《土木工程專業(yè)英語 第2版》 課件 Unit4 Seismic Design

Unit4SeismicDesignEnglishforCivilEngineering——Teacher：Prof.ZhengLuE-mail:luzheng111@（SchoolofCivilEngineering,TONGJIUNIVERSITY）Unit4SeismicDesign

4.1Introduction（引言）4.2StructuralResponse（結(jié)構(gòu)響應(yīng)）4.2.1StructuralConsiderations（結(jié)構(gòu)方面考慮）4.2.2MemberConsiderations（構(gòu)件方面考慮）4.3SeismicLoadingCriteria（地震作用指標(biāo)）4.3.1EquivalentLateralForceProcedure（等效側(cè)向力法）4.3.2DynamicLateralForceProcedure（動態(tài)側(cè)向力法）4.1IntroductionEarthquakesresultfromthesuddenmovementoftectonicplatesintheearth’scrust.Themovementtakesplaceatfaultlines,andtheenergyreleasedistransmittedthroughtheearthintheformofwavesthatcausegroundmotionmanymilesfromtheepicenter.Regionsadjacenttoactivefaultlinesarethemostpronetoexperienceearthquakes.內(nèi)容大意：地震起因及能量傳播方式tectonicplates構(gòu)造板塊

earth’scrust地殼

epicenter震中4.1IntroductionThevalues,expressedasapercentofgravity,representtheexpectedpeakaccelerationofasingle-degree-of-freedomsystemwitha0.2secperiodand5percentofcriticaldamping.Knownasthe0.2secspectralresponseaccelerationSs(subscriptsforshortperiod),itisused,alongwiththe1.0secspectralresponseaccel-erationS1(mappedinasimilarmanner),toestablishtheloadingcriteriaforseismicdesign.AccelerationsSsandS1arebasedonhistoricalrecordsandlocalgeology.Formostofthecountry,theyrepresentearthquakegroundmotionwitha“l(fā)ikelihoodofexceedanceof2percentin50years,”avaluethatisequivalenttoareturnperiodofabout2500years.內(nèi)容大意：地震加速度圖的含義及制定標(biāo)準(zhǔn)peakacceleration加速度峰值

spectralresponseacceleration反應(yīng)譜加速度

geology地質(zhì)學(xué)likelihoodofexceedance超越概率4.1IntroductionAsexperiencedbystructures,earthquakesconsistofrandomhorizontalandverticalmovementsoftheearth’ssurface.Asthegroundmoves,inertiatendstokeepstructuresinplace(Fig.4-1),resultingintheimpositionofdisplacementsandforcesthatcanhavecatastrophicresults.Thepurposeofseismicdesignistoproportionstructuressothattheycanwithstandthedisplacementsandtheforcesinducedbythegroundmotion.內(nèi)容大意：地震慣性力horizontal

水平向

vertical

豎向

inertia慣性imposition施加catastrophic災(zāi)難性的Fig.4-1Structuresubjectedtogroundmotion.4.1IntroductionHistoricallyinNorthAmerica,seismicdesignhasemphasizedtheeffectsofhorizontalgroundmotionbecausethehorizontalcomponentsofanearthquakeusuallyexceedtheverticalcomponentsandbecausestructuresareusuallymuchstifferandstrongerinresponsetoverticalloadsthantheyareinresponsetohorizontalloads.Experiencehasshownthatthehorizontalcomponentsarethemostdestructive.內(nèi)容大意：地震荷載特點groundmotion地面運動component成分stiff堅硬的

destructive破壞性的4.1IntroductionForstructuraldesign,theintensityofanearthquakeisusuallydescribedintermsofthepeakgroundaccelerationasafractionoftheaccelerationofgravity,i.e.,0.lg,0.2g，or0.3g.Althoughpeakaccelerationisanimportantdesignparameter,thefrequencycharacteristicsanddurationofanearthquakearealsoimportant;thecloserthefre-quencyoftheearthquakemotionistothenaturalfrequencyofastructureandthelongerthedurationoftheearthquake,thegreaterthepotentialfordamage.內(nèi)容大意：地震運動特性intensity

