Influence of modeling assumptions and aftershock hazard level in the seismic response of post-mainshock steel framed buildings

Seismic response under strong aftershocks has become an important topic in performance-based earthquake engineering recently. This paper examines the influence of the modeling approach in the response of a case-study four-story steel framed building designed with modern seismic provisions when subjected to two sets of aftershocks representing different aftershock-hazard levels. It was assumed that the building models experienced specific post-mainshock residual drifts prior of being subjected to the aftershocks. Results shown that including additional sources of stiffness and strength (i.e. inclusion of the interior gravity framing and participation of the slab in the beams) in the building analytical model lead to a different response under aftershocks in terms of maximum and residual interstory drifts than that of the analytical model commonly used in previous studies. Particularly, additional overstrength and post-yield stiffness ratio help to constrain residual drift demands under strong aftershocks, and decrease the probability of imminent demolition due to excessive post-mainshock residual drifts.