房屋建筑毕业设计外文翻译---钢筋混凝土板的拉伸硬化过程分析

'毕业设计(论文)外文翻译设计（论文）题目：宁波天合家园某住宅楼2号轴框架结构设计与建筑制图学院名称：建筑工程学院专业：土木工程姓名：陈绍樑学号09404010421指导教师：马永政、陶海燕2012年12月10日 宁波工程学院本科毕业设计（论文）—外文翻译外文原稿1TensionStiffeninginLightlyReinforcedConcreteSlabs1R.IanGilbert1Abstract:Thetensilecapacityofconcreteisusuallyneglectedwhencalculatingthestrengthofareinforcedconcretebeamorslab,eventhoughconcretecontinuestocarrytensilestressbetweenthecracksduetothetransferofforcesfromthetensilereinforcementtotheconcretethroughbond.Thiscontributionofthetensileconcreteisknownastensionstiffeninganditaffectsthemember’sstiffnessaftercrackingandhencethedeflectionofthememberandthewidthofthecracksunderserviceloads.Forlightlyreinforcedmembers,suchasfloorslabs,theflexuralstiffnessofafullycrackedsectionismanytimessmallerthanthatofanuncrackedsection,andtensionstiffeningcontributesgreatlytothepostcrackingstiffness.Inthispaper,theapproachestoaccountfortensionstiffeningintheACI,European,andBritishcodesareevaluatedcriticallyandpredictionsarecomparedwithexperimentalobservations.Finally,recommendationsareincludedformodelingtensionstiffeninginthedesignofreinforcedconcretefloorslabsfordeflectioncontrol.CEDatabasesubjectheadings:Cracking;Creep;Deflection;Concrete,reinforced;Serviceability;Shrinkage;Concreteslabs.1ProfessorofCivilEngineering,SchoolofCivilandEnvironmentalEngineering,Univ.ofNewSouthWales,UNSWSydney,2052,Australia.Note.AssociateEditor:RobY.H.Chai.DiscussionopenuntilNovember1,2007.Separatediscussionsmustbesubmittedforindividualpapers.Toextendtheclosingdatebyonemonth,awrittenrequestmustbefiledwiththeASCEManagingEditor.ThemanuscriptforthistechnicalnotewassubmittedforreviewandpossiblepublicationonMay22,2006;approvedonDecember28,2006.ThistechnicalnoteispartoftheJournalofStructuralEngineering,Vol.133,No.6,June1,2007.11ProfessorofCivilEngineering,SchoolofCivilandEnvironmentalEngineering,Univ.ofNewSouthWales,UNSWSydney,2052,Australia.28 宁波工程学院本科毕业设计（论文）—外文翻译JournalofStructuralEngineering,Vol.133,No.6,June1,2007.1.IntroductionThetensilecapacityofconcreteisusuallyneglectedwhencalculatingthestrengthofareinforcedconcretebeamorslab,eventhoughconcretecontinuestocarrytensilestressbetweenthecracksduetothetransferofforcesfromthetensilereinforcementtotheconcretethroughbond.Thiscontributionofthetensileconcreteisknownastensionstiffening,anditaffectsthemember’sstiffnessaftercrackingandhenceitsdeflectionandthewidthofthecracks.Withtheadventofhigh-strengthsteelreinforcement,reinforcedconcreteslabsusuallycontainrelativelysmallquantitiesoftensilereinforcement,oftenclosetotheminimumamountpermittedbytherelevantbuildingcode.Forsuchmembers,theflexuralstiffnessofafullycrackedcrosssectionismanytimessmallerthanthatofanuncrackedcrosssection,andtensionstiffeningcontributesgreatlytothestiffnessaftercracking.Indesign,deflectionandcrackcontrolatservice-loadlevelsareusuallythegoverningconsiderations,andaccuratemodelingofthestiffnessaftercrackingisrequired.Themostcommonlyusedapproachindeflectioncalculationsinvolvesdetermininganaverageeffectivemomentofinertia[Ie]foracrackedmember.SeveraldifferentempiricalequationsareavailableforIe,includingthewell-knownequationdevelopedbyBranson[1965]andrecommendedinACI318[ACI2005].OthermodelsfortensionstiffeningareincludedinEurocode2[CEN1992]andthe[BritishStandardBS81101985].Recently,Bischoff[2005]demonstratedthatBranson’sequationgrosslyoverestimatesthtieaveragesffnessofreinforcedconcretememberscontainingsmallquantitiesofsteelreinforcement,andheproposedanalternativeequationforIe,whichisessentiallycompatiblewiththeEurocode2approach.Inthispaper,thevariousapproachesforincludingtensionstiffeninginthedesignofconcretestructures,includingtheACI318,Eurocode2,andBS8110models,areevaluatedcriticallyandempiricalpredictionsarecomparedwithmeasureddeflections.Finally,recommendationsformodelingtensionstiffeninginstructuraldesignareincluded.28 