Coupled aerodynamic and hydrodynamic response of a long span bridge suspended from floating towers

The present study introduces a fully coupled time-domain analysis of a multi-span suspension bridge supported by two floating towers, considered for crossing the wide and deep fjords along the west coast of Norway. The time-domain analysis is performed with a finite element model considering simultaneously the turbulent wind, irregular inhomogeneous ocean waves and sheared ocean current. The numerical results suggest that under extreme conditions with a return period of 100 years, the bridge horizontal response is dominant and governed by the low-frequency modes. For the vertical and torsional responses, the largest contributions are due to the respective motion components of the low-frequency horizontal motion-dominated modes. The investigation into the significance of the aerodynamic and hydrodynamic load reveals that in the case studied, over 80% of the bridge girder response is due to the aerodynamic excitation. The hydrodynamic loads acting on the floating towers are small due to a relatively small significant wave height in the fjord and the counteracting aerodynamic damping effect. By considering the inhomogeneity of the waves, i.e. different conditions at the two floating supports, the contribution of the aerodynamic action to the lateral, vertical and torsional dynamic responses increases by 6%, 7% and 9% respectively.