Peculiarities of the response of steel special moment frames to megathrust earthquakes

Abstract

While most of the current research on the seismic performance of Steel Special Moment Frames (SSMFs) is based on seismic hazard due to crustal earthquakes, research on the response of SSMFs to megathrust earthquakes is generally neglected. This study aims at shedding needed light on the behavior of SSMFs at locations where the seismic hazard is due mainly to subduction earthquakes, such as Chile, Japan or the Pacific Northwest of the US. A probabilistic hazard-consistent collapse analysis, considering a vector ground motion intensity measure (IM) that includes spectral amplitude (Sa(T1)), spectral shape (SaRatio) and ground motion duration (DS5-95), is carried out on 40 modern SSMFs having 2 to 20 stories and designed assuming US locations having high levels of seismic activity. The median collapse capacity and the mean probability of collapse in 50 years of mid- and high-rise SSMFs subjected to a megathrust scenario are, on average, 25% smaller and 100% greater than those of the same SSMFs subjected to a crustal scenario. Results of this study are significant because system- and component-level force and displacement limit states of current seismic design codes are intended to achieve 1% probability of collapse in 50 years at all locations.