Frequency Domain Dynamic Analysis of a Floating Bridge

This paper describes a dynamic analysis of a floating bridge across Lake Okanagan at Kelowna, British Columbia, Canada. The structure is a replacement for an existing floating bridge that was opened to traffic in 1958. The floating section of the proposed new bridge consists of continuous concrete pontoons with a total length of 697 m. Due to the exposure of the bridge to wind generated waves and the large horizontal dimensions of the structure, a short-crested wave field was used to model the correlation of wave forces along the structure length. Numerical wave hindcasting was conducted to determine the design wave conditions, including the effects of directional spreading. A two-dimensional wave diffraction numerical model was used to calculate the frequency dependent hydrodynamic coefficients (added masses, damping and exciting forces) used in the dynamic analysis. The response of the bridge to wind and wave loads was evaluated in the frequency domain using a commercial finite element structural model. The response parameters of interest included the motions of the bridge, the anchor cable tensions and the six sectional forces in the pontoons (two bending moments, torque, two shears and an axial load).