Enhancement of seismic performance of reinforced concrete columns with buckling-restrained reinforcement

Reinforced concrete (RC) columns with light confinement prevalent in developing countries exhibit low ductility with brittle shear failure, especially when buckling of longitudinal rebars takes place. This study applies the buckling restraining concept widely used in seismic resistant steel structures to reinforcing bars. Two RC columns 270 mm×300 mm in cross section with a height of 1200 mm and minimum (non-seismic) transverse reinforcement were tested under cyclic lateral loading. Buckling-restrained reinforcement was provided over the critical zone. The buckling-restraining casing effectively prevented buckling of slender vertical bars under a substantially high axial load level, resulting in a more ductile mode of failure with the evident formation of plastic hinge at the base of the column. Prior to gravity load collapse, the drift capacities and the degraded concrete shear capacities of the specimens were significantly increased compared to their counterparts without casings.