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REPORT
This report is an archived publication and may contain dated technical, contact, and link information
Publication Number:  FHWA-HRT-14-067    Date:  September 2014
Publication Number: FHWA-HRT-14-067
Date: September 2014

 

Dynamic Properties of Stay Cables on The Penobscot Narrows Bridge

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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 full scale forced vibration tests on the cables of a new cable-stayed bridge to characterize cable dynamic behavior and evaluate effectiveness of mitigation details such as dampers. 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.

This report will be of interest to bridge engineers, wind engineers, and consultants involved in the design of cable-stayed bridges. It is the second 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-14-067

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

Dynamic Properties of Stay Cables on the Penobscot Narrows Bridge

5. Report Date

September 2014

6. Performing Organization Code
7. Author(s)

Harold R. Bosch and James R. Pagenkopf

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

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 December 2006 to December 2010

14. Sponsoring Agency Code

HRDI-50

15