Simulation Of FRP-concrete Interface Based On CZM

Interfacial cohesive properties of fiber reinforced polymer (FRP)-to-concrete dominate the reinforcement of concrete structures with FRP. Many formulas of anchorage strength and local bond-slip relationship have been established based on vast experimental work both domestic and overseas. The failure of strengthened structures is usually induced by the peeling off of concrete near FRP-concrete interface, rather than the rupture of FRP. Thus, the ideal way of FE method is to directly simulate the failure of concrete. But a very fine mesh has to be used to mimic the local failure of concrete and convergence difficulties may frequently occur, let alone some important parameters in constitutive models of concrete are lack of theoretical background. CZM (Cohesive Zone Model) based on fracture mechanics is drawing more and more attention and researchers have established the closed-form solutions of both intermediate crack induced debonding and edge debonding of FRP. However such analytical solutions cannot be extended to general cases for the limitation of strict boundary conditions. Based on CZM, this paper analyzes the debonding failure of FRP-concrete interface using FE method and the main work and conclusions are as follows:1. Numerical study on simple shear test is conducted and the outcomes, including load-displacement curves and load capacities, are well agreeable with the experimental ones. Interfacial shear stress and slip, as well as stress in FRP, are observed under different load levels. Parameter research indicates that bond strength has no significant influence on anchorage strength while a larger fracture energy leads to a higher load capacity, given a long enough bond length.2. A plane FE model is established to simulate cracked beams strengthened with FRP. Numerical load peaks are quiet close to the experimental ones. Two peak loads will occur in order within the loading process. The later one is related to properties of FRP-concrete interface, therefore it is not influenced by initial crack length of concrete beam. The whole process of intermediate crack induced FRP debonding is observed at the same time.3. A 3-D FE model is established to simulate strengthened beams previously mentioned, including the influence of unbounded area near crack. Moreover an exponent form softening model of concrete is adopted and FRP is simulated with shell elements. Such improvements uncover FRP debonding process in a more realistic way and the variation of shear stress and slip on interface can be observed directly.4. Influence of interfacial properties on load-deflection curves of FRP strengthened reinforced concrete beams is analyzed. It shows that bond strength within a certain rage has limited effect on load capacity but affect the failure mode of strengthened beams. This paper advices a reduction factor of 0.4 on bond strength predicted by Lu X Z's bond-slip model and no change on predicted fracture energy. Based on adjusted parameters, the whole process of edge debonding of FRP is discussed.