Confined UHPFRC for retrofitting of RC beam column joint: An experimental study

Beam column joint (BCJ) is considered as a critical region in the framed structure because during events like earthquake it is susceptible to earlier failure as compared to adjacent members; it will lead to shear failure and endanger users of the building if not designed properly. The BCJs designed using pre-seismic codal provisions follow the non-ductile approach and thus the joint may not be capable enough to resist the post elastic rotation without enduring greater damage. Retrofitting techniques offer great opportunities for strengthening the damaged BCJs. In the present study, the effectiveness of a novel retrofitting scheme based on carbon fibre reinforced polymer (CFRP) confined ultra high performance fibre reinforced concrete (UHPFRC) in rehabilitating the initially damaged BCJ specimens has been assessed by evaluating the seismic performance of retrofitted specimens in terms of hysteresis plots, stiffness degradation, ductility, energy dissipation and joint principle tensile stresses. Three retrofitting schemes using UHPFRC with and without confinement are proposed: (1) in-situ casting of 25 mm thick UHPFRC jacket, (2) in-situ casting of steel wire-mesh confined UHPFRC and (3) in-situ casting of CFRP confined UHPFRC. Park and Ang model has been used to define the damage levels to initially damage the specimens. The confining action is achieved by sandwiching wire mesh and/or CFRP mesh in between two layers of UHPFRC. The test results of this experimental study indicate that BCJ specimens retrofitted with confined UHPFRC improved the overall seismic response as compared to those retrofitted with UHPFRC only. Further, the wire mesh based retrofitting scheme proved to be more efficient in contrast with CFRP mesh based scheme.