Improving cyclic response of heat-damaged non-ductile RC joints using CFRP hybrid systems

The behavior of non-ductile, heat-damaged reinforced concrete (RC) beam column joints was investigated in this experimental research work. A hybrid system formed of carbon fiber-reinforced polymer (CFRP) sheets and strings was used to improve the cyclic response of these non-ductile, heat-damaged joints. To evaluate the cyclic performance of these joints, twelve RC beam-column joints were cast and classified into four categories: Three joints were kept without strengthening as control specimens. Three joints were strengthened with one layer of CFRP sheets and one NSM-CFRP string in the beam and in the column; three joints were strengthened with two layers of CFRP sheets and two NSM-CFRP strings in the beam and in the column; and three joints were strengthened with three layers of CFRP sheets and three NSM-CFRP strings in the beam and in the column. In addition, the joints were tested at three different temperatures, which are: ambient, 400 degrees C, and 600 degrees C. The experimental findings show a considerable improvement in the cyclic performance of non-ductile heat-damaged RC beam-column joints strengthened with a hybrid CFRP system (greater lateral displacement, higher load ca-pacity, higher energy dissipation, higher displacement ductility, and slower secant stiffness degradation). Furthermore, the effectiveness of CFRP composites increases as the degree of heat damage increases.