The building codes and seismic design specifications restricted using high strength steel in lateral load resisting systems because of its less ductility. However, it is possible to use lower grade steel in design of lateral load resisting systems, including X-Braces. In addition, the seismic design specifications generally do not consider significant difference in seismic design parameters of steel with different grades. In this research, effects of using steel with different grades in seismic behavior of X-Bracing system studied using nonlinear dynamic analyses. The frames with 4, 8 and 12 stories in high seismic zone designed with conventional design methods and regarding requirements of building codes. Two different steel grades considered in design of diagonals in X-Braced frames.
According to nonlinear static and dynamic analyses on different frames, it is found that the seismic performance of frames designed with lower grade steel is higher under near and far field earthquakes. In addition, the analysis of both type of frames under near-field ground motions showed more sever responses and bigger displacements, especially in progressive-direction faults.