Effects of aerodynamic damping on freestanding bridge tower under the joint action of wind and wave loads

This study uses a time-domain simulation to investigate the effect of aerodynamic damping on a freestanding bridge tower under the joint action of wind and wave loads. The physical model of the bridge tower, which has been tested in laboratory, is numerically reconstituted considering structural nonlinearities obtained from free oscillation tests. Random wind fields are generated using the harmonic superposition method, and the wind flow characteristics, such as mean wind velocity and turbulence intensity, are identified based on the data collected in the laboratory. The wave loads measured at the bottom of the foundation during the experimental model tests are used for the simulation. The dynamic responses of the tower under the joints action of wind and wave loads are successfully simulated. A clear reduction in structural vibration in the wave-controlled region is confirmed by simulation results. Further numerical investigation indicates that an increase in the mean wave velocity produces additional aerodynamic damping in the structural motion system, which significantly dampens the responses of the wave-induced vibration. A simple method for determining the dynamic responses of a bridge tower under the joint action of wind and wave loads, using the data obtained from wind- and wave-only cases, is proposed.