SEISMIC VULNERABILITY MODELS OF PIERS UNDER NEAR-FAULT GROUND MOTIONS

Abstract eng:
Seismic vulnerability models of typical highway piers under the near-fault ground motions were developed based on the incremental dynamic analysis (IDA) method. On the selection criteria of ground motions determined by the authors, totally 30 near-fault or farfield earthquake records were selected. Totally 36 piers were designed as samples by using the orthogonal experimental design method. Each sample was matched by all of the selected ground motions. The numerical models of the piers were established by using OpenSees, in which the nonlinear time history analyses were carried out by the incremental dynamic analysis method. For estimation of the seismic fragility parameters, three different methods were adopted, including the estimation method based on the multiple-stripe analysis idea, the frequency point regression methods from the Monte Carlo sampling and the two-dimensional probability density function integration. The fragility curves were then built up accordingly. The following results can be obtained from the analysis: I) the probability of collapse is higher under near-fault ground motions whereas lower under the far-field motions, i.e., the other three damage states are more likely to happen, when given the same intensity of ground motions; II) by considering two damage indexes, the median values of the fragility curves decrease sharply compared to those with single damage index, which means the pier damage probability increased. Based on the results, it is found that the use of two damage indexes yields more accurate evaluation for the seismic risks of the pier damage and decision making of the seismic retrofit prioritization.

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