عنوان مقاله [English]
In this paper, a new nonlinear static (pushover) analysis method is presented to evaluate the displacement-based demands of steel moment resisting frames (MRFs) at the collapse prevention performance level. In this method, the modal pushover responses are integrated using modal combination coefficients, which are calculated from optimization procedures. Two metaheuristic algorithms, including particle swarm optimization and colliding bodies optimization, are utilized in for this purpose. In the proposed procedure, the collapse prevention performance level is obtained by a new suggested criterion, which is based on the onset of severe local damages at the structure. This criterion corresponds to occur backward shape in the story capacity curves. The modal combination coefficients are obtained from incremental dynamic analysis (IDA) results of 5, 9, and 11 story steel moment resisting frames. The optimized modal pushover (OMPA) method is applied to two 9 and 12 story steel MRF buildings. The results show that the proposed method is easy to implement and is accurate enough to evaluate the displacement-based responses at the CP performance level.