Spectrum Analysis Using Staad

24/03/2015 www.sefindia.org::ViewtopicSpectrumAnalysisUsingStaad.ProV8i

http://www.sefindia.org/forum/viewtopic.php?t=13615 1/10

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sharathknSEFIMember

Joined:10Jun2011Posts:17

Posted:MonFeb11,201312:37pmPostsubject:SpectrumAnalysisUsingStaad.ProV8i

Hi,

Ihaveafewurgentqueries,regardingthespectrumanalysisusingStaad.Prov8i,asfollows:

1.firstiwouldliketoknowwhileinloadcaseforSeismicSpectrum,whetherselfweightforyisonlyenough,orforalldirectionsitshouldbeapplied.Alsothemaximumforceasappliedonthenodesshallbeonlyapplyforonedirection,sayXtogetherwithresponsespectrum,oralsoithastobeagainapplyfordefiningresponsespectrumforzdirectionalso.

2.Alsoiwouldliketoknow,whetherdesigningcommandcanbefollowedaftertheanalysishasbeendoneinthesamestaadfile,oraseparatefilehastobecreatedwheretheseinterpretedforcesshouldbeappliedasanaxialforceforeachnodesforcarryingoutthedesignoftheframe

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nssenthilkumaranSEFIMember

Joined:27Oct2010Posts:2

Posted:TueFeb12,20137:53amPostsubject:SpectrumAnalysisUsingStaad.ProV8i

DearSefian,Hereismyreplytothequeries.Ifiamincorrect,othersmaycorrectme.1)InSTAADPro,wedonothaveanoptionofdefiningmasselementswhichareneddedfortheSpectrumanalysis.Sowhatwegenerallydois,firstapplytheDl+0.5LLonthestructure,Secondlyapplypinnedsupportstoallthenodes,analyseandgettheverticalforceineachnodeandapplytheforceinallthethreedirectionsforthecorrespondingnodeintheresponsespectrumloadcase.IfyourDLcasedoesnthaveselfweightinit,Youwillhavetoapplyitalongwiththeabovementionedforcesinallthethreedirections,i.e)selfweighty1,selfweightx1,selfweightz1.IfyourDLcasealreadyhasselfweightinit,youdontneedtoseperatelyspecifyselfweightcommandinthespectrumloadcase.Ihopeiamclear.Thereasonforapplyingallforcesinallthethreedirectionsisbecausethemasscalculatedatthenode(doneinternallyinSTAAD)mustbeappliedinallthreedirectionsinordertoprovideinertialforces.2)Asforyoursecondquery,itispossibletogivethedesigncommandaftertheresponsespectrumanalysisinSTAAD.Butiwouldnotrecommendit.Becauseincaseofspectrumanalysis,theforcesofallthemodesaresummedupusingtheSRSS(sumofsquarerootofsquares)method.andbecauseofthisthesignsofthebendingmomentswouldbelosti.e)ifyouseetheBendingmomentvaluesforthespectrumcase,allthevalueswouldbepositive.Thismayleadtooverdesignofsomesectionsandunfortunatelyunderdesignofsomesections.WhatiwouldrecommendisfindtheVb(Baseshear)valuesofdominantmodes(modesinwhichconsiderableamountofmassesparticipate),sumitupandthendistributeittoeachnodeusingtheformulainequivalentstaticmethod.Thenapplytheforces(nodalforcesstatic)ineachdirectionasa



seperateloadcaseandanalyseandobtaintheresults.Theforcesobtainedintheabovementionedmethodcanbeusedforthedesign.Regars,N.S.SenthilKumaran.StructuralEngineer,Tamilnadu,India

OnMon,Feb11,2013at6:07PM,sharathknwrote:

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nrupenyadahalliSEFIMember

Joined:09Sep2009Posts:17

Posted:WedFeb13,20135:57amPostsubject:SpectrumAnalysisUsingStaad.ProV8i

Hi,

IfyouareusingSRSSmethodforthisinSTAADthenSW&othermasshastobedefinedinall3orthogonaldirections.Sinceonecantunderstandcompletebehavourofmodeshapeswithmassparticipatinginall3directions...

MaybeIS1893part1&4mayhelpuonmassparticipationinXY&Znmodeshape.

Nrupen

OnMon,Feb11,2013at6:07PM,sharathknwrote:Quote:

Hi,






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va...

