土木毕业设计外文翻译近表面埋置加固的钢筋混凝土梁抗弯性能实验研究.docx
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土木毕业设计外文翻译近表面埋置加固的钢筋混凝土梁抗弯性能实验研究.docx
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土木毕业设计外文翻译近表面埋置加固的钢筋混凝土梁抗弯性能实验研究
中文2630字
ANEXPERIMENTALSTUDYONFLEXURALBEHAVIOROFRCBEAMS
STRENGTHENEDWITHNSMREINFORCEMENT
Woo-TaiJUNG1,Young-HwanPARK2,Jong-Sup
ABSTRACT:
ThisstudypresentstheresultsofexperimentsperformedonRC(ReinforcedConcrete)beamsstrengthenedwithNSM(NearSurfaceMounted)reinforcement.Atotalof6specimenshavebeentested.ThespecimenscanbeclassifiedintoEBR(ExternallyBondedReinforcement)specimenandNSMreinforcementsspecimens.TwoNSMspecimenswithspacevariableswerestrengthenedwith2CFRP(CarbonFiberReinforcedPolymer)strips.ExperimentalresultsrevealedthatNSMspecimensusedCFRPreinforcementsmoreefficientlythantheEBRspecimens.EvenifCFRPcrosssectionareasofNSMspecimenshave30%,50%ofEBRSpecimen,thestrengtheningeffectofNSMspecimensissuperiortoEBRspecimen.NSMspecimenswithspacevariablesshowedthatthstrengtheningeffectofthespecimenwithnarrowspaceisslightlyincreasedascomparedtothespecimenwithwidespaceu
KEYWORDS:
carbonfiberreinforcedpolymer,externallybondedCFRPreinforcements,nearsurfacemountedCFRPreinforcements,strengthening
1.INTRODUCTION
AmongthevariousstrengtheningtechniquesthathavebeendevelopedandappliedtostrengthendeterioratedRCstructures,anumberofapplicationsusingFRPreinforcementshavesignificantlyincreasedrecently.FRPreinforcementsarebondedtoconcretesurfacesbyadhesivesbutfrequentlyexperiencedebondingfailureattheinterfacebetweenFRPreinforcementsandconcrete.Mostresearch,todate,hasfocusedoninvestigatingthestrengtheningeffectsandfailuremodesofEBRsystem
TheproblemofprematurefailureofEBRsystemmaybesolvedbyincreasingtheinterfacebetweenFRPandconcrete.Usingthisprinciple,theNSMsystemhasbeenintroducedrecently.TheNSMsystemforconcretestructureusingsteelreinforcementalreadybeganin1940s.However,thecorrosionofthesteelreinforcementandthepoorbondingperformanceofthegroutingmateriallargelyimpaireditsapplication.ThedevelopmentofimprovedepoxyandtheadoptionofFRPreinforcementofferedtheopportunitytoimplementNSMsystem(HassanandRizkalla2003;TäljstenandCarolin2001).Becauseoftheirlightweight,easeofinstallation,minimallaborcostsandsiteconstraints,highstrength-to-weightratios,anddurability,FRPrepairsystemscanprovideaneconomicallyviablealternativetotraditionalrepairsystemsandmaterials(Mirmiranetal.2004).RizkallaandHassan(2002)havecomparedEBRandNSMsystemintermsofcost,includingcostsofmaterialsandlabor,
andstrengtheningeffect.TheyconcludedthattheNSMsystemwasmorecost-effectivethantheEBRsystemusingCFRPstrips.
ThisexperimentalstudyinvestigatestheapplicabilityandstrengtheningperformancesofNSMusingCFRPstrips.Forcomparison,flexuraltestsonRCbeamsstrengthenedbyEBRandbyNSMhavebeenperformed.Inaddition,specimenswithspacevariableshavebeentestedtocomparethestrengtheningperformancebycrosssectionwithwideandnarrowspace.
