Bi-directional Effects on the Response of an Isolated Bridge

The seismic design of bridge structure is influenced by the bi-directional excitation phenomenon. The bi-directional effects have been ignored in most of the past studies. The calculation of maximum isolator displacements (as per the equation prescribed by AASHTO) also ignores the bi-directional effects of ground motion. In the formulation, the coupled behaviour of the isolation systems has also been ignored. However, these effects can play significant role in the seismic response of the bridge. In the present paper, the effet of bi-directional excitation on the seismic response of a continuous bridge has been studied, considering the interaction effects in Bearings and piers. The study has also been performed considering the effect of orientation of the major component of ground motion with respect to the axis of the bridge. Comparison of the responses obtained from the Nonlinear (Static) Pushover analysis and Nonlinear Dynamic Time History analysis have also been performed. It has been found that the bidirectional excitation has resulted in significantly higher response especially in case of PF system, where the unidirectional analysis yield significantly underestimated results.