Numerical simulation of the influence of bond strength degradation on the behavior of reinforced concrete beam-column joints externally strengthened with FRP sheets

Limited information is known about the effects of bond strength degradation during installation on the bond's quality and performance between fiber-reinforced polymer (FRP) reinforcement and substrate material. This research study's primary focus is to investigate the efficiency of the external FRP composites in rescuing the structural performance and controlling the mode of failure of the reinforced concrete (RC) beam-column joint with different bond strength degradation percentages nonlinear finite element analysis (NLFEA). Firstly, the RC beam-column model was validated against the published experimental results and then was expanded to consider the effect of the degradation percentages in bond strength between concrete and FRP composite (0 % (Fully bond), 10 %, 20 %, 30 %, 40 %, 50 %, 60 %, 70 %, 80 %, 90 %, and 100 % (control or un-strengthened joint). The structural performance was evaluated in terms of failure mode, stress distribution, pulling and pushing ultimate load capacity and corresponding displacement, horizontal load-displacement hysteretic loops, horizontal load-displacement envelopes, displacement ductility, energy dissipation, stiffness degradation, and equivalent hysteretic damping factor. The NLFEA results showed that the FRP strengthening technique with bond strength degradation percentages less than 30 % enhanced the cyclic performance (higher load capacity, larger horizontal displacement, higher displacement ductility, higher energy dissipation, and slower secant stiffness degradation). Also, the utilized FRP method with bond strength degradation percentage less than 30 % performed well in eliminating any surface debonding or buckling in the FRP composite because of the proper lateral support provided for the strengthening sheets. Finally, the bond strength degradation percentage less than 30 % could significantly enhance the deficient joints' seismic performance under strong beam-weak column conditions by changing its behavior to a more ductile one, including the beam flexural hinging. Moreover, the relocation of a plastic hinge in the beam provided more lateral strength for the joint specimens.