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Publication Number: FHWA-HRT-09-041
Date: October 2009

Bridge Pressure Flow Scour for Clear Water Conditions

PDF Version (1.87 MB)

Table of Contents

FOREWARD

The Bridge Pressure Flow Scour for Clear Water Conditions Study described in this report was conducted at the Federal Highway Administration's (FHWA) Turner-Fairbank Highway Research Center (TFHRC) J. Sterling Jones Hydraulics Laboratory. The study was in response to a request of several State transportation departments asking for a new design guidance to predict bridge pressure flow scour for clear water conditions. The new pressure flow scour procedure will replace the existing pressure flow scour prediction method in the FHWA Hydraulic Engineering Circular No. 18 (4th edition) Evaluating Scour at Bridges. The study includes experiments (physical modeling) at the Hydraulics Laboratory. This report will be of interest to hydraulic and bridge engineers who are involved in estimating pressure flow scour for inundated bridge decks. This report is being distributed as an electronic document through the TFHRC Web site (www.fhwa.dot.gov/research/tfhrc/).

Cheryl Allen Richter
Acting Director, Office of Infrastructure
Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for its contents or use thereof. This report does not constitute a standard, specification, policy, or regulation.

The U.S. Government does not endorse products or manufacturers. Trade and manufacturers' names appear in this report only because they are considered essential to the object of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

TECHNICAL REPORT DOCUMENTATION PAGE

1. Report No.
FHWA-HRT-09-041 		2. Government Accession No. 3. Recipient's Catalog No.
N/A

4. Title and Subtitle
Bridge Pressure Flow Scour for Clear Water Conditions

5. Report Date
October 2009

6. Performing Organization Code
N/A

7. Author(s)
Junke Guo, Kornel Kerenyi, and Jorge E. Pagan-Ortiz

8. Performing Organization Report No.
9. Performing Organizations Names and Addresses
GKY and Associates, Inc.
4229 Lafayette Center Dr.
Suite 1850
Chantilly, VA 20151		 University of Nebraska
312 N. 14th Street
Alexander Building West
Lincoln, NE 68588-0430

10. Work Unit No.(TRAIS)
N/A

11. Contract or Grant No.

12. Sponsoring Agency Name and Address
Office of Infrastructure Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

13. Type of Report and Period Covered
Laboratory Report

14. Sponsoring Agency Code

15. Supplementary Notes
The Contracting Officer's Technical Representative (COTR) was Kornel Kerenyi, HRDI-07. Oscar Berrios assisted with experimentation and produced some of the figures. Kevin Flora, Denis Lyn, and Bart Bergendahl provided constructive suggestions.

16. Abstract
The equilibrium scour at a bridge caused by pressure flow with critical approach velocity in clear-water simulation conditions was studied both analytically and experimentally. The flume experiments revealed that (1) the measured equilibrium scour profiles under a bridge are more or less consistent across the channel width; (2) all the measured scour profiles can be described by two similarity equations where the horizontal distance is scaled by the deck width and the local scour is scaled by the maximum scour depth; (3) the maximum scour position is located under the bridge and at a location approximately 15.4 percent of the deck width from the downstream edge of the deck; (4) scour begins at approximately one deck width upstream of the bridge, and deposition begins at approximately 2.5 deck widths downstream of the bridge; and (5) the maximum scour depth decreases with increasing median sediment size but increases with higher levels of deck inundation. The analytical analysis shows that (1) bridge scour can be divided into three cases: downstream unsubmerged, partially submerged, and totally submerged;
(2) for downstream unsubmerged flows, the maximum scour depth is an open channel problem where the conventional methods in terms of critical velocity or bed shear stress can be applied; and (3) for partially and totally submerged flows, the maximum scour depth can be described by scour and inundation similarity numbers, which has been confirmed by experiments with two sediment sizes (0.039 and 0.078 inches (1 and 2 mm)) and two types of decks with three and six girders, respectively. For application, a design and field evaluation procedure with examples is presented, including the maximum scour depth and scour profile.

17. Key Words
Bridge decks, Bridge design, Bridge foundations, Bridge hydraulics, Bridge inundation, Bridge scour, Pressure flows, Pressure scour, Submerged flows

18. Distribution Statement
No restrictions. This document is available to the public through the National Technical Information Service (NTIS), Springfield, VA 22161.

19. Security Classif. (of this report)
Unclassified

20. Security Classif. (of this page)
Unclassified

21. No. of Pages
60

22.Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized.


