土木工程外文翻译-高层建筑结构的发展

DevelopmentofStructuralFormsForTallBuildingsThefirststepstowardsthemodernmultistorybuildingappeartohavebeentakenintheBrongeAge,withtheappearanceoftheemergenceofpropercities.Eventodaythereappearstobeaninstrincrelationshipbetweenthetallbuilding,andthecity.MultistorybuildingswereconsideredacharacteristicofancientRome,andfourandfive-storywoodentenementbuildingswerecommon.ThosebuiltafterthegreatfireofNerousedthenewburntbrickandconcretematerialsintheformofarchandbarrelvaultstructures,whichreplacedtheearlierpostandlintelconstruction.Throughoutthefollowingcenturies,thetwobasicmaterialsusedinbuildingconstructionweretimberandmasonry,althoughtheformerlackedthestrengthrequiredforbuildingsofmorethanabout16minheight,andalwayspresentedafirehazard.Thelatterhadtheadvantagesofhighcompressivestrengthandfireresistance,butsufferedfromitshighweight,whichtendedtooverloadthelowersupports.Thelimitsofthisformofconstructionbecameapparentin1891inthe16-storyMonadnockBuildinginChicagowhichrequiredthelowerwallstobeover2mthick,andwasthelasttallbuildinginthecityforwhichload-bearingmasonrywallswereemployed.Thesocio-econormicproblemswhichfollowedtheindustrializationofthe19thcentury,alliedtotheinsatiabledemandforspaceintheUScities,gaveabigimpetustotallbuildingconstruction.However,thegrowthcouldnothavebeensustainedwithouttwomajortechnicalinnovationsduringthemiddleofthatcentury,namely,thedevelopmentofnewhigherstrengthandstructurallymoreefficientmaterials,wroughtironandsubsequentlysteel,andtheintroductionoftheelevatortofacilitateverticaltransportation.Thenewmaterialallowedthedevelopmentoflightweightframedorskeletalstructures,permittinggreaterheightsandmoreandlargeropeningsinthebuilding.TheforerunnerofthesteelframewhichappearedinChicagoaround1890maywellhavebeenaseven-storyiron-framedManchestercottonmill,builtin1801,inwhichthecontemporaryI-beamshapeappearstohavebeenusedforthefirsttime.TheCrystalPalace,builtfortheLondonInternationalExhibitionof1851,usedacompletelyautonomousironframe,withcolumnsofcastironandbeamsofcastorwroughtiron.Oneofthenotablefeaturesofthisdesignwasthelarge-scaleapproachtowardsmass-productiontechniquestofacilitatefabricationanderection.Althoughthefirstelevatorappearedin1851,inaNewYorkhotel,itspotentialinhigh-risebuildingwasapparentlynotrealizeduntilitsincorporationintheEquitableLifeInsuranceCompanyBuildinginNewYorkin1870.Forthefirsttime,thismadetheupperstoriesasattractivearentingpropositionasthelowerones,andinsodoingmadethetaller-than-averagestructurefinanciallyviable.Improvedsteeldesignmethodsandconstructiontechniquesallowedsteel-framedstructuretogrowsteadilyupwards,althoughprogresssloweddownduringtheperiodoftheFirstWorldWar.In1909,the50-storyMetropolitanTowerBuilding.ThisgoldenageofAmericanskyscraperconstructionculminatedin1931initscrowningglory,theEmpireStateBuilding.Its102storiesrosetoaheightof381mwhichhasnowincreasedto449mwiththeadditionofaTVaerial.Thebuildingused57000t(US)ofstructuralsteel,nearly53500mofconcrete,andwasdesignedandbuiltintherecordtimeof17months.Althoughreinforcedconcreteconstructionbegantobeadoptedseriouslyaroundtheturnofthecentury,itdosenotappeartohavebeenusedproperlyformultistorybuildingsuntilaftertheendoftheFirstWorldWar.Theinherentadvantagesofthecompositematerialwerenotatthattimefullyappreciated,andtheearlysystemsweredevelopedpurelyasimitationsofsteelstructures.Anearlylandmarkwasthe16-storyIngallsBuildinginCincinnatti,Ohio,(1903),whichwasnotsupersededuntil1915whenthe19-storyMedicalArtsBuildinginDallaswashailedastheword'stallestreinforcedconcretebuilding.Thereafter,progresswasslowandintermittent,andwhentheEmpireStateBuildingwascompleted,theExchangeBuildinginSeattlehadattainedaheightofonly23stories.Theeconomicdepressionofthe1930sputanendtothegreatskyscraperera,anditwasnotuntilsomeyearsaftertheendoftheSecondWorldWarthattheconstructionofhigh-risebuildingrecommend,bringingwithitnewstructuralandarchitecturalsolution.However,moderndevelopmentshaveproducednewstructurallayouts,improvedmaterialqualities,andbetterdesignandconstructiontechniquesratherthansignificantincreasesinheight.Designphilosophiesalteredduringtheperiodofrecessionandwar.Theearliertallbuildingswerecharacterizedbyhavingheavystructuralelementsandbeingverystiffduetothehighin-planerigiditiesoftheinteriorpartitionsandfaadecladdingwithlowareasoffenestrastion.However,modernofficeblockstendtobecharacterizedbylightdemountablepartitionstoaloeplanningflexibilityofoccupancy,exteriorglasscurtainwalls,andlightersectionsasaresultofhigh-strengthconcreteandsteelmaterial,whilstnon-load-bearinginfillshavegivewaytoload-bearingwallswhichsimultaneouslydivideandenclosespace.Asaresult,muchofthehiddenreserveoftheearlierbuildingshasdisappeared,andthebasicstructuremustnowprovideboththerequiredstrengthandstiffnessagainstverticalandlateralloads.Consequently,thelasttheredecadeshaveseenmajorchangesinstructuralframingsystemsfortallbuilding.Thebuildingframewastraditionallydesignedtoresistthegravitationalloadswhicharealwayspresentandformthereasonforitsveryexistence.Theseloadsderivefromtheself-weightoftheverticalandhorizontalstructuralcomponents,includingthecladding,andthesuperimposedfloorloadings.Therewillgiverisetonecessaryminimumcross-sectionalareas,basedonallowablestresslevels,fortheverticalcolumnandwallelements,inthedesign.Inthepastthreedecades,therefore,designershavesoughttoevolvestructuralsystemswhichwillreduceasfaraspossiblethecostandweightofmaterials,whilesimultaneouslyfulfillingtheprimarybuildingfunction.Asuitablearrangementoftheverticalcolumnandwallelements,alliedtothehorizontalfloorsystem,isrequiredwhichwillprovideaneconomicmethodofresistinglateralforcesandminimizingtheadditionalheightpremium.Althoughtheprovisionofloadpathsforgravitationalforcesislimited,thereisconsiderablescopefororganizingthestructuralsystemtoresistlateralforcesasefficientlyaspossible.Thismaybeachievedbythejudiciousdispositionoftheverticalelementsandtheirinterconnectionbyhorizontalstructuralcomponentsinordertoresistmomentbyaxialforcesratherthanbendingmomentsintheseverticalelements.Ingeneral,differentstructuralsystemshaveevolvedforresidentialandofficebuildingshavebeenconstructedinwhichthetwocategorieshavebeenmixed,inadeliberateattempttorevitalizemoribundcitycenterareas.Thebasicfunctionalrequirementofaresidentialbuildingistheprovisionofdiscretedwellingunitsforgroupsofindividuals.Thesehavecommonrequirementsofliving,sleeping,cookingandtoiletareas,whichmustbeseparatedbypartitionswhichofferfireandacousticinsulationbetweendwelling.Framedstructuresmaybeusefullyemployedforresidentialbuildings,sincethepresenceofpermanentpartitionsallowsthecolumnlayouttothecorrespondtothearchitecturalplan.However,thesedependontherigidityofthejointsfortheirresistancetolateralforces,andtendtobecomeuneconomicatheightsabove20-25stories,dependingontheoveralldimensions,whenwindforcesbegintocontrolthedesign,anditbecomesincreasinglydifficulttomeetstiffnessrequirements.Sincetheirintroductioninthelate1940s,shearwalls,actingeitherindependenceorintheformofcoreassemblies,havebeenusedextensivelyasadditionalstiffeningelementsfortraditionalframestructures.Inordertoprovideadequatefireandacousticinsulationbetweendwellings,infillpanelsofbrickworkorblockworkareintroducedintotheframes.Althoughtechniquesexistforassessingtheinfluenceoftheseinfillpanelsonthestrengthandstiffnessoftheframe,theyaregenerallyassumedtobenon-load-bearing,inviewofthedesigner,sfearthattheymaybeeitherremovedorperforatedforachangeoffunctionatsomefuturedate,aswellasthedifficultyofachievingatightfitbetweenaninfillpanelandthesurroundingframe.Consequently,latertrendsweretoutilizethewallswhicharerequiredforspacedivisioninastructuralcontext,andomittherelativelyheavyinfillswhichcouldnotbeemployedinaloadresistingcapacity.Thishasledtothedevelopmentoftheshearwallbuilding,inwhichstructuralwallsareusedtodivideandenclosespace,whilesimultaneouslyresistingbothverticalandhorizontalloads.Thesewallsaregenerallyofprecastlargepanelorreinforcedconcretein-situconstruction,butconcreteblockworkandbrickworkhavealsobeenemployed,alliedtoprecastfloorslabconstruction.Sincethefunctionalplanrequiresalargenumberofdivisionwallsbetweendwellings,itisfrequentlyfoundthattheminimumthicknessrequiredforfireandacousticinsulationwillbeadequateforstructuralrequirementsalso.Functionalrequirementsforthisformofbuildinghavegivenrisetotheslabblockofcross-wallconstruction,inwhichhorizontalmovementofoccupantsisachievedbylongcorridorsrunningalongthelengthofthebuilding,withapartmentspositionedoneitherside,ortopointblocksinwhichapartmentsaregroupedaroundtheareaofverticaltransportation,liftsandstairwells.Ineachcase,thebasicstructureconsistsoforthogonalsystemsofshearwalls,connectedbyfloorslabsandperhapslintelbeamsspanningacrossdoor,windoworcorridoropenings,toformastiffstructure.Structuralcores,whichconsistofassembliesofwallsalongtheirverticaledgestoformopenorpartiallyclosedboxsectionsenclosingliftshaftsandstairwellsactasadditionalstrongpointsinsuchbuildings,andcanplayamajorroleinresistinglateralforces.Inadesign,theshearwallsmustbesufficientlystifftomeettheimposeddeflectioncriterion,andinaddition,shouldbesoarrangedthattensilestressescausedbywindforcesarelessthanthecompressivestressesproducedbytheweightofthebuilding.Acarefularrangementofwallscanimprovestructuralefficiencywhichconsistsofaseriesofcross-wallsandtwoflankwallsrunningacrossthewidthofthebuilding.Asareasonableapproximation,eachwallwillcarrytheverticalloadsassociatedwiththesurroundingtributaryareashownhatchedinthefigure,sothatthecompressivestressesinthecrosswallswillberoughlytwicethoseintheflankwalls,iftheyareofthesamethickness,However,ifallwallsdeflectequallyundertheactionofthewindforces,asaresultofthehighin-planerigidityofthefloorslabs,thebendingmomentandassociatedstressesineachwallwillbeproportionalrespectivelytoitsmomentofinertiaandsectionmodulus.Consequently,themaximumtensilestressesintheflankwallswillberoughlyfourtimesthoseinthecross-walls.Theflankwallsmaythenbesubjectedtounacceptabletensilestresses.Amoreefficientstructurecouldbeachievedbysplittingeachflankwallintotwounits,perhapsbyforminganarchitecturalfeaturebyhavingthemoutofalignment.Theflankwallswouldthenbesubjectedtoroughlythesamewindmomentsasthecross-walls,andthetensilewindstressesreducedbyafactorofmorethanfour.Shearwallstructuresarewellsuitedforresistingseismicloadings,andhaveperformedwellinrecentdisasters.Theytendtobecomeeconomicalassoonaslateralforcesaffectthedesignandproportioningofflatplateorframedsystems.However,theydopossessthedisadvantageofaninherentlackofflexibilityforfuturemodifications,whilediscontinuitiesarefrequentlyrequiredatthecriticalgroundlevelareatoprovideadifferentarchitecturalfunctiononthegroundfloor,andspecialdetailingbecomesnecessary.Arelativerecentinnovationwhichisparticularlysuitableforresidentialblocksisthestaggeredwall-beamsystem.Thestructureconsistsofaseriesofparallelbents,eachcomprisingcolumnswithperforatedstory-heightwallsbetweenthem,inalternatebays.Eachwallpanelactsinconjunctionwith,andsupports,theslababoveandbelowtoformacompositeI-beam.Bythisdevice,largeclearareasarecreatedoneachfloor,yetthefloorslabsspanonlyhalfthedistancebetweenadjacentwallbeams,fromthebottomofonetothetopofthenext.Thewindshearsaretransmittedthroughthefloorslabsfromthewallbeamsononestorytoshoesonthenext.Similarsystemsarepossiblewithstaggeredtrussesratherthanstagteredwalls.Theessentialfunctionalrequirementofanofficebuildingistheprovisionofareasunobstructedaspossiblebywallsorcolumnstoalloweachoccupanttodesignthepartitioningandspaceenclosuremostsuitableforhisparticularbusinessorganization.Thepartitionlayoutwillgenerallyalterwhentenantschange,andthisnecessitatesflexibilityinthedistributionofthevariousservicestoanyparticularfloor.Asaresult,servicestendtobecarriedverticallywithinoneormoreservicecores,andadistributionnetworkrunbeneaththestructuralfloorslabtotheentirefloorarea.Byjudiciousplanningofthecolumnlayouttomaximizetheopenfloorareas,shearwall-frameinteractivestructuresmayalsobeemployedforofficeblocks,althoughthepresenceofthecolumnsmaymakeitdifficulttoachievethedesiredplanningflexibility.Possiblythesimplestmethodofcreatingopenfloorareasistouseacentralconcreteshearcore,whichcarriesallessentialservicesandwhichisdesignedtoresistalllateralforces.Thefloorsystemspansbetweenthecentralcoreandtheexteriorfacadecolumns,andalargeunobstructedfloorareaiscreatedbetweenthetwoverticalcomponents.Theexteriorcolumnscanbedesignedtobeeffectivelypin-connectedateachfloorlevel,sothattheytransmitverticalforcesonly,inconjunctionwiththeinteriorcore.Theseexteriorcolumnsarefrequentlyprecasttoformasculpturedfacade.Anotherpossibilityistoprovideacoreateachend,especiallyifthebuildingisslender.However,inordertosupportthefloorslabsintheinterior,itisthennecessarytoprovideaspinebeamrunningbetweenthecores,whichwillrequireadditionalsupportinginteriorcolumns.Ifthefloorspansarelong,itmaybecomeeconomictointroduceadditionalcolumnsintheinteriortoreducethespanoftheslabs.Insomesituations,adifferentarchitecturalarrangementisdesiredatgroundlevel,whichprecludesthecolumnsbeingtakenrightdowntogroundlevel.Inthatcase,heavycantileversarerequiredtocollectthecolumnloadsfromthelevelsaboveandtransmitthentothecentralcore.Analternativeapproachistointroducearooftrussineitherprestressedconcreteorsteelconstruction,atthetopofthecore.Thefloorslabsmaythenbesupportedbetweenthecoreandasystemofsteelhangerssuspendedfromtherooftruss.Thesystemhasthearchitecturaladvantageoflightnessoffacade,andcansimplifyconstructiononacongestedcitysite.Thecoremaybeslipformed,andthefloorslabscastonsiteandsimplyhoistedintoposition.However,thereistheinherentstructuraldisadvantagethatthecoreissubjectedtotheentireweightofthebuilding,compressiveforcesarehighatrooflevel,andsettlementmayposeproblems.Intermediateleveltrusseswillassistincarryingtheexternaltieforcesandreducetheextensionsofthehangers.Afurtherincreaseinlateralstiffnesscanbeachievedifthecentralcoreorshearwallsystemistiedtotheexteriorcolumnsbydeep(usuallystoryheight)flexuralmembersortrussesatthetopandpossiblyatotherintermediatelevels.Theeffectoftheseconnectionsistocreateanoverallframedsystem,whichmobilizestheaxialstiffnessoftheexteriorcolumnstoresistwindforces.Theobjectiveistocausethestructuretoactmoreasaverticalcantileverbeam,andsoresistthewindbyaxialforcesin,ratherthanbybendingof.Thelargerleverarminvolvedensuresthatlargemomentsofresistancemaybeproducedbyrelativelylowcolumnforces.Thefirstreinforcedconcretebuildingtoutilizethisconceptwasthe51-storyPlaceVictoriaBuildinginMontreal(1964),inwhichanX-shapedcoreislinkedatfourlevelsbystory-highgraderstothemassivecornercolumns.Asbuildingbecometaller,theuseofacoreonitsowntoresistlateralforceswillleadtounusuallylargecores,occupyingtoolargearatioofagivenfloorarea,andleadingtouneconomicsolutions.Theefficiencycanbeincreasedsubstantiallyiftheouterfacadeisreplacedbyarigidly-jointedframework,whichcanbeusedtoresistlateralaswellasverticalforces.Theoutershellthenactseffectivelyasaclosedbox-likestructure,whosefacesareformedofrigidly-jointedframepanels,orasahighlyperforatedtube,whosecross-sectionalshapeismaintainedbythefloorslabsactingashorizontaldiaphragms.Acombinationoftheframed-tubeconceptwiththeshearwall-frameinteractionconceptyieldsthestructuralfromtermedthetube-intubesystem,inwhichanexteriorcloselyspacedcolumnsystemisconstrainedbythefloorslabstoactincollaborationwithaverystiffshearcoreenclosingthecentralservicearea.Thefirstdesignapplicationofthisformofshearwall-frameinteractivebehaviourappearstohavebeeninthe38-storyBrunswickBuildinginChicago,completedin1962.Inthiscase,thelateralforcesareresistedbyboththeinteriorcoreandouterframedtube,inproportiontotheirstiffnesses.Thelargeleverarminvolvedbetweenoppositenormalfacesoftheexteriortubegiverisetoanefficientmoment-resistingstructure,akintoanordinarytubularstructuralcomponent.Whilethesystemisveryusefulinthecreationofflexiblespacesinofficebuildings,itislesssuitableforverytallapartmentbuildings.Analternativesolutionusingtheframed-tubeconceptwasdevisedfirstforthe43-storyDeWittChestnutApartmentBuildinginChicagoin1965.Inthiscase,theexteriorcolumnswerecloselyspacedat1.68mcentresand,whenrigidlyconnectedto600mmdeepspandrelbeams,gaverisetoarelativelystiffexteriorperforatedtubewhichwasdesignedtoresistallwindforces.Asystemofinteriorcolumnsatapproximately6mspacingwasprovidedtosupporttheflatplatetypeoffloorconstruction.Thecloselyspacedexteriorcolumnsinthisformofconstructionallowsimplermethodsoffixingthewindowglazingdirectlytothecolumnsthemselves.Theclosely-spacedcolumnsinaframedtubemayposeproblemsingainingacrosstothebuildingatgroundlevel,andsomestructuralrearrangementmaybenecessaryinthatregion.Severalcolumnsmayberunintooneatregularintervals,asintheWorldTradeCenter,oradeepgirdermaybeprovidedatfirst-floorleveltotransfercolumnforcestomorewidelyspacedfirst-floorcolumns.Thepureframedtubehasthedisadvantagethatunderbendingaction,aconsiderabledegreeofshearlagoccursinthefacesnormaltothewind,asaresultoftheflexibilityofthespandrelbeams.Thishastheeffectofincreasingthestressesinthecornercolumns,andofreducingthoseintheinnercolumnsofthenormalpanels,andresultsinalossofefficiencyinthedesiredpuretubularactionofthestructure.Warpingofthefloorslabs,andconsequentlydeformationsofinteriorpartitionsandsecondarystructurewilloccur,whichmaybecomeofimportanceindesign.Onetechniquewhichhasbeenemployedtohelpovercomethisproblemistoaddsubstantialdiagonalbracingmembersintheplanesoftheexteriorframes.Theexteriorcolumnsmaythenbemorewidelyspaced,andthediagonals,alignedatsome45°tothevertical,servetotietogethertheexteriorcolumnsandspandrelbeamstoformfacadetrusses.Consequently,averyrigidcantilevertubeisproduced.Thediagonals,however,posetheirownspecialproblemsinthedesignofthecurtainwallsystem.Althoughthetechniquehasbeenusedonlyinsteelconstructionsofar,thereappearstobenointrinsicreasonwhyitshouldnotbeafeasiblesolutionfortallconcretestructures.Forverytallbuildings,theshearlageffectmaybegreatlyreducedbyaddingadditionalinteriorwebpanelsacrosstheentirewidthofthebuildingineachdirectiontoformamodulartubeorbundled-tubesystem.Theadditionalstiffeningofthestructureproducedbytheinteriorwebsincreasethelocalstresslevelsattheexteriorframejunctionandtherebyreducessubstantiallythenonuniformityofcolumnforcescausedbyshearlag.Thestructuremayberegardedasasetofmodulartubeswhichareinterconnectedwithcommonpanelstoformaperforatedmulti-celltube,inwhichtheframesinthewinddirectionresistthewindshears.Thesystemissuchthatmodulescanbeomittedatdifferentheightstoreducethecross-sectionandstillmaintainthestructuralintegrity.Anytorsionarisingfromtheresultingunsymmetryisreadilyresistedbytheclosed-sectionalformofthemodules.Thebestknownexampleofthisformofconstructionisthe109-story,442mhigh,SearsTowerinChicago,theworld’stallestbuilding.Completedin1974,thebasiccross-sectionalshapeconsistsofnine22.86msquaremodulartubes,foranoverallfloorarea68.58msquare,whichcontinuesuptothe50thfloor.Stepbacks,producedbyaterminationofoneormoreofthemodulartubes,thenoccuratfloor50,66and90,creatingavarietyoffloorconfigurations.Analternativepossibility,yieldingthesamegeneralformofstructuralbehaviour,istouseshearwallstoformtheinteriorwebsoftheframedtubeandcreateanalternativeformofmulti-cellularconstruction.Thisapproachhasbeenadoptedforthe74-story,262mhighWaterTowerPlaceBuilding,Chicago(1976),theworld’stallestconcretebuilding.The64-storytowerwhichrisesfroma12-storybaseisaslendertubeofcross-sectionaldimensions67x29mwhichisbisectedbyaninternaltransverseperforatedshearwalltoformatwo-cellstructure.Thebuildingisamulti-purposeoneandencompassesanhotelandapartmentsinadditiontoofficespace.译文:高层建筑结构的发展建筑的出现应该追溯到青铜器时代，伴随着真正的城市的出现，房子也出现了两层的。甚至是今天高层建筑与城市发展似乎有着本质的联系。多层建筑被认为是古罗马的一大特征。在古罗马，四到五层的木制建筑是很普遍的。那些在尼罗特大火灾后建成的建筑，采用新型的烧制砖块和混凝土材料作成拱门和大量拱形圆顶结构，取代了早期的柱和横梁结构。纵观后来的几个世纪，木材和石材成为应用于建筑结构的两大基本材料。虽然在高于16米的建筑中木材缺乏所需的强度，而且还有着火的危险。而石材具有很高的抗压强度和耐火能力，但是其自重大，易使下部的支撑负荷过重。这种结构形式的限制在1891年芝加哥的16层建筑中显得十分明显，它要求下部的墙有2米多厚，因此它成为城市里最后一座采用承重石墙的建筑。伴随着19世纪工业化发展，社会经济问题与美国城市对空间要求的无法满足，对高层建筑产生了巨大冲击。然而若在那个世纪中叶没有两大主要技术革新，即新型高强且在结构上更有效的材料一精炼的铁及后来的钢材的发展，还有电梯的引入，使得垂直交通变得便利，高层建筑的增长也不可能得到支持。新材料的出现使得轻质框架结构或骨架结构得到发展，还使得建筑有了更高的高度以及更多更大的洞口。大约在1890年出现于芝加哥的钢框架结构的先行者被认为是1801年建成的七层铁框架结构的曼彻斯特棉纺厂，再其建筑过程中当代的工字梁第一次出现了。水晶宫一为1851年伦敦国际汇展而建，采用了完全独立的铁框架，其中柱是由铸铁制成繁荣，而梁是由铸铁或精炼的铁制的。这一设计的显著特征之一就是大规模的运用大量技术成果，使得建筑和施工相当方便。