Study On Bond-slip Behavior Between FRP Bars And Concrete

Over a few last years, the durability of in-service structure is attached high importance to by researchers. Generally, the study on the corrosion of steel reinforcement is an important task in conventional reinforced concrete structure. In order to solve the problem and improve the durability, it is an effective approach that the Fiber Reinforced Polymer (FRP) Bars instead of steel bar are introduced as reinforcement for the concrete structures.Based on this, the different parameters (embedment length, type of FRP bars, deformations of the bar surface, diameter of FRP bars and concrete strength) were considered in this paper. The specimens of concrete reinforced with FRP bars were tested in direct pullout and those in the test with strain stuck on the internal groove of the bars. Base on the experiment, the bond-slip behavior and mode of failure of concrete with FRP bars were studied. The mechanics and the influence on bond strength were discussed. The distributions of basic bond variables (tensile stress of FRP bars, bond stress and slip) of concrete reinforced with FRP bars along the embedment length were obtained. The pullout results showed that the mode of failure was divided into two types if the deformations rib of FRP bars was collapsed. One of which is the deformation rib non-broken, the other is broken. The adhesion, friction and mechanic interlock are the primary component of bond of FRP bars to concrete. The parameters including diameter of FRP bars, the embedment length, deformations of the bar surface and type of FRP bars affected primarily the bond. The bond stress decreased as the diameter of the bars and the embedment length increased. The bond behaviors between the "double ribs" of bar and concrete is better than those between "single rib" of bars and concrete. And the bond of CFRP bars to concrete is prior to that of GFRP bars to concrete. The conclusion which the bond strength is in direct proportion to square root of the concrete compression strength or to the tensile strength was not the same with concrete reinforced with FRP bars. Base on the pull test with stain stuck on the internal groove of the bars, the results showed that the distribution of tensile stress of FRP bars along the embedment length was nonlinear, and the distribution law of bond stress is distinctly different with that in reinforced concrete. The characteristic of FRP bars brought the result.Based on the analysis of experimental results, the new bond-slip constitutive law of concrete reinforced with FRP bars was established in this paper. The model could correctly simulate the bond behavior of FRP bars to concrete. And according to the four types of bond-slip relationships, the theoretical formula of tensile, bond stresses and slip of FRP bars along the embedment length were deduced. Found on those, the formula of minimal development length of FRP bars was presented. The results showed the calculations were in agreement with the experimental data.The numerical simulation of specimens used ANSYS accounting to the actual bond-slip relationship and constitutive law were done. That the numerical results contrasted to experimental results showed that using the ANSYS could correctly simulate the actual bond behavior and distributions of bond basic variables.The three types of failure mode of concrete beams reinforced with FRP bars were discussed in this paper. The calculational method of ultimate flexural capacity of beams was studied. Based on the finite-element method, the behavior of concrete beam reinforced with FRP rods was given by a nonlinear full-range program of beam. The studies indicated that the failure model of beam was divided into three types including tension failure, balanced failure and compression failure. According to this, the formulas of ultimate flexural capacity of beams were put forward. A theoretical and experimental comparison between flexural behaviors was made better. The study showed the reinforcement ratio and concrete strength affected mainly on ultimate flexural capacity of beams. And the ultimate and cracked flexural capacity increased as the reinforcement ratio.