土木工程外文文獻及翻譯

爨兒/如禁出孝

本科畢業(yè)設(shè)計外文文獻及譯文文獻、資料題目：DesigningAgainstFireOfBuilding文獻、資料來源：國道數(shù)據(jù)庫文獻、資料發(fā)表（出版）日期：2008.3.25院（部）：土木工程學(xué)院專業(yè)：土木工程班級：土木輔修091姓名：xxxx外文文獻：DesigningAgainstFireOfBulidingxxxABSTRACT:Thispaperconsidersthedesignofbuildingsforfiresafety.Itisfoundthatfireandtheassoci-atedeffectsonbuildingsissignificantlydifferenttootherformsofloadingsuchasgravityliveloads,windandearthquakesandtheirrespectiveeffectsonthebuildingstructure.Fireeventsarederivedfromthehumanactivitieswithinbuildingsorfromthemalfunctionofmechanicalandelectricalequipmentprovidedwithinbuildingstoachieveaserviceableenvironment.Itisthereforepossibletodirectlyinfluencetherateoffirestartswithinbuildingsbychanginghumanbehaviour,improvedmaintenanceandimproveddesignofmechanicalandelectricalsystems.Furthermore,shouldafiredevelops,itispossibletodirectlyinfluencetheresultingfireseveritybytheincorporationoffiresafetysystemssuchassprinklersandtoprovidemeasureswithinthebuildingtoenablesaferegressfromthebuilding.Theabilitytoinfluencetherateoffirestartsandtheresultingfireseverityisuniquetotheconsiderationoffirewithinbuildingssinceotherloadssuchaswindandearthquakesaredirectlyafunctionofnature.Thepossibleapproachesfordesigningabuildingforfiresafetyarepresentedusinganexampleofamulti-storeybuildingconstructedoverarailwayline.Thedesignofboththetransferstructuresupportingthebuildingovertherailwayandthelevelsabovethetransferstructureareconsideredinthecontextofcurrentregulatoryrequirements.Theprinciplesandassumptionsassoci-atedwithvariousapproachesarediscussed.INTRODUCTIONOtherpaperspresentedinthisseriesconsiderthedesignofbuildingsforgravityloads,windandearthquakes.Thedesignofbuildingsagainstsuchloadeffectsistoalargeextentcoveredbyengineeringbasedstandardsreferencedbythebuildingregulations.Thisisnotthecase,tonearlythesameextent,inthecaseoffire.Rather,itisbuildingregulationssuchastheBuildingCodeofAustralia(BCA)thatdirectlyspecifymostoftherequirementsforfiresafetyofbuildingswithreferencebeingmadetoStandardssuchasAS3600orAS4100formethodsfordeterminingthefireresistanceofstructuralelements.Thepurposeofthispaperistoconsiderthedesignofbuildingsforfiresafetyfromanengineeringperspective(asiscurrentlydoneforotherloadssuchaswindorearthquakes),whilstatthesametime,puttingsuchapproachesinthecontextofthecurrentregulatoryrequirements.Attheoutset,itneedstobenotedthatdesigningabuildingforfiresafetyisfarmorethansimplyconsideringthebuildingstructureandwhetherithassufficientstructuraladequacy.Thisisbecausefirescanhaveadirectinfluenceonoccupantsviasmokeandheatandcangrowinsizeandseverityunlikeothereffectsimposedonthebuilding.Notwithstandingthesecomments,thefocusofthispaperwillbelargelyondesignissuesassociatedwiththebuildingstructure.Twosituationsassociatedwithabuildingareusedforthepurposeofdiscussion.Themulti-storeyofficebuildingshowninFigure1issupportedbyatransferstructurethatspansoverasetofrailwaytracks.Itisassumedthatawiderangeofrailtrafficutilisesthesetracksincludingfreightanddiesellocomotives.Thefirstsituationtobeconsideredfromafiresafetyperspectiveisthetransferstructure.ThisistermedSituation1andthekeyquestionsare:whatleveloffireresistanceisrequiredforthistransferstructureandhowcanthisbedetermined?Thissituationhasbeenchosensinceitclearlyfallsoutsidethenormalregulatoryscopeofmostbuildingregulations.Anengineeringsolution,ratherthanaprescriptiveoneisrequired.Thesecondfiresituation(termedSituation2)correspondstoafirewithintheofficelevelsofthebuildingandiscoveredbybuildingregulations.Thissituationischosenbecauseitwillenableadiscussionofengineeringapproachesandhowtheseinterfacewiththebuildingregulationssincebothengineeringandprescriptivesolutionsarepossible.