宁波工程学院本科毕业设计（论文）—外文翻译2.FlexuralResponseafterCrackingConsidertheload-deflectionresponseofasimplysupported,reinforcedconcreteslabshowninFig.1.Atloadslessthanthecrackingload,Pcr,thememberisuncrackedandbehaveshomogeneouslyandelastically,andtheslopeoftheloaddeflectionplotisproportionaltothemomentofinertiaoftheuncrackedtransformedsection,Iuncr.ThememberfirstcracksatPcrwhentheextremefibertensilestressintheconcreteatthesectionofmaximummomentreachestheflexuraltensilestrengthoftheconcreteormodulusofrupture,fr.Thereisasuddenchangeinthelocalstiffnessatandimmediatelyadjacenttothisfirstcrack.Onthesectioncontainingthecrack,theflexuralstiffnessdropssignificantly,butmuchofthebeamremainsuncracked.Asloadincreases,morecracksformandtheaverageflexuralstiffnessoftheentirememberdecreases.Ifthetensileconcreteinthecrackedregionsofthebeamcarriednostress,theload-deflectionrelationshipwouldfollowthedashedlineACDinFig.1.Iftheaverageextremefibertensilestressintheconcreteremainedatfraftercracking,theloaddeflectionrelationshipwouldfollowthedashedtheactualresponseliesbetweenthesetwoextremesandisshowninFig.1asthesolidlineAB.Thedifferencebetweentheactualresponseandthezerotensionresponseisthetensionstiffeningeffect（inFig.1）.Astheloadincreases,theaveragetensilestressintheconcretereducesasmorecracksdevelopandtheactualresponsetendstowardthezerotensionresponse,atleastuntilthecrackpatternisfullydevelopedandthenumberofcrackshasstabilized.Forslabscontainingsmallquantitiesoftensilereinforcement[typicallytensionstiffeningmayberesponsibleformorethan50%ofthestiffnessofthecrackedmemberatserviceloadsandremainssignificantuptoandbeyondthepointwherethesteelyieldsandtheultimateloadisapproached].Thetensionstiffeningeffectdecreaseswithtimeundersustainedloads,probablyduetothecombinedeffectsoftensilecreep,creeprupture,andshrinkagecracking,andthismustbeaccountedforinlong-termdeflectioncalculations.28 宁波工程学院本科毕业设计（论文）—外文翻译3.ModelsforTensionStiffeningTheinstantaneousdeflectionofbeamorslabatserviceloadsmaybecalculatedfromelastictheoryusingtheelasticmodulusofconcreteEcandaneffectivemomentofinertia,Ie.ThevalueofIeforthememberisthevaluecalculatedusingEq.[1]atmidspanforasimplysupportedmemberandaweightedaveragevaluecalculatedinthepositiveandnegativemomentregionsofacontinuousspan（1）whereIcr=momentofinertiaofthecrackedtransformedsection;Ig=momentofinertiaofthegrosscrosssectionaboutthecentroidalaxis[butmorecorrectlyshouldbethemomentofinertiaoftheuncrackedtransformedsection,Iuncr];Ma=maximummomentinthememberatthestagedeflectioniscomputed;Mcr=crackingmoment=(frIg/yt);fr=modulusofruptureofconcrete(=7.5fcinpsiand0.6fcinMpa);andyt=distancefromthecentroidalaxisofthegrosssectiontotheextremefiberintension.AmodificationoftheACIapproachisincludedintheAustralianStandardAS3600-2001(AS2001)toaccountforthefactthatshrinkage-inducedtensionintheconcretemayreducethecrackingmomentsignificantly.ThecrackingmomentisgivenbyMcr=(fr−fcs)Ig/yt,wherefcsismaximumshrinkage-inducedtensilestressintheuncrackedsectionattheextremefibreatwhichcrackingoccurs（Gilbert2003）.