外文翻译-抗侧向荷载的结构体系

StructuralsystemstoresistlateralloadsCommonlyusedstructuralsystemsWithloadsmeasuredintensofthousandskips,thereislittleroominthedesignofhigh-risebuildingsforexcessivelycomplexthoughts.Indeed,thebetterhigh-risebuildingscarrytheuniversaltraitsofsimplicityofthoughtandclarityofexpression.Itdoesnotfollowthatthereisnoroomforgrandthoughts.Indeed,itiswithsuchgrandthoughtsthatthenewfamilyofhigh-risebuildingshasevolved.Perhapsmoreimportant,thenewconceptsofbutafewyearsagohavebecomecommonplaceintoday’stechnology.Omittingsomeconceptsthatarerelatedstrictlytothematerialsofconstruction,themostcommonlyusedstructuralsystemsusedinhigh-risebuildingscanbecategorizedasfollows:Moment-resistingframes.Bracedframes,includingeccentricallybracedframes.Shearwalls,includingsteelplateshearwalls.Tube-in-tubestructures.Tube-in-tubestructures.Core-interactivestructures.Cellularorbundled-tubesystems.Particularlywiththerecenttrendtowardmorecomplexforms,butinresponsealsototheneedforincreasedstiffnesstoresisttheforcesfromwindandearthquake,mosthigh-risebuildingshavestructuralsystemsbuiltupofcombinationsofframes,bracedbents,shearwalls,andrelatedsystems.Further,forthetallerbuildings,themajoritiesarecomposedofinteractiveelementsinthree-dimensionalarrays.Themethodofcombiningtheseelementsistheveryessenceofthedesignprocessforhigh-risebuildings.Thesecombinationsneedevolveinresponsetoenvironmental,functional,andcostconsiderationssoastoprovideefficientstructuresthatprovokethearchitecturaldevelopmenttonewheights.Thisisnottosaythatimaginativestructuraldesigncancreategreatarchitecture.Tothecontrary,manyexamplesoffinearchitecturehavebeencreatedwithonlymoderatesupportfromthestructuralengineer,whileonlyfinestructure,notgreatarchitecture,canbedevelopedwithoutthegeniusandtheleadershipofatalentedarchitect.Inanyevent,thebestofbothisneededtoformulateatrulyextraordinarydesignofahigh-risebuilding.Whilecomprehensivediscussionsofthesesevensystemsaregenerallyavailableintheliterature,furtherdiscussioniswarrantedhere.Theessenceofthedesignprocessisdistributedthroughoutthediscussion.Moment-ResistingFramesPerhapsthemostcommonlyusedsysteminlow-tomedium-risebuildings,themoment-resistingframe,ischaracterizedbylinearhorizontalandverticalmembersconnectedessentiallyrigidlyattheirjoints.Suchframesareusedasastand-alonesystemorincombinationwithothersystemssoastoprovidetheneededresistancetohorizontalloads.Inthetallerofhigh-risebuildings,thesystemislikelytobefoundinappropriateforastand-alonesystem,thisbecauseofthedifficultyinmobilizingsufficientstiffnessunderlateralforces.AnalysiscanbeaccomplishedbySTRESS,STRUDL,orahostofotherappropriatecomputerprograms;analysisbytheso-calledportalmethodofthecantilevermethodhasnoplaceintoday’stechnology.Becauseoftheintrinsicflexibilityofthecolumn/girderintersection,andbecausepreliminarydesignsshouldaimtohighlightweaknessesofsystems,itisnotunusualtousecenter-to-centerdimensionsfortheframeinthepreliminaryanalysis.Ofcourse,inthelatterphasesofdesign,arealisticappraisalin-jointdeformationisessential.BracedFramesThebracedframe,intrinsicallystifferthanthemoment–resistingframe,findsalsogreaterapplicationtohigher-risebuildings.Thesystemischaracterizedbylinearhorizontal,vertical,anddiagonalmembers,connectedsimplyorrigidlyattheirjoints.Itisusedcommonlyinconjunctionwithothersystemsfortallerbuildingsandasastand-alonesysteminlow-tomedium-risebuildings.Whiletheuseofstructuralsteelinbracedframesiscommon,concreteframesaremorelikelytobeofthelarger-scalevariety.Ofspecialinterestinareasofhighseismicityistheuseoftheeccentricbracedframe.Again,analysiscanbebySTRESS,STRUDL,oranyoneofaseriesoftwo–orthreedimensionalanalysiscomputerprograms.Andagain,center-to-centerdimensionsareusedcommonlyinthepreliminaryanalysis.ShearwallsTheshearwallisyetanotherstepforwardalongaprogressionofever-stifferstructuralsystems.Thesystemischaracterizedbyrelativelythin,generally(butnotalways)concreteelementsthatprovidebothstructuralstrengthandseparationbetweenbuildingfunctions.Inhigh-risebuildings,shearwallsystemstendtohavearelativelyhighaspectratio,thatis,theirheighttendstobelargecomparedtotheirwidth.Lackingtensioninthefoundationsystem,anystructuralelementislimitedinitsabilitytoresistoverturningmomentbythewidthofthesystemandbythegravityloadsupportedbytheelement.Limitedtoanarrowoverturning,Oneobvioususeofthesystem,whichdoeshavetheneededwidth,isintheexteriorwallsofbuilding,wheretherequirementforwindowsiskeptsmall.Structuralsteelshearwalls,generallystiffenedagainstbucklingbyaconcreteoverlay,havefoundapplicationwhereshearloadsarehigh.Thesystem,intrinsicallymoreeconomicalthansteelbracing,isparticularlyeffectiveincarryingshearloadsdownthroughthetallerfloorsintheareasimmediatelyabovegrade.Thesystemhasthefurtheradvantageofhavinghighductilityafeatureofparticularimportanceinareasofhighseismicity.Theanalysisofshearwallsystemsismadecomplexbecauseoftheinevitablepresenceoflargeopeningsthroughthesewalls.Preliminaryanalysiscanbebytruss-analogy,bythefiniteelementmethod,orbymakinguseofaproprietarycomputerprogramdesignedtoconsidertheinteraction,orcoupling,ofshearwalls.FramedorBracedTubesTheconceptoftheframedorbracedorbracedtubeeruptedintothetechnologywiththeIBMBuildinginPittsburgh,butwasfollowedimmediatelywiththetwin110-storytowersoftheWorldTradeCenter,NewYorkandanumberofotherbuildings.Thesystemischaracterizedbythree–dimensionalframes,bracedframes,orshearwalls,formingaclosedsurfacemoreorlesscylindricalinnature,butofnearlyanyplanconfiguration.Becausethosecolumnsthatresistlateralforcesareplacedasfaraspossiblefromthecancroidsofthesystem,theoverallmomentofinertiaisincreasedandstiffnessisveryhigh.Theanalysisoftubularstructuresisdoneusingthree-dimensionalconcepts,orbytwo-dimensionalanalogy,wherepossible,whichevermethodisused,itmustbecapableofaccountingfortheeffectsofshearlag.Thepresenceofshearlag,detectedfirstinaircraftstructures,isaseriouslimitationinthestiffnessofframedtubes.Theconcepthaslimitedrecentapplicationsofframedtubestotheshearof60stories.Designershavedevelopedvarioustechniquesforreducingtheeffectsofshearlag,mostnoticeablytheuseofbelttrusses.Thissystemfindsapplicationinbuildingsperhaps40storiesandhigher.However,exceptforpossibleaestheticconsiderations,belttrussesinterferewithnearlyeverybuildingfunctionassociatedwiththeoutsidewall;thetrussesareplacedoftenatmechanicalfloors,mushtothedisapprovalofthedesignersofthemechanicalsystems.Nevertheless,asacost-effectivestructuralsystem,thebelttrussworkswellandwilllikelyfindcontinuedapprovalfromdesigners.Numerousstudieshavesoughttooptimizethelocationofthesetrusses,withtheoptimumlocationverydependentonthenumberoftrussesprovided.Experiencewouldindicate,however,thatthelocationofthesetrussesisprovidedbytheoptimizationofmechanicalsystemsandbyaestheticconsiderations,astheeconomicsofthestructuralsystemisnothighlysensitivetobelttrusslocation.Tube-in-TubeStructuresThetubularframingsystemmobilizeseverycolumnintheexteriorwallinresistingover-turningandshearingforces.Theterm‘tube-in-tube’islargelyself-explanatoryinthatasecondringofcolumns,theringsurroundingthecentralservicecoreofthebuilding,isusedasaninnerframedorbracedtube.Thepurposeofthesecondtubeistoincreaseresistancetooverturningandtoincreaselateralstiffness.Thetubesneednotbeofthesamecharacter;thatis,onetubecouldbeframed,whiletheothercouldbebraced.Inconsideringthissystem,isimportanttounderstandclearlythedifferencebetweentheshearandtheflexuralcomponentsofdeflection,thetermsbeingtakenfrombeamanalogy.Inaframedtube,theshearcomponentofdeflectionisassociatedwiththebendingdeformationofcolumnsandgirders(i.e,thewebsoftheframedtube)whiletheflexuralcomponentisassociatedwiththeaxialshorteningandlengtheningofcolumns(i.e,theflangesoftheframedtube).Inabracedtube,theshearcomponentofdeflectionisassociatedwiththeaxialdeformationofdiagonalswhiletheflexuralcomponentofdeflectionisassociatedwiththeaxialshorteningandlengtheningofcolumns.Followingbeamanalogy,ifplanesurfacesremainplane(i.e,thefloorslabs),thenaxialstressesinthecolumnsoftheoutertube,beingfartherformtheneutralaxis,willbesubstantiallylargerthantheaxialstressesintheinnertube.However,inthetube-in-tubedesign,whenoptimized,theaxialstressesintheinnerringofcolumnsmaybeashigh,orevenhigher,thantheaxialstressesintheouterring.Thisseeminganomalyisassociatedwithdifferencesintheshearingcomponentofstiffnessbetweenthetwosystems.Thisiseasiesttounder-standwheretheinnertubeisconceivedasabraced(i.e,shear-stiff)tubewhiletheoutertubeisconceivedasaframed(i.e,shear-flexible)tube.CoreInteractiveStructuresCoreinteractivestructuresareaspecialcaseofatube-in-tubewhereinthetwotubesarecoupledtogetherwithsomeformofthree-dimensionalspaceframe.Indeed,thesystemisusedoftenwhereintheshearstiffnessoftheoutertubeiszero.TheUnitedStatesSteelBuilding,Pittsburgh,illustratesthesystemverywell.Here,theinnertubeisabracedframe,theoutertubehasnoshearstiffness,andthetwosystemsarecouplediftheywereconsideredassystemspassinginastraightlinefromthe“hat”structure.Notethattheexteriorcolumnswouldbeimproperlymodelediftheywereconsideredassystemspassinginastraightlinefromthe“hat”tothefoundations;thesecolumnsareperhaps15%stifferastheyfollowtheelasticcurveofthebracedcore.Notealsothattheaxialforcesassociatedwiththelateralforcesintheinnercolumnschangefromtensiontocompressionovertheheightofthetube,withtheinflectionpointatabout5/8oftheheightofthetube.Theoutercolumns,ofcourse,carrythesameaxialforceunderlateralloadforthefullheightofthecolumnsbecausethecolumnsbecausetheshearstiffnessofthesystemisclosetozero.Thespacestructuresofoutriggergirdersortrusses,thatconnecttheinnertubetotheoutertube,arelocatedoftenatseverallevelsinthebuilding.TheAT&Theadquartersisanexampleofanastonishingarrayofinteractiveelements:Thestructuralsystemis94ft(28.6m)wide,196ft(59.7m)long,and601ft(183.3m)high.Twoinnertubesareprovided,each31ft(9.4m)by40ft(12.2m),centered90ft(27.4m)apartinthelongdirectionofthebuilding.Theinnertubesarebracedintheshortdirection,butwithzeroshearstiffnessinthelongdirection.Asingleoutertubeissupplied,whichencirclesthebuildingperimeter.Theoutertubeisamoment-resistingframe,butwithzeroshearstiffnessforthecenter50ft(15.2m)ofeachofthelongsides.Aspace-trusshatstructureisprovidedatthetopofthebuilding.AsimilarspacetrussislocatednearthebottomofthebuildingTheentireassemblyislaterallysupportedatthebaseontwinsteel-platetubes,becausetheshearstiffnessoftheoutertubegoestozeroatthebaseofthebuilding.CellularstructuresAclassicexampleofacellularstructureistheSearsTower,Chicago,abundledtubestructureofnineseparatetubes.WhiletheSearsTowercontainsninenearlyidenticaltubes,thebasicstructuralsystemhasspecialapplicationforbuildingsofirregularshape,astheseveraltubesneednotbesimilarinplanshape,Itisnotuncommonthatsomeoftheindividualtubesoneofthestrengthsandoneoftheweaknessesofthesystem.Thisspecialweaknessofthissystem,particularlyinframedtubes,hastodowiththeconceptofdifferentialcolumnshortening.Theshorteningofacolumnunderloadisgivenbytheexpression△=ΣfL/EForbuildingsof12ft(3.66m)floor-to-floordistancesandanaveragecompressivestressof15ksi(138MPa),theshorteningofacolumnunderloadis15(12)(12)/29,000or0.074in(1.9mm)perstory.At50stories,thecolumnwillhaveshortenedto3.7in.