《土木工程專業(yè)英語 第2版》 翻譯版 課件 Unit 4 Seismic Design

Unit4SeismicDesignEnglishforCivilEngineering——Unit4SeismicDesign

4.1Introduction（引言）4.2StructuralResponse（結構響應）4.2.1StructuralConsiderations（結構方面考慮）4.2.2MemberConsiderations（構件方面考慮）4.3SeismicLoadingCriteria（地震作用指標）4.3.1EquivalentLateralForceProcedure（等效側向力法）4.3.2DynamicLateralForceProcedure（動態(tài)側向力法）4.1IntroductionEarthquakesresultfromthesuddenmovementoftectonicplatesintheearth’scrust.Themovementtakesplaceatfaultlines,andtheenergyreleasedistransmittedthroughtheearthintheformofwavesthatcausegroundmotionmanymilesfromtheepicenter.Regionsadjacenttoactivefaultlinesarethemostpronetoexperienceearthquakes.內容大意：地震起因及能量傳播方式tectonicplates構造板塊

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.內容大意：地震加速度圖的含義及制定標準peakacceleration加速度峰值

spectralresponseacceleration反應譜加速度

geology地質學likelihoodofexceedance超越概率4.1IntroductionEarthquakesresultfromthesuddenmovementoftectonicplatesintheearth’scrust.Themovementtakesplaceatfaultlines,andtheenergyreleasedistransmittedthroughtheearthintheformofwavesthatcausegroundmotionmanymilesfromtheepicenter.Regionsadjacenttoactivefaultlinesarethemostpronetoexperienceearthquakes.Thevalues,expressedasapercentofgravity,representtheexpectedpeakaccelerationofasingle-degree-of-freedomsystemwitha0.2secperiodand5percentofcriticaldamping.Knownasthe0.2secspectralresponseaccelerationSs(subscriptsforshortperiod),itisused,alongwiththe1.0secspectralresponseaccel-erationS1(mappedinasimilarmanner),toestablishtheloadingcriteriaforseismicdesign.

AccelerationsSsandS1arebasedonhistoricalrecordsandlocalgeology.Formostofthecountry,theyrepresentearthquakegroundmotionwitha“l(fā)ikelihoodofexceedanceof2percentin50years,”avaluethatisequivalenttoareturnperiodofabout2500years.地震是由地殼上的構造板塊突然運動造成的。這種運動發(fā)生在斷層線上，所釋放出的能量以波的形式在地球內部傳播，即便是離震中許多英里之外的地方也會發(fā)生地面運動?；钴S斷層線的鄰近地區(qū)最容易發(fā)生地震。這個數(shù)值，以重力的百分數(shù)表示，代表單自由度體系在0.2s的周期和5%的臨界阻尼下的預期加速度峰值。公認地，用0.2s譜反應加速度Ss（下標s代表短周期）和1.0s譜應加速度S1（同理），為抗震設計建立荷載標準。加速度Ss和S1根據(jù)史料記載和當?shù)氐牡刭|情況確定。大多數(shù)國家用“50年內超越2%的概率”來表示地面運動，一個相當于2500年一遇的數(shù)值。4.1IntroductionAsexperiencedbystructures,earthquakesconsistofrandomhorizontalandver-ticalmovementsoftheearth’ssurface.Asthegroundmoves,inertiatendstokeepstructuresinplace(Fig.4-1),resultingintheimpositionofdisplacementsandforcesthatcanhavecatastrophicresults.Thepurposeofseismicdesignistoproportionstructuressothattheycanwithstandthedisplacementsandtheforcesinducedbythegroundmotion.內容大意：地震慣性力horizontal