（2）wheredistributioncoefficientaccountingformomentlevelanddegreeofcrackingandisgivenby（3）and1=1.0fordeformedbarsand0.5forplainbars;2=1.0forasingle,short-termloadand0.5forrepeatedorsustainedloading;sr=stressinthetensilereinforcementattheloadingcausingfirstcracking(i.e.,whenthemomentequalsMcr),calculatedwhileignoringconcreteintension;sisreinforcementstressatloadingunderconsideration(i.e.,whenthein-servicemomentMsisacting),calculatedwhileignoringconcreteintension;cr=curvatureatthesectionwhileignoringconcreteintension;anduncr=curvatureontheuncrackedtransformedsection.Forslabsinpureflexure,ifthecompressiveconcreteandthereinforcementarebothlinearandelastic,theratiosr/sinEq.(3)isequaltotheratioMcr/Ms.UsingthenotationofEq.（1）,Eq.(2)canbereexpressedas（4）28 宁波工程学院本科毕业设计（论文）—外文翻译Foraflexuralmembercontainingdeformedbarsundershorttermloading,Eq.(3)becomes=1−（Mcr/Ms）2andEq.（4）canberearrangedtogivethefollowingalternativeexpressionforIeforshort-termdeflectioncalculations[recentlyproposedbyBischoff(2005)]:(5)Thisapproach,whichhasnowbeensupersededintheU.K.bytheEurocode2approach,alsoinvolvesthecalculationofthecurvatureatparticularcrosssectionsandthenintegratingtoobtainthedeflection.Thecurvatureofasectionaftercrackingiscalculatedbyassumingthat(1)planesectionsremainplane;(2)theconcreteincompressionandthereinforcementareassumedtobelinearelastic;and（3）thestressdistributionforconcreteintensionistriangular,havingavalueofzeroattheneutralaxisandavalueatthecentroidofthetensilesteelof1.0MPainstantaneously,reducingto0.55MPainthelongterm.4.ComparisonwithExperimentalDataTotesttheapplicabilityoftheACI318,Eurocode2,andBS8110approachesforlightlyreinforcedconcretemembers,themeasuredmomentversusdeflectionresponsefor11simplysupported,singlyreinforcedone-wayslabscontainingtensilesteelquantitiesintherange0.0018<<0.01arecomparedwiththecalculatedresponses.Theslabs(designatedS1toS3,S8,SS2toSS4,andZ1toZ4)wereallprismatic,ofrectangularsection,850mmwide,andcontainedasinglelayeroflongitudinaltensilesteelreinforcementataneffectivedepthd(withEs=200,000MPaandthenominalyieldstressfsy=500Mpa).DetailsofeachslabaregiveninTable1,includingrelevantgeometricandmaterialproperties.Thepredictedandmeasureddeflectionsatmidspanforeachslabwhenthemomentatmidspanequals1.1,1.2,and1.3McrarepresentedinTable2.Themeasuredmomentversusinstantaneousdeflectionresponseatmidspanoftwooftheslabs(SS2andZ3)arecomparedwiththecalculatedresponsesobtainedusingthethreecodeapproachesinFig.2.Alsoshownaretheresponsesifcrackingdidnotoccurandiftensionstiffeningwasignored.28 宁波工程学院本科毕业设计（论文）—外文翻译5.DiscussionofResultsItisevidentthatfortheselightlyreinforcedslabs,tensionstiffeningisverysignificant,providingalargeproportionofthepostcrackingstiffness.FromTable2,theratioofthemidspandeflectionobtainedbyignoringtensionstiffeningtothemeasuredmidspandeflection(overthemomentrangeMcrto1.3Mcr)isintherange1.38–3.69withameanvalueof2.12.Thatis,onaverage,tensionstiffeningcontributesmorethan50%oftheinstantaneousstiffnessofalightlyreinforcedslabaftercrackingatserviceload.Foreveryslab,theACI318approachunderestimatestheinstantaneousdeflectionaftercracking,particularlysoforlightlyreinforcedslabs.Inaddition,ACI318doesnotmodeltheabruptchangeindirectionofthemoment-deflectionresponseatfirstcracking,nordoesitpredictthecorrectshapeofthepostcrackingmoment-deflectioncurve.Theunderestimationofshort-termdeflectionusingtheACI318modelisconsiderablygreaterinpracticethanthatindicatedbythelaboratorytestsreportedhere.UnliketheEurocode2andBS8110approaches,theACI318modeldoesnotrecognizeoraccountforthereductioninthecrackingmomentthatwillinevitablyoccurinpracticeduetotensioninducedintheconcretebydryingshrinkageorthermaldeformations.Formanyslabs,crackingwilloccurwithinweeksofcastingduetoearlydryingortemperaturechanges,oftenwellbeforetheslabisexposedtoitsfullserviceloads.Bylimitingtheconcretetensilestressatthelevelofthetensilereinforcementtojust1.0MPa,theBS8110approachoverestimatesthedeflectionofthetestslabsbothbelowandimmediatelyabovethecrackingmoment.Thisisnotunreasonableandaccountsforthelossofstiffnessthatoccursinpracticeduetorestrainttoearlyshrinkageandthermaldeformations.Nevertheless,theBS8110approachprovidesarelativelypoormodelofthepostcrackingstiffnessandincorrectlysuggeststhattheaveragetensileforcecarriedbythecrackedconcreteactuallyincreasesasMincreasesandtheneutralaxisrises.Asaresult,theslopeoftheBS8110postcrackingmoment-deflectionplotissteeperthanthemeasuredslopeforallslabs.TheapproachisalsomoretedioustousethaneithertheACIorEurocode2approaches.Inallcases,deflectionscalculatedusingEurocode2[Eqs.(3)–(5)]areinmuchcloseragreementwiththemeasureddeflectionovertheentirepostcrackingloadrange.AscanbeseeninFig.2,theshapeoftheload-deflectioncurveobtainedusingEurocode2isafarbetterrepresentationoftheactualcurvethanthatobtainedusingEq.(1).Consideringthevariabilityoftheconcretematerialpropertiesthataffectthein-servicebehaviorofslabs28 宁波工程学院本科毕业设计（论文）—外文翻译andtherandomnatureofcracking,theagreementbetweentheEurocode2predictionsandthetestresultsoversuchawiderangeoftensilereinforcementratiosisquiteremarkable.Withtheratioof()inTable2varyingbetween0.80and1.39withameanvalueof1.07,theEurocode2approachcertainlyprovidesabetterestimateofshort-termbehaviorthaneitherACI318orBS8110.6.ConclusionsAlthoughtensionstiffeninghasonlyarelativelyminoreffectonthedeflectionofheavilyreinforcedbeams,itisverysignificantinlightlyreinforcedmemberswheretheratioIuncr/Icrishigh,suchasmostpracticalreinforcedconcretefloorslabs.ThemodelsfortensionstiffeningincorporatedinACI（2005）,Eurocode2(CEN1992),andBS8110（1985）havebeenpresentedandtheirapplicabilityhasbeenassessedforlightlyreinforcedconcreteslabs.Instantaneousdeflectionscalculatedusingthethreecodemodelshavebeencomparedwithmeasureddeflectionsfrom11laboratorytestsonslabscontainingvaryingquantitiesofsteelreinforcement.TheEurocode2approach（Eq.（5）hasbeenshowntomoreaccuratelymodeltheshapeoftheinstantaneousload-deformationresponseforlightlyreinforcedmembersandbefarmorereliablethantheACI318approach（Eq.（1）.28 宁波工程学院本科毕业设计（论文）—外文翻译中文翻译1钢筋混凝土板的拉伸硬化过程分析R.IanGilbert摘要：混凝土的抗拉能力在计算钢筋混凝土梁或板的强度时通常被忽视,尽管具体的拉应力继续进行，由于拉钢筋到混凝土之间裂缝的转换力量。这一种混凝土的拉力被称为混凝土的张力硬化。在开裂后它会影响钢筋混凝土的刚度，因此它的挠度和裂缝宽度必须根据屈服强度负载。对轻混凝土，例如楼板，全部裂缝的弯曲刚度比没有裂缝部分的要小很多，张力加劲有助于刚度。在本文中，ACI方法必须考虑到紧张加劲，欧洲和英国的方法是严格评估和预测与实验结果进行比较。最后，建议依据钢筋混凝土楼板的建模张力加劲设计控制偏转。关键词：开裂，蠕变挠度，混凝土，钢筋，适用性，收缩，混凝土砖。28 宁波工程学院本科毕业设计（论文）—外文翻译1.引言由于拉钢筋到混凝土之间裂缝的转换力量，拉伸能力在计算时通常忽略钢筋混凝土梁或板的强度,尽管具体的拉应力将持续。这一种混凝土的拉力被称为张力硬化,它会影响各部分的刚度，因此必须考虑其挠度和裂缝宽度。随着高强度钢筋的运用，增强混凝土板通常使用相对少量的拉钢筋，经常接近相关建筑法规允许的最低允许值。对于这样的构件，弯曲完全开裂的一个截面刚度比未开裂的截面小许多倍，张力加劲大大促进了开裂后构件的刚度。在设计中，挠度和裂缝的控制通常是在屈服水平调整考虑的，并在开裂后刚度的建模精确是必需的。挠度计算中最常用的方法包括确定破解构件平均有效的转动惯量（）。几种不同的经验公式可用于，包括著名的方程开发Branson（1965）和ACI318（ACI2005）。其他的张力硬化模式包括在Eurocode2（CEN1992)和（BritishStandardBS81101985），最近，Bischoff（2005）表明，布兰森的方程对含有少量的钢筋混凝土构件钢筋平均刚度评估过高，他提出了一个对于的替代方程，这基本上是与Eurocode2方案兼容。在本文中，包括张力加劲在内的各种方法在混凝土结构设计，包括在Eurocode2，ACI318，BS8110模式，批判性进行评估经验预测与实测挠度进行了比较。最后，模拟张力加劲的建议结构设计均被包括在内。2.开裂后弯曲响应考虑一个简支负载的变形响应，钢筋混凝土板如图1所示。在负载小于开裂负载的情况下，，该构件未开裂和表现均匀的弹性，以及挠度斜率是成正比的未开裂的转动惯量的换算界面，。该构件的第一裂缝在当极端纤维在混凝土拉应力的最大部分到达混凝土弯拉强度破裂或时。有一个刚度突变，并立即出现裂纹。在包含了破碎的部分，抗弯刚度显着下降，但大部分仍然未开裂的梁，随着负载的增加，出现更多的裂缝形式和整个构件的平均抗弯构件减少。如果在梁的混凝土开裂区域内施加拉力而没有压力，负载变形关系将遵循虚线ACD，如图1。如果平均极端纤维拉伸应力在混凝土开裂后留在fr，将遵循虚线AE。事实上，实际的反应是介于这两个极端自建，如图1所示为实线AB型。实际反应之间的区别和零张力反应的张力是加强效应。28 宁波工程学院本科毕业设计（论文）—外文翻译随着越来越多的裂缝发展和实际响应趋向于零紧张反应，一般的拉应力混凝土减少，至少要等到裂缝模式充分开发和裂缝的数量趋于稳定。对于含有少量的拉结钢筋砖（通常=As/bd0.003），紧张硬化可能超过50％的钢筋混凝土的刚度破坏屈服加载而且仍然要达到和超过的钢产量和负荷接近极限地步。