Spectral evaluation of seismic fragility of structures

ABSTRACT: An approach for assessing the seismic fragility of inelastic structures is presented. In this approach, the structural response, which is evaluated from response spectra with an associated probability distribution, is compared with the performance limits states to assess fragility. 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 verified within a numerical study. It is shown that a Gaussian distribution can be assumed for the response of hysteretic systems under this type of excitations and 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.