Experimental Study On The Lap Performance Of Tensile GFRP Bars

Fiber Reinforced Polymer (FRP) bars has the following advantages: light weight,high tensile strength, corrosion resistance and so on. FRP bars can be used inreinforcing concrete structure instead of steel bars or as a supplementary reinforcingmaterial. Therefore, FRP bars have received significant attentions and practicalapplication in civil engineering field. With the use of FRP bars in large spanstructures, the corresponding connection problems of FRP bars gradually raiseconcern.Compared to existing casing connections and expansion joints,lap splicewhich has the advantages of reliable load transmission and convenient construction,therefore,can be widely applied. Lap anchor is actually the bonding of FRP bars andconcrete.Each lap bar is lack of the wrap of concrete due to the contact between them,then the bond between the bars and concrete both weakened. Hence, the lap length ofbars should be more than the bond anchorage length of a single bar in order to ensurethe structural safety. In this case, the lap strength and the recommended values of laplength are essential.In this paper,129lap specimens are designed in the text. The testmainly involves the following five parameters: lap length of GFRP bars, coverthickness of the concrete, concrete strength, stirrup ratio and diameter of GFRP bars.Then the lap properties of GFRP bars under the influence of five factors is researched.The main contents are as follows:(1) Research the longitudinal tensile properties of GFRP bars used in theexperiment. Then determine their main mechanical properties(including tensilestrength, elastic modulus and ultimate strain) to provide material basis for suchreinforcement research.(2)Variation of bond strength between GFRP bars and concrete under theinfluence of five factors is researched. The test results show that the bond strength ofGFRP bars and concrete reduces with the increase of lap length, the greater the laplength, the more uneven distribution of bond stress. With the increase of theprotective layer thickness, concrete strength and the stirrup rate, the anti-splitting ability of the specimen enhanced and the bond strength between GFRP bars andconcrete improved. With the increase of the diameter of GFRP bars, the bond strengthreduces accordingly.(3)The variation of bond-slip curve under the influence of five factors can beobtained through the experiment. The test results show that with the increase of thelap length, the relative slip value of the two free ends decrease, which is closelyrelated to the failure modes of the specimen. With the increase of the thickness ofprotective layer, concrete strength and stirrup ratio, the anti-splitting capability of theperipheral concrete enhance and slip fully. Then the relative slip value of the two freeends increases. The slip of the specimens which have large-diameter GFRP barsoccurs earlier and the relative slip value of the two free ends is large.(4)For some members, the strain gauges are attached to the quarter points andthe midpoint of lap segment. The approximate location and direction of the peak bondstress can be obtained through observing and analyzing the strain variation of the lapsegment. The test results show that with the load increases, the peak bondstress gradually moves from the loading end to the free end.(5)Based on the test results, the formula for overlap bond strength of GFRPbars,and recommended lap length value is given.