GLOBAL SPECTRAL EVALUATION OF SEISMIC FRAGILITY OF STRUCTURES

An approach for assessing the global seismic fragility of inelastic structures is presented. The fragility is obtained from the distribution of structural response, which is evaluated from response spectra with an associated probability distribution, compared with the performance limits states. Formulas that provide the probability distribution of spectral ordinates are developed based on the crossing theory of random functions and the equivalent linearization method. The ground motion is modeled as a stationary zero-mean Gaussian process with a Fourier spectrum typical of far-field earthquakes. The theoretical results are compared within a numerical simulation study. It is shown that a Gaussian distribution can be assumed for the distribution of response of hysteretic systems under far-field excitations. It is shown also that a white noise representation may lead to large inelastic displacements that are not likely to not occur under earthquake excitations. An application example is presented to illustrate the use of this approach