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Thispaperconsidersthedesignofbuildingsforfiresafety.这篇论文研究的是建筑防火,Itisfoundthatfireandtheassoci-atedeffectsonbuildingsissignificantlydifferenttootherformsofloadingsuchasgravityliveloads,windandearthquakesandtheirrespectiveeffectsonthebuildingstructure.火作用在建筑上与重力荷载,风荷载以及地震力对建筑结构的作用有很大的不同。
Fireeventsarederivedfromthehumanactivitieswithinbuildingsorfromthemalfunctionofmechanicalandelectricalequipmentprovidedwithinbuildingstoachieveaserviceableenvironment.火是由于建筑内的人类活动或者机械鼓掌,建筑内的电器引起Itisthereforepossibletodirectlyinfluencetherateoffirestartswithinbuildingsbychanginghumanbehaviour,improvedmaintenanceandimproveddesignofmechanicalandelectricalsystems.Furthermore,shouldafiredevelops,itispossibletodirectlyinfluencetheresultingfireseveritybytheincorporationoffiresafetysystemssuchassprinklersandtoprovidemeasureswithinthebuildingtoenablesaferegressfromthebuilding.Theabilitytoinfluencetherateoffirestartsandtheresultingfireseverityisuniquetotheconsiderationoffirewithinbuildingssinceotherloadssuchaswindandearthquakesaredirectlyafunctionofnature.Thepossibleapproachesfordesigningabuildingforfiresafetyarepresentedusinganexampleofamulti-storeybuildingconstructedoverarailwayline.Thedesignofboththetransferstructuresupportingthebuildingovertherailwayandthelevelsabovethetransferstructureareconsideredinthecontextofcurrentregulatoryrequirements.Theprinciplesandassumptionsassoci-atedwithvariousapproachesarediscussed.
1INTRODUCTION
Otherpaperspresentedinthisseriesconsiderthedesignofbuildingsforgravityloads,windandearthquakes.对比于其他研究重力荷载,风荷载和地震力对建筑的影响,Thedesignofbuildingsagainstsuchloadeffectsistoalargeextentcoveredbyengineeringbasedstandardsreferencedbythebuildingregulations.建筑物针对这些负载设计很大程度上涵盖了建筑法规的工程设计标准。
Thisisnotthecase,tonearlythesameextent,inthecaseoffire.万一发生火灾,事实并非如此。
Rather,itisbuildingregulationssuchastheBuildingCodeofAustralia(BCA)thatdirectlyspecifymostoftherequirementsforfiresafetyofbuildingswithreferencebeingmadetoStandardssuchasAS3600orAS4100formethodsfordeterminingthefireresistanceofstructuralelements.相反,澳大利亚建筑法中明确规定了建筑防火的安全标准,比如用AS3600或者AS4100的方法来确定结构构件的耐火程度。
Thepurposeofthispaperistoconsiderthedesignofbuildingsforfiresafetyfromanengineeringperspective(asiscurrentlydoneforotherloadssuchaswindorearthquakes),这篇论文研究的目的是从工程的角度去考虑建筑的防火设计(和现在所做的风作用力和地震作用力一样),whilstatthesametime,puttingsuchapproachesinthecontextofthecurrentregulatoryrequirements.于此同时把这类方法应用到现行的规范要求中。
Attheoutset,itneedstobenotedthatdesigningabuildingforfiresafetyisfarmorethansimplyconsideringthebuildingstructureandwhetherithassufficientstructuraladequacy.首当其冲需要注意的是设计一幢防火的大楼仅仅简单考虑建筑结构或是否有足够的结构性是远远不够的,Thisisbecausefirescanhaveadirectinfluenceonoccupantsviasmokeandheatandcangrowinsizeandseverityunlikeothereffectsimposedonthebuilding.这是因为火不像其他因素它能通过烟雾和热量直接影响住户并且可以扩散从而增加其严重性。
Notwithstandingthesecomments,thefocusofthispaperwillbelargelyondesignissuesassociatedwiththebuildingstructure.不只是这些论点,这篇文章的主旨将集中在建筑结构的设计问题。
Twosituationsassociatedwithabuildingareusedforthepurposeofdiscussion.本篇文章选用一栋大楼的两种情况来讨论,Themulti-storeyofficebuildingshowninFigure1issupportedbyatransferstructurethatspansoverasetofrailwaytracks.图1所示一栋多层办公楼用转换结构跨过了一条铁路,Itisassumedthatawiderangeofrailtrafficutilisesthesetracksincludingfreightanddiesellocomotives.这是假定了广泛轨道交通作用在这些轨道上同时考虑了运费和内燃机。
Thefirstsituationtobeconsideredfromafiresafetyperspectiveisthetransferstructure.第一种情况从防火安全考虑,就是转换结构。
ThisistermedSituation1andthekeyquestionsare:
这就是情况1,主要的问题是:
whatleveloffireresistanceisrequiredforthistransferstructureandhowcanthisbedetermined?
