Uncertainty and dependence analysis of performance limit state for structural multidimensional fragility evaluation

Abstract

Considering uncertainty and dependence of performance limit states (PLSs), the study addresses a methodology to evaluate multidimensional fragility. The purpose is to identify the PLS uncertainty quantitatively. The dependence between each PLS parameters is also investigated. The limit state band is firstly proposed to describe the bi-dimensional case. Through interval estimation, the band area with a certain confidence level is determined. A reinforcement concrete bridge is used as example to illustrate the proposed approach for developing fragility curves. PLS threshold samples are obtained to formulate limit state function using incremental dynamic analysis. The study investigates the sensitivity of the method for fragility assessment when different confidence levels are considered. In addition, influence of correlation coefficient between PLSs is evaluated. Results show that a fragility interval is obtained with the introduction of limit state band. The interval length decreases as with the reduction of the confidence level. The probability of failure becomes smaller when the dependence between PLSs is ignored, which will result in overestimation of the structural seismic performance.