Contribution of debris and substructures to hydrodynamic forces on bridges

Abstract

The frequency and intensity of recent flood events demonstrate the need for investigating the forces exerted on inundated bridges. The hydrodynamic force coefficients for bridge superstructures are well established in the literature, but they can be significantly affected by the accumulation of debris upstream and the presence of substructures (e.g., piers, bent caps). The aim of this study is to evaluate the effects of debris-damming and substructures on hydrodynamic forces exerted on bridge superstructures. For this purpose, a series of laboratory experiments on the small-scale bridge and debris models was performed, and the lift and drag forces and overturning moments on bridge decks with debris and substructures were measured and compared to the hydrodynamic forces generated by the flow on superstructures without blockages. The total streamwise and vertical forces and overturning moment were used to investigate the effects of debris and substructures on superstructure forces. Results are also presented on drag, lift, and moment coefficients, as they revealed a considerable change in the hydrodynamic force and moment coefficients because of the additional flow blockages created by debris and substructures. Maximum drag coefficients were observed for a flat plate debris model, combined bridge model (i.e., superstructure, debris, and superstructure), partially submerged model, and a substructure-superstructure model of a fully submerged bridge. Maximum lift and moment coefficients occurred for the substructure and wedge debris models, respectively.