水平向

ver-tical

豎向

inertia慣性imposition施加catastrophic災難性的Fig.4-1Structuresubjectedtogroundmotion.4.1IntroductionAsexperiencedbystructures,earthquakesconsistofrandomhorizontalandver-ticalmovementsoftheearth’ssurface.Asthegroundmoves,inertiatendstokeepstructuresinplace(Fig.4-1),resultingintheimpositionofdisplacementsandforcesthatcanhavecatastrophicresults.Thepurposeofseismicdesignistoproportionstructuressothattheycanwithstandthedisplacementsandtheforcesinducedbythegroundmotion.正如結構所經(jīng)歷的那樣，地震是由是地球表面隨機的橫向和豎向運動組成的。隨著地面的運動，慣性傾向于使結構保持原位（圖4.1），使結構承受可導致災難性的后果的位移和力?？拐鹪O計的目標就是確定結構的尺寸，使它們能夠承受地面運動所引起的位移和力。Fig.4-1Structuresubjectedtogroundmotion.4.1IntroductionHistoricallyinNorthAmerica,seismicdesignhasemphasizedtheeffectsofhorizontalgroundmotionbecausethehorizontalcomponentsofanearthquakeusuallyexceedtheverticalcomponentsandbecausestructuresareusuallymuchstifferandstrongerinresponsetoverticalloadsthantheyareinresponsetohorizontalloads.Experiencehasshownthatthehorizontalcomponentsarethemostdestructive.內容大意：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4.1IntroductionHistoricallyinNorthAmerica,seismicdesignhasemphasizedtheeffectsofhorizontalgroundmotionbecausethehorizontalcomponentsofanearthquakeusuallyexceedtheverticalcomponentsandbecausestructuresareusuallymuchstifferandstrongerinresponsetoverticalloadsthantheyareinresponsetohorizontalloads.Experiencehasshownthatthehorizontalcomponentsarethemostdestructive.Forstructuraldesign,theintensityofanearthquakeisusuallydescribedintermsofthepeakgroundaccelerationasafractionoftheaccelerationofgravity,i.e.,0.lg,0.2g，or0.3g.Althoughpeakaccelerationisanimportantdesignparameter,thefrequencycharacteristicsanddurationofanearthquakearealsoimportant;thecloserthefre-quencyoftheearthquakemotionistothenaturalfrequencyofastructureandthelongerthedurationoftheearthquake,thegreaterthepotentialfordamage.歷史上，北美的抗震設計強調水平地面運動的影響，這是因為地震的水平分量通常超過其垂直分量，并且在抵抗垂直荷載時結構的剛度和強度要比抵抗水平荷載時大得多。經(jīng)驗表明，水平分量最具破壞性。對于結構設計，地震的強度通常用地面加速度峰值來描述，即部分的重力加速度，如0.lg,0.2g，或0.3g。雖然加速度峰值是一個重要的設計參數(shù)，但是頻率特性和地震的持續(xù)時間也是很重要的，地震運動的頻率與結構的固有頻率越接近、地震持續(xù)時間越長，損壞的可能性就越大。4.1IntroductionBasedonelasticbehavior,structuressubjectedtoamajorearthquakewouldberequiredtoundergolargedisplacements.However,NorthAmericanpracticerequiresthatstructuresbedesignedforonlyafractionoftheforcesassociatedwiththosedisplacements.Therelativelylowdesignforcesarejustifiedbytheobservationsthatbuildingsdesignedforlowforceshavebehavedsatisfactorilyandthosestructuresdissipatesignificantenergyasthematerialsyieldandbehaveinelastically.Thisnonlinearbehavior,however,usuallytranslatesintoincreaseddisplacements,whichmayrequiresignificantductilityandresultinmajornonstructuraldamage.Displacementsmayalsobeofsuchamagnitudethatthestrengthofthestructureisaffectedbystabilityconsiderations.內容大意：結構位移與相關設計elastic彈性

displacements位移

dissipate耗能

inelastically非彈性

ductility

延性magnitude

量級stability穩(wěn)定性4.1IntroductionBasedonelasticbehavior,structuressubjectedtoamajorearthquakewouldberequiredtoundergolargedisplacements.However,NorthAmericanpracticerequiresthatstructuresbedesignedforonlyafractionoftheforcesassociatedwiththosedisplacements.Therelativelylowdesignforcesarejustifiedbytheobservationsthat

buildings

designedforlowforceshavebehavedsatisfactorilyandthosestructuresdissipatesignificantenergy

asthematerialsyieldandbehaveinelastically.

