土木外文翻译高温下钢筋混凝土中钢筋的性能.docx
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土木外文翻译高温下钢筋混凝土中钢筋的性能.docx
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土木外文翻译高温下钢筋混凝土中钢筋的性能
土木外文翻译--高温下钢筋混凝土中钢筋的性能
外文原文:
ResearchLettersinMaterialsScience
Volume2008(2008),ArticleID814137,4pages
doi:
10.1155/2008/814137
ResearchLetter
PropertiesofReinforcedConcreteSteelRebarsExposedtoHighTemperatures
İlkerBekirTopçuandCenkKarakurt
DepartmentofCivilEngineering,EskişehirOsmangaziUniversity,26480Eskişehir,Turkey
Received12February2008;Accepted31March2008
AcademicEditor:
RajivS.Mishra
Copyright©2008İlkerBekirTopçuandCenkKarakurt.ThisisanopenaccessarticledistributedundertheCreativeCommonsAttributionLicense,whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited.
Abstract
Thedeteriorationofthemechanicalpropertiesofyieldstrengthandmodulusofelasticityisconsideredastheprimaryelementaffectingtheperformanceofsteelstructuresunderfire.Inthisstudy,hot-rolledS220andS420reinforcementsteelrebarsweresubjectedtohightemperaturestoinvestigatethefireperformanceofthesematerials.Itisaimedtodeterminetheremainingmechanicalpropertiesofsteelrebarsafterelevatedtemperatures.Steelsweresubjectedto20,100,200,300,500,800,and950∘Ctemperaturesfor3hoursandtensiletestswerecarriedout.EffectoftemperatureonmechanicalbehaviorofS220andS420weredetermined.Allmechanicalpropertieswerereducedduetothetemperatureincreaseofthesteelrebars.ItisseenthatmechanicalpropertiesofS420steelwasinfluencedmorethanS220steelatelevatedtemperatures.
1.Introduction
Fireremainsoneoftheseriouspotentialriskstomostbuildingsandstructures.Sinceconcreteiswidelyusedinconstruction,researchonfireresistanceofconcretebecomesmoreandmoreimportant.Manyresearchersallovertheworldhavedonesomeresearchesonthissubject.Themechanicalpropertiesofallcommonbuildingmaterialsdecreasewithelevationoftemperature.Thebehaviorofareinforcedconcretestructureinfireconditionsisgovernedbythepropertiesoftheconstituentmaterials,concrete,andsteel,athightemperature.Bothconcreteandsteelundergoconsiderablechangeintheirstrength,physicalproperties,andstiffnessbytheeffectsofheating,andsomeofthesechangesarenotrecoverableaftersubsequentcooling[1].
Itisnecessarytohavesafe,economical,andeasilyapplicabledesignmethodsforsteelmemberssubjectedtofire.However,withoutfireprotection,steelstructuresmaysufferseriousdamageorevencollapseinafirecatastrophe.Thisisbecausethemechanicalpropertiesofsteeldeterioratebyheatduringfires,andtheyieldstrengthofconventionalsteelat600°Cislessthan1/3ofthespecifiedyieldstrengthatroomtemperature[2].Therefore,conventionalsteelsnormallyrequirefire-resistantcoatingtobeapplied[3].Thetemperatureincreaseinthesteelmemberisgovernedbytheprinciplesofheattransfer.Consequently,itmustberecognizedthatthetemperatureofthesteelmember(s)willnotusuallybethesameasthefiretemperatureinacompartmentorintheexteriorflameplume.Protectedsteelwillexperienceamuchslowertemperatureriseduringafireexposurethanunprotectedsteel.Also,fireeffectonsteelmemberisinfluencedwithitsdistancefromthecenterofthefire,andifmoreventilationoccursnearthesteelinafuel-controlledcondition,whereintheventilationhelpstocoolthesteelbydissipatingheattothesurroundingenvironment[4].
Especially,temperatureincreaseofsteelandconcreteincompositesteel-concreteelementsleadstoadecreaseofmechanicalpropertiessuchasyieldstress,Young'smodulus,andultimatecompressivestrengthofconcrete[5].Thus,loadbearingofsteeldecreaseswhensteelorcompositestructureissubjectedtoafireaction.Ifthedurationandtheintensityofthefirearelargeenough,theloadbearingresistancecanfalltotheleveloftheappliedloadresultinginthecollapseofthestructure.However,thefailureoftheWorldTradeCentreon11thSeptember2001and,inparticular,ofbuildingWTC7alertedtheengineeringprofessiontothepossibilityofconnectionfailureunderfireconditions[6].Inthisstudy,S220andS420ribbedconcretesteelrebarsweresubjectedto7differenttemperaturestodeterminethehightemperaturebehaviorofreinforcementsteels.
2.ExperimentalStudy
Experimentalstudieswereconductedwith10and16 mmindiameterand200 mminlengthS220andS420reinforcementsteelrebars.Testspecimensweresubjectedto20,100,200,300,500,800,and950°Ctemperaturesinahighfurnacefor3hours,respectively.Attheendofthecuringprocess,steelswerecoolednaturallytotheroomtemperature.Subsequently,tensiletestswereappliedtosteelreinforcementrebars.AccordingtoEN10002-1tensilestrength,yieldstrengthandelongationofthesteelrebarsweredeterminedforelevatedtemperatures[7].Thesteelspecimenstensilestrengthtestswereperformedwith60tonsofloadingcapacityuniversaltensilestrengthtestmachine.TheloadingspeedofthetestmachineisadjustedaccordingtoTS708code[8].
