Earthquake Response Analysis Model of Offshore Bridge Piers Considering Fluid-Structure-Soil Interaction

An analysis method for earthquake responses of offshore bridge piers is developed considering the effects of fluid-structure-soil interaction. The pier is modeled as lumped mass at the top of a tower, idealized as a cantilever founded on the flexible seabed. Substructure method and Rayleigh-Ritz method are used to derive governing equations of a coupled structure-fluid-soil system

incorporating interactions between tower and sea water and between foundation and flexible seabed. The sea water is assumed to be compressible but non-viscous fluid. Impedance functions of a rigid foundation in water-saturated soil strata are obtained from thin-layer method and combined with the superstructure model. The developed method is applied to earthquake response analysis of an offshore bridge pier model. The effects of several factors such as flexibility of the pier and stiffness of soil are examined. It is observed from the calculations that the flexibility of the pier and the stiffness of soil can influence responses of the offshore bridge piers.