highway bridge structures

8/13/2019 Highway Bridge Structures

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Highway Bridge Structures


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is a structure built to span physicalobstacles such as a body ofwater, valley, or road, for the

purpose of providing passage overthe obstacle.

Bridge


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A type of bridge composed ofa deck resting on a set of

primary members.Also known as Slab-on-

Girder.

Slab on Stringer


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A typical single span slab-on-stringer bridgesite and its representative components.


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1. Deck and Overpass

2. tringer

!. "earing

#. $edestal%. &ooting

'. $iles

(. )nderpass

*. +mbankment

. -ive -oading

Legend


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1. Dec

is a flat surface capable ofsupporting weight, similarto a floor.

t is the roadway, or the

pedestrian walkway,surface of a bridge.


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1. !verpass

a bridge, road,

railway or similarstructure thatcrosses over

another road orrailway.


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". Stringer

a longitudinalbridge girder for

supporting partof a deck orrailroad trackbetween bents

or piers.


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#. Bearing

is a component

of a bridge which

typicallyconnects

the bridge piers

to the bridge

deck.


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$. %edestal

A short columnon an abutment

or pier whichdirectly supportsa superstructure

primarymember.


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&. 'ooting

A concrete support

under a foundation

thatrests in solid ground

and is wider than the

structure supported.


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(. %iles

a long column oftimber, concrete, orsteel that is driveninto the ground toprovide a

foundation for avertical load.


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). *nderpass

A passageunderneathsomething,

especially asection of roadthat passes

under anotherroad.


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+. ,mbanment

A long artificialmound of stone

or earth/ built tohold back wateror to support a

road or asprotection.


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A moving, variable weight added tothe dead load or intrinsic weight of astructure or vehicle.

. Live Loading


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0he part of a building or otherstructure above the foundation.

Superstructure


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0he wearing surface course is thatportion of the deck cross sectionwhich resists traffic wear.

t is the top layer of a road thatcarries the traffic.

earing sur/ace


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0he deck is the physical e3tension ofthe roadway across the obstructionto be bridged.

Dec


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$rimary members distribute loadslongitudinally and are usuallydesigned principally to resist fle3ure

and shear."eam type primary members such asthis are also called stringersor

girders.

%rimary 0ember


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econdary members are bracingbetween primary members designedto resist cross4sectional deformation

of the superstructure frame andhelp distribute part of the vertical

load

between stringers.

Secondary 0embers


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0he substructure consists of allelements re5uired to support thesuperstructure and overpass

roadway.

Substructure


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Abutments are earth4retainingstructures which support thesuperstructure and overpass

roadway at the beginning and end ofa bridge.

Abutments


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$iers are structures which supportthe superstructure at intermediatepoints between the end supports

abutments.

%iers


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"earings are mechanical systemswhich transmit the vertical andhori6ontal loads of the superstructure

to the substructure, andaccommodate movements betweenthe superstructure and the

substructure.

Bearings


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A pedestal is a short column on anabutment or pier under a bearingwhich directly supports a

superstructure primary member.

%edestal


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A backwall, sometimes called thestem, is the primary component ofthe abutment acting as a retaining

structure at each approach.

Bacwall


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A wingwall is a side wall to theabutment backwall or stem designedto assist in confining earth behind

the abutment.

ingwall


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As bearings transfer thesuperstructure loads to thesubstructure, so in turn do the

abutment and pier footings transferloads from the substructure to thesubsoil or piles.

'ooting


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A footing supported by soil without piles iscalled a spread footing. A footingsupported by piles, like the one in previousfigure is known as a pile cap.


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7hen the soil under a footing cannotprovide ade5uate support for thesubstructure in terms of bearing

capacity, overall stability, or settlement, support is obtained

through the use of piles, which e3tend

down from the footing to a strongersoil layer or to bedrock.

%iles


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n cofferdams or shallow e3cavation,the vertical planks which are driveninto the ground to act as temporary

retaining walls permitting e3cavationare known as sheeting.

Sheeting


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is any part of the bridge or bridgesite which is not a ma8or structuralcomponent yet serves some purpose

in the overall functionality of thestructure e.g., guardrail.

Appurtenances


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A long artificial mound of stone orearth/ built to hold back water or tosupport a road or as protection.

,mbanment


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is a drainage system made ofperforated pipe or other suitableconduit that transports runoff away

from the structure and intoappropriate drainage channelseither natural or man4made.

*nderdrain


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0he section of overpass roadwaywhich leads up to and away from thebridge abutments is called the

approach or approach roadway.

Approach


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is a protective device 9used to shield motorists from obstacles or slope

located along either side of

roadway:.On bridges, they are usually calledbridge railings.

ra//ic Barriers


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2ertical clearance is the minimumdistance between the structure andthe underpass. AA;0O specifies an

absolute minimum

of 1# ft #.2( mand a design clearance of 1' ft #.**m.

0iscellaneous erms


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Load 3ating is an analysis of astructure to compute the ma3imumallowable loads that can be carried

across a bridge.


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Dead Load is a permanent loadsplaced on a structure before theconcrete slab hardens.


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Superimposed dead loads arepermanent loads placed on thestructure after the concrete hashardened e.g., bridge railing,sidewalks, wearing surface, etc..

Superimposed dead loads aregenerally considered part of total

dead loads.


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Live Loads are temporary loadsplaced on the structure, such asvehicles, wind, pedestrians, etc.


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Sheeted %it is a temporary bo3structure with only four sides whichcan be used as an earth support

system in e3cavation forsubstructure foundations.


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highway bridge structures

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