Seismic Analysis of Base-Isolated San Bernardino County Building

Abstract

The authors investigate the seismic behavior of an existing base isolated building and interpret its recorded response to the 1990 Upland California earthquake. They formulate a linear-elastic model that accurately represents the building during the earthquake and infer its response behaviors. Additional analyses using severe earthquake excitations demonstrate the building behavior in major events and hypothetical seismic gap pounding situations. Key findings include the following: • The Upland earthquake resulted in relatively low intensity shaking at the site, and the building did not exhibit a classic soft story effect in the isolation system. • A linear-elastic model can accurately idealize the building during this event. • Under major earthquake excitation, base isolation can lead to peak story drifts, shears, overturning moments, and accelerations that are much smaller than those of nonisolated buildings. • Pounding at seismic gaps can produce large story drifts, shears and accelerations. These peak pounding responses can be greater than those from nonisolated buildings (i.e., having no pounding).