Correlation Between Intensity Measures of Long-Period Ground Motions and Responses of Base-Isolated Structures

Long-period ground motions (LPGMs), characterized by their extended low-frequency energy content, produce markedly greater response amplification in base-isolated structures than normal ground motions (NGMs). On the other hand, peak ground acceleration (PGA) scaling, which is mandated by many national seismic codes, tends to amplify LPGM-induced demands more severely than those from NGMs, reliance on PGA alone can overstate structural responses because of LPGMs’ distinctive spectral profiles. Accordingly, the selection of an appropriate seismic intensity measure (IM) is essential for the accurate assessment of base-isolated systems under LPGM excitation. This investigation employs three reinforced concrete frame-shear wall buildings of varying heights to examine the influence of IM choice on dynamic response predictions. A suite of ground motions is applied to both isolated and non-isolated models, and Pearson’s correlation coefficients are computed between key response quantities and several candidate IMs. Results indicate that, relative to non-isolated structures, base-isolated structures exhibit over 70% increase in displacement but 30% to 70% reductions in acceleration and shear force when subjected to LPGMs. Furthermore, seismic isolation alters the correlation patterns between IMs and structural responses, underscoring the necessity for IM selection that is tailored to isolation systems. Notably, the velocity-related IMs, Housner intensity (HI), velocity spectral intensity (VSI), and period-related IM (Tm) correlate strongly ([Formula: see text]) with response parameters for isolated models under LPGMs. These findings furnish a robust framework for refining seismic isolation design, improving predictive accuracy of LPGM effects, and enhancing overall seismic resilience of isolated structures.