Seismic performance of base-isolated steel frames considering the influence of rotational ground motions

The torsional component and near-fault pulse-like ground motions can bring additional damage to the structure. However, the coupling effect of the abovementioned two factors has not been thoroughly examined in the seismic performance evaluation of base-isolated steel frames. This study examines the individual and combined impacts of torsional and near-fault pulse-like ground motions on the seismic behavior of base-isolated structures. The torsional component record is extracted using the frequency domain approach. A series of base-isolated structures with three length-width ratios are used as case buildings, and the corresponding finite element models are developed using ABAQUS software. A shaking table tests is conducted to validate the finite element model. A comprehensive analysis is carried out on the structural seismic responses. Base shear, floor acceleration, interstory drift, and isolation layer displacement are selected as damage indices for the base-isolated structures. The results indicate that the coupling effect of near-fault pulse-like and torsional components significantly increases the structural seismic response. Additionally, the length-width ratios also bring an obvious growth for structural damage. Specifically, as the length-width ratio increases from 1 to 3, under the combined influence of near-fault pulse-like and torsional ground motions, the floor acceleration increases by 35.85%, 39.75%, and 43.33%, while the displacement of the isolation layer increases by 48.23%, 48.10%, and 49.74%, respectively. The findings point out that ignoring near-fault pulselike and torsional ground motions would lead to an underestimation of seismic demands in damage assessment.