Analytical evaluation of essential facilities fragility curves by using a stochastic approach

The study presented in this paper is focused on an analytical method for constructing fragility curves of a given class of existing structures, based on a stochastic approach and which makes use of the Hazus database. The analysed structure is a non-linear one degree of freedom (SDoF) system: its constitutive law is described by means of a hysteretic model, whose parameters are obtained by an identification procedure starting from the Hazus data. A particular class of structures, the essential facilities, are analyzed. The system's response to seismic action, here modelled by means of the modulated Clough and Penzien filtered stochastic process, is obtained by using the stochastic linearization technique and the covariance analysis. In order to develop the fragility curves, a displacement based damage index is adopted and, finally, fragility curves are obtained in terms of the probability of exceeding a given damage level, by using an approximate theory of stochastic processes. The main innovation of the proposed approach is that it can be directly extended to other kinds of structures which are not included in the Hazus database, since the procedure requires only the knowledge of the capacity curve, which can be obtained by standard procedures.