Seismic performance of circular RC columns retrofitted with prefabricated steel wrapping jackets

This paper presents experimental results on a seismic retrofit of circular reinforced concrete (RC) columns with lap-spliced longitudinal reinforcement using prefabricated steel wrapping jackets. The effects of a split jacket and the use of adhesive were also assessed. A special system to provide external pressure on the steel jackets was devised and the active confining pressure and its effect on the peak strength of concrete were assessed. It was found that the steel wrapping jackets improve the seismic performance of the retrofitted columns by delaying the buckling of longitudinal reinforcing bars and increasing the bond strength at lap-spliced zones; they thus increase ductile behaviour and energy dissipation capacity of the columns in lateral force–displacement response. The split jacket was proved to be effective, but epoxy application did not improve the seismic behaviour of the jacketed RC columns. An equation is proposed to estimate the effective stiffness of ductile reinforced columns for all range of drift ratios. The external pressing method described is effective at increasing the peak flexural strength and ductile behaviour of jacketed columns.