Numerical study on the stochastic response of a long-span sea-crossing bridge subjected to extreme nonlinear wave loads

In current practice, linear wave load theory is widely employed in the wave force evaluation of sea-crossing bridges. However, the observation of nonlinear wave loads in shallow waters suggests that second-order wave loads might be essential to the dynamic behavior of marine structures. In this paper, a framework to investigate the stochastic response of a long-span sea-crossing bridge under extreme nonlinear wave loads was proposed based on the combined use of the spectral wave model MIKE21 SW, the 3D diffraction theory hydrodynamic solver AQWA and the structural analysis tool ANSYS. An extreme wave condition of a 300-year return period at the exact bridge site is estimated from offshore statistical wave data by utilizing the state-of-the-art spectral wave model MIKE21 SW by considering of the complex nearshore wave transformation. Linear as well as nonlinear stochastic wave loads are modeled in AQWA and subsequently fed into the finite-element model to assess the responses. The results indicate that the nonlinear wave loads could remarkably increase the dynamic responses of the internal base forces of bridge foundations as well as displacements of superstructures. The sum-frequency second-order components in nonlinear loads, though not large in magnitude, might overlap with the first few eigenfrequencies of the bridge and thus excite these modes and increase the responses.