-
CE434,Spring2010 BeamColumnDesignExample 1/4
Designthecolumnsandgirderfortheonestory,onebayframeshownbelow.Assumethatthewindcanblowineitherdirection.UseA992Steel.Loads:DL=0.2klf(includesweightofgirder)SnowLoad(SL)=0.8klfWindLoad(WL)=0.1klfvertical(downward),0.4klflateralUsethefollowingloadcombination:1.2D+1.6S+0.8W
BuildtheRISAmodelasfollows:1. Layoutthemembers1.1.
SetuptwoSectionSets,onelabeledcolumnsandonelabeledgirder.Assignthe
heaviestwshapetoShapeandA992toMaterial.
1.2.
Modifythedrawinggridtoaccommodatetheframe(Xdirection:1spaceat75ft,Y
direction:1spaceat25ft.)
75ft
25ft
5Typ.
6Typ.
-
CE434,Spring2010 BeamColumnDesignExample 2/4
1.3.
Drawthetwocolumns,thentheconnectinggirder.AssigntheappropriateSectionSettoeach.Splitthecolumnsinto5equalpiecesusingtheSplitMemberstabontheDrawnewmembersmenu.SelecttheJustAddJointstoPHYSICALmembersbutton.Splitthegirderintoeleven6sectionswitha4.5sectiononeitherend.
1.4.
Orientthememberssothatthelocalyaxisispointingoutsideoftheframe(selectlocalaxesunderPlotOptions/Members/Labelingtodisplaythelocal(member)axes).Thelocalyaxiscanbemadetopointoutsidetheframebydoubleclickingthememberandtyping180inthexAxisRotatefieldoftheGeneraltab.
1.5.
SpecifytheunbracedlengthsforeachmemberontheHotRolledtaboftheMembersscreen.TypeSegmentunderLbyyforallmemberstotellRISAtousethesegmentsofeachphysicalmemberastheunbracedlengthforaxialbucklingabouttheyaxis.LeavetheLbzzfieldsblankasthemembersarenotbracedforbucklingaboutthestrongaxis(bucklingintheplaneoftheframe).RISAwillautomaticallysetL_comp_toptoLbyy.Thisiswhyweorientedthememberssothattheirtopflangeswereontheoutsideoftheframe,wherethegirtsandpurlinsareattached.
Wewilllearnwherethe13ftunderLcomp_botforthegirdercamefromlater.
ChecktheZswayboxandspecifyLateralforallmembersintheframesothatRISAwillapplythestiffnessreductionfortheDirectAnalysismethodtothesemembers.
1.6.
Settheboundaryconditions.AllnodesareFIXEDintheZtranslation,XrotationandYrotationdirections.SpecifyREACTIONSintheXandYdirectionsatthecolumnbases.
2. Specifytheloads2.1.
TypethefollowinglabelsontheBasicLoadCase(BLC)sheet:DL,SL,WL_vert,WL_lat,N
-
CE434,Spring2010 BeamColumnDesignExample 3/4
2.2.
NisthenotionalloadforLoadCombination1.Itisahorizontalforceappliedatthe
elevationofthegirder=0.002totalfactoredgravityloadforLoadCombination1.
FactoredGravityLoad=(1.2x0.2klf+1.6x0.8klf+0.8x0.1klf)x75ft=120k
N=0.002x120k=0.24k
2.3.
Applytheappropriateloadstothemembersgraphically.BecarefultoassigneachloadtotheappropriateBLC.
2.4.
SetuptheLoadCombination:1.2D+1.6S+0.8W_vert+0.8W_lat+N.TypeYunderPDelta.
3. Analyzetheframe3.1.
UnderGlobalParameters/Codes,selectAISC13thLRFDandcheckAdjustStiffness
(DirectAnalysisMethod).
3.2.
AnalyzethestructurebyplacingthecurseronLC1andselectingSolveCurrent.Make
RISAselectmoreefficientshapesbyrightclickingontheSuggestedShapesandselectingSolveagain...untilnomoreshapesaresuggested.SelectSectionSetstodisplayaW30x90forthecolumnsandaW27x84forthegirder.
3.3.
SelectDesignResultsandobservethatMemberM2(rightcolumn)controlsthedesign(hasthehighestUCMax)forthecolumns.AlsoobservethattheUCMaxforthegirderoccurredatLocation25ft(therightend).
-
CE434,Spring2010 BeamColumnDesignExample 4/4
3.4.
DisplaythemomentdiagrambyselectingzzMomentunderMemberResultsonunderPlotOptions/Members.
Observethatthenegativemomentattherightendofthegirderisoveraspanofapproximately13.5ft.Thisistheunbracedlengthofthecompression(bottom)flangethatcontrolsthegirderdesign(regionofmaximummoment).
3.5.
Displaydetailresultsfortherightcolumn(atleftbelow)andforthegirder(atright)andcomparewithaspreadsheet.
