Investigating the Effect of Combination of Buckling Restrained Brace and Moment Frame in Height on the Seismic Collapse of Steel Frames

In this study, firstly, the 12-story 3D structure with hybrid system of buckling restrained brace and moment frame with 6 states such as 1) whole stories with buckling restrained brace system, 2) the first 6 stories with buckling restrained brace system and the second one with moment frame, 3) the first 5 stories with buckling restrained brace and the 7 stories with moment frame, 4) the first 7 stories with buckling restrained brace and the 5 stories with moment frame, 5) the first 3 stories with buckling restrained brace and the 9 stories with moment frame, 6) the first 9 stories with buckling restrained brace and the 3 stories with moment frame. Then, using Opensees software, the side axle frame is modeled subjected to incremental nonlinear static analysis and incremental nonlinear dynamic analysis (IDA) with the intensity parameter (IM) corresponding to the maximum relative displacement and the DM response parameter corresponding to the first mode spectral acceleration Sa (T1, 5%)and the level of collapse prevention performance (CP) has been evaluated. In the following, fragility curves and modification factor are presented. By investigation of the results, it is observed that the frame with more braces, at a constant seismic intensity level, is less likely to fail than other frames. Therefore, increasing the percentage of brace use leads to a higher modifaction factor and less probability of failure than other cases, and by reducing the ductility of the frames, the probability of their failure also decreases.