桥梁毕业设计外文翻译.docx
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桥梁毕业设计外文翻译.docx
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桥梁毕业设计外文翻译
外文资料
TheTenthEastAsia-PacificConferenceonStructuralEngineeringandConstruction
August3-5,2006,Bangkok,Thailand
StructuralRehabilitationofConcreteBridgeswithCFRPComposites-PracticalDetailsandApplications
RiyadS.ABOUTAHA1,andNuttawatCHUTARAT2
ABSTRACT:
Manyoldexistingbridgesarestillactiveinthevarioushighwaytransportationnetworks,carryingheavierandfastertrucks,inallkindsofenvironments.Water,salt,andwindhavecauseddamagetotheseoldbridges,andscarcityofmaintenancefundshasaggravatedtheirconditions.Oneattempttorestoretheoriginalcondition;andtoextendtheservicelifeofconcretebridgesisbytheuseofcarbonfiberreinforcedpolymer(CFRP)composites.ThereappeartobeverylimitedguidesonrepairofdeterioratedconcretebridgeswithCFRPcomposites.Inthispaper,guidelinesfornondestructiveevaluation(NDE),nondestructivetesting(NDT),andrehabilitationofdeterioratedconcretebridgeswithCFRPcompositesarepresented.TheeffectofdetailingonductilityandbehaviorofCFRPstrengthenedconcretebridgesarealsodiscussedandpresented.
KEYWORDS:
Concretedeterioration,corrosionofsteel,bridgerehabilitation,CFRPcomposites.
1Introduction
Thereareseveraldestructiveexternalenvironmentalfactorsthatlimittheservicelifeofbridges.Thesefactorsincludebutnotlimitedtochemicalattacks,corrosionofreinforcingsteelbars,carbonationofconcrete,andchemicalreactionofaggregate.Ifbridgeswerenotwellmaintained,thesefactorsmayleadtoastructuraldeficiency,whichreducesthemarginofsafety,andmayresultinstructuralfailure.Inordertorehabilitateand/orstrengthendeterioratedexistingbridges,thoroughevaluationshouldbeconducted.Thepurposeoftheevaluationistoassesstheactualconditionofanyexistingbridge,andgenerallytoexaminetheremainingstrengthandloadcarrycapacityofthebridge.
1AssociateProfessor,SyracuseUniversity,U.S.A.
2Lecturer,SripatumUniversity,Thailand.
Oneattempttorestoretheoriginalcondition,andtoextendtheservicelifeofconcretebridgesisbytheuseofcarbonfiberreinforcedpolymer(CFRP)composites.
InNorthAmerica,EuropeandJapan,CFRPhasbeenextensivelyinvestigatedandapplied.SeveraldesignguideshavebeendevelopedforstrengtheningofconcretebridgeswithCFRPcomposites.However,thereappeartobeverylimitedguidesonrepairofdeterioratedconcretebridgeswithCFRPcomposites.Thispaperpresentsguidelinesforrepairofdeterioratedconcretebridges,alongwithproperdetailing.Evaluation,nondestructivetesting,andrehabilitationofdeterioratedconcretebridgeswithCFRPcompositesarepresented.SuccessfulapplicationofCFRPcompositesrequiresgooddetailingastheforcesdevelopedintheCFRPsheetsaretransferredbybondattheconcrete-CFRPinterface.TheeffectofdetailingonductilityandbehaviorofCFRPstrengthenedconcretebridgeswillalsobediscussedandpresented.
2DeterioratedConcreteBridges
Durabilityofbridgesisofmajorconcern.Increasingnumberofbridgesareexperiencingsignificantamountsofdeteriorationpriortoreachingtheirdesignservicelife.Thisprematuredeteriorationconsideredaproblemintermsofthestructuralintegrityandsafetyofthebridge.Inaddition,deteriorationofabridgehasaconsiderablemagnitudeofcostsassociatedwithit.Inmanycases,therootofadeteriorationproblemiscausedbycorrosionofsteelreinforcementinconcretestructures.Concretenormallyactstoprovideahighdegreeofprotectionagainstcorrosionoftheembeddedreinforcement.However,corrosionwillresultinthosecasesthattypicallyexperiencepoorconcretequality,inadequatedesignorconstruction,andharshenvironmentalconditions.Ifnottreatedadurabilityproblem,e.g.corrosion,mayturnintoastrengthproblemleadingtoastructuraldeficiency,asshowninFigure1.
Figure1Corrosionofthesteelbarsisleadingtoastructuraldeficiency
3Non-destructiveTestingofDeterioratedConcreteBridgePiers
Inordertodesignasuccessfulretrofitsystem,theconditionoftheexistingbridgeshouldbethoroughlyevaluated.Evaluationofexistingbridgeelementsorsystemsinvolvesreviewoftheasbuiltdrawings,aswellasaccurateestimateoftheconditionoftheexistingbridge,asshowninFigure2.Dependingonthepurposeofevaluation,non-destructivetestsmayinvolveestimationofstrength,saltcontents,corrosionrates,alkalinityinconcrete,etc.
Figure2Visibleconcretedistressmarkedonanelevationofaconcretebridgepier
Althoughmostofthenon-destructivetestsdonotcauseanydamagetoexistingbridges,someNDTmaycauseminorlocaldamage(e.g.drilledholes&coring)thatshouldberepairedrightaftertheNDT.Thesetestsarealsoreferredtoaspartialdestructivetestsbutfallundernon-destructivetesting.
