Seismic fragility analysis of bridge piers using methods of moment

In this paper, an efficient method is proposed for constructing the seismic fragility curves of bridge piers, in which the dynamical reliability assessment is developed from methods of moment. The main procedure for constructing seismic fragility curves consists of four steps. First, the non-stationary seismic acceleration process samples are simulated by the random function-spectrum representation model (RFSRM) with one elementary random variable at a given PGA value. Second, the first four moments (i.e., mean value, standard deviation, skewness and kurtosis) of extreme structural response are then evaluated from the extremum of each nonlinear time-history seismic response based on RFSRM. Third, the failure probability is then estimated by the fourth-moment reliability index, which is derived from an explicit fourth-moment transformation. Finally, the seismic fragility curves can be constructed by repeating the three steps and considering different PGA values and damage levels (i.e., slight, moderate, extensive, and complete). The efficiency and accuracy of the proposed methodology are demonstrated by a numerical example for constructing the fragility curves of a high-speed railway bridge pier in which the direct incremental dynamic analysis (IDA) method based on Monte Carlo simulations are employed for comparison.