土木工程英文翻译

TheFireResistanceofSteelStructuresE.GEHRIFederalInstituteofTechnology,Zurich,SwitzerlandINTRODUCTIONSTEELISanoncombustiblematerial,butthemechanicalpropertiesofstructuralsteelareaffectedbyheat.Thefireresistanceormoreexactly,thefireenduranceofasteelelementvariesgreatlyand,therefore,weneedabetterunderstandingoftheconditionswhichaffectfireresistance.Fireresistanceisunderstoodasthetimeduringwhichthestructuralelementcanwithstandthestandardprovisionsofafiretest.Forstructuralelementstheonlycriteriontobeconsideredisthestructuralcollapseoftheelement.Othercriterialiketemperaturetransmissionmaybedisregarded.ForasteelcolumnthestandardprovisionsforafiretestaregiveninFigure1.Wemustnotethatthestandardtestprescribestheuseofaconstantloadcorrespondingtothemaximumdesignvalue.Thethermallongitudinaloraxialexpansionofthecolumnwillbecompensatedduringthetest,i.e.thereisnorestraint,thecolumncanmovefreelyintheaxialdirection.Bytestswecanfindtheultimatestrengthofthecolumnfordifferentfireendurances.Usingthesametypeofcolumnandsamedimensionsweobtainaninteractiondiagram(Figure2).Thereductioninstrengthwiththepassingoftimedependsonthetemperatureincreaseinthespecimentested.Thetemperatureincreaseisafunctionoftheso-calledsectionfactorandoftheinsulationapplied.Thescatteroftestresultsisquitenormal,sincethecolumnstestedarenotidenticalduetothedimensionaltolerancesandthevariationinstrengthofthesteel.Moreorlessthesamescatterisfoundwhentestingsteelcolumnsatroomtemperature.

SteelStructureshMHh4attn^ingslffindord,e.n.ISO83』，祯furno^eIp*iMFfitfp-innndodmum、figure2.Rcduetronofstreng1ftoftestedeolumnu'ithhMHh4attn^ingslffindord,e.n.ISO83』，祯furno^eIp*iMFfitfp-innndodmum、figure2.Rcduetronofstreng1ftoftestedeolumnu'iththepassingofr/mtduetof^frtpemfureincreasein>teel-23NowintroducingthedesignvalueintoFigure2,wecandirectlyfindthefireresistance.Generally,themeanvalueofthetestresultswillbehigherthanthefireresistancebasedonthenominalguaranteedstrengthofthesteel.FromFigure2itcanalsoeasilybeseen,thatacolumnwhichissubjectedtoalowerstresslevel--i.e.,toaneffectiveloadlowerthanthedesignload--willhavehigherfireresistance.Finally,wemustnotethattheconditionsduringthefiretestdonotcorrespondtothoseinpractice.Besidesdifferentheatingratesinanaturalfire,wehavetoconsidertherealboundaryconditions.Supportconditionsandthelongitudinalrestraintmayresultinsubstantiallydifferentfireresistances.FIRERESISTANCEOFCONCRETEThefireresistanceofconcretemembersismuchhigherthanthatofnoinsulatedsteelmembers.Howeverthetendencytousehigherstrengthconcreteandsteelreinforcementsleadstosmallersectionsandthereforetolowerfireresistance.Furthermore,manysteelconstructionsincludeconcreteelementstoalargeextentorhaveso-calledcompositesteel-concreteelements.Wethereforeneedageneralproceduretoanalyzethefireresistanceofdifferentstructuralmaterialsandofcompositeelements.Wecouldalsotreatthereinforcedconcreteasacompositematerial,whichitis.FIRERESISTANCE---ASPECIALASPECTOFFIREPROTECTIONThefireresistanceofsteelstructuresisonlyasmallpartofthefireprotectionproblem.Wehavetostartbyreducingthefireload,byusingsmallcompartments,bytryingtoremovetheheatasquicklyaspossible,andfinally,bypreventingheattransfertothestructuralmembers.Thecalculationoffireresistanceisthelastresort,whichdoesnotmeanthatfireresistancehasnoimportance.Butbeforecalculatingweshoulddetermineifthefireresistanceproblemcannotbeminimizedbyacombinationofdifferentsubdivisionsofthevolume,orbyplacingthemainstructuralpartsinlessexposedareasorbyremovingtheheatthroughopenings.Furthermore,wehavetoacknowledgethattheactualfireconditionsaredifficulttoknow,whichmeansthatwehave,ontheso-calledloadside,greatuncertainties.STRUCTURALPERFORMANCEREQUIREDFIRERESISTANCE--COLLAPSELOADIntheintroduction,fireresistanceisdefinedasthetimeafterwhichacollapseofthestructuralelementoccurs,assumingariseoftemperatureinthefurnaceaccordingtoISO834.Weknowfromexperiencethattestspecimensmayalsocollapseafterthetestduringthecoolingphase.Thismaybeduetocontinuinglossofstrengthandduetoredistributionoftemperatureinthespecimen.Forsteel,ingeneral,wedonotneedtoconsiderthatcase,butitshowsthedifficultyofaproperdefinitionofthefireendurancebasedonthecollapseload.FIRERESISTANCE--DAMAGELEVELTheassumptionofcollapseasacriteriondoesnotmeanthatweexpect--eveninaseverefire--thetotalcollapseofthestructure.Itseemsfurthermore,usefultoconsiderdifferentcriteriaformainstructuralandforsecondarystructuralelements.Whetherastructuralelementispartofthemainstructureorsecondarystructureisnotalwaysobvious.Aguidelinetofollowcanbe:ifthetotalcollapseofanelementdoesnotseriouslyaffectthestructuralbehaviorasawhole,itcanbeconsideredsecondary.Thereforelowerrequirements-evennone--maybelaiddownforsuchstructuralelements.Weshould,therefore,discussmainstructuralorsecondarystructuralelements,totalcollapseorpartialorlocalcollapse,degreesofdamageandpossibilitiesofrepair.

