土木外文翻译--高温下钢筋混凝土中钢筋的性能

外文原文RESEARCHLETTERSINMATERIALSSCIENCEVOLUME20082008,ARTICLEID814137,4PAGESDOI101155/2008/814137RESEARCHLETTERPROPERTIESOFREINFORCEDCONCRETESTEELREBARSEXPOSEDTOHIGHTEMPERATURESİLKERBEKIRTOPUANDCENKKARAKURTDEPARTMENTOFCIVILENGINEERING,ESKIEHIROSMANGAZIUNIVERSITY,26480ESKIEHIR,TURKEYRECEIVED12FEBRUARY2008ACCEPTED31MARCH2008ACADEMICEDITORRAJIVSMISHRACOPYRIGHT2008İLKERBEKIRTOPUANDCENKKARAKURTTHISISANOPENACCESSARTICLEDISTRIBUTEDUNDERTHECREATIVECOMMONSATTRIBUTIONLICENSE,WHICHPERMITSUNRESTRICTEDUSE,DISTRIBUTION,ANDREPRODUCTIONINANYMEDIUM,PROVIDEDTHEORIGINALWORKISPROPERLYCITEDABSTRACTTHEDETERIORATIONOFTHEMECHANICALPROPERTIESOFYIELDSTRENGTHANDMODULUSOFELASTICITYISCONSIDEREDASTHEPRIMARYELEMENTAFFECTINGTHEPERFORMANCEOFSTEELSTRUCTURESUNDERFIREINTHISSTUDY,HOTROLLEDS220ANDS420REINFORCEMENTSTEELREBARSWERESUBJECTEDTOHIGHTEMPERATURESTOINVESTIGATETHEFIREPERFORMANCEOFTHESEMATERIALSITISAIMEDTODETERMINETHEREMAININGMECHANICALPROPERTIESOFSTEELREBARSAFTERELEVATEDTEMPERATURESSTEELSWERESUBJECTEDTO20,100,200,300,500,800,AND950CTEMPERATURESFOR3HOURSANDTENSILETESTSWERECARRIEDOUTEFFECTOFTEMPERATUREONMECHANICALBEHAVIOROFS220ANDS420WEREDETERMINEDALLMECHANICALPROPERTIESWEREREDUCEDDUETOTHETEMPERATUREINCREASEOFTHESTEELREBARSITISSEENTHATMECHANICALPROPERTIESOFS420STEELWASINFLUENCEDMORETHANS220STEELATELEVATEDTEMPERATURES1INTRODUCTIONFIREREMAINSONEOFTHESERIOUSPOTENTIALRISKSTOMOSTBUILDINGSANDSTRUCTURESSINCECONCRETEISWIDELYUSEDINCONSTRUCTION,RESEARCHONFIRERESISTANCEOFCONCRETEBECOMESMOREANDMOREIMPORTANTMANYRESEARCHERSALLOVERTHEWORLDHAVEDONESOMERESEARCHESONTHISSUBJECTTHEMECHANICALPROPERTIESOFALLCOMMONBUILDINGMATERIALSDECREASEWITHELEVATIONOFTEMPERATURETHEBEHAVIOROFAREINFORCEDCONCRETESTRUCTUREINFIRECONDITIONSISGOVERNEDBYTHEPROPERTIESOFTHECONSTITUENTMATERIALS,CONCRETE,ANDSTEEL,ATHIGHTEMPERATUREBOTHCONCRETEANDSTEELUNDERGOCONSIDERABLECHANGEINTHEIRSTRENGTH,PHYSICALPROPERTIES,ANDSTIFFNESSBYTHEEFFECTSOFHEATING,ANDSOMEOFTHESECHANGESARENOTRECOVERABLEAFTERSUBSEQUENTCOOLING1ITISNECESSARYTOHAVESAFE,ECONOMICAL,ANDEASILYAPPLICABLEDESIGNMETHODSFORSTEELMEMBERSSUBJECTEDTOFIREHOWEVER,WITHOUTFIREPROTECTION,STEELSTRUCTURESMAYSUFFERSERIOUSDAMAGEOREVENCOLLAPSEINAFIRECATASTROPHETHISISBECAUSETHEMECHANICALPROPERTIESOFSTEELDETERIORATEBYHEATDURINGFIRES,ANDTHEYIELDSTRENGTHOFCONVENTIONALSTEELAT600CISLESSTHAN1/3OFTHESPECIFIEDYIELDSTRENGTHATROOMTEMPERATURE2THEREFORE,CONVENTIONALSTEELSNORMALLYREQUIREFIRERESISTANTCOATINGTOBEAPPLIED3THETEMPERATUREINCREASEINTHESTEELMEMBERISGOVERNEDBYTHEPRINCIPLESOFHEATTRANSFERCONSEQUENTLY,ITMUSTBERECOGNIZEDTHATTHETEMPERATUREOFTHESTEELMEMBERSWILLNOTUSUALLYBETHESAMEASTHEFIRETEMPERATUREINACOMPARTMENTORINTHEEXTERIORFLAMEPLUMEPROTECTEDSTEELWILLEXPERIENCEAMUCHSLOWERTEMPERATURERISEDURINGAFIREEXPOSURETHANUNPROTECTEDSTEELALSO,FIREEFFECTONSTEELMEMBERISINFLUENCEDWITHITSDISTANCEFROMTHECENTEROFTHEFIRE,ANDIFMOREVENTILATIONOCCURSNEARTHESTEELINAFUELCONTROLLEDCONDITION,WHEREINTHEVENTILATIONHELPSTOCOOLTHESTEELBYDISSIPATINGHEATTOTHESURROUNDINGENVIRONMENT4ESPECIALLY,TEMPERATUREINCREASEOFSTEELANDCONCRETEINCOMPOSITESTEELCONCRETEELEMENTSLEADSTOADECREASEOFMECHANICALPROPERTIESSUCHASYIELDSTRESS,YOUNGSMODULUS,ANDULTIMATECOMPRESSIVESTRENGTHOFCONCRETE5THUS,LOADBEARINGOFSTEELDECREASESWHENSTEELORCOMPOSITESTRUCTUREISSUBJECTEDTOAFIREACTIONIFTHEDURATIONANDTHEINTENSITYOFTHEFIREARELARGEENOUGH,THELOADBEARINGRESISTANCECANFALLTOTHELEVELOFTHEAPPLIEDLOADRESULTINGINTHECOLLAPSEOFTHESTRUCTUREHOWEVER,THEFAILUREOFTHEWORLDTRADECENTREON11THSEPTEMBER2001AND,INPARTICULAR,OFBUILDINGWTC7ALERTEDTHEENGINEERINGPROFESSIONTOTHEPOSSIBILITYOFCONNECTIONFAILUREUNDERFIRECONDITIONS6INTHISSTUDY,S220ANDS420RIBBEDCONCRETESTEELREBARSWERESUBJECTEDTO7DIFFERENTTEMPERATURESTODETERMINETHEHIGHTEMPERATUREBEHAVIOROFREINFORCEMENTSTEELS2EXPERIMENTALSTUDYEXPERIMENTALSTUDIESWERECONDUCTEDWITH10AND16MMINDIAMETERAND200MMINLENGTHS220ANDS420REINFORCEMENTSTEELREBARSTESTSPECIMENSWERESUBJECTEDTO20,100,200,300,500,800,AND950CTEMPERATURESINAHIGHFURNACEFOR3HOURS,RESPECTIVELYATTHEENDOFTHECURINGPROCESS,STEELSWERECOOLEDNATURALLYTOTHEROOMTEMPERATURESUBSEQUENTLY,TENSILETESTSWEREAPPLIEDTOSTEELREINFORCEMENTREBARSACCORDINGTOEN100021TENSILESTRENGTH,YIELDSTRENGTHANDELONGATIONOFTHESTEELREBARSWEREDETERMINEDFORELEVATEDTEMPERATURES7THESTEELSPECIMENSTENSILESTRENGTHTESTSWEREPERFORMEDWITH60TONSOFLOADINGCAPACITYUNIVERSALTENSILESTRENGTHTESTMACHINETHELOADINGSPEEDOFTHETESTMACHINEISADJUSTEDACCORDINGTOTS708CODE83TESTRESULTSANDEVALUATIONS31STRESSSTRAINRELATIONSTHEAVERAGEVALUESFORSTRESSSTRAINRELATIONSHIPFORSPECIMENSTHATWEREEXPOSEDTOVARIOUSTEMPERATURESAREGIVENINFIGURES1AND2THECURVESINFIGURES1AND2WEREDRAWNWITHTHEAVERAGETESTRESULTSOF10AND16MMINDIAMETERSTEELSPECIMENSTHETESTCONDITIONSWEREMEANTTOSIMULATEABUILDINGTHATHADAFIRESOTHECHANGESINTHEMECHANICALPROPERTIESOFREINFORCINGSTEELSUSEDINSTRUCTURESEXPOSEDTOHIGHTEMPERATURECOULDBEDETERMINEDASSEENFROMFIGURE1,TEMPERATURESBELOW500CHAVENOSIGNIFICANTEFFECTONMECHANICALPROPERTIESOFPREHEATEDANDCOOLEDS220STEELREBARSTHEYIELDSTRENGTHANDSPLITTINGTENSILESTRENGTHSOFS220STEELSWERESIMILARUPTOTHISTEMPERATUREHOWEVER,THEYIELDSTRENGTHANDSPLITTIN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C高温下，普通钢筋的区服强度还不及室温下钢筋屈服强度的三分之一。因此，普通钢筋一般需要涂膜防火。钢材中温度的升高主要受温度传递的控制。总之，必须意识到钢材的温度不会总和火焰的温度一样。耐火处理后的钢材其暴露在火焰环境下温度是上升速度会比不做耐火处理的钢材慢的多。同样的，高温对钢材的影响程度受其到火源距离的影响，在一个受控于燃料的环境下如果钢材附近有通风设备，那么通风设备会帮助冷却钢材，将热量带到其周围的环境中去。尤其是在复合钢筋混凝土原件中，钢筋和混凝土温度的升高会导致诸如屈服应力，杨氏模量，和混凝土极限抗压强度这些机械性能的下降。此外，当钢筋或复合结构承受高温时，钢筋的承载能力会下降。如果火的持续时间和强度足够大，其荷载抵抗能力会降到与外部荷载相当的水平，从而导致结构的破坏。然而，2001年911事件美国世贸大厦的倒塌尤其是WTC7楼的倒塌向工程专业发出了警告，揭示出建筑倒塌与高温条件的关联。在这个研究中，S220和S420两种钢材会经受七种不同的温度，以此来得出钢筋对于高温的反应。2实验性研究实验性研究会分析直径为10MM和16MM，长200MM的S220和S420钢筋，测试试样会放在温度分别为20,100,200,300,500,800和950C的火炉中三个小时。在固化过程的结尾，钢筋会被自然的回复到室温。随后，将对这些钢筋进行抗拉强度试验。根据EN100021，钢筋在温度升高条件下的抗拉强度，屈服强度和伸长率是已经确定的。钢筋试样的抗拉强度测试由60吨一般抗拉强度测试机器进行。测试机器的荷载施加速度按照TS708CODE。3测试结果和评估31应力应变关系实验中不同温度下样本的应力应变关系均值已表示在图形1和2中。图形1和2中的曲线是通过直径为10和16的钢筋试样的平均试验值绘制的。该实验条件旨在模仿建筑遭受火灾时的状况，所以高温环境下结构中的钢筋的机械性能也就能够确定了。就像图形1中所表示的那样，低于500C的温度对于预热并冷却的S220钢筋的机械性能并没有太大的影响。S220钢筋的屈服强度和劈裂抗拉强度在这些温度下是相似的。然而，当温度上升至800C以上时，S220钢筋的屈服强度和劈裂抗拉强度会出现下降。相似的反应同样发生在S420钢筋的实验结果中。暴露在高温下的钢筋在温度上升至800C以上时其延性会上升。FIGURE1STRESSSTRAINCURVEOFS220STEELREBARFIGURE2STRESSSTRAINCURVEOFS420RIBBEDSTEELREBAR图1S220钢筋的应力应变曲线图2S420钢筋的应力应变曲线32屈服强度两种钢筋的屈服强度都受到了外界温度升高的影响。从图形3中我们可以总结出钢筋的屈服强度在300C以内的条件下并没有太大的变化。光圆钢筋的机械加工中已经经历过这种温度。根据EUROCODE和TSEN1993，在400C前，屈服强度没有太大的降低，但在这个温度以后，会出现一个明显的屈服强度损失。暴露在800C温度下，S220和S420钢筋各自的屈服强度损失分别为46和84。当温度进一步升高到950C时，屈服强度的损失将各自达到64和89。