Experimental study on the investigation of strengthening the insufficient reinforced concrete beam-column joints by post-tensioning

The efficiency of proposed strengthening methods using externally applied post-tension rods and CFRPs in the reinforced concrete external beam-column joints is investigated. Seven full-scale specimens were tested in the laboratory. One of the tested specimens, which is the reference specimen of well-detailed joint, complies with the current code requirements. On the other hand, remaining specimens have certain deficiencies resulting from lack of shear reinforcement in the joint and poor material properties such as low strength concrete and the presence of plain round bars. All specimens were subjected to quasi-static cyclic loading in the laboratory and different levels of structural damage were observed. A ductile response with the damage concentrated in the beam was found in the well-detailed specimen. However, the reference specimen of substandard joints displayed a brittle behavior with severe damage mostly in the joint while the rest of the RC components were almost in their elastic range. Depending on the damage type, the damaged members of both substandard and well-detailed reference specimens were repaired by CFRPs wrapped with different configurations. While one specimen was retrofitted by CFRPs, before the occurrence of damage, four of them were strengthened by externally applied post-tensioning. After testing all specimens, the ultimate lateral load capacity was improved considerably by proposed retrofit techniques. Experimental studies show that, lateral force capacities of the retrofitted specimens were mostly improved by either axial load in the post-tensioned rods or the number of CFRPs layers.