Seismic strengthening of deficient ground soft-story RC frames with inadequate lap splice using chevron brace

Abstract

Deficient RC frames with ground soft-story irregularity have been constructed in many countries. Past earthquakes have shown that such structures are vulnerable and must be retrofitted. This study investigated the cyclic response of two one-bay, two-story, 1/2.5-scaled RC frames with inadequate lap splice length through experimental works and numerical simulations. One of the frames was kept as the reference, and the other was strengthened using a chevron brace system. The frames were subjected to displacement-controlled quasi-static cyclic loading, and their cyclic responses were recorded and compared. Besides, the lumped plasticity model was used to investigate the effect of the strength of infill walls on the force-displacement response of the retrofitted frame. The experimentally obtained results indicated that the employed chevron brace system significantly enhanced the cyclic response of the reference frame. The retrofitted frame exhibited a 171% greater ultimate strength than the reference frame. Besides, the retrofitted frame's initial and post-yield stiffness were 2.2 and 6.9 times greater than that of the reference frame. At a 3.5% drift ratio, the retrofitted frame dissipated 233% more energy than the reference frame. In small drift ratios, the retrofitted frame exhibited a faster decay in the lateral stiffness; however, at large drift ratios, both frames showed a comparable stiffness degradation rate. Numerical simulations showed that the infill wall's lateral strength could alter the retrofitted frame's failure mode and significantly affect its force-displacement response.