Earthquake Resistant Structural Systems 土木工程外文翻译.docx

Earthquake Resistant Structural Systems 土木工程外文翻译.docx

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EarthquakeResistantStructuralSystems土木工程外文翻译

EarthquakeResistantStructuralSystems-土木工程外文翻译

3BuildingEngineeringⅡ:

BuildingStructuresandSeismic

Resistance

3.1Text

3.1.1Passage

EarthquakeResistantStructuralSystems

1RigidFrameStructures

Rigidframestructurestypicallycomprisefloordiaphragmssupportedonbeamswhichlinktocontinuouscolumns（Figure3-1）.Thejointsbetweenbeamandcolumnsareusuallyconsideredtobe“rigid”.Theframesareexpectedtocarrythegravityloadsthroughtheflexuralactionofthebeamsandtheproppingactionofthecolumns.Negativemomentsareinducedinthebeamadjacenttothecolumnscausingthemid-spanpositivemomenttobesignificantlylessthaninasimplysupportedspan.Instructuresinwhichgravityloadsdictatethedesign,economiesinmembersizethatarisefromthiseffecttendtobeoffsetbythehighercostoftherigidjoints.

Figure3-1Rigidframestructure

Lateralloads,imposedwithintheplaneoftheframe,areresistedthroughthedevelopmentofbendingmomentsinthebeamsandcolumns.Framedbuildingsoftenemploymomentresistantframesintwoorthogonaldirections,inwhichcasethecolumnelementsarecommontobothframes.

Rigidframestructuresarewellsuitedtoaccommodatehighlevelsofinelasticdeformation.Whenacapacitydesignapproachisemployed,itisusualtoassigntheendzonesoftheflexuralbeamstoacceptthepost-elasticdeformationexpected,andtodesignthecolumnmemberssuchthattheirdependablestrengthisinexcessoftheover-strengthcapacityofthebeamhinges,therebyensuringtheyremainwithintheirelasticresponserangeregardlessoftheintensityofgroundshaking.Rigidframestructuresare,however,oftenquiteflexible.Whentheyaredesignedtobefullyductile,specialprovisionsareoftenneededtopreventtheprematureonsetofdamagetonon-structuralcomponents.

Rigidframeconstructionisideallysuitedforreinforcedconcretebuildingbecauseoftheinherentrigidityofreinforcedconcretejoints.Therigidframeformisalsousedforsteelframe

buildings.Butmomentresistantconnectionsinsteeltendtobecostly.Thesizesofthecolumnsandgirdersatanylevelofarigid-framearedirectlyinfluencedbythemagnitudeoftheexternalshearatthatlevel,andtheythereforeincreasetowardthebase.Consequently,thedesignofthefloorframingcannotberepetitiveasitisinsomebracedframes.Afurtherresultisthatsometimesitisnotpossibleintheloweststoreystoaccommodatetherequireddepthofgirderwithinthenormalceilingspace.

Whilerigidframesofatypicalscalethatservealonetoresistlateralloadinghaveaneconomicheightlimitofabout25storeys,smallerscalerigidframesintheformofaperimetertube,ortypicallyscaledrigidframesincombinationwithshearwallsorbracedbents,canbeeconomicuptomuchgreaterheights.

2InfilledFrameStructures

Infilledframes（Figure3-2）arethemostusualformofconstructionfortallbuildingsofupto30storeysinheight.Columnandgirderframingofreinforcedconcrete,orsometimessteel,isinfilledbypanelsofbrickwork,orcast-in-placeconcrete.

Figure3-2Infilledframe

Whenaninfilledframeissubjectedtolateralloading,theinfillbehaveseffectivelyasastrutalongitscompressiondiagonaltobracetheframe.Becausetheinfillsservealsoasexternalwallsorinternalpartitions,thesystemisaneconomicalwayofstiffeningandstrengtheningthestructure.

Thecomplexinteractivebehavioroftheinfillintheframe,andtheratherrandomqualityofmasonry,hadmadeitdifficulttopredicatewithaccuracythestiffnessandstrengthofaninfilledframe.Forthesereasons,theuseoftheinfillsforbracingbuildingshasmainlybeensupplementarytotherigidframeactionofconcreteframes.

3ShearWalls

Ashearwallisaverticalstructuralelementthatresistslateralforcesintheplaneofthewallthroughshearandbending.Thehighinplanstiffnessandstrengthofconcreteandmasonrywallsmakethemideallysuitableforbracingbuildingasshearwalls.

Ashearwallactsasabeamcantileveredoutofthegroundorfoundation9and,justaswithabeam,partofitsstrengthderivesfromitsdepth.Figure3-3showstwoexamplesofashearwall,oneinasimpleone-storeybuildingandanotherinamultistoreybuilding.InFigure3-3a,theshearwallsareorientedinonedirection,soonlylateralforcesinthisdirectioncanberesisted.Theroofservesasthehorizontaldiaphragmandmustalsobedesignedtoresistthelateralloadsandtransferthemtotheshearwalls.

a）Endshearwallsandinteriorshearwallb）InteriorshearwallsforbracingintwodirectionFigure3-3Shearwall

Figure3-3aalsoshowsanimportantaspectofshearwallsinparticularandverticalelementsingeneral.Thisistheaspectofsymmetrythathasabearingonwhethertorsionaleffectswillbeproduced.TheshearwallsinFigure3-3ashowtheshearwallssymmetricalintheplaneofloading.

