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1、出处：安瑞克．混凝土桥梁结构形式[J]．建筑实录(美)，2010，33(36)：34—36TheStructureofConcreteBridgePre-stressedconcretehasprovedtobetechnicallyadvantageous,economicallycompetitive,andestheticallysuperiorbridges,fromveryshortspanstructuresusingstandardcomponentstocable-stayedgirdersandcontinuousboxgirderswithclearspansofne
2、arly100aft.Nearlyallconcretebridges,eventhoseofrelativelyshortspan,arenowpre-stressed.Pre-casting,cast-in-placeconstruction,oracombinationofthetwomethodsmaybeused.Bothpre-tensioningandposttensioningareemployed,oftenonthesameproject.IntheUnitedStates,highwaybridgesgenerallymust-meetloading,design,
3、andconstructionrequirementsoftheAASHTOSpecification.Designrequirementsforpedestriancrossingsandbridgesservingotherpurposesmaybeestablishedbylocalorregionalcodesandspecifications.ACICodeprovisionsareoftenincorporatedbyreference.Bridgesspanstoabout100ftoftenconsistofpre-castintegral-deckunits,which
4、offerlowinitialcost,minimum,maintenance,andfasteasyconstruction,withminimumtrafficinterruption.Suchgirdersaregenerallypre-tensioned.Theunitsareplacedsidebyside,andareoftenpost-tensionedlaterallyatintermediatediaphragmlocations,afterwhichshearkeysbetweenadjacentunitsarefilledwithnon-shrinkingmorta
5、r.Forhighwayspans,anasphaltwearingsurfacemaybeapplieddirectlytothetopofthepre-castconcrete.Insomecases,acast-in-placeslabisplacedtoprovidecompositeaction.Thevoidedslabsarecommonlyavailableindepthsfrom15to21in.andwidthsof3to4ft.ForastandardhighwayHS20loading,theyaresuitableforspanstoabout50ft,Stan
6、dardchannelsectionsareavailableindepthsfrom21to35inavarietyofwidths,andareusedforspansbetweenabout20and60ft.Thehollowboxbeams-andsingle-teegirdersareintendedforlongerspansuptoabout100ft.Formedium-spanhighwaybridges,toabout120ft,AASHTOstandardIbeamsaregenerallyused.Theyareintendedforusewithacompos
7、itecast-in-placeroadwayslab.Suchgirdersoftencombinepre-tensioningofthepre-castmemberwithpost-tensioningofthecompositebeamafterthedeckisplaced.Inanefforttoobtainimprovedeconomy,somestateshaveadoptedmorerefineddesigns,su
