عنوان مقاله [English]
An intense earthquake can make a large number of aftershocks due to the complex interaction of tension between and within tectonic plates. Aftershocks magnitudes are usually less than the main shocks, but an aftershock record may have longer duration, Peak ground acceleration and greater intensity than the main shock. Aftershock occurrence could cause an increasingly deterioration in buildings damaged in the main shock. Seismic designs codes are provided design process based on a "design earthquake" and do not take into account the effects of aftershocks on design. In researcher’s studies, investigating the effect of seismic sequences on structures with different lateral resistance systems can compensate existing gap of code. In this regard, according to the common usage of steel structures with dual moment frame system and concentrically brace, its performance has been investigated by seismic sequence. For this reason, based on Iran’s code, the structure of three, five, seven, ten, fifteen and twenty-stories is designed and is analyzed base on the non-linear software of perform 3D. The fragility curves of the structures studied are plotted at different levels of performance and the seismic vulnerability of the structures has been investigated. The results of present study show that the effect of earthquakes on higher structures has decreased as a result of decreasing the magnitude of the earthquake spectrum in larger periods, which has led to a reduction of vulnerability. Also, the structures at the performance level of life safety (LS), which are intended to design codes had a good performance in the earthquake and sequences near-field and base of them, the design would be reliable. According to the results presented in present study, the second earthquake is effective on the structure response in the seismic sequence, if its PGA be more than the first earthquake. The probability of Exceedance damage at the performance level (IO), in the far-fault earthquake and the sequence is more than the near-field, while the probability of exceedance damage at the performance levels (LS) and (CP), in 10-, 15- and 20-story structures in the near-field earthquake and sequence.