Seismic Fragility Analysis of Pile-Supported Wharves Subjected to Bi-Directional Ground Motions

The purpose of this study is to determine the effect of the angle of seismic incidence on the fragility of regular pile-supported wharves. The investigation is performed by selecting the displacement demand at the deck level of critical piles located at the segment ends as the engineering demand parameter, in accordance with the current seismic design practices. Then, probabilistic seismic demand analyses are conducted on nine pile-supported wharf structures with 80 pairs of bi-directional earthquake ground motion records to determine the optimal probabilistic seismic demand models. During demand analyses, both the accurate procedure for addressing the effect of bi-directional earthquake loading and the correspondingly simplified procedures in current design practices are included. Thus, seismic fragility curves of wharves are developed with respect to both the optimal intensity measure (IM) and incident angles. The results highlight that the directivity of ground motion excitation may have a minor impact on the fragility of wharves subjected to bi-directional ground motions. Consequently, probabilistic seismic demand analyses can be performed by simultaneously applying bi-directional ground motions only along the principal axes of the wharves. Meanwhile, the resultant displacement demand under simultaneous seismic excitation can be approximately determined by combining the displacement demand resulting from 100% of the loading in one direction with the corresponding displacement demand from 30% of the loading in the perpendicular direction. This simplified procedure for demand analyses can also yield satisfactory results in fragility analysis.