Seismic Rehabilitation of Corner RC Beam-Column Joints Using CFRP Composites

In this paper, efficiency and effectiveness of carbon fiber reinforced polymers (CFRPs) in upgrading the shear strength and ductility of seismically deficient corner or knee reinforced concrete beam-column joints have been studied. For this purpose, four as-built corner/knee joints were constructed with no transverse reinforcement, representing extreme case of preseismic code design construction practice of joints and encompassing many existing beam-column corner joints. Out of these four as-built specimens, two specimens were used as baseline specimens (control specimens) and other two were strengthened with CFRP sheets under two different schemes (strengthened specimens). In the first scheme, CFRP sheets were epoxy bonded to joint, beams, and part of the column regions. In the second scheme, however, sheets were epoxy bonded to joint region only but they were effectively prevented against any possible debonding through mechanical anchorages. All these four subassemblages were subjected to cyclic lateral load histories to simulate loading due to earthquake and provide the equivalent of severe earthquake damage. The damaged control specimens were then repaired by filling their cracks through epoxy and externally bonding them with CFRP sheets under the same above two schemes. These repaired specimens were subjected to the similar cyclic lateral load history and their response histories were obtained. Response histories of control, repaired, and strengthened specimens were then compared. The results were compared through hysteretic loops, load-displacement envelopes, column profiles, ductility, and stiffness degradation. The comparison shows that CFRP sheets are very effective in improving shear resistance and deformation capacity of the corner beam-column joints and delaying their stiffness degradation. Shear capacities of control, repaired, and strengthened specimens were also predicted using writers’ published formulation. The predicted shear capacities were in a good agreement with the experimental values.