文献翻译一个未完工的二层预制混凝土结构物的抗震测试.docx
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文献翻译一个未完工的二层预制混凝土结构物的抗震测试.docx
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文献翻译一个未完工的二层预制混凝土结构物的抗震测试
TestsonaHalf-ScaleTwo-StorySeismic-ResistingPrecastConcreteBuilding
Thispaperdescribesexperimentalstudiesontheseismicbehavioranddesignofprecastconcretebuildings.Ahalf-scaletwo-storyprecastconcretebuildingincorporatingadualsystemandrepresentingaparkingstructureinMexicoCitywasinvestigated.Thestructurewastesteduptofailureinalaboratoryundersimulatedseismicloading.Insomeofthebeam-to-columnjoints,thebottomlongitudinalbarsofthebeamwerepurposelyundevelopedduetodimensionalconstraints.
Emphasisisgiveninthestudyontheevaluationoftheobservedglobalbehavioroftheteststructure.Thisbehaviorshowedthatthewallsoftheteststructurecontrolledtheforcepathmechanismandsignificantlyreducedthelateraldeformationdemandsintheprecastframes.Seismicdesigncriteriaandcodeimplicationsforprecastconcretestructuresresultingfromthisresearcharediscussed.
TheendresultofthisresearchisthatabetterunderstandingofthestructuralbehaviorofthistypeofbuildinghasbeengainedresultsofsimulatedseismicloadtestsofatwostoryprecastconcretebuildingconstructedwithprecastconcreteelementsthatareusedinMexicoaredescribedherein.Thestructuralsystemchosenintheteststructureisthesocalleddualtype,definedasthecombinationofstructuralwallsandbeam-to-columnframes.Connectionsbetweenprecastbeamsandcolumnsintheteststructureareofthe"window"type.Thistypeofconstructionistypicallyusedinlow-andmediumrisebuildingsinwhichcolumnsareconnectedwith"windows"ateachstorylevel.These"windows"containthetopandbottomreinforcement.Fig.1showsthistypeofconstructionforacommercialbuildinginMexicoCity.
InmostprecastconcreteframessuchasthoseshowninFig,1,longitudinalbeambottombarsarenotfullydevelopedduetoconstraintsimposedbythedimensionsoffilecolumnsinbeam-to-columnjoints.Inanefforttoovercomethisdeficiency,andasdescribedlater,somepracticingengineersinMexicodesignthesejointsbyprovidinghoopsaroundthehooksofthatreinforcementinordertoachieveitsrequiredcontinuity.However,thispracticeisnotcoveredintheACIBuildingCode(ACI318-02),norintheMexicoCityBuildingCode(MCBC,1993).Partofthisresearchwasdonetoaddressthisissue.
TheobjectivesofthisresearchwereIoevaluatetheobservedbehaviorofaprecastconcretestructuresinthelaboratoryandtoproposetheuseofprecaststructuralelementsorprecaststructureswithbothanacceptablelevelofexpectedseismicperformanceandappealingfeaturesfromtheviewpointofconstructionEmphasisisgiveninthispaperontheglobalbehavioroftheteststructure.Inthesecondpartofthisresearchwhichgillbepresentedinacompanionpaper,theobservedbehaviorofconnectionsbetweenprecastelementsintheteststructure,aswellasthebehavioroftheprecastfloorsystemwillbediscussedindetail.
Structuralandnonstructuraldamagesobservedinbuildingsduringpastearthquakesthroughouttheworldhaveshowntheimportanceofcontrollinglateraldisplacementinstructurestoreducebuildingdamageduringearth-quakes.Itisalsorelevanttomentionthatthereareseveralcasesofstructuresinmoderateearthquakesinwhichtheobserveddamageinnon-structuralelementsinbuildingswasconsiderableeventhoughthestructuralelementsshowedlittleornodamage.ThisbehaviorisalsorelatedIoexcessivelateraldisplacementdemandsinthestructure.
Tominimizeseismicdamageduringearthquakes,theabovediscussionsuggeststheconvenienceofusingastructuralsystemcapableofcontrollinglateraldisplacementsinstructures.Asolutionofthistypeistheso-calleddualsystem.StudiesbyPaulayandPriestley4ontheseismicresponseofdualsystemshaveshownthatthepresenceofwallsreducethedynamicmomentdemandsinstructuralelementsintheframesubsystem.Alsoinconjunctionwithshaketabletestsconductedonacast-in-placereinforcedconcretedualsystem.Bertero5hasshownthepotentialofthedualsystem,inachievingexcellentseismicbehavior[nthisinvestigation,thedualsystemisappliedtothecaseofprecastconcretestructures.
DUCTILITYDEMANDINDUALSYSTEMS
Inordertodevelopabaseforalateranalysisoftheobservedseismicresponseoftheteststructurestudiedinthisprojectasimpleanalyticalmodelisusedtoevaluatethemainfeaturesofductilitydemandsindualsystems.
