HSSSplicesbyJeffreyA.Packer11Bahen/TanenbaumProfessorofCivilEngineering,UniversityofToronto,Ontario,Canada_____________________________________________________________________________________ Identical, or similar-sized, HSSmembers frequently need to be joined end-to-end, or spliced,particularlyinlong-spanconstructionandintallcolumns.Thefamiliarsteelconstructionmaximof“weldintheshop,boltinthefield”,naturallyapplies.BoltedSplicesBoltsLoadedinShear Duetotheclosedshapeofthecrosssection,boltingdirectlyintothewallsofahollowsectionisdifficultwithregularhigh-strengthbolts.Ahand(oraccess)holemaybenecessaryinordertopositionthenutsontheinsideoftheHSS(Figure1).WithspliceplatesjustontheoutsideoftheHSStheboltswillbeinsingleshear,butifspliceplatesareusedontheinsideoftheHSSaswelltheboltswillbeindoubleshear;thenumberofboltswillthenbehalvedandtheconnectionlengthwillbesubstantiallyless.TheprotrudingbeadoftheHSSlongitudinalseamweld,ontheinsideoftheHSS,needstobeconsideredifusinginteriorspliceplates.ShouldspliceplatesbeutilizedonallfourinsidefacesoftheHSSthisweldbeadwillinterferewithoneplatebutcanpotentiallybegrounddownbyreachingintotheHSSfromtheopenend,providingtheconnectionlengthisnottoolong.Part7oftheAISCManual(2011)notesthatboltsizes,regardlessofthetypeandgradeselected,of3/4”,7/8”,1”and1-1/8”arethepreferredchoice.Standardmethods forboltedshearconnectionsapply,using theapplicable limitstates inAISC360-10ChapterJ,butoneshouldalwaysonlydesignfortheappliedload(s)ontheconnection.SinceboltholesreducetheHSSnetcross-sectionalareathelimitstateofHSSnetsectionfracturemaygovernovergrossareayielding,thusillustratingthatfullHSSyieldcapacityisunlikely.Nevertheless,suchconnectionsarestillidealforlesserforces,whicharetypicallypresentintrusswebandchordmembers,forexample.

Figure1:Exterior/interiorspliceplatestosquare/rectangularHSS

TheconceptofusingblindboltswithHSS,inwhichthefastenerisinsertedandtightenedfrom

oneside(theoutside)withoutanutontheinside(theblindside),hasbecomepopularandanumberoffastenerdeviceshavebeenadvocated(PackerandHenderson,1997).Themostpopular,widelyavailableandstructurallyviableblindfasteneratpresentistheLindapterHollo-Bolt®(Figure2).Theseexpansionboltshaverecentlyreceivedstructuralapprovalforresistingcertifiedshearandtensionloadsinbearing-typeconnections,instaticandseimicloadingapplications,byICC-ES(2015).Thelargestavailablenominaldiameterisonly3/4”(M20)andsignificantclearanceholesareneededintheHSSwalltoaccommodatethefastener(e.g.1-5/16”holeforthe3/4"sizeHollo-Bolt),whichfurtherdecreasestheHSSnetsectionfracturecapacity.

Figure2:ClampingmethodoftheLindapterHollo-Bolt®

BoltingoutsidetheHSS,forshearconnections,isthuscommonsinceregularASTMhigh-strengthboltscanbeusedandthefullcross-sectionalareaoftheHSSispreserved.SomeexamplesareillustratedinFigure3,whichalsoshowthesuitabilityforroundHSS.BothpermitsealingtheHSSendswithcapplates.

Figure3:Boltedconnectionsusinggussetswithexternalsplicebars,forroundandrectangularHSS

Theaboveconnectionsmaybestructurallyefficientbut theywouldgenerallybeperceivedasbeing unsuitable for architecturally exposed structural steel (AESS). If bolted connections need to behiddenfromview,coverplates–shapedtomatchtheHSS–canobscuretheboltedshearconnection(Figure4).Siteboltingcanstillbeperformedandthincoverplateslightlyscrewedintoplaceafter.