虽然第一部电梯出现于1851年纽约的一座酒店里但是它在高层建筑中的潜力直到1870年用于纽约的家庭生命保险大楼的建筑中才得以明显证实。就这样第一次使得上部楼层和下部楼层一样成为备受欢迎的出租场所，也正因为这样使得高层建筑在财政上要比普通建筑可行。钢结构设计方法和施工技术的改进，使得钢框架结构得以稳步发展。当然这一发展在第一次世界大战期间曾有所减慢。1909年50层的大都市塔楼在纽约建成，紧接着1913年60层高241米的伍尔沃斯大楼也竣工。美国摩天大楼的黄金时期随着1931年帝国大厦圆满竣工而达到顶峰。因为增建了电视天线使得102层的帝国大厦由原来的381米升高到现在的449米。这栋建筑耗用了五万七千吨美国建筑钢材，将近五万三千五百立方的混凝土，而且从设计到竣工仅用了17个月的时间。虽然大约在本世纪初开始认真地采用钢筋混凝土，但是第一次世界大战末以前，它在多层建筑中似乎一直没有被正确使用。组合材料的固有优势再那个时候没有得到完全的重视；而且组合结构早期的设计方法也只是纯粹地模仿钢结构。最早的钢砼建筑便是1903年建成于俄亥俄州的辛辛那提的16层高的英戈尔斯大楼，直到1915年它才被称为世界上最高的钢砼建筑的19层高的达拉斯医学技术大楼所替代。此后，钢砼结构的发展缓慢下来，时有是无，而且在帝国大厦建成的同时，西雅图交易大厦仅仅只建到23层高。二十世纪三十年代的经济萧条给摩天大楼的伟大时期划上了一个句点，直到第二次世界大战末后的一些年里，高层建筑的建造才又恢复，而且引入了新的结构和建筑方案，然而现代发展产生的是新的结构布局、改良的材料质量以及更好的设计技术和施工技术，而不是高度上的巨大增长。设计原理在经济萧条和战争中改变了。早期的高层建筑特征是具有重的结构构件且因为内部隔墙平面刚度很大而非常坚硬，还有在建筑正立面上开有小面积的窗，然而当代的办公楼却以轻质可拆卸隔墙、外部玻璃幕墙、更轻的各结构部分、承重墙代替非承重填充墙为特征。采用轻质可拆卸隔墙可以灵活的布置空间，各部分变轻是因为采用了高强混凝土和钢材，而承重墙可以同时用来分隔空间和围绕空间。结果，大多数早期建筑物的隐蔽部分消失了，而现在的基础结构必须达到所许的强度和刚度，能够承受垂直压力和侧压力。因此在最近的三十年里高层建筑结构框架体系发生了主要变化。由于物体的重力随物体存在而存在，传统的建筑框架都被设计成为来抵抗重力荷载。这些荷载来源于水平的、垂直的各结构部分的自重，包括了装饰层、楼板层的荷载。这样在设计柱和墙体结构中就产生了根据允许应力范围而设计的必需的最小的横截面面积。因此在过去的三十年里设计者门一直在尝试发展尽可能减少成本和材料重量而同时又能满足主要的建筑功能的结构体系，这就需要对与水平楼板系统相连的柱和墙体结构进行合理布置，从而提供一个能抵抗侧向力和最小化附加高度的额外费用的经济方案。虽然所提供的重力荷载路径是有限的，但是仍有相当大的范围来组织结构体系使其尽可能有效的抵抗侧向力。为了抵抗垂直构件中的轴力力矩而不是弯矩，可以通过对垂直构件以及其与水平结构连接部分做审慎明确的处理来实现。总的来说，不同的结构体系已经形成为住宅和办公楼两大体系，反映在它们不同的功能需求上。然而，一些著名的建筑在修建中，故意将这两类建筑混合在一起，试图使垂死的市中心地区获得新生。住宅建筑的基本功能要求是为群体成员提供分割的居住单元。这些居住单元还有生存、睡觉、做饭和厕所的普通功能要求。这就必须要用隔墙分割开来，而且隔墙还要具有在各层居住单元间有防火和隔声的功能。因为永久性隔墙的出现，允许柱的设计与建筑设计相符，框架结构可能会有效地被住宅建筑采用。然而，这些结构的稳定将处决于连接处抵抗侧向力的刚度，而且当结构达到20~25层时会变得不够经济，因为依据结构的整体尺寸，风力将在设计中起控制作用，要达到所需的刚度也就会越来越困难。自从二十世纪四十年代末引入了剪力墙一一要么独立存在，要么以核心组装的形式存在。它已经广泛的被采用，用来作为传统框架结构的附加刚度部分。为了在住宅间提供足够的防火、隔音功能，砖和砌块砌筑的填充嵌板被引入到框架结构中，虽然存在可用来评估这些填充板材对框架强度和刚度影响的技术，但是依据设计者的想法，担心这些板材在将来末一天因功能改变要么被去掉要么就是被打孔，还有填充嵌板与周围框架达到紧密地适应的困难性，所以这些嵌板都被认为是不承重的。因此后来的趋势都是利用墙体来在结构物中划分空间，并省去了相对较重的不能用于承受荷载的填充墙。由此导致了剪力墙建筑物的出现一在该类建筑中结构墙用来划分和围隔空间，同时也承受竖向和水平荷载。这些墙一般都是预制的大块嵌板或者是现场浇注的钢筋混凝土结构，但是混凝土砌块结构和砖结构也被采用，与预制楼板结构相似。因为功能设计中要求住宅间有许多隔墙，所以也就频繁地发现防火隔音所需的最小厚度也将要充分满足结构需求。这种建筑形式的功能要求导致了厚板块横墙建筑和尖头块建筑的出现；前者中，居住者书评方向的活动就是靠在建筑物中间的沿纵向的走廊实现的，而走廊两边便是一套套公寓房间；后者中公寓房间是围绕着垂直交通部分一一电梯和楼梯而布局的。在每种建筑中，基本结构都是由垂直的剪力墙体系组成，而这些剪力墙又通过楼板或是宽约门窗、走廊洞口的横梁联系起来，形成一个稳定的结构。结构的核心部分是由集在一起的墙体组成。这些墙体沿着它们的垂直边缘连接起来，形成一些全开或半开的围绕电梯井和楼梯间的盒子似的部分。结构的这些核心在建筑物中起着加强点的作用，在承担侧向力方面起着主要作用。在设计中，剪力墙必须有足够刚度来符合强制的侧移标准，且除此之外，还应该布置合理使得由风力引起的拉应力小于建筑物自重引起的压应力。这种能提高结构功效的墙体布局可以通过图19.3简单描述；它由一系列的横墙和两道穿越建筑宽度方向的侧墙组成。我们作一个有理由的近似处理认为：每道横墙承受了图中阴影部分面积的荷载，如果横墙与纵墙一样厚，这样横墙上的压应力将会是侧墙上的两倍，然而如果所有的墙在风荷载作用下发生的侧移都相等，作为钢筋混凝土楼板平面内刚度很大的结果就是，每道墙的弯矩和联系应力将分别与它的截面抗弯和剪切模量成比例。因此侧墙上的最大拉应力大约是横墙撒谎能够的4倍，侧墙将由拉应力控制。一种更有效的结构可以通过将每道侧墙分开为两个单元，或是为了形成一种建筑效果而使它们有所错开来实现。这样侧墙大体上与横墙一样由相同风荷载引起的弯矩来控制，而且风力产生的拉应力减少了4成多。剪力墙结构非常适应于抵抗地震荷载，而且在最近的地震灾害中表现得非常好。当侧向力影响到设计和楼板或框架体系的均衡时，剪力墙结构变得很经济。然而它们也有固有的缺点：将来改建缺乏灵活性；因要在地下室提供不同的建筑功能而需要底层有些地方剪力墙不落地，这就出现了剪力墙的不连续性，在设计时这就需要特别详细的说明。一种特别适合住宅群的相对新近的结构改革便是交错的墙梁体系结构这种结构由一系列平行的单元组成，每一个单元都包含有柱子和柱子间开有洞口的墙。每片墙