Fig2showstheresultsofasimpleapproachtoanalyzethelateralloadresponseiiiadualsystem.Thelateralloadhasbeennormalizedinsuchamannerthatthecombinationofmaximumlateralresistanceinbothsubsysterni.e.wallsandframes--leadstoalateralresistanceoftheglobalsystemequaltounitybisalsoassumedthatbothsubsystemshavethesamemaximumlateralresistance.Inthefirstcase(Fig2a),itisassumedthatthewallandframesubsystemshaveglobaldisplacementductilitycapacitiesequalto4and2respectively.Inthesecondcase(Fig.2b),theframesubsystemresponseisassumedtobeelastic,andthelateralstiffnessofthewallsubsystemistakentobe4timesthatoftheframesubsystem.
AsshowninFig2,thelateraldeformationcompatibilityofthecombinedsystemiscontrolledbythelateraldeformationcapacityofthewallsubsystem.InthefirstcaseFig2akanelastic-plasticenvelopeforthelateralglobalresponseofthedualsystemisassumed,andthecorrespondingdisplacementductility(u)isequalto33.Forthesecondcase(Fig.2b)withanelasticbehavioroftheframesubsystem,thisductilityisequalto25.
Thesesimpleexamplesillustratethatintheanalyzedcases,duetothehigherflexibilityintheframesubsystemsascomparedtothoseofthewallsubsystern,inadualsystem,theductilitydemandsintheframesubsystemresultinsmallerductilityvaluesthanthoseofthewallsubsystem.Thisanalyticalfindingwasverifiedinthisstudyfromtheexperimentalstudiesconductedontheteststructure.ThisverificationislaterdiscussedinthepaperItisofinteresttonotethatresultsofthetypeshowninFig.2havebeenalsofoundbyBertero'inshaketabletestsofadualsystem.DESCRIPTIONOFTESTSTRUCTURE
Theteststructureusedinthisinvestigationisatwo-storyprecastconcretebuilding,representativeofalow-riseparkingstructurelocatedinthehighestseismiczoneofMexicoCity.Theprototypewasconstructedatone-halfscale.Forthesakeofsimplicity,rampsrequiredinaparkingstructurehavenotbeenconsideredintheselectedprototypestructure.Theiruse,requiringlargeopeningsinthefloorsystem,wouldhaverequiredaverycomplexmodelofthefloorsystemforbothlinearandnonlinearanalysisofthestructure.
Adetaileddescriptionofthedimensions,materials,designprocedures,andconstructionoftheteststructurecanbefoundelsewhere.6Asummaryofthisinformationisgivenbelow.
ThedimensionsandsomecharacteristicsoftheteststructureareshowninFig.3.ThelongitudinalandtransverseareshowninFig3a.Also,theexterior(longitudinal)framecontainingthewall(ColumnLines1and3)aretermedthelateralframe(seeFig,3b),andtheinternal(longitudinal)framewiththesingletee(ColumnLine2)aretermedthecentralframe.
DoableteesspanninginthelongitudinaldirectionaresupportedbyL-shapedprecastbeamsinthetransversedirectionasshowninFig3a.Thestructureusesprecastframesandprecaststructuralwalls,thelatterelementsfunctioningasthemainlateralloadresistingsystem.Fig.4showsanearlyphaseoftheconstructionoftheteststructure.Ascanbeseen,the"windows''inthecolumnsandwallsareleftintheseelementsforalaterassemblagewiththeprecastbeams.
TheunfasteneddesignbaseshearrequiredbytheMexicoCityBuildingCode(MCBC,1993)2is0.2WT,whereWTisthetotalweightoftheprototypestructure,assumingadeadloadof5,15KPa(108psi)andaliveloadof0.98KPa(20.5psi).TheprototypestructurewasdesignedusingproceduresofelasticanalysesandproportioningrequirementsoftheMCBC,Intheseanalyses,thegrossmomentofinertiaofthemembersinthestructurewasconsideredandrigidoffsets(distancesfromthejointstothefaceofthesupports)wereassumedforallbeamsinthestructureexceptforbeamsinthecentralframe,whichhadsubstandarddetailingaswillbedescribedlatch.
Resultsfromtheseanalysesindicatedthatthestructuralwallsintheteststructurewouldtakeabout65percentofthedesignlateralloads.AreviewofthenominallateralresistanceofthestructureusingtheMCBCproceduresshowedthatthisresistingforcewasabout1.3timestherequiredcodelateralresistance(0,2Wr),Thisisoneofseveralfactors,laterdiscussed,thatcontributedtotheover-strengthofthestructure.
ThelongitudinalreinforcementinallthestructuralelementsoftheteststructorewasdeformedbarsfromGrade420steel.Table1liststheconcretecompressivecylinderstrengthsfordifferentmembersoftheprototypestructure.Fig.5showstypicalreinforcingdetailsforprecastbeamsspanninginthedirectionoftheappliedlateralload(seeFig.3).
Figs.6and7showreinforcingdetailsforthecolumns,andforthestructuralwailsandtheirfoundation,respectively.ItshouldbementionedthattheteststructurewasdesignedwiththerequirementsformoderatelyductilestructuresspecifiedbytheMCBC.Accordingtotheseprovisions,theteststructuredidnotrequirespecialstructuralwallswithboundaryelementssuchasthosespecifiedinChapter21ofAC131802.
Theprecasttwo-storycolumnswereconnectedtotheprecastfoundationbyunthreadingthemin
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