Estimation of seismic demands on isolators in asymmetric buildings using non‐linear analysis

Abstract A procedure based on rigorous non‐linear analysis is presented that estimates the peak deformation among all isolators in an asymmetric building due to strong ground motion. The governing equations are reduced to a form such that the median normalized deformation due to an ensemble of ground motions with given corner period T d depends primarily on four global parameters of the isolation system: the isolation period T b , the normalized strength η, the torsional‐to‐lateral frequency ratio Ω θ , and the normalized stiffness eccentricity e b /r . The median ratio of the deformations of the asymmetric and corresponding symmetric systems is shown to depend only weakly on T b , η, and Ω θ , but increases with e b /r . The equation developed to estimate the largest ratio among all isolators depends only on the stiffness eccentricity and the distance from the center of mass to the outlying isolator. This equation, multiplied by an earlier equation for the deformation of the corresponding symmetric system, provides a design equation to estimate the deformations of asymmetric systems. This design equation conservatively estimates the peak deformation among all isolators, but is generally within 10% of the ‘exact’ value. Relative to the non‐linear procedure presented, the peak isolator deformation is shown to be significantly underestimated by the U.S. building code procedures. Copyright © 2003 John Wiley & Sons, Ltd.