Seismic Response of Box Girder Bridge Columns to Forward-Directivity and Fling-Step Ground Motions

Until recently, seismic design codes were generally based on research addressing far-field earthquake characteristics. However, with the increasing in recording the near-fault ground motions, it has been realized that special considerations should be considered for bridges located in near-fault regions. Several studies have investigated how the unique characteristics of near-fault motions, such as forward-directivity and fling-step, influence the seismic response and damage to concrete structures. The objective of this research was to investigate the effects of near-fault ground motions on the columns of box girder concrete bridges. to accomplish these goals, two and three spans of reinforced concrete bridges having box girder deck slab system using different columns height were developed in CSI-BRIDGE software package through three-dimensional nonlinear finite element models and subjected to fourteen types of near-fault records with pulse and characteristics representing forward-directivity and fling-step effects using nonlinear time-history analysis. The results showed that seismic inputs related to fling-step and forward-directivity effects greatly increase the seismic demands on the substructure elements in the longitudinal direction. Furthermore, the simulations reveal a significant impact of column height and number of spans on the seismic response of the bridge. The study found that records with a fling-step effect have a more pronounced effect on the seismic response of columns for the box girder bridges especially at columns with the greater heights. In addition, reducing the number of spans amplifies the disparity between fling-step and forward-directivity responses.