Author: Max Thomson Dean

Publisher:

Published: 2021

Total Pages: 69

ISBN-13:

Bridges are designed to withstand flood and debris loads; however, it is reported that 53% of bridge failures in the U.S. are caused by hydraulic events, including floods, scour, debris, and drifts. A series of scale flume experiments were conducted to determine flood force effects on bridge superstructures. 1:50 scale models of the Texas Department of Transportation's typical reinforced concrete bridge superstructures were tested. The bridge superstructures included beams (TX28 and TX54 girders, slab beams, and box beams) and an accompanying bridge deck and railing. The drag and lift forces and overturning moments were measured by load sensors for various flow conditions. The experiments were carried out for Froude numbers of 0.2, 0.27, and 0.34 and submergence ratios between 0.25 and 3. The scale model of the superstructure was also tested with debris accumulated on the upstream side of the bridge. Different shapes and amounts of debris were simulated under various flow conditions. The drag, lift, and moment coefficients were calculated and compared to those in literature. The drag coefficients were found to switch from a decreasing to increasing value around an inundation ratio of 0.8 for all superstructure geometries and follow a third-order polynomial distribution. The lift coefficients also followed a similar third-order polynomial distribution pattern with the inflection point at an inundation ratio of 1.0 for the lower Froude number scenario and 0.8 for the high Froude number scenario. The moment coefficients were found to follow logarithmic distribution patterns and to be affected by bridge deck length and superstructure height. The presence of debris increased the observed drag coefficients for a given Froude number. More studies are required to better understand the interaction between the flood flow and bridge structures at the inundation ratios less than one where the inflection points observed on the drag, lift, and moment coefficient graphs. Also, further study of hydrodynamic forces on scale models of a full-bridge structure, including abutments, pier foundation, pier cap, and bearing, and bridge deck system, is recommended.