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1、THERMALBEHAVIOROFCOMPOSITEBRIDGESByH.C.Fu,1S.F.Ng,2andM.S.Cheung3ABSTRACT:Thispaperpresentstheanalyticalresultsobtainedfromaparametricstudyonthethermalbehaviorofthreetypesofcompositebridgestructuressub•jectedtosolarradiation,namely,aplate-girder,asingle-cellbox,andatwo-cellbox-gir
2、derconcrete-steelcompositebridge.Aseriesoftransienttemperaturedis•tributionsandthethermalstressesforafewselectedtemperaturecasescorrespond•ingtoagivengeographiclocationandassumedenvironmentalconditionsarecom•puted.Theresultsofthisstudyconfirmthatasteady-statethermalconditionnevere
3、xistswithinabridgestructure,inthatambientairtemperatureandintensityofsolarradiationarebothtime-dependent.Theeffectsofconvectioncoefficient,slaboverhang,andairtemperatureinsideanenclosedboxonthetemperaturedistri•butionsofthebridgedeckareexaminedanddiscussed.INTRODUCTIONBridgesaresu
4、bjectedtorepeatedcyclesofheatingandcoolingfromsolarradiationandthesurroundingair.Forasimplysupportedconcreteorsteelbridge,constanttemperaturechangesresultinthermaldisplacementswithnothermalstressesinducedwithinthebridge.Onthecontrary,forcontin•uousconcrete-steelcompositebridges,en
5、vironmentalexposureproducesthermalmovementsaswellasthermalstressesinbridgesdueto:(1)Dis•similarmaterialpropertiesofthetwoconstituentcomponents,concreteandsteel;and(2)externalrestraints.TheFederalHighwayAdministrationwarnedthat"oneoutofeveryfourbridgedecksintheUnitedStates,manyofwh
6、icharelessthan20yearsold,isbadlydeteriorated...rehabilitationorreplacement...estimatedashighas$25billion..."(PublicRoads1983).Accordingtoareportpub•lishedrecentlybytheDepartmentofTransport,anestimated$880,000,000needstobespentonrepairingBritain'sconcretebridges(TheStructural1989).
7、Ina1986conferenceheldinOttawa,Ontario,Canada,onbridgestructures,itwasnotedthatabout130(or1%)ofOntario'sbridgesrequiredrehabilitation,carryingapotentialpricetagofhundredsofmillionsofdol•lars.Themajorbridgedeckdeteriorationproblemcanbeattributedtocorrosionofreinforcedsteelasaresulto
8、fchlorideattackfromdeicingsalts.F
