土木工程外文翻译-抗震钢筋混凝土结构设计原则及土木工程实习报告

附录SeismologyCivilEngineeringSEISMICRESISTANTREINFORCEDCONCRETESTRUCTURES-DESIGNPRINCIPLESSUMMARY:Earthquakescauseconsiderableeconomiclosses.Itispossibletominimizetheeconomiclosesbyproperseismicdesign.Inthispaperbasicprinciplesforseismicdesignaresummarized.Therearethreebasicrequirementstobesatisfied;(a)strength,(b)ductilityand(c)stiffness.Inthepaperthesearebrieflydiscussed.Inthesecondpartofthepapertheauthorsummarizeshisviewsonthedamagesobservedinthepastearthquakes.Heconcludesthatmostofthedamageshavebeendueto,(a)badconfiguration,(b)inadequatedetailingand(c)inadequatesupervision.Inthepaperthesearediscussed,pointingoutthecommonmistakesmadeanddamagesobservedasaresultofthesemistakes.Inthelastpartofthepapersomesimplerecommendationsaremadeforproducingseismicresistantreinforcedconcretestructures,emphasizingondetailingandproportioning.KeyWords:Seismicresistance,reinforcedconcrete.1.INTRODUCTIONEveryyearmorethan300000earthquakesoccurontheearth.Manyoftheseareofsmallintensityanddonotcauseanydamagetoourstructures.However,earthquakesoflargerintensityinthevicinityofpopulatedareascauseconsiderabledamageandlossoflife.Itisestimatedthatontheaverage15000peoplehavebeenkilledeachyearthroughouttheworldbecauseofearthquakes.Sinceancienttimesmankindhassoughtwaysandmeansofminimizingthedamagecausedbyearthquakes.Thegreatmastersoftheartofbuildinghavebeenabletobuildstructureswhichhavewithstoodmanysevereearthquakesforcenturies.MagnificentmosquesandbridgesintheMiddleEastbuiltbyourancestorsarestillinservice,Thesemastersdidnotknowseismicanalysis,butwereabletoevaluatepastexperiencewiththeirexcellentengineeringintuitionandjudgement.Mosques,bridgesandschools(Medrese)builtbySinaninIstanbulandEdirnearenotonlybeautiful,butarealsoengineeringmasterpieces.Todaywehavegreatadvantagesascomparedtoourancestors.Wehavemoreexperience,wehavehighlydevelopedanalyticaltoolsandconsiderableexperimentaldata.Itshouldalsobenotedthatcomputersenableustoconsidermorevariablesandseveralalternativesintheanalysis.Themainobjectiveofthispaperistolaydownsomebasicprinciplesforproducingearthquakeresistantreinforcedconcretestructures.Thesearesimpleprinciplesandeasytoapply.Theyhavebeendevelopedinthelightofanalyticalandexperimentalresearchdoneandonobservationsmadefrompastearthquakes.2.BASICPHILOSOPHYANDREQUIREMENTSDesignprinciplescannotbelaiddownunlessthereisawelldefineddesignphilosophy.Thedesignphilosophygenerallyacceptedissummarizedbelow:-Buildingsshouldsuffernostructuraldamageinminor,frequentearthquakes.Normallythereshouldbenononstructuraldamageeither.-Buildingsshouldsuffernoneofminorstructuraldamage(repairable)inoccasionalmoderateearthquakes.