強度peakgroundacceleration地面運動加速度峰值fraction部分duration持續(xù)時間potential潛力4.1IntroductionBasedonelasticbehavior,structuressubjectedtoamajorearthquakewouldberequiredtoundergolargedisplacements.However,NorthAmericanpracticerequiresthatstructuresbedesignedforonlyafractionoftheforcesassociatedwiththosedisplacements.Therelativelylowdesignforcesarejustifiedbytheobservationsthatbuildingsdesignedforlowforceshavebehavedsatisfactorilyandthosestructuresdissipatesignificantenergyasthematerialsyieldandbehaveinelastically.Thisnonlinearbehavior,however,usuallytranslatesintoincreaseddisplacements,whichmayrequiresignificantductilityandresultinmajornonstructuraldamage.Displacementsmayalsobeofsuchamagnitudethatthestrengthofthestructureisaffectedbystabilityconsiderations.內(nèi)容大意：結(jié)構(gòu)位移與相關(guān)設(shè)計elastic彈性

displacements位移

dissipate耗能

inelastically非彈性

ductility

延性magnitude

量級stability穩(wěn)定性4.2StructuralResponseThesafetyofastructuresubjectedtoseismicloadingrestsonthedesigner’sunderstandingoftheresponseofthestructuretogroundmotion.Formanyyears,thegoalofearthquakedesigninNorthAmericahasbeentoconstructbuildingsthatwillwithstandmoderateearthquakeswithoutdamageandsevereearthquakeswithoutcollapse.Buildingcodeshaveundergoneregularmodificationasmajorearthquakeshaveexposedweaknessesinexistingdesigncriteria.內(nèi)容大意：抗震設(shè)計目標(biāo)groundmotion地面運動

moderateearthquakes中震

severe/majorearthquakes大震

collapse

倒塌

modification修改

designcriteria設(shè)計標(biāo)準(zhǔn)4.2StructuralResponseDesignforearthquakesdiffersfromdesignforgravityandwindloadsintherelativelygreatersensitivityofearthquake-inducedforcestothegeometryofthestructure.Withoutcarefuldesign,forcesanddisplacementscanbeconcentratedinportionsofastructurethatarenotcapableofprovidingadequatestrengthorductility.Stepstostrengthenamemberforonetypeofloadingmayactuallyincreasetheforcesinthememberandchangethemodeoffailurefromductiletobrittle.內(nèi)容大意：抗震設(shè)計與抗風(fēng)設(shè)計區(qū)別sensitivity敏感

geometry幾何

portion

部分

mode

模式ductile延性brittle脆性4.2.1StructuralConsiderationThecloserthefrequencyofthegroundmotionistooneofthenaturalfrequenciesofastructure，thegreaterthelikelihoodofthestructureexperiencingresonance，resultinginanincreaseinbothdisplacementanddamage.Therefore,earthquakeresponsedependsstronglyonthegeometricpropertiesofastructure,especiallyheight.Tallbuildingsrespondmorestronglytolong-period(low-frequency)groundmotion,whileshortbuildingsrespondmorestronglytoshort-period(high-frequency)groundmotion.Fig.4-2showstheshapesfortheprincipalmodesofvibrationofathree-storyframestructure.Therelativecontributionofeachmodetothelateraldisplacementofthestructuredependsonthefrequencycharacteristicsofthegroundmotion.Thefirstmode(Fig.4-2a)usuallyprovidesthegreatestcontributiontolateraldisplacement.內(nèi)容大意：結(jié)構(gòu)振動模態(tài)naturalfrequencies自振頻率resonance自振long-period長周期principalmodes主模態(tài)lateraldisplacement側(cè)向位移4.2.1StructuralConsiderationTheconfigurationofastructurealsohasamajoreffectonitsresponsetoanearthquake.Structureswithadiscontinuityinstiffnessorgeometrycanbesubjectedtoundesirablyhighdisplacementsorforces.Forexample,thediscontinuanceofshearwalls,infillwalls,orevencladdingataparticularstorylevel,suchasshowninFig.4-3,willhavetheresultofconcentratingthedisplacementintheopen,or“soft”story.Thehighdisplacementwill,inturn,requirealargeamountofductilityifthestructureisnottofail.Suchadesignisnotrecommended,andtheFig.4-4illustratesstructureswithverticalgeometricandplanirregularities,whichresultintorsioninducedbygroundmotion.內(nèi)容大意：結(jié)構(gòu)布局configuration布局

discontinuity不連續(xù)

shearwalls剪力墻

infillwalls填充墻

cladding覆蓋層ductility塑性4.2.2MemberConsiderationsMembersdesignedforseismicloadingmustperforminaductilefashionanddissipateenergyinamannerthatdoesnotcompromisethestrengthofthestructure.Boththeoveralldesignandthestructuraldetailsmustbeconsideredtomeetthisgoal.Theprincipalmethodofensuringductilityinmemberssubjecttoshearandbendingistoprovideconfinementfortheconcrete.Thisisaccomplishedthroughtheuseofclosedhoopsorspiralreinforcement,whichenclosethecoreofbeamsandcolumns.Whenconfinementisprovided,beamsandcolumnscanundergononlinearcyclicbendingwhilemaintainingtheirflexuralstrengthandwithoutdeterioratingduetodiagonaltensioncracking.Theformationofductilehingesallowsreinforcedconcreteframestodissipateenergy.內(nèi)容大意：構(gòu)件構(gòu)造方法compromise

