Seismic fragility analysis: Application to simple linear and nonlinear systems

Seismic fragility of a structural, nonstructural and/or geotechnical system is the probability that a system response exceeds a critical value under seismic ground motions of specified intensities. Fragility curves are plots of system fragilities versus a scalar measure of seismic intensity. Traditionally, peak ground acceleration (PGA) has been used as an intensity measure. Recent studies show that pseudo-spectral acceleration provides a superior measure of seismic intensity than PGA. It is shown that pseudo-spectral acceleration may not be a satisfactory measure of seismic intensity for the fragility analysis of nonlinear systems, so that fragility curves based on pseudo-spectral acceleration are not recommended for these systems. An alternative intensity measure based on two parameters, the earthquake moment magnitude m and the distance r from the seismic source to system site, is proposed for the fragility analysis of nonlinear systems. The relationship between a system probability of failure and (m, r) is called fragility surface. Findings are for single degree of freedom systems and synthetic ground motion records. Copyright (C) 2007 John Wiley & Sons, Ltd.