Figure1AMulti-storeyofficebuildingUNIQUENESSOFFIREIntroductionWindandearthquakescanbeconsideredtobe“natural”phenomenaoverwhichdesignershavenocontrolexceptperhapstochoosethelocationofbuildingsmorecarefullyonthebasisofhistoricalrecordsandtodesignbuildingtoresistsufficientlyhighloadsoraccelerationsfortheparticularlocation.Deadandliveloadsinbuildingsaretheresultofgravity.Alloftheseloadsarevariableanditispossible(althoughgenerallyunlikely)thattheloadsmayexceedtheresistanceofthecriticalstructuralmembersresultinginstructuralfailure.Thenatureandinfluenceoffiresinbuildingsarequitedifferenttothoseassociatedwithother“l(fā)oads”towhichabuildingmaybesubjectedto.Theessentialdifferencesaredescribedinthefollowingsections.OriginofFireInmostsituations(ignoringbushfires),fireoriginatesfromhumanactivitieswithinthebuildingorthemalfunctionofequipmentplacedwithinthebuildingtoprovideaserviceableenvironment.Itfollowsthereforethatitispossibletoinfluencetherateoffirestartsbyinfluencinghumanbehaviour,limitingandmonitoringhumanbehaviourandimprovingthedesignofequipmentanditsmaintenance.Thisisnotthecasefortheusualloadsappliedtoabuilding.AbilitytoInfluenceSincewindandearthquakearedirectlyfunctionsofnature,itisnotpossibletoinfluencesucheventstoanyextent.Onehastoanticipatethemanddesignaccordingly.Itmaybepossibletoinfluencethelevelofliveloadinabuildingbyconductingauditsandplacingrestrictionsoncontents.However,inthecaseofafirestart,therearemanyfactorsthatcanbebroughttobeartoinfluencetheultimatesizeofthefireanditseffectwithinthebuilding.Itisknownthatoccupantswithinabuildingwilloftendetectafireanddealwithitbeforeitreachesasig-nificantsize.Itisestimatedthatlessthanonefireinfive(Favre,1996)resultsinacalltothefirebrigadeandforfiresreportedtothefirebrigade,themajoritywillbelimitedtotheroomoffireorigin.Inoc-cupiedspaces,olfactorycues(smell)providepowerfulevidenceofthepresenceofevenasmallfire.Theadditionofafunctionalsmokedetectionsystemwillfurtherimprovethelikelihoodofdetectionandofactionbeingtakenbytheoccupants.Firefightingequipment,suchasextinguishersandhosereels,isgenerallyprovidedwithinbuildingsfortheuseofoccupantsandmanyorganisationsprovidetrainingforstaffinrespectoftheuseofsuchequipment.Thegrowthofafirecanalsobelimitedbyautomaticextinguishingsystemssuchassprinklers,whichcanbedesignedtohavehighlevelsofeffectiveness.Firescanalsobelimitedbythefirebrigadedependingonthesizeandlocationofthefireatthetimeofarrival.EffectsofFireThestructuralelementsinthevicinityofthefirewillexperiencetheeffectsofheat.Thetemperatureswithinthestructuralelementswillincreasewithtimeofexposuretothefire,therateoftemperaturerisebeingdictatedbythethermalresistanceofthestructuralelementandtheseverityofthefire.Theincreaseintemperatureswithinamemberwillresultinboththermalexpansionand,eventually,areductioninthestructuralresistanceofthemember.Differentialthermalexpansionwillleadtobowingofamember.Significantaxialexpansionwillbeaccommodatedinsteelmembersbyeitheroverallorlocalbucklingoryieldingoflocal-isedregions.Theseeffectswillbedetrimentalforcolumnsbutforbeamsformingpartofafloorsystemmayassistinthedevelopmentofotherloadresistingmechanisms(seeSection4.3.5).Withtheexceptionofthedevelopmentofforcesduetorestraintofthermalexpansion,firedoesnotimposeloadsonthestructurebutratherreducesstiffnessandstrength.Sucheffectsarenotinstantaneousbutareafunctionoftimeandthisisdifferenttotheeffectsofloadssuchasearthquakeandwindthataremoreorlessinstantaneous.

