《土木工程专业英语 第2版》 翻译版 课件 Unit 4 Seismic Design

Unit4SeismicDesignEnglishforCivilEngineering——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4.1IntroductionEarthquakesresultfromthesuddenmovementoftectonicplatesintheearth’scrust.Themovementtakesplaceatfaultlines,andtheenergyreleasedistransmittedthroughtheearthintheformofwavesthatcausegroundmotionmanymilesfromtheepicenter.Regionsadjacenttoactivefaultlinesarethemostpronetoexperienceearthquakes.Thevalues,expressedasapercentofgravity,representtheexpectedpeakaccelerationofasingle-degree-of-freedomsystemwitha0.2secperiodand5percentofcriticaldamping.Knownasthe0.2secspectralresponseaccelerationSs(subscriptsforshortperiod),itisused,alongwiththe1.0secspectralresponseaccel­erationS1(mappedinasimilarmanner),toestablishtheloadingcriteriaforseismicdesign.

AccelerationsSsandS1arebasedonhistoricalrecordsandlocalgeology.Formostofthecountry,theyrepresentearthquakegroundmotionwitha“likelihoodofexceedanceof2percentin50years,”avaluethatisequivalenttoareturnperiodofabout2500years.地震是由地壳上的构造板块突然运动造成的。这种运动发生在断层线上，所释放出的能量以波的形式在地球内部传播，即便是离震中许多英里之外的地方也会发生地面运动。活跃断层线的邻近地区最容易发生地震。这个数值，以重力的百分数表示，代表单自由度体系在0.2s的周期和5%的临界阻尼下的预期加速度峰值。公认地，用0.2s谱反应加速度Ss（下标s代表短周期）和1.0s谱应加速度S1（同理），为抗震设计建立荷载标准。加速度Ss和S1根据史料记载和当地的地质情况确定。大多数国家用“50年内超越2%的概率”来表示地面运动，一个相当于2500年一遇的数值。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.4.1IntroductionAsexperiencedbystructures,earthquakesconsistofrandomhorizontalandver­ticalmovementsoftheearth’ssurface.Asthegroundmoves,inertiatendstokeepstructuresinplace(Fig.4-1),resultingintheimpositionofdisplacementsandforcesthatcanhavecatastrophicresults.Thepurposeofseismicdesignistoproportionstructuressothattheycanwithstandthedisplacementsandtheforcesinducedbythegroundmotion.正如结构所经历的那样，地震是由是地球表面随机的横向和竖向运动组成的。随着地面的运动，惯性倾向于使结构保持原位（图4.1），使结构承受可导致灾难性的后果的位移和力。抗震设计的目标就是确定结构的尺寸，使它们能够承受地面运动所引起的位移和力。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4.1IntroductionHistoricallyinNorthAmerica,seismicdesignhasemphasizedtheeffectsofhorizontalgroundmotionbecausethehorizontalcomponentsofanearthquakeusuallyexceedtheverticalcomponentsandbecausestructuresareusuallymuchstifferandstrongerinresponsetoverticalloadsthantheyareinresponsetohorizontalloads.Experiencehasshownthatthehorizontalcomponentsarethemostdestructive.Forstructuraldesign,theintensityofanearthquakeisusuallydescribedintermsofthepeakgroundaccelerationasafractionoftheaccelerationofgravity,i.e.,0.lg,0.2g，or0.3g.Althoughpeakaccelerationisanimportantdesignparameter,thefrequencycharacteristicsanddurationofanearthquakearealsoimportant;thecloserthefre­quencyoftheearthquakemotionistothenaturalfrequencyofastructureandthelongerthedurationoftheearthquake,thegreaterthepotentialfordamage.历史上，北美的抗震设计强调水平地面运动的影响，这是因为地震的水平分量通常超过其垂直分量，并且在抵抗垂直荷载时结构的刚度和强度要比抵抗水平荷载时大得多。经验表明，水平分量最具破坏性。对于结构设计，地震的强度通常用地面加速度峰值来描述，即部分的重力加速度，如0.lg,0.2g，或0.3g。虽然加速度峰值是一个重要的设计参数，但是频率特性和地震的持续时间也是很重要的，地震运动的频率与结构的固有频率越接近、地震持续时间越长，损坏的可能性就越大。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4.1IntroductionBasedonelasticbehavior,structuressubjectedtoamajorearthquakewouldberequiredtoundergolargedisplacements.However,NorthAmericanpracticerequiresthatstructuresbedesignedforonlyafractionoftheforcesassociatedwiththosedisplacements.Therelativelylowdesignforcesarejustifiedbytheobservationsthat

buildings

designedforlowforceshavebehavedsatisfactorilyandthosestructuresdissipatesignificantenergy

asthematerialsyieldandbehaveinelastically.

