Experimental study to investigate the effects of bridge geometry and flow condition on hydrodynamic forces

Abstract

Stream-crossing bridges are designed to pass the design flow while maintaining a minimum freeboard; however, flood events are reported as the most frequent cause of bridge failure in the U.S. and around the world. Floodwater exerts significant forces on bridges, shearing and overturning their decks, which may cause them to fail. When a bridge fails, it loses its total or partial serviceability, causing fatalities, delays in emergency transportation and evacuation efforts, and economic losses. An accurate estimation of hydrodynamic forces on a bridge superstructure, therefore, is vital to assess its vulnerability to flooding. The purpose of this study is to investigate the effects of bridge geometry and flow conditions on hydrodynamic forces. A series of experiments on bridge scale models were performed in a laboratory flume to analyze the response of the drag, lift and moment coefficients to bridge geometry (deck width, and girders height and shape) and flow conditions (inundation ratio, proximity ratio, blockage ratio, and Froude number). The experimental results showed that hydrodynamic force and moment coefficients are dependent on the extent of the bridge submergence, Froude number, and proximity of the bridge to the streambed. The relationship between bridge geometry and force coefficients indicated that the geometric features of bridges have a large influence on flow field as well as drag, lift, and moment coefficients.