哪种等级的防火需要用这种转换情况以及怎样去确定它?
Thissituationhasbeenchosensinceitclearlyfallsoutsidethenormalregulatoryscopeofmostbuildingregulations.它显然不属于大多数建设法规的监管范围,所以已经被确定。
Anengineeringsolution,ratherthanaprescriptiveoneisrequired.我们需要的是工程解决办法而不是指令性的。
Thesecondfiresituation(termedSituation2)correspondstoafirewithintheofficelevelsofthebuildingandiscoveredbybuildingregulations.第二种情形(称为情况2)相应的建筑官方等级Thissituationischosenbecauseitwillenableadiscussionofengineeringapproachesandhowtheseinterfacewiththebuildingregulations–sincebothengineeringandprescriptivesolutionsarepossible.选择这种情况是因为它可以讨论工程学方法以及怎样和建设法规相接,因为工程和指令问题都能解决。
2UNIQUENESSOFFIRE
火的独特性
2.1Introduction
2.1介绍
Windandearthquakescanbeconsideredtobe“natural”phenomenaoverwhichdesignershavenocontrolexceptperhapstochoosethelocationofbuildingsmorecarefullyonthebasisofhistoricalrecordsandtodesignbuildingtoresistsufficientlyhighloadsoraccelerationsfortheparticularlocation.设计师不能控制被认为是“自然”现象的风和地震,只能通过历史记载更加仔细去选择建筑物的位置或者提高建筑物的承受强大荷载能力。
Deadandliveloadsinbuildingsaretheresultofgravity.建筑物静荷载和或荷载都是是由重力产生的,Alloftheseloadsarevariableanditispossible(althoughgenerallyunlikely)thattheloadsmayexceedtheresistanceofthecriticalstructuralmembersresultinginstructuralfailure.所有的这些荷载是可变荷载并且有可能(尽管不常见)通过关键构件的阻力造成结构性的破坏。
Thenatureandinfluenceoffiresinbuildingsarequitedifferenttothoseassociatedwithother“loads”towhichabuildingmaybesubjectedto.火灾的性质以及其对建筑的影响与其他荷载存在很大的不同。
Theessentialdifferencesaredescribedinthefollowingsections.这些关键不同点将在接下来的章节作描述。
2.2OriginofFire
2.2火灾的源头
Inmostsituations(ignoringbushfires),在多数情况下(排除丛林大火),fireoriginatesfromhumanactivitieswithinthebuildingorthemalfunctionofequipmentplacedwithinthebuildingtoprovideaserviceableenvironment.火灾源头来自在建筑内的人类活动或内部的装置的设备故障提供的环境。
Itfollowsthereforethatitispossibletoinfluencetherateoffirestartsbyinfluencinghumanbehaviour,可以通过约束人的活动来影响起火的发生率,limitingandmonitoringhumanbehaviourandimprovingthedesignofequipmentanditsmaintenance.限制和监视人类行为和改进设备及其维护保养。
Thisisnotthecasefortheusualloadsappliedtoabuilding.而建筑物的正常荷载不用这么做。
2.3AbilitytoInfluence
2.3影响能力
Sincewindandearthquakearedirectlyfunctionsofnature,因为风和地震是自然直接作用,itisnotpossibletoinfluencesucheventstoanyextent.人类不可能对他们的活动产生很大影响,Onehastoanticipatethemanddesignaccordingly.仅仅能预测和以此设计。
Itmaybepossibletoinfluencethelevelofliveloadinabuildingbyconductingauditsandplacingrestrictionsoncontents.可以通过审计和限制容积来影响建筑活荷载等级。
However,inthecaseofafirestart,然而在火灾发生之初,therearemanyfactorsthatcanbebroughttobeartoinfluencetheultimatesizeofthefireanditseffectwithinthebuilding.可以通过很多因素来影响火灾的最终规模和火灾对建筑的影响程度。
