Application of ACM Brace Retrofitting Countermeasure to Steel Structure.docx
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Application of ACM Brace Retrofitting Countermeasure to Steel Structure.docx
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ApplicationofACMBraceRetrofittingCountermeasuretoSteelStructure
ApplicationofACMBraceRetrofittingCountermeasuretoSteelStructure
Abstract
AnadvancedseismicretrofittingworkforsteelbuildingstructurewithadoubtfulseismicperformanceusingACM(AdvancedCompositeMaterial)bracingmethod,whichconsistsofCFRP(CarbonFiberReinforcedPlastic)rodandsteelsleeve,wasproposedinthispaper.Inordertosavealotofresidents’livesagainstalarge-damagedearthquake,theretrofittingworkusingACMbracingmethodtosteelstorybuildingstructurebuiltbyanoldearthquakeresistantdesigncodewasconducted.ACMbracingmethodwasmoreeconomicallyandquicklyappliedtosteeltwo-storybuildingstructuresincomparisonwiththesteelK-shapedbracingmethodusedasbefore.Thiskindofretrofittingcountermeasurewillleadtoanextremedecreaseinearthquakedamagesfortheexistingoldsteelbuildingstructuresbuiltbysomeoldearthquakeresistantdesigncodes.
1.Introduction
ItiswellknowninJapanthatalotofreinforcedconcretestorybuildingsbuiltbysomeoldearthquakeresistantdesigncodesbefore1981weredestroyedinthe1995HyogokenNanbuEarthquake.Therefore,JapaneseGovernmenthasadoptedseveralsignificantpoliticsconcerningthisissuesince1995inordertoreducealotofearthquakedamagesforRCandsteelstorybuildingstructures(referredtoasSbuilding)builtbefore1981asquicklyaspossible.AssomeseismicretrofittingpoliciesadoptedbyJapaneseGovernmenthadbeennotcarriedoutsmoothly,JapaneseGovernmenthasbeendemandinganumericaltargettoquicklyimproveaseismicretrofittingratioforallbuildingsbymanylocalself-governmentsinJapan.ThisnumericaltargetofseismicretrofittingratioincludingRCandSbuildingsaswellaswoodenhousesis90%until2017.
Ingeneral,aseismicretrofittingworkforRCandSbuildingstructureusingatypicalsteelbracerequiresnotonlyalargeamountofcostbutalsotheresidents'removalortemporaryevacuation.ItismoredesirableandconvenientforalotofRCandSbuildingownersthattheseismicretrofittingworkisconductedasquicklyandeconomicallyaspossible.ItisthereforeveryimportantforstructuralengineertoproposeanewretrofittingtechniqueinsteadofXandKshapesteelbraces.Atthepresenttime,aseismicresistantperformanceofRCorSbuildingstructureisjudgedfromaseismicindexofstructure,Is,evaluatedbysomecriteriaestablishedbytheJapanbuildingdisasterpreventionassociation(HousingBureauintheMinistryofLand,TransportandTourisminJapan2001;JapaneseStructuralEngineerAssociation2006).ThenumberofsteelbracerequiredfortheseismicretrofittingworkofRCandSbuildingstructurescanbedecidedtosatisfyagivenseismicjudgmentindexvalue,Iso.
TheauthorhasalreadyproposedaseismicretrofittingcountermeasureforRCbuildingstructureusinganadvancedcompositematerial(referredtoasACM)bracingmethod(Takatani2008andTakatani2011),whichconsistsofacarbonfiberreinforcedplastic(referredtoasCFRP)material,steelsleevesandanchors,inordertosavealotofresidents’livesagainstalarge-damagedearthquake.ItiswellknownthatCFRPmaterialhasseveraladvantagesofstrongandlight-weightfeature,gooddurability,andwideapplicabilityincomparisonwiththesteelmaterial.Inthispaper,ACMbracingmethodisappliedfortheseismicretrofittingworkofStwo-storybuildingstructureinsteadofsteelbracingmethod.
2.SeismicRetrofittingWorkusingACMBracing
Heretofore,thesteelbracingmethodhasbeenusedfortheseismicretrofittingworkofRCandSbuildingstructuresinJapan.ThesteelbraceasshowninFigure1(a)isusedontheoutsideofRCbuilding,andisusuallydoneintheinsideofstructure.While,Figure1(b)showsACMbraceinstalledontheoutsideofstructure.ItismoredesirableandveryimportantforalotofRCbuildingstructureownersthatanearthquakeresistantreinforcementworkforRCbuildingstructurecanbeconductedasquicklyandeconomicallyaspossible,andalsocanbedonewithoutresidents’removalortemporaryevacuation.TheseismicretrofittingworkconductedontheoutsideofRCbuildingstructureshowninFigure1maybemoreconvenientforboththeresidentsinRCbuildingsandtheirowners.Itis,therefore,veryimportantforstructuralengineertoproposeanewseismicretrofittingtechniqueinsteadofthesteelbracetechniqueunderconditionswithlowcostandshortconstructionperiod.
