外文翻译通过建筑结构设计以改善建筑物的抗倒性Word格式文档下载.docx

外文翻译通过建筑结构设计以改善建筑物的抗倒性Word格式文档下载.docx

《外文翻译通过建筑结构设计以改善建筑物的抗倒性Word格式文档下载.docx》由会员分享，可在线阅读，更多相关《外文翻译通过建筑结构设计以改善建筑物的抗倒性Word格式文档下载.docx（11页珍藏版）》请在冰豆网上搜索。

toProgressiveCollapse

DANethercota

aDepartmentofCivilandEnvironmentalEngineering,ImperialCollegeLondon

Abstract：

Itisrarenowadaysfora“newtopic”toemergewithintherelativelymaturefieldofStructuralEngineering.Progressivecollapse-or,moreparticularly,understandingthemechanicsofthephenomenonanddevelopingsuitablewaystoaccommodateitsconsiderationwithinournormalframeworksforstructuraldesign-canbesoregarded.BeginningwithillustrationsdrawnfromaroundtheworldoverseveraldecadesandculminatinginthehighlypublicWTCcollapses,thosefeaturesessentialforarepresentativetreatmentareidentifiedandearlydesignapproachesarereviewed.Morerecentworkisthenreported,concentratingondevelopmentsofthepastsevenyearsatImperialCollegeLondon,whereacomprehensiveapproachcapableofbeingimplementedonavarietyoflevelsandsuitablefordirectusebydesignershasbeenunderdevelopment.Illustrativeresultsareusedtoassistinidentifyingsomeofthekeygoverningfeatures,toshowhowquantitativecomparisonsbetweendifferentarrangementsmaynowbemadeandtoillustratetheinappropriatenessofsomepreviousdesignconceptsasawayofdirectlyimprovingresistancetoprogressivecollapse.

2011PublishedbyElsevierLtd.

Keywords:

Compositestructures;

ProgressiveCollapse;

Robustness;

Steelstructures;

Structuraldesign

1.Introduction

Overtimevariousdifferentstructuraldesignphilosophieshavebeenproposed,theirevolutionarynaturereflecting：

*Growingconcerntoensureadequateperformance.

*Improvedscientificknowledgeofbehaviour.

*Enhancedabilitytomovefromcraftbasedtosciencebasedandthusfromprescriptivetoquantitativelyjustifiedapproaches

Thiscanbetracedthroughconceptssuchas:

permissiblestress,ultimatestrength,limitstatesandperformancebased.Asclients,usersandthegeneralpublichavebecomeincreasinglysophisticatedandthusmoredemandingintheirexpectations,soitbecamenecessaryfordesignerstocoveraneverincreasingnumberandrangeofstructuralissues–mostlythroughconsiderationofthe“reachingthisconditionwouldbetoagreaterorlesserextentunacceptable”approach.Thereforeissuesnotpreviouslyconsidered（oronlyallowedforinanimplicit,essentiallycopyingpastsatisfactoryperformance,way）startedtorequireexplicitattentionintheformof:

anassessmentofdemand,modellingbehaviourandidentificationofsuitablefailurecriteria.Thetreatmentoftopicssuchasfatigue,fireresistance,durabilityandserviceabilitycanallbeseentohavefollowedthispattern.

Totakeaspecificexample:

designingadequatefireresistanceintosteelframedbuildingsbegan（oncetheneedhadbeenrecognised）withsimpleprescriptiverulesforconcreteencasementofvulnerablemembersbutithas,inrecentyears,evolvedintoasophisticateddisciplineoffireengineering,concernedwithfireloading,theprovisionofprotectivesystemssuchassprinklers,calculationofresponseintheeventofafireandtheabilitytomakequantitativecomparisonsbetweenalternativestructuralarrangements.Notonlyhasthisledtoobviouseconomicbenefitsinthesenseofnotprovidingfireprotectionwhereitgaveonlynegligiblebenefit,ithasalsoledtoincreasedfiresafetythroughbetterunderstandingofthegoverningprinciplesandtheabilitytoactintelligentlyindesigningsuitablearrangementsbasedonaproperassessmentofneed.

PriortotheRonanPointcollapseinLondonin1968thetermsrobustness,progressivecollapse,

disproportionatecollapseetc.,werenotpartofStructuralEngineeringvocabulary.Theconsequencesofthedamagedonetothat22storeyblockofpre-castconcreteapartmentsbyaverymodestgasexplosiononthe18thfloorledtonewprovisionsintheUKBuildingRegulations,outlawingformanyyearsofsocalledsystembuiltschemes,demolitionofseveralcompletedbuildings,temporaryremovalofgasinhighriseconstructionandtheformationoftheStandingCommitteeonStructuralSafety.Eventually,thebenefitsofproperlyengineeredpre-fabricationwererecognised,safemethodsfortheinstallationofgasweredevisedandtheindustrymovedon.However,thestructuraldesignguidanceproducedatthattime-thatstillunderpinsmuchpresentdayprovision-wasessentiallyprescriptiveinnaturewithnoreallinktoactualperformance.

