1D Bridges: Difference between revisions

The entry/exit loss coefficients are not used in the legacy B bridge. Instead, the bridge opening ratio is used to obtain the backwater coefficient Kb value from Figure 6 "Backwater coefficient base curves" of <u>[https://www.fhwa.dot.gov/engineering/hydraulics/pubs/hds1.pdf Hydraulics of Bridge Waterways (Bradley, 1978)]</u>.

Pier loss coefficients are treated as a direct energy (form) loss and can be derived from information in publications such as ''Hydraulics of Bridge Waterways'' ([http://www.ciccp.es/ImgWeb/Castilla%20y%20Leon/Documentaci%C3%B3n%20T%C3%A9cnica/Hydraulics%20of%20Bridge%20Waterways%20(1978).pdf FHA, 1978]) or [https://austroads.com.au/publications/bridges/agbt08 AUSTROADS, 2019].

Energy loss estimates from bridge piers (or other obstructions, vertical or horizontal, that do not cause upstream controlled flow regimes like pressure flow), are dependent on the ratio of the obstruction's area perpendicular to the flow direction to the gross flow area of the bridge opening, the shape of the piers or obstruction, and the angularity of the piers/obstruction to the flow direction. For example, using FHABradley (1978) the approach is:

<li>Calculate the ratio of the water area occupied by piers to the gross water area of the constriction (both based on the normal water surface) and the angularity of the piers. These inputs are used to calculate "J" in the FHABradley (1978) documentation.</li>

<li>Use the FHABradley (1978) ''Incremental Backwater Coefficient for Piers'' data to calculate Kp. This is the value that will be entered into the bridge's LC (loss vs height) table as the energy or form loss coefficient. For piers or obstructions that are non-uniform in dimensions or shape the LC table can be used to vary the losses with height accordingly noting that losses will need to be proportioned with depth to reflect the combined effect of the different obstruction shapes/dimensions.<br>