Structuralmaterialslikesteel,timberorconcrete,showdifferentreactionstofire.Afterafire,concreteandtimbershowalossofresistancewhereasprotectedsteelstructuresmayhavetheoriginalstrengthaftercooling.Repairpossibilitiesandrepaircostsmaythereforebeverydifferent.Inextremecasesareplacementofaconcretestructurewillberequired,whereasonlyasimplereapplicationoffireprotectionsurfacestothesteelelementswillbenecessary.Dependingonthestructuralperformancerequiredduringandafterafire,wemustestablishreasonableandrealisticcriteria.Thepresentorientationbasedonlyonthecollapseofanindividualisolatedelementcannotbetheentirebasisoffireresistanceclassification.SteelStructuresFigure3.DifferenSteelStructuresFigure3.Differen：boundaryconditionsforacolumn.FIRERESISTANCECLASSIFICATIONSTANDARDFURNACETESTSThewell-knownproceduretoestablishfire-resistancetimeneedsnoexplanation.IcanreferheretoISO834whereacceptanceconditionsarespecified.Thereisacertaincriticismaboutthoseconditions,namelyabouttherequirementtotestthespecimen,asfaraspossible,undersupportingandrestrainingconditionsthataresimilartothoseinservice.Theseconditionsareseldomfulfilledinstandardfurnacetests,butIseenoprobleminitaslongastheactualboundaryconditionsaregiveninconnectionwiththeobservedfireresistance.Thesameconditionholdsfortestinginsulatedsteel

