Base Plate and Anchor Rod Design.ppt

BasePlateandAnchorRodDesign,ConcentricCompressiveAxialLoadsTensileAxialLoadsBasePlateswithSmallMomentsBasePlatesLargeMomentsDesignforshear,ForTypicalColumnbasePlateConnectionsinBuildings,FiveDifferentDesignLoadCasesinColumnBasePlateConnections.,1.ConcentricCompressiveAxialLoads,1.1ConcreteBearingLimit,Onthefullareaofaconcretesupport,Whentheconcretebaseislargerthantheloadedareaonallfoursides,Baseplatelength,Baseplatewidth,Columnflangewidth,Overallcolumndepth,1.2Requiredminimumthicknessofthebaseplate,Conservativetotakeas1.0,Resistancefactorforflexure,0.90,FactorofsafetyforASD,1.67,NOTE:,2.1AnchorRodTension,Tensilestressarea,Majordiameter,Numberofthreadsperin,2005AISCSpecification,2.2ConcreteAnchorageforTensileForces,(锚栓拔出强度),iftheanchorislocatedwheretheconcreteisnotcrackedatserviceload,otherwise,thebearingareaoftheanchorrodheadornut,designtensilestrength=,allowabletensilestrength=,2.TensileAxialLoads,consideringtheconcretetobeuncrackedatserviceloads,otherwise,concretebreakoutconeareaforgroup,concretebreakoutconeareaforsingleanchor,depthofembedment,in,(锚栓群混凝土拉破强度),为防止混凝土侧面胀破，建议锚栓与侧面混凝土最小距离为6d(d为锚栓直径),FromACI-318,anchorrodembedmentlengthequalsthetopcovertoreinforcingplusorplus0.75timesg(seeFigure3.2.5).Theminimumlengthis17timestheroddiameter.,埋入深度规定:,DesignProcedure：,DeterminetheaxialloadandmomentPickatrialbaseplatesize，Determinetheequivalenteccentricity，andthecriticaleccentricityIfgotonextstep;otherwise,refertodesignofthebaseplatewithlargemomentDeterminethebearinglength，,3.ColumnBasePlateswithSmallMoments,DeterminetherequiredminimumbaseplatethicknessDeterminetheanchorrodsize,NOTE:公制与英制使用公式的系数相同,DesignProcedure：,DeterminetheaxialloadandmomentPickatrialbaseplatesize，Determinetheequivalenteccentricity，andthecriticaleccentricityDeterminethebearinglength，andtensileforceintheanchorrod，DeterminetherequiredminimumbaseplatethicknessDeterminetheanchorrodsize,4.ColumnBasePlateswithLargeMoments,5.1Frictionbetweenthebaseplateandthegroutorconcretesurface,0.55forsteelongrout,0.7forsteelonconcrete,5.2Bearingofcolumnandbaseplate,and/orshearlug,againstaconcretesurface,Forshearlugs,Forbearingonacolumnorthesideofabaseplate,5.DesignforShear,5.3shearintheanchorrods,Theedgedistance(in)inthedirectionofload,Concretecompressivestrength,ksi,Theembedmentdepth,in,Theroddiameter,in,(Allanchorsatsameload),amodifiertoreflectthecapacityreductionwhensidecoverlimitsthesizeofthebreakoutcone,Thetotalbreakoutshearareaforasingleanchor,Example1：BasePlateforAxialCompressiveLoad,W12X96column,24X24inpedestal,LRFD:,Try,Try,Determineifthefollowinginequalityismet,OK!,Calculaterequiredbaseplatethickness,USE,Determinetheanchorrodsize:,Sincenoanchorrodforceexist,theanchorrodsizecanbedeterminedbasedontheOSHArequirements,andpracticalconsiderations.,USE4indiameterrods,ASTMF1554,Grades36,Rodlength=12in,ASD:,Try,Try,Determineifthefollowinginequalityismet,OK!,Calculaterequiredbaseplatethickness,USE,Determinetheanchorrodsize:,Sincenoanchorrodforceexist,theanchorrodsizecanbedeterminedbasedontheOSHArequirements,andpracticalconsiderations.,USE4indiameterrods,ASTMF1554,Grades36,Rodlength=12in,Example2：ColumnAnchorageforTensileLoads,DesignabaseplateandanchorageforaW10X45columnsubjectedtoanetuplift,asaresultofnominalloadsshown,Procedure:,DeterminetherequiredstrengthduetoupliftonthecolumnSelectthetypeandnumberofanchorrodsDeterminetheappropriatebaseplatethicknessandweldingtotransfertheupliftforcesfromthecolumntotheanchorrodsDeterminemethodfordevelopingtheanchorrodsintheconcreteinthespreadfootingReevaluatetheanchorageifthecolumnisona20-in20-inpier,LRFD:,Uplift=1.6WL-0.9DL=1.6(56)-0.9(22)=69.8kips,T/rod=69.8/4=17.5kips,UsinganASTMF1554Grade36material,selecta7/8indiameterrod,Thedesignstrengthoftherod,OK,Therodsarepositionedinsidethecolumnprofilewitha4-in.squarepattern.Pryingforcesarenegligible.Tosimplifytheanalysis,conservativelyassumethetensileloadsintheanchorrodsgenerateone-waybendinginthebaseplateaboutthewebofthecolumn.Ifthecolumnwebstrengthcontrolsthedesign,thenconsiderdistributingtheforcestotheflangesaswellastheweb.Iftheboltsareplacedoutsideoftheflanges,the45degreeloaddistributioncanbeusedtodistributetheforcestotheflanges.,Use1inthickplate(Fy=36ksi),Maximumweldload=,Maximumweldfor0.35incolumnweb=3/16in,Nominalweldstrengthperinfora3/16infilletweldwithE70electrode(usingthe50%directionalincrease),3/16infilletweldoneachsideofthecolumnwebisO.K.,Checkweb:,Webstress=Forceperin/Areaofwebperin,ASD:,Uplift=WL-0.6DL=56-0.6(22)=42.8kips,T/rod=42.8/4=10.7kips,UsinganASTMF1554Grade36material,selecta7/8indiameterrod,Theallowablestrengthoftherod,OK,Therodsarepositionedinsidethecolumnprofilewitha4-in.squarepattern.Pryingforcesarenegligible.Tosimplifytheanalysis,conservativelyassumethetensileloadsintheanchorrodsgenerateone-waybendinginthebaseplateaboutthewebofthecolumn.Ifthecolumnwebstrengthcontrolsthedesign,thenconsiderdistributingtheforcestotheflangesaswellastheweb.Iftheboltsareplacedoutsideoftheflanges,the45degreeloaddistributioncanbeusedtodistributetheforcestotheflanges.,Use1inthickplate(Fy=36ksi),Maximumweldload=,Maximumweldfor0.35incolumnweb=3/16in,Nominalweldstrengthperinfora3/16infilletweldwithE70electrode(usingthe50%directionalincrease),3/16infilletweldoneachsideofthecolumnwebisO.K.,Checkweb:,Webstress=Forceperin/Areaofwebperin,Example3：SmallMomentBasePlateDesign,Designabaseplateforaxialdeadandliveloadsequalto100and160kips,respectively,andmomentsfromthedeadandliveloadsequalto250and400kip-in,respectively.BendingisaboutthestrongaxisforwideflangecolumnW12X96withd=12.7inandbf=12.2in.Theratiooftheconcretetobaseplateareaisunity;Fyofthebaseplateis36ksiandfcoftheconcrete4ksi,LRFD:,TryN=19inandB=19in,Determineand,Therefore,andthedesignmeetsthecrteriaforthecaseofabaseplatewithsmallmoment,Determinebearinglength,Y,Y=N-2e=19-(2)(2.50)=14in,Verifybearingpressure:,OK,Determineminimumplatethickness,Checkthethicknessusingthevalueofn,controls,Usingabaseplate1“X19”X1-7”,Determinetheanchorrodsize,Sincenoanchorrodforcesexist,theanchorrodsizecanbedeterminedbasedontheOSHArequirementsandpraticalconsiderations,Usingfourindiameterrods,ASTMF1554,Grade36;rodlength=12in,ASD:,TryN=19inandB=19in,Determineand,Therefore,andthedesignmeetsthecrteriaforthecaseofabaseplatewithsmallmoment,Determinebearinglength,Y,Y=N-2e=19-(2)(2.50)=14in,Verifybearingpressure:,OK,Determineminimumplatethickness,Checkthethicknessusingthevalueofn,controls,Usingabaseplate1“X19”X1-7”,Determinetheanchorrodsize,Sincenoanchorrodforcesexist,theanchorrodsizecanbedeterminedbasedontheOSHArequirementsandpraticalconsiderations,Usingfourindiameterrods,ASTMF1554,Grade36;rodlength=12in,Example4：LargeMomentBasePlateDesign,Designabaseplateforaxialloadandliveloadsequalto100and160kips,respectively,andmomentsfromthedeadandliveloadsequalto1000and1500kip-in.,respectively.BendingisaboutthestrongaxisforaW12X96wideflangecolumnwithd=12.7in.andbf=12.2in.Conservatively,considertheratiooftheconcretetobaseplateareaisunity.Fyofthebaseplateis36ksiandfcofconcreteis4ksi.,LRFD:,TryN=19inandB=19in,Determineand,Therefore,thisisthecaseofbaseplatewithlargemoment.,Assumethattheanchorrodedgedistanceis1.5in.Therefore,Since315306,alargerplatedimensionisrequired.,Astheseconditeration,trya20X20plate,324306,alargerplatedimensionisrequired.,Astheseconditeration,trya20X20plate,324342,thereforearealsolutionforYexists,Determinebearinglength,Y,andanchorrodtension,or,Determineminimumplatethickness,Because,Attensioninterface:,Checkthethicknessusingthevalueofn,Bearinginterfacegovernsthedesignofbaseplatethickness.Use2in.plate.,Example5：ShearTransferUsingBearing,CalculatetheminimumembedmentdepthofashallowlyembeddedW12X50in6000groutforafactoredshearloadof100kips.Thebaseplateis15in.X15in.andis1.5in.thick.Theprojectedareaoftheplate=(1.5)(15)=22.5in2.ThedesignshearstrengthinbearingonthebaseplateedgeperACI318-02is,Theremaining31.2kipsmustbetakenbybearingoftheflangeoftheW12X50againsttheconcrete.Thewidthoftheflangeis8.08in.Therequiredbearingareais:,Thus,therequiredflangeembedmentdepthis,Useatotalembedmentof4in.fortheflangeandbaseplate.,Example6：AnchorRodResistingCombinedTensionandshear,Determinetherequiredsizeoffouranchorrodsfor