Assessing residual deformation of bridge piers under bidirectional near-fault motions with forward directivity and fling-step

A reasonable estimate of residual deformation is crucial for assessing a structure's post-earthquake performance, safety, and serviceability. Residual deformation may be significant, especially in near-fault regimes. Residual deformation is also influenced by the simultaneous action of two horizontal components of a motion that may incident at an arbitrary angle. However, conducting bidirectional analyses across admissible incidence angles is challenging and time-consuming. Against this background, changes in the (i) appropriate ground motion parameters over orientations and (ii) residual deformation of a bridge column over incidence angles under unidirectional and bidirectional shaking are collectively explored. Ground motions are selected and modeled to represent the effects of forward directivity and fling-step. It is shown that, for a given pair of ground motions, there exist two characteristic orientations namely, the most preferred orientation and the least preferred orientation. As the names suggest, the most preferred orientation corresponds to the smallest difference between the responses obtained from the unidirectional and the bidirectional analyses while the least preferred orientation corresponds to the largest difference between those two responses. The values of the residual deformation estimated per unidirectional analysis in the most preferred orientation can be further improved by using the 40% combination rule. Based on a more straightforward unidirectional analysis in a predefined orientation, the proposed strategy may prove helpful for practical purposes.