Effects of Near-Fault Earthquakes on the Seismic Performance of Steel-Frame Buildings with Vertical Mass Irregularities

This study explores the effects of vertical mass irregularities on the seismic response of multistoried moment-resisting steel structures by considering mass discontinuity at the top and first stories. Perform 3D software is used to carry out an inelastic dynamic analysis of time histories of 3-, 5-, and 8-storey steel frame buildings subjected to 10 near-field earthquake events. Comparison of the analytical results reveals that the axial forces on both the interior and exterior columns in all cases are at their maxima (30%-40%) in the top storey and at their minima in the 1st storey, respectively. Structures with mass irregularities in their top stories are observed to experience slightly larger horizontal roof displacements than those with irregularities in their 1st storey. Larger vertical displacements at beam mid-points are observed in structures with mass irregularities in their top stories than in those with irregularities in their 1st storey while the base shear forces are found to decrease by about 6%. Compared to structures with mass irregularities in their lower stories, those with vertical irregularities in their top stories exhibit a poorer performance under near-field earthquakes.