依据在长期挠度的计算下，可能是由于综合作用的拉伸蠕变、蠕变断裂,收缩开裂，在持续负载下张力加劲效应随着时间而减少。3.加劲的张力模型梁的弯曲或板在使用载重挠度可以瞬间从弹性论计算通过混凝土弹性模量Ec和有效的惯性矩。的价值对于构件是计算使用Eq.[1]计算公式为一个在跨中简支构件和加权平均计算价值在正，负弯矩区的一个连续的跨度。（1）为破碎的换算截面的惯性矩；为总截面的质心轴的惯性矩，但更正确的应该是换算截面的未开裂的惯性矩；为在构件的最大弯矩阶段的计算挠度；为开裂力矩（=）；为混凝土断裂模数；为从质心的距离轴的毛截面的纤维在极端的张力。ACI方法的修改包括在澳大利亚标准AS3600-2001(AS2001)解释的收缩引起的张力可能会显著的降低混凝土的开裂构件这个事实。开裂的构件由公式决定，是纤维在最大收缩引起的拉在未开裂截面应力在极端的情况发生开裂（Gilbert2003）。Eurocode2（1994）这种方法涉及到在特定的曲率计算交叉部分，然后结合取得的挠度。开裂后曲率K的计算为(2)为分配系数占目前水平和打击的程度，并给出（3）为变形钢筋=1.0，光圆钢筋=0.5；为单一的，短期负荷为1.0，重复或持续荷载为0.5；在应力加载造成的受拉钢筋首先开裂，计算混凝土张力；是考虑钢筋的加载应力；为忽略应力混凝土的曲率部分；28 宁波工程学院本科毕业设计（论文）—外文翻译曲率的未开裂换算截面。在纯弯曲的板，如果抗压混凝土和钢筋都是线性和弹性，等于，结合公式1和2能得（4）对于一个包含变形钢筋受弯构件在短期的加载，公式3和公式4可以重新安排，以提供下列替代表达式短期挠度[最近提出Bischoff(2005)](5)这种做法，目前在英国已经取代了Eurocode2的方法，还涉及到在特定的截面曲率的计算，然后结合获得的挠度。开裂后的曲率K计算假设（1）、平面为平截面；（2）、压缩的钢筋混凝土被认为是线弹性；（3）、凝固的混凝土应力分布是三角形的，在中性轴和一个值为零值在1.0MPa的瞬间强度钢质心，减少至0.55MPa。4.与实验数据的比较为了测试ACI318，欧洲规范的适用性和BS8110轻型钢筋混凝土构件的方法，测量的力矩与11简支的挠度反应相对，单钢筋单向拉伸板含钢量计算结果在范围进行比较，该板块（指定S1至S3，S8的，到SS2的SS4型，和Z1到Z4）都是柱状，矩形截面，850mm，并在一个有效深度载有纵向拉伸单层钢筋d(Es=200000MPa和屈服应力=500MPa)。每个板块的详细情况见表1，包括有关的几何和材料特性。在每个板跨中挠度的预测结果与实测时，在跨中力矩等于1.1，1.2和1.3Mcr列出在表2。与瞬时变形响应的测量力矩的两跨中的板。（SS2andZ3）进行比较和计算结果获得图2，使用三个代码方式同时显示的结果，如果没有出现开裂，如果张力加劲被忽略。5.讨论结果很明显，这些轻型钢筋板，张力加劲非常显著，提供一个大比例的开裂后刚度。从表2，跨中挠度的比例得到了加劲，对测量张力跨中挠度忽视（在Mcr和1.3Mcr范围）是在1.38-3.69范围，取平均值2.12。也就是说，平均而言，张力加劲超过50％的一个轻型钢筋板在屈服荷载的瞬间开裂。28 宁波工程学院本科毕业设计（论文）—外文翻译对于每一个板，在ACI318的方法低估了瞬间挠度后开裂，特别是对于轻型钢筋板。此外，在这一时刻ACI318突然不成模型，在起初开裂处，突然改变力矩偏转结果的方向，也没有预测的正确形状矩挠度曲线。在短期挠度的低估使用ACI318模式是经化验报告在这里在表示实践中相当大的比。不同于Eurocode2和BS8110，ACI318模型不承认或为在开裂的力矩，这将不可避免地减少在实践中出现的由于张力引起的混凝土干燥收缩或热变形。对于许多板，因早期干燥或温度变化在数周内将发生铸件的开裂，以及经常暴露之前，其板全方位服务的负荷。通过限制混凝土拉伸应力水平的拉伸筋只有1.0MPa，BS8110的方法对测试板的上下挠度和立即高于开裂力矩的高估。由于约束的早期收缩和热变形，这并非不合理和占损失的刚度发生在实践中。不过，BS8110提供了一个相对较差模型刚度，并错误地认为，平均拉力混凝土裂缝进行了实际调高M增大和中性轴的上升。因此，BS8110开裂后力矩偏转斜率图甚至超过了所有板测量斜坡。这种方法使用比Eurocode2或ACI两种方式更繁琐。在所有情况下，Eurocode2挠度计算[EPS.(3)-(5)]是在更接近与实测挠度在整个负载范围内协议。可以看出在图2，荷载—挠度曲线的形状并使用Eurocode2是一个比这更好的代表性实际曲线结果，使用EP.(1)。考虑到具体的变异材料性能影响的板，该协议Eurocode2在运行特征和对开裂的随机性之间的预测和试验结果在如此广泛的受拉钢筋比率是相当显著的。在图2（）0.80和1.39之间的值平均值为1.07，Eurocode2的方法提供了ACI318或BS8110更好地估计短期行为。6.结论虽然张力加劲只对重钢筋梁挠度的影响相对较小，这是非常重要的对于Iuncr/ICR的比例很高的轻型钢筋构件，例如作为最实用的钢筋混凝土楼板。加劲张力的模型纳入ACI(2005)，Eurocode2(CEN1993)，和BS8110(1985)已提交并且轻型钢筋混凝土楼板的适用性已进行评估。计算模型的三个代码瞬时挠度进行了比较与来自11个实验室测试测量挠度在含有不同数量的钢筋板。在Eurocode2方案EP.(5)已被证明是更准确地模拟了瞬时负载变形的加固构件轻型钢筋构件的波形和ACI318（EP.(1)比更为可靠的方法。出自：JOURNALOFSTRUCTURALENGINEERING©ASCE/JUNE200728 宁波工程学院本科毕业设计（论文）—外文翻译参考文献[1]AmericanConcreteInstitute（ACI）.（2005）.“Buildingcoderequirementsforstructuralconcrete.”ACI318-05,ACICommittee318,Detroit.[2]Bischoff,P.H.(2005).“Reevaluationofdeflectionpredictionforconcretebeamsreinforcedwithsteelandfiber-reinforcepolymerbars.”J.Struct.Eng.,131(5),752–767.[3]Branson,D.E.(1965).“Instantaneousandtime-dependentdeflectionsofsimpleandcontinuousreinforcedconcretebeams.”HPRRep.No.7,1,AlabamaHighwayDept.,BureauofPublicRoads,Ala.[4]BritishStandardsInstitution(BS).（1985）.“Structuraluseofconcrete,Part2,codeofpracticeforspecialcircumstances.”BS8100:Part2:1985,BritishStandard,London,England.[5]EuropeanCommitteeforStandardization（CEN）.（1992）.“Eurocode2:DesignofconcretestructuresPart1-1:Generalrulesforbuildings.”DDENV1992-1-1,EuropeanPrestandard,Brussels,Belgium.[6]Gilbert,R.I.（2003）.“DeflectionbysimplifiedcalculationinAS3600-2001—Onthedeterminationoffcs.”AustralianJ.StructuralEngineering,5（1）,61–71.[7]StandardsAustralia（AS）.（2001）.