78732661-Structural-Design-of-RCC-Bridge.docx

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STRUCTURAL DESIGN OF

REINFORCED CONCRETE BRIDGES

Collection by : Skumar


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Types of Bridges

Bridges are often built over huge landmasses or water bodies. Their design depends on theirfunction. To know about the various types of bridges, read on...

Bridge is not merely a piece of construction, it's a concept, I think sometimes. It represents theidea of crossing over large spans of land or water, thus 'bridging' the gaps spanning long

distances. A bridge connects two far-off points thus reducing the distance between them andbringing them within reach. hat does it take to construct this 'idea'! It takes ingenuity" #ere,

we take you through all the different types of bridges, and tell you about the civil engineering

and aesthetics they involve.

Arch Bridge:It is arch-shaped and has supports at both its ends. The weight of an arch-shaped

bridge is borne by the supports at its ends. TheMycenaean Arkadiko Bridge in Greeceof $%&&

B is the oldest e(isting arch-shaped bridge. )truscans and ancient *reeks were aware of the

concept of arches since a very long time. But the +omans were foremost in discovering the useof arches in the construction of bridges. Arch bridges have now evolved into compression arch

suspended-deck bridges that enable the use of light and tensile materials in their construction.

oon arch, pointed arch, deck arch and two or three storied arches are some of the designs inthis type of bridges.

Quick Fact The haotianmen Bridge in honging, /outhwest hina is the largest arch bridgein the world. It is $01$ meters in length.


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Beam Bridge:A beam bridge was derived from the log bridge. It is built from shallow steelbeams, bo( girders and concrete. #ighway overpasses, flyovers or walkways are often beam

bridges. A hori2ontal beam supported at its ends is roughly how the structure of a beam bridge is.

The construction of a beam bridge is the simplest of all types of bridges. The design of a beam

bridge should be such that it does not bend under load. 3or this, the top surface of this bridge iscompressed and the bottom surface is under tension, thus helping the beam remain in a straight

line.

Quick Fact The longer a beam bridge, the weaker it is" Typically, beam bridges are not more

than 04 meters long.

Cable-stayed Bridge:/tructured similar to suspension bridges, the difference lies in the way

they support load. In cable-stayed bridges, the cables are attached to the towers, which bear theload. Two variants of cable-stayed bridges are harp and fan. In the harp design, cables are

attached to multiple points of the tower in a parallel manner. In the fan variant, all the cables

connect to the tower or pass over it. able-stayed bridges are much stiffer than suspensionbridges. The cables serve as a good support for the bridge deck. Also any number of towers can

be used and it reuires less cable than a suspension bridge does.

Quick Fact /kybridge, anada is the longest transit-only cable-supported bridge in the world.


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Cantilever bridge:antilevers are structures that pro5ect along the 6-a(is in space. They aresupported on one end only. Bridges intended to carry lesser traffic may use simple beams while

those meant to handle larger traffic make use of trusses or bo( girders. In a typical cantilever

bridge, cantilever arms e(tending from opposite ends meet at the center, while in a suspended

span design, they do not meet. The 3orth Bridge in /cotland is a railway bridge using thecantilever design and is one of the oldest known cantilever bridges. /an 3rancisco-7akland Bay

Bridge that is $1&& feet long is another known e(ample of a cantilever bridge.

Quick Fact The $8&& feet 9uebec Bridge of anada holds the record of being the world's

longest cantilever bridge.

Drawbridge:The term is used to refer to a bridge-like structure which is movable. Typically, a

drawbridge opens up to e(tend over the distance it is meant to span. A castlebridge, for e(ample,opens like a door, serving as a doorway to the castle. It could be in the form of a plank that is

pivoted to the center that rotates along a designated circumference. This type of construction is

often used above tidal waters, where the water levels rise and fall. A vertical lift bridge is adrawbridge that moves vertically in a plane parallel to its deck. Bascule bridges are drawbridges

that swing up and down to facilitate boat traffic.

Quick Fact Tower Bridge across Thames in :ondon is a well-knownbascule bridge.


