Estimating the seismic displacement of friction pendulum isolators based on non-linear response history analysis

A procedure for developing equations that estimate the isolator displacement due to strong ground motion is applied to buildings isolated with the friction pendulum system. The resulting design equations, based on rigorous non-linear analysis, offer an alternative to the iterative equivalent-linear methods used by current U.S. building codes. The governing equations of the system are reduced to a form such that the median normalized displacement of the system due to an ensemble of ground motions is found to depend on only the isolation period-a function of the curvature of the isolator-and the friction force at incipient slip normalized by peak ground velocity. The normalization is effective in minimizing the dispersion of the normalized displacement for an ensemble of ground motions, implying that the median normalized displacement is a reliable estimate of response. The design equations reflect the significant (20 to 38%) increase in displacement when the excitation includes two lateral components of ground motion instead of just one component. Equivalent-linear methods are shown to underestimate by up to 30% the exact median displacement determined by non-linear response history analysis for one component of ground motion, and building codes include at most a 4.4% increase for a second component. Copyright (C) 2003 John Wiley Sons, Ltd.