《土木工程专业英语 第2版》 课件 Unit4 Seismic Design

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

4.1Introduction（引言）4.2StructuralResponse（结构响应）4.2.1StructuralConsiderations（结构方面考虑）4.2.2MemberConsiderations（构件方面考虑）4.3SeismicLoadingCriteria（地震作用指标）4.3.1EquivalentLateralForceProcedure（等效侧向力法）4.3.2DynamicLateralForceProcedure（动态侧向力法）4.1IntroductionEarthquakesresultfromthesuddenmovementoftectonicplatesintheearth’scrust.Themovementtakesplaceatfaultlines,andtheenergyreleasedistransmittedthroughtheearthintheformofwavesthatcausegroundmotionmanymilesfromtheepicenter.Regionsadjacenttoactivefaultlinesarethemostpronetoexperienceearthquakes.内容大意：地震起因及能量传播方式tectonicplates构造板块

earth’scrust地壳

epicenter震中4.1IntroductionThevalues,expressedasapercentofgravity,representtheexpectedpeakaccelerationofasingle-degree-of-freedomsystemwitha0.2secperiodand5percentofcriticaldamping.Knownasthe0.2secspectralresponseaccelerationSs(subscriptsforshortperiod),itisused,alongwiththe1.0secspectralresponseaccel­erationS1(mappedinasimilarmanner),toestablishtheloadingcriteriaforseismicdesign.AccelerationsSsandS1arebasedonhistoricalrecordsandlocalgeology.Formostofthecountry,theyrepresentearthquakegroundmotionwitha“likelihoodofexceedanceof2percentin50years,”avaluethatisequivalenttoareturnperiodofabout2500years.内容大意：地震加速度图的含义及制定标准peakacceleration加速度峰值

spectralresponseacceleration反应谱加速度

geology地质学likelihoodofexceedance超越概率4.1IntroductionAsexperiencedbystructures,earthquakesconsistofrandomhorizontalandverticalmovementsoftheearth’ssurface.Asthegroundmoves,inertiatendstokeepstructuresinplace(Fig.4-1),resultingintheimpositionofdisplacementsandforcesthatcanhavecatastrophicresults.Thepurposeofseismicdesignistoproportionstructuressothattheycanwithstandthedisplacementsandtheforcesinducedbythegroundmotion.内容大意：地震惯性力horizontal

水平向

vertical

竖向

inertia惯性imposition施加catastrophic灾难性的Fig.4-1Structuresubjectedtogroundmotion.4.1IntroductionHistoricallyinNorthAmerica,seismicdesignhasemphasizedtheeffectsofhorizontalgroundmotionbecausethehorizontalcomponentsofanearthquakeusuallyexceedtheverticalcomponentsandbecausestructuresareusuallymuchstifferandstrongerinresponsetoverticalloadsthantheyareinresponsetohorizontalloads.Experiencehasshownthatthehorizontalcomponentsarethemostdestructive.内容大意：地震荷载特点groundmotion地面运动component成分stiff坚硬的

destructive破坏性的4.1IntroductionForstructuraldesign,theintensityofanearthquakeisusuallydescribedintermsofthepeakgroundaccelerationasafractionoftheaccelerationofgravity,i.e.,0.lg,0.2g，or0.3g.Althoughpeakaccelerationisanimportantdesignparameter,thefrequencycharacteristicsanddurationofanearthquakearealsoimportant;thecloserthefre­quencyoftheearthquakemotionistothenaturalfrequencyofastructureandthelongerthedurationoftheearthquake,thegreaterthepotentialfordamage.内容大意：地震运动特性intensity