Joined:26Jan2003Posts:59

Posted:WedFeb13,201310:30amPostsubject:SpectrumAnalysisUsingStaad.ProV8i

DearAll,1)InthelatestversionofSTAADproV8iselectseries4thereisaprovisiontoprovideareferencemassloadcase.Thismasswillbeusedduringdynamicanalysis.2)Secondly,thereisafacilitytoattachasignofdominantmodetotheresultsofresponsespectrumanalysiswhichareotherwiseabsolutevalues.Regards.HemantVadalkar,ConsultingEngineerSTADDEngineersMumbaiFrom:nssenthilkumaran[mailto:forum@sefindia.org]Sent:Wednesday,February13,20133:40PMTo:general@sefindia.orgSubject:[SEFI]Re:SpectrumAnalysisUsingStaad.ProV8i

DearSefian,

Hereismyreplytothequeries.Ifiamincorrect,othersmaycorrectme.

1)InSTAADPro,wedonothaveanoptionofdefiningmasselementswhichareneddedfortheSpectrumanalysis.Sowhatwegenerallydois,firstapplytheDl+0.5LLonthestructure,Secondlyapplypinnedsupportstoallthenodes,analyseandgettheverticalforceineachnodeandapplytheforceinallthethreedirectionsforthecorrespondingnodeintheresponsespectrumloadcase.

IfyourDLcasedoesnthaveselfweightinit,Youwillhavetoapplyitalongwiththeabovementionedforcesinallthethreedirections,i.e)selfweighty1,selfweightx1,selfweightz1.

IfyourDLcasealreadyhasselfweightinit,youdontneedtoseperatelyspecifyselfweightcommandinthespectrumloadcase.Ihopeiamclear.Thereasonforapplyingallforcesinallthethreedirectionsisbecausethemasscalculatedatthenode(doneinternallyinSTAAD)mustbeappliedinallthreedirectionsinordertoprovideinertialforces.

2)Asforyoursecondquery,itispossibletogivethedesigncommandaftertheresponsespectrumanalysisinSTAAD.Butiwouldnotrecommendit.Becauseincaseofspectrumanalysis,theforcesofallthemodesaresummedupusingtheSRSS(sumofsquarerootofsquares)method.andbecauseofthisthesignsofthebendingmomentswouldbelosti.e)ifyouseetheBendingmomentvaluesforthespectrumcase,allthevalueswouldbepositive.

Thismayleadtooverdesignofsomesectionsandunfortunatelyunderdesignofsomesections.WhatiwouldrecommendisfindtheVb(Baseshear)valuesofdominantmodes(modesinwhichconsiderableamountofmassesparticipate),sumitupandthendistributeittoeachnodeusingtheformulainequivalentstaticmethod.Thenapplytheforces(nodalforcesstatic)ineachdirectionasaseperateloadcaseandanalyseandobtaintheresults.

Theforcesobtainedintheabovementionedmethodcanbeusedforthedesign.

Regars,

N.S.SenthilKumaran.StructuralEngineer,Tamilnadu,India

OnMon,Feb11,2013at6:07PM,sharathknforum@sefindia.org(forum@sefindia.org))>wrote:autoremoved

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sharathknSEFIMember


Posted:ThuFeb14,201311:45amPostsubject:

Hi,earlierIaskedafewqueriesonresponsespectrumanalysisinstaad.pro.thankyouforresponse.Keepinginmind,Ifollowedthebelowmentionedsteps,kindlycorrectitwhereeverIwentwrong,asImdoingitfirsttime.

1)TakingacombinationofDL+0.5LLinstaad.proandassigningeverybeamcolumnjunctionnodeasFixedSupport,Ifoundoutthejointweights.

2)Inanotherstaadfileofthesamemodel,Ifirstassignedthesejointweightsunderseismicdefinition.AfterthatIcreated1stloadcasesasspectrumXinwhichItookthemaximumwhichistheFyjointloadandassigneditforX,Y&ZdirectiontogetherwiththeresponsespectrumloadUsingIS1893andCQCmethodforXdirection.

Thenafter,Icreated2ndloadcaseasspectrumZinwhichIonlyassignedtheresponsespectrumloadforZdirection.

AfterthisIcreatedloadcasesforDeadLoadinwhichselfweightiny(1)hasbeenassigned,LiveloadsandLoadCombinations.

3)AfterthisIneedtoknow,howtointerpretthePeakstoryshear,modalbaseactionandparticipationfactorsfromtheoutputofthestaadanalysissoastocalculatethenassignthelateralforcesoneachnodeoneachstoreyinXandZdirectionina3rdstaadfileofthesamemodel,tocarryouttheequivalentstaticearthquakeanalysis._________________KNSharath

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shivrajekadamGeneralSponsor

Joined:30Dec2012Posts:8Location:Mumbai.