Heatingeffectsassociatedwithafirewillnotbesignificantortherateoflossofcapacitywillbeslowedif:thefireisextinguished(e.g.aneffectivesprinklersystem)thefireisofinsufficientseverity-insufficientfuel,and/orthestructuralelementshavesufficientthermalmassand/orinsulationtoslowtheriseininternaltemperaturethicknessofprotectionFiguit2ConcreteandSteelElementsthicknessofprotectionFireprotectionmeasuressuchasprovidingsufficientaxisdistanceanddimensionsforconcreteelements,andsufficientinsulationthicknessforsteelelementsareexamplesof(c).TheseareillustratedinFigure2.Thetwosituationsdescribedintheintroductionarenowconsidered.FIREWITHINBUILDINGSFireSafetyConsiderationsTheimplicationsoffirewithintheoccupiedpartsoftheofficebuilding(Figure1)(Situation2)arenowconsidered.Firestatisticsforofficebuildingsshowthataboutonefatalityisexpectedinanofficebuildingforevery1000firesreportedtothefirebrigade.Thisisanorderofmagnitudelessthanthefatalityrateassociatedwithapartmentbuildings.Morethantwothirdsoffiresoccurduringoccupiedhoursandthisisduetothegreaterhumanactivityandthegreateruseofserviceswithinthebuilding.Itistwiceaslikelythatafirethatcommencesoutofnormalworkinghourswillextendbeyondtheenclosureoffireorigin.Arelativelysmallfirecangeneratelargequantitiesofsmokewithintheflooroffireorigin.Ifthefloorisofopen-planconstructionwithfewpartitions,thepresenceofafireduringnormaloccupiedhoursisalmostcertaintobedetectedthroughtheobservationofsmokeonthefloor.Thepresenceoffullheightpartitionsacrossthefloorwillslowthespreadofsmokeandpossiblyalsothespeedatwhichtheoccupantsdetectthefire.Anymeasuresaimedatimprovinghousekeeping,fireawarenessandfireresponsewillbebeneficialinreducingthelikelihoodofmajorfiresduringoccupiedhours.Formulti-storeybuildings,smokedetectionsystemsandalarmsareoftenprovidedtogive“automatic”detectionandwarningtotheoccupants.Analarmsignalisalsotransmittedtothefirebrigade.Shouldthefirenotbeabletobecontrolledbytheoccupantsonthefirefloor,theywillneedtoleavetheflooroffireoriginviathestairs.Stairenclosuresmaybedesignedtobefire-resistantbutthismaynotbesufficienttokeepthesmokeoutofthestairs.Manybuildingsincorporatestairpressurisationsystemswherebypositiveairflowisintroducedintothestairsupondetectionofsmokewithinthebuilding.However,thisincreasestheforcesrequiredtoopenthestairdoorsandmakesitincreasinglydifficulttoaccessthestairs.Itisquitelikelythatexcessivedooropeningforceswillexist(Fazioetal,2006)Fromafireperspective,itiscommontoconsiderthatabuildingconsistsofenclosuresformedbythepresenceofwallsandfloors.Anenclosurethathassufficientlyfire-resistantboundaries(i.e.wallsandfloors)isconsideredtoconstituteafirecompartmentandtobecapableoflimitingthespreadoffiretoanadjacentcompartment.However,theabilityofsuchboundariestorestrictthespreadoffirecanbeseverelylimitedbytheneedtoprovidenaturallighting(windows)andaccessopeningsbetweentheadjacentcompartments(doorsandstairs).Firespreadviatheexternalopenings(windows)isadistinctpossibilitygivenafullydevelopedfire.Limitingthewindowsizesandgeometrycanreducebutnoteliminatethepossibilityofverticalfirespread.Byfarthemosteffectivemeasureinlimitingfirespread,otherthanthepresenceofoccupants,isaneffectivesprinklersystemthatdeliverswatertoagrowingfirerapidlyreducingtheheatbeinggeneratedandvirtuallyextinguishingit.EstimatingFireSeverityIntheabsenceofmeasurestoextinguishdevelopingfires