Cyclic Behavior of Steel Tube-Confined Circular RC Columns under High Axial Load

This study builds on existing researches to further investigates cyclic responses of the steel tube-confined reinforced concrete (RC) columns, with a primary focus on those subjected to high-axial load. A total of eleven column specimens were tested under lateral displacement reversal and axial load of either 0.3Agfcm,c or 0.5Agfcm,c, where Ag and fcm,c refers to concrete cross section area and tested concrete strength of the column, respectively. Three specimens represented the conventional reinforced concrete (RC) columns while the rest were the steel tube-confined circular RC columns. The key test parameters included (1) amount of longitudinal reinforcement, (2) axial load level, (3) continuity of the confining steel tube, and (4) clear cover of the longitudinal reinforcement. Test results showed that all the steel tube-confined RC specimens sustained the target axial load and maximum lateral strength up to around 10% drift ratio. A simple strength model was proposed to reasonably estimate the maximum strength of the steel tube-confined RC columns. The flexural rigidity ratio, (EI)test/Ecm,cIg, for RC specimens and specimens confined by continuous steel tube ranged between 0.6 and 0.8, approximately. Specimens confined by the cutoff steel tube showed lower (EI)test/Ecm,cIg ratio between approximately 0.3 and 0.6.