Cast-in-place and prefabricated UHPC jackets for retrofitting shear-deficient RC columns with different axial load levels

Ultra-high performance concrete (UHPC) is a new class of concrete materials that features high strength, ductility, and damage tolerance. This study experimentally evaluated three new UHPC jacketing strategies for retrofitting shear-deficient reinforced concrete (RC) columns, including cast-in-place UHPC jackets with or without steel bar mesh and prefabricated UHPC panels with steel bar mesh. The steel mesh had a high nominal yielding strength of 550 MPa. The impact of different axial load levels on the seismic performance of the retrofitted columns was also explored. Two control columns and five retrofitted columns were tested under lateral displacement reversals. Results showed that while all retrofitting methods enhanced the strength capacity of the shear-deficient column, the UHPC jacketing without steel mesh failed to improve the shear-critical behavior and drift capacity of the column. With the inclusion of high-strength steel mesh in the UHPC jacket, the control columns' brittle shear failure was significantly improved. The proposed novel UHPC jacketing method with on-site installation of prefabricated UHPC panels showed comparable seismic retrofitting performance to the cast-in-place UHPC jacketing. In addition to the experimental study, suitable strength models, which can reasonably evaluate the strength and failure mode of the RC columns retrofitted using the proposed UHPC jackets, were suggested.