Seismic performance of full-scale UHPC-jacket-strengthened RC columns under high axial loads

Ultra-high-performance concrete (UHPC) is a class of concrete materials that have high strength and ductility capacities. This study developed two UHPC jacketing methods to improve the seismic performance of shear-deficient RC columns in mid- to high-rise buildings without enlarging the cross-section of the columns. In the first method, the original concrete cover was replaced with a cast-in-place UHPC jacket that was reinforced by steel bar mesh. To simplify the on-site construction process, the second method utilized prefabricated UHPC panels incorporating steel bar mesh. The performance of the proposed strengthening methods was evaluated using cyclic loading tests on three full-scale RC columns with a high axial load demand. The test results showed that the developed UHPC jacketing methods improved the lateral strength and drift capacity of the shear-deficient column by at least 40% and 30%, respectively. They also reduced the residual displacement of the column by 65%-80%. Compared to the cast-in-place jacketing, the discontinuity in the prefabricated UHPC jackets inhibited full composite action of the jacketing, thus reducing the retrofitting efficiency. In addition to the experimental study, evaluation methods were proposed to evaluate the strength and behavior of the retrofitted columns.