“Australianstandardforconcretestructures.”AS3600-2001,Sydney,Australia.JOURNAL28 宁波工程学院本科毕业设计（论文）—外文翻译外文原稿2TheTwelfthEastAsia-PacificConferenceonStructuralEngineeringandConstructionDesignofBuildingStructurestoImprovetheirResistancetoProgressiveCollapseDANethercotaaDepartmentofCivilandEnvironmentalEngineering,ImperialCollegeLondonAbstract：Itisrarenowadaysfora“newtopic”toemergewithintherelativelymaturefieldofStructuralEngineering.Progressivecollapse-or,moreparticularly,understandingthemechanicsofthephenomenonanddevelopingsuitablewaystoaccommodateitsconsiderationwithinournormalframeworksforstructuraldesign-canbesoregarded.BeginningwithillustrationsdrawnfromaroundtheworldoverseveraldecadesandculminatinginthehighlypublicWTCcollapses,thosefeaturesessentialforarepresentativetreatmentareidentifiedandearlydesignapproachesarereviewed.Morerecentworkisthenreported,concentratingondevelopmentsofthepastsevenyearsatImperialCollegeLondon,whereacomprehensiveapproachcapableofbeingimplementedonavarietyoflevelsandsuitablefordirectusebydesignershasbeenunderdevelopment.Illustrativeresultsareusedtoassistinidentifyingsomeofthekeygoverningfeatures,toshowhowquantitativecomparisonsbetweendifferentarrangementsmaynowbemadeandtoillustratetheinappropriatenessofsomepreviousdesignconceptsasawayofdirectlyimprovingresistancetoprogressivecollapse.2011PublishedbyElsevierLtd.Keywords:Compositestructures;ProgressiveCollapse;Robustness;Steelstructures;Structuraldesign28 宁波工程学院本科毕业设计（论文）—外文翻译1.IntroductionOvertimevariousdifferentstructuraldesignphilosophieshavebeenproposed,theirevolutionarynaturereflecting：*cGrowingconcerntoensureadequateperformance.*cImprovedscientificknowledgeofbehaviour.*cEnhancedabilitytomovefromcraftbasedtosciencebasedandthusfromprescriptivetoquantitativelyjustifiedapproachesThiscanbetracedthroughconceptssuchas: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,28 宁波工程学院本科毕业设计（论文）—外文翻译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,itsuseonseveralexamplesdescribedandresultspresentedtoillustratehowitisleadingtoabetterunderstandingofboththemechanicsofprogressivecollapseandthewaysinwhichstructuralengineerscanbestconfiguretheirstructuressoastoprovideenhancedresistance28 宁波工程学院本科毕业设计（论文）—外文翻译2.DesigntoresistprogressivecollapseThetwomostfrequentlyuseddesignapproachesintendedtoaddresstheissueofprogressivecollapseare:*cProvidingtyingcapacity*cCheckingalternateloadpathsFigure1:TieForcesinaFrameStructureThefirstisessentiallyprescriptiveandconsistsofensuringthatbeams,columns,connectionsandfloor(orroof)canacttogethertoprovideaspecifiedminimumlevelofhorizontaltyingresistance;theactualvaluesrequiredarenormallyrelatedtotheverticalloading.Figure1,whichistakenfromrecentUSGuidance(SEI2010),illustratestheprinciple.Theapproachissimpletoappreciate,requiresminimalstructuralcalculationand,insituationswheretheoriginalprovisionsarefoundtobeinadequate,canbemadetoworkbyprovidingmoresubstantialconnectionsand/oradditionalreinforcementinfloor28 宁波工程学院本科毕业设计（论文）—外文翻译slabsInaninterestingrecentdevelopment,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.28 宁波工程学院本科毕业设计（论文）—外文翻译3.EssentialfeaturesofprogressivecollapseThreefeatureshavepreviously(Nethercot2010)beingidentifiedasessentialcomponentsofanyreasonablyrealisticapproachtodesignagainstprogressivecollapse:*cEventstakeplaceoveraveryshorttimescaleandtheactualfailureisthereforedynamic.*cItinvolvesgrossdeformations,generatinglargestrains,leadingtoinelasticbehaviouraswellaschangeofgeometryeffects.*cFailureessentiallycorrespondstoaninabilityofthestructureinitsdamagedstatetoadoptanewpositionofequilibriumwithoutseparationofkeyelements.Figure2:Simplifiedmulti-levelapproachforprogressivecollapseassessmentAdditionalfeatures,designedtomaketheapproachattractiveforusebypracticing28 宁波工程学院本科毕业设计（论文）—外文翻译Engineershavealsobeenproposed(Nethercot2010):*cProcessshouldconsistofaseriesofstepsbroadlysimilarinconcepttothoseusedfor“conventional”structuraldesign.