An Experimental Study of a Spherical Sliding Isolation System Subjected to Pulse‐Like Ground Motions

A series of shaking table tests for a spherical sliding isolation system were conducted at the National Center for Research on Earthquake Engineering (NCREE) Tainan Laboratory to investigate critical challenges in seismic isolation design: (1) the influence of ground motion characteristics, particularly pulse‐related features, on the response of a spherical sliding isolation system and (2) the applicability of equivalent linear design procedures for the isolation system subjected to such ground motions. Four distinct ground motion sets were carefully selected and processed: short‐period and medium‐period pulse‐like, non‐pulse‐like, and spectrally matched motions, with the latter three sets having similar average spectral acceleration. Results showed that medium‐period pulse‐like motions induce significantly larger displacement demands than the other sets, despite comparable average spectral accelerations, underscoring the inadequacy of using spectral acceleration alone in capturing the impact of pulse‐like ground motions on isolation responses. Additionally, evaluation of the equivalent linear procedure for the isolation system revealed that the code‐specified damping reduction factors fail to account for the distinct characteristics of pulse‐like and non‐pulse‐like motions, resulting in significant variability in displacement predictions and inconsistent levels of conservatism across different ground motion sets. The damping reduction factors appropriate for pulse‐like and non‐pulse‐like ground motions should be differentiated.