Hydrodynamic loading on river bridges

During a flood, a bridge may be partially or entirely submerged by the flow and the subsequent loading of fluid plays a major role in assessing the vulnerability of the structure. We have performed laboratory experiments to quantify the hydrodynamic loading on a bridge deck with rectangular cross section. We measured the time-varying hydrodynamic forces acting on the obstacle for various submergences and Deck Froude numbers. The experimental results have been analyzed via dimensional analysis and relationships between time-averaged force coefficients (drag, lift, and moment coefficients), the Deck Froude number and geometrical parameters of the problem are discussed and compared against relevant literature. Due to the presence of a free surface, force coefficients can be either larger (by more than a factor of 2) or lower than the corresponding values of the unbounded domain. The experimental drag coefficients are then compared with the results obtained by the momentum equation.