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Suspension Bridge:/imply put, a bridge suspended from cables is a suspension bridge./uspension cables are anchored at each end of the bridge. The load that the bridge bears converts

into the tension in the cables and is transferred to the towers. ables stretch beyond the pillars up

to the dock-level supports further to the anchors in the ground. ;ertical cables suspended down,

bear the weight of the deck. 7ne advantage of this bridge design is that it can span longdistances and resist earthuakes. It reuires less construction material, which reduces its cost of

construction. The Tsing a Bridge of hina and the #umber Bridge of )ngland are some of the

famous suspension bridges.

Parts of a Suspension Bridge

A suspension bridge suspends a roadway by cables. Because

the bridge uses these cables as an integral part of its design,

the bridge is exible and aected by wind. Engineers plan

the design to account for this and to increase stability.

! Su"er#tructure an$ Sub#tructure

o A suspension bridge has two types of parts. The superstructure above includes the

deck, towers and main suspension cables. The substructure below includes piers

and anchorages.

Deck

o The deck is the roadway or walkway of a suspension bridge and can be made of

one or more pieces. The deck is also called the girder.

Lar%e Anc&or#

o Anchorages of rock or concrete hold the cables at both ends of a suspension

bridge. ables entering the anchors are separated into strands within the rock to

distribute the tension load.

'ier# an$ To(er#

o


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Quick Fact The *olden *ate Bridge of =/A, declared as one of the odern onders of theorld is a suspension bridge.

Truss Bridge:A truss bridge is built by connecting straight elements with the help of pin 5oints.

Triangular units connected at 5oints form the skeleton of a truss bridge. 7wing to the abundanceof wood in the =nited /tates, truss bridges of the olden times used timber for compression and

iron rods for bearing tension. Truss bridges came to be commonly constructed from the $80&s to

the $>%&s. Truss is the oldest form of modern bridge design. ?eck truss railroad bridge thate(tends over the )rie anal is one of the many famous truss bridges. 3or more on this bridge

type, go through Truss bridge design and types.

Quick Fact 9uebec Bridge, the longest cantilever bridge span, has a

riveted steel truss structure.

an's desire to reach the 'unreachable' and venture new places led him to construct bridges that

spanned huge distances and helped him overcome obstacles. A log of wood floating on water

might have inspired man to build bridges for the very first time" Thanks to the developments inengineering and architecture, distances could be bridged and seemingly unreachable destinations

came within man's reach.

Main ypes of Bridges in the !orld

Below is the list of @ main types of bridges
http://www.buzzle.com/articles/truss-bridge-design.htmlhttp://www.buzzle.com/articles/truss-bridge-design.html


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". #irder bridges

$. Arch bridges

%. &able'stayed bridges

(. )igid *ra+e Bridges

. russ bridges.

! Gir$er bri$%e#:

It is the most common and most basic bridge type. In its simplest form, a log across a creek is an

e(ample of a girder bridge the two most common girders are I-beam girders and bo(-girders

used in steel girder bridges. )(amining the cross section of the I-Beam speaks for its so name.

The vertical plate in the middle is known as the web, and the top and bottom plates are referred

to asflanges.

A box girdertakes the shape of a bo(. The typical bo( girder has two webs and two flanges.

#owever, in some cases there are more than two webs, creating a multiple chamber bo( girder.

7ther e(amples of simple girders include pi girders, named for their likeness to the mathematical

symbol for pi, and T shaped girders. /ince the ma5ority of girder bridges these days are built with

bo( or I-beam girders we will skip the specifics of these rarer cases.

An I-beam is very simple to design and build and works very well in most cases. #owever, if the

bridge contains any curves, the beams become sub5ect to twisting forces, also known as torue.

The added second web in a bo( girder adds stability and increases resistance to twisting forces.

This makes the bo( girder the ideal choice for bridges with any significant curve in them. Bo(

girders, being more stable are also able to span greater distances and are often used for longer

spans, where I-beams would not be sufficiently strong or stable. #owever, the design and

fabrication of bo( girders is more difficult than that of I beam. 3or e(ample, in order to weld the

inside seams of a bo( girder, a human or welding robot must be able to operate inside the bo(

girder.

