Seismic Performance of Base-Isolated Structure Under Very Rare Pulse-Type Earthquake

Current research lacks a clear understanding of very rare ground motions, especially pulse-type events, and the performance of isolated structures under such conditions remains underexplored. This study addresses this gap by proposing that very rare ground motions include both pulse-type and non-pulse motions. The response spectra of pulse-type motions are compared with design spectra from Isolation Standard. Using a typical intensity VIII isolated frame structure, dynamic elastoplastic time-history analysis is conducted to evaluate seismic performance. Results show that pulse-type motions significantly amplify long-period spectral values and exhibit a “double peak” phenomenon, especially for softer sites and higher intensities. The Isolation Standard design spectrum can be adjusted in spectral values or characteristic periods to better match pulse-type responses. Pulse-type motions considerably increase structural response compared to non-pulse motions. It is suggested that isolated structures designed for very rare earthquakes should be built in regions with fortification intensity of VI-VIII and on sites of category I-II. The seismic performance of these structures under pulse-type ground motions must be verified, considering pulse effects through either direct input or amplified non-pulse motions. This study provides important references for the design of seismic isolation structures under extremely rare earthquake conditions, emphasizing the necessity of considering the special characteristics of pulse type seismic motion in seismic design. The research results have guiding significance for revising relevant design specifications and improving the safety of isolation structures in extreme earthquake events.