Numerical Study On Interfacial Bebonding Of RC Beams Strengthened With CFRP Sheets

Fiber reinforced polymer (FRP) has been widely used in the reinforcement engineering for several decades. Many experimental research and theoretical derivation have been taken by researchers, getting lots of data and conclusions. But the relevant numerical analysis doesn’t take the effect on FRP strain and stress that’s from concrete cracking and propagation into consideration, so that the analysis of FRP debonding failure caused by concrete crack cannot be achieved. Above all, there should be a new model established, in which the crack propagation is taken into account. Acccording to the degree of cracking, the slip between concrete and FRP near the crack, and the FRP strain can be discussed and investigated. From these the interfacial debonding failure caused by concrete crack can be observed.The main work and conclusions are as follows:1.Establish a CFRP reinforced concrete model with a initial vertical crack at the midspan, changing the length of the initial crack and using different methods for the concrete and CFRP nodes, then observe the mechanical behavior of the beam. For this model, according to the state of crack propagation, theoretical derivation can be divided into four stages, the analysis can be taken respectively. The results compared to the experimental data from literature are accurate.2.ANSYS will be used to simulate the model, also can simulate the reinforced concrete beam strengthened with CFRP. Different initial crack length affects the opening of crack tip, and the maximum strain of CFRP, and for the model adding spring element to simulate the bond-slip between nodes, it also has an influnce on the maximum of relative slip. The maximum value will decrease when the length of initial crack decreases.3.U-wrap will improve the capacity of the beam and decrease the deformation than the beam only strengthened FRP at bottom. Before the steel yield, the CFRP anchorage doesn’t much affect deformation, but when the steel reaches yield, the amounts of U-wrap will make a big difference on the capacity and deformation. When the amounts exceed a certain number, concrete will fail before the FRP at the ultimate state. Approptite amounts of U-wrap will improve the capacity of models, get a reasonable destruction as well. But although the maximum CFRP strain is same, but U-wrap bonded to the end of beam will make CFRP peel off entirely at the mid-span of the beam, while bonded properly throuth beam will make CFRP peel off at a local place.