Experimental and numerical studies on the behavior of RC exterior beam–column joints strengthened with fiber sheets under cyclic loads

Joints are important regions in reinforced concrete (RC) buildings, which are most susceptible to seismic loads. Many retrofitting works utilizing fiber reinforced polymers (FRP) composites are in all developed countries. In this study, there was a change in the strengthening of  joints using carbon fiber (CFRP), glass fiber (GFRP), and carbon with glass ( hybrid fiber ). A total of seven specimens were designed and tested by cyclic loading (controlled displacement- load of frequency of 0.05 Hz). The details of the specimens are as follows: one unstrengthened reference specimen, six specimens for wrapping with fiber  (two are carbon strengthened , two are glass strengthened, and the other two for HFRP wrapping). The results of the testing were compared with those of the reference specimen and strengthened specimens. The behavior of the strengthening joints was studied by the following parameters: first and ultimate load cracking, energy dissipation, ductility, also ultimate stiffness. Based on the results of the test, the hybrid combination was more effective in improving beam-column joints at a highly competitive cost. Furthermore, a comparison of the experimental test and the numerical model results shows that the proposed model is almost identical.