Numerical Modeling of Wave Forces on Movable Bridge Decks

This paper presents a numerical analysis of the nonlinear interaction between water waves and the movable superstructure of a coastal bridge. An improved mesh update method is used to dynamically configure the computational meshes solving the Navier-Stokes equations for viscous and incompressible free surface flows with the volume of fluid (VOF) method. To maintain the mesh quality as the bridge deck is displaced, the computational domain is separated into several parts corresponding to a specific type of body motion. The numerical model results have been compared with the laboratory experiments conducted at Oregon State University with good agreement. This hydrodynamic model is then used to simulate the failure process of the prototype U.S. Highway 90 (US 90) Bridge during Hurricane Katrina (2005). It is found that the bridge deck is most vulnerable to be displaced by the waves when the bridge is partially submerged because of the combined effects of the vertical and horizontal wave forces. Numerical experiments of the US 90 Bridge shed light on the sway and heave responses of the bridge deck to different wave height conditions. It is shown that a significant wave height of 2.6 m would result in a failure of the bridge deck. A critical wave height (2 m) based on the incipient motion of the bridge deck is recommended for screening the vulnerability of other bridges similar to the US 90 Bridge in hurricane-prone areas. Moreover, the computed maximum heave response can be used as a reference for engineers to design the shear key height to prevent a bridge deck from horizontal displacement.