5/11/2015 PlateElementStressMx/MyvsGlobalMomentBentley:STAADproductsEngTips

http://www.engtips.com/viewthread.cfm?qid=252946 1/2

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PlateElementStressMx/MyvsGlobalMomentthread750252946

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I'mnewtousingSTAADforplateelementdesign.Iamtryingtodesignamatfoundationusingplateelements.Inpostprocessing,thereareMxandMymomentsaswellas'GlobalMoment'asoptionsforthestresstypes.

TheMxandMycanbeusedtodeterminetheappropriaterebarneededtoresistthemomentsinthierrespectivedirectionsfortheplateelement.Butwheredoesthegloablmomentcomeintoplay?AtfirstIthoughtthatitwasaresultantmoment,buttheMxyistheresultantmomentleadingtotorsionintheplateelement.Anyclarificationwouldbegreatlyappreciated.

Don'tknowifitwillhelp,butIamattachingscreenclipsforMx,My,andGlobalMomentpostprocessingstresses.

MxLocalMomenthttp://files.engineering.com/getfile.aspx?folder=ee582b7d9cbc46e38653f0628fa06339&file=Mx_Local_Moment.bmp

MyLocalMomenthttp://files.engineering.com/getfile.aspx?folder=d97348c58a0045e5893d2fc11e5fc7a1&file=My_Local_Moment.bmp

GlobalMomenthttp://files.engineering.com/getfile.aspx?folder=28d461dbef3840f2b435977e78be08a5&file=Global_Moment.bmp

Thanks

Hi!

GlobalmomentshouldhavethesameanswerwiththelocalMxandMy.Ithinkglobalmomentisconvenientwhentheplatesaredividedtriangularly.

Actually,globalmomentsarenotquitethesameastheMxandMy.ThisisbecauseoftheeffectoftheMxymomentasyouhavementioned.

RefertotheWoodArmermethodofcombiningplatemomentstogethertogetdesignmoments.ThatwillgivetruedesignmomentsintheMxandMylocaldirections.

Seethisthreadformoredetail:http://www.engtips.com/viewthread.cfm?qid=24256

Josh

PSWhyamI(aRISAguy)answeringquestionsonSTAAD'sforum?

ThanksfortheinformationontheWoodArmermethod.Thatshouldhelpoutalot.

AsforyouquestionJosh,fromaSTAADguytoaRISAguy,maybethisisthefirststeptoprogramcompatibility.LOL.

Thanksagain.

5/11/2015 PlateElementStressMx/MyvsGlobalMomentBentley:STAADproductsEngTips

http://www.engtips.com/viewthread.cfm?qid=252946 2/2

Iknowthisisalittleafterthefact,butbetterlatethannever...

WhenreferingtoMxandMyforplatemoments,besuretokeepthenomenclaturestraight.Mxdoesnotmeanmomentabouttheplatelocalxaxis.ItactuallymeansmomentontheXface,wherethexfaceistheedgethatthelocalxaxis"pokesoutof".ItturnsoutthatMxisactuallythemomentABOUTtheplatelocalyaxis,whichcanbealittleconfusing.Butitmayhelptothinkofitthisway...Mxisthemomentyouwanttousetodesigntherebarthatrunsparalleltotheplatelocalxaxis.

STAAD

SodoyoumeantosaythatusingtheWoodArmermethodasJoshPlumreferencedisincorrect?

WoodArmerisadesignmethod.

Mx,My,Mxy,andGlobalMomentsareanalysisresults.

Let'ssaywehaveameshofquadplatesthatisorientedasfollows:

platelocalxaxespointinthepositiveglobalXdirection

platelocalyaxespointinthenegativeglobalZdirection

platelocalzaxespointinthepositiveglobalYdirection

ThenMxisthemomentonthexfaceoftheplate.ThisismomentABOUTtheplatelocalyaxis,whichisthesameasdescribingmomentABOUTtheglobalZaxisfortheorientationdescribedabove.NowamomentABOUTtheglobalZaxisproducestensileandcompressivestressesintheglobalXdirection.Soifyouweretoreviewtheglobalmomentsforthesameplate,lookinthecolumnsthatrelatetotheGlobalXstressdirection,usethecolumnthatiscoordinatedwithourplate"top"orientationofY(+ve),youwillreadtheexactsamemomentaswasreportedforMxforthesameplate.

Hopethathelps.

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