Improving shear capacity of existing RC beams using external(3)

AscanbeseenfromFig.9,thespacingofthesteelstrapswasasigni cantparameteraffectingtheultimateloadcarryingcapacity,displacementcapacityandfailuremodeofthespecimen.Beam-3andBeam-4carried11%lessloadthanthecontrolmemberultimately.Thespecimenshad41%and61%lessdisplacementcapacitythanthecontrolspecimen,respectively.Ofthespecimensstrengthenedwithnarrowsteelstraps,onlyBeam-5showedductile exuralbehavior.Beam-5behavedsimilarlytothecontrolmember,

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781–791

Fig.7.Beam-9after

failure.

Fig.8.Beam-10after

failure.

Fig.9.Load–displacementcurvesofspecimensstrengthenedwithnarrowsteelstraps.

whentheultimateloadcarryingcapacity,failuremodeanddisplacementcapacityaretakenintoaccount.AscanbeseenfromFig.10,theultimateloadanddisplacementcapacitiesforBeam-6,Beam-7andBeam-8thatwerestrengthenedwithwidesteelstrapsweresigni cantlylowerthanthecorrespondingquantitiesforthecontrolmember.Afteryielding,Beam-4andBeam-7thatwere

strengthened

Fig.10.Load–displacementcurvesofspecimensstrengthenedwithwidesteel

straps.

Fig.11.Load–displacementcurvesofspecimensstrengthenedwithsteelplates.

with“L”shapedsteelstrapslostloadsuddenly,whentheshortlegsof“L”separatedfromtheconcretesurface.Attheultimateloadbothspecimensreachedapproximately60%lessdisplacementthanthecontrolspecimen.AscanbeseenfromFig.11,specimensthatwerestrengthenedwithsteelplatesalongthewholeshearspanshowedverysimilarload–displacementbehaviortothecontrolspecimen.Beam-9andBeam-10hadslightlymoreductilitythanthecontrolspecimen.Beam-11hadtheleastultimateductilityofallspecimensstrengthenedwithsteelplatesalongthewholeshearspan.Beam-11had20%lessultimatedisplacementthanthecontrolspecimen.3.3.Ductility

DisplacementductilityratiosofthespecimensarepresentedinTable3.Thatratiowascalculatedasthedisplacementatthemaximumloaddividedbythatattheyieldload.Beam-9andBeam-10thatwerestrengthenedwithsteelplatesalongthewholeshearspanhadmore

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Table4

ComparisonoftestandcalculatedresultsSpecimen#(1)Beam-1Beam-2Beam-3Beam-4Beam-5Beam-6Beam-7Beam-8Beam-9Beam-10Beam-11

(Control)(Strengthening)(Strengthening)(Strengthening)(Strengthening)(Strengthening)(Strengthening)(Strengthening)(Strengthening)(Strengthening)

ExperimentalstrengthsMU(kNm)(2)130.581.5117.2113.1122.2115.7113.4118.8129.9127.9124.6

VU(kN)(3)90.455.381.079.783.679.980.280.188.687.584.7

VU(Beam1)

VU

VU(Beam2)

VU

789

CalculatedstrengthsMU(kNm)(6)121.9122.6122.8122.4122.5122.5121.9122.0122.4122.4122.3

VU(kN)(7)104.653.586.185.9101.7101.7101.2117.0118.1117.6117.9

(4)1.000.610.900.880.930.880.890.890.980.970.94

(5)1.631.001.461.441.511.441.451.451.601.581.53

Experimental/calculatedMexp./Mcal.(8)1.070.660.950.921.000.940.930.971.061.051.02

Vexp./Vcal.(9)0.861.040.940.930.820.790.790.680.750.740.72

ductilitythanBeam-1.TheductilityratioofBeam-11was32%lessthanBeam-9’sductilityratio.Beam-4andBeam-7thatwerestrengthenedwith“L”shapedsteelstrapshadthelowestdisplacementductilityratiosamongthestrengthenedspecimens.

Beam-3andBeam-5thatwerestrengthenedwithnarrowsteelstrapsshowed44%and15%lessductilitythanBeam-1,respectively.Beam-6andBeam-8thatwerestrengthenedwithwidesteelstrapshadapproximately50%lessductilitythanBeam-1.Thebehaviorofthespecimensthatwerestrengthenedwithsteelstrapsshowedthatthespacingofthesteelstrapswascloselyrelatedtotheductilityratio.3.4.Strength

Effectsofthestrengtheningtechniqueonthespecimens’ultimatestrengthsaresummarizedinTable4.Ratiosoftheultimatestrengthofstrengthenedspecimenstothecontrolmember’sultimatestrengthwerebetween0.88and0.98.TheultimatestrengthsofBeam-4andBeam-7thatwerestrengthenedwith“L”shapedsteelstrapswereobtainedas12%lessthantheultimatestrengthofthecontrolmember.Thelargestultimatestrengthswereforthespecimensstrengthenedwithsteelplatesalongthewholeshearspan.TheratiosoftheultimatestrengthsofBeam-9,Beam-10andBeam-11totheultimatestrengthofthecontrolspecimenwere0.98,0.97and0.94,respectively.ThelargestincreaseinstrengthattheultimatestagewasforBeam-5forthespecimensstrengthenedwithsteelstraps.TheratiooftheultimatestrengthofBeam-5tothecontrolmember’sultimatestrengthwas0.93.

parisonofexperimentalandanalyticalresultsComparisonsofcalculatedandexperimentalstrengthsarepresentedinTable4.Forcalculationsofthemomentcapacitiesofthespecimens,themaximumconcretestrainwastakenas0.003.Calculated exuralcapacitiesagreed

wellwiththeexperimentalresultsforallspecimensexceptforBeam-2thatfailedinshear.

Thestrengthenedspecimens’shearforcecapacities(VU)werecalculatedbysummingtheshearforcecarriedbyconcrete(VC),theshearforcecarriedbytheshearreinforcements(VS)andtheshearforcecarriedbythebondedsteelmembers(VP)(Eq.(1)):VU=VC+VS+VPwhere:VU:VC:VS:VP:

Shearcapacity

Shearforcecarriedbyconcrete

ShearforcecarriedbyshearreinforcementsShearforcecarriedbysteelplatesorstraps.

(1)

Eqs.(2)and(3)wereusedforcalculatingtheshearloadcarriedbythesteelstrapsandplates,respectively[8].TheshearforcecarriedbytheconcretewascalculatedaccordingtoACIregulations[13]:

tShS

2τave2d

(2)VP=

SPwhere:VP:Sp:ts:hs:d:τave:

ShearforcecarriedbysteelstrapsSpacingofsteelstrapsWidthofsteelstrapsHeightofsteelstraps

EffectiveheightofcrosssectionAverageshearstressofepoxy.

(3)

dhW

VP=2τave

2where:VP:hW:d:τave:

ShearforcecarriedbysteelplatesHeightofsteelplates

EffectiveheightofcrosssectionAverageshearstressofepoxy.

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