Seismic Fragility Assessment of Steel SMRF Structures under Various Types of Near Fault Forward Directivity Ground Motions

In this paper, the seismic collapse probability of special steel moment-resisting frame (SSMRF) structures under near fault pulse-like and far fault ordinary ground motions is evaluated through fragility analysis. For this purpose, five sample frames with 3 to 15 stories are designed and imposed to the ground motion excitations with different characteristics. Fragility curves are derived for the sample frames using the results of incremental dynamic analyses. Three sets of ten near fault ground motions with different range of pulse periods and one set of ten ordinary ground motions are used in dynamic analyses. Based on the obtained results, it was found that the impulsive characteristic and the pulse period of the records highly affect the damaging potential of near fault records. The fragility analysis reveals that the collapse probability for the case study frames under the near and far fault ground motions at the intensity of 0.35g equals to 4.3% and 10.3%, respectively. These values are 15.9%and 38.6%, for PGA of 0.53g. It is also found that the increase in the height, leads to increase in higher modes effect to transfer drift demands toward upper stories.