(a)Steelbrace(b)ACMbrace
Figure1.SketchforseismicretrofittingworksusingsteelbraceandACMbrace
ACMbracingmethodwasproposedinordertoaimatbothlowcostandshortconstructionperiodincomparisonwiththesteelbracingmethod.ACMbracingmethodconsistsofCFRProdandCFRPsheet,steelsleeve,andsteelanchor.Figure2showsACMbracerodincludingCFRProdandsteelsleeveforACMbracingmethod.Thelength600mmofsteelsleevewasdecidedfromCFRProdpull-outexperimentsfromsteelcircularcylindersleeve,andalsocanbearabout500kNpull-outforce.While,CFRProdswithvariousdiametersareshowninFigure3,andthematerialpropertiesforCFRProdisindicatedinTable1.ThediameterofCFRProdusedforACMbracingmethodis10mm,anditstensilestrengthis169.5kN.Accordingly,threeCFRProdswith10mmdiametercanbearabout500kNpull-outforce.AnadvancedEpoxyresindevelopedbyKonishiCo.Ltd.wasemployedforbondingbetweenCFRProdsandsteelcylindersleeve(Horii2007).
Figure4indicatessteelanchorsembeddedinRCcolumn,andtheanchordiameterandlengthweredecidedfrompull-outexperimentunder500kNshearforce.Figure5showssteelcylindersleeveandnutsfortheACMbracing,whosepull-outbearingcapacityisabout500kNHisabe(2007).Also,theCFRProdoftheACMbracingisshowninFigure6,andthelengthoftheCFRProdis500mrequiredforACMbracingmethodappliedtoRC3-storybuildingstructure.Figure7indicatesaCFRPsheetusedtomakeareinforcementofRCcolumnagainsttensileforceduetoearthquakemotions.
Figure2.ACMbraceusingCFRProd
Figure3.CFRProd(IntendedType,MitsubishiPlasticsCo.Ltd.)
Figure4.AnchorsforACMbraceFigure5.SteelsleevesforACMbrace
Figure6.CFRProd(VΦ10mm,5@100m)Figure7.CFRPsheetforACMbrace
RCcolumnsurfacearoundananchorwaspastedandcoveredwithfourCFRPsheetlayerswithdifferentdirectionstakingintoconsiderationatensileforcedirection.
Figure8.ElevationviewofRCbuildingwiththeACMbrace
Figure8illustratestwotypicalelevationsfortheseismicretrofittingworkusingACMbracingmethod.AstheanchorembedmentpointinPlanAshowninFigure8(a)islocatedattheintersectionareaofRCcolumnandbeamwheremanyreinforcingsteelbarsinRCcolumnandbeamgatheraround,itmaybenotsoeasyforaboringworkmantomakeananchorholeforACMbracingmethodwithoutcuttingthereinforcingsteelbarsinthisintersectionarea.Therefore,PlanBshowninFigure8(b)wasproposedinsteadofPlanA,andtheanchorembedmentpointavoidstheintersectionareaofRCcolumnandbeam.Inaddition,itisfoundthatthestaticdeformationofRCbuildingstructureinPlanBissmallerthanthatinPlanAthroughthestructuralanalysesforbothPlanAandB.ThisisbecausethattherigidpartaroundtheintersectionareaofRCcolumnandbeamisusuallyassumedonthestructuralanalysis.Conformingtocustomonstructuralanalysis,thisrigidpartaroundtheintersectionareaisdefinedbythewidthofRCcolumnorbeam(Aoyama1988).
Figure9indicatesRC3-storystructureretrofittedbyACMbraces(Takatani2008andTakatani2011).AftertheinstallationofACMbrace,thesteelanchorandsleeveweretreatedwithatarnishpreventive.Afterthiswork,thesteelcoverwasfixedonRCcolumnsurfaceasshowninFigure9.AftercoveringworkofACMbrace,thefinalpaintingworkwasconductedandthecoveringboxwasmadewaterproof.
Figure9.CompletionofACMbraces
3.ApplicationofACMBracetoSteelStructure
TheseismicretrofittingworkusingACMbracingmethodwasconductedforStwo-storystructureshowninFigure5.Figure5showsthefloorplanandtheelevationviewofthisSstructure.ThenumberofACMbraceisdecidedbytheseismicindexofstructure,Is,evaluatedbysomecriteriaestablishedbytheJapanbuildingdisasterpreventionassociationin2001(HousingBureauintheMinistryofLand,TransportandTourisminJapan2001).Theseismicindexofstructure,Is,mustsatisfyagivenseismicjudgmentindexvalue,Iso,oftheseismicindexofstructure.Inthiscase,theseismicjudgmentindexvalue,Iso,is0.7.
Figure10.Floorplanandelevationview
Table2showstheseismicindexofstructure,Is,oftheSbuildingstructure.ItcanbeseenfromTable2thattheseismicindexvalueofstructure,Is,ofthefirstfloorinXdirectionislessthantheseismicjudgmentindexvalue,Iso=0.7,andtheseismicindexvaluesofstructure,Is,inYdirectionaremorethanIso=0.7.Accordingtotheseismicindexvaluesofstructure,IsesarelocatedontheeastsideandthewestoneofthisSstructure.
Next,theconstructionprocessofthisACMbracingmethodisdescribed.Figure11showssteelanchorfixedonsteelcolumn,andtheanchorsizewasdecidedfrompull-outexperimentunder500kNshearforce.Figure12indicatessteelcylindersleevesforACMbrace,whosepull-outbearingcapacityisabout500kNandlengthis600mm.
Figure11.AnchorsforACMbrace
Figure12.SteelsleevesforACMbrace
Figure12showsabracketfixedonsteelcolumn,andthesteelcolumnbeforeACMbraceinstallati
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