-1-TestsonaHalf-ScaleTwo-StorySeismic-ResistingPrecastConcreteBuildingThispaperdescribesexperimentalstudiesontheseismicbehavioranddesignofprecastconcretebuildings.Ahalf-scaletwo-storyprecastconcretebuildingincorporatingadualsystemandrepresentingaparkingstructureinMexicoCitywasinvestigated.Thestructurewastesteduptofailureinalaboratoryundersimulatedseismicloading.Insomeofthebeam-to-columnjoints,thebottomlongitudinalbarsofthebeamwerepurposelyundevelopedduetodimensionalconstraints.Emphasisisgiveninthestudyontheevaluationoftheobservedglobalbehavioroftheteststructure.Thisbehaviorshowedthatthewallsoftheteststructurecontrolledtheforcepathmechanismandsignificantlyreducedthelateraldeformationdemandsintheprecastframes.Seismicdesigncriteriaandcodeimplicationsforprecastconcretestructuresresultingfromthisresearcharediscussed.TheendresultofthisresearchisthatabetterunderstandingofthestructuralbehaviorofthistypeofbuildinghasbeengainedresultsofsimulatedseismicloadtestsofatwostoryprecastconcretebuildingconstructedwithprecastconcreteelementsthatareusedinMexicoaredescribedherein.Thestructuralsystemchosenintheteststructureisthesocalleddualtype,definedasthecombinationofstructuralwallsandbeam-to-columnframes.Connectionsbetweenprecastbeamsandcolumnsintheteststructureareofthewindowtype.Thistypeofconstructionistypicallyusedinlow-andmediumrisebuildingsinwhichcolumnsareconnectedwithwindowsateachstorylevel.Thesewindowscontainthetopandbottomreinforcement.Fig.1showsthistypeofconstructionforacommercialbuildinginMexicoCity.InmostprecastconcreteframessuchasthoseshowninFig,1,longitudinalbeambottombarsarenotfullydevelopedduetoconstraintsimposedbythedimensionsoffilecolumnsinbeam-to-columnjoints.Inanefforttoovercomethisdeficiency,andasdescribedlater,somepracticingengineersinMexicodesignthesejointsbyprovidinghoopsaroundthehooksofthatreinforcementinordertoachieveitsrequiredcontinuity.However,thispracticeisnotcoveredintheACIBuildingCode-2-(ACI318-02),norintheMexicoCityBuildingCode(MCBC,1993).Partofthisresearchwasdonetoaddressthisissue.TheobjectivesofthisresearchwereIoevaluatetheobservedbehaviorofaprecastconcretestructuresinthelaboratoryandtoproposetheuseofprecaststructuralelementsorprecaststructureswithbothanacceptablelevelofexpectedseismicperformanceandappealingfeaturesfromtheviewpointofconstructionEmphasisisgiveninthispaperontheglobalbehavioroftheteststructure.Inthesecondpartofthisresearchwhichgillbepresentedinacompanionpaper,theobservedbehaviorofconnectionsbetweenprecastelementsintheteststructure,aswellasthebehavioroftheprecastfloorsystemwillbediscussedindetail.Structuralandnonstructuraldamagesobservedinbuildingsduringpastearthquakesthroughouttheworldhaveshowntheimportanceofcontrollinglateraldisplacementinstructurestoreducebuildingdamageduringearth-quakes.Itisalsorelevanttomentionthatthereareseveralcasesofstructuresinmoderateearthquakesinwhichtheobserveddamageinnon-structuralelementsinbuildingswasconsiderableeventhoughthestructuralelementsshowedlittleornodamage.ThisbehaviorisalsorelatedIoexcessivelateraldisplacementdemandsinthestructure.Tominimizeseismicdamageduringearthquakes,theabovediscussionsuggeststheconvenienceofusingastructuralsystemcapableofcontrollinglateraldisplacementsinstructures.Asolutionofthistypeistheso-calleddualsystem.StudiesbyPaulayandPriestley4ontheseismicresponseofdualsystemshaveshownthatthepresenceofwallsreducethedynamicmomentdemandsinstructuralelementsintheframesubsystem.Alsoinconjunctionwithshaketabletestsconductedonacast-in-placereinforcedconcretedualsystem.Bertero5hasshownthepotentialofthedualsystem,inachievingexcellentseismicbehaviornthisinvestigation,thedualsystemisappliedtothecaseofprecastconcretestructures.DUCTILITYDEMANDINDUALSYSTEMSInordertodevelopabaseforalateranalysisoftheobservedseismicresponseoftheteststructurestudiedinthisprojectasimpleanalyticalmodelisusedtoevaluatethemainfeaturesofductilitydemandsindualsystems.-3-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.2havebeenalsofoundbyBerteroinshaketabletestsofadualsystem.DESCRIPTIONOFTESTSTRUCTURETheteststructureusedinthisinvestigationisatwo-storyprecastconcretebuilding,representativeofalow-riseparkingstructurelocatedinthehighestseismiczoneofMexicoCity.Theprototypewasconstructedatone-halfscale.Forthesakeofsimplicity,rampsrequiredinaparkingstructurehavenotbeenconsideredintheselectedprototypestructure.Theiruse,requiringlargeopeningsinthefloorsystem,wouldhaverequiredaverycomplexmodelofthefloorsystemforbothlinearandnonlinearanalysisofthestructure.-4-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,thewindowsinthecolumnsandwallsareleftintheseelementsforalaterassemblagewiththeprecastbeams.TheunfasteneddesignbaseshearrequiredbytheMexicoCityBuildingCode(MCBC,1993)2is0.2WT,whereWTisthetotalweightoftheprototypestructure,assumingadeadloadof5,15KPa(108psi)andaliveloadof0.98KPa(20.5psi).Theprototypestructurewasdesig