外文翻译试验研究钢筋混凝土柱改造方法.docx
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外文翻译试验研究钢筋混凝土柱改造方法.docx
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外文翻译试验研究钢筋混凝土柱改造方法
EXPERIMENTALRESEARCHOFREINFORCEDCONCRETECOLUMN
RETROFITMETHODS
Introduction
Astheinfrastructureofourcountrycontinuestoage,theneedforeffectiveretrofittreatmentshasincreased.Manybuildingandbridgestructuralcomponentsnolongerprovidecapacitysufficienttomeettherequiredcodestandards.Seismicupgradingandreinforcementprotectionaretwoofthemajorissuesrequiringretrofits.Additionally,manyagingstructuralmembersnolongerprovidetheloadcapacityoftheoriginaldesignbecauseofconcretecracking,steelcorrosion,orotherdamage.Inthisresearch,severalretrofitmethodsforincreasingtheaxialloadcapacityofreinforcedconcretecolumnsweretestedandanalyzed.
Severalcurrentlyappliedmethodsforretrofittingcolumnsincludeconcretejacketing,steeljacketing,andfiberreinforcedpolymer(FRP)jacketing.Allthreemethodshavebeenshowntoeffectivelyinincreasetheaxialloadcapacityofcolumns.Inaddition,anewreinforcementproduct,PrefabricatedCageSystem(PCS)reinforcement,wasintroducedasapossiblereinforcementoptionforconcretejacketretrofitapplications.
ProjectScope
Threeretrofitreinforcementoptions,concretejacketing,steeljacketing,andFRP
wrapping,wereexperimentallyanalyzedintheresearch.Threedifferentmaterials
providedreinforcementfortheconcretejackets:
arebarcagewithspiraltransverse
reinforcement,weldedwirefabric(WWF),andtheaforementionedPCS.Allspecimensweretestedunderaxialcompressionloadingonly.Appliedloadanddisplacementweremeasuredforallspecimensthroughouttestinguntilfailure.Additionally,responseoftheloadedspecimenswasobservedanddocumentedthroughoutthetesting.BehaviorofthenewlyintroducedPCSreinforcementwascomparedwithtraditionallyusedretrofitapplicationsalreadycurrentlyutilizedinthestructuralengineeringindustry.Advantagesanddisadvantagesofeachretrofitmeasurewereidentified.Additionally,modelconceptswerepresentedfortheresponseofconcretejacketretrofittedcolumnsbasedontheworkofManderetal.(1988)andCai(1987).
ProjectSummary
Seventeencircularcolumnswereconstructedandtestedtofailureincompression.First,similarreinforcedconcretebasecolumnswereconstructedwithspiraltransverse
reinforcement.Allbasespecimenshadthesamedimensions,transverse,andlongitudinaleinforcement.Thebasespecimenswerethenretrofittedwiththedifferentretrofitmethodspreviouslydiscussed.Onespecimen,referredtoasthebasespecimen,wastestedwithoutanyretrofitapplied.Threespecimenswereretrofittedwithaspiralrebarreinforcedconcretejacket.Twospecimenswerereinforcedwithaweldedwirefabricreinforcedconcretejacket.ThreespecimenswereretrofittedwithFRPwrapsandtwomorespecimenswereretrofittedwithsteeljackets.Inaddition,sixspecimenswereretrofittedwithaPCSreinforcedconcretejacket,includingtwodifferentthicknessesofPCS.
Ninespecimenshadtheentirecrosssectionofthebasecolumnandretrofitarealoaded.Thissimulatedaretrofitconditionwhentheappliedloadisdistributedacrosstheentirecrosssection.Fivespecimenshadthecrosssectionofonlythebasecolumnloaded,whichsimulatedaconditionwhentheloadisonlyappliedtotheoriginalmember.Threeotherspecimenshadincreasedlateralreinforcementspacingwithsimilartransversereinforcementstrengthperspacing.Thesespecimensalsohadtheentireretrofitandbasecolumncross-sectionloaded.
RETROFITOFEXISTINGSTRUCTURES
Manystructureshavehistoricallybeenconstructedusingreinforcedconcrete.Typicalordinaryconcreteconsistsoffourconstituents:
gravel,sand,water,andcement.Reinforcedconcretehassometypeofreinforcement,typicallysteel,combinedwithconcretetoproduceastrongersystemthanplainconcrete.Concreteisstrongin
compressionbutweakintension.Tensileforcescauseconcretetocrackandeventuallyfailinabrittlemanneratstressessignificantlylowerthanthecompressionstrengthofconcrete.Steel,oranothertypeofreinforcementmaterial,canbeusedtocompensatefortheweaktensilestrengthofconcrete.Thissystemisreferredtoasreinforcedconcrete.
Asreinforcedconcreteages,avarietyofdetrimentaleffectscanoccur.Theseincludespalling,flaking,orcrackingoftheconcrete,andsubsequentcorrosionofthereinforcingsteel.Theseoccurrencescansignificantlyaffectthestrengthofstructuralmembers.Membersdisplayingtheseadverseaffectsmayberehabilitatedusinganappropriateretrofitmethod.
