Effect of Active versus Passive Confinement on Seismic Response of Wide RC Columns with Lap Splices

Abstract

The results of an experimental study on seismic bond strengthening of spliced reinforcement in wide RC columns using external confinement are presented. Two types of confinement techniques were evaluated and compared, as follows: (1) a combination of external carbon fiber-reinforced polymer (CFRP) jacket and CFRP anchors, and (2) active confinement by means of pretensioned steel anchor rods. The effectiveness of the different strengthening techniques was evaluated by comparing with test results of companion as-built columns, and earthquake-designed columns which were detailed in accordance with the seismic provisions of a national building code. The columns were subjected to a quasi-static cyclic loading, simulating regions of high seismic hazard. In addition to the type of the strengthening system used, the test variables included area and diameter of the column longitudinal reinforcement. The as-built columns suffered bond and load degradation immediately after yielding of the spliced reinforcement. The actively confined specimens developed considerably larger lateral load, drift, and energy dissipation capacities than the as-built specimens, and performed better than the specimens strengthened using a combination of CFRP jacket and CFRP anchors, and even slightly better than the earthquake-designed specimens. A simple approach is presented for designing the strengthening systems required for effective bond strengthening.