Download - 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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