Metric Conversion Table

TABLE OF CONTENTS

CHAPTER 1. INTRODUCTION
CHAPTER 2. LITERATURE REVIEW
CHAPTER 3. EXPERIMENTAL STUDY

CHAPTER 4. ANALYTICAL STUDY OF MAXIMUM SCOUR DEPTH

CHAPTER 5. DESIGN PROCEDURE AND APPLICATION EXAMPLES

CHAPTER 6. FURTHER RESEARCH NEEDS
CHAPTER 7. CONCLUSIONS
APPENDIX A. MAXIMUM SCOUR DEPTH FOR CASE 1
APPENDIX B. DERIVATION OF PRESSURE UNDER BRIDGE DECK
ACKNOWLEDGEMENTS
REFERENCES

LIST OF FIGURES

Figure 1. Photo. Partially inundated bridge deck at Salt Creek, NE
Figure 2. Photo. Completely inundated bridges at Cedar River, IA
Figure 3. Equation. Arneson and Abt's scour depth equation
Figure 4. Equation. Upstream critical velocity
Figure 5. Equation. Lyn's scour depth equation
Figure 6. Equation. Umbrell et al.'s scour depth equation
Figure 7. Equation. Modified Umbrell et al. scour depth equation
Figure 8. Photo. Approach section of the test flume
Figure 9. Illustration. Plan and side schematic of the test flume
Figure 10. Illustration. Detail of sand bed and sediment recess in test flume
Figure 11. Illustration. 3D view of a six-girder bridge deck
Figure 12. Illustration. Cross section view of a six-girder bridge deck
Figure 13. Illustration. Cross section view of a three-girder bridge deck
Figure 14. Equation. Operating discharge Q
Figure 15. Photo. Automated flume carriage with laser distance sensor perched over the test flume
Figure 16. Graph. 3D scour map at equilibrium scour
Figure 17. Graph. Scour profiles at various bridge openings for the three-girder bridge deck
Figure 18. Graph. Scour profiles at various bridge openings for the six-girder bridge deck
Figure 19. Graph. Scour profiles at various bridge openings for the six-girder bridge deck (d50 = 0.078 inches (2 mm))
Figure 20. Graph. Similarity profile for equilibrium scour for the three-girder bridge deck
Figure 21. Graph. Similarity profile for equilibrium scour for the six-girder bridge deck
Figure 22. Equation. Similarity scour profile, x is less than or equal to zero
Figure 23. Equation. Similarity scour profile, x is greater than zero
Figure 24. Equation. X-coordinate of scour initiation
Figure 25. Equation. X-coordinate of scour initiation normalized to bridge width
Figure 26. Equation. Upstream dimensional abscissa, x1
Figure 27. Equation. Dimensionless abscissa upstream
Figure 28. Equation. Distance from scour initiation position to bridge deck face
Figure 29. Equation. Initiation of sediment deposition position
Figure 30. Equation. Dimensionless abscissa downstream
Figure 31. Equation. Distance from bridge deck to deposition position
Figure 32. Equation. Scour depth at deck edges
Figure 33. Graph. Normalized scour profile
Figure 34. Graph. Arneson and Abt's scour depth equation agreement with experimental data
Figure 35. Graph. Lyn's scour depth equation agreement with experimental data
Figure 36. Graph. Umbrell et al.'s scour depth equation agreement with experimental data
Figure 37. Illustration. Plan view of bridge over stream
Figure 38. Illustration. Pressure flow for case 1
Figure 39. Illustration. Pressure flow for case 2
Figure 40. Illustration. Pressure flow for case 3
Figure 41. Equation. Energy equation along streamline 1-2
Figure 42. Equation. Pressure under the bridge, p2
Figure 43. Equation. Energy equation including curvature coefficient
Figure 44. Equation. Model describing difference bridge energy loss coefficient and curvature coefficient
Figure 45. Equation. Energy equation including empirical parameters
Figure 46. Equation. Rearrangement of energy equation including empirical parameters
Figure 47. Equation. Continuity equation
Figure 48. Equation. Pressure flow scour design equation
Figure 49. Equation. Downstream flow depth approximation
Figure 50. Equation. Inundation Froude number
Figure 51. Equation. Pressure flow scour design equation including inundation Froude number
Figure 52. Equation. Effective velocity equation
Figure 53. Graph. Scour number versus inundation Froude number
Figure 54. Equation. Unit discharge
Figure 55. Equation. Velocity at maximum scour section
Figure 56. Equation. Pressure flow scour design equation including effective velocity
Figure 57. Equation. Deck block depth for cases 2 and 3
Figure 58. Equation. Inundation Froude number for cases 2 and 3
Figure 59. Equation. Effective velocity for cases 2 and 3
Figure 60. Equation. Maximum scour depth calculation
Figure 61. Graph. Maximum scour depth versus bridge opening height
Figure 62. Graph. Maximum scour depth versus bridge thickness
Figure 63. Equation. Critical velocity
Figure 64. Equation. Manning coefficient
Figure 65. Equation. Critical velocity
Figure 66. Equation. Dimensionless diameter
Figure 67. Equation. Critical Shields number
Figure 68. Equation. Critical approach velocity
Figure 69. Equation. Deck block depth evaluation
Figure 70. Equation. Inundation Froude number evaluation to determine pressure flow
Figure 71. Equation. Scour depth evaluation
Figure 72. Equation. Maximum scour depth position
Figure 73. Equation. Equilibrium scour profile equation, x is less than or equal to zero
Figure 74. Equation. Equilibrium scour profile equation, x is greater than zero
Figure 75. Equation. Simplified equilibrium scour profile equation, x is greater than zero
Figure 76. Graph. Scour profile for example problem
Figure 77. Equation. Scour depth at the upstream deck edge
Figure 78. Equation. Maximum scour depth solution
Figure 79. Equation. Downstream flow depth
Figure 80. Equation. Critical Shields number approximation by Guo
Figure 81. Equation. Shields number
Figure 82. Equation. Dimensionless diameter
Figure 83. Equation. Energy equation between points 1 and 2
Figure 84. Equation. Scour depth
Figure 85. Equation. Bernoulli equation across streamlines
Figure 86. Equation. Bernoulli equation applied to circular streamlines
Figure 87. Illustration. Radii of curvature
Figure 88. Equation. Integration of figure 86
Figure 89. Equation. Bernoulli equation solved at point 2
Figure 90. Equation. Pressure at point 2 when Vb equals zero
Figure 91. Equation. Solution for integration constant
Figure 92. Equation. Pressure at point 2
Figure 93. Equation. Curvature coefficient
Figure 94. Equation. Pressure at point 2 with curvature coefficient simplification