Posted:ThuFeb14,20133:06pmPostsubject:SpectrumAnalysisUsingStaad.ProV8i

DearSenthil,

Ihavegonethroughurreply,iagreedwithuropinionasfarasfirstpointisconsideredbutnotwiththesecondcase.

2)Ifurdoingdynamicanalysisofbuildinganduraddingalltheresponsesusinganyoneofmodalcombinationmethodi.eCQC,SRSSorABS,allmemberforcessignedisgettinglostduetosquarerootandsquaringoperationbuttosatisfythisconditionweareconsideringallloadcombinationsgivenin1893:2002(24numbers),Sourstructuralmemberdesignisalwaysonaconservativeside.Butifurfoundationisraftfoundationorcombinedfoundattionthenuneedtobringbackthesignesofreactionsforaccurateanalysisotherwiseurfdndesignmaybeeitherconseravativeorunderdesign.Secondlyasfarasmyknowledgeitisnotpossibletodistributetheloadateachandeverynodebyusingformulegiveninequivalentstaticmethodbecauseudonotknowthemassparticipationatthatnodeinthatmode.

Regards,ShivrajKadam.

On2/13/13,nssenthilkumaranwrote:Quote:

DearSefian,










Regars,



Quote:

Hi,




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arvind_kumar49SEFIMember

Joined:13Mar2011Posts:17

Posted:FriFeb15,20136:20pmPostsubject:SpectrumAnalysisUsingStaad.ProV8i

Thereisneedtoclarifythatmassinallthethreedirectionsshouldnotbeappliedsimultaneously.e.g.forseismicinXdirectionapplymassinXdirection..

OnWed,Feb13,2013at3:39PM,nssenthilkumaranwrote:[quote]DearSefian,



Hereismyreplytothequeries.Ifiamincorrect,othersmaycorrectme.1)InSTAADPro,wedonothaveanoptionofdefiningmasselementswhichareneddedfortheSpectrumanalysis.Sowhatwegenerallydois,firstapplytheDl+0.5LLonthestructure,Secondlyapplypinnedsupportstoallthenodes,analyseandgettheverticalforceineachnodeandapplytheforceinallthethreedirectionsforthecorrespondingnodeintheresponsespectrumloadcase.IfyourDLcasedoesnthaveselfweightinit,Youwillhavetoapplyitalongwiththeabovementionedforcesinallthethreedirections,i.e)selfweighty1,selfweightx1,selfweightz1.IfyourDLcasealreadyhasselfweightinit,youdontneedtoseperatelyspecifyselfweightcommandinthespectrumloadcase.Ihopeiamclear.Thereasonforapplyingallforcesinallthethreedirectionsisbecausethemasscalculatedatthenode(doneinternallyinSTAAD)mustbeappliedinallthreedirectionsinordertoprovideinertialforces.2)Asforyoursecondquery,itispossibletogivethedesigncommandaftertheresponsespectrumanalysisinSTAAD.Butiwouldnotrecommendit.Becauseincaseofspectrumanalysis,theforcesofallthemodesaresummedupusingtheSRSS(sumofsquarerootofsquares)method.andbecauseofthisthesignsofthebendingmomentswouldbelosti.e)ifyouseetheBendingmomentvaluesforthespectrumcase,allthevalueswouldbepositive.Thismayleadtooverdesignofsomesectionsandunfortunatelyunderdesignofsomesections.WhatiwouldrecommendisfindtheVb(Baseshear)valuesofdominantmodes(modesinwhichconsiderableamountofmassesparticipate),sumitupandthendistributeittoeachnodeusingtheformulainequivalentstaticmethod.Thenapplytheforces(nodalforcesstatic)ineachdirectionasaseperateloadcaseandanalyseandobtaintheresults.Theforcesobtainedintheabovementionedmethodcanbeusedforthedesign.Regars,N.S.SenthilKumaran.StructuralEngineer,Tamilnadu,India

OnMon,Feb11,2013at6:07PM,sharathknforum@sefindia.org(forum@sefindia.org))>wrote:autoremoved

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prof.arc...