,orshouldsuchsystemsfail;severefirescandevelopwithinbuildings.Infireengineeringliterature,theterm“fireload”referstothequantityofcombustibleswithinanenclosureandnottheloads(forces)appliedtothestructureduringafire.Similarly,fireloaddensityreferstothequantityoffuelperunitarea.ItisnormallyexpressedintermsofMJ/m2orkg/m2ofwoodequivalent.Surveysofcombustiblesforvariousoccupancies(i.eoffices,retail,hospitals,warehouses,etc)havebeenundertakenandagoodsummaryoftheavailabledataisgiveninFCRC(1999).Aswouldbeexpected,thefireloaddensityishighlyvariable.PublicationssuchastheInternationalFireEngineeringGuidelines(2005)givefireloaddataintermsofthemeanand80thpercentile.ThelatterleveloffireloaddensityissometimestakenasthecharacteristicfireloaddensityandissometimestakenasbeingdistributedaccordingtoaGumbeldistribution(Schleichetal,1999).Therateatwhichheatisreleasedwithinanenclosureistermedtheheatreleaserate(HRR)andnormallyexpressedinmegawatts(MW).Theapplicationofsufficientheattoacombustiblematerialresultsinthegenerationofgasessomeofwhicharecombustible.Thisprocessiscalledpyrolisation.Uponcomingintocontactwithsufficientoxygenthesegasesignitegeneratingheat.Therateofburning(andthereforeofheatgeneration)isthereforedependentontheflowofairtothegasesgeneratedbythepyrolisingfuel.Thisflowisinfluencedbytheshapeoftheenclosure(aspectratio),andthepositionandsizeofanypotentialopenings.ItisfoundfromexperimentswithsingleopeningsinapproximatelycubicenclosuresthattherateofburningisdirectlyproportionaltoAhwhereAistheareaoftheopeningandhistheopeningheight.Itisknownthatfordeepenclosureswithsingleopeningsthatburningwilloccurinitiallyclosesttotheopeningmovingbackintotheenclosureoncethefuelclosesttotheopeningisconsumed(Thomasetal,2005).Significanttemperaturevariationsthroughoutsuchenclosurescanbeexpected.Theuseoftheword‘opening’inrelationtorealbuildingenclosuresreferstoanyopeningspresentaroundthewallsincludingdoorsthatareleftopenandanywindowscontainingnonfire-resistantglass.Itispresumedthatsuchglassbreaksintheeventofdevelopmentofasignificantfire.Ifthewindowscouldbepreventedfrombreakingandothersourcesofairtotheenclosurelimited,thenthefirewouldbepreventedfrombecomingaseverefire.Variousmethodshavebeendevelopedfordeterminingthepotentialseverityofafirewithinanenclosure.ThesearedescribedinSFPE(2004).Thepredictionsofthesemethodsarevariableandaremostlybasedonestimatingarepresentativeheatreleaserate(HRR)andtheproportionoftotalfuelglikelytobeconsumedduringtheprimaryburningstage(Figure4).Furtherstudiesofenclosurefiresarerequiredtoassistwiththedevelopmentofimprovedmodels,asthebehaviourisverycomplex.RoleoftheBuildingStructureIfthedesignobjectivesaretoprovideanadequatelevelofsafetyfortheoccupantsandprotectionofadjacentpropertiesfromdamage,thenthestructuraladequacyofthebuildinginfireneedonlybesufficienttoallowtheoccupantstoexitthebuildingandforthebuildingtoultimatelydeforminawaythatdoesnotleadtodamageorfirespreadtoabuildinglocatedonanadjacentsite.TheseobjectivesarethoseassociatedwithmostbuildingregulationsincludingtheBuildingCodeofAustralia(BCA).Therecouldbeotherobjectivesincludingprotectionofthebuildingagainstsignificantdamage.Inconsideringthesevariousobjectives,thefollowingshouldbetakenintoaccountwhenconsideringthefireresistanceofthebuildingstructure.Non-StructuralConsequencesSincefirecanproducesmokeandflame,itisimportanttoaskwhethertheseoutcomeswillthreatenlifesafetywithinotherpartsofthebuildingbeforethebuildingiscompromisedbyalossofstructuraladequacy?Issearchandrescuebythefirebrigadenotfeasiblegiventhelikelyextentofsmoke?Willthelossofuseofthebuildingduetoaseverefireresultinmajorpropertyandincomeloss?Iftheanswertothesequestionsisintheaffirmative,thenitmaybenecessarytominimisetheoccurrenceofasignificantfireratherthansimplyassumingthatthebuildingstructureneedstobedesignedforhighlevelsoffireresistance.Alow-riseshoppingcentrewithlevelsinterconnectedbylargevoidsisanexampleofsuchasituation.OtherFireSafetySystemsThepresenceofothersystems(e.g.sprinklers)withinthebuildingtominimisetheoccurrenceofaseriousfirecangreatlyreducetheneedforthestructuralelementstohavehighlevelsoffireresistance.Inthisregard,theuncertaintiesofallfire-safetysystemsneedtobeconsidered.Irrespectiveofwhetherthefiresafetysystemisthesprinklersystem,stairpressurisation,compartmentationorthesystemgivingthestructureafire-resistancelevel(e.g.concretecover),thereisanuncertaintyofperformance.Uncertaintydataisavailableforsprinklersystems(becauseitisrelativelyeasytocollect)butisnotreadilyavailablefortheotherfiresafetysystems.Thissometimesresultsinthedesignersandbuildingregulatorsconsideringthatonlysprinklersystemsaresubjecttouncertainty.Inreality,itwouldappearthatsprinklerssystemshaveahighlevelofperformanceandcanbedesignedtohaveveryhighlevelsofreliability.HeightofBuildingIttakeslongerforatallbuildingtobeevacuatedthanashortbuildingandthereforethestructureofatallbuildingmayneedtohaveahigherleveloffireresistance.Theimplicationsofcollapseoftallbuildingsonadjacentpropertiesarealsogreaterthanforbuildingsofonlyseveralstoreys.LimitedExtentofBurningIfthelikelyextentofburningissmallincomparisonwiththeplanareaofthebuilding,thenthefirecannothaveasignificantimpactontheoverallstabilityofthebuildingstructure.Examplesofsituationswherethisisthecaseareopen-deckcarparksandverylargeareabuildingsuchasshoppingcomplexeswherethefire-effectedpartislikelytobesmallinrelationtoareaofthebuildingfloorplan.BehaviourofFloorElementsTheeffectofrealfiresoncompositeandconcretefloorscontinuestobeasubjectofmuchresearch.ExperimentaltestingatCardingtondemonstratedthatwhenpartsofacompositeflooraresubjecttoheating,largedisplacementbehaviourcandevelopthatgreatlyassiststheloadcarryingcapacityofthefloorbeyondthatwhichwouldpredictedbyconsideringonlythebehaviourofthebeamsandslabsinisolation.Thesesituationshavebeenanalysedbybothyieldlinemethodsthattakeintoaccounttheeffectsofmembraneforces(Bailey,2004)andfiniteelementtechniques.Inessence,themethodsillustratethatitisnotnecessarytoinsulateallstructuralsteelelementsinacompositefloortoachievehighlevelsoffireresistance.Thisworkalsodemonstratedthatexposureofacompositefloorhavingunprotectedsteelbeams,toalocalisedfire,willnotresultinfailureofthefloor.Asimilarrealfiretestonamultistoryreinforcedconcretebuildingdemonstratedthattherealstructuralbehaviourinfirewassignificantlydifferenttothatexpectedusingsmalldisplacementtheoryasfornormaltemperaturedesign(Bailey,2002)withtheperformancebeingsuperiorthanthatpredictedbyconsideringisolatedmemberbehaviour.3.4PrescriptiveApproachtoDesignThebuildingregulationsofmostcountriesprovideprescriptiverequirementsforthedesignofbuildingsforfire.Theserequirementsaregenerallynotsubjecttointerpretationandcompliancewiththemmakesforsimplerdesignapproval-althoughnotnecessarilythemostcost-effectivedesigns.Theseprovisionsareoftentermeddeemed-to-satisfy(DTS)provisions.Allaspectsofdesigningbuildingsforfiresafetyarecovered-theprovisionofemergencyexits,spacingsbetweenbuildings,occupantfirefightingmeasures,detectionandalarms,measuresforautomaticfiresuppression,airandsmokehandlingrequirementsandlast,butnotleast,requirementsforcompartmentationandfireresistancelevelsforstructuralmembers.However,thereislittleevidencethattherequirementshavebeendevelopedfromasystematicevaluationoffiresafety.Ratheritwouldappearthatmanyoftherequirementshavebeenaddedonetoanothertodealwithanotherfireincidentortoincorporateanewformoftechnology.Theredoesnotappeartohavebeenanyrealattempttodeterminewhichprovisionhavethemostsignificantinfluenceonfiresafetyandwhethersomeoftheformerprovisionscouldbemodified.TheFRLrequirementsspecifiedintheDTSprovisionsaretraditionallyconsideredtoresultinmemberresistancesthatwillonlyrarelyexperiencefailureintheeventofafire.Thisiswhyitisacceptabletousetheabovearbitrarypointintimeloadcombinationforassessingmembersinfire.Therehavebeenattemptstoevaluatethevariousdeemed-to-satisfyprovisions(particularlythefire-resistancerequirements)fromafire-engineeringperspectivetakingintoaccountthepossiblevariationsinenclosuregeometry,openingsizesandfireload(seeFCRC,1999).Oneoftheoutcomesofthisevaluationwastherecognitionthatdeemed-to-satisfyprovisionsnecessarilycoverthebroadrangeofbuildingsandthusmust,onaverage,bequiteonerousbecauseofthemagnitudeoftheabovevariations.ItshouldbenotedthattheDTSprovisionsassumethatcompartmentationworksandthatfireislimitedtoasinglecompartment.Thismeansthatfireisnormallyonlyconsideredtoexistatonelevel.Thusfloorsareassumedtobeheatedfrombelowandcolumnsonlyoveronestoreyheight.Performance-BasedDesignAnapproachthatofferssubstantialbenefitsforindividualbuildingsisthemovetowardsperformance-basedregulations.ThisispermittedbyregulationssuchastheBCAwhichstatethatadesignermustdemonstratethattheparticularbuildingwillachievetherelevantperformancerequirements.Theprescriptiveprovisions(i.e.theDTSprovisions)arepresumedtoachievetheserequirements.ItisnecessarytoshowthatanybuildingthatdoesnotconformtotheDTSprovisionswillachievetheperformancerequirements.Butwhataretheperformancerequirements?Mostoftenthespecifiedperformanceissimplyasetofperformancestatements(suchaswiththeBuildingCodeofAustralia)withnoquantitativelevelgiven.Therefore,althoughthesestatementsremindthedesignerofthekeyelementsofdesign,theydonot,inthemselves,provideanymeasureagainstwhichtodeterminewhetherthedesignisadequatelysafe.Possibleacceptancecriteriaarenowconsidered.3.5.1AcceptanceCriteriaSomeguidanceastothebasisforacceptabledesignsisgiveninregulationssuchastheBCA.Tparethelevelsofsafety(withrespecttoachievingeachofthedesignobjectives)oftheproposedalternativesolutionwiththoseasso-ciatedwithacorrespondingDTSsolutionforthebuilding.Thiscomparisonmaybedoneoneitheraqualitativeorqualitativeriskbasisorperhapsacombination.Inthiscase,thebasisforcomparisonisanacceptableDTSsolution.Suchanapproachrequiresa“holistic”approachtosafetywherebyallaspectsrelevanttosafety,includingthestructure,areconsidered.Thisis,byfar,themostcommonbasisforacceptance.undertakeaprobabilisticriskassessmentandshowthattheriskassociatedwiththeproposeddesignislessthanthatassociatedwithcommonsocietalactivitiessuchasusingpublictransport.Undertakingafullprobabilisticriskassessmentcanbeverydifficultforallbutthesimplestsituations.Assumingthatsuchanassessmentisundertakenitwillbenecessaryforthestakeholderstoacceptthenominatedlevelofacceptablerisk.Again,thisrequiresa“holistic”approachtofiresafety.adesignispresentedwhereitisdemonstratedthatallreasonablemeasureshavebeenadoptedtomanagetherisksandthatanypossiblemeasuresthathavenotbeenadoptedwillhavenegligibleeffectontheriskofnotachievingthedesignobjectives.asfarasthebuildingstructureisconcerned,benchmarktheacceptableprobabilityoffailureinfireagainstthatfornormaltemperaturedesign.ThisissimilartotheapproachusedwhenconsideringBuildingSituation1butonlyconsidersthebuildingstructureandnottheeffectsofflameorsmokespread.Itisnotaholisticapproachtofiresafety.Finally,thequestionsofarsonandterrorismmustbeconsidered.Deliberateactsoffireinitiationrangefromrelativelyminorincidentstoactsofmassdestruction.Actsofarsonarewellwithintheacceptedrangeoffireeventsexperiencedbybuild-ings(e.g.8%offirestartsinofficesaredeemed"suspicious").Thesimplestactistouseasmallheatsourcetostartafire.Theresultingfirewilldevelopslowlyinonelocationwithinthebuildingandwillmostprobablybecontrolledbythevariousfire-safetysystemswithinthebuilding.Theoutcomeislikelytobethesameevenifanaccelerantisusedtoassistfirespread.AnimportantillustrationofthisoccurredduringtheraceriotsinLosAngelesin1992(Hart1992)whenfireswerestartedinmanybuildingsoftenatmultiplelocations.Inthecaseofbuildingswithsprinklersystems,thedamagewaslimitedandthefiressignificantlycontrolled.Althoughtheintentwastodestroythebuildings,thefire-safetysystemswereabletolimittheresultingfires.Securitymeasuresareprovidedwithsystemssuchassprinklersystemsandinclude:lockingofvalves-anti-tampermonitoringlocationofvalvesinsecurelocationsFurthermore,accesstosignificantbuildingsisoftenrestrictedbysecuritymeasures.Theveryfactthattheabovestepshavebeentakendemonstratesthatactsofdestructionwithinbuildingsareconsideredalthoughmostactsofarsondonotinvolveanyattempttodisablethefire-safetysystems.Attheoneendofthespectrumis"simple"arsonandattheotherend,extremelyrareactswhereattemptsaremadetodestroythefire-safetysystemsalongwithsubstantialpartsofthebuilding.Thiscanbeonlyachievedthroughmassiveimpactortheuseofexplosives.Thelattermaybeachievedthroughexplosivesbeingintroducedintothebuildingorfromoutsidebymissileattack.Theformercouldresultfrommissileattackorfromthecollisionofalargeaircraft.Thegreaterthedestructivenessoftheact,thegreaterthemeansandknowledgerequired.Conversely,themoreextremetheact,thelessconfidencetherecanbeindesigningagainstsuchanact.Thisisbecausethemoreextremetheevent,theharderitistopredictpreciselyandthelessunderstoodwillbeitseffects.Theimportantpointtorecogniseisthatifsufficientmeanscanbeassembled,thenitwillalwaysbepossibletoovercomeaparticularbuildingdesign.Thustheseactsarecompletelydifferenttotheotherloadingstowhichabuildingissubjectedsuchaswind,earthquakeandgravityloading.Thisisbecausesuchactsofdestructionaretheworkofintelligentbeingsandtakeintoaccountthecharacteristicsofthetarget.Shouldhigh-risebuildingsbedesignedforgiventerroristactivities,thenterroristswillsimplyusegreatermeanstoachievetheendresult.Forexample,ifbuildingsweredesignedtoresisttheimpacteffectsfromacertainsizeaircraft,thentheuseofalargeraircraftormorethanoneaircraftcouldstillachievedestructionofthebuilding.Anappropriatestrategyisthereforetominimisethelikelihoodofmeansofmassdestructiongettingintothehandsofpersonsintentonsuchacts.Thisisnotanengineeringsolutionassociatedwiththebuildingstructure.Itshouldnotbeassumedthatstructuralsolutionsarealwaysthemostappropriate,orindeed,possible.Inthesameway,aircraftsarenotdesignedtosurviveamajorfireoracrashlandingbutstepsaretakentominimisethelikelihoodofeitheroccurrence.Themobilizationoflargequantitiesoffireload(thenormalcombustiblesonthefloors)simultaneouslyonnumerouslevelsthroughoutabuildingiswelloutsidefiresituationsenvisagedbycurrentfireteststandardsandprescriptiveregulations.Riskmanagementmeasurestoavoidsuchapossibilitymustbeconsidered.CONCLUSIONSFiredifferssignificantlyfromother“l(fā)oads”suchaswind,liveloadandearthquakesinrespectofitsoriginanditseffects.Duetothefactthatfireoriginatesfromhumanactivitiesorequipmentinstalledwithinbuildings,itispossibletodirectlyinfluencethepotentialeffectsonthebuildingbyreducingtherateoffirestartsandprovidingmeasurestodirectlylimitfireseverity.ThedesignofbuildingsforfiresafetyismostlyachievedbyfollowingtheprescriptiverequirementsofbuildingcodessuchastheBCA.Forsituationsthatfalloutsideofthescopeofsuchregulations,orwhereproposeddesignsarenotinaccordancewiththeprescriptiverequirements,itispossibletoundertakeperformance-basedfireengineeringdesigns.However,therearenodesigncodesorstandardsordetailedmethodologiesavailableforundertakingsuchdesigns.Buildingregulationsrequirethatsuchalternativedesignssatisfyperformancerequirementsandgivesomeguidanceastothebasisforacceptanceofthesedesigns(i.e.acceptancecriteria).Thispaperpresentsanumberofpossibleacceptancecriteria,allofwhichusethemeasureofrisklevelasthebasisforcomparison.Strictly,whenconsideringtherisksassociatedwithfireaholisticapproachthatconsidersalloftheaspectsrelevanttoachievingthedesignobjectivesandtheinterrelationshipsbetweentheseaspects,shouldbeadopted.Insomesituations,theperformanceofthebuildingstructuremaywellbesecondaryasfaraslifesafetyisconcerned.Inothersituations,theperformanceofthestructuremaybeoffundamentalimportancewithrespecttothedesignobjectives.Forsituationswheretheperformanceofthestructureiscriticalorwhereitisconsideredinisolationtootherfiresafetyaspects(i.e.directeffectsofheatandsmoke),itispossibletoassesstherequiredfireresistancebyusingFOSMorsimilartheoryasusedfornormaltemperaturedesign.Suchanapproachisdescribedinthispaper.Firedifferssignificantlyfromother“l(fā)oads”suchaswind,liveloadandearthquakesinrespectofitsori-ginanditseffects.Duetothefactthatfireorigi-natesfromhumanactivitiesorequipmentinstalledwithinbuildings,itispossibletodirectlyinfluencethepotentialeffectsonthebuildingbyreducingtherateoffirestartsandprovidingmeasurestodirectlylimitfireseverity.ThedesignofbuildingsforfiresafetyismostlyachievedbyfollowingtheprescriptiverequirementsofbuildingcodessuchastheBCA.Forsituationsthatfalloutsideofthescopeofsuchregulations,orwhereproposeddesignsarenotinaccordancewiththeprescriptiverequirements,itispossibletoundertakeperformance-basedfireengineeringdesigns.However,therearenodesigncodesorstandardsordetailedmethodologiesavailableforundertakingsuchdesigns.Buildingregulationsrequirethatsuchalternativedesignssatisfyperformancerequirementsandgivesomeguidanceasto