CCTV新主楼结构设计全程记录多图Word文档格式.docx
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Publicspaceandcirculation.
Arup
1
TosupporttherapidexpansionofChinaCentralTelevision(CCTV),aninternationaldesigncompetitionwaslaunchedin2002foracentralizedheadquartersbuildinginBeijing.WinningthecommissionwasRemKoolhaas(OfficeforMetropolitanArchitecture,OMA),teamedwithengineeringfirmArupandtheEastChinaArchitectureandDesignInstituteasbotharchitectandengineerofrecord.KoolhaasimaginedabuildingwhosethreedimensionalformbringsCCTV'
sstaffandfunctionsintoa"
continuoustube."
Thisispartofthestoryoftheengineeringchallenge.?
Editor
BecausetheseismicdesignoftheCCTVbuildinglayoutsidethescopeoftheprescriptiveChinesecodesofpractice,Arupproposedaperformance-baseddesignapproachfromtheoutset,adoptingfirstprinciplesandstate-of-the-artmethodsandguidelinestoachievesetperformancetargetsatdifferentlevelsofseismicevent.Explicitandquantitativedesignchecksusingappropriatelinearandnonlinearseismicanalysisweremadetoverifytheperformanceforallthreelevelsofdesignearthquake.
Thebasicqualitativeperformanceobjectiveswere:
·
nostructuraldamagewhensubjectedtoalevel1earthquakewithanaveragereturnperiodof50years.
repairablestructuraldamagewhensubjectedtoalevel2earthquakewithanaveragereturnperiodof475years.
severestructuraldamagepermittedbutcollapsepreventedwhensubjectedtoalevel3earthquakewithanaveragereturnperiodof2500years.
StudioandbroadcastspaceswithintheCCTVheadquarters,Beijing,designedbyRemKoolhaas,engineeredbyArup.
StaffandVIPfacilities.
Partofthetubestructure:
regulargridofcolumnsandedgebeams.
patterneddiagonalbracing.
TheCCTV'
stubestructureisacompositeofaregulargridofcolumnsandedgebeamspluspatterneddiagonalbracing.
Internalcolumnsstartingfrompilecaplevel.
Internalcolumnssupportedontransferstructures.
TheCCTVfoundationsystem.
2
FortheCCTVdevelopmentsite,thepeakhorizontalgroundaccelerationvaluesassociatedwiththethreelevelsofdesignearthquakeare7,20,and40percentofgravityrespectively.
ElasticSuperstructureDesign
Withthestructuralbracingpatterndeterminedfromtheinitialconceptwork,afullsetoflinearelasticverificationanalyseswereperformed,coveringallloadingcombinationsincludinglevel1seismicloading,forwhichmodalresponsespectrumanalyseswereused.
Allindividualelementswereextensivelycheckedandthebuilding'
sglobalperformanceverified.Selectedelementswerealsoinitiallyassessedunderalevel2earthquakebyelasticanalysis,thusensuringthatkeyelementssuchascolumnsremainedelastic.
TheelasticanalysisanddesignwasprincipallyperformedusingSAP2000(limitednonlinearstructuralanalysisanddesignwithstatic,dynamic,andpush-overcapability)andacustom-writtenpostprocessorfortheChinesesteelworkcode,whichautomaticallycombinedtheindividualloadcasesappliedtothebuildingforthelimit-statedesign.
Capacityratioswerethenvisuallydisplayed,allowingdetailedinspectionofthecriticalcasesforeachmember.Duetothevastnumberofelementsinthemodel?
10,060elementsrepresentingnearly300,000feet(90,000meters)ofsteelandsteel-reinforcedconcrete(SRC)sections?
andthemultitudeofloadcases,fourpostprocessorswereruninparallel,oneforsteelcolumns,oneforSRCcolumns,oneforbraces,andanotherfortheedgebeamsthattogetherformthecontinuoustube.
TheSRCcolumnsusedamodifiedpostprocessortoaccountforthedifferencesbetweenthesteelandSRCcodes;
sectionpropertiesofthesecolumnsweredeterminedusingXtract(nonlinearlargestraincompositecross-sectionanalysis),whichalsocomputedthepropertiesforthesubsequentnonlinearanalyses.
ThepostprocessorprovidedarevisedelementlistwhichwasimportedbackintoSAP2000,andtheanalysisandpostprocessingrepeateduntilallthedesigncriteriaweremet.Asthestructureishighlyindeterminateandtheloadpathsareheavilyinfluencedbystiffness,eachsmallchangeinelementpropertymovesloadaroundlocally.
Optimizingtheelementsonlyforcapacitywouldresultintheentireloadgraduallybeingattractedtotheinsidecornercolumns,makingthemprohibitivelylarge,socarefulcontrolhadtobemadeofwhenanelement'
ssectionsizecouldbereducedandwhentherewasaminimumsizerequiredtomaintainthestiffnessofthetubeatthebackface.
Tofurthervalidatethemultidirectionalmodalresponsespectrumanalyses,level1time-historycheckswerealsomadeusingrealandartificiallygeneratedseismicrecords.
DesignandPerformanceVerification
Fortheperformance-baseddesign,asetofproject-specific"
designrules"
wereproposedbythedesignteamandreviewedandapprovedbytheChineseMinistryofConstruction'
sexpertreviewpanel,creatinga"
roadmap"
toachievethestatedseismicperformanceobjectives.
Appropriatelinearandnonlinearseismicresponsesimulationmethodswereselectedtoverifytheperformanceofthebuildingunderallthreelevelsofdesignearthquake.Seismicforceanddeformationdemandswerecomparedwiththeacceptancelimitsestablishedearliertorigorouslydemonstratethatallthreequalitativeperformanceobjectiveswereachieved.
Inelasticdeformationacceptancelimitsforthekeystructuralbracemembersinthecontinuoustubeweredeterminedbynonlinearnumericalsimulationofthepostbucklingbehavior.LS-DYNA(softwarefornonlinearexplicittimehistoryanalysis),commonlyusedtosimulatecarcrashbehavior,wasusedforthiswork.
Thebracesarecriticaltoboththelateralandthegravitysystemsofthebuildingandarealsotheprimarysourcesofductilityandseismicenergydissipation.Nonlinearnumericalsimulationofthebraceswasneededtoestablishthepostbucklingaxialforce/axialdeformationdegradationrelationshiptobeusedintheglobal3Dnonlinearsimulationmodel.
Thissimulationwasalsousedtodeterminetheinelasticdeformation(axialshortening)acceptancelimitinrelationtothestatedperformancecriteria.Postbucklinginelasticdegradationrelationshipcurvesillustratethestrengthdegradationastheaxialshorteningincreasesundercyclicaxialdisplacementtimehistoryloading.
ModelsillustratingthedevelopmentoftheCCTVheadquarters'
facadepattern,designedbyRemKoolhaas,engineeredbyArup.
©
Bracestressesforauniformgrid.
SUBSCRIPTIONSAMPLE
Unfoldedviewofthestructureshowingareastodensifyorrarefythemesh.
Nonlinearfiniteelementsimulationmodelshowinglocalbucklingofatypicalsteelbrace.
GSRaftmodelofthepiledfoundation.
ThevonMisesstressdistributionofalargeconnectionplateunderthemostunfavorableloadingcombination.
3
Theacceptableinelasticdeformationwasthendeterminedfromthestrengthdegradation"
backbone"
curvetoensurethattherewassufficientresidualstrengthtosupportthegravityloadsafterasevereearthquakeevent.
Havingestablishedtheinelasticglobalstructureandlocalmemberdeformationacceptancelimits,thenextstepwastocarryoutnonlinearnumericalseismicresponsesimulationoftheentire3Dbuildingsubjectedtolevel2andlevel3designearthquakes.Boththenonlinearstaticpushoveranalysismethodandthenonlineardynamictimehistoryanalysismethodwereusedtodeterminetheseismicdeformationdemandsintermsofthemaximuminelasticinter-storydriftsandthemaximuminelasticmemberdeformation.
Thesedeformationdemandswerecomparedagainstthestructure'
sdeformationcapacitiesstory-by-storyandmember-by-membertoverifytheseismicperformanceoftheentirebuilding.Allglobalandlocalseismicdeformationdemandswereshowntobewithintheirrespectiveacceptancelimits,demonstratingthatthebuildingachievesthequantitativeandhencequalitativeperformanceobjectiveswhensubjectedtolevel2orlevel3earthquakes.
FoundationDesign
Thedesignofthefoundationsrequiredthattheappliedsuperstructureloadsberedistributedacrossthepilecap(raft)soastoengageenoughpilestoprovideadequatestrengthandstiffness.Tovalidatetheloadspreadtothepilegroup,acomplexiterativeanalysisprocesswasusedadoptinganonlinearsoilmodel.
Thesuperstructureloadswereappliedtoadiscretemodelofthepiledraftsystem.SeveralhundreddirectionalloadcasecombinationswereautomatedinaspreadsheetcontrollingGSRaft,iterativenonlinearsoil-structureinteractionanalysissoftware.
Thisprocedureiterativelychangedtheinputdatainresponsetotheanalysisresultstomodeltheredistributionofloadbetweenpileswhentheirsafeworkingloadwasreached.Theanalysiswasthenrepeateduntiltheresultsconvergedandallpileswerewithintheallowablecapacities.Theenvelopeoftheseseveral-hundredanalyseswasthenusedtodesignthereinforcementintheraftitself.
Connections
Theforcefromthebracesandedgebeamsmustbetransferredthroughandintothecolumnsectionswithminimaldisruptiontothestressesalreadypresentinthecolumn.Theconnectionisformedbyreplacingtheflangesofthesteelcolumnwithlarge"
butterfly"
plates,whichpassthroughthefaceofthecolumnandthenconnectwiththebracesandtheedgebeams.Tosimplifythedetailingandcon