Thisnonlinearbehavior,however,usuallytranslatesintoincreaseddisplacements,whichmayrequiresignificantductilityandresultinmajornonstructuraldamage.Displacementsmayalsobeofsuchamagnitude

thatthestrengthofthestructureisaffectedbystabilityconsiderations.基于彈性性能，大地震下的結構一定會產(chǎn)生比較大的位移。然而，北美的慣例是要求僅采用部分的位移相關力來進行結構設計。采用相對低的設計力的理由是通過觀測按較低的力設計的結構，發(fā)現(xiàn)它們的表現(xiàn)非常令人滿意，并且這些結構在材料屈服和表現(xiàn)出非彈性變形時可以消耗極多的能量。然而，這種非線性的行為通常會轉化為位移的增大，這可能需要極大的塑性，并且會導致嚴重的非結構損傷。位移的幅值可能太大，導致結構的強度受到穩(wěn)定性考慮的影響。4.2StructuralResponseThesafetyofastructuresubjectedtoseismicloadingrestsonthedesigner’sunderstandingoftheresponseofthestructuretogroundmotion.Formanyyears,thegoalofearthquakedesigninNorthAmericahasbeentoconstructbuildingsthatwillwithstandmoderateearthquakeswithoutdamageandsevereearthquakeswithoutcollapse.Buildingcodeshaveundergoneregularmodificationasmajorearthquakeshaveexposedweaknessesinexistingdesigncriteria.內容大意：抗震設計目標groundmotion地面運動

moderateearthquakes中震

severe/majorearthquakes大震

collapse

倒塌

modification修改

designcriteria設計標準4.2StructuralResponseDesignforearthquakesdiffersfromdesignforgravityandwindloadsintherelativelygreatersensitivityofearthquake-inducedforcestothegeometryofthestructure.Withoutcarefuldesign,forcesanddisplacementscanbeconcentratedinportionsofastructurethatarenotcapableofprovidingadequatestrengthorductility.Stepstostrengthenamemberforonetypeofloadingmayactuallyincreasetheforcesinthememberandchangethemodeoffailurefromductiletobrittle.內容大意：抗震設計與抗風設計區(qū)別sensitivity敏感

geometry幾何

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.地震荷載作用下結構的安全性依賴于設計者們對地面運動下結構響應的理解。多年來，北美的抗震設計目標一直是中震不壞，大震不倒。由于大震暴露了現(xiàn)有設計標準的缺陷，建筑規(guī)范開始進行定期修改?？拐鹪O計與（抵抗）重力和風載設計的不同之處在于地震引起的力對結構的幾何形狀有更高的靈敏度。如果不仔細設計，力和位移會集中在結構不能提供足夠的強度和塑性的部位（薄弱層）。針對一種荷載來加強一個構件的措施實際上可能會增大該構件（承受）的力，并且可能使其失效的模式從塑性轉為脆性。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.內容大意：結構振動模態(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.地面運動的頻率越接近一個結構的固有頻率之一，結構產(chǎn)生共振的可能性就越大，從而導致位移和損傷程度的增大。因此，地震響應極大的取決于結構的幾何特性，尤其是高度。高大建筑物對長周期（低頻）的地面運動反應更強烈，而低矮的建筑物對短周期（高頻）的地面運動反應更強烈。圖4-3顯示了一個三層框架結構的主振型圖。各振型對結構側向位移的相應貢獻取決于地面運動的頻率特性。通常第一振型（圖4-3a）對側向位移的貢獻最大。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.內容大意：結構布局configuration布局

discontinuity不連續(xù)