Figure3-3billustratesacommonuseofshearwallsattheinteriorofamulti-storeybuilding.Becausewallsenclosingstairways,elevatorshafts,andmechanicalchasesaremostlysolidandruntheentireheightofthebuilding,theyareoftenusedforshearwalls.Althoughnotasefficientfromastrictlystructuralpointofview,interiorshearwallsdoleavetheexteriorofthebuildingopenforwindows.

NoticethatinFigure3-3bthereareshearwallsinbothdirections,whichisamorerealisticsituationbecausebothwindandearthquakeforcesneedtoberesistedinbothdirections.Inthisdiagram,thetwoshearwallsaresymmetricalinonedirection,butthesingleshearwallproducesanonsymmetricconditionintheothersinceitisoffcenter.Shearwallsdonotneedtobesymmetricalinabuilding,butsymmetryispreferredtoavoidtorsionaleffects.

If,inlow-tomedium-risebuilding,shearwallsarecombinedwithframes,itisreasonabletoassumethattheshearwallattractallthelateralloadingsothattheframemaybedesignedforonlygravityloading.Itisessentiallyimportantinshearwallstructurestotrytoplanthewalllayoutsothatthelateralloadtensilestressesaresuppressedbythegravityloadstresses.Thisallowsthemtobedesignedtohaveonlytheminimumreinforcement.

Sinceshearwallsaregenerallybothstiffandcanbeinherentlyrobust,itispracticaltodesignthemtoremainnominallyelasticunderdesignintensityloadings,particularlyinregionsoflowormoderateseismicity.Underincreasedloadingintensities,post-elasticdeformationswilldevelopwithinthelowerportionofthewall（generallyconsideredtoextendoveraheightoftwicethewalllengthabovethefoundationsupportsystem）.Goodpost-elasticresponsecanbereadilyachievedwithinthisregionofreinforcedconcreteormasonryshearwallsthroughtheprovisionofadequateconfinementoftheprincipalreinforcingsteelandtheprohibitionoflapsplicesofreinforcingbars.

Shearwallstructuresaregenerallyquitestiffand,assuchinterstoreydriftproblemsarerareandgenerallyeasilycontained.Theshearwalltendstoactasarigidbodyrotatingaboutaplastichingewhichformsatthebaseofthewall.Overallstructuraldeformationisthusafunctionofthewallrotation.Inter-storeydriftproblemswhichdooccurarelimitedtothelowerfewfloors.

Amajorshortcomingwithshearwallswithinbuildingsisthattheirsizeprovidesinternal（orexternal）accessbarrierswhichmaycontravenethearchitecturalrequirements.Thisproblemcan

bealleviatedbycouplingadjacentmoreslendershearwallssoacoupledshearwallstructureisformed.Thecouplingbeamsthenbecomeshearlinksbetweenthetwowallsandwithcarefuldetailingcanprovideaveryeffective,ductilecontrolmechanism（Figure3-4）.

Figure3-4Coupledshearwallstructure

4BracedFrames

Abracedframeisatrusssystemoftheconcentricoreccentrictypeinwhichthelateralforcesareresistedthroughaxialstressesinthemembers.Justaswithatruss,thebracedframedependsondiagonalmemberstoprovidealoadpathforlateralforcesfromeachbuildingelementtothefoundation.Figure3-5showsasimpleone-storeybracedframe.Atoneendofthebuildingtwobaysarebracedandattheotherendonlyonebayisbraced.Thisbuildingisonlybracedinonedirectionandthediagonalmembermaybeeitherintensionorcompression,dependingonwhichwaytheforceisapplied.

a）Singlestorybracedbuildingb）MultistorybracedbuildingFigure3-5Bracedframe

Figure3-5bshowstwomethodsofbracingamultistoreybuilding.Asinglediagonalcompressionmemberinonebaycanbeusedtobraceagainstlateralloadscomingfromeitherdirection.Alternately,tensiondiagonalscanbeusedtoaccomplishthesameresult,buttheymustberunbothwaystoaccountfortheloadcomingfromeitherdirection.

Bracedframingcanbeplacedontheexteriororinteriorofabuilding,andmaybeplacedinonestructuralbayorseveral.Obviously,abracedframecanpresentdesignproblemsforwindowsanddoorways,butitisaveryefficientandrigidlateralforceresistingsystem.

Twomajorshortcomingsofbracedsystemsarethattheirinclineddiagonalorientationoften

conflictswithconventionaloccupancyusepatterns;andsecondlytheyoftenrequirecarefuldetailingtoavoidlargelocaltorsionaleccentricitiesbeingintroducedattheconnectionswiththediagonalbracebeingoffsetfromtheframenode.

5Wall-frameStructures

Whenshearwallsarecombinedwithrigidframes（Figure3-6）,thewalls,whichtendtodeflectinaflexuralconfiguration,andtheframes,whichtendtodeflectinashearmode,areconstrainedtoadoptacommonshapebythehorizontalrigi