Non-linear Finite Element Analysis On The Peeling-Off Failure In Midspan Of FRP Strengthened Concrete Beams

Fibre Reinforced Polymer (FRP) has been extensively used in concrete strengthening field for its outstanding performance such as high strength-weight ratio and simple construction process. While using FRP to strengthen reinforced concrete (RC) beams for increasing flexural capacity, peeling failure may happen in the concrete cover of beam mid-span. The peeling-off failure makes the load carrying capacity and ductility of the strengthened beams to decrease significantly. The peeling-off failure, therefore, should be avoided. In this thesis, peeling-off stress in concrete cover and failure mode of beam mid-span were investigated to provide a reference for anti-peeling-off design.Finite element method (FEM) is one of the useful tools to study peeling-off. FEM had been used to investigate the peeling-off failure through an analysis on a whole reinforced concrete beam strengthened with FRP. Unfortunately, it is difficult to simulate all the cracks in a whole strengthened beam. To avoid the above difficulty in FEM analysis, a simple and reliable"beam-segment"model for FEM had been developed by Shantou University, and ANSYS software had been used for the numerical study. Noticing that ABAQUS software has strong capabilities in nonlinear analysis, this thesis uses ABAQUS software to investigate the bond failure of beam mid-span based on"beam-segment"model.At first, a simple mechanical model based on beam-segment was proposed, and then, a FEM model by ABAQUS software was established. The symmetry of the geometry, the non-linear properties of the materials and the FRP-to-concrete interface were considered. A calculation example was demonstrated to simulate the whole process of the model establishment. In the model, the internal cracks in the beam-segment were considered to make the simulation to approach the practice much more. Based on the FEM analysis results, the mechanism of peeling-off in mid-span was deeply investigated.For better simulation, relative rotative angle between beam-segment sections under flexural load was introduced into the model. Based on the stiffness of FRP strengthened beams under different load levels, the relative rotative angels between beam segment sections were calculated. The results by FEM showed that, considering the rotation of the beam-segment sections has little influence on stress distribution in concrete cover of mid-span. A parametric study including the geometry, material behavior, interfacial bond-slip models and load process was performed to evaluate their influence on peeling-off failure of the mid-span. The results show that the interfacial bond-slip models and the layer number of FRP affect the stress in concrete cover significantly.