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Publication Number:  FHWA-HRT-14-070    Date:  September 2014
Publication Number: FHWA-HRT-14-070
Date: September 2014

 

Wind Tunnel Investigations of An Inclined Stay Cable With A Helical Fillet

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FOREWORD

Cable-stayed bridges have become the form of choice over the past several decades for bridges in the medium-to-long-span range. In some cases, serviceability problems involving large amplitude vibrations of stay cables under certain wind and wind-rain conditions have been observed. This study was conducted in response to State transportation departments’ requests to develop improved design guidance for mitigation of excessive cable vibrations on cable-stayed bridges. The study included wind tunnel testing of a full-scale cable model to evaluate the influence of damping, turbulence, and aerodynamic surface treatment on cable stability. The results of this study will be made available to the Post-Tensioning Institute’s DC-45 Cable-Stayed Bridge Committee for consideration during their periodic updates of the Guide Specification, Recommendations for Stay Cable Design, Testing, and Installation.(1)

This report will be of interest to bridge engineers, wind engineers, and consultants involved in the design of cable-stayed bridges. It is the third in a series of reports addressing the subject of aerodynamic stability of bridge stay cables that will be published in the coming months.

Jorge E. Pagán-Ortiz
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 the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective 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-14-070

2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

Wind Tunnel Investigations of an Inclined Stay Cable with a Helical Fillet

5. Report Date

September 2014

6. Performing Organization Code
7. Author(s)

Guy L. Larose and Annick D’Auteuil

8. Performing Organization Report No.

LTR-AL-2011-0093

9. Performing Organization Name and Address

National Research Council of Canada
Institute for Aerospace Research
1200 Montreal Road
Ottawa, Ontario Canada K1A OR6

 

Genex Systems, LLC
2 Eaton Street, Suite 603
Hampton, VA 23669

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61–07–D–00034

12. Sponsoring Agency Name and Address

Office of Infrastructure R&D
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

13. Type of Report and Period Covered

Laboratory Report
March 2011–March 2012

14. Sponsoring Agency Code

HRDI-50

15. Supplementary Notes

The Contracting Officer’s Technical Representative (COTR) was Harold R. Bosch, (HRDI-50).

16. Abstract

Cable-stayed bridges have been recognized as the most efficient and cost effective structural form for medium-to-long-span bridges over the past several decades. With their widespread use, cases of serviceability problems associated with large amplitude vibration of stay cables have been reported. Stay cables are laterally flexible structural members with very low inherent damping and thus are highly susceptible to environmental conditions such as wind and rain/wind combination.

 

Recognition of these problems has led to the incorporation of different types of mitigation measures on many cable-stayed bridges around the world. These measures include surface modifications, cable crossties, and external dampers. Modification of cable surfaces has been widely accepted as a means to mitigate rain/wind vibrations. Recent studies have firmly established the formation of a water rivulet along the upper side of the stay and its interaction with wind flow as the main cause of rain/wind vibrations. Appropriate modifications to exterior cable surfaces effectively disrupts the formation of a water rivulet.

 

The objective of this study is to supplement the existing knowledge base on some of the outstanding issues of stay cable vibrations and to develop technical recommendations that may be incorporated into design guidelines. Specifically, this project focused on the wind-cable interaction, with particular interest in details of the air flow and flow field close to the cable as well as forces on the cable surface. A helical fillet was attached to an existing cable model to evaluate the influence of this common mitigation feature on dynamic behavior. The cable inclination angle was varied during testing to represent field orientations, and the model was rotated on its longitudinal axis to assess the influence of high-density polyethylene roundness. Tests were conducted at various levels of damping, with and without the fillet, and in turbulent as well as smooth flow conditions.

17. Key Words

Cable-stayed bridges, Cables, Vibrations, Wind, Rain, Wind tunnel testing, Wind turbulence, Galloping, Vortex shedding, Aerodynamic surface treatment, Helical fillet

18. Distribution Statement

No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161.
http://www.ntis.gov

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

222

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

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

EXECUTIVE SUMMARY

CHAPTER 1: INTRODUCTION

CHAPTER 2: EXPERIMENTAL CONDITIONS

CHAPTER 3: EXPERIMENTAL PROCEDURES AND ANALYSIS

CHAPTER 4: RESULTS AND DISCUSSION OF EXPERIMENTS

CHAPTER 5: CONCLUSIONS

APPENDIX A. DETAILED LIST OF RUNS AND EXPERIMENTAL CONDITIONS

APPENDIX B. SUMMARY OF RESULTS

ACKNOWLEDGEMENTS

REFERENCES

LIST OF FIGURES

LIST OF TABLES

LIST OF SYMBOLS

Symbols
Cd Drag coefficient.
Cx Along-wind force coefficient.
Cy Across-wind force coefficient
d, D Cable diameter.
f Frequency.
I Turbulence intensity.
L Wind exposed length of cable model.
xL Integral length scale of turbulence.
m Mass per unit exposed length of cable model.
q Dynamic pressure
Re Reynolds number.
Sc Scruton number.
U Mean wind speed.
U/ f B Reduced velocity.
ɑ Spring rotation.
β Flow yaw angle.
ζ Damping ratio as a fraction of critical.
θ Stay cable inclination.
μ Air viscosity
ρ Air density.
φ Model inclination.
Subscripts
h Heave, along-wind.
s Sway, across-wind.
u,v,w Longitudinal, lateral, and vertical components of the flow fluctuations.

 

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