Retrofittingistypicallydonefortworeasons:
rehabilitationorstrengthening.As
previouslydiscussed,rehabilitationisfixingthestructuraldeficienciesofadamaged
structureorstructuralmember.Thismaybenecessaryforagingmembersthatnolongerdisplaythestrengthoftheoriginaldesign.Strengtheningincreasestheload-carryingcapacityofastructuralmember(Ersoyetal.1993).Thismaybenecessaryifthesupportedloadisalteredthroughthelifeofthestructuralmember,orifcurrentdesignstandardshavemorestringentreinforcementrequirements.Additionally,structuralmembersinseismicregionsmayneedtobeupgradedtocurrentseismicrequirements.
Retrofittingcanbeappliedtoanystructuralmembers,includingbeamsandcolumns.Severalmethodsaretraditionallyutilizedforretrofitting.Theseincludeconcretejacketing,steeljacketing,andFRPstrengthening(Wipfetal.1997).Reinforcementforconcretejacketscanbeprovidedbyrebarreinforcementorweldedwirefabric(WWF).Additionally,arelativelynewproduct,PrefabricatedCageSystemreinforcement(PCS),issuggestedasapossiblereinforcementalternativeforconcretejacketretrofits.
PCSBenefits
PCSreinforcementhassomeuniqueproperties.Thelongitudinalandlateral
reinforcementforPCSarelocatedthesamedistancefromthecenterofthemember
cross-section.Thisprovidesincreasedflexuralcapacity,usingthesameamountofsteelasatraditionalrebarsystem,andresultsinmoreefficientuseofthereinforcingsteel.ThemonolithicactionofPCSeliminatesseparationoflongitudinalandtransverseeinforcement.Additionally,PCSreinforcementisspreadinaplanarconfigurationwhichoffersgreaterconfinementthanrebarreinforcement,asdisplayedinFigure2.4.ThicknessofthePCSsteeldeterminesthedimensionsofthereinforcementconfiningtheconcrete.
PCSreinforcementoffersseveraladditionalbenefits.Dimensionsofthereinforcementaredeterminedbythedesignertoproduceanydesiredamountoftransverseandlongitudinalreinforcement.Thisallowsagreatdealofflexibilityandefficiencyinthedesignprocess,asreinforcementchoicesarenotlimitedtoavailablestockmaterials.Additionally,PCSreinforcementcanbefabricatedoff-siteandimmediatelyplacedforconcretecastingwithoutadditionalfieldwork,suchastying,cutting,orbendingofreinforcement,whichprolongconstructiontime.Off-sitefabricationalsoprovidesanincreasedlevelofqualitycontrolforthereinforcement.InPCSproduction,dimensionsandspacingarefarmoreaccuratewhichminimizesopportunitiesforhumanerrorandeliminatesacceptanceofsub-pardetailingorinadequateconstruction.This,inturn,resultsinanincreasedfactorofsafetyforconstructionprojects
RetrofitMethods
Aspreviouslymentioned,commonretrofittechniquesincludeconcrete,FRP,andsteeljackets.Concretejacketsareconstructedbyenlargingtheexistingcrosssectionwithanewlayerofconcreteandreinforcement(Ersoyetal.1993).Thisreinforcementistraditionallyprovidedbyhooporspiralrebar,orweldedwirefabric.FRPreinforcementistypicallyappliedtwoways:
prefabricatedjacketsorwraps.Bothmethodshavebeenexperimentallyresearched(MorshedandKazemi2005).Steeljacketsareconstructedbyplacingasteeltubewithaslightlylargerdiameteraroundthemembertoberetrofitted.Theareabetweentheexistingmemberandsteeltubeistypicallyfilledwithgrout(Priestleyetal.1996).
ConcreteJacketing
Additionofaconcretejacketisusedtoenhanceflexuralstrength,ductility,andshearstrengthofcolumns.ThistechniqueismorecommonlyusedforbuildingcolumnsbuthasbeenappliedtosomebridgemembersinJapan.Theenhancedconfinementisachievedwiththeuseoftiesorspiralsatasmallpitch,ortransversereinforcementspacing(Priestleyetal.1996).Concretejacketscanbeusedtoretrofitbeamsaswellascolumns(CheongandMacAlevey2000).Additionalmaterialscanbeusedtoreinforcetheretrofit,aslongasconfinementisenhanced.
RebarReinforcement
Concretejacketedcolumnswithhoopandspiralreinforcementeffectivelyenhancethestructuralcapacityofretrofittedmembers.Ersoyetal.(1993)rantwoseriesofteststostudythebehaviorofstrengthenedandrepairedconcretejacketedcolumns.Thefirstseriescomparesthebehaviorofjacketedcolumnswithamonolithicreferencespecimenundermonotonicaxialloading.Alltheconcreteforthemonolithicspecimenwascastwiththebasecolumnandretrofitreinforcementinplace,toprovideaspecimenwithperfectinteractionandbondbetweenthebasecolumnandretrofitmaterial.Hoopreinforcementisusedinthebasecolumnandretrofitreinforcement,asshowninFigure2.5.Thejacketsareappliedundertwoconditions:
afterthecompressionloadingwasappliedandremoved,aswellaswhiletheaxialloadisstillapplied.Itisdeterminedthatcolumnsjacketedafterunloadingperformedwell,reaching80to90percentofthestrengthofthemonolithicreferencespecimen.Repairjacketsappliedwhilethecolumnisstillunderloaddidnotperformaswellandonlyreached50percentoftheaxialloadcarriedbythemonolithicspecimen.Thesecondseriesoftestsstudytheeffectivenessofconcretejac
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