members,where,inadditiontotheinsulation,thesectionfactororthesteelelementhastobeintroduced(seeFigures3and4).Ifappropriatedesignloadsareapplied(useofthesamesafetyfactoratroomtemperature}thefireresistanceofthethreecolumnsinFigure3willbenearlythesame,ifthereisnoaxialrestraint.Withfullknowledgeoftestingconditionsandtestlimitations{onlysimpleelementslikecolumnsandsimplegirders;dimensionallimitationsinsectionandinlength}testsmadeinaccordancewithISO834andfireresistanceclassificationre-mainavaluabletool.Figured.Difffir«ntFigured.Difffir«ntfir&尸。duo比s^otiefn.fggrinidenticalifliANALYTICALPROCEDURESApartfromthelimitationsmentioned,thefurnacetestshavethemajordisadvantagesofbeinglaboriousandcostly.Thiswasthereasonfordevelopingdifferentanalyticalproceduresinthelast10years.Forsteelelementstheanalyticalprocedureconsistsof(seealsoFigure5)Acalculationofthetemperaturelevelinthesteelelement,assumingaheatingprocesscorrespondingtostandardfiretests.Acalculationoftheeffectofthetemperatureontheloadbearing"capacityoftheelement.Withsuchananalyticalprocedureitshouldbepossibletoreproducetheresultsoffiretestsinfurnaces.Iftheanalyticalprocedureiscorrect,thecalculatedtimeoffailureshouldbeidenticalwiththefire-resistancetimeobtainedinatest,assumingstructuralelementsofthesamemechanicalcharacteristicsandthesameloadlevel.However,somedissimilaritymustbeexpected,sincealsoatroomtemperature,predictionsofultimatestrengthshowacertainscatter.Oftheexistinganalyticalproceduresitispreferabletousethosewhichareeasytohandlebutstillhaveanappropriatelevelofaccuracy.Thisleadstosimplificationsandasaresult,therangeofvaliditymaybenarrower.Anideaoftheappropriatelevelofaccuracymaybeseenfromthefollowingchart.condition：必&sid&fireresistancerequired£resistancesideexistingfiregi云皿remarks：requirementfixedstepwiseF30一F60-F9C•Fl20+100%+50哓十33%requirement^havetocoveruncertumtieshowaccurate?notasaccurateaspossiblebutlhaccuraceasneededMostanalyticalproceduresaretoogood.Theyarealsotoolaboriousandpronetoerrors.Wethereforeneedasimpletooltoestimatewithreasonable.Precisionthefireresistanceofasteelelement.SuchatoolwasrecentlypublishedbytheEuropeanConventionforConstructionalSteelworkunderthetitle"CalculationoftheFireResistanceofLoadBearingElementsandStructuralAssembliesExposedtotheStan-dardFire.Thefollowingcalculationprocedureisbasedontheabovepublication,butintroducessomesmallmodificationswhichallowaverysimpleandquickdeterminationofthefireresistanceofnoinsulatedandinsulatedsteelelements.Themethodallowsusalsototakeadvantageofalowerstresslevelthantheallowabledesignvalue.Wehaveseenbeforethatalowerstresslevelleadstohigherfireresistanceofthemember.PRACTICALAPPROACHASSUMPTIONSThefollowingassumptionsaremade:TemperatureinfurnaceaccordingtoISO834Theheatingofthesteelelementisuniform(largeandcompactsteelsectionsdonothoweverShowauniformtemperature)Thereductionofallstrengthandstiffnesscharacteristicsisproportionaltothereductionoftheyieldpoint(validforstructuralsteels)Steelelements:simplesupportedgirdersandcentrallyloadedcolumnsNoaxialrestraint,whichisalsoabsentinstandardfurnacetests,thereforenoinfluenceofthermalexpansionThefireresistanceofnoinsulatedsteelmembersisadirectfunctionofthesectionfactorU/Aandofthedegreeofutilization7.ThesectionfactorU/Aisgivenbythesurfaceareaofthememberexposedtothefiredividedbythevolumeofthemember.Forsteelelementsitcanbesubstitutedbytheperimeterofthesectionexposedtothefiredividedbythesectionalarea.Thedegreeofutilization~isdefinedastheratiooftheeffectiveloadtotheultimatestrengthvalue(middlevalue,assumedtobeapproximately15percenthigherthanthenominalvalue).Forclassificationofthesteelelement,wehavetosubstitutethedesignloadfortheeffectiveload.Theinterrelationbetweenthethreevalues,fireresistance,degreeofutilizationandsectionfactorisgiveninFigure6.

Byintroducinganewsectionfactor,aso-calledthermalsectionfactorasimilar400-FiffUreGInterrelariattByintroducinganewsectionfactor,aso-calledthermalsectionfactorasimilar400-FiffUreGInterrelariatt加加ipfjifiegn>^叩llif.iza.tKyn九加小tcfUJAandfiremsEMrw;Ktcmperoiure/TDDU/A^30m\600^U/AIm1]300460Crninures]itlizotensecF.orfactorU/4~j衍eresistanceiQ~iQ^VithM——i—i

