Study On Fatigue Behaviour Of Interface Between Fibre Reinforced Polymer And Concrete

Fiber reinforced polymer (FRP) materials are widely used to strengthen reinforced concrete (RC) structures due to it’s advantages, including light-weight and high-strength, anti-fatigue, good durability and good anti-corrosion ability. In recent years, with the rapid increasing of the transportation in China, more and more fatigue damage of the bridges in service due to have got public attention. For FRP sheet strengthening technology, the interface between FRP and concrete is the key part, and also the weak link of strengthening component. Fatigue failure of FRP-concrete interface is one of the main failure modes of FRP reinforced concrete structures. Hence, the study on the interface properties of FRP reinforced concrete components and life prediction under fatigue loading is of great significance to secure the safety and reliability of FRP reinforced concrete components, and to maintain reinforcement circle.This paper took the flexural strengthened concrete members with carbon fiber reinforced polymer (CFRP) as the research object, by theoretical and experimental analysis, discussed the fatigue behavior of CFRP concrete interface, the fatigue crack growth, the relationship of bond-slip under fatigue load, the prediction method of interface fatigue life. The main research contents and conclusions of this paper are as follows:(1)Based on a series of the existing experimental results of the FRP-concrete interface, the present constitutive model and anchorage strength model of interfacial bond slip are summarized systematically. The influence factors on the interfacial bond performance index are studied by analyzing the bonding mechanism of FRP concrete interface. Results show that the main factors that affect the interfacial bond properties deeply are concrete strength, bond length of FRP, FRP stiffness, width ratio, adhesive property and so on. The bond slip constitutive relation of the interface is close to the parabola model. And bilinear model is the most commonly used simplified model. Compared with the empirical model and the design model, the model of interfacial debonding bearing capacity based on fracture mechanics is more reasonable to explain the bond failure mechanism(2) The static load test of CFRP concrete interface with different concrete strength are carried out, by the design of CFRP concrete bending shear lap joint components. There is something that was been analyzed such like the CFRP concrete interface failure mode, anchorage strength, strain distribution, and the bond slip relationship. On this basis, CFRP concrete interfacial bond slip constitutive relationship is put forward,which is based on the hyperbola model, bilinear model or parabola model. The advantages and disadvantages of each model are analyzed, and the calculation formula of the characteristic parameters of the curve is given out. The research results show that the failure mode of CFRP concrete flexural interface is the interface debonding failure and delamination in the concrete layer. Compared with other models, the model presented in this paper is in good agreement with the experimental results and had better prediction results.(3) By using the constant amplitude fatigue test of the CFRP concrete interface, the interface failure mechanism and the interface crack propagation under the action of fatigue load are discussed. Combined with the fatigue test results, the influence of fatigue experience on the interfacial bonding properties is preliminarily verified and a simplified model of interfacial bond slip under fatigue loading is established. It shows that while under fatigue loading, CFRP concrete interface failure can occur in two layers:the layer between adhesive and concrete or adhesive and CFRP. The law of crack growth under fatigue load is divided into 3 stages:the fast growth stage, the stable growth stage, and the unstable growth stage. With the increase of the fatigue load times, the interfacial bond stiffness decrease gradually, and the residual slip can be generated during the cyclic loading and unloading.(4) According to the analysis of the existing fatigue life prediction method and the relevant data of this experiment, the fitting formula with energy release rate for predicting the fatigue life of the interface is been carried out. The research results show that when the CFRP bond length is greater than the effective bond length, CFRP concrete interface delamination fatigue strength and static stripping bearing force is approximately 65%. While the interfacial energy release rate of fatigue stress upper limit is lower than 43% of the interfacial fracture energy, the fatigue failure of CFRP-concrete interface will not occur.