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3DEC建模.pdf

3DEC建模.pdf

上传者: zhangqiang2025 2012-05-14 评分1 评论0 下载46 收藏0 阅读量673 暂无简介 简介 举报

简介:本文档为《3DEC建模pdf》,可适用于学术研究领域,主题内容包含NONLINEARSTATICANDDYNAMICANALYSISOFTHECUSHMANARCHDAMSUSINGDISTINCTELEMENTS符等。

NONLINEARSTATICANDDYNAMICANALYSISOFTHECUSHMANARCHDAMSUSINGDISTINCTELEMENTSDDCurtisJPAglaweEBKollgaardDEBowesSHFischerABSTRACTThepaperpresentsthedetailednonlinearstaticanddynamicanalysisoftheCushmanNoarchdamTheCushmanNoarchdamisownedandoperatedbytheCityofTacoma,DepartmentofPublicUtilitiesTheanalyseswereundertakenaspartoftheFERCPartinvestigationsThestaticanddynamicanalysesareuniqueinthatopening,closing,andslidingalongjointsismodeledinconsiderabledetailThedistinctelementprogramDECisusedinthenonlinearanalysisofthedamandfoundationWebelievethatthesophisticatednonlinearanalysesthathavebeencarriedoutonthesedams’advancesthestateoftheartofdamassessmentunderseismicloadingIntheDECanalysis,allthedamcontractionjointsandthedamfoundationinterfacejointsareallowedtoopen,close,andslideunderstaticanddynamicloadingInaddition,jointsinthefoundationrockaremodeledsuchthatstabilityanalysisofthedamandfoundationaremadewithinoneDECmodelThestaticanalysissimulatesdamconstruction,groutingofcontractionjoints,andreservoirimpoundmentThestaticstabilityofthedamischeckedbygraduallyreducingthefrictionalstrengthofthejointsuntildisplacementsbecomeexcessiveAdetailednonlinearstaticanalysiswasundertakentoinvestigatesliponthedamfoundationinterface,particularlyattherightabutmentwherethecontactgeometryisadverselyslopeddownstreamInthenonlinearseismicanalysis,thedamjointsanddamfoundationinterfaceopenandcloseduringtheearthquakeAtseveraltimeinstancesduringtheearthquake,theshearstrengthalongvariousjointsurfaceswasexceededandthiscausedrelativeshearslipdisplacementsThepostearthquakestabilityofthedamwasassessedbyincreasingupliftandgraduallyreducingthestrengthofthejointsBythismeansthedamwasfoundtobesafeSeniorCivilEngineer,AcresInternational,QueenSt,POBox,NiagaraFalls,OntarioCanada,LEW,Tel:,Fax:,dcurtisacrescomSeniorGeotechnicalEngineer,AcresInternational,QueenSt,POBox,NiagaraFalls,OntarioCanada,LEW,Tel:,Fax:,jaglaweacrescomConsultingEngineer,EagleWay,Concord,CA,USA,,Tel:,Fax:,ebkollgaardcaastoundnetConsultingEngineer,thAveCtNW,GigHarbor,WA,USA,,Tel:,Fax:,bowespehalcyoncomSeniorPrincipalEngineer,TacomaPower,Generation,SouththStreet,Tacoma,WA,USA,,Tel:,Fax:,sfischercitacomawausINTRODUCTIONTheCushmanDamsareonthelowerstretchoftheNorthForkoftheSkokomishRiveronthesoutheasternsideoftheOlympicpeninsulanearthesouthernendoftheHoodCanalTheCityofTacomaownsboththedamsCushmanDamisasinglecurvatureconcretearchdamwithanoverallheightofftabovethestreambedTheftlongcrestofthedamisatElThereservoirnormalmaximumstoragelevelisElThedamwascompletedandplacedintooperationinTheCushmandamfoundationcontactispoorlyshapedespeciallyattherightabutmentwhereitisslopedadverselyinthedownstreamdirectionThisfactledtothequestionofabilityofthedamtowithstandthestronggroundmotionsassociatedwiththeseismicloadingItwasrecommendedtoperformasophisticatednonlinearnumericalanalysistoascertaintheseriousnessoftheseismicresponseandevaluationofremedialmodificationsThenonlinearstaticanddynamicanalyseswereperformedwithDEC,athreedimensionaldistinctelementanalysisprogramTheDECprogramwasusedtoperformanonlinearstaticanalysisofdamfollowedbyanonlineardynamictimehistoryanalysisTheDECprogramwasusedtoanalyzebothCushmananddams,butduetospacelimitations,themainresultsfromtheCushmananalysisarepresentedhereinMODELINGAPPROACHBriefDescriptionofDECTheDEC(DimensionalDistinctElementCode)programisthethreedimensionalextensionofItasca'stwodimensionalcodeUDECItisspecificallydesignedforsimulatingeitherthequasistaticordynamicresponsetoloadingofrockmediacontainingmultiple,intersectingjointstructuresTheDECmodelisanassemblageofdiscretepolyhedrasrepresentingdiscontinuousmediumDiscontinuitiesaretreatedasboundaryconditionsbetweenblocksLargedisplacementonthediscontinuitiessuchasslipandopeningissimulatedinadiscontinuousmediumRelativemotionalongdiscontinuitiesisgovernedbylinearandnonlinearforcedisplacementrelationsformovementinboththenormalandsheardirectionsTheprogramusesanexplicitsolutionscheme,whichgivesastablesolutiontounstablephysicalprocessesDECisparticularlywellsuitedtosimulateblockystructures,suchasstonemasonryarchesAssessmentofthesafetyconditionsofoldmasonrybridges(Lemos,)andtheseismicbehaviorofstonemasonryarches(Lemos,)hasbeendoneusingDECIthasbeensuccessfullyemployedtosimulatethebehaviorofaconcretearchdamconstructedonajointedrockfoundation(Lemos,)andalsotoperformstabilityanalysisofundergroundpowerhousestation(DasguptaandLorig,,Dasgupta,etal,)GeologicalSettingThebriefreviewoftheengineeringgeologyofCushmanDamNoisgivenbyCoombs()RecentgeologicalcompilationandreviewwasdonebyHamilton()fortherightabutmentofCushmanDamThebedrockintheareaofCushmanprojectsconsistsofthicksequenceofbasaltandandesiteflowswithlocalinterflowlayersoftuffandagglomerate,oftheEoceneageCrescentFormationAtthedamsitetheCrescentFormationlayeringstrikesaboutNESW,crossingthecanyonatahighangleanddipstodegreesSEdownstreamVariousjointsinthefoundationrockarepresentStrikeanddipanglesforthevariousjointsaregiveninTableThejointplaneAintersectsnearthecontractionjointatstationofthedamFigureshowsthejointplanesD,A,AandBTherightabutmentwedgeisformedbyanassumedverticalplaneDontheupstream,rampfractureplaneBbelowthedamfoundationcontact,andthejointplanesAandAThesejointplanesformarightabutmentwedgewithatotalweightofabout,tonsTableOrientationsoftheDiscontinuitiesJointPlaneStrikeDipDNWVerticalBNENWANESEANESEModelDevelopmentDECmodelwasdevelopedasanassemblageofdiscreteblocksusingcommerciallyavailableprogramDISPLAY(EMRC,)Foundationrock,concretedam,andreservoirwaterelementswerediscretizedAnexplodedviewoffoundationrock,concretedam,andthereservoirisshowninFigureInFigure,thereservoirisshownintheupperpartofthefigure,thedaminthemiddleandthereservoirinthelowerpartofthefigureThereservoirwasextendedmorethanthreetimesthedamheightintheupstreamdirectionItisnotedthatthebulkofthemodelwascreatedusingaDAutoCadmodel,whichwassuppliedbyTacomaPowerInthefoundationrock,fourjointsetswereusedIntheconcretedam,thesevenverticalcontractionjointsandthedamfoundationcontactjointsweremodeledVariousrockjointsformingarightabutmentwedgeareshowninFigureFigureprovidesanillustrationofrightabutmentwedgealongwithdamRightabutmentgravitysectionsandthestartofthearchsectionofthedamarealsoshowntoobtainspatiallocationandorientationofthewedgewithrespecttothedamFigureDamFoundationContact,ContractionJointsandFoundationRockMassDiscontinuitiesFigureExplodedViewofFoundation,DamandReservoirFigureDECmodelofCushmanArchDamNoFigureaFigureRightAbutmentWedgeGeometryandtheDamTheRockWedgeAloneisshownintheInsetVariousFISHfunctionswerewrittentosimulatetheeffectofgroutingoftheindependentcantilevermonolithsatthecontractionjoints,theupliftpressuredistributionatthedamfoundationcontactandwaterpressureinthejointsontherightabutmentwedgesurfacesFISHfunctionsprovideaprogrammingcapabilityinDECthatallowstheusertoprogramsuchfeaturesasgroutingjoints,ie,closinggapsatthedamjointsModelingSequenceFigurepresentsvariousstagesduringthemodelingsequencetoestablishinitialstateofstressInitialrockstresseswerecomputedusinggravityloadingThedammonolithicblockswerethenconstructedGroutingoftheindependentcantileverswassimulatedbyspecifyingaclosedgapbetweenthecontractionjointsaftergravityloadswereequilibratedThereservoirelementswereturnedontoloadthedamhydrostaticallyParametricstudieswereperformedtoexaminethesensitivityoftheDECtoreducedfrictionalstrengthatthedamfoundationcontactandonthejointsformingtherightabutmentwedgeFinally,thedynamicanalysiswasperformedusingJuandeFucaandCascadiaseismicrecordsforMCEloadingPropertiesThejointsbetweenthedamreservoirandreservoirfoundationareassumedtobeelasticContractionjointswithinthedamanddamfoundationcontactareassumedtohavezerocohesionanddegreesfrictionangleThedamfoundationwasquiterough,therefore,theassumedfrictionangleisconsideredconservativeIntherightabutmentwedgeanalysis,thecohesiononthejointplaneswassettozeroTheassumedtotalcombined(cohesiveandfrictional)shearstrengthonjointsB,D,AandAistakenasdegreesRkItwasassessedthatthetotalshearstrengthofthejointplanesisatleastequivalenttothatwithacombinedfrictionangleofdegreesFigureModelingMethodologyAdoptedforDynamicAnalysisofCushmanArchDamCreateDamRockFoundationReservoirblocksfromSADSAPmodelExtendfarfieldboundariesforrockfoundationandreservoirDiscretizemodelApplyboundaryconditionsRockonlyanalysisEquilibriaterockfoundationundergravityConstructarchdamrightandleftwingwalldamsasmonolithswithcontractionjointsContractionjoint:coh=psi,fricdegRockdamcontact:coh=psi,fricdegEquilibriatethemodelGroutingClosethegapsonthecontractionjointsbetweentheconcretemonolithsContractionjoint:coh=psi,fricdegActivatereservoirelementswaterel'(ftaboveNormal)ElasticcontactbetweendamreservoirreservoirfoundationReducestrengthparametersonRockdamcontactcoh=psi,fricdegDynamicAnalysisReducestiffnessofjointstoepsiinApplyviscousboudariestothesidesPerformTimeHistoryAnalysisIncludequietperiodatendoftimehistoryThebulkmodulusoftheelementsinthereservoirregionwassettoxpsiTheshearmoduluswascalculatedusingPoisson’sratioof,ie,acompressiblefluidDampingParametersandDiscretization:ThehydrodynamicinteractionbetweenthedamandthereservoirismodeledusingsolidelementsforthedamconcreteandreservoirwaterThehighlyunevensurfacetopographyintheupstreamregionresultedincomplexgeometricalshapeforreservoirregionThedominantfrequencyrangefortheearthquakeanddamresponseisbetweenandHzThemassproportionalcomponentofRayleighdampingisemployedThefractionofcriticaldampingofwasobtainedasoperatingatthecenterfrequencyofHzTheDECzone(element)sizewasadjustedtoensurethisfrequencywascapturedintheanalysisSTATICANALYSESInitialSetupTworeservoirelevationscorrespondingtousualloadingcase(ft)andthePMFunusualloadingcase(ft)wereconsideredTheloadingduetoreservoirimpoundmentwassimulatedbyactivatingthereservoirelementsAcomparisonofresultswasmadeusingthereservoirmodeledwithsolidelementandmerelyapplyingthehydraulicloadsasnodalforcesSimilarresponseofthedamwasobservedwhenthereservoirwassimulatedbyappliedhydraulicloadsontheupstreamfaceofthedamFortheusualloadconditionwithajointfrictionangleofdegrees,themaximumcomputedslipdisplacementattherightabutmentcontactwasinWhenthefrictionanglewasreducedtodegrees,themaximumcomputedjointsheardisplacementofinisobservedatthedamfoundationcontactasshowninFigureThesheardisplacementisconcentratedontherightsideofthemidcantilever,ie,wherethecontactisadverselyslopeddownstreamItisnotedthatFiguredoesnotshowthedamelementsbutratherthegeometryasinputtoDECThemodelcontainsmorethan,elementsWedgeAnalysisThestaticnumericalanalysescarriedoutshowedthattherightabutmentwedgeattheCushmanDamisstablewithfrictionanglesofreducedtodegreesonthediscontinuitieswithintherockmassTheglobaldisplacementvectorpatternwithindamdidnotaltersignificantlyuntilthefrictionanglewasreducedtodegreesHowever,evenforafrictionangleofdegrees,themaximumdisplacementsafterthereservoirimpoundingarelessthaninwithinthedamandlesswithinthefoundationTherefore,forbothusualandunusualloadingthefactorofsafetyagainstrightabutmentwedgefailureisgreaterthanie,tan()tan()isgreaterthanAsimilarconclusiononthewedgestabilitywasreachedusingamanualstabilityanalysisFigureShearDisplacementattheDamFoundationContactSurfaceDYNAMICANALYSESThedynamicloadingofthedamrepresentstheextremeloadingconditionforthedamstabilityassessmentTwocontrollingearthquakesgroundmotionsfortheCushmandamsitesaretheCascadia(interplate)andtheJuandeFuca(intraplate)(Abrahamson,)TheanalyseswereperformedwithboththerecordsTheresultsfortheJunadeFucaarediscussedinthispaper,althoughtheCascadiarecordgavesimilarresultsSeismicRecordThepeakaccelerationsinthehorizontalplanearegThepeakaccelerationintheverticalplaneisgIntheanalysis,thethreecomponentsoftheearthquakeareappliedsimultaneouslyAquietperiodoffivesecondswasusedtocheckthattherelativemovementtojointshadstoppedaftertheearthquakeTheinputaccelerationrecordwasintegratedtoobtainthevelocitiesThevelocitieswereusedastheprimaryseismicinputfortheDECanalysisResultsofDynamicAnalysisTheresponseofanarchdamtoanearthquakeloadingisinfluencedtoagreatextentbyseismicinputcharacteristicsandthephysicomechanicalpropertiesoftheintactconcrete,rockblocks,andthediscontinuitieswithinthemThestaticstateisaninitialconditionforthedynamicanalysisTherelativedisplacementsofthecrowncantileverwerefoundandsnapshotsofstressesonthedamatthecriticaltimeswerestudiedtoexaminethestresseswithinthedambodyandshearingatthedamfoundationcontactThestateofstresswasalsoexaminedatthetimeofmaximumopeningofthecontractionjointswithinthedamItwasfoundthatthesevarioussnapshots,ofstress,thestressesremainedwithinacceptablelimitsDstressvectorplotonthedamsurface,beforeandaftertheseismicshakingonthedownstreamfaceareshowninFiguresandrespectivelyItcanbenotedthattheprincipalstressvectorsareorientednormaltothefoundationsurfaceandareparalleltothearchdirectionatthetopofthedamComparisonofstressvectorsbeforeandaftertheseismicshakingshowsthatsignificantstressredistributionwithintheconcretearchdamtakesplaceasaresultoftheseismicshakingForexample,asslipdisplacementsoccurattherightabutment,thenstressesaretransferredtotheleftabutmentbyarchactionFigureStressDistributiononDownstreamFaceBeforeEarthquakeFigureStressDistributiononDownstreamFaceAfterEarthquakeThenonlinearanalysisperformedwithDECoffersaninterestinginsightintovariousfailuremechanismsthatcandevelopastheblocksslide,slipandopenduringstaticanddynamicloadingTheDECresultswereusedintheDISPLAYprogramtoplotdeformedshapesFigureshowstheexaggerateddeformedshapesofthedamItshouldbenotedthatthedisplacementsaregreatlyexaggeratedotherwiseitwouldbedifficulttoseethemovementsFigureisazoomedviewofthedamblocksontherightsideRelativeseparationandrotationofthedamblockscanbeeasilyseeninthesefiguresFromthesefigurestherelativemovementofvariousdamblockscanbeobservedFigureExaggeratedDeformedShapeoftheDamattheEndofEarthquakeRecordFigureZoomedofExaggeratedDeformedShapeoftheDamattheEndofEarthquakeRecordThemaximumcomputedshearslipdisplacementwasintherangeoftoinApostearthquakeanalysiswasundertakenwiththedaminitsdisplacedconfigurationandtheupliftwasincreasedtofullreservoirheadontheupstreamhalfofthecontactAsensitivityanalysisoffrictionalstrengthshowedthedamremainsstableinitspostearthquakeconditionItisinterestingtonotethatthedamwaslesssensitivetoreducedfrictionalstrengthinitspostearthquakedeformedconditioncomparedtoresultsfromitspreearthquakesensitivityanalysisCONCLUSIONSThefollowingconclusionsaredrawn•Thedamisacceptablystableforthestatic,dynamicseismicandpostearthquakeloadingconditions•Undersevereseismicloading,thedamwillexperiencepermanentmovementonthedamcontractionanddamfoundationjointsThecomputedmovementsareconsideredconservativebecausethedamshearkeysarenotmodeledandthecohesivestrengthoftheroughdamfoundationcontactisignoredintheanalysisThemagnitudeofthemovementsisfoundtobeacceptable•Modelingofmovementsonjointsasshownherein,allowsrealisticassessmentofdamsinstatic,dynamicandpostearthquakeconditionsREFERENCESAbrahamson,N,,TimeHistoriesforCushmanDam,ReporttoSteveFischer,January,Coombs,HA,,TheSkokomishRiverProjects,CushmanDamNoandCushmanDamNo,EngineeringGeologyinWashington,Volume,WashingtonDivisionofGeologyandEarthResourcesBulletin,,ppDasgupta,BandLorig,LJ,,NumericalModelingofUndergroundPowerhousesinIndia,inProceedingsoftheInternationalWorkshoponObservationalMethodofConstructionofLargeUndergroundCavernsinDifficultGroundConditions,(thISRMInternationalCongressonRockMechanics,Tokyo,September,pp,SSakurai,EdEMRC(EngineeringMechanicsResearchCorporation),DISPLAYIII,PreandPostProcessingProgram,Version,February,Troy,Michigan,USAHamilton,DH,,EvaluationoftheEngineer

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