Ad1+p2cgramasfornoinsulatedsteelmemberscanbedrawn.Thecorrectionfactorisonlyvalidforheavyweightinsulations,i.e.,withhighthermalcapacity.Forlightweightinsulations(°-0)theformulacanbesimplifiedtowhere七representsthethermalconductivityoftheinsulationandd,thethicknessofthediinsulation.Theeffectofmoisturecontentintheinsulation--reductionofthetemperatureriseandcorrespondingincreaset~ofthefireresistance--canbeevaluatedbythefollowingformula:,p$Qd2「1t=—直i「inminutesJiwhereprepresentsthemoisturecontentoftheinsulationinpercentbyweight.Theinterrelationbetweenthethreevalues,fireresistance,degreeofutilizationandthermalsectionfactorisgiveninFigure7.FigureZint-erreiat:ion如gz。ofutilization却另况珀＞舞factorandfire；K,FINALREMARKSSteelMembersandStructuralAssembliesTheprocedureshownisvalidonlyforsimplegirdersandcentrallyloadedcolumnswithoutlongitudinalrestraint.Therestraintcouldalsobetakenintoaccount.Anotherpossibilitydepartsfromtherestraintfactoratroomtemperature,whichdependsontheratioofstiffnessofthecolumntotherestofthestructure.Theproposedmethodmaybeextendedtoothercases,forinstancetothecaseofacolumnwithbothaxialforceandmoment.Itisalsopossibletouseheretheterm"degreeofutilization."Thedegreeofutilizationofthestructureatroomtemperatureisaknownquantityandresultsfromtheusualstaticcalculation.Structuralassembliescouldbetreatedinthesameway.GeneralBehaviorofaStructureTestresultsshowthatvariationsintherestraintconditionsmayaffectthefireresistanceconsiderably.Restraintcanincertaincasesbebeneficialbutmayalsoresultinareductionoffireresistance.Ifwetakeaclassifiedcolumn,with,say,90minutesfireendurance,andthiscolumnisplacedinstructureswithdifferentlongitudinalrestraintconditions,wewillhavequitedifferentfireresistances.Wethereforeneedanapproachwhichtakesintoconsiderationthegeneralbehaviorofthestructureunderfire,anapproachwhichallowsstructuresofhigherfireresistancewithoutmajorcosts.Thiscouldbeachievedby:IntroductionofthenotionofmainandsecondarystructuralelementsPlacingmainstructuralelementsasfaraspossible,incompartmentswithlowerfireload(i.e.,incorridors}Choiceofstructureswhicharelessvulnerabletocollapseofindividualmembers{staticallyhighlyindeterminatestructures,i.e.,structureswithhighredundancy}Separationoflargerstructurestolimitstructuraldamagetoonlyonepartofthestructure(jointsshouldallowforenoughmovementtoreducerestraintforces}Deliberateintroductionofweakpointstoreducetheextentofcollapse(similareffectasseparationofthestructureintoindependentparts}.CompositeSteel-ConcreteElementsInearlytimesconcretewasusedmerelyasaninsulationmaterial.Todaywearetryingtomakethebestuseofthestrengthcapacityoftheconcreteactingtogetherwiththesteel.Wehavemoreorlessaconcretesectionwithlarger"reinforcementbars."Importantforacompositeactionisanefficientbondbetweenbothmaterials{noslip}.Incaseoflargerreinforcementsthisbondisdependentonthecharacteristicsoftheshearconnectors.Sincecompositesteel-concreteelementsplayanimportantroleinsteelconstructionsweneedbettertoolsforestimatingthefireresistanceofsuchconstructions.Analyticalmethodscanhelptodevelopmoreefficientconfigurationsbutwewillstillneedaccompanyingfiretests,sincebondingcharacteristicsmaybemorestronglyinfluencedbyfireaction,thansay,thecompressionstrengthoftheconcrete.REFERENCE'EuropeanConventionforConstructionalSteelwork,TC3,"FireSafetyofSteelStructures:EuropeanRecommendationsfortheFireSafetyofSteelStructures--CalculationoftheFireResistanceofLoadBearingElementsandStructuralAssembliesExposedtotheStandardFire."Elsevier1983.

