Seismic rehabilitation of reinforced concrete beam–column joints by bonding with concrete covers and wrapping with FRP composites

This study evaluates the effectiveness of a new method for seismic strengthening of exterior RC beam–column connections and develops a joint shear strength model for the strengthened connections. Four RC exterior connections without transverse reinforcement at the joints were cast and tested under reverse cyclic loading. The first connection was tested as the control specimen while the three remaining connections were glued with concrete covers around the columns at the joint area to modify them from square to circular sections and then they were wrapped with different ratios of CFRP for strengthening. The joint shear strength model was developed based on average plane stress concept and it was evaluated with a collected database containing 32 connections strengthened with the conventional FRP methods and three connections strengthened with the new method. Experimental results showed that the variation of the CFRP ratios wrapped around the specimens led to different failure modes of the examined connections; despite the differences in the failure modes, shear capacity and seismic performance of the strengthened connections improved significantly. The new strengthening method could eliminate two of the primary disadvantages (debonding and/or bulging of FRP from the concrete surface and a low confinement effect) of the existing method. The experimental and analytical results showed that the new strengthening method improved the ability of FRP and concrete working together to resist the joint shear forces. The proposed model predicted the joint shear strength of the FRP-strengthened connections accurately. Due to their superior performance, the proposed strengthening method and the proposed model are expected for practical application.