《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(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4.1IntroductionEarthquakesresultfromthesuddenmovementoftectonicplatesintheearth’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(gòu)造板塊突然運(yùn)動造成的。這種運(yùn)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(nèi)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(yùn)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?jǐn)?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(yù)期加速度峰值。公認(rèn)地，用0.2s譜反應(yīng)加速度Ss（下標(biāo)s代表短周期）和1.0s譜應(yīng)加速度S1（同理），為抗震設(shè)計建立荷載標(biāo)準(zhǔn)。加速度Ss和S1根據(jù)史料記載和當(dāng)?shù)氐牡刭|(zhì)情況確定。大多數(shù)國家用“50年內(nèi)超越2%的概率”來表示地面運(yùn)動，一個相當(dāng)于2500年一遇的數(shù)值。4.1IntroductionAsexperiencedbystructures,earthquakesconsistofrandomhorizontalandver-ticalmovementsoftheearth’ssurface.Asthegroundmoves,inertiatendstokeepstructuresinplace(Fig.4-1),resultingintheimpositionofdisplacementsandforcesthatcanhavecatastrophicresults.Thepurposeofseismicdesignistoproportionstructuressothattheycanwithstandthedisplacementsandtheforcesinducedbythegroundmotion.內(nèi)容大意：地震慣性力horizontal

水平向

ver-tical

豎向

inertia慣性imposition施加catastrophic災(zāi)難性的Fig.4-1Structuresubjectedtogroundmotion.4.1IntroductionAsexperiencedbystructures,earthquakesconsistofrandomhorizontalandver-ticalmovementsoftheearth’ssurface.Asthegroundmoves,inertiatendstokeepstructuresinplace(Fig.4-1),resultingintheimpositionofdisplacementsandforcesthatcanhavecatastrophicresults.Thepurposeofseismicdesignistoproportionstructuressothattheycanwithstandthedisplacementsandtheforcesinducedbythegroundmotion.正如結(jié)構(gòu)所經(jīng)歷的那樣，地震是由是地球表面隨機(jī)的橫向和豎向運(yùn)動組成的。隨著地面的運(yùn)動，慣性傾向于使結(jié)構(gòu)保持原位（圖4.1），使結(jié)構(gòu)承受可導(dǎo)致災(zāi)難性的后果的位移和力?？拐鹪O(shè)計的目標(biāo)就是確定結(jié)構(gòu)的尺寸，使它們能夠承受地面運(yùn)動所引起的位移和力。Fig.4-1Structuresubjectedtogroundmotion.4.1IntroductionHistoricallyinNorthAmerica,seismicdesignhasemphasizedtheeffectsofhorizontalgroundmotionbecausethehorizontalcomponentsofanearthquakeusuallyexceedtheverticalcomponentsandbecausestructuresareusuallymuchstifferandstrongerinresponsetoverticalloadsthantheyareinresponsetohorizontalloads.Experiencehasshownthatthehorizontalcomponentsarethemostdestructive.內(nèi)容大意：地震荷載特點(diǎn)groundmotion地面運(yùn)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(yùn)動特性intensity