3.TestResultsandEvaluations
3.1.Stress-StrainRelations
Theaveragevaluesforstress-strainrelationshipforspecimensthatwereexposedtovarioustemperaturesaregiveninFigures1and2.ThecurvesinFigures1and2weredrawnwiththeaveragetestresultsof10and16 mmindiametersteelspecimens.Thetestconditionsweremeanttosimulateabuildingthathadafiresothechangesinthemechanicalpropertiesofreinforcingsteelsusedinstructuresexposedtohightemperaturecouldbedetermined.AsseenfromFigure1,temperaturesbelow500°ChavenosignificanteffectonmechanicalpropertiesofpreheatedandcooledS220steelrebars.TheyieldstrengthandsplittingtensilestrengthsofS220steelsweresimilaruptothistemperature.However,theyieldstrengthandsplittingtensilestrengthoftheS220steelrebarsarereducingwiththeincreaseoftemperaturesover800°C.AsimilarbehaviorcanbeseenfromthetestresultsofS420-ribbedsteelrebars(Figure2).Allhightemperaturesubjectedsteelspecimensbecamemoreductiletemperaturesabove800°C.
Figure1:
Stress-straincurveofS220steelrebar.
Figure2:
Stress-straincurveofS420-ribbedsteelrebar.
3.2.YieldStrength
Yieldstrengthofbothreinforcingsteelrebarswasaffectedwiththeelevatedexposuretemperatures.ItcanbeconcludedfromFigure3thatthereisnovariationinyieldstrengthofreinforcingsteelswithcoverupto300°C.Plainreinforcingsteelrebarshaveexperiencedthestrainhardeningalreadyforthistemperature.AccordingtoEurocodeandTSEN1993,before400°Cthereisnodecreaseinyieldstrength,butafterthistemperatureasignificantyieldstrengthlossoccurs[9].TheyieldstrengthlossesofbothS220andS420steelrebarswere46%and84%for800°Cexposuretemperature,respectively.Forfurtherincreaseoftemperatureat950°C,yieldstrengthdecreaseswere64%and89%,respectively.Accordingtotheseresults,theremainingyieldstrengthofS220steelreinforcingrebarishigherthanS420-ribbedsteelrebarafterhigh-temperatureexposure.
Figure3:
Yieldstrengthofsteelrebarsagainsttemperature.
3.3.TensileStrength
ThetensilestrengthvariationofsteelreinforcementrebarsexposedtoelevatedtemperaturesisgiveninFigure4.Onthelightoftheseresults,therewasnosignificancereducingoftensilestrengthforbothtypesofsteelrebarsupto500°Ctemperature.ThetensilestrengthlossesofbothS220andS420steelrebarswere51%and85%for800°Cexposuretemperature,respectively.Forthehighestexposuretemperatureat950°C,tensilestrengthdecreaseswere60%and90%,respectively.Accordingtotheseresults,theremainingtensilestrengthofS220steelreinforcingrebarishigherthanS420-ribbedsteelrebarafterhigh-temperatureexposure.However,itshouldbeconsideredthatthepossibilityofcompletestrengthlossofsteelrebarsathightemperatureswhenastructureissubjectedtoahugefire.Theremainingstrengthsofbothreinforcingsteelrebarsafter500°Carelowerthanthedesignstrengthsofthesesteels.Consequently,theremainingstrengthofthesteelrebarsinstructuresisinfluencedwiththeexposuretimeandtypeoffiredependingontheheattransferthroughconcretecovertosteelparts[10].
Figure4:
Tensilestrengthofsteelrebarsagainsttemperature.
3.4.Elongation
TherelationbetweenhightemperatureandsplittingelongationratiocanbeseenfromFigure5.Thefigureisdemonstratedthatbothsteelrebarsshowasameelongationbehaviorunderelevatedtemperatures.TheelongationratiosofS220steelrebarsarehigherthanS420rebarsdependingontheductilefracturebehaviorofthissteel.Afterafireinsidethereinforcedconcretebuilding,thedeflectionsofthestructuralmembersincreasewiththeductilebehaviorofthesteelreinforcementathightemperatures.
Figure5:
Elongationratiosofsteelrebarsagainsttemperature.
Theelongationratioswereslightlyincreasedupto300°C,however,abovethistemperaturematerialbecomesbrittlewithdecreaseoftheelongationvalues.TheelongationlossesofbothS220andS420steelrebarswere1.2%and1.6%for800°Cexposuretemperature,respectively.Forfurtherincreaseoftemperatureat950°C,elongationratiosdecreaseswere1.6%and3.3%,respectively.Accordingtotheseresults,theelongationcapacityofS420steelislowerthanS220steelunderelevatedtemperatures.TheS420steelshowedabrittlefracturebehaviorunderelevatedtemperatures.Thisbehaviorisnotsufficientforrebarsteelinreinforcedconcretestructures.
3.5.Toughness
Theenergyabsorbentcapacityof
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