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外文-翻译--随时间变化的钢筋混凝土阻力分析.pdf

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外文-翻译--随时间变化的钢筋混凝土阻力分析.pdf

Vol.17No.4JournalofWuhanUniversityofTechnologyMater.Sci.Ed.Dec.2002RandomTimeDependentResistanceAnalysisonReinforcedConcreteStructures3GUANChang2sheng1WULing21WuhanUniversityofTechnology2WuhanUniversityofScienceandTechnologyReceivedAug.20,2001AbstractTheanalysismethodonrandomtimedependenceofreinforcedconcretematerialisintroduced,theeffectmechanismonreinforcedconcretearediscussed,andtherandomtimedependenceresistanceofreinforcedconcreteisstudied.Furthermore,thecorrosionofsteelbarinreinforcedconcretestructuresisanalyzed.Apracticalstatisticalmethodofevaluatingtherandomtimedependentresistance,whichincludesmaterial,structuralsizeandcalculationinfluence,isalsoestablished.Inaddition,anexampleofpredictingrandomtimedependentresistanceofreinforcedconcretestructuralelementisgiven.KeywordsrandomanalysistimedependentresistancereinforcedconcreteGUANChang2sheng管昌生Bornin1957Prof.InstituteofArchitectureandCivilEngineering,WuhanUniversityofTechnol2ogy,Wuhan430070,China3FundedbyHubeiProvinceConstructionBureauG2002191IntroductionReinforcedconcreteisoneofthemostusefulmateri2alsincivilengineeringforitssuitabilityandinexpensiveprice.Therefore,alargenumberofthiskindmaterialisused.However,intraditionaldesignofconstructionstructureandmaterialresearchofreinforcedconcrete,litteattentiontothetimedependentstrengthofreinforcedconcreteispaid,especiallytherandompropertiesofthevariouseffectsonthematerialsarehardlystudied\1,2\.Untilrecentyearthereareafewresearchesthatmentiontheproblemabouttherandomtimedependenceofrein2forcedconcreteinengineeringstructures.LiandMelch2ers\3\havestudiedthefailureprobabilityofreinforcedconcretecolumnsunderstochasticloads,andgivenatech2niquetocalculatethetime2variantfailureprobability.LiandLiu\4\havestudiedthedurabilityofconcretestructureconsideringtheeffectofreinforcedcorrosion.Leng\5\etalhavediscussedthestatusandproblemofstudyonthestresscorrosionofconcrete.AlsoLu\6\etalhavedis2cussedthestateofreinforcementcorrosion.Generallyspeaking,reinforcedconcreteresistanceobviouslyde2crease,whichdependsondifferentfactors\7\.Toevaluatethesafetyofconcretestructure,abasictheoryforanalyz2ingdurabilityofreinforcedconcreteshouldbeproposed.Itisnecessorytostudyrandomtimedependentpropertiesofreinforcedconcretestructures.2TimeDependentEffectMechanismsofReinforcedConcreteTherearemanyfactorsaffectingtheresistanceofre2inforcedconcrete.Morethan50kindsofchemicalcorro2sionfactorsexistonlyintheareaofwaterbasin,waterworksandwaterconditioning.Thepracticalmethodtoob2tainatimedependentmodelofreinforcedconcreteisamulti2factorcomprehensiontechnique.Ingeneral,forsin2gle2factor,manyresultshavebeenshownthatifonlycon2cretecarbonizationisconsidered,aformulaofpredictingcarbonizationthickcanbewrittenasDtKt1whereDt,Kandtarethick,speedcoefficientandtimeofcarbonization,respectively.Uptonowmanypredictingmodelsareusedinsteelcorrosion,fatiguedamage,andchemicalerosion,butnocommonrecognizedresultsunanimouslyexist.Generallyspeaking,thedecreasingresistancefunctionofreinforcedconcreteincludessomevariablesthatcanexpressassteelbar,concrete,geometricsize,environmentconditionnear2by,andpropertiesofrandomandtimedependenceofre2sistance\1,5\.Obviously,reinforcedconcreteresistanceisafunctionofrandomprocessorvariableofseriesofmate2rialsandstructures.Reinforcedconcretecarbonizationinairiscalledneutralization,whichisacomplexandslowneutralizationprocessofCO2intheairandalkalinemate2rialinreinforcedconcrete.Inairitwilltakeseveraldecadestocompletelycarbonizetheprotectivecoatingofsteelbarindenseconcrete,butonlytakeafewyearsinnon2denseconcrete.Iffinenessofcarbonizedmaterialsishigher,itsstrengthislowerandcarbonizationprocessisfasterindecreasingcrosssectionofstructure.Carboniza2tionmakesalkalinitylowerandsteelbarcorrosion\2\.Steelbarcorrosionisaprocessthatironinsteelbarsur2facelosseselectroncontinuallyanddissolvesinwaterun2dertheconditionofoxygenandwaterinteraction.There2fore,thevolumeoferodedmaterialsisexpendedseveraltimes,whichcanmaketheprotectivecoatingofreinforcedconcretecrack,drop,andcohesiondamagebetweensteelbarandconcretealongsteelbardirectionsothatrein2forcedconcretestructurelossesbearingcapability.Recentresearchesshowthatthesteelbargetsintoaseriouscor2rosionstatewhennon2carbonizedprotectivecoatingisonly15mmthick.Ontheotherhand,thestarttimeofcorro2sionmaybeinadvanceduetoincompletecoatingandcrackinconcrete,alsocorrosionvelocitymayincreasegreatly.Whensteelstressislessthanyieldingpoint,thecorrosionvelocityisstable,butincreasesseveraltimesifthecorrosionvelocitypassesovertheyieldingpoint.Thelatteriscalledstresscorrosion,whichisofbrittlenessandmoredangerous.Steelcorrosioncanmakebearingareaofsteelbardecrease,cohesiondamage,andlosestructureeffectiveness.Erosionairandliquidallhavestrongeffectonreinforcedconcrete,whichcanmakereinforcedcon2creteerosion,decreaseprotectivecoatingofconcrete,andfinallyacceleratesteelcorrosion.Whenbearingdynamicload,reinforcedconcretestructurecanundergofatiguedamage,leadingstrengthandrigiditytodecreasing,form2ingcrackandexpansion.Usuallyfatiguedamagecanbedividedintodetermineandrandommodels,theformerdealswithdetermineperiodloading,andthelatterisrel2ativetotherandomofmaterialandload.Besidesallmentionedabove,therearemanyotherfactors,suchastemperatureincludinghighorlow,andcyclictemperature,freezingdamage,humidity,includingcyclicofdryandhumid,andtheamplitudeofloading,whichcanresultinresistancedecreasingofreinforcedconcretestructure.3RandomTimeDependenceAnalysisUndertheconditionthateveryrandomvariableofstructureisindependentoneachother,andconsideringtimedependencecharacteristicofmaterial,therandomtimedependentfunctionofreinforcedconcretematerialcharacteristiccanbewrittenas\8\KMtk10K0tKf2whereK0tisarandomvariableindicatingpropertydif2ferenceofstructuralmaterialandtestingmaterialk0isacoefficientofpropertydifferenceofstructuralandtestingmaterial,andKfisarandomvariableoftestingmaterial.Asstatisticstheory,themeanvalueandstandarddeviationcoefficientofKMtareasfollowsrespectivelyμKMtk10μk0tμKf3δKMtδ2KKM0tδ2Kf4whereμk0tandδKKM0trespectivelyaremeanvalueandstandarddeviationcoefficientofrandomprocess.K0t,μKfandδKfarethemeanvalueandstandarddevia2tioncoefficientoftestingmaterialpropertyandrandomvariableKf,respectively.Bythesamewaythesimilarrandomanalyticalmodelmaybesetupforstudyingtherandomnessandtimede2pendencetogeometricparametersandcalculationmethodsofreinforcedconcretestructure.Theresistanceofreinforcedconcretecanbeex2pressedbyresistancefunctionRx1,x2,,xn,inwhichxidenotestheparametersofmaterials,geometryandcalculationprocedureofstructuralmaterial.Ifrandomandtimedependenceareappliedsimultaneouslytoresis2tanceandrelativevariables,xicanbedealtwithasaran2domprocess.Moreover,consideringfatiguemechanics,calculationmodelandinitialconditions,timedependentresistancemodelcanbewrittenasRR0,tηR0KpRx1,x2,,xn5whereRR0,tisresistancerandomprocess,R0isini2tialresistance,ηisarandomprocessoffatiguedamage,andKpisanundeterminableparameterofcalculationmodel,xidenotesarandomprocessofmaterialparame2ters.Manyexperimentsonsteelcorrosionindicatethatsteelerosionprocessaccordswithnormalrandomprocess.Byseparationprocedure,randomtimedependentresis2tanceRR0,tcansimplybeexpressedasRR0,tRtR06whereRtisadeterminingtimedependentfunction,andR0israndominitialresistance.Inaddition,someotherundeterminedconditionsshouldbeemployed,suchasundeterminedresistanceofactualmaterial,geometricsizeandcalculationmodel.Astoasimplestructure,resistancefunctionofrandompro2cessalsocanbesimplifiedasRtgtKpyRpt7wheregtistimedependentfunction,Kptisunde2terminableparameterofcalculationmodel,andRptisstructureresistancedeterminedbycalculatingmodel.Toasinglestructuralelementequation7canbewrittenasRtKptKMtKAtRKt8whereKpt,KMt,andKAtarerespectivelytimedependentparameterofcalculation,geometryandmaterialcharacteristicofreinforcedconcretestructuralelement.RKtisstandardvalueofmaterialresistance.Themeanvalueandstandarddeviationofequation8arerespectivelyasfollowsμRtμKPtμKMtμKAtRKt9σRtσ2KPtσ2KMtσ2KAt1/210Inengineeringapplication,decreasingfunctionrandomprocessofconcretestructuralresistancecanbeexpressedbyRtζt11whereRtisrandomprocessofconcretestructuralre2sistance,ζisrelativerandomvariable,andtistimedependentdeterminingfunction.Basedondurabilitygrade95Vol.17No.4GUANChang2shengetalRandomTimeDependentResistanceAnalysison...ofdesignedconcretestructure,equation11canbees2tablishedasμcutμcu1α1t12δcutδcu13μytμy1α2t14δytδy15whereμcutandμytarerespectivelyresistancemeanvalueofconcreteandsteelbarwhenreinforcedconcreteisuseduptotimetδcutandδytarestandarddevia2tioncoefficientsofconcreteandsteelbarofreinforcedconcreteattimetrespectivelyμcu,μy,δcu,δyareinitialvaluesofvariousvariablesα1andα2areresistancede2creasecoefficientsofconcreteandsteelrespectively,whichrelatetostructuralmaterialandcanbeobtainedfrommaterialexperiment.4EngineeringApplicationAstructuralelementofreinforcedconcretebearingaxialpressureistested,somestatisticaldataofstructuralresistanceiscalculated.ConsiderinitialvaluesC30con2crete,themeanvalueμcu1.41andstandarddeviationσcu0.1920MnSisteelbar,meanvalueμy1.14andstandarddeviationσy0.07initialsectionsizeis1m2.Thereare0.02variationoneachsideofthestructuralel2ement.ResistancedecreasecoefficientsofconcreteandsteelobtainedfromRef.\4\arerespectivelyα18107andα22.2106.Undertheseconditionstherandomtimedependentresistanceofthereinforcedcon2cretestructurebearingaxialloadcanbeobtained.Accordingtodesigntheoryofreinforcedconcretestructures,resistancefunctioncanbeformedbyRAcuRcuAyRy,inwhichRcuandRyareinitialresistanceofconcreteandsteelbarrespectively,andthenusingthetheorysuggestedinthispaper,therandomtimedepen2dentresistancecanbecalculated.SomestatisticaldataarelistedinTable1.Fromtheresultsitisseenthattheresistancechangeofreinforcedconcreteisobviousde2creasingwithtime.Thisphenomenonissignificantandnottobeignoredforevaluatingthesafetyofreinforcedconcrete.Table1RandomTimeDependentResistanceofReinforcedConcreteStructuralElementBearingAxialLoadt/year01020304050Meanvalue/KN7625.207323.957136.566885.756517.445987.32Standarddeviation/KN1248.631193.801164.731129.491080.281011.05Variationcoefficient0.16370.16290.16320.16400.16570.16885ConclusionsThecharacteristicofreinforcedconcretestructuresisimportantforresearch,designandconstructionofcivilen2gineering.Thestudyofrandomandtimedependenceofreinforcedconcretematerialisnecessaryforstructuraltesting,maintainingandsafetyevaluationofreinforcedconcretestructures.Forstructuralreliabilitydesign,apracticalrandomandtimedependentresistanceshouldbeestablished.Inthispaperrandomtimedependentcharac2teristicsofreinforcedconcretematerialsarestudied,whichincludemulti2factoreffectonconcretecarbonizatioo,steelbarcorrosion.Otherfactorstoreinforcedconcretemateri2al,andtheanalysismethodforrandomtimedependentre2sistanceofreinforcedconcretestructureareproposed.References1JLPan.EvaluationandTestingonPropertiesofConcreteStruc2tures.HeilongjiangHeilongjiangScienceandTechnologyPress,19972MLu.PXWang.JYLu.StateofArtofReinforcementCorro2sionStudies.Concrete,2000,837413QLi,REMelchers.FailureProbabilityofReinforcedConcreteColumnsunderStochasticloads.EngineeringStructures,1995,1744194244LiTian.LiuXila.AnalysisandDesignonheDurabilityofCon2creteStructures.BeijingSciencePress,19995LengFaguang,FengNaiqian,XingFeng.TheStatusandProblemofStudyofStressCorrosionofConcrete.Concrete,2000,8696LSGong.CPLiu.ConcreteDurabilityandItsRepairProtec2tion.BeijingConstructionIndustryPressofChina,19907YZChen.StudyonHydrationPhasesandSteelProtectionProp2ertiesofSilicate.\MasterDissertation\.WuhanWuhanUniversi2tyofTechnology,19898WRuan.CSGuan.GQL.AnalysisofTimeDependentStrengthofReinforcedConcreteStructure.JournalofShangDongInst.ofBuildingMaterial,1996,104687206JournalofWuhanUniversityofTechnologyMater.Sci.Ed.Dec.2002

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