Numerical investigation on the hysteretic behavior of RC joints retrofitted with different CFRP configurations

The strengthening of beam-column joints in RC structures is considered an effective approach for improving their seismic resistance and overall performance. This paper presents a numerical investigation into the effectiveness of carbon fiber-reinforced polymer (CFRP) sheets in enhancing the seismic performance of RC joints under combined axial and cyclic loads. For this purpose, a case-study joint subassemblage was retrofitted using three different retrofitting configurations (L-shaped, web bonded, and flange bonded), all commonly used for external strengthening with composite materials. Following the verification of the nonlinear numerical model against the existing experimental data, the analysis outcomes of the retrofitted specimens were compared with those of the control specimen in terms of the tip beam load distribution versus tip beam displacement, energy dissipation, and plastic hinge relocation. Compared with the results of the original joint, the results of the retrofitted joints confirmed an improved load-carrying capacity for all strengthening schemes. However, some configurations led to a decrease in the ductility and dissipated energy. It was shown that the L-shaped and flange-bonded retrofitting schemes could relocate the plastic hinge from the column face toward the beam. This represents a good outcome because it can potentially eliminate the possibility of joint core brittle failure.