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EVALUATING SELECTED SCOUR EQUATIONS FOR BRIDGE PIERS IN COARSE STREAMBEDS IN NEW YORK

EVALUATING SELECTED SCOUR EQUATIONS FOR BRIDGE PIERS IN COARSE STREAMBEDS IN NEW YORK. by. L.J. Welch, Jr. and G.K. Butch. In cooperation with New York State Department of Transportation. Field Conditions. Turbulent flow. Armored streambed. Scour is the result of work.

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EVALUATING SELECTED SCOUR EQUATIONS FOR BRIDGE PIERS IN COARSE STREAMBEDS IN NEW YORK

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  1. EVALUATING SELECTED SCOUR EQUATIONS FOR BRIDGE PIERS IN COARSE STREAMBEDS IN NEW YORK by L.J. Welch, Jr. and G.K. Butch In cooperation with New York State Department of Transportation

  2. Field Conditions Turbulent flow Armored streambed

  3. Scour is the result of work Sf = stream force (kgm/s2); D84 = grain size >84 % of armor layer (mm).

  4. Stream Force Sf = stream force (kgm/s2);  = water density (103 kg/m3); y1 = water depth (m); w = flow width (1 m); V0= flow velocity (m/s).

  5. Database Statistics

  6. Model Calibration Calculated 19 scour depths measured in 1996 (10 = 0.0 m) MEAN ERROR 1996 MEAN ERROR (m)

  7. New York Equation (1972-96) . Sf = stream force (kg m/s2); D84 = grain size >84 % of armor layer (mm).

  8. Relation of Scour Depth to Stream Force and Bed Material

  9. Sensitivity Analysis

  10. FHWA Equation , ys = scour depth; K1 = pier-nose shape; a = pier width; K2 = pier shape & flow alignment; y1 = water depth; K3 = streambed condition; Fr1= Froude number; K4 = armoring by bed-material size.

  11. K4 (modified by Mueller) If D50> 2 mm and D95> 20 mm and f(V) > 0, otherwise K4 = 1 D50= median grain size; D95 = grain size >95 percent of armor layer; V0 = approach flow velocity; V/cD50= approach velocity corresponding to critical velocity at pier for D50 ; V /cD95= approach velocity corresponding to critical velocity at pier for D95 ; VcD50 = critical velocity for incipient motion for D50 . ,

  12. Froehlich Equation ys = scour depth;  = pier shape; g = gravity; V0 = flow velocity; y0 = water depth; b = pier width; D50 = median grain size.

  13. EstimatedScourvsMeasuredScour

  14. Summary ofEstimated and Measured Scour

  15. New Hampshire Study Field measurements

  16. New Hampshire Study GPR & fixed instruments

  17. SUMMARY • New York equation:- scour a function of stream force and bed material - derived from field measurements- alternative for coarse streambeds - estimates associated with specific peak discharges • Mueller modified-K4 and Froehlich equations:- less error than FHWA equation in New York study

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