Three-dimensional finite element modeling of debonding failure of skew FRP-bonded concrete joints

Despite the extensive investigations on the shear strengthening of reinforced concrete (RC) beams using externally bonded fiber-reinforced polymer (EB-FRP) composites, the critical problem of how the skew angle (angle between FRP and crack opening direction) influences the bond capacity of FRP has drawn little concern and remains unsolved. This paper presents the first three-dimensional (3D) finite element (FE) model for studying the failure of skew FRP-bonded concrete joints. The concrete was simulated using the concrete damaged plasticity model, and the FRP was modeled as an orthotropic material equipped with the LARC05 model as the damage criterion. The FRP-to-concrete interface was described using a linear elastic cohesive law. The 3D FE model, which provided a relatively large convergent mesh size of 2.5 mm, was calibrated and validated using the bond tests of aligned and skew FRPs. Both the tests and FE results revealed a notable decrease in the bond capacity of FRP at the skew angle of 45°. The parametric analysis demonstrated that the adverse skew effect was reduced when the FRP width increased or FRP thickness decreased, by delaying the onset of the stable peeling-off of concrete along the FRP fiber axis. Compared with FRP, steel plate suffered less from the skew effect, due to its isotropic nature. This study can provide valuable implications for more effective shear-strengthening methods of RC beams and facilitate novel insights for the development of more robust design models. The 3D FE framework can also serve as a versatile tool for analyzing the complicated failure modes of various FRP-strengthened concrete systems.