WV2

127 R

Where c=centrifugal force in KN

w=live in KN

v=speed of vehicle in KMPH

R= radius of horizontal curve in M.

5.Wind load

Assumed as horizontal forces on an area which are-

For DECK structure- area of floor slab and railing

For a through or half through structure- area of elevation of the windward tress flows half the area of elevation above the deck slab.

Considered as acting at 15m above the roadway and have the following values

highway ordinary bridges – 3.0 KN per meter

highway bridges carrying framework- 4.5 KN per meter.

6. Longitudinal forcesForces result from vehicle braking or acceletrating while travelling on bridge.

As the vehicle brakes the load of the vehicle is transferred from its wheels to bridge deck.

IRC specifies a longitudinal forces of 20% is appropraite of live load and the force is applied at 1.2m above the level of deck.

7.Seismic forcesDepends upon geographical location of the bridge.

These are the temparory forces act for the short duration. An earthquake forces is the fuction of following.

(a) Dead load of structure Calculated as- F= ahW

(b) Ground motion where F=horizontal forces owing to earthquake

(c) Period of vibration ah=seismic coefficients for respective regions

(d) Nature of soil W=DL+LL acting above the section

Some basic points regarding WSM and LSMWorking Stress Method

The Stresses in an element is obtained from the working loads and compared with permissible stresses.

The method follows linear stress-strain behaviour of both the materials.

Modular ratio can be used to determine allowable stresses. For bridge construction in

case of WSM the Modular ratio is constant 10.Material capabilities are under estimated to large extent. Factor of safety are used in working stress method.

The member is considered as working stress.

Ultimate load carrying capacity cannot be predicted accurately.

The main drawback of this method is that it results in an uneconomical section.

All kind of major structure or important structure like bridge construction & tank construction (rectangular tank & intz tank etc.) is still usually designed by only WSM.

Limit State Method

The stresses are obtained from design loads and compared with design strength.

In this method, it follows linear strain relationship but not linear stress relationship (one of the major difference between the two methods of design).

The ultimate stresses of materials itself are used as allowable stresses.

The material capabilities are not under estimated as much as they are in working stress method. Partial safety factors are used in limit state method.

T-BEAM BRIDGEThis is most commonly adopted type of bridge for span range of 10 to 25m.

It is so name because the main longitudinal girder are designed as T-beam which is integral part of deck slab cast monolithically with the deck slab.

Simply supported T-beam spans of over 25m are rare as the dead load then becomes too heavy. However there is a bridge have single span of 35m named “ Advice bridge” in “Goa”.

In other words we can say T-beam bridge is the combination of [ deck slab with longitudinal girders & cross girders ] superstructure & [piers , abutment & foundations] substructure.

COMPONENT OF A T-BEAM BRIDGEDeck slab

Cantilever portion

Longitudinal girders

Cross girders

Abutments & piers

Bearing

Foundations

Design of deck slabIt is designed by either “effective width method” or by “Pigeauds curve method” as bending moment calculation.

After calculation of bending moment we provide reinforcement and then do check for shear as accordance by WSM mtehod of RCC design.

Normal depth of deck slab is very from 350mm to 500mm.

EFFECTIVE WIDTH METHOD

It is applicable when the slab is designed by assuming its a one way slab or supported only on two apposite edge or a very long slab supported on all four edge.

Effective width is the width of wheel imprint on deck perpendicular to the movement of vehicle that is actually bears the load of wheel tyre it is calculated by following expressions.

FOR SIMPLY SUPPORTED CASE

beff.=k x(1-x/L) + bw

FOR CANTILEVER CASE

beff=1.2x + bw

Where beff= effective widht of dispersion

k = constant depend upon b/L (widht/length) ratio specified in IRC-6.

X=Distance of center of gravity of wheel from the nearest support in case of simply supported and distance of center of gravity of wheel From the cantilever phase. in case of

L= effective span of bridge in case of simply supported and clear span in case of cantilever.

bw= w+2h (width of wheel + 2 thickness of wearing coat)

EFFECTIVE LENGTH OF DISPERSION

In the same manner as effective width of dispersion there is also a effective length of dispersion measured along the direction of movement of vehicle.

calculated as- for both simply supported case as well as cantilever case

dispersion length= length of tyre contact + 2(overall thickness of deck including wearing coat)

LEFF.= B + 2(D+2h) where Leff.=effective length of dispersion

d=overall thickness of bridge deck

h=thickness of wearing coat

Pigeauds method

short span(B) & long span(L) bending moment coeeficients are read from curves developed by M. Pigeaud.

Used for only 2-way slab design or slabs supported along four edges with restrained corners and subjected to symmetrically placed loads distributed over some well defined area.

Curves developed for thin plates using the elastic flexural theory. However their use has been extended to concrete slab too.

Poision’s ratio of 0.15 is considered.

The short span(B) & long span (L) bending moment is calculated by following expressions.

short span B.M.=W(m1 +0.15m2) along the widht(B) of slab.

long span B.M.=W(0.15m1 +m2) along the length (L) of slab.

Design of cantilever slab portion

It designed by effective width method only. The cantilever slab portion slab portion usually carries the KERB , HANDRAILS , FOOTHPATH if provided and a part of carriageway.

The critical section for bending moment is the vertical section at the junction of the cantilever portion and the end of longitudinal girder.