*cItshould,preferably,becapableofimplementationatavarietyatlevelsofcomplexity–withthechoicereflectingtheimportanceofthestructure.*cAnyrequiredanalysisshouldutilisefamiliartechniques;wheretheserequirecomputationsbeyond“handmethods”,theseshouldbebasedontheuseofavailableanalysissoftware.*cArealisticandrecognisablecriterionoffailureshouldbeused.*cApproachshouldpermitstudyofcauseandeffectandbesuitableforthemakingofquantitativecomparisons.ItwasagainstthisbackgroundthatthestudiesatImperialCollegeLondonhavebeenundertaken.Anapproachincorporatingthethreeessentialfeaturesbutobservingthefivedesirablefeatureswasoriginallydeveloped(Vlassis2007);ithassubsequentlybeenrefined(Stylianidis2010).Althoughthestartingpointwascolumnremoval,theapproachcontainsanumberofdistinctivefeatures:*cAlthoughdynamicresponseisallowedfor,onlystaticanalysisisrequired(Izzuddinetal2007).*cTheapproachmaybeimplementedatstructure,sub-structure,floorgrillageorindividualbeamlevel,seeFigure2.*cArealisticcriterionoffailureisemployed,correspondingtoreachingtheductilitylimitsinconnections.*cQuantitativecomparisonsbetweenalternativestructuralarrangementsmayreadilybemade.*cTheapproachmaybeimplementedusingonlyexplicitformulae,therebypermittingsimpleandrapidcalculation.Fulldetailsofthemethod,bothinitsoriginalformwhichutilisesADAPTICtoperformthecalculationsandinitssimplifiedform,maybefoundintheseriesofImperialpapers(2-12).28 宁波工程学院本科毕业设计（论文）—外文翻译*a)Firstyieldingofthetensilecomponents(topboltrowofthesupportconnection)*b)Ultimatecapacityofthebeamflangeatoneoftheconnections(support)*c)Ultimatecapacityofthesystem(failureofthebottomboltrowofthemid-spanconnection)*d)Theaxialloadbecomeszero(thedeflectionofthebeamwheretheaxialloadchangesfromcompressivetotensile)*e)Thedeflectionofthebeamwheretheaxialloadbecomesequaltotheflangecapacityofoneoftheconnections(mid-spanconnection)Figure3:Non-linearstaticresponseforasinglebeam28 宁波工程学院本科毕业设计（论文）—外文翻译中文翻译2通过建筑结构设计以改善建筑物的抗倒性DANethercota土木与环境工程学院——伦敦帝国学院摘要：如今的“新话题”出现在相对成熟的结构工程领域这是一件罕见的事。抗连续倒塌，或者，更特别的是，了解力学的现象和发展适当的方式，以适应我们正常的框架内审议的结构设计，可以这么认为。在过去的几十年，从来自世界各地的插图画开始，到高高的世贸中心倒塌为止，这些功能必不可少的为具有代表性的治疗和早期的设计方法进行了综述。最近的工作是当时的报道，集中精力在过去7年在伦敦大学帝国学院的发展，在一个能使用各种水平和由设计师一直在发展适合直接使用的综合方法。说明性的结果是用来帮助发现一些关键的管理功能，去展示如何定量比较安排现在可能使和说明赫尔墨斯的一些以前的设计概念之间的不同来直接改善抗倒性。关键词：复合结构，渐进式折叠，鲁棒性，钢铁结构，结构设计28 宁波工程学院本科毕业设计（论文）—外文翻译1.引言随着时间的推移各种不同的结构设计原理被提出,他们发展的自然回想：*c越来越关注确保足够的性能。*c改进过的性能的科学知识。*c加强能力从工艺为基础的移动科学依据从而从规范的定量合理的方法。这可以通过追踪的概念,如:容许应力，强度极限，极限状态和基础性能。作为客户：用户和公众已经变得越来越复杂,因此要求更高的期望，因此，它成为必要的设计师代替一个永久的越来越多的结构性问题的范围的主要是通过考虑达到这个条件将或多或少受到不可接受的方法。所以问题不是以前认为（或只允许在一个隐式的,基本上复制过去的令人满意的性能,方式）开始需要显式的形式的关注：需求评估，模型行为和识别合适的失效准则。论题的处理比如疲劳，耐火性，耐久性和适用性都可以被看作是这个模式。举一个具体的例子：设计充分耐火钢框架建筑开始(已经被认可的)和简单的法定规则对混凝土外层脆弱的构件。但是,近年来,发展成为一个复杂的消防工程学科，关心火灾荷载，提供防护系统,如洒水装置，在发生火灾情况下的反应的计算,能够使定量对比结构安排之间选择。不仅导致了在某种意义上不提供防火时明显的经济效益,在它给了只有微不足道的好处的时候；它也导致了消防安全通道更好的调节原则的理解和明智的行事能力在设计适合安排一个合适的评估基础上的需要。在罗南点于1968年在伦敦坍塌之前，鲁棒性原则，抗连续性倒塌，非比例破坏等是不属于工程词汇里的。这栋在18层发生瓦斯爆炸被破坏的22层预制混凝土公寓建筑导致了新的英国建筑法规诞生。取缔了多年来所谓的系统构建方案，拆除了几个完整的建筑物，排除高层建筑物里的临时瓦斯和建立建构安全方面的常务委员会。最终，合理设计的预处理的好处是公认的，安全的方法来安装燃气设计然后开始进入工业。然后，结构设计指导在当时产生——仍然决定了很多现在的条款——是自然本质上的处方式,没有真正的链接到实际的性能。后来，连续倒塌的发生率如同MurraghBuilding和世贸中心带来增加如何合理地考虑那些结构的设计实际现象和问题的关注，它被认为是合适的。在这样做,当然,至关重要的风险,包括一个触发事件和失败的结果,所以更繁重的结构要求被适当地使用。可以说，一个不成比例的反应在风险/后果是很低/很轻的地方要求昂贵的附加条款的情况下，也许如同未能解决那些情况在风险/后果是高/严重的地方一样有害。28 宁波工程学院本科毕业设计（论文）—外文翻译本文将回顾当前用来设计抵制连续倒塌的方法和对比过去七年在伦敦大学帝国理工学院进行的这些工作，那里的目标是提供一个依据于实际方法适合用在常规设计。