强度peakgroundacceleration地面运动加速度峰值fraction部分duration持续时间potential潜力4.1IntroductionBasedonelasticbehavior,structuressubjectedtoamajorearthquakewouldberequiredtoundergolargedisplacements.However,NorthAmericanpracticerequiresthatstructuresbedesignedforonlyafractionoftheforcesassociatedwiththosedisplacements.Therelativelylowdesignforcesarejustifiedbytheobservationsthatbuildingsdesignedforlowforceshavebehavedsatisfactorilyandthosestructuresdissipatesignificantenergyasthematerialsyieldandbehaveinelastically.Thisnonlinearbehavior,however,usuallytranslatesintoincreaseddisplacements,whichmayrequiresignificantductilityandresultinmajornonstructuraldamage.Displacementsmayalsobeofsuchamagnitudethatthestrengthofthestructureisaffectedbystabilityconsiderations.内容大意：结构位移与相关设计elastic弹性

displacements位移

dissipate耗能

inelastically非弹性

ductility

延性magnitude

量级stability稳定性4.2StructuralResponseThesafetyofastructuresubjectedtoseismicloadingrestsonthedesigner’sunderstandingoftheresponseofthestructuretogroundmotion.Formanyyears,thegoalofearthquakedesigninNorthAmericahasbeentoconstructbuildingsthatwillwithstandmoderateearthquakeswithoutdamageandsevereearthquakeswithoutcollapse.Buildingcodeshaveundergoneregularmodificationasmajorearthquakeshaveexposedweaknessesinexistingdesigncriteria.内容大意：抗震设计目标groundmotion地面运动

moderateearthquakes中震

severe/majorearthquakes大震

collapse

倒塌

modification修改

designcriteria设计标准4.2StructuralResponseDesignforearthquakesdiffersfromdesignforgravityandwindloadsintherelativelygreatersensitivityofearthquake-inducedforcestothegeometryofthestructure.Withoutcarefuldesign,forcesanddisplacementscanbeconcentratedinportionsofastructurethatarenotcapableofprovidingadequatestrengthorductility.Stepstostrengthenamemberforonetypeofloadingmayactuallyincreasetheforcesinthememberandchangethemodeoffailurefromductiletobrittle.内容大意：抗震设计与抗风设计区别sensitivity敏感

geometry几何

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.内容大意：结构振动模态naturalfrequencies自振频率resonance自振long-period长周期principalmodes主模态lateraldisplacement侧向位移4.2.1StructuralConsiderationTheconfigurationofastructurealsohasamajoreffectonitsresponsetoanearthquake.Structureswithadiscontinuityinstiffnessorgeometrycanbesubjectedtoundesirablyhighdisplacementsorforces.Forexample,thediscontinuanceofshearwalls,infillwalls,orevencladdingataparticularstorylevel,suchasshowninFig.4-3,willhavetheresultofconcentratingthedisplacementintheopen,or“soft”story.Thehighdisplacementwill,inturn,requirealargeamountofductilityifthestructureisnottofail.Suchadesignisnotrecommended,andtheFig.4-4illustratesstructureswithverticalgeometricandplanirregularities,whichresultintorsioninducedbygroundmotion.内容大意：结构布局configuration布局

discontinuity不连续

shearwalls剪力墙

infillwalls填充墙

cladding覆盖层ductility塑性4.2.2MemberConsiderationsMembersdesignedforseismicloadingmustperforminaductilefashionanddissipateenergyinamannerthatdoesnotcompromisethestrengthofthestructure.Boththeoveralldesignandthestructuraldetailsmustbeconsideredtomeetthisgoal.Theprincipalmethodofensuringductilityinmemberssubjecttoshearandbendingistoprovideconfinementfortheconcrete.Thisisaccomplishedthroughtheuseofclosedhoopsorspiralreinforcement,whichenclosethecoreofbeamsandcolumns.Whenconfinementisprovided,beamsandcolumnscanundergononlinearcyclicbendingwhilemaintainingtheirflexuralstrengthandwithoutdeterioratingduetodiagonaltensioncracking.Theformationofductilehingesallowsreinforcedconcreteframestodissipateenergy.内容大意：构件构造方法compromise

