CCTV新主楼结构设计全程记录多图Word文档格式.docx

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