Seismic retrofit of URM-infilled RC frames by the steel-jacketed hybrid walls

The present study aims at using the hybrid wall technique to prevent the occurrence of shear failure of the reinforced concrete (RC) columns in the unreinforced masonry walls (URMs) infilled in the RC frames and to increase their lateral strength, stiffness, and ductility. The hybrid wall integrates a boundary RC column with its adjacent URM infill with the help of jacketing steel plates, to make them perform as a unified member. Two series of experimental tests, including one element test (RC column with URM wing-wall) and five frame tests (one-bay one-story RC frames with URM infills), were conducted under reversed cyclic loading. The interaction between the masonry infill wall and the boundary RC columns before and after retrofitting by the hybrid wall technique is studied, and a corresponding design framework is suggested. The experimental results of the retrofitted frames demonstrated not only enhancing lateral strength, stiffness, and ductility of the URM-infilled RC frames but also the prevention of the shear failure of the boundary RC columns and postponement of the occurrence of the URM infills' failure to larger drifts. The columns' shear failure is a significant concern due to infill-column interaction in URM-infilled RC frames. However, one of the important impacts of the thick hybrid walls is that the boundary RC columns remained undamaged even in large lateral drifts due to flexural behavior. From the viewpoint of applicability, the thick hybrid walls technique does not require relocation of occupants and does not disturb RC buildings' operations during construction. Moreover, it is not a labor-intensive technique.