Experimental study of shear retrofit of RC beam-column joints using external post-tensioned bolts

RC beam-column joints play a crucial role in transferring gravity and lateral loads from beam to column. By examining damaged buildings in recent earthquakes, RC beam-column joints are among the most vulnerable members of RC moment frames. The main type of failure of RC joints is shear failure due to the lack of transverse reinforcement and confinement in this area. The laboratory program of the current study suggests external post-tensioned bolts to retrofit RC joints. External post-tensioned bolts increase the confinement and enlargement of the joint panel zone and subsequently eliminate the deficient shear joints. Regarding that the forces applied to the joint panel zone are implemented diagonally, the external post-tensioned bolts were used in two horizontal-vertical (HV) and diagonal (Di) patterns around the joint. The test program includes four RC beam-column joint specimens with half-scale. One specimen was constructed as a standard criterion with all seismic requirements, and three specimens were made at the joint without implementing transverse reinforcement. One deficient specimen was used as a control specimen, and two specimens were subjected to cyclic loading after retrofitting by the proposed patterns. In order to investigate the effect of the proposed method, parameters such as; the force-displacement hysteresis response, energy absorption and damping value of the specimens were considered. The test results confirm the significant effect of the retrofit system against seismic loading so that in retrofitted specimens. The final capacity of the retrofitted specimens increased by about 50% and their energy absorption by about 200%.