Seismic Upgrading of Existing RC Ordinary Moment Resisting Frames using FRPs

Upgrading of existing RC Ordinary Moment Resisting Frames (OMRF) (in which the ductility capacity of hinges to accommodate the predicted ductility demand is questionable) into a Ductile Moment Resisting Frame (DMRF) is desirable in seismic regions. One possible method of upgrading is relocation of plastic hinges away from the column face toward the beam. This paper presents the results of an experimental study carried out at the University of Queensland in order to examine the capability of CFRP sheets in doing this task. The proposed method called "web-bonded FRP" works by bonding FRP sheets of specific lengths to the sides of the beam's ends of reinforced concrete beams leading to the joints. In this study, five 1/2.2 scaled-down RC exterior joints of a typical Ordinary Moment Resisting Frame (OMRF) were tested under monotonic/cyclic loads. Two specimens were used as control specimens while the other three were strengthened with CFRP sheets of different lengths. All specimens were loaded under a displacement-controlled regime to failure. The load-deflection and hysteresis curves, modes of failure and ductility gain are presented in this paper. The results show that carbon fibre sheets (when carefully designed) can effectively relocate the plastic hinge away from the face of the column.