shearwalls剪力墻

infillwalls填充墻

cladding覆蓋層ductility塑性4.2.1StructuralConsiderationTheconfigurationofastructurealsohasamajoreffectonitsresponsetoanearthquake.Structureswithadiscontinuityinstiffnessorgeometrycanbesubjectedtoundesirablyhighdisplacementsorforces.Forexample,thediscontinuanceofshearwalls,infillwalls,orevencladdingataparticularstorylevel,suchasshowninFig.4-4,willhavetheresultofconcentratingthedisplacementintheopen,or“soft”story.Thehighdisplacementwill,inturn,requirealargeamountofductilityifthestructureisnottofail.Suchadesignisnotrecommended,andtheFig.4-6illustratesstructureswithverticalgeometricandplanirregularities,whichresultintorsioninducedbygroundmotion.結構體型對其在地震下的響應也具有重要的影響。剛度或幾何不連續(xù)的結構可能會承受（不合期望的）過大的位移或力。例如，剪力墻、填充墻或者甚至是特定樓層的覆蓋層的中斷，如圖4-4所示，將會在敞開的或者薄弱的樓層產(chǎn)生位移集中。反過來，為了使結構不破壞，大位移要求結構有極大的塑性。但這樣的設計并不被推薦，圖4-6展示了豎向不規(guī)則和平面不規(guī)則的結構，此類結構在地震作用下會發(fā)生扭轉。Fig.4-4Softfirststorysupportingastiffupperstructure.4.2.2MemberConsiderationsMembersdesignedforseismicloadingmustperforminaductilefashionanddissipateenergyinamannerthatdoesnotcompromisethestrengthofthestructure.Boththeoveralldesignandthestructuraldetailsmustbeconsideredtomeetthisgoal.Theprincipalmethodofensuringductilityinmemberssubjecttoshearandbendingistoprovideconfinementfortheconcrete.Thisisaccomplishedthroughtheuseofclosedhoopsorspiralreinforcement,whichenclosethecoreofbeamsandcolumns.Whenconfinementisprovided,beamsandcolumnscanundergononlinearcyclicbendingwhilemaintainingtheirflexuralstrengthandwithoutdeterioratingduetodiagonaltensioncracking.Theformationofductilehingesallowsreinforcedconcreteframestodissipateenergy.內容大意：構件構造方法compromise

折中

hoop箍筋spiralreinforcement螺旋箍筋deteriorate降低4.2.2MemberConsiderationsMembersdesignedforseismicloadingmustperforminaductilefashionanddissipateenergyinamannerthatdoesnotcompromisethestrengthofthestructure.Boththeoveralldesignandthestructuraldetailsmustbeconsideredtomeetthisgoal.Theprincipalmethodofensuringductilityinmemberssubjecttoshearandbendingistoprovideconfinementfortheconcrete.Thisisaccomplishedthroughtheuseofclosedhoopsorspiralreinforcement,whichenclosethecoreofbeamsandcolumns.Whenconfinementisprovided,beamsandcolumnscanundergononlinearcyclicbendingwhilemaintainingtheirflexuralstrengthandwithoutdeterioratingduetodiagonaltensioncracking.Theformationofductilehingesallowsreinforcedconcreteframestodissipateenergy.在抗震荷載下設計的構件必須以塑性的方式工作，并以不影響結構強度的方式耗散能量。為了實現(xiàn)這一目標，必須將整體設計和結構細節(jié)兩者都進行考慮。確保受剪、受彎構件的塑性的主要方式是為混凝土施加約束。這一點通過用封閉的箍筋或螺旋箍筋包在梁芯和柱芯的四周來實現(xiàn)。當提供了約束之后，梁和柱能承受非線性循環(huán)彎曲而其抗彎強度保持不因斜拉裂縫衰減。塑性鉸的形成可以使混凝土框架消耗能量。4.2.2MemberConsiderationsSuccessfulseismicdesignofframesrequiresthatthestructuresbepropor-tionedsothathingesoccuratlocationsthatleastcompromisestrength.Foraframeundergoinglateraldisplacement,suchasshowninFig.4-5a,theflexuralcapacityofthemembersatajoint(Fig.4-5b)shouldbesuchthatthecolumnsarestrongerthanthebeams.Inthisway,hingeswillforminthebeamsratherthanthecolumns,minimizingtheportionofthestructureaffectedbynonlinearbehaviorandmaintainingtheoverallverticalloadcapacity.Forthesereasons,the“weakbeam-strongcolumn”approachisusedtodesignreinforcedconcreteframessubjecttoseismicloading.內容大意：強柱弱梁flexuralcapacity抗彎承載力weakbeam-strongcolumn強柱弱梁4.2.2MemberConsiderationsSuccessfulseismicdesignofframesrequiresthatthestructuresbepropor-tionedsothathingesoccuratlocationsthatleastcompromisestrength.Foraframeundergoinglateraldisplacement,suchasshowninFig.4-5a,theflexuralcapacityofthemembersatajoint(Fig.4-5b)shouldbesuchthatthecolumnsarestrongerthanthebeams.Inthisway,hingeswillforminthebeamsratherthanthecolumns,minimizingtheportionofthestructureaffectedbynonlinearbehaviorandmaintainingtheoverallverticalloadcapacity.Forthesereasons,the“weakbeam-strongcolumn”approachisusedtodesignreinforcedconcreteframessubjecttoseismicloading.成功的框架抗震設計要求結構的尺寸合理，使塑性鉸出現(xiàn)在最不影響強度的位置。對于一個發(fā)生側向位移的框架，如圖4-5a所示，節(jié)點處構件的抗彎能力（圖4-5b）應確保柱（承載力）大于梁（承載力）。這樣，鉸就會形成在梁上而不是柱上，從而使受非線性行為影響的結構區(qū)域最小化，并保持整體豎向承載能力。為此，采用“強柱弱梁”原則進行設計鋼筋混凝土框架的抗震設計。Fig.4-8Framesubjectedtolateralloading:(a)deflectedshape;(b)momentsactingonbeam-columnjoint;(c)deflectedshapeandforcesactingonabeam;(d)forcesactingonfacesofajointduetolateralload.4.2.2MemberConsiderationsWhenhingesfrominabeam,orinextremecaseswithinacolumn,themomentsattheendofthemember,whicharegovernedbyflexuralstrength,determinetheshearthatmustbecarried,asillustratedinFig.4-5c.TheshearVcorrespondingtoaflexuralfailureatbothendsofabeamorcolumnis內容大意：彎曲破壞剪力計算flexuralfailure