折中

hoop箍筋spiralreinforcement螺旋箍筋deteriorate降低4.2.2MemberConsiderationsSuccessfulseismicdesignofframesrequiresthatthestructuresbepropor­tionedsothathingesoccuratlocationsthatleastcompromisestrength.Foraframeundergoinglateraldisplacement,suchasshowninFig.4-5a,theflexuralcapacityofthemembersatajoint(Fig.4-5b)shouldbesuchthatthecolumnsarestrongerthanthebeams.Inthisway,hingeswillforminthebeamsratherthanthecolumns,minimizingtheportionofthestructureaffectedbynonlinearbehaviorandmaintainingtheoverallverticalloadcapacity.Forthesereasons,the“weakbeam-strongcolumn”approachisusedtodesignreinforcedconcreteframessubjecttoseismicloading.内容大意：强柱弱梁flexuralcapacity抗弯承载力weakbeam-strongcolumn强柱弱梁4.2.2MemberConsiderationsWhenhingesfrominabeam,orinextremecaseswithinacolumn,themomentsattheendofthemember,whicharegovernedbyflexuralstrength,determinetheshearthatmustbecarried,asillustratedinFig.4-5c.TheshearVcorrespondingtoaflexuralfailureatbothendsofabeamorcolumnis内容大意：弯曲破坏剪力计算flexuralfailure

受弯破坏4.2.2MemberConsiderationsThemembermustbecheckedforadequacyundertheshearVinadditiontoshearresultingfromdeadandlivegravityloads.Transversereinforcementisadded,asrequired.Formemberswithinadequateshearcapacity,theresponsewillbedomi­natedbytheformationofdiagonalcracks,ratherthanductilehinges,resultinginasubstantialreductionintheenergydissipationcapacityofthemember.

内容大意：抗剪构造transversereinforcement

横向钢筋shearcapacity抗剪承载力diagonalcrack斜裂缝4.2.2MemberConsiderationsIfshortmembersareusedinaframe，themembersmaybeunintentionallystronginflexurecomparedtotheirshearcapacity.Anexamplewouldbecolumnsinastruc­turewithdeepspandrelbeamsorwith“nonstructural”wallswithopeningsthatexposeaportionofthecolumnstothefulllateralload.Asaresult,theexposedregion,calledacaptivecolumn,respondsbyundergoingashearfailure,asshowninFig.4-6.内容大意：短柱nonstructural

非结构的captivecolumn窗台柱4.2.2MemberConsiderationsThelateraldisplacementofaframeplacesbeam-columnjointsunderhighshearstressesbecauseofthechangefrompositivetonegativebendingintheflexuralmembersfromonesideofthejointtotheother,asshowninFig.4-5d.Thejointmustbeabletowithstandthehighshearstressesandallowforachangeinbarstressfromtensiontocompressionbetweenthefacesofthejoint.Suchatransferofshearandbondisoftenmadedifficultbycongestionofreinforcementthroughthejoint.Thus,designersmustensurethatjointsnotonlyhaveadequatestrengthbutarealsoconstructible.Two-waysystemswithoutbeamsareespeciallyvulnerablebecauseoflowductilityattheslab-columnintersection.内容大意：节点设计joint

节点

congestion

冲突

vulnerable易破坏的4.3SeismicLoadingCriteriaIntheUnitedStates,thedesigncriteriaforearthquakeloadingarebasedondesignproceduresdevelopedbytheBuildingSeismicSafetyCouncilandincor­poratedinMinimumDesignLoadsforBuildingsandOtherStructures(ASCE/SEI7).ThevaluesofthespectralresponseaccelerationsSSandS1,areobtainedfromdetailedmapsproducedbytheUnitedStatesGeologicalSurveyandincludedinASCE/SEI7.ThevaluesofSSandS1areusedtodeterminethespec­tralresponseaccelerationsSDSandSD1thatareusedindesign.内容大意：设计反应谱参数designcriteria设计指标spectralresponseaccelerations反应谱加速度4.3SeismicLoadingCriteriawhereFaandFvaresitecoefficientsthatra