Abstract Addressing flood-induced erosion problems at bridges is critical to maintain the safety of the transportation infrastructure. Better design of scour prevention measures will result is less failure of bridges during natural disasters. A numerically-based approach will be used to propose a new design formula for determining minimum riprap stone size needed for riprap apron protection against erosion at circular, rectangular and oblong bridge piers. The proposed approach was already validated for abutments. The flow fields predicted using fully 3-D RANS simulations will be used to estimate the maximum bed shear stress over the riprap layer and the critical Froude number corresponding to the shear-failure entrainment threshold for the riprap stone. A comprehensive parametric study will be conducted to understand how pier shape and aspect ratio influence the peak shear stress over the riprap region. Results will be compared with those given by present formulas including by those recommended by HEC-18. A new multi-parameter design formula that incorporates the effect of pier shape and aspect ratio will be developed. The research also aims to develop procedures for riprap sizing at bridge piers under pressurized flow conditions due to bridge deck overtopping at high flow conditions. Simulations will be conducted to understand how the critical Froude number varies with increasing flow depth in between open-channel and pressurized flow conditions at the bridge. Recommendations will be made on how to use the design formula developed for open channel flow regime for cases when the flow at the bridge site is pressurized.
Description Addressing flood-induced erosion problems at bridges is critical to maintain the safety of the transportation infrastructure. Better design of scour prevention measures will result is less failure of bridges during natural disasters. A numerically-based approach will be used to propose a new design formula for determining minimum riprap stone size needed for riprap apron protection against erosion at circular, rectangular and oblong bridge piers. The proposed approach was already validated for abutments. The flow fields predicted using fully 3-D RANS simulations will be used to estimate the maximum bed shear stress over the riprap layer and the critical Froude number corresponding to the shear-failure entrainment threshold for the riprap stone. A comprehensive parametric study will be conducted to understand how pier shape and aspect ratio influence the peak shear stress over the riprap region. Results will be compared with those given by present formulas including by those recommended by HEC-18. A new multi-parameter design formula that incorporates the effect of pier shape and aspect ratio will be developed. The research also aims to develop procedures for riprap sizing at bridge piers under pressurized flow conditions due to bridge deck overtopping at high flow conditions. Simulations will be conducted to understand how the critical Froude number varies with increasing flow depth in between open-channel and pressurized flow conditions at the bridge. Recommendations will be made on how to use the design formula developed for open channel flow regime for cases when the flow at the bridge site is pressurized.
Objective Bridges are critical links in urban system since they are associated with little redundancy and a high (re)construction cost (Pregolato et al., 2022). A failed link in the transportation infrastructure system can greatly impact communities by threatening evacuation capability, recovery operations and the overall economy. Better design of scour prevention measures will result in fewer bridges failing during natural disasters during floods. As such, the project will enhance the safety of our transportation infrastructure and make our transportation safer that is also one of USDOT’s strategic goals. It will contribute to more reliable, resilient and safe design of bridges for flooding events. One of the main consequences of the climate crisis is the increase in the frequency and magnitude of floods. Development of novel design methodologies that will ensure bridges will not collapse because of severe erosion during floods also aligns with the US DOT strategic goal of promoting design for the future that will lead to engineering sound solutions for the decades to come.
Impacts/Benefits The broader impacts of the proposed project include getting a better understanding of why existing riprap sizing design formulas for bridge piers are not conservative enough in some cases and on proposing ways to improve the performance of these formulas. The availability of more accurate design formulas for sizing riprap at bridge piers that can be used for a wide range of flow and site conditions in the field will enhance the capabilities of state Department of Transportations (DOTs) and other agencies (e.g., US DOT Federal Highway Administration TFHRC) in charge of maintaining operational our bridges. The new methodology/formula will increase the efficiency of scour protection measures for the most common types of pier shapes used at bridges in the US. Better design of scour erosion countermeasures will result in significant reduction of the costs to operate roads during and after flood events. It will also contribute to reducing the risk for hazards associated with bridge failure during floods by avoiding structural failure and decrease the costs associated with maintaining such bridges operational after flooding events. The present procedure based on 3D simulations can be extended to piers with a non-zero angle of attack and piers of complex shape (e.g., multi-pile piers). Results of simulations conducted with pressurized flow at the bridge site will also allow directly estimating the streamwise and vertical hydrodynamic forces acting per unit length of the bridge deck. These forces are a critical input for structural calculations conducted to address possible damage of the bridge structure which can result in bridge deck failure and, in some cases, the bridge being washed away by floodwaters.