折中

hoop箍筋spiralreinforcement螺旋箍筋deteriorate降低4.2.2MemberConsiderationsSuccessfulseismicdesignofframesrequiresthatthestructuresbepropor-tionedsothathingesoccuratlocationsthatleastcompromisestrength.Foraframeundergoinglateraldisplacement,suchasshowninFig.4-5a,theflexuralcapacityofthemembersatajoint(Fig.4-5b)shouldbesuchthatthecolumnsarestrongerthanthebeams.Inthisway,hingeswillforminthebeamsratherthanthecolumns,minimizingtheportionofthestructureaffectedbynonlinearbehaviorandmaintainingtheoverallverticalloadcapacity.Forthesereasons,the“weakbeam-strongcolumn”approachisusedtodesignreinforcedconcreteframessubjecttoseismicloading.內(nèi)容大意：強柱弱梁flexuralcapacity抗彎承載力weakbeam-strongcolumn強柱弱梁4.2.2MemberConsiderationsWhenhingesfrominabeam,orinextremecaseswithinacolumn,themomentsattheendofthemember,whicharegovernedbyflexuralstrength,determinetheshearthatmustbecarried,asillustratedinFig.4-5c.TheshearVcorrespondingtoaflexuralfailureatbothendsofabeamorcolumnis內(nèi)容大意：彎曲破壞剪力計算flexuralfailure

受彎破壞4.2.2MemberConsiderationsThemembermustbecheckedforadequacyundertheshearVinadditiontoshearresultingfromdeadandlivegravityloads.Transversereinforcementisadded,asrequired.Formemberswithinadequateshearcapacity,theresponsewillbedomi-natedbytheformationofdiagonalcracks,ratherthanductilehinges,resultinginasubstantialreductionintheenergydissipationcapacityofthemember.

內(nèi)容大意：抗剪構(gòu)造transversereinforcement

橫向鋼筋shearcapacity抗剪承載力diagonalcrack斜裂縫4.2.2MemberConsiderationsIfshortmembersareusedinaframe，themembersmaybeunintentionallystronginflexurecomparedtotheirshearcapacity.Anexamplewouldbecolumnsinastruc-turewithdeepspandrelbeamsorwith“nonstructural”wallswithopeningsthatexposeaportionofthecolumnstothefulllateralload.Asaresult,theexposedregion,calledacaptivecolumn,respondsbyundergoingashearfailure,asshowninFig.4-6.內(nèi)容大意：短柱nonstructural

非結(jié)構(gòu)的captivecolumn窗臺柱4.2.2MemberConsiderationsThelateraldisplacementofaframeplacesbeam-columnjointsunderhighshearstressesbecauseofthechangefrompositivetonegativebendingintheflexuralmembersfromonesideofthejointtotheother,asshowninFig.4-5d.Thejointmustbeabletowithstandthehighshearstressesandallowforachangeinbarstressfromtensiontocompressionbetweenthefacesofthejoint.Suchatransferofshearandbondisoftenmadedifficultbycongestionofreinforcementthroughthejoint.Thus,designersmustensurethatjointsnotonlyhaveadequatestrengthbutarealsoconstructible.Two-waysystemswithoutbeamsareespeciallyvulnerablebecauseoflowductilityattheslab-columnintersection.內(nèi)容大意：節(jié)點設(shè)計joint

節(jié)點

congestion

沖突

vulnerable易破壞的4.3SeismicLoadingCriteriaIntheUnitedStates,thedesigncriteriaforearthquakeloadingarebasedondesignproceduresdevelopedbytheBuildingSeismicSafetyCouncilandincor-poratedinMinimumDesignLoadsforBuildingsandOtherStructures(ASCE/SEI7).ThevaluesofthespectralresponseaccelerationsSSandS1,areobtainedfromdetailedmapsproducedbytheUnitedStatesGeologicalSurveyandincludedinASCE/SEI7.ThevaluesofSSandS1areusedtodeterminethespec-tralresponseaccelerationsSDSandSD1thatareusedindesign.內(nèi)容大意：設(shè)計反應(yīng)譜參數(shù)designcriteria設(shè)計指標(biāo)spectralresponseaccelerations反應(yīng)譜加速度4.3SeismicLoadingCriteriawhereFaandFvaresitecoefficientsthatra