Itisknownthatoccupantswithinabuildingwilloftendetectafireanddealwithitbeforeitreachesasig-nificantsize.大家都知道建筑物里的住户经常会在火蔓延到更大的范围前将它扑灭。
Itisestimatedthatlessthanonefireinfive(Favre,1996)resultsinacalltothefirebrigadeandforfiresreportedtothefirebrigade,据估计不到五分之一的火灾需要报警,themajoritywillbelimitedtotheroomoffireorigin.大多数都在火灾源头的房间得到了控制。
Inoccupiedspaces,olfactorycues(smell)providepowerfulevidenceofthepresenceofevenasmallfire.在封闭的空间里,对火花的嗅觉(味道)可以为火灾的发生提供强有力有理的证据。
Theadditionofafunctionalsmokedetectionsystemwillfurtherimprovethelikelihoodofdetectionandofactionbeingtakenbytheoccupants.烟雾监测系统的安装将更进一步提高火灾监测的可能性从而住户可以第一时间采取行动。
Firefightingequipment,suchasextinguishersandhosereels,isgenerallyprovidedwithinbuildingsfortheuseofoccupantsandmanyorganisationsprovidetrainingforstaffinrespectoftheuseofsuchequipment.在建筑物内都有供用户使用的消防设备,如灭火器,消防栓等,也有很多机构提供如何使用这些消防设备的训练。
Thegrowthofafirecanalsobelimitedbyautomaticextinguishingsystemssuchassprinklers,whichcanbedesignedtohavehighlevelsofeffectiveness.自动灭系统也可以限制火灾的蔓延,如自动喷水系统有很高的效率。
Firescanalsobelimitedbythefirebrigadedependingonthesizeandlocationofthefireatthetimeofarrival.火灾也可以由消防队员控制,依据火灾发生大小,位置和到达时间来确定。
2.4EffectsofFire
2.4火灾的影响
Thestructuralelementsinthevicinityofthefirewillexperiencetheeffectsofheat.火对建筑材料的影响是火周围热效应的结果。
Thetemperatureswithinthestructuralelementswillincreasewithtimeofexposuretothefire,建筑材料的温度会随着火灾时间的增长而升高,therateoftemperaturerisebeingdictatedbythethermalresistanceofthestructuralelementandtheseverityofthefire.建筑材料温度升高快慢程度取决于隔热材料和火势大小。
Theincreaseintemperatureswithinamemberwillresultinboththermalexpansionand,eventually,areductioninthestructuralresistanceofthemember.随着温度的升高,材料会热膨胀从而导致整个结构破坏。
Differentialthermalexpansionwillleadtobowingofamember.不同程度的热膨胀会导致材料变形,Significantaxialexpansionwillbeaccommodatedinsteelmembersbyeitheroverallorlocalbucklingoryieldingoflocal-isedregions.无论是整体或局部弯曲变形部位,重大轴向扩张被安装在钢材料上。
Theseeffectswillbedetrimentalforcolumnsbutforbeamsformingpartofafloorsystemmayassistinthedevelopmentofotherloadresistingmechanisms(seeSection4.3.5).这些作用将会对柱产生破坏影响,但是组成楼面部分的横梁可以发展产生其他的负荷抵御机制(见章节4.3.5)。
Withtheexceptionofthedevelopmentofforcesduetorestraintofthermalexpansion,力量的发展归咎于firedoesnotimposeloadsonthestructurebutratherreducesstiffnessandstrength.火灾不会增加结构荷载而是降低它的硬度和刚度,Sucheffectsarenotinstantaneousbutareafunctionoftimeandthisisdifferenttotheeffectsofloadssuchasearthquakeandwindthataremoreorlessinstantaneous.不同与像地震和风这类短时间作用的荷载,火灾的作用效果不是瞬间的,而是一个长时间的作用。
Heatingeffectsassociatedwithafirewillnotbesignificantortherateoflossofcapacitywillbeslowedif:
在下列情况下,火灾的热作用不显著或者蔓延速度变慢:
(a)t