Joined:26Jan2003Posts:648

Posted:SatFeb16,201312:46amPostsubject:SpectrumAnalysisUsingStaad.ProV8i

Iamnotcommentingontheuseofcommercialsoftwareasitisthepracticenowadaystousethemratherthantowriteapplicationsoftwarebytheuseritself.

useofSRSShaspitfallsbecausethe"sign"islostifyourefertoBISHandbookonIS:1893,theproblemisexplainedinthechapteronstacklikestructurestwodifferentshapesaregivenforshearforceandbendingmomentalongtheheight.inmodalcombinations,NEVERUSESRSSforcombinationofmodalstressesalsodonotuseSRSStofirstobtainLOADSandthenderiveshears&bendingmomentsfromthatcombinedLoaddiagramLesserevilistocombinemodalshearsandmodalmomentsseparately

ihadalwayspreferredtodotimehistoryanalysiswherethe"SIGN"ispreserved

Protectiontotheanalystliesinfollowingthecodalprovisionseventhoughsuchprovisionsmaybetheoreticallywrong!!

ARC



On2/15/13,shivrajekadamwrote:Quote:

DearSenthil,

Ihavegonethroughurreply,iagreedwithuropinionasfarasfirstpointisconsideredbutnotwiththesecondcase.

2)Ifurdoingdynamicanalysisofbuildinganduraddingalltheresponsesusinganyoneofmodalcombinationmethodi.eCQC,SRSSorABS,allmemberforcessignedisgettinglostduetosquarerootandsquaringoperationbuttosatisfythisconditionweareconsideringallloadcombinationsgivenin1893:2002(24numbers),Sourstructuralmemberdesignisalwaysonaconservativeside.Butifurfoundationisraftfoundationorcombinedfoundattionthenuneedtobringbackthesignesofreactionsforaccurateanalysisotherwiseurfdndesignmaybeeitherconseravativeorunderdesign.Secondlyasfarasmyknowledgeitisnotpossibletodistributetheloadateachandeverynodebyusingformulegiveninequivalentstaticmethodbecauseudonotknowthemassparticipationatthatnodeinthatmode.

Regards,ShivrajKadam.

On2/13/13,nssenthilkumaranwrote:

Quote:

DearSefian,








Regars,





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sudippaulSEFIMember


Posted:SatFeb16,20134:39pmPostsubject:SpectrumAnalysisUsingStaad.ProV8i

DearSefians,

Pls.gothroughthe"SIGN"and"DOMINANT"commandin"STAAD".Itwillprovidetheresponsesoutofamodalcombinationwithsignofthedominantmodeorwithsigngovernedbythesignofthedominantmodes.

Further,somewhereinSTAAD,IreadthatbydefaultthemodalcombinationruleautomaticallychangesinternallyfromSRSStoCSMandfromCSMtoCQC,dependingontheclosenessofthemodes,somaybeknowinglyorunknowingly,thebestcombinationrulewillbefollowed..butthesameshallbechecked...

Timehistoryanalysisisnotalwaysrequiredfornormalcivilengineeringstructures.....afrequencydomainapproachwitheitherfewmodesorafullfledgedresponsespectrumanalysisismorethanenough....

Regards

Dr.S.Paul,Manager,Struc.Engg.Dept.,EngineersIndiaLtd.,1BCP,ND66

Ihadalwayspreferredtodotimehistoryanalysiswherethe"SIGN"ispreservedFurther,

On16February201312:11,prof.arcwrote:[quote]Iamnotcommentingontheuseofcommercialsoftwareasitisthepracticenowadaystousethemratherthantowriteapplicationsoftwarebytheuseritself.






ARC

On2/15/13,shivrajekadamwrote:autoremoved

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nssenthilkumaranSEFIMember

Joined:27Oct2010Posts:2

Posted:MonFeb18,20136:42amPostsubject:SpectrumAnalysisUsingStaad.ProV8i

Dearshivraj,Iconcurwithprof.arc'sreply.Whatimeantby'signswouldbelost'isthatthebendingmomentvariation,shearforcevariationetcacrossthespanofthememberwouldbelost.I.e,therewouldnotbenegativemomentsatsupportsorpositivemomentsatthespan.Allthemomentvalueswouldbepositiveforthemember.Sotherealvariationwillnotbecapturedifweusesrss.Andthereisaformulafordistributingthebasesheartodifferentfloorsineq.Staticmethodin1893code.Wehavetosubstitutetheahwiththeresponsespectrumsaccelerationcoeffecientcorrespondingtothefrequencyofthemodeconsideredandtheweightateachfloorlevelcanbereplacedbyweightateachnode.OnFeb16,201312:39PM,"prof.arc"wrote:[quote]Iamnotcommentingontheuseofcommercialsoftwareasitisthepracticenowadaystousethemratherthantowriteapplicationsoftwarebytheuseritself.




ARC

On2/15/13,shivrajekadamwrote:autoremoved

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