LIST OF TABLES

Table 1. Experimental results for the three-girder bridge (d50 = 0.039 inches (1 mm))
Table 2. Experimental results for the six-girder bridge (d50 = 0.039 inches (1 mm))
Table 3. Experimental results for the six-girder bridge, (d50 = 0.078 inches (2 mm))
Table 4. Maximum scour depth estimates by four different methods

LIST OF ABBREVIATIONS AND SYMBOLS


Abbreviations
2D Two-dimensional
3D Three-dimensional
FHWA Federal Highway Administration
TFHRC Turner-Fairbank Highway Research Center

 

Symbols
a
 Deck block depth
b Thickness of bridge deck including girders
B Width of a river
d* Dimensionless sediment diameter
d50 Median diameter of sediment
F Inundation Froude number
Fr Froude number
g Gravitational acceleration
h Downstream flow depth in case 1
hb Bridge opening
hd Bridge downstream flow depth
hu Depth of headwater
Kb Bridge energy loss coefficient
Kp Curvature pressure coefficient
Ks Critical Shields number
m Fitting parameter in the bridge energy loss coefficient
n
 Manning coefficient, or normal direction of a streamline
p1 Pressure at point 1
p2 Pressure at point 2
Q Operating discharge in the flume
q Unit discharge of a river
q1 Unit discharge through the bridge
R Local radius of curvature of a streamline
R0 Radius of curvature at the maximum scour point
R2 Correlation coefficient
Re Reynolds number
s Specific gravity of sediment
ν Kinematic viscosity of water
Va Velocity through the bridge before scour
Vb Velocity through the bridge at the maximum scour depth
Vc Critical velocity
Vu Velocity of the headwater
Vuc Upstream critical velocity
Vue Upstream effective velocity
W Width of bridge
x Coordinate along a river
x1 Coordinate of upstream face of deck
x2 Coordinate of downstream face of deck
xd Coordinate of initiation of deposition
xs Coordinate of initiation of scour
ys Maximum scour depth
z Vertical direction
α1,α2 Energy correction coefficients
ß Correction factor for hydrostatic pressure under bridge
λ An empirical fitting factor
γ Specific weight of water
τc Critical shear stress

 

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