Fiber-Reinforced Polymer-Confined Circular Columns under Simulated Seismic Loads

This paper presents results from tests on nine reinforced concrete circular columns subjected to simulated seismic loads. All the specimens contained widely spaced steel spirals, while seven were retrofitted with lateral fiber-reinforced polymer (FRP) wraps. A number of ductility parameters related to curvature, displacement, and energy dissipation were used to evaluate the effects of FRP confinement. The results showed that FRP confinement effectively improved the seismic resistance of columns but displayed different characteristics from steel-confined columns. While curvature ductility and energy dissipation capacity of a section increase with an increase in FRP confinement, the displacement ductility does not increase beyond a limit. Lateral confinement also significantly enhances flexural strength of columns subjected to high axial loads. This is generally neglected by most design codes and may cause unsafe shear design. A procedure to evaluate the strength enhancement owing to lateral FRP confinement is proposed.