2.EXPERIMENTALPROGRAM
2.1MANUFACTUREOFSPECIMENS
Atotalof6specimensofsimplysupportedRCbeamswithspanof3mhavebeencast.Thedetailsandcross-sectionofthespecimensareillustratedinFigure1.Aconcretewithcompressivestrengthof31.3MPaat28dayshasbeenused.SteelreinforcementsD10(φ9.53mm)ofSD40havebeenarrangedwithsteelratioof0.0041andalayerofthreeD13(φ12.7mm)hasbeenarrangedascompressionreinforcements.ShearreinforcementsofD10havebeenlocatedevery10cmintheshearzonetoavoidshearfailure.Table1summarizesthematerialpropertiesusedforthetestbeams.
2.2EXPERIMENTALPARAMETERS
Table2liststheexperimentalparameters.Thecontrolspecimen,anunstrengthenedspecimen,hasbeencasttocomparethestrengtheningperformancesofthevarioussystems.CPL-50-BOND,EBRspecimen,hasbeenstrengthenedwithCFRPstrip.Theremaining4specimenswerestrengthenedwithNSMCFRPstrips.AmongthespecimensstrengthenedwithNSMreinforcements,anembedding64depthofNSM-PL-15andNSM-PL-25is15mmand25mm,respectively.AspacebetweengroovesofNSM-PL-25*2andNSM-PL-2Sis60mmand120mm,respectively.Thestrengthenedlengthofallthespecimenshasbeenfixedto2,700mm
2.3INSTALLATIONOFTHEFRPREINFORCEMENTS
Figure2showsthedetailsofcross-sectionsofthespecimens.ThestrengtheningprocessofEBRspecimen(CPL-50-BOND)wasproceededbythesurfacetreatmentusingagrinder,followedbythebondingoftheCFRPstrip.Thestrengthenedbeamswerecuredatambienttemperaturefor7daysforthecuringofepoxyadhesive.TheprocessforNSMstrengtheningprogressedbycuttingthegroovesatthebottomofthebeamsusingagrinder,cleaningthedebris,andembeddingtheCFRPstripafterapplicationoftheadhesive.Thestrengthened
beamswerecuredfor3dayssothattheepoxyadhesiveachievesitsdesignstrength.
2.4LOADINGANDMEASUREMENTMETHODS
Allspecimensweresubjectedto4-pointbendingteststofailurebymeansofUTM(UniversalTestingMachine)withcapacityof980kN.Theloadingwasappliedunderdisplacementcontrolataspeedof0.02mm/secuntilthefirst15mmand0.05mm/secfrom15mmuntilfailure.Themeasurementofalltestdatawasrecordedbyastaticdataloggerandacomputeratintervalsof1second.Electricalresistancestraingaugeswerefixedatmid-spanandL/4tomeasurethestrainofsteelreinforcements.Straingaugestomeasurethestrainofconcretewerelocatedatthetop,5cmand10cmawayfromthetopononesideatmid-span.StraingaugeswerealsoplacedontheFRPreinforcementlocatedatthebottomofthemid-spanandloadedpointstomeasurethestrainaccordingtotheloadingprocess.
3.EXPERIMENTALRESULTS
3.1FAILUREMODES
Beforecracking,allthestrengthenedspecimensexhibitedbendingbehaviorsimilartothe
unstrengthenedspecimen.ThisshowsthattheCFRPreinforcementisunabletocontributetotheincreaseofthestiffnessandstrengthintheelasticdomain.However,aftercracking,thebendingstiffnessandstrengthofthestrengthenedspecimenswereseentoincreasesignificantlyuntilfailurecomparedtotheunstrengthenedspecimens.Examiningthefinalfailure,theunstrengthenedcontrolspecimenpresentedtypicalbendingfailuremodewhichproceedsbytheyieldingofsteelreinforcementfollowedbycompressionfailureofconcrete.ThefailureofCPL-50-BOND,EBRspecimen,beganwiththeseparationofCFRPreinforcementandconcreteatmid-spantoexhibitfinallybrittledebondingfailure(Figure3).FailureofNSM-PL-15,NSMspecimen,occurredwiththeruptureoftheFRPreinforcement.FailureoftheremainingNSMspecimens(NSM-PL-25,NSM-PL25*2,andNSM-PL-2S)occurredthroughthesimultaneousseparationoftheCFRPreinforcementandepoxyfromconcrete(Figure4,5,and6).Table3summarizesthefailuremodes.
