碳纤维材料混凝土桥梁中英文对照外文翻译文献Word格式文档下载.docx

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StructuralRehabilitationofConcreteBridgeswithCFRPComposites-PracticalDetailsandApplications

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.

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.

Deteriorationofconcretebridgemembersduetocorrosionofsteelbarsusuallyleadsinlossofsteelsectionanddelaminationofconcretecover.Asaresult,suchdeteriorationmayleadtostructuraldeficiencythatrequiresimmediateattention.Figure4showsrehabilitationofstructurallydeficientconcretebridgepierusingCFRPc