強(qiáng)度peakgroundacceleration地面運(yùn)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(shè)計強(qiáng)調(diào)水平地面運(yùn)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(jié)構(gòu)的剛度和強(qiáng)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(jié)構(gòu)設(shè)計，地震的強(qiáng)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(shè)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(yùn)動的頻率與結(jié)構(gòu)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(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4.1IntroductionBasedonelasticbehavior,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(jié)構(gòu)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(guān)力來進(jìn)行結(jié)構(gòu)設(shè)計。采用相對低的設(shè)計力的理由是通過觀測按較低的力設(shè)計的結(jié)構(gòu)，發(fā)現(xiàn)它們的表現(xiàn)非常令人滿意，并且這些結(jié)構(gòu)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(zhuǎn)化為位移的增大，這可能需要極大的塑性，并且會導(dǎo)致嚴(yán)重的非結(jié)構(gòu)損傷。位移的幅值可能太大，導(dǎo)致結(jié)構(gòu)的強(qiáng)度受到穩(wěn)定性考慮的影響。4.2StructuralResponseThesafetyofastructuresubjectedtoseismicloadingrestsonthedesigner’sunderstandingoftheresponseofthestructuretogroundmotion.Formanyyears,thegoalofearthquakedesigninNorthAmericahasbeentoconstructbuildingsthatwillwithstandmoderateearthquakeswithoutdamageandsevereearthquakeswithoutcollapse.Buildingcodeshaveundergoneregularmodificationasmajorearthquakeshaveexposedweaknessesinexistingdesigncriteria.內(nèi)容大意：抗震設(shè)計目標(biāo)groundmotion地面運(yùn)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4.2StructuralResponseThesafetyofastructuresubjectedtoseismicloadingrestsonthedesigner’sunderstandingoftheresponseofthestructuretogroundmotion.Formanyyears,thegoalofearthquakedesigninNorthAmericahasbeentoconstructbuildingsthatwillwithstandmoderateearthquakes(withoutdamage)andsevereearthquakes(withoutcollapse).Buildingcodeshaveundergoneregularmodificationasmajorearthquakeshaveexposedweaknessesinexistingdesigncriteria.Designforearthquakesdiffersfromdesignforgravityandwindloadsintherelativelygreatersensitivityofearthquake-inducedforcestothegeometryofthestructure.Withoutcarefuldesign,forcesanddisplacementscanbeconcentratedinportionsofastructurethatarenotcapableofprovidingadequatestrengthorductility.Stepstostrengthenamemberforonetypeofloadingmayactuallyincreasetheforcesinthememberandchangethemodeoffailurefromductiletobrittle.地震荷載作用下結(jié)構(gòu)的安全性依賴于設(shè)計者們對地面運(yùn)動下結(jié)構(gòu)響應(yīng)的理解。多年來，北美的抗震設(shè)計目標(biāo)一直是中震不壞，大震不倒。由于大震暴露了現(xiàn)有設(shè)計標(biāo)準(zhǔn)的缺陷，建筑規(guī)范開始進(jìn)行定期修改?？拐鹪O(shè)計與（抵抗）重力和風(fēng)載設(shè)計的不同之處在于地震引起的力對結(jié)構(gòu)的幾何形狀有更高的靈敏度。如果不仔細(xì)設(shè)計，力和位移會集中在結(jié)構(gòu)不能提供足夠的強(qiáng)度和塑性的部位（薄弱層）。針對一種荷載來加強(qiáng)一個構(gòu)件的措施實際上可能會增大該構(gòu)件（承受）的力，并且可能使其失效的模式從塑性轉(zhuǎn)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(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4.2.1StructuralConsiderationThecloserthefrequencyofthegroundmotionistooneofthenaturalfrequenciesofastructure，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(yùn)動的頻率越接近一個結(jié)構(gòu)的固有頻率之一，結(jié)構(gòu)產(chǎn)生共振的可能性就越大，從而導(dǎo)致位移和損傷程度的增大。因此，地震響應(yīng)極大的取決于結(jié)構(gòu)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(yùn)動反應(yīng)更強(qiáng)烈，而低矮的建筑物對短周期（高頻）的地面運(yùn)動反應(yīng)更強(qiáng)烈。圖4-3顯示了一個三層框架結(jié)構(gòu)的主振型圖。各振型對結(jié)構(gòu)側(cè)向位移的相應(yīng)貢獻(xiàn)取決于地面運(yùn)動的頻率特性。通常第一振型（圖4-3a）對側(cè)向位移的貢獻(xiàn)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(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4.2.1StructuralConsiderationTheconfigurationofastructurealsohasamajoreffectonitsresponsetoanearthquake.Structureswithadiscontinuityinstiffnessorgeometrycanbesubjectedtoundesirablyhighdisplacementsorforces.Forexample,thediscontinuanceofshearwalls,infillwalls,orevencladdingataparticularstorylevel,suchasshowninFig.4-4,willhavetheresultofconcentratingthedisplacementintheopen,or“soft”story.Thehighdisplacementwill,inturn,requirealargeamountofductilityifthestructureisnottofail.Suchadesignisnotrecommended,andtheFig.4-6illustratesstructureswithverticalgeometricandplanirregularities,whichresultintorsioninducedbygroundmotion.結(jié)構(gòu)體型對其在地震下的響應(yīng)也具有重要的影響。剛度或幾何不連續(xù)的結(jié)構(gòu)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(jié)構(gòu)不破壞，大位移要求結(jié)構(gòu)有極大的塑性。但這樣的設(shè)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(jié)構(gòu)，此類結(jié)構(gòu)在地震作用下會發(fā)生扭轉(zhuǎn)。Fig.4-4Softfirststorysupportingastiffupperstructure.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4.2.2MemberConsiderationsMembersdesignedforseismicloadingmustperforminaductilefashionanddissipateenergyinamannerthatdoesnotcompromisethestrengthofthestructure.Boththeoveralldesignandthestructuraldetailsmustbeconsideredtomeetthisgoal.Theprincipalmethodofensuringductilityinmemberssubjecttoshearandbendingistoprovideconfinementfortheconcrete.Thisisaccomplishedthroughtheuseofclosedhoopsorspiralreinforcement,whichenclosethecoreofbeamsandcolumns.Whenconfinementisprovided,beamsandcolumnscanundergononlinearcyclicbendingwhilemaintainingtheirflexuralstrengthandwithoutdeterioratingduetodiagonaltensioncracking.Theformationofductilehingesallowsreinforcedconcreteframestodissipateenergy.在抗震荷載下設(shè)計的構(gòu)件必須以塑性的方式工作，并以不影響結(jié)構(gòu)強(qiáng)度的方式耗散能量。為了實現(xiàn)這一目標(biāo)，必須將整體設(shè)計和結(jié)構(gòu)細(xì)節(jié)兩者都進(jìn)行考慮。確保受剪、受彎構(gòu)件的塑性的主要方式是為混凝土施加約束。這一點(diǎn)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(dāng)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(qiáng)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(nèi)容大意：強(qiáng)柱弱梁flexuralcapacity抗彎承載力weakbeam-strongcolumn強(qiáng)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(shè)計要求結(jié)構(gòu)的尺寸合理，使塑性鉸出現(xiàn)在最不影響強(qiáng)度的位置。對于一個發(fā)生側(cè)向位移的框架，如圖4-5a所示，節(jié)點(diǎn)處構(gòu)件的抗彎能力（圖4-5b）應(yīng)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(jié)構(gòu)區(qū)域最小化，并保持整體豎向承載能力。為此，采用“強(qiáng)柱弱梁”原則進(jìn)行設(shè)計鋼筋混凝土框架的抗震設(shè)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(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4.2.2MemberConsiderationsWhenhingesfrominabeam,orinextremecaseswithinacolumn,themomentsattheendofthemember,whicharegovernedbyflexuralstrength,determinetheshearthatmustbecarried,asillustratedinFig.4-5c.TheshearVcorrespondingtoaflexuralfailureatbothendsofabeamorcolumnisThemembermustbecheckedforadequacyundertheshearVinadditiontoshearresultingfromdeadandlivegravityloads.Transversereinforcementisadded,asrequired.Formemberswithinadequateshearcapacity,theresponsewillbedomi-natedbytheformationofdiagonalcracks,ratherthanductilehinges,resultinginasubstantialreductionintheenergydissipationcapacityofthemember.