SubsequentincidencesofprogressivecollapsesuchastheMurraghBuildingandtheWorldTradeCentrebroughtincreasedattentiontotheactualphenomenonandissuesofhowitmightreasonablybetakenintoaccountforthosestructuraldesignswhereitwasconsideredappropriate.Indoingthisitis,ofcourse,essentialtoincludeboththeriskofatriggeringincidentandtheconsequencesofafailuresothattheresultingmoreonerousstructuraldemandsareusedappropriately.Arguably,adisproportionateresponseintermsofrequiringcostlyadditionalprovisionsincaseswheretherisks/consequencesareverylow/veryminormaybeasharmfulasfailingtoaddressthosecaseswheretherisks/consequencesarehigh/severe.

ThispaperwillreviewcurrentapproachestodesigntoresistprogressivecollapseandcontrastthesewithworkundertakenoverthepastsevenyearsatImperialCollegeLondon,wherethegoalhasbeentheprovisionofarealisticallybasedmethodsuitableforuseinroutinedesign.Theessentialfeaturesofthemethodwillbepresented,itsuseonseveralexamplesdescribedandresultspresentedtoillustratehowitisleadingtoabetterunderstandingofboththemechanicsofprogressivecollapseandthewaysinwhichstructuralengineerscanbestconfiguretheirstructuressoastoprovideenhancedresistance

2.Designtoresistprogressivecollapse

Thetwomostfrequentlyuseddesignapproachesintendedtoaddresstheissueofprogressivecollapseare:

*Providingtyingcapacity

*Checkingalternateloadpaths

Figure1:

TieForcesinaFrameStructure

Thefirstisessentiallyprescriptiveandconsistsofensuringthatbeams,columns,connectionsandfloor（orroof）canacttogethertoprovideaspecifiedminimumlevelofhorizontaltyingresistance;

theactualvaluesrequiredarenormallyrelatedtotheverticalloading.Figure1,whichistakenfromrecentUSGuidance（SEI2010）,illustratestheprinciple.Theapproachissimpletoappreciate,requiresminimalstructuralcalculationand,insituationswheretheoriginalprovisionsarefoundtobeinadequate,canbemadetoworkbyprovidingmoresubstantialconnectionsand/oradditionalreinforcementinfloorslabsInaninterestingrecentdevelopment,thatrecognizesthelinktothegenerationofcatenaryaction,USGuidancehasrestrictedtheuseoftyingbetweenthestructuralmemberstosituationsinwhichitcanbedemonstratedthattheassociatedconnectionscancarrytherequiredforceswhilstundergoingrotationsof0.2radiance.Wherethisisnotpossible,tyingshouldactthroughthefloorsandtheroof.However,recentstudies（Nethercotetal2010a;

Nethercotetal2010b）havesuggestedthattyingcapacitycorrelatespoorlywithactualresistancetoprogressivecollapse.Moreover,beingprescriptive,itdoesnotpermitthemeaningfulcomparisonofalternativearrangements-afundamentalfeatureofstructuraldesign.

Initsmostfrequentlyusedformthealternativeloadpathapproachpresumestheinstantaneouslossofasinglecolumnandthenrequiresthattheabilityoftheresultingdamagedstructuretobridgethelossbedemonstratedbysuitablecalculation（GudmundssonandIzzuddin2010）.Theapproachmaybeimplementedatvaryinglevelsofsophisticationintermsoftheanalysis;

forexample,recentthinkingintheUnitedStates（SEI2010）makesprovisionforanyof:

linearstatic,non-linearstaticornon-lineardynamicanalysisandprovidessomeguidanceontheuseofeach.Itmayalsobeusedasthebasisformoresophisticatednumericalstudiesofparticularstructuresandparticularincidentse.g.forensicwork;

thebestofthese–whicharelikelytobecomputationallyverydemanding–havedemonstratedtheirabilitytocloselyreplicateactualobservedbehaviour.

3.Essentialfeaturesofprogressivecollapse

Threefeatureshavepreviously（Nethercot2010）beingidentifiedasessentialcomponentsofanyreasonablyrealisticapproachtodesignagainstprogressivecollapse:

*Eventstakeplaceoveraveryshorttimescaleandtheactualfailureisthereforedynamic.

*Itinvolvesgrossdeformations,generatinglargestrains,leadingtoinelasticbehaviouraswellaschangeofgeometryeffects.

*Failureessentiallycorrespondstoaninabilityofthestructureinitsdamagedstatetoadoptanewpositionofequilibriumwithoutseparationofkeyelements.

Figure2:

Simplifiedmulti-levelapproachforprogressivecollapseassessment

Additionalfeatures,designedtomaketheapproachattractiveforusebypracticingEngineershavealsobeenproposed（Nethercot2010）:

*Processshouldconsistofaseriesofstepsbroadlysimilarinconcepttothoseusedfor“conventional”structuraldesign.

*Itshould,preferably,becapableofimplementationatavarietyatlevelsofcomplexity–withthechoicereflectingtheimportanceofthestructure.

*Anyrequiredanalysisshouldutilisefamiliartechniques;

wheretheserequirecomputationsbeyond“handmethods”,theseshouldbebasedontheuseofavailableanalysissoftware.

*Arealisticandrecognisablecriterionoffailureshouldbeused.

*Approachshouldpermitstudyofcauseandeffectandbesuitableforthemaking