The design bending moment for cantilever slab portion is calculated as the sum of 0.2 times of dead load bending moment plus 0.3 times of live load bending moment.

design moment= 0.2 dead load BM + 0.3 live load BM

Design of longitudinal girder

There are 3 method of design of longitudinal girder

(a) courbon’s method

(b) Hendry-jaegar method

(c) Morice and little version of huyon and massonnet method

In india the courbon’s method is standerized for design of longitudinal girder.

normal size of longitudinal girder is (300×1200)mm

Courbon’s methodAccording to his theory no flexural of transverse deck is possible because of presence of infinitely rigid diaphragms ( cross girder or cross beam) and a concentrated load instead of one pushing down only nearly girders , causes equal deflection of all girders.

The design bending moment for longitudinal girder is calculated with the help of rection factor or distribution coefficient which is calculated by following expressions given by courbon.

Where W=ecentric concentrated load

n= no. of longitudinal girder

e=ecentricity of the wheel load from center line of the deck

x1=distance of girder under considerations from central axis of the beam

∑x2 = sum of distance of longitudinal girders from the centre line of deck

LIMITATIONS OF COURBON’S METHOD O THEORY

(a) span-width ratio should be between 2 to 4.

(b) Atleast five symmetrical cross girder connecting the longitudinal girders

(c) The minimum depth of cross girder should be atleast ¾ depth of longitudinal girder.

Design of cross girderProvided mainly to stiffen the girders and to reduce torssion in the exterior girders.

Another function of the cross beam is to equalize the deflections of the girders carrying heavy loading with those of the girders with less loading.

This is particularly important when the design loading consist of concentrated wheel loads such as IRC CLASS AA Loading to be placed in most unfavourable positions.

The thickness of cross beams should not be less than the minimum thickness of the webs of longitudinal girders.

The depth of the end cross girders should be such as to permit access for inspection of bearings and to facilitate positionings of jacks for lifting of superstructure for replacement of bearings.

normally we use same size as that of longitudinal girders.

Dead load bending moment is computed considering a trapezoidal distribution of weight of deck slab and wearing coarse.

The live load bending moment is calculated as the bending moment calculated simply for a beam.

TYPICAL EXAMPLE OF CROSS GIRDER DEAL LOAD B.M. CALCULATION

PIERS

A support of concrete or masonry for superstructure of bridge.

The base of a pier may rest directly over firm round or it may be supported on piles.

Center line of pier normally coincide with the center line of the superstructure. The dimensions of the top of a pier depends on distances between girder(longitudinal girder) and distance required to provide for the expansion of girder , size of bearing etc.

IRC 40 gives minimum top width of pier and abutment.

Basic Types of Bridge Piers

Design loads for piersa) dead load of superstructure

b) Dead load of pier

c) Live load on superstructure

d) Lateral forces perpendicular to centerline of superstructure (wind portion on pier above water level , presure due to water , wave action of current)

e) Longitudinal forces parllel to the direction of the bridge (includes braking of vehicles , tractive force of vehicle (high in case of train)).

f) Seismic force.

ABUTMENTSAn abutment is a structure that support one end of a bridge in other word we can say that it is a structure located at the end & at the beginning of a bridge.

Functions of abutment

a) Support the bridge deck at end.

b) Retain the embankment of approaching road.

c) Connected the approach road to the bridge deck.

Basic Types of Bridge Abutments –Wall & Counterfort

Wall Abutment Counterfort

Basic Types of Bridge Abutments –Open Type

Types of Wall Abutments

Forces acting on abutmentDead load due to superstructure

Live load on superstructure

Self weight of abutment

Longitudinal forces (traction and boiling)

Earth presure due to soil embankment

Design of abutmentHieght- Kept equal to hieght of pier

Abutment- provided with a better of 1 in 3 to 1 in 6 or it may be stepped down

Abutment width- top width according to space needed by the single bearing and bottom width 0.4 to 0.5 times of height of abutment

Length- minimum equal to width of bridges

Abutment cap- thickness 450 to 600 mm.

Stability of abutmentIt should be chack and safe against the following-

Oveturning

Sliding

Ecentricity of resultant with respect to center of the base

Maximum base presure or earth presure .

BEARING

Bearing are mechanical arrangement provided in the superstructure to transmit the load to the sub- structure. Thus it is a via media between superstructure and sub-structure which transmit the load from superstructure in such a manner that bearing stresses induced in the subset are within permissible limits.

Purpose of bearingsTo absorb movements of girder

To distribute load on a large area

To keep compressive stress within safe limits

To simplify the procedure in design

To take up the vertical movement due to sinking of the the support.

Type or category of bearingFree bearing or expansion bearing

free to slide or move or roll and thus it allows longitudinal movement of girder.

Fixed bearing

it allows free angular movement and it does not permit any longitudinal movement of the girder

Free bearing or expansion bearing are of following type-

RC rocker expansion bearing

Elastomeric bearing

Steel roller –cum rocker bearing

Sliding own rocker bearing

Sliding plate bearing

Fixed bearing are of following type-

Rocker bearing

Steel hinge

Steel rocker bearing

RC rocker fixed bearing

FORCES ON BEARING

(1)Reactive forces (2) longitudinal forces (3)uplift forces (4)transverse forces

MATERILAS FOR BEARING

(1)Cast steel (2)mild steel (3) lead (4)RCC (5)Rubber (6)Tar paper (7) Kraft paper

BASIS FOR SELECTION OF BEARING

a) High vertical load taking capability.

b) Rotational capability.

c) Good seismic resistance

d) Overall cost (initial, maintenance) should be low.

e) Capability to resist external horizontal forces.

f) Aesthetic considerations.

Typical view of complete T-Beam bridge construction arrangement

REFERENCE-

“D.J. VICTOR”

THANK YOU (for giving your valuable time)