(94mm)lessthanitsunstressedlength.Whereonecellofabundledtubesystemis,say,50storieshighandanadjacentcellis,say,100storieshigh,thosecolumnsneartheboundarybetween.thetwosystemsneedtohavethisdifferentialdeflectionreconciled.Majorstructuralworkhasbeenfoundtobeneededatsuchlocations.Inatleastonebuilding,theRialtoProject,Melbourne,thestructuralengineerfounditnecessarytoverticallypre-stressthelowerheightcolumnssoastoreconcilethedifferentialdeflectionsofcolumnsincloseproximitywiththepost-tensioningoftheshortercolumnsimulatingtheweighttobeaddedontoadjacent,highercolumns.抗侧向荷载的结构体系常用的结构体系若已测出荷载量达数千万磅重，那么在高层建筑设计中就没有多少可以进行极其复杂的构思余地了。确实，较好的高层建筑普遍具有构思简单、表现明晰的特点。这并不是说没有进行宏观构思的余地。实际上，正是因为有了这种宏观的构思，新奇的高层建筑体系才得以发展，可能更重要的是：几年以前才出现的一些新概念在今天的技术中已经变得平常了。如果忽略一些与建筑材料密切相关的概念不谈，高层建筑里最为常用的结构体系便可分为如下几类：抗弯矩框架。支撑框架，包括偏心支撑框架。剪力墙，包括钢板剪力墙。筒中框架。筒中筒结构。核心交互结构。框格体系或束筒体系。特别是由于最近趋向于更复杂的建筑形式，同时也需要增加刚度以抵抗几力和地震力，大多数高层建筑都具有由框架、支撑构架、剪力墙和相关体系相结合而构成的体系。而且，就较高的建筑物而言，大多数都是由交互式构件组成三维陈列。将这些构件结合起来的方法正是高层建筑设计方法的本质。其结合方式需要在考虑环境、功能和费用后再发展，以便提供促使建筑发展达到新高度的有效结构。这并不是说富于想象力的结构设计就能够创造出伟大建筑。正相反，有许多例优美的建筑仅得到结构工程师适当的支持就被创造出来了，然而，如果没有天赋甚厚的建筑师的创造力的指导，那么，得以发展的就只能是好的结构，并非是伟大的建筑。无论如何，要想创造出高层建筑真正非凡的设计，两者都需要最好的。虽然在文献中通常可以见到有关这七种体系的全面性讨论，但是在这里还值得进一步讨论。设计方法的本质贯穿于整个讨论。设计方法的本质贯穿于整个讨论中。抗弯矩框架抗弯矩框架也许是低，中高度的建筑中常用的体系，它具有线性水平构件和垂直构件在接头处基本刚接之特点。这种框架用作独立的体系，或者和其他体系结合起来使用，以便提供所需要水平荷载抵抗力。对于较高的高层建筑，可能会发现该本系不宜作为独立体系，这是因为在侧向力的作用下难以调动足够的刚度。我们可以利用STRESS，STRUDL或者其他大量合适的计算机程序进行结构分析。所谓的门架法分析或悬臂法分析在当今的技术中无一席之地，由于柱梁节点固有柔性，并且由于初步设计应该力求突出体系的弱点，所以在初析中使用框架的中心距尺寸设计是司空惯的。当然，在设计的后期阶段，实际地评价结点的变形很有必要。支撑框架支撑框架实际上刚度比抗弯矩框架强，在高层建筑中也得到更广泛的应用。这种体系以其结点处铰接或则接的线性水平构件、垂直构件和斜撑构件而具特色，它通常与其他体系共同用于较高的建筑，并且作为一种独立的体系用在低、中高度的建筑中。尤其引人关注的是，在强震区使用偏心支撑框架。此外，可以利用STRESS，STRUDL，或一系列二维或三维计算机分析程序中的任何一种进行结构分析。另外，初步分析中常用中心距尺寸。剪力墙剪力墙在加强结构体系刚性的发展过程中又前进了一步。该体系的特点是具有相当薄的，通常是（而不总是）混凝土的构件，这种构件既可提供结构强度，又可提供建筑物功能上的分隔。在高层建筑中，剪力墙体系趋向于具有相对大的高宽经，即与宽度相比，其高度偏大。由于基础体系缺少应力，任何一种结构构件抗倾覆弯矩的能力都受到体系的宽度和构件承受的重力荷载的限制。由于剪力墙宽度狭狭窄受限，所以需要以某种方式加以扩大，以便提从所需的抗倾覆能力。在窗户需要量小的建筑物外墙中明显地使用了这种确有所需要宽度的体系。钢结构剪力墙通常由混凝土覆盖层来加强以抵抗失稳，这在剪切荷载大的地方已得到应用。这种体系实际上比钢支撑经济，对于使剪切荷载由位于地面正上方区域内比较高的楼层向下移特别有效。这种体系还具有高延性之优点，这种特性在强震区特别重要。由于这些墙内必然出同一些大孔，使得剪力墙体系分析变得错综复杂。可以通过桁架模似法、有限元法，或者通过利用为考虑剪力墙的交互作用或扭转功能设计的专门计处机程序进行初步分析框架或支撑式筒体结构：框架或支撑式筒体最先应用于IBM公司在Pittsburgh的一幢办公楼，随后立即被应用于纽约双子座的110层世界贸易中心摩天大楼和其他的建筑中。这种系统有以下几个显著的特征：三维结构、支撑式结构、或由剪力墙形成的一个性质上差不多是圆柱体的闭合曲面，但又有任意的平面构成。由于这些抵抗侧向荷载的柱子差不多都被设置在整个系统的中心，所以整体的惯性得到提高，刚度也是很大的。在可能的情况下，通过三维概念的应用、二维的类比，我们可以进行筒体结构的分析。不管应用那种方法，都必须考虑剪力滞后的影响。这种最先在航天器结构中研究的剪力滞后出现后，对筒体结构的刚度是一个很大的限制。这种观念已经影响了筒体结构在60层以上建筑中的应用。设计者已经开发出了很多的技术，用以减小剪力滞后的影响，这其中最有名的是桁架的应用。框架或支撑式筒体在40层或稍高的建筑中找到了自己的用武之地。除了一些美观的考虑外，桁架几乎很少涉及与外墙联系的每个建筑功能，而悬索一般设置在机械的地板上，这就令机械体系设计师们很