Seismic performance of FRP-strengthened RC joints by applying bond effects of concrete-FRP interface

In this research, a numerical study has been performed on the seismic behavior of the deficient RC beam-column joints (with non-seismic detailing), and the seismic rehabilitation of these joints by using FRP composite laminates. At first, based on previous experimental studies, a series of RC joint specimen were considered to verification the proposed numerical model. These series of specimens include six RC interior joint specimens with non-seismic detailing and retrofitted with FRP laminates under cyclic loading. Comparison between the load-displacement curves obtained from numerical model with corresponding experimental data show that the proposed model is capable to high accurately predict the response of RC joints under cyclic loading. Then, based on the verified model, the performance of two dimensional (2-D) deficient and strengthened exterior RC joint, three dimensional (3-D) interior and exterior RC joints with considering the effect of slab and beam perpendicular to the plane of frame and also strengthening of (3-D) RC joints with focusing on the behavior of the FRP to concrete interface is evaluated. It was observed that the failure mode of the retrofitted RC exterior specimens, unlike the deficient specimens, is the formation of the plastic hinge in the beam section. In addition, it is seen that the slab and the lateral beam have a significant effect on the performance of deficient joints, which can increase the resistance of the 3-D specimens by more than 20%; also, in 3D strengthened joints, the possibility debonding of FRP laminates from concrete is higher than the 2-D model.