-Buildingsshouldnotcollapseinrarelyoccurringmajorearthquakes.Duringsuchearthquakesstructuresarenotexpectedtoremainintheelasticrange.Yieldingofreinforcingstellweillleadtoplastichingesatcriticalsections.Thegeneraldesignphilosophywillnothavemuchpracticaluseunlessdesignrequirementsaredevelopedinparallelwiththisphilosophy.Theauthorbelievesthatthedesignrequirementscanbesummarizedinthreegroups.a.Strengthrequirementsb.Ductilityrequirementsc.Stiffnessrequirements(ordriftcontrol).Thesethreerequirementswillbebrieflydiscussedinthefollowingparagraphs.2.1.StrengthRequirementsMembersinthestructureshouldhaveadequatestrengthtocarrythedesignloadssafely.Sincethedesignersarewellacquaintedwiththisrequirement,itwillnotbediscussedindetail.However,itshouldbepointedoutthatthedesignershouldavoidbrittletypeoffailure,bymakingacapacitydesign(1).ThebasicprinciplesincapacitydesignareillustratedforabeaminFigure1.Ifthedesignsheariscomputedbyplacingtheultimatemomentcapacitiesateachendofthebeam,thedesignercanmakesurethatductileflexuralfailurewilltakeplacepriortoshearfailure.2.2.DuctilityRequirementsIngeneralitisnoteconomicaltodesignR/Cstructurestoremainelasticduringamajorearthquake.Ithasbeendemonstratedthatstructuresdesignedforhorizontalloadsrecommendedinthecodescanonlysurvivestrongearthquakesiftheycanhavetheabilitytodissipateconsiderableamountofenergy.Theenergydissipationisprovidedmainlybylargerotationsatplastichinges.Theenergydissipationbyinelasticdeformationsrequiresthemembersofthestructureandtheirconnectionstopossessadequate"ductility”.Ductilityistheabilitytodissipateasignificantamountofenergythroughinelasticactionunderlargeamplitudedeformations,withoutsubstantialreductionofstrength.Adequateductilitycanbeaccomplishedbyspecifyingminimumrequirementsandbyproperdetailing(2).2.3.StiffnessRequirementsIndesigningabuildingforgravityloads,thedesignershouldconsiderserviceabilityinadditiontoultimatestrength.Inseismicdesign,driftlimitationsimposedmightbeconsideredtobesomekindofaserviceabilityrequirement.However,thedriftlimitationinseismicdesignismoreimportantthantheserviceabilityrequirement.Thelimitingdriftisusuallyexpressedastheratiooftherelativestoreydisplacementtothestoreyheight(interstoreydrift).Excessiveinterstoreydriftleadstoconsiderabledamageinnonstructuralelements.Inmanycasesthecostofreplacingorrepairingofsuchelementsisveryhigh.Excessiveinterstoreydriftcanalsoleadtoverylargesecondordermoments(P-effect)whichcanendangerthesafetyandstabilityofthestructure.Thereforeinterstoreydriftcontrolisconsideredtobeoneofthemostimportantrequirementsinseismicdesign.TherecentMexicoandChileearthquakeshavedemonstratedtheimportanceofthisrequirement(1).InTurkishCodetheinterstoreydriftislimitedto0.0025h,wherehisthestoreyheight.3.LESSONSLEARNEDFROMPASTEARTHQUAKESOurknowledgeinseismicdesignhasdevelopedhasdevelopedasaresultofanalyticalandexperimentalresearchandexperiencegainedfrompastearthquakes.Theauthorbelievesthatlessonslearnedfrompastearthquakeshavebeenthemostimportantsourceamongallothers,becauseearthquakesperformthemostrealisticlaboratorytestsonthebuildings.Theauthorhasreevaluatedthedamagesobservedinearthquakesduringthepast30yearsinTurkey.Thisreevaluationhasrevealedthatmorethan90%ofthedamagescanbeattributedtooneofthefollowingcausesorcombinationsofthese:a.Mistakesmadeinchoosingthebuildingconfiguration(generalconfigurationorthestructuralsystemchosen).b.Inadequatedetalingandproportioningorerrorsmadeindetailing.c.Poorconstructionqualitycausedbyinadequatesupervision.Itisinterestingtonotethatcausesofdamagegroupedintotheabovethreecategoriesseemtoapplytoearthquakedamagesobservedinothercountriesalso.Thesethreecauseswillbediscussedbrieflyintheparagraphstofollow.3.1.BuildingConfigurationSeismicresistanceshouldbeinitiatedatthearchitecturaldesignstage.Ifthegeneralconfigurationchosenbythearchitectiswrong,itisverydifficultandexpensiveforthestructuralengineertomakethebuildingseismicresistant.Asageneralprinciplethefloorplanshouldbeassymmetricalaspossible.Thelengthofwings(T,L,.crossshapedbuildings)causingre-entrantcornersshouldnotbelarge.Ifthelengthofthewingsisnotshort,thentheseshouldbeseparatedfromthemainbuildingbyanexpansionJoint.Symmetryabouttheelevationalaxisisnotassignificantastheplansymmetry.However,abruptchangesinbuildingplanalongtheheightofthebuildingarenotdesirablefromtheseismicresistancepointofview.Setbacksarecommonverticalirregularitiesinbuildinggeometry.Setbackscausediscontinuitiesandabruptchangesinstrengthandstiffness.Theseriousnessofthesetbackeffectdependsontherelativeproportionsandabsolutesizeofseparatepartsofthebuilding.Ingeneralthedesignershouldtrytomakechangesinstrengthandstiffnessalongthebuildingheightassmallaspossible.Asfarasthestructuralsystemisconcerned,onecansetoutsomebasicrulesforbetterseismicresistance.Beforesettingouttheserules,itwouldbeappropriatetoremindtheengineersthatnonstructuralinfillwallswillinfluencetheframebehavioursignificantlyunlessseparatedfromtheframe.Suddenchangesinstiffnessalongtheheightofthebuildingshouldbeavoided.Ifthestiffnessofonestoreyissignificantlysmallerthantheothers(softstorey),prematurefailurecanoccurduetoexcessivelateraldisplacementatthisfloorlevel.AsshowninFigure2,changesinthestoreystiffnesscanbecausednotonlybystructuralelements,butalsobynonstructuralelementssuchasinfillwalls.Twoadjacentbuildingsshouldbeseparatedfromeachotherbyanadequatedistanceinordertoavoidthedamagecausedbypoundingorreciprocalhammeringofthebuildings.Theverticalloadcarryingelementsinafloorshouldbesoproportionedandarrangedthatthecenterofmassandcenterofresistanceshouldnearlycoincide.Ifthesetwocentersareawayfromeachother,theresultingeccentricitycancauseseverefloortorsion,increasingtheshearforcesattheboundaryelementsconsiderably.Torsionisnotonlycreatedbystructuralelements(Figure3b)butcanalsobecreatedbyinfillwallsunlessseparatedfromtheframe,Figure3a.Themaximumshearforcewhichbeactingonacolumncanbefoundbyaddingthemomentcapacities(ultimatemoments)ateachendofthecolumnanddividingbythecolumnlengthFigure4.Thissimplymeansthat,ifthelengthofthecolumnis/5,thenthecolumnwillcarryfivetimesasmuchshear.Forthisreason,shortcolumnsshouldbeavoidedwheneveritispossible,becauseoftheFigure3.dangerofshearfailure.AsillustratedinFigure4,shortcolumnsarecreatedbyeitherstructuralornonstructural(infill)elements.Structureswithflexiblefloormembers(flatplatesorjoistsystemwithshallowbeams)shouldeitherhaverigidcolumnsorshearwalls(orcross-bracing)topreventexcessivedrift.Iftheverticalloadcarryingmembersarenotrigidenough,veryhighsecondordermomentscanresultasshowninFigure5.In1967Adapazariand1985Mexicoearthquakesnumerousfailureshavebeenobservedinbuildingswithflexiblefloorsandslendercolumns.Foramoredetaildiscussiononconfiguration,thereaderisdirectedtoReference2.3.2.ProportioningandDetailingThedimensionsofstructuralmembersnotonlyinfluencethestrength,butalsotheoverallstiffnesofthestructure.Inthelightofexperiencegainedfromthepastearthquakes,theauthorbelievesthattheratioofthesumofthecross-sectionalareasofverticalloadcarryingmemberstothefloorareaisanimportantparameterinseismicresistance.Thisratiowillbecalledthe"DensityRatio".TheauthorhasstudiedthevariationofthisratiointhemonumentalhistoricalbuildingsinIstanbul,whichhavewith-stoodseveralsevereearthquakesduringthepastcenturies.Itwasfoundoutthatthisratiovariedbetween0.2and0.28.Asanexample,thefloorplanoftheSüleymaniye.MosqueisshowninFigure6.Theauthorwouldliketopointoutthesymmetryinthearrangementofloadcarryingmembers.InSüleymaniyethedensityratiowasabout0.24.AnotherinvestigationmadeonmodernreinforcedconcretebuildingsbuiltinseismicareasinTurkeyrevealthattheaveragedensityratioislessthan0.01.Theauthorfindstheratioratherlowandsuggeststhatitshouldbeabout0.015-0.0020.InthecityofVinadelMar,Chiletheaveragedensityratioinreinforcedconcretebuildings(4to23stories)isquitehigh,0.06(3).Thisseemstobeoneofthereasonswhyrelativelysmalldamageoccurredduringthe1985Chileearthquake,whichcreatedquiteaseveregroundmotion.Itshouldbepointedoutthatalthoughdensityratioisaveryimportantparameterforlateralstiffness,therelativestiffnessoffloormembershavealsoasignificantinfluenceonthestiffness.Ductilityrequiredforenergydissipationduringanearthquakeiscloselyrelatedtodetailing.AwelldesignedR/Cstructurecansufferconsiderabledamageifitisnotproperlydetailed.Detailingisanartwhichcannotberealizedunlesstheseismicbehaviourofreinforcedconcreteiswellunderstood.Thebasicprincipleindetailingistoprovidethenecessarystrengthandductilityatcriticalsectionsandjoints.Incuttingthebarsandinmakinglappedsplices,adequateanchoragelengthshouldbeprovided.Thecriticalregionswhereplastichingingisexpectedtooccurshouldbewellconfinedbycloselyspacedhoops.OurexperienceinTurkeyshowsthatinadequatedetailingplayedaveryimportantroleintheearthquakedamageobservedduringthepast30years.Mostofthedamagesattributedtodetailingwereduetoinadequateanchorageorsplicelengthandinadequateconfinement.Basicrulesfordetailingofbeams,columnsandstructuralwallsaresummarizedinFigures7,8and9.3.3.ConstructionTheearthquakewillberesistedbythestructurewhichisactuallybuiltandnotbythestructureshownonthedesigndrawings.Nomatterhowgoodthedesignmethodsusedare,itisnotpossibletoproduceaseismicresistantbuildingunlessthestructureisconstructedinaccordancewiththedesignprojectunderpropersupervision.Inmostofthedevelopingcountriesemphasisisonthedesignstage;qualitycontrolandsupervisionareusuallylookeddownuponandignoredbytheengineer.Theengineershouldrealizethattheimportantrequirementsforseismicresistance,i.e.thestrength,ductilityandstiffnessdependontheactualdimensions,materialqualitiesandreinforcementdetailsaccomplishedonthesite.Poorsupervisionresultsinpoormaterialqualityanderrorsintheplacementofthereinforcingsteel.OurexperienceinTurkeyshowsthatinadequatesupervisionhasbeenthemostimportantcauseofstructuredamageduringpastearthquakes.Inthelightofthesediscussionsonecanconcludethat,forbetterseismicresistance,thefirststepshouldbeinthedirectionofcorrectingthemistakesmadeinthepast.Ifconfiguration,detailingandconstructionsupervisioncannotbeimproved,wellwrittencodesandsophisticatedmethodsofanalyseswillnotbeabletopreventdamageandfailuresinfutureearthquakes.4RECOMMENDATIONSFORDESIGNThemainobjectiveofthissectionistospecifysomesimplerulesforthedesignofordinaryreinforcedconcretestructures.Byordinary,theauthormeansregularstructuresuptosaytenstories.4.1.SummaryofFactsBeforestatingthedesignrules,itwouldbeusefultostatesomebasicfactsabouttheseismicactionandseismicresistanceofreinforcedconcretestructures.-Thecharacteristicsofthegroundmotionexpectedcannotbefullydefined.-Thestructurecannotremainelasticwhensubjectedtoastronggroundmotion.Yieldingwilloccuratdifferentlocationsandmostoftheenergywillbedissipatedatthesesections.-Responseofthestructuredependsnotonlyonthegroundmotion,butalsoonthedynamiccharacteristicsofthestructure,suchasmass,stiffnessanddamping.Forreinforcedconcretestructuresitisverydifficulttoestimatethestiffnessanddamping,becauseofcrackingandtimedependentdeformationswhichhavetakenplacepriortotheearthquake.