Investigating the Influence of Bay Number on the Possibility of the Occurrence of Seismic Collapse in Moment and Braced Frames

Seismic collapse of buildings is the level of structural performance in which the amount of damage reaches its maximum, so this event can be the worst happening in the construction industry. Due to the seismicity of Iran, more accurate assessment of the collapse of structures under earthquakes is one of the important challenges of structural engineering. In this paper, the effect of the number of bays on the seismic response of three sets of short steel frames is investigated. In all three sets, moment frame, an eccentric braced frame and the concentric braced frame are considered in the regular state. Then, the number of bays in all three sets of frames are 2, 3 and finally 4, respectively. Nonlinear static analysis is conducted based on base shear and roof displacement to determine the possible failure mechanisms of these frames and incremental nonlinear dynamic analysis is performed with intensity parameter (IM) corresponding to maximum relative displacement between stories and damage measure parameter (DM) corresponding to the spectral acceleration of the first mode Sa (T1, 5%) were considered. In addition, the collapse-preventing performance level of CP was analyzed. The results of the fragility curves in the limit state (CP) indicate that with increasing the number of bays, the probability of failure of ten percent for all studied frames has increased and consequently their vulnerability has decreased.