钢结构耐火性E.GEHRI苏黎世，瑞士联邦技术研究所简介钢是一种不燃材料，但受热钢结构性能有影响。钢的耐火性变化很大，因此，我们需要更好地了解影响抗火性能的条件。抗火被理解为在该期间的结构元素可以承受的防火测试标准规定的时间。对于结构元素被考虑的唯一标准是该元素的结构崩溃。其他像温度传输的标准可不理会。图1为钢结构柱防火测试标准规定，我们必须注意到标准试验规定的对应于最大设计值的常量负载使用。列的纵向或轴向热膨胀将补偿在测试期间，即有无节制，列可以自由轴向方向移动。通过测试我们可以找到不同的火耐力列的极限强度。使用相同类型的列和相同的尺寸，我们获得的相互作用图（图2）。减少强度与传递的时间取决于测试的试样温度增加。温度增加的功能和应用的绝缘的所谓的部分因素。测试结果的分散性是挺正常的因为测试的列不相同尺寸的公差和钢的强度的变化。更多或更少测试钢列在室温时发现相同的散点图。SteelStructuresntxlriinrlr-启Hno口商用W*attn^difig仍SteelStructuresntxlriinrlr-启Hno口商用W*attn^difig仍Elandnd,A.k.]$083』-iHdfurnorfi—炽ihmr?U盹屈—pnnndKl匚Aumn23Figure2.ReductionofstrengthoftestedviflufnnuJfrft£屁&gsi，褪“/自：地书duegtemperatureincreaseinthe^teel.现在图2中引入的设计值，我们可以直接找到抗火。一般情）兄下，测试结果的均值将高于基于的名义保证强度钢的耐火性。从图2它可以也很容易看出，遭受到较低的应力水平，即，低于设计荷载一一种有效负载的列将有较高的耐火性能。最后，我们必须注意到期间火灾的测试条件不对应于那些在实践中。除了不同的加热率自然火灾中，我们要考虑真正的边界条件。支持条件和纵向约束可能会导致极大地不同火抵抗。混凝土的抗火性能混凝土构件的耐火能力是比没有绝缘的钢构件高得多。但是利用高强度混凝土和钢增援部队较小导致的倾向节，因此抗火性底。此外，许多钢结构建筑包括具体的元素，很大程度上，或有所谓复合钢-混凝土元素。因此，我们需要分析的耐火性和复合元素的不同结构材料的一般过程。我们也可以作为一种复合的材料，它就是钢筋混凝土。抗火性能——特别方面的防火保护钢结构抗火性只是小部分的防火问题。我们必须开始通过减少火灾荷载、使用的小隔间，由试图尽可能快移除作为热和最后，通过防止传热结构构件。抗火性计算是最后的手段，这并不意味着抗火性能已不重要。但在计算之前我们应该确定由不同细分的卷的组合或通过放置较少暴露地区主要结构部件或通过删除通过开口热是否无法减小火抗药性的问题。此外，我们必须承认实际火灾的条件是很难知道，这意味着我们有，在所谓负荷侧，极大的不确定性。结构性能：抗火性能崩溃负载在介绍，抗火被定义为发生后，结构元素的崩溃时，假设根据ISO834炉内温度的升高的时间。我们从经验知道试验样品可能还折叠后在冷却阶段测试。这可能是强度的因为持续损失和由于温度的标本的再分配。对于钢，一般情况下，我们不需要考虑这种情况下，但它显示了基于崩溃的负载的火耐力的适当定义的困难。抗火性能一一损坏程度崩溃的假设作为一项标准并不意味着我们希望在严重的火灾结构的彻底崩溃。此外，考虑主要结构和次要结构元素的不同标准似乎很有用。一个结构元素是否是主体结构或二级结构的一部分并不总是显而易见的。遵循的准则可以是:

如果一个元素的总崩溃不严重影响的结构行为作为一个整体，它可以考虑中学。因此要求可能奠定了，这种结构的元素。因此，我们应该讨论主要结构或二级结构元素，彻底崩溃或部分或局部倒塌，修复的可能性和程度的损害。结构材料如钢铁、木材或混凝土，显示要火的不同反应。发生火灾后，混凝土和木材显示抵抗的损失而受保护的钢结构可能冷却后有原始的力量。修复的可能性和修理费用因此可能非常不同。在极端情况下更换混凝土结构的需要，而只简单移居的消防保护表面到钢元素将是必要。根据所需期间及火灾后的结构性能，我们必须建立合理和现实的标准。只有基于崩溃的孤立的个别元素的本取向不能火抵抗分类的整个基础。25figuredDifferenthmifidnryegdi血ym凡r火抵抗分类标准炉测试要建立抗火时间的知名过程需要没有任何解释。我可以在这里指ISO834指定验收条件的位置。有这些条件，即有关要求测试标本，尽可能支持和约束条件，类似于那些在服务下的某些批评。在标准炉测试中，很少符合这些条件，但看在它没有问题，只要实际边界条件给予的观察到的耐火。相同的条件认为测试绝缘的钢构件，哪里，绝缘，除了部分因子或钢元素有需要引入（见图3和4）。如果适当设计的负荷（使用相同的安全因子在室温的｝在图3中的三个列的抗火将几乎相同，如果有没有轴向约束。

在充分了解的测试条件和测试按照ISO834做出限制，只简单元素，如列和简单大梁、尺寸限制一节中和的长度，测试和火抵抗分类仍然是一个宝贵的工具。；；；；i：i；:京|科二3由切习*盐4z如!■ffidenticalifliUatrorL分析程序从限制部分提及，炉测试已正在费力且成本高昂的主要缺点。这是在过去的10年发展不同的分析程序的原因。钢元素的分析过程：（请参见图5）计算温度水平钢元素中，假设对应标准火加热过程测试计算的承载负荷对温度的影响〃的元素的能力designvaliieO:fireloadcapacity>isfstancsclassification.与这种分析的程序应该有可能重现火在炉中的测试的结果。如果分析过程是正确的失败的计算出的时间应该是在测试中获得的抗火时间与相同，假设结构元素相同的机械特性和相同的负载水平。然而，必须预期有些不同，因为还在室温下的极限强度的预测显示某些散点图。现有的分析过程是精度的最好使用那些很容易就可以处理，但仍有适当级别。这将导致简化，因此，有效范围可能较