Thisnonlinearbehavior,however,usuallytranslatesintoincreaseddisplacements,whichmayrequiresignificantductilityandresultinmajornonstructuraldamage.Displacementsmayalsobeofsuchamagnitude

thatthestrengthofthestructureisaffectedbystabilityconsiderations.基于弹性性能，大地震下的结构一定会产生比较大的位移。然而，北美的惯例是要求仅采用部分的位移相关力来进行结构设计。采用相对低的设计力的理由是通过观测按较低的力设计的结构，发现它们的表现非常令人满意，并且这些结构在材料屈服和表现出非弹性变形时可以消耗极多的能量。然而，这种非线性的行为通常会转化为位移的增大，这可能需要极大的塑性，并且会导致严重的非结构损伤。位移的幅值可能太大，导致结构的强度受到稳定性考虑的影响。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4.2StructuralResponseThesafetyofastructuresubjectedtoseismicloadingrestsonthedesigner’sunderstandingoftheresponseofthestructuretogroundmotion.Formanyyears,thegoalofearthquakedesigninNorthAmericahasbeentoconstructbuildingsthatwillwithstandmoderateearthquakes(withoutdamage)andsevereearthquakes(withoutcollapse).Buildingcodeshaveundergoneregularmodificationasmajorearthquakeshaveexposedweaknessesinexistingdesigncriteria.Designforearthquakesdiffersfromdesignforgravityandwindloadsintherelativelygreatersensitivityofearthquake-inducedforcestothegeometryofthestructure.Withoutcarefuldesign,forcesanddisplacementscanbeconcentratedinportionsofastructurethatarenotcapableofprovidingadequatestrengthorductility.Stepstostrengthenamemberforonetypeofloadingmayactuallyincreasetheforcesinthememberandchangethemodeoffailurefromductiletobrittle.地震荷载作用下结构的安全性依赖于设计者们对地面运动下结构响应的理解。多年来，北美的抗震设计目标一直是中震不坏，大震不倒。由于大震暴露了现有设计标准的缺陷，建筑规范开始进行定期修改。抗震设计与（抵抗）重力和风载设计的不同之处在于地震引起的力对结构的几何形状有更高的灵敏度。如果不仔细设计，力和位移会集中在结构不能提供足够的强度和塑性的部位（薄弱层）。针对一种荷载来加强一个构件的措施实际上可能会增大该构件（承受）的力，并且可能使其失效的模式从塑性转为脆性。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4.2.1StructuralConsiderationThecloserthefrequencyofthegroundmotionistooneofthenaturalfrequenciesofastructure，thegreaterthelikelihoodofthestructureexperiencingresonance，resultinginanincreaseinbothdisplacementanddamage.Therefore,earthquakeresponsedependsstronglyonthegeometricpropertiesofastructure,especiallyheight.Tallbuildingsrespondmorestronglytolong-period(low-frequency)groundmotion,whileshortbuildingsrespondmorestronglytoshort-period(high-frequency)groundmotion.Fig.4-3showstheshapesfortheprincipalmodesofvibrationofathree-storyframestructure.

