Energy and spectral indicators support screening for soil structure interaction sensitivity in steel moment frames

Abstract

Soil–structure interaction (SSI) can increase or decrease seismic demand depending on structural, foundation, and ground-motion characteristics. This study evaluates whether SSI-sensitive cases in steel special moment-resisting frames can be prioritized using energy-based flexibility indices and record-specific spectral information. Three 4-, 8-, and 16-story frames were analyzed under five far-field records, three intensity levels, and three soil-stiffness levels, yielding 180 nonlinear analyses and 135 fixed-base/SSI comparisons. Larger translational and rocking flexibility contributions were associated with larger absolute drift changes, while spectral information improved directional interpretation within the development data. A frozen model was then tested without recalibration on 17 additional FEMA P695 records, adding 204 analyses. For 81 spectral-eligible comparisons from 10 independent new events, the combined model yielded an RMSE of 0.0191, a sign balanced accuracy of 0.628, and a three-class balanced accuracy of 0.514, and did not outperform a zero-change baseline in continuous RMSE. Thus, the indices retain value for mechanistic interpretation and within-domain prioritization, but the fitted coefficients and screening performance are not uniformly transferable. The framework is therefore a screening heuristic, not a substitute for direct nonlinear SSI analysis.