Manning's roughness coefficient for buried composite arch bridges.
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Manning's roughness coefficient for buried composite arch bridges.

Filetype[PDF-3.44 MB]


English
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  • Creators:
  • Corporate Creators:
    University of Maine. Advanced Structures and Composites Center
  • Subject/TRT Terms:
  • Publication/ Report Number:
    ME 14-15
  • Resource Type:
    Tech Report
  • Geographical Coverage:
    Maine
  • Corporate Publisher:
    Maine. Dept. of Transportation
  • Abstract:
    This report includes fulfillment of Task 9 of a multi-task contract to further enhance concrete filled FRP tubes, or

    the Bridge in a Backpack. Task 9 investigates the interaction of water flow under the bridge with the tubes and

    decking and recommends Manning’s roughness coefficients for water flow under the composite backpack bridge

    system.

    There are three flow regimes and each has a different resistance relationship. Quasi-smooth flow occurs only when

    there are depressions or when roughness elements are spaced very close. Hyper-turbulent flow occurs when

    roughness elements are sufficiently close so each element is in the wake of the previous element and rough surface

    vortices are the primary source of the overall friction drag. Isolated roughness flow occurs when roughness spacing

    is large and overall resistance is due to drag on the decking surface and form drag on the arches. Due to the large

    sizes of the tubes and tube spacing, the conventional method of computing roughness coefficient using the formula

    for rough pipe is not applicable here. Instead, we have to use a more complex procedure to calculate the roughness

    coefficient using different formula for different flow regimes described above.

    In this report, Manning’s roughness coefficients are provided when the flow is perpendicular to the bridge and when

    the angle between flow and the bridge is 45 and 30 degrees (Appendix 1). Depending on the arch radius and tube

    size and spacing, Manning’s roughness coefficient of the bridge ranges from 0.016 to 0.045, which is significantly

    larger than that for smooth concrete (n=0.012), due to the large tubes underneath the bridge. These results are

    important findings and should be incorporated in a hydraulic model such as HECRAS to more accurately predict

    water flows and backwater profiles at the FRP tubular bridge.

  • Format:
    PDF
  • Funding:
    20111223*2878
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