-Nonstructuralelementsinfluencethebehaivour.-Inordertoanalyzeabuilding,firstasimplephysicalmodeliscreatedbymakingmanysimplifyingassumptions.Theanalysismadeisforthismodelandnotfortherealbuilding.Theassumptionsmadeincreatingthismodelintroduceerrors.-Importantdynamiccharacteristicsuchasmass,stiffnessanddampingdependontheactualdimensionsandmaterialstrengthsobtainedduringconstruction.Thesecanbequitedifferentfromtheonesassumedatthedesignstage.Inthelightofthesefacts,onecaneasilyseethattherearemanyuncertaintiesinvolvedintheseismicdesignofreinforcedconcretebuildings.Theengineershouldbewellawareofthesefactsandshouldnotrelyentirelyonthenumbershehasobtainedfromanalyses.Moresophisticatedandmorecomplicatedmethodsofanalysescaneasilycarrytheengineerawayfromtheactualbehaviourandmakehimaslaveofnumbers.Usuallysimplemethodssupportedbysoundjudgementbasedonbehaviourwillresultinassatisfactoryseismicdesign.4.2.AsimpleApproachSeismicresistancecanbeaccomplishedbyfollowingthebasicstepsgivenbelow:a.Choosingagoodconfigurationb.Makingasatisfactoryanalysis(Staticordynamic)c.Proportioninganddetailingthemembersproperly.d.Constructingthebuildinginaccordancewiththedesignproject,undergoodsupervision.Theauthorbelievesthatforordinaryresidentialorofficebuildingsuptosaytenstories,seismicresistancecanbeobtainedtoagreatextentbyfollowingsomesimplerules.TherulesgivenbelowarebeingusedbyamunicipalityinTurkeyasaguidetodesignersandforcheckingthedesignssubmittedtothismunicipality.Thefirstruleconcernsthedensityratiomentionedpreviously.Forresidentialandofficebuildingsuptotenstories,thesummationofthecross-sectionalareasofverticalloadcarryingmembers(structuralwallsandcolumns)shouldsatisfythefollowingequation.Av0.020Ap(1)Av-summationcross-sectionalareasofallverticalstructuralmembersatthefloor(m2)Ap-planareaatthatfloor(m2)Inadditiontothisrule,thecross-sectionalareaofeachindividualcolumnshouldsatisfythefollowingcondition:Ac0.0015At(n)(2)Howevertheminimumcolumndimensionscannotbelessthan25x25cm.Ac-cross-sectionalareaofthecolumn(m2)At-tributoryareaofthecolumn(m2)n-numberofstoriesaboveThesecondsetofrulesareaboutminimumrequirementsanddetailing.ThesearesummarizedinFigures7,8and9forbeams,columnsandstructuralwalls.Inadditiontothesetwosetsofrules,thedesignershouldchooseareasonableconfigurationandpropersupervisionshouldbeprovidedattheconstructionstage.Ifthesesimplerulesarefollowedandiftherequirementsaresatisfied,mostprobablyadequateseismicresistancewillbeobtainedforthebuildingclassesspecified,evenifalateralloadanalysisisnotperformed.5.CONCLUSIONSTheresponseofreinforcedconcretebuildingsunderseismicactiondependsnotonlyonthenatureofthegroundmotion,butalsoonthedynamiccharacteristicsofthestructure.Duetouncrtaintiesinvolvedinestimatingthenatureofthegroundmotionandthestructuralcharacteristics,onlyapproximateresultscanbeexpectedfromanalyses.Thenumbersobtainedfromanalysesshouldbefilteredbymakinguseofpastexperienceandjudgement.Soundjudgementcanonlybebasedonafirmknowledgeabouttheseismicbehaivourofstructures.Are-evaluationofdamageobservedduringpastearthquakeshasrevealedthatseismicresistancecansignificantlybeimprovedbyfollowingsomesimplerules.Suchsimpleruleshavebeensummarizedinthispaper.REFERENCES1.SözenMA:"TowardaBehaviourBasedDesignofR/CFramestoResistEarhquakes",9.TechnicalConferenceofTurkishSocietyofCivilEngineers.VI.1,pp.1-44,Ankara,1978.2.ErsoyU:"BasicPrinciplesfortheDesignofSeismicResistantR/CStructures",WorkshoponSeismicDesign,RSS,Amman,Jordan,Nov.1987.3.RiddellR,WoodSL,DeLaLleraJC:"The1985ChileEarthquake",CivilEngineeringStudies,StructuralResearchSeriesNo.534,UILU-ENG.87-2005,UniversityofIllinois,Urbana,April1987.外文资料翻译土木工程地震学抗震钢筋混凝土结构设计原则摘要：地震造成相当多的经济损失。通过适当的抗震设计将经济减到最少是可能的。本论文中概述了地震设计的基本原则。有三个基本要求需要满足：(a)强度，(b)延性和(c)刚度。本论文对这些进行了简短的讨论。在本论文的第二部份中，作者观察过去地震中所造成的破坏并概述了自己的看法。他总结出大部份的损害可以归结于：(a)不规则的外形，(b)不充分的细节设计，(c)不充分的监督。本论文都对这些进行了讨论，作者指出那种常见的错误和观察到的破坏就是由这些错误引起的。在论文的最后一个部份中作者为钢筋混凝土结构的抗震设计给出一些简单的建议，并强调结构的细节设计使其成比例。关键字：抗震，钢筋混凝土。1介绍每年有超过300000个地震在地球上发生。多数地震强度小而且不会对我们的建筑物造成破害。然而，较大强度的地震如果发生在人口稠密的邻近区域，将会造成大量的破害和人员伤亡。据估计全世界每年平均有15000个人在地震中丧身。自从远古时代以来，人类已经寻找了大量方法和手段把地震引起的破坏减少到最少。建筑大师们已经能够建造出可以在几个世纪中抵抗强烈地震的建筑物。我们的祖先在中东建造的雄伟的清真寺和桥梁至今仍然在使用中，这些大师们不知道如何地震分析，但是他们凭借优秀的工程直觉和判断力能够评估过去的经验。由西纳在伊斯坦布尔和Edirne建造的清真寺，桥梁和学校(Medrese)不仅美丽，而且是工程的杰出作品。今天与我们的祖先相比较，我们有许多优势。我们有更多经验，有高度发达的分析工具和相当多的实验数据。同样计算机使我们能够考虑更多的不确定因素和并在分析中采用一些替代方法。本论文的主要目的是为钢筋混凝土结构的抗震提供一些基本原则。有一些简单的并且容易实施的抗震的基本原则。它们在地震分析和实验研究中，和对过去地震的观察报告中得到不断的发展。2基本原理及要求除非定义了很好的设计原理，否则不能够舍弃基本的设计原则。普遍接受的设计原理可以如下概述：1、建筑物在小型和频繁的地震中不能有结构破坏，通常也不能有非结构性破坏。2、建筑物在偶然的，中等的地震中不应该有结构性破坏（可修复）。3、建筑物在罕遇地震中不能倒塌。在这种地震中，结构不能作为处于弹性范围内考虑。钢筋的屈服使得构件在关键部位产生塑性铰。除非设计要求超出了设计原理，一般的设计原理才不会有实际意义。作者认为设计要求可以概括为以下三组：1、强度要求2、延性要求3、刚度要求(位移控制)这三个要求将会简短地在下列段落中讨论。2.1强度要求结构中的构件应该有足够的强度来安全地承受设计荷载。由于设计者已经熟知这一需求,在此不再详细讨论。然而，需要指出设计者应该通过承载力设计来避免构件的脆性失效（1）。图1展示了梁在承载力设计时需要满足的基本原则。如果设计剪力是通过在梁两端布置极限弯矩计算出来的,设计者就能确定弯曲破坏会在受剪破坏之前发生。2.2延性要求一般来说把钢筋混凝土结构设计成在大多数地震中是处于弹性状态的，是不经济的。人们已经证明出如果结构有能力消耗大量的能量，并满足由规范建议的水平线荷载的建筑物就可以在强烈的地震中幸存下来。能源的消耗主要是由塑料铰的大旋转提供。通过非线性变形的能源消耗需要结构中的构件和它们的连接拥有足够的“延性”。延性是指构件在巨大幅度的变形下通过非线性变形来消耗能量，并且没有巨大的强度损失。足够的延性可以通过指定最小量和恰当的细节设计来完成（2）。2.3刚度要求设计一幢建筑物的重力负荷时，设计者应该考虑适用性和极限强度。在抗震设计中，强加的极限侧移可以被考虑为对实用性的要求。然而，抗震设计中的侧移限值比实用性要求更重要。刚度限值通常是表示为相对的层间侧移与层高的比值(层间刚度)。过度的层间侧移将引起非结构构件的损害。在多数情况更换或修理此构件是昂贵的。过度的层间侧移会引起非常大的第二弯矩重分部(P-效果)，它能危及结构的安全和稳定性。因此对层间位移的控制被认为是抗震设计中最重要的要求之一。最近墨西哥和智利的地震就证明了这一要求的重要性(1)。在土耳其建筑法规中，层间位移的限值是0.0025h，这里的h是层高。