)! Arc& bri$%e#:

Arch bridges pose a classic architecture and the oldest after the girder bridges. =nlike simple

girder bridges, arches are well suited to the use of stone. /ince the arch doesnt reuire piers inthe center so arches are good choices for crossing valleys and rivers. Arches can be one of the

most beautiful bridge types. Arches use a curved structure which provides a high resistance to

bending forces. Arches can only be used where the ground or foundation is solid and stable

because unlike girder and truss bridges, both ends of an arch are fi(ed in the hori2ontal direction

Ci.e. no hori2ontal movement is allowed in the bearingD. Thus when a load is placed on the bridge


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Ce.g. a car passes over itD hori2ontal forces occur in the bearings of the arch. :ike the truss, the

roadway may pass over or through an arch or in some cases.

/tructurally there are four basic arch types

". -inge'less

$. wo'hinged

%. hree hinged

(. ied arches

The hinge-less arch uses no hinges and allows no rotation at the foundations. As a result a great

deal of force is generated at the foundation Chori2ontal, vertical, and bending forcesD and the

hinge-less arch can only be built where the ground is very stable. #owever, the hinge-less arch is

a very stiff structure and suffers less deflection than other arches. The two hinged arch uses

hinged bearings which allow rotation.

The only forces generated at the bearings are hori2ontal and vertical forces. This is perhaps the

most commonly used variation for steel arches and is generally a very economical design. The

three-hinged arch adds an additional hinge at the top or crown of the arch. The three-hinged arch

suffers very little if there is movement in either foundation Cdue to earthuakes, sinking, etc.D

#owever, the three-hinged arch e(periences much more deflection and the hinges are comple(

and can be difficult to fabricate. The three-hinged arch is rarely used anymore. The tied arch is a

variation on the arch which allows construction even if the ground is not solid enough to deal

with the hori2ontal forces. +ather than relying on the foundation to restrain the hori2ontal forces,

the girder itself EtiesE both ends of the arch together, thus the name Etied arch.E

*! Cable #taye$ bri$%e#:

A typical cable stayed bridge is a continuous girder with one or more towers erected above piers

in the middle of the span. 3rom these towers, cables stretch down diagonally Cusually to both

sidesD and support the girder. /teel cables are e(tremely strong but very fle(ible. ables are very

economical as they allow a slender and lighter structure which is still able to span great

distances. Though only a few cables are strong enough to support the entire bridge, theirfle(ibility makes them weak to a force we rarely consider the wind.

3or longer span cable-stayed bridges, careful studies must be made to guarantee the stability of

the cables and the bridge in the wind. The lighter weight of the bridge, though a disadvantage in

a heavy wind, is an advantage during an earthuake. #owever, should uneven settling of the

foundations occur during an earthuake or over time, the cable-stayed bridge can suffer damage


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so care must be taken in planning the foundations. The modern yet simple appearance of the

cable-stayed bridge makes it an attractive and distinct landmark.

The uniue properties of cables, and the structure as a whole, make the design of the bridge a

very comple( task. 3or longer spans where winds and temperatures must be considered, the

calculations are e(tremely comple( and would be virtually impossible without the aid of

computers and computer analysis. The fabrication of cable stay bridges is also relatively difficult.

The cable routing and attachments for the girders and towers are comple( structures reuiring

precision fabrication. There are no distinct classifications for cable-stayed bridges.

#owever, they can distinguish by the number of spans, number of towers, girder type, number of

cables, etc. There are many variations in the number and type of towers, as well as the number

and arrangement of cables. Typical towers used are single, double, portal, or even A-shaped

towers. able arrangements also vary greatly. /ome typical varieties are mono, harp, fan, and

star arrangements. In some cases, only the cables on one side of the tower are attached to the

girder, the other side being anchored to a foundation or other counterweight.

