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Identify and Analyze Inundated Bridge Superstructures in High Velocity Flood Events: Final Report
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2021-12-01
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[PDF-21.62 MB]
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Edition:Technical Report, November 2020 - October 2021
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Abstract:Flood events are reported as the most frequent cause of bridge failure in the United States. Current design guidelines and standards specify the use of 100-year flood for analyzing the overtopping of bridges. Still, many bridge failures in the U.S. occur during floods with return periods smaller than 100 years. These guidelines only address hydrodynamic forces on substructures and do not provide any information on estimating flood force on superstructures. Also, the effectiveness of structural countermeasures, recommended by several state departments of transportation, to prevent hydraulic failure of bridges is unknown. In this project, the magnitude of potential hydraulic parameters at bridges in riverine and coastal areas in Texas was determined. The parameters were used in physical and numerical modeling of bridge structures to assess the efficacy of using countermeasures, particularly shear keys and earwalls, to reduce the risk of bridge failure during flood events. A series of small-scale laboratory experiments and computational fluid dynamics (CFD) modeling were conducted to examine the hydrodynamic forces on typical TxDOT bridge decks. The effects of a range of parameters, including bridge geometry and orientation, flow velocity and depth, and the presence of debris, on hydrodynamic forces on bridges were tested under steady flow and wave loading conditions. Full-scale CFD modeling was also performed to calculate the magnitude of hydrodynamic forces on typical TxDOT bridges. Finite element models for single-span TxDOT bridges with typical I-girders, box beams, and slab beams were developed. Results from the CFD analyses were used to conduct a structural analysis of each bridge geometry to determine whether current shear key details are adequate, or if modified details are warranted. It was found from this study that the drag force can be much greater than the capacity of the shear key or earwall especially for the cases with a Froude number of 0.9. Debris also considerably increases the drag forces. For the cases where the interface shear strength is not sufficient, several approaches are recommended to increase the interface shear capacity: (1) increase the size and/or quantity of the interface shear reinforcement, (2) increase the quantity of the shear keys, and (3) increase the length of the bent cap hence the length of the earwall.
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