Seismic assessment of a dual concentrically braced steel structure under near-fault ground motions

In this paper, the seismic performance of a five-story steel structure with a dual system used as a lateral load resisting system comprised of a moment-resisting frame and a concentrically braced frame is evaluated under near-field ground motion records with and without pulses. This research paper aims to evaluate the pulses’ effects on the probability of the collapse, global damage index, and the annual and 50-year collapse risks of the structure with such dual systems, which have been less considered in previous research works. To this end, incremental dynamic analyses are performed, and to determine the probability that the studied structure will exceed a specific damage state, fragility functions are developed. The global damage index of the structure is also computed, and a full assessment of the collapse risk of the structure is carried out under the near-field ground motion records with and without pulses. Finally, It is concluded that the probability of collapse, global damage index, and the annual and 50-year collapse risks of the structure subjected to the ground motions with pulses are higher than the ground motions without pulses. For the pulse periods larger than two times the period of the first mode of the structure, the intensification occurs due to the equalization of the increased period of the first mode of the structure and the period of the pulse.