Seismic performance of high-strength concrete square columns confined with carbon fiber reinforced polymers (CFRPs)

This paper presents the results of an experimental and analytical study on high-strength, reinforced-concrete (RC) columns with different levels of initial ductility enhanced with carbon fiber reinforced polymer (CFRP) wraps. Six square columns 260 mm wide and 1650 mm long were tested under constant axial load and reversed cyclic lateral load. The test specimens were divided into three groups. Groups I and II were designed and detailed according to the requirements of American Concrete Institute ACI318-02 for intermediate-moment frames. Group I was wrapped with CFRP, group II was control specimens, and group III was designed and detailed according to the requirements of ACI318-02 for special-moment frames. Each group consisted of two columns with p(sl) = 1.5% and 3.0% longitudinal steel rebars, where p(sl) is the ratio of area of longitudinal reinforcement to gross area of concrete. The moment-curvature is numerically calculated for sections with fiber reinforced polymer (F RP) confinement. The theoretical prediction provides conservative results compared with the test data. Based on the test results, CFRP enhanced ultimate displacement and curvature ductility by 53% and 79%, respectively, in column WI4 with four longitudinal bars and 27% and 28%, respectively, in column WI8 with eight longitudinal bars. Moreover, the performance of wrapped columns was enhanced to a level higher than that of unwrapped columns designed according to special-moment frames.