3.2STRENGTHENINGEFFECT
Figure7plotedtheload-deflectioncurvesofEBRandNSMspecimens.ThespecimenswithEBR,CPL-50-BOND,presentedultimateloadincreasedby30%comparedtotheunstrengthenedspecimen,whileNSMspecimens(NSM-PL-15,NSM-PL-25)increasedtheultimateloadby40to53%.ObservationofFigure7revealsthatevenifCPL-50-BONDwithrelativelylargecross-sectionalareaofCFRPreinforcementdevelopedlargerinitialstiffness,prematuredebondingfailureoccurredbecauseitsbondingareaismuchsmallerthanNSM-PL-15,NSM-PL-25.EBRspecimenbehavedsimilarlytotheunstrengthenedcontrolspecimenafterdebondingfailure.InFigure7,thestiffnessofNSMspecimensbeforeyieldingofsteelreinforcementwassmallerthanthestiffnessdevelopedbyEBRspecimenbecauseNSMspecimenshavethesmallercross-sectionalareaofCFRPreinforcementthanEBRspecimen.Theultimateloadandyieldloadareseentoincreasewiththecross-sectionalareaofNSMreinforcement.ExaminingtheultimatestrainofFRPsummarizedinTable3,themaximumstrainforEBRspecimenappearstoattain30%oftheultimatestrain,and80to100%forNSMspecimens.ThisprovesthattheNSMsystemisutilizingCFRPreinforcementefficiently(2Swiththesamecross-sectionalareaasCPL-50-Bondresentedultimateloadincreasedby95%,90%comparedtotheunstrengthenedspecimen,respectively.Consideringthesamecross-sectionalarea,thestrengtheningeffectofNSMspecimensissuperiortotheEBRspecimen.
InFigure8,NSM-PL-25*2andNSM-PL-2S,NSMspecimenswithspacevariables,showedthatthestrengtheningeffectofthespecimenwithnarrowspaceisslightlyincreasedby2.5%ascomparedtothespecimenwithwidespace.
4.CONCLUSIONS
PerformancetestshavebeencarriedoutonRCbeamsstrengthenedwithNSMsystems.Thefollowingconclusionswerederivedfromtheexperimentalresults.IthasbeenseenthatNSMspecimensutilizedtheCFRPreinforcementmoreefficientlythantheEBRspecimen.Accordingtothestaticloadingtestresults,thestrengtheningperformanceswereimproved
inNSMspecimenscomparedwithEBRspecimen.However,thespecimensNSM-PL-25,NSM-PL-25*2andNSM-PL-2SfailedbytheseparationoftheCFRPreinforcementsandepoxyadhesivefromtheconcrete.Consequently,itisnecessarytotakesomecountermeasurestopreventdebondingfailureforNSMspecimens.Consideringthesamecross-sectionalarea,thestrengtheningeffectofNSMspecimensissuperiortoEBRspecimen.NSM-PL-25*2andNSM-PL-2S,NSMspecimenswithspacevariables,showedthatthestrengtheningeffectofthespecimenwithnarrowspaceisslightlyincreasedascomparedtothespecimenwithwidespace.
5.REFERENCES
1.Hassan,T.andRizkalla,S.(2003),InvestigationofBondinConcreteStructuresStrengthenedwithNearSurfaceMountedCarbonFiberReinforcedPolymerStrips”,JournalofComposite
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