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

內容大意：抗剪構造transversereinforcement

橫向鋼筋shearcapacity抗剪承載力diagonalcrack斜裂縫4.2.2MemberConsiderationsWhenhingesfrominabeam,orinextremecaseswithinacolumn,themomentsattheendofthemember,whicharegovernedbyflexuralstrength,determinetheshearthatmustbecarried,asillustratedinFig.4-5c.TheshearVcorrespondingtoaflexuralfailureatbothendsofabeamorcolumnisThemembermustbecheckedforadequacyundertheshearVinadditiontoshearresultingfromdeadandlivegravityloads.Transversereinforcementisadded,asrequired.Formemberswithinadequateshearcapacity,theresponsewillbedomi-natedbytheformationofdiagonalcracks,ratherthanductilehinges,resultinginasubstantialreductionintheenergydissipationcapacityofthemember.

當鉸形成在梁上，或極端情況下形成在柱上，抗彎強度支配構件端部的彎矩大小，并決定其必須承載的剪力，如圖4-5c所示。梁柱兩端對應于彎曲破壞的剪力V是必須驗算構件能否承受剪力V與恒載及活載作用下產(chǎn)生的剪力作用的合力。按照要求，應當加入橫向鋼筋。對于抗剪能力不足的構件，其響應會受控于斜拉裂縫的形成，而不是塑性鉸（的形成），導致構件耗能能力的明顯減小。4.2.2MemberConsiderationsIfshortmembersareusedinaframe，themembersmaybeunintentionallystronginflexurecomparedtotheirshearcapacity.Anexamplewouldbecolumnsinastruc-turewithdeepspandrelbeamsorwith“nonstructural”wallswithopeningsthatexposeaportionofthecolumnstothefulllateralload.Asaresult,theexposedregion,calledacaptivecolumn,respondsbyundergoingashearfailure,asshowninFig.4-6.內容大意：短柱nonstructural

非結構的captivecolumn窗臺柱4.2.2MemberConsiderationsIfshortmembersareusedinaframe，themembersmaybeunintentionallystronginflexurecomparedtotheirshearcapacity.Anexamplewouldbecolumnsinastruc-turewithdeepspandrelbeamsorwith“nonstructural”wallswithopeningsthatexposeaportionofthecolumnstothefulllateralload.Asaresult,theexposedregion,calledacaptivecolumn,respondsbyundergoingashearfailure,asshowninFig.4-9.如果在框架中用了短構件，這些構件的抗彎能力很可能會明顯比抗剪能力強（盡管不是故意的）。例如，在帶有裙深梁的結構中的柱，或在帶有開口的“非結構”墻中的柱，將會使柱的一部分承受全部側向荷載。因此，暴露出的區(qū)域（被稱為窗臺柱），最終產(chǎn)生剪切破壞，如圖4-9所示。Fig.4-9