+! Ri%i$ ,rame bri$%e#:

+igid frame bridges are sometimes also known as ahmen bridges. In a standard girder bridge

type, the girder and the piers are separate structures. #owever, a rigid frame bridge is one in

which the piers and girder are one solid structure.

The cross sections of the beams in a rigid frame bridge are usually I shaped or bo( shaped.

?esign calculations for rigid frame bridges are more difficult than those of simple girder bridges.

The 5unction of the pier and the girder can be difficult to fabricate and reuires accuracy andattention to detail.

hough there are +any possible shapes, the styles used al+ost exclusiely these

days are the pi'shaped fra+e, the batter post fra+e, and the / shaped fra+e. he

batter post rigid fra+e bridge is particularly well suited for rier and alley crossings

because piers tilted at an angle can straddle the crossing +ore eectiely without

re0uiring the construction of foundations in the +iddle of the rier or piers in deep

parts of a alley. / shaped fra+es +a1e eectie use of foundations. Each /'shaped

pier proides two supports to the girder, reducing the nu+ber of foundations and

creating a less cluttered pro2le. Pi shaped rigid fra+e structures are used fre0uently

as the piers and supports for inner city highways. he fra+e supports the raised

highway and at the sa+e ti+e allows tra3c to run directly under the bridge.

-! Tru## bri$%e#:

Thus, for the most part, all beams in a truss bridge are straight. Trusses are comprised of many

small beams that together can support a large amount of weight and span great distances. In most

cases the design, fabrication, and erection of trusses is relatively simple. #owever, once


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assembled trusses take up a greater amount of space and, in more comple( structures, can serve

as a distraction to drivers. :ike the girder bridges, there are both simple and continuous trusses.

The small si2e of individual parts of a truss make it the ideal bridge for places where large parts

or sections cannot be shipped or where large cranes and heavy euipment cannot be used during

erection. Because the truss is a hollow skeletal structure, the roadway may pass over or even

through the structure allowing for clearance below the bridge often not possible with other bridge

types. Trusses are also classified by the basic design used. The most representative trusses are the

arren truss, the


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3igure $ /pan ;ersus ost for /uperstructureF/ubstructur

Three Types of !oads Considered in Bridge

Construction

hen building a bridge, engineers need to consider the weight and environment, or load types the bridge

will encounter over a long period of time. These factors determine what material should be used to build

the bridge as well as the type of structure that will best withstand the loads. Also known as forces, the

type of loads considered in bridge construction is vital to its integrity.

! Dea$ Loa$

o The dead load of a bridge is the bridge itself -- all the parts and materials that are

used in the construction of the bridge. This includes the foundation, beams,

cement, cables, steel or anything else that comprises the parts of the bridge. It's

called a dead load because it doesn't move. It may breathe with the seasons or

sway with the wind, but those movements are almost imperceptible.

Li.e Loa$

o A live load is the moving weight the bridge will hold, such as traffic. It is basedon traffic patterns that include the number of cars, trucks and other vehicles that

will travel across it at any given time. ertain variables, such as snow, may be

calculated into the total live weight for a more accurate estimate. The heaviest

possible weight in the most e(treme conditions is also a factor despite the rarity of

such an occurrence.


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Dynamic Loa$

o ?ynamic loads are outside forces that cannot be accurately measured such as

wind, vibration and e(treme weather. These factors need to be considered in the

construction of a bridge to build EbreathingE room into the structure. This

breathing room allows the bridge to move or ad5ust to the dynamic loads without

collapsing or permanently shifting. As solid as a bridge may seem, it still has the

ability to sway when a strong wind is present.

Ot&er Loa$#

o hen building a bridge, there are other types of loads that need to be considered

that are specific to the terrain in which the foundation will be laid. )nvironmental

factors and weather patterns are also considered when calculating load-bearing

needs. The load e(pectation of a bridge will determine the best design for strength

and to ensure its longevity, whether the bridge is to span over large bodies of

water or between rising mountaintops.


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"ote3or more design consideration refer H+ vol-G, by B


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78732661-Structural-Design-of-RCC-Bridge.docx

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