Inordertoselectthemostappropriatenon-destructivetestforaparticularcase,thepurposeofthetestshouldbeidentified.Ingeneral,therearethreetypesofNDTtoinvestigate:
(1)strength,
(2)otherstructuralproperties,and(3)qualityanddurability.Thestrengthmethodsmayinclude;compressivetest(e.g.coretest/reboundhammer/ultrasonicpulsevelocity),surfacehardnesstest(e.g.reboundhammer),penetrationtest(e.g.Windsorprobe),andpullouttest(anchortest).
Otherstructuraltestmethodsmayinclude;concretecoverthickness(cover-meter),locatingrebars(rebarlocator),rebarsize(somerebarlocators/rebardatascan),concretemoisture(acquameter/moisturemeter),cracking(visualtest/impactecho/ultrasonicpulsevelocity),delamination(hammertest/ultrasonicpulsevelocity/impactecho),flawsandinternalcracking(ultrasonicpulsevelocity/impactecho),dynamicmodulusofelasticity(ultrasonicpulsevelocity),Possion’sratio(ultrasonicpulsevelocity),thicknessofconcreteslaborwall(ultrasonicpulsevelocity),CFRPdebonding(hammertest/infraredthermographictechnique),andstainonconcretesurface(visualinspection).
Qualityanddurabilitytestmethodsmayinclude;rebarcorrosionrate–fieldtest,chlorideprofilefieldtest,rebarcorrosionanalysis,rebarresistivitytest,alkali-silicareactivityfieldtest,concretealkalinitytest(carbonationfieldtest),concretepermeability(fieldtestforpermeability).
4Non-destructiveEvaluationofDeterioratedConcreteBridgePiers
Theprocessofevaluatingthestructuralconditionofanexistingconcretebridgeconsistsofcollectinginformation,e.g.drawingsandconstruction&inspectionrecords,analyzingNDTdata,andstructuralanalysisofthebridge.Theevaluationprocesscanbesummarizedasfollows:
(1)Planningfortheassessment,
(2)Preliminaryassessment,whichinvolvesexaminationofavailabledocuments,siteinspection,materialsassessment,andpreliminaryanalysis,(3)Preliminaryevaluation,thisinvolves:
examinationphase,andjudgmentalphase,andfinally(4)thecost-impactstudy.
Iftheinformationisinsufficienttoconductevaluationtoaspecificrequiredlevel,thenadetailedevaluationmaybeconductedfollowingsimilarstepsfortheabove-mentionedpreliminaryassessment,butin-depthassessment.Successfulanalyticalevaluationofanexistingdeterioratedconcretebridgeshouldconsidertheactualconditionofthebridgeandlevelofdeteriorationofvariouselements.Factors,e.g.actualconcretestrength,levelofdamage/deterioration,actualsizeofcorrodedrebars,lossofbondbetweensteelandconcrete,etc.shouldbemodeledintoadetailedanalysis.Ifsuchdetailedanalysisisdifficulttoaccomplishwithinareasonableperiodoftime,thenevaluationbyfieldloadtestingoftheactualbridgeinquestionmayberequired.
5BridgeRehabilitationwithCFRPComposites
ApplicationofCFRPcompositematerialsisbecomingincreasinglyattractivetoextendtheservicelifeofexistingconcretebridges.ThetechnologyofstrengtheningexistingbridgeswithexternallybondedCFRPcompositeswasdevelopedprimarilyinJapan(FRPsheets),andEurope(laminates).Theuseofthesematerialsforstrengtheningexistingconcretebridgesstartedinthe1980s,firstasasubstitutetobondedsteelplates,andthenasasubstituteforsteeljacketsforseismicretrofitofbridgecolumns.CFRPCompositematerialsarecomposedoffiberreinforcementbondedtogetherwitharesinmatrix.Thefibersprovidethecompositewithitsuniquestructuralproperties.Theresinmatrixsupportsthefibers,protectthem,andtransfertheappliedloadtothefibersthroughshearingstresses.MostofthecommerciallyavailableCFRPsystemsintheconstructionmarketconsistofuniaxialfibersembeddedinaresinmatrix,typicallyepoxy.Carbonfibershavelimitedultimatestrain,whichmaylimitthedeformabilityofstrengthenedmembers.However,undertrafficloads,localdebondingbetweenFRPsheetsandconcretesubstratewouldallowforacceptablelevelofglobaldeformationsbeforefailure.
CFRPcompositescouldbeusedtoincreasetheflexuralandshearstrengthofbridgegirdersincludingpiercapbeams,asshowninFigure3.InordertoincreasetheductilityofCFRPstrengthenedconcretegirders,thelongitudinalCFRPcompositesheetsusedforflexuralstrengtheningshouldbeanchoredwithtransverse/diagonalCFRPanchorstopreventprematuredelaminationofthelongitudinalsheetsduetolocalizeddebondingattheconcretesurface-CFRPsheetinterface.InordertopreventstressconcentrationandprematurefractureoftheCFRPsheetsatthecornersofconcretemembers,thecornersshouldberoundedat50mm(2.0inch)radius,asshowninFigure3.
Deteriorationofconcretebridgemembersduetocorrosionofsteelbarsusuallyleadsinlossofsteelsectionandde
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