Figure4:Hiddenconnectionconcept,withnon-visibleboltsbeneathanon-structural,shapedcoverBoltsLoadedinTension Boltedend-plateconnections(Figure5)areanotherwidelyusedmethodforboltingbeyondtheHSSmember,whetherthememberisintensionorcompression(orincombinationwithbending).Designprocedures(anddesignexamples)foraxiallyloadedtensionconnections,forbothrectangular(boltedontwosidesoronallfoursides)androundHSS,aregiveninAISCDesignGuideNo.24(Packeretal.,2010).Thesedesignmethodsentail a considerationofpryingactionon thebolts,which shouldbe fullypre-tensioned. Oneadvantageof this connection type is that it allowsHSSofdifferent size tobe splicedtogether.Whenboltedend-plateconnectionsaresubjecttobothaxialload(P)andbendingmoment(M),ahypothetical“effectiveaxialload”canbecomputedequaltoP±(M/W).A,whereAisthecross-sectionalareaoftheHSSandWistheelastic(S)orplastic(Z)sectionmodulusoftheHSS(Packeretal.,2009).Theconnectioncanthenbeconservativelydesignedonthebasisofthemaximumeffectivetensionload.

Figure5:Boltedend-plateconnectionsforsquare,rectangularandroundHSSWeldedSplices Weldedsplices,whenused,generallyariseincolumns.Whereasthesplicelocationsinlong-spanconstructionarerelativelyoptionalandoftendictatedbyhandlingandtransportationrequirements,incolumns the splice positions are dictated by the supplied HSS lengths, OSHA requirements andconstructability.Boulangeretal.(2016)recommendthatcolumnsplicesbeconservativelylocated5feetabovethetopsoffloorbeams.Forbuildingssubjecttoseismicloading,AISC341-10ChapterD2.5a

requiresthatcolumnsplicesbelocatedatleast4feetabovethefinishedfloorleveltopermitinstallationofperimetersafetycablespriortoerectionofthenexttierandtoimproveaccessibility.Withcompletejointpenetration(CJP)grooveweldsplices,AISC341-10relaxesthisruletoaheightabovethebeam-to-columnflangeconnectionofatleastH(thedepthoftheHSScolumn). For field welding, great care must be taken with regard to temporary support and splicealignment,pre-welding.ColumnspliceswithinseismicforceresistingsystemssuchasMomentResistingFrames(MRFs)haveaveryhighdemandontheweldedbuttjoint,suchthatmemberanticipatedover-capacitycanbeattained.CJPgrooveweldswillbenecessaryinsuchsituations,typicallydetailedwitharootopening.Forcolumnsplicesinseismicallyloadedbuildingswithlowerdemand,andthoseinnon-seismicconstruction,partialjointpenetration(PJP)grooveweldswilloftenbeadequateand–wherefitforpurpose–shouldbefavoredoverCJPwelds.PJPweldsaretypicallydetailedwithnorootgap,allowingpartialbearingofthematingHSSmembers.RelativetoCJPwelds,PJPweldshaveareducedweldingcost,lowertestingrequirementsandrequireless-specializedwelders(Boulangeretal.,2016).PrequalifiedjointdetailsandWeldingProcedureSpecifications(WPSs)aregiveninAWSD1.1(2015).ReferencesAISC.2010.“SpecificationforStructuralSteelBuildings”,ANSI/AISC360-10,AmericanInstituteofSteelConstruction,Chicago,IL.AISC. 2010. “Seismic Provisions for Structural Steel Buildings”, ANSI/AISC 341-10, American Institute of SteelConstruction,Chicago,IL.AISC.2011.“SteelConstructionManual”,14thedition,AmericanInstituteofSteelConstruction,Chicago,IL.AWS.2015.“StructuralWeldingCode–Steel”,AWSD1.1/D1.1M,23rdedition,AmericanWeldingSociety,Miami,FL.Boulanger,S.,Drucker,C.,Kruth,L.F.,Miller,D.K.andMeyerBoake,T.2016.“TheSplice isRight”,ModernSteelConstruction,March,pp.48-51,andNASCC:TheSteelConference,April,Orlando,FL.ICC.2015.“Hollo-Bolt®3PartandHollo-Bolt®5PartFasteners”,ICC-ESReportESR-3330,InternationalCodeCouncilEvaluationService,Brea,CA.Packer,J.A.andHenderson,J.E.1997.“HollowStructuralSectionConnectionsandTrusses–ADesignGuide”,2ndedition,CanadianInstituteofSteelConstruction,Toronto,ON.Packer,J.A.,Sherman,D.andLecce,M.2010.“HollowStructuralSectionConnections”,SteelDesignGuideNo.24,AmericanInstituteofSteelConstruction,Chicago,IL.Packer, J.A.,Wardenier, J.,Zhao,X.-L.,vanderVegte,G.J.andKurobane,Y.2009.“DesignGuideforRectangularHollowSection(RHS)JointsunderPredominantlyStaticLoading”,CIDECTDesignGuideNo.3,2ndedition,ComitéInternationalpourleDéveloppementetl’ÉtudedelaConstructionTubulaire,Geneva,Switzerland.July2016