Therelativecontributionofeachmodetothelateraldisplacementofthestructuredependsonthefrequencycharacteristicsofthegroundmotion.Thefirstmode(Fig.4-3a)usuallyprovidesthegreatestcontributiontolateraldisplacement.地面运动的频率越接近一个结构的固有频率之一，结构产生共振的可能性就越大，从而导致位移和损伤程度的增大。因此，地震响应极大的取决于结构的几何特性，尤其是高度。高大建筑物对长周期（低频）的地面运动反应更强烈，而低矮的建筑物对短周期（高频）的地面运动反应更强烈。图4-3显示了一个三层框架结构的主振型图。各振型对结构侧向位移的相应贡献取决于地面运动的频率特性。通常第一振型（图4-3a）对侧向位移的贡献最大。Fig.4-3Modalshapesforathree-storybuilding:(a)firstmode;(b)secondmode;(c)thirdmode.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4.2.1StructuralConsiderationTheconfigurationofastructurealsohasamajoreffectonitsresponsetoanearthquake.Structureswithadiscontinuityinstiffnessorgeometrycanbesubjectedtoundesirablyhighdisplacementsorforces.Forexample,thediscontinuanceofshearwalls,infillwalls,orevencladdingataparticularstorylevel,suchasshowninFig.4-4,willhavetheresultofconcentratingthedisplacementintheopen,or“soft”story.Thehighdisplacementwill,inturn,requirealargeamountofductilityifthestructureisnottofail.Suchadesignisnotrecommended,andtheFig.4-6illustratesstructureswithverticalgeometricandplanirregularities,whichresultintorsioninducedbygroundmotion.结构体型对其在地震下的响应也具有重要的影响。刚度或几何不连续的结构可能会承受（不合期望的）过大的位移或力。例如，剪力墙、填充墙或者甚至是特定楼层的覆盖层的中断，如图4-4所示，将会在敞开的或者薄弱的楼层产生位移集中。反过来，为了使结构不破坏，大位移要求结构有极大的塑性。但这样的设计并不被推荐，图4-6展示了竖向不规则和平面不规则的结构，此类结构在地震作用下会发生扭转。Fig.4-4Softfirststorysupportingastiffupperstructure.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4.2.2MemberConsiderationsMembersdesignedforseismicloadingmustperforminaductilefashionanddissipateenergyinamannerthatdoesnotcompromisethestrengthofthestructure.Boththeoveralldesignandthestructuraldetailsmustbeconsideredtomeetthisgoal.Theprincipalmethodofensuringductilityinmemberssubjecttoshearandbendingistoprovideconfinementfortheconcrete.Thisisaccomplishedthroughtheuseofclosedhoopsorspiralreinforcement,whichenclosethecoreofbeamsandcolumns.Whenconfinementisprovided,beamsandcolumnscanundergononlinearcyclicbendingwhilemaintainingtheirflexuralstrengthandwithoutdeterioratingduetodiagonaltensioncracking.Theformationofductilehingesallowsreinforcedconcreteframestodissipateenergy.在抗震荷载下设计的构件必须以塑性的方式工作，并以不影响结构强度的方式耗散能量。为了实现这一目标，必须将整体设计和结构细节两者都进行考虑。确保受剪、受弯构件的塑性的主要方式是为混凝土施加约束。这一点通过用封闭的箍筋或螺旋箍筋包在梁芯和柱芯的四周来实现。当提供了约束之后，梁和柱能承受非线性循环弯曲而其抗弯强度保持不因斜拉裂缝衰减。塑性铰的形成可以使混凝土框架消耗能量。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4.2.2MemberConsiderationsSuccessfulseismicdesignofframesrequiresthatthestructuresbepropor­tionedsothathingesoccuratlocationsthatleastcompromisestrength.Foraframeundergoinglateraldisplacement,suchasshowninFig.4-5a,theflexuralcapacityofthemembersatajoint(Fig.4-5b)shouldbesuchthatthecolumnsarestrongerthanthebeams.Inthisway,hingeswillforminthebeamsratherthanthecolumns,minimizingtheportionofthestructureaffectedbynonlinearbehaviorandmaintainingtheoverallverticalloadcapacity.Forthesereasons,the“weakbeam-strongcolumn”approachisusedtodesignreinforcedconcreteframessubjecttoseismicloading.成功的框架抗震设计要求结构的尺寸合理，使塑性铰出现在最不影响强度的位置。对于一个发生侧向位移的框架，如图4-5a所示，节点处构件的抗弯能力（图4-5b）应确保柱（承载力）大于梁（承载力）。这样，铰就会形成在梁上而不是柱上，从而使受非线性行为影响的结构区域最小化，并保持整体竖向承载能力。为此，采用“强柱弱梁”原则进行设计钢筋混凝土框架的抗震设计。Fig.4-8Framesubjectedtolateralloading:(a)deflectedshape;(b)momentsactingonbeam-columnjoint;(c)deflectedshapeandforcesactingonabeam;(d)forcesactingonfacesofajointduetolateralload.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4.2.2MemberConsiderationsWhenhingesfrominabeam,orinextremecaseswithinacolumn,themomentsattheendofthemember,whicharegovernedbyflexuralstrength,determinetheshearthatmustbecarried,asillustratedinFig.4-5c.TheshearVcorrespondingtoaflexuralfailureatbothendsofabeamorcolumnisThemembermustbecheckedforadequacyundertheshearVinadditiontoshearresultingfromdeadandlivegravityloads.Transversereinforcementisadded,asrequired.Formemberswithinadequateshearcapacity,theresponsewillbedomi­natedbytheformationofdiagonalcracks,ratherthanductilehinges,resultinginasubstantialreductionintheenergydissipationcapacityofthemember.

当铰形成在梁上，或极端情况下形成在柱上，抗弯强度支配构件端部的弯矩大小，并决定其必须承载的剪力，如图4-5c所示。梁柱两端对应于弯曲破坏的剪力V是必须验算构件能否承受剪力V与恒载及活载作用下产生的剪力作用的合力。按照要求，应当加入横向钢筋。对于抗剪能力不足的构件，其响应会受控于斜拉裂缝的形成，而不是塑性铰（的形成），导致构件耗能能力的明显减小。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4.2.2MemberConsiderationsIfshortmembersareusedinaframe，themembersmaybeunintentionallystronginflexurecomparedtotheirshearcapacity.Anexamplewouldbecolumnsinastruc­turewithdeepspandrelbeamsorwith“nonstructural”wallswithopeningsthatexposeaportionofthecolumnstothefulllateralload.Asaresult,theexposedregion,calledacaptivecolumn,respondsbyundergoingashearfailure,asshowninFig.4-9.如果在框架中用了短构件，这些构件的抗弯能力很可能会明显比抗剪能力强（尽管不是故意的）。例如，在带有裙深梁的结构中的柱，或在带有开口的“非结构”墙中的柱，将会使柱的一部分承受全部侧向荷载。因此，暴露出的区域（被称为窗台柱），最终产生剪切破坏，如图4-9所示。Fig.4-9

Shearfailureinacaptivecolumnwithoutadequatetransversereinforcement.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4.2.2MemberConsiderationsThelateraldisplacementofaframeplacesbeam-columnjointsunderhighshearstressesbecauseofthechangefrompositivetonegativebendingintheflexuralmembersfromonesideofthejointtotheother,asshowninFig.4-8d.Thejointmustbeabletowithstandthehighshearstressesandallowforachangeinbarstressfromtensiontocompressionbetweenthefacesofthejoint.Suchatransferofshearandbondisoftenmadedifficultbycongestionofreinforcementthroughthejoint.Thus,designersmustensurethatjointsnotonlyhaveadequatestrengthbutarealsoconstructible.Two-waysystemswithoutbeamsareespeciallyvulnerablebecauseoflowductilityattheslab-columnintersection.框架的侧向位移使梁柱节点承受极大的剪切应力，这是因为受弯构件节点两侧的弯矩正负号发生变化，如图4-8d所示。节点必须能够承受极大的剪切应力，并允许节点表面之间的钢筋应力可以从受拉变为受压。由于通过节点的钢筋非常稠密，因此剪力和粘结力的传递通常非常困难。因此，设计者必须保证节点不但有足够的强度，而且是便于施工的。无梁双向系统特别容易破坏，因为板柱交汇处塑性特别差。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4.3SeismicLoadingCriteriaIntheUnitedStates,thedesigncriteriaforearthquakeloadingarebasedondesignproceduresdevelopedbytheBuildingSeismicSafetyCouncilandincor­poratedinMinimumDesignLoadsforBuildingsandOtherStructures(ASCE/SEI7).ThevaluesofthespectralresponseaccelerationsSSandS1,

areobtainedfromdetailedmapsproducedbytheUnitedStatesGeologicalSurveyandincludedinASCE/SEI7.ThevaluesofSSandS1areusedtodeterminethespec­tralresponseaccelerationsSDSandSD1thatareusedindesign.在美国，地震荷载的设计标准是以由建筑抗震安全委员会发布并被纳入建筑物和其他结构的最小设计荷载中的设计方法为依据制定的(ASCE/SEI7)。谱响应加速度值SS和S1是从美国地质调查局发布并包含在ASCE/SEI7中的详细地图中取得的。SS和S1的值用来确定在设计中需要用到的频谱响应加速度SDS和SD1。4.3SeismicLoadingCriteriawhereFaandFvaresitecoefficientsthatrangefrom0.8to0.25andfrom0.8to0.35,respectively,asafunctionofthegeotechnicalpropertiesofthebuildingsiteandthevaluesofSsandS1,respectively.HighervaluesofFa