Statistical evaluation of steel moment frames response under crustal and subduction seismic environments

In this paper, the influence of the two main types of earthquake mechanisms (i.e., subduction and crustal) on the seismic performance of steel moment frames (SMFs) is investigated. For this purpose, nonlinear time history analyses of five archetype SMFs are conducted using two suites of spectrally equivalent as-recorded ground motions originating from crustal and subduction seismic environments. The differences between the two environments are first analyzed by conducting a sensitivity analysis of the SMFs' seismic response against six ground motion intensity measures, representing amplitude, duration, energy, and frequency content. From the sensitivity analysis results, it can be primarily demonstrated that the behavior of SMFs is more prone to the duration of subduction ground motions than the duration of crustal ground motions. Further comparison of the SMFs' responses allows the authors to indicate that peak floor accelerations and inter-story drift ratios under subduction earthquakes are statistically higher than their spectrally equivalent counterparts from crustal earthquakes. These statistical analyses are complemented by incremental dynamic analysis (IDA) to compare the influence of the two seismic environments at three different intensity levels, i.e., design basis earthquake (DE), maximum considered earthquake (MCE), and collapse. Results from IDA at the DE and MCE levels are consistent with the findings from the statistical analysis using as-recorded ground motions showing differences in the frame responses between the two seismic environments. Moreover, in most cases, the collapse margin ratios (CMR) obtained from the SMFs subjected to crustal ground motions are higher than the CMRs for their corresponding subduction earthquakes, indicating a clear impact of the seismic source on the collapse capacity of SMFs. As the design guidelines of the US are primarily developed using the experimental and analytical results under records of crustal earthquakes, the findings of this research raise concerns for the design and analysis of SMFs located in areas prone to subduction earthquakes, such as Washington, Seattle, Anchorage, etc. or other countries that adopt US standards such as Ecuador or Peru.