當(dāng)鉸形成在梁上，或極端情況下形成在柱上，抗彎強(qiáng)度支配構(gòu)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(yīng)于彎曲破壞的剪力V是必須驗算構(gòu)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(yīng)當(dāng)加入橫向鋼筋。對于抗剪能力不足的構(gòu)件，其響應(yīng)會受控于斜拉裂縫的形成，而不是塑性鉸（的形成），導(dǎo)致構(gòu)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(nèi)容大意：短柱nonstructural

非結(jié)構(gòu)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(gòu)件，這些構(gòu)件的抗彎能力很可能會明顯比抗剪能力強(qiáng)（盡管不是故意的）。例如，在帶有裙深梁的結(jié)構(gòu)中的柱，或在帶有開口的“非結(jié)構(gòu)”墻中的柱，將會使柱的一部分承受全部側(cè)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(nèi)容大意：節(jié)點(diǎn)設(shè)計joint

節(jié)點(diǎn)

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(cè)向位移使梁柱節(jié)點(diǎn)承受極大的剪切應(yīng)力，這是因為受彎構(gòu)件節(jié)點(diǎn)兩側(cè)的彎矩正負(fù)號發(fā)生變化，如圖4-8d所示。節(jié)點(diǎn)必須能夠承受極大的剪切應(yīng)力，并允許節(jié)點(diǎn)表面之間的鋼筋應(yīng)力可以從受拉變?yōu)槭軌骸Ｓ捎谕ㄟ^節(jié)點(diǎn)的鋼筋非常稠密，因此剪力和粘結(jié)力的傳遞通常非常困難。因此，設(shè)計者必須保證節(jié)點(diǎn)不但有足夠的強(qiáng)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(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4.3SeismicLoadingCriteriaIntheUnitedStates,thedesigncriteriaforearthquakeloadingarebasedondesignproceduresdevelopedbytheBuildingSeismicSafetyCouncilandincor-poratedinMinimumDesignLoadsforBuildingsandOtherStructures(ASCE/SEI7).ThevaluesofthespectralresponseaccelerationsSSandS1,

areobtainedfromdetailedmapsproducedbytheUnitedStatesGeologicalSurveyandincludedinASCE/SEI7.ThevaluesofSSandS1areusedtodeterminethespec-tralresponseaccelerationsSDSandSD1thatareusedindesign.在美國，地震荷載的設(shè)計標(biāo)準(zhǔn)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(jié)構(gòu)的最小設(shè)計荷載中的設(shè)計方法為依據(jù)制定的(ASCE/SEI7)。譜響應(yīng)加速度值SS和S1是從美國地質(zhì)調(diào)查局發(fā)布并包含在ASCE/SEI7中的詳細(xì)地圖中取得的。SS和S1的值用來確定在設(shè)計中需要用到的頻譜響應(yīng)加速度SDS和SD1。4.3SeismicLoadingCriteriawhereFaandFvaresitecoefficientsthatrangefrom0.8to0.25andfrom0.8to0.35,respectively,asafunctionofthegeotechnicalpropertiesofthebuildingsiteandthevaluesofSsandS1,respectively.HighervaluesofFa