方法的基本特征将被提交，它被使用在几个例子的描述和结果来说明它是如何导致更好的连续倒塌的机制的原理和结构工程师的方式能最好的配置结构,以提供增强的抗性。28 宁波工程学院本科毕业设计（论文）—外文翻译2.设计抵抗连续倒塌两种最常用设计方法旨在解决连续倒塌这一问题：*c提供绑扎能力*c检查交替的荷载通道图1:领带部队在一个框架结构首先，本质上的规范和包括确保梁，柱，楼梯和楼板（或者屋盖）可以联合起来提供一个规定的低级的水平联系抗力等级；垂直荷载的实际值要求是通常有相关的。图1，这个来自最近的USGuidance，演示了原理。这个方法对于观察是简单的，只需要很少的结构计算和在最初的规定被发现是不充分的的情况下，能通过提供更多的实质性的连接或在一个有趣的近代发展中水泥楼板中施加额外加固，认识到链式反应的连接的生成，USGuidance已经限制可以展示相关的连接可以携带所需的弹性元件同时进行0.2光辉的旋转的情况的结构构件之间的绑扎的使用。这是不可能的，连系材料应该通过楼板和屋盖。无论如何，近代研究（Nethercotetal2010a;Nethercotetal2010b）都建议绑扎力相关较弱和实际抗力去抗连续倒塌。此外，它被规范不允许有意义的替代安排的比较——结构设计的一个基本特征。在其最频繁使用的形式替代负载路径方法假定一个单柱的瞬时损耗，然后需要这作为结果的被损伤的构件的能力去渡过这个损失已经被合适的计算证明（GudmundssonandIzzuddin2010）。该方法可以在分析方面的高度化的不同程度被实现；比如，在美国最近的研究为线性静力分析，非线性静态或28 宁波工程学院本科毕业设计（论文）—外文翻译非线性动态分析制定规定和为各自的使用提供一些指导。它也可以被使用作为基点为特定结构或特定工作（如法医）的更精致的数字的研究；最好的这些——可能是计算非常苛刻的——已经证明了他们的能力去紧密地复制的真实的可观察的特性。3.抗连续倒塌的基本特性三个特征已经预先被鉴证出作为任何合理的现实的方法去设计对抗连续倒塌的必要部分：*c事件发生在非常短的时间段内和正在的失败是因此动态。*c它包括总变形，发生大应变，导致非弹性行为和几何效果的改变一样。*c失败基本上对应于在受损状态下构件的无能通过一个新的没有关键元素的分离的平衡位置图2:简化的多层次评估方法抗连续倒塌附加装置也有人提出，为了让这种方法被工程师使用。*c程序应该由一序列的在概念中广泛相似于那些用于“传统”的结构设计的步骤构成28 宁波工程学院本科毕业设计（论文）—外文翻译*c从实际出发，合理的，能够实现在一个复杂水平上的一个品种——伴随选择反映结构的重要性。*c任何必需的验定都应该利用熟悉的技术；这里需要的计算多于“手工”，是基于可用的分析软件的使用的计算。*c一个现实的知名的破坏的准则应该被使用。*c方法应该允许原因和结果研究和适用于定量判断的制定。正是在这样的背景之下,伦敦帝国学院的研究正在进行。一个结合了三个基本特征但是观察五个理想功能的方法最初被开发（Vlassis2007）；它后来被开发的跟精确（Stylianidis2010）。尽管出发点是柱移动，但该方法包含一些独特的特性：*c虽然动态反应是被允许的，但是只有静态分析是必需的（Izzuddinetal2007）。*c该方法可以实现在结构，亚结构，地板格栅或单梁的标准（见图2）.*c一个现实的破坏标准被采用，对应于在连接中到达延性限制。*c定量对比替代结构安排可能容易就能做出。*c该方法可以实现只使用显式公式，从而允许简单和快速计算。该方法的完整细节，无论是原来利用ADAPTIC执行计算的形式还是在它的简化形式，应该都能在帝国文件中被找到（2-12）。图3：单梁的非线性静力反应28 宁波工程学院本科毕业设计（论文）—外文翻译*a)首先拉力组件的产生（支撑连接的顶级螺栓排）*b)其中的一个连接（支撑）的光束翼缘的总功率*c)系统的总功率（底部中跨连接的螺栓行的破坏）*d)轴向载荷变成零（在轴向载荷从抗压到抗拉变化的地方的梁的挠度）*e)一个连接的翼缘力在轴向荷载变相等的地方的梁的挠度28 宁波工程学院本科毕业设计（论文）—外文翻译参考文献[1]GudmundssonGVandIzzuddinBA.TheSuddenColumnLossIdealisationforDisproportionateCollapseAssessment.TheStructuralEngineer;2010.88pp.22-26.[2]IzzuddinBA,VlassisAG,ElghazouliAY,andNethercotDA.AssessmentofProgressiveCollapseofMulti-StoreyBuildings.ProceedingsICEStructuresandBuildings;2007,Vol.160.No.SB4pp.197-206.[3]IzzuddinBA,VlassisAG,ElghazouliAY,andNethercotDA.ProgressiveCollapseofMulti-StoreyBuildingsduetoSuddenColumnLoss-PartISimplifiedAssessmentFramework,EngineeringStructures;2008,Vol.30,No.5,pp.1308-1318.[4]IzzuddinBA,VlassisAG,ElghazouliAY,andNethercotDA.ProgressiveCollapseofMulti-StoreyBuildingsduetoSuddenColumnLoss-PartII,ApplicationsEngineeringStructures;2008,Vol.30,No.5pp.1424–1438.[5]NethercotDA.UtilisingStrength,StiffenersandDuctilityinEnhancingtheRobustnessofSteelCompositeFrameStructures,inCongressodeConstrucaoMetalicaeMistro,edLdaSilvael,Lisbon;2009,pp.1-3-1-19.[6]NethercotDA.ProgressiveCollapseAnalysisofSteelandCompositeFrameStructures.AIASMaratea;2010,7–10Sept,pp.5-15.[7]NethercotDA,StylianidisP,IzzuddinBA,andElghazouliAY.EnhancingtheRobustnessofSteelandCompositeBuildings,ICASS’09HongKong;2009,pp.105-122.[8]NethercotDA,StylianidisP,IzzuddinBA,andElghazouliAY.ResistingProgressiveCollapsebytheUseofTyingResistance,4thInternationalConferenceonSteel&CompositeStructuresSydneyAustralia;2010a[9]NethercotDA,BlundellD,andStylianidisP.ProgressiveCollapseBehaviourofBareSteelFrames,IvanyiConference;2010b[10]SEIDisproportionateCollapseStandardsandGuidanceCommittee.DesignProcedures,DraftCommitteeDocument;2010[11]StylianidisPM,PhDThesis,DepartmentofCivilandEnvironmentalEngineering,ImperialCollegeLondon,inPreparation;2010[12]VlassisAG.ProgressiveCollapseAssessmentofTallBuildings;PhDThesis,DepartmentofCivilandEnvironmentalEngineering,ImperialCollegeLondon;200728'