Shearfailureinacaptivecolumnwithoutadequatetransversereinforcement.4.2.2MemberConsiderationsThelateraldisplacementofaframeplacesbeam-columnjointsunderhighshearstressesbecauseofthechangefrompositivetonegativebendingintheflexuralmembersfromonesideofthejointtotheother,asshowninFig.4-5d.Thejointmustbeabletowithstandthehighshearstressesandallowforachangeinbarstressfromtensiontocompressionbetweenthefacesofthejoint.Suchatransferofshearandbondisoftenmadedifficultbycongestionofreinforcementthroughthejoint.Thus,designersmustensurethatjointsnotonlyhaveadequatestrengthbutarealsoconstructible.Two-waysystemswithoutbeamsareespeciallyvulnerablebecauseoflowductilityattheslab-columnintersection.內容大意：節(jié)點設計joint

節(jié)點

congestion

沖突

vulnerable易破壞的4.2.2MemberConsiderationsThelateraldisplacementofaframeplacesbeam-columnjointsunderhighshearstressesbecauseofthechangefrompositivetonegativebendingintheflexuralmembersfromonesideofthejointtotheother,asshowninFig.4-8d.Thejointmustbeabletowithstandthehighshearstressesandallowforachangeinbarstressfromtensiontocompressionbetweenthefacesofthejoint.Suchatransferofshearandbondisoftenmadedifficultbycongestionofreinforcementthroughthejoint.Thus,designersmustensurethatjointsnotonlyhaveadequatestrengthbutarealsoconstructible.Two-waysystemswithoutbeamsareespeciallyvulnerablebecauseoflowductilityattheslab-columnintersection.框架的側向位移使梁柱節(jié)點承受極大的剪切應力，這是因為受彎構件節(jié)點兩側的彎矩正負號發(fā)生變化，如圖4-8d所示。節(jié)點必須能夠承受極大的剪切應力，并允許節(jié)點表面之間的鋼筋應力可以從受拉變?yōu)槭軌?。由于通過節(jié)點的鋼筋非常稠密，因此剪力和粘結力的傳遞通常非常困難。因此，設計者必須保證節(jié)點不但有足夠的強度，而且是便于施工的。無梁雙向系統(tǒng)特別容易破壞，因為板柱交匯處塑性特別差。4.3SeismicLoadingCriteriaIntheUnitedStates,thedesigncriteriaforearthquakeloadingarebasedondesignproceduresdevelopedbytheBuildingSeismicSafetyCouncilandincor-poratedinMinimumDesignLoadsforBuildingsandOtherStructures(ASCE/SEI7).ThevaluesofthespectralresponseaccelerationsSSandS1,areobtainedfromdetailedmapsproducedbytheUnitedStatesGeologicalSurveyandincludedinASCE/SEI7.ThevaluesofSSandS1areusedtodeterminethespec-tralresponseaccelerationsSDSandSD1thatareusedindesign.內容大意：設計反應譜參數(shù)designcriteria設計指標spectralresponseaccelerations反應譜加速度4.3SeismicLoadingCriteriaIntheUnitedStates,thedesigncriteriaforearthquakeloadingarebasedondesignproceduresdevelopedbytheBuildingSeismicSafetyCouncilandincor-poratedinMinimumDesignLoadsforBuildingsandOtherStructures(ASCE/SEI7).ThevaluesofthespectralresponseaccelerationsSSandS1,

areobtainedfromdetailedmapsproducedbytheUnitedStatesGeologicalSurveyandincludedinASCE/SEI7.ThevaluesofSSandS1areusedtodeterminethespec-tralresponseaccelerationsSDSandSD1thatareusedindesign.在美國，地震荷載的設計標準是以由建筑抗震安全委員會發(fā)布并被納入建筑物和其他結構的最小設計荷載中的設計方法為依據(jù)制定的(ASCE/SEI7)。譜響應加速度值SS和S1是從美國地質調查局發(fā)布并包含在ASCE/SEI7中的詳細地圖中取得的。SS和S1的值用來確定在設計中需要用到的頻譜響應加速度SDS和SD1。4.3SeismicLoadingCriteriawhereFaandFvaresitecoefficientsthatrangefrom0.8to0.25andfrom0.8to0.35,respectively,asafunctionofthegeotechnicalpropertiesofthebuildingsiteandthevaluesofSsandS1,respectively.HighervaluesofFa