Improving shear capacity of existing RC beams using external(2)

(c)Twotypesofsteelplateswithdimensions1550×285×

4mmandthesamedimensionalplateswithopeningsweremanufactured.Thesteelplateswithopeningsweremanufacturedfrom1550×285×4mmplatesbycuttingthreesymmetricalopeningswithdimensions317×125mm.SteelstrapandplatearrangementsofstrengthenedspecimensaregiveninFig.3.2.2.Bondingprocedure

Thesameapplicationstepswereusedforstrengtheningallspecimens.Beforebondingthesteelmemberstotheconcretesurface,specialconsiderationwasgiventopreparationofthebeam’swebsurface.Bothsidesofthebeamwebwereroughenedbyamechanicalgrindingmachineuntiltheaggregatewasexposed,brushedandthenthesurfacesvacuumcleanedtoremovelooseparticlesanddust.Thebondingfacesofthesteelplateswerealsoroughenedbyamechanicalgrindingmachineandcleanedthoroughlywithacetone.Thenepoxyresinwasmixedinaccordancewiththemanufacturer’sinstruction.Mixingwascarriedoutinametalcontainerandwascontinueduntilthemixturewasauniformcolor.Theepoxy(Sikadur32)wasspreadalloverthewebofthebeamsandthesteelplatestoathicknessof1.5mm.Theenvironmentalconditionofthesiteatwhichepoxywasappliedwascrucial.Conditionstobeobservedbeforeandduringinstallationincludethesurfacetemperatureoftheconcrete,airtemperature,relativehumidityandcorrespondingdewpoint.Thetemperatureduringapplicationwas20±2 Cinallcases.Thehumidityofthesurfacesatwhichtheepoxywasappliedandthecalculateddewpointsaccordingtothehumiditiesofthesurfacesmustbe ttedtotheregulations.DewpointcalculationsweremadeaccordingtohumiditymeasurementsandISO8502-4regulations[12].Theageoftheconcreteatthetimeofbondingoftheplateswasbetween80and90days.Thesuccessoftheepoxywascloselyrelatedtothestrengthoftheconcrete.Duetothefactthatthestrengthoftheconcretewascloselyrelatedtoitsage,aftercompletingallofthespecimens,epoxywasappliedtoallofthemtogether.Afterbondingoperationswascompleted,specimenswerecuredfor15daysunderlaboratoryconditionsbeforetesting.

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Fig.2.Steelstrapsandplatesusedfor

strengthening.

Fig.3.Steelstrapandplatearrangementsofstrengthenedspecimens.

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785

Fig.3.(continued).

2.3.Experimentalset-up

Aschematicviewoftheexperimentalset-upandthearrangementofthemeasurementdevicesisshowninFig.4.Beamsweretestedunderfour-pointloading.Theloadappliedtothemid-pointofthereactionbeamwasdividedsymmetricallyintotwoconcentratedloadsandappliedtothespecimens.Theratiooftheshearspanlength,1450mm,totheeffectiveheightofthebeam,335mm,was4.3andwasthesameforallspecimens.Specimensweretestedundermonotonicloadingtofailure.Loadwasappliedwitha600kNcapacityhydraulicjackandwascontrolledwitha300kNcapacityloadcell.Themid-pointde ectionandshearcracksofthespecimensweremeasured.ShearcrackwidthsweremeasuredelectronicallybyattachingeightLVDTsdiagonallytorectangularregionswithdimensionsof300×210mmatequalintervalsforshearspans.Shearcrackmeasurementsofthespecimensforwhichalltheshearspanwascoveredwithsteelplatesweretakenbydrillingholestothemeasurementpoints.Themeasurementdevicesweremountedsothattheydidnottouchthewebsofthebeamsorthesteelmembers.

3.Experimentalresultsandevaluation3.1.Observedbehaviorandfailuremodes

TestresultsaresummarizedinTable3.Fig.5showscrackingpatternsandfailuremodesofspecimens.Inallspecimens,the rstcrackalwaysappearedasa exuralcrackinthemaximumbendingmomentregionofthebeam.Ingeneral rst exuralcracksdevelopedat17%oftheultimatestrengthsofthespecimens.Shearcracksdevelopedatloadlevelsbetween40%and50%oftheultimateloadalongtheshearspanofallspecimensexceptBeam-2.ThreetypicalexamplesthatshowthediagonalcrackpropagationthatoccurredbytheseventhLVDTmeasurementrangearepresentedinFig.6.ControlspecimenBeam-1showedductile exuralbehaviorasaresultoflongitudinaltensionreinforcementyielding.Afteryielding,Beam-1developedlargemid-spandisplacements,andreachedanultimateloadvaluethatwas11%greaterthantheyieldload.Beam-1failedbecauseofcrushingoftheconcreteintheextremecompression ber.Beam-2withde cientshearreinforcementcollapsedwithabrittleshearfailureand

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Fig.4.Testset-upandinstrumentation.

Table3TestresultsSpecimen#(1)Beam-1Beam-2Beam-3Beam-4Beam-5Beam-6Beam-7Beam-8Beam-9Beam-10Beam-11

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

Crackingload(kN)FlexureShear(2)(3)13.412.614.014.112.913.613.712.412.812.213.5

36.034.536.337.540.635.734.334.338.238.037.8

Yieldload(kN)(4)81.0–79.281.280.079.080.180.681.381.081.0

Ultimateload(kN)(5)90.455.381.079.783.679.980.280.188.687.584.7

Yielddisp.(mm)(6)23.5–25.224.924.822.822.225.122.020.723.5

Ultimatedisp.(mm)(7)84.920.550.433.076.040.733.546.093.788.067.9

Stiffnessatyield(kN/mm)(8)3.45–3.143.263.233.473.603.213.693.913.44

Ductilityratio(9)3.61–2.001.333.061.791.511.834.264.252.89

Failuremodeatultimate(10)FlexureShearShearShearFlexureShearShearShearFlexureFlexureShear

withoutreachingits exuralcapacity.Twoshearcracksdevelopedintheleftshearspan.Beam-2carried39%lessultimateloadthanBeam-1.

Flexuralcracksofspecimensstrengthenedwithsteelstrapspropagatedasobliquecracksbetweenthesteelstrapsalongtheshearspanwithincreasingload.Shearcracksreachedtothesteelstrapsataloadlevelof55%oftheultimatestrengthofthespecimens.Attheseloadslevelspropagationoftheshearcrackswasrestrictedbythesteelstrapsandcracksdidnotpassunderthesteelstraps.Someshearcracksfollowedtheedgeofthesteelstrapsandpropagatedtothebeam’stop.Thelongitudinaltensionreinforcementofallspecimensyielded.Noneofthesteelmembersseparatedfromthewebsidesofthespecimensbeforetheyieldloadwasreached.Afteryielding,thearrangementofthesteelmembersdeterminedthebehaviorofthespecimens.Theendso …… 此处隐藏：5833字，全部文档内容请下载后查看。喜欢就下载吧 ……