3从过去地震学习到的经验教训对过去地震的分析和实验研究所获得的经验使我们关于抗震设计的知识不断得到发展。作者相信从过去地震中学习到的经验教训是所有其它经验来源之中最重要的，因为地震在建筑物上做了最现实的实验测试。作者对土耳其过去30年期间的地震所造成的破坏进行了重新评估。这次再评估显示超过90%的损害是由下列因素之一或其中某几个原因共同导致的：a.建筑物外形的错误选择(总体外形或结构的体系选择)。b.不充分的细节设计及细节设计中的比例关系和错误。c.不充分的监督引起的工程质量的不佳。值得一提的是由以上三类造成的破坏似乎同样适用于在其他国家观察到的地震损害。这三种原因将会简短地在接下来的段落中得到讨论。3.1建筑物外形建筑物的抗震设计应该在建筑设计阶段就开始。如果建筑师选择的总体外形是错误的，它对结构工程师来说会使建筑物抗震变得非常困难和昂贵。总的原则是平面设计应尽可能的对称。翼缘的长度(T型，L型，十字型建筑物)引起的新转角不应该太大。如果翼缘的长度不是短的，那么这些应该通过是扩充的连接使其与主体建筑物分开。正立面的对称性没有比平面的对称性重要。然而，在建筑设计中沿建筑高度的突变从抗震观点看不可取的。建筑几何中垂直方向的不规则是常见的。建筑外形的突变引起强度和刚度的不连续和突然变化。突变的影响程度跟建筑物的分开部分的大小和相对比例有关系。大体上设计者应该使建筑物沿高度方向的强度和刚度变化尽可能小。就结构的体系来说，每个人都可以展示一些更好的抗震设计的基本规则。在展示这些规则之前,需要提醒工程师的是非结构的填充墙会极大影响框架的受力，除非它是独立于框架的。沿建筑物高度的刚度突变应该避免。如果某一楼层的刚度明显比其余各层小(软层)，会由于该层过度的侧移导致该层过早的失效。如图2所示，楼层的刚度变化不仅与结构构件有关，而且与非结构构件比如填充墙有关。柱子的最大剪力值可以用柱子两端施加的弯矩容许值(极限弯矩)的和除以层高取得图4。这就意味着，如果柱子的长度是五分之一的层高，那么该柱将承受五倍大的剪力值。由于这个原因将引起剪力破坏的危险，所以短柱无论在哪都应该避免。图4展示了由结构或非结构构件引起的短柱。有柔性地板构件的结构(平板或由浅梁构成的托梁体系)应该有坚固的柱子或剪力墙(或斜支撑)来避免过度的侧移。如果承受竖向荷载的构件不够坚固，会引起如图5所示的高度的弯矩二次重分部。1967年Adapazari和1985年在墨西哥发生的地震中发现破坏的建筑物中有柔性楼板和细柱。更多关于建筑外形的讨论，请读者参考文献23.2比例和细节设计结构构件的尺寸不仅影响强度，而且影响建筑的整体刚度。鉴于从过去地震得到的经验，作者认为承受竖向荷载的构件的截面积和与楼板面积的比值是衡量抗震性能的一个重要的参数。这一比值也叫“密度比”。作者研究了伊斯坦布尔的历史纪念建筑物中这一比值的变化，这些建筑物在过去的几个世纪中承受了一些严重的地震。发现这一比值在0.2和0.28之间变化。比如，图6显示的Süleymaniye的清真寺的平面图。作者将指出其中承重构件的几何布置的对称性。在Süleymaniye中的密度比大约是0.24对土耳其的抗震设防地区建造的现代混凝土建筑物的调查研究，显示平均密度比少于0.01。作者发现它的比值非常低，估计大约在0.015到0.0020之间。在VinadelMar城市，智利的混凝土建筑物(4到23层)的密度比很高，为0.06(3)。这似乎是1985年期间在智利发生的地震中建筑物只产生了较小破坏的原因之一，地震当时引起了强烈的地面运动。需要指出密度比是衡量侧移刚度的一个重要参数，楼板的相对刚度也对总体刚度产生很大影响。细节设计应该为抗震期间的耗能考虑必要的延性。一个设计优秀但是没有足够细节设计的钢筋混凝土结构将会遭受相当大的破坏。细节设计不能实现除非设计者能对混凝土的抗震性能有了深刻的理解。细节设计的基本原则是在紧要部位和结合处提供必需的强度和延性。必要时还应切断钢筋并重叠接合，并有足够的锚固长度。在关键部位即会产生塑性铰的地方应采用加密箍筋。土耳其的经验显示不充分的细节设计跟过去30年内发生的地震中观察到的破坏关系很大。大部份的破坏归结于不充分的锚固长度或者不充分的接合长度和不充分的位移限制。图7，8和9概述了梁，柱和建筑墙体的基本设计规则。3.3工程实际建造的结构可以抵抗地震作用，然而设计图纸上的结构不能抵抗地震作用。不管设计的方法有多好，不可能设计出抗震建筑物除非设计的工程项目是在适当的监督下完成的。大部份的发展中国家强调设计阶段，质量控制，监督通常是被看不起，而且被工程师忽略。工程师应该认识到抗震的一些重要要求，也就是由实际尺寸，材料的性质和在现场工地完成的加固措施决定的结构的强度，延性和刚度。差的监督造成不佳的材料质量和钢筋的错误安放。土耳其的经验显示不充分的监督已经成为过去发生的地震造成的破坏的最主要因素。根据这些讨论，我们可以得出结论，为了更好的抗震，第一步是纠正过去范的错误。如果建筑外形，细节设计和建筑监督不能改进的话，完善的法规和精密的分析方法也是不能避免未来地震导致的破坏。4设计的建议这个部分的主要目标是详细说明普通钢筋混凝土结构设计的一些简单规则。一般来说，作者所说的一般结构是十层的。4.1各因素的概括在说设计规则之前，有必要先陈述一些有关地震作用和钢筋混凝土结构抗震的实际情况。-地面运动的特性不能被人们充分认识。-当受到强烈的地面运动时，结构不再处于弹性状态。屈服点可能在不同的位置产生，并且大部份的能源消耗发生在这些部位。-结构的反应不仅和地面运动有关，同样跟结构的动力因素有关，比如质量，刚度和阻尼。对于钢筋混凝土结构来说，很难估计它的刚度和阻尼，因为裂痕和徐变在地震作用之前就发生了。-非结构构件影响结构的受力。-为了分析一幢建筑，第一，通过许多简单的假设，来制作出一个简单的模型。分析仅针对这个模型而不针对真正的建筑物。由假定制作的模型也会产生一些错误。一些重要的动力因素如质量，刚度和阻尼决定于实际尺寸和材料在施工期间获得的强度。这些因素跟设计者在设计阶段所假设的不同。鉴于这些事实，我们可以很容易看出在钢筋混凝土结构的抗震设计中有许多不确定因素。工程师必须意识到这些因素的存在，不能仅依靠分析得到的数据。更加精密，复杂的分析方法很容易使工程师忽略结构的真实受力，使其成为数字的奴隶。一般来说，简单的方法加上根据受力做出的正确判断可以进行良好的抗震设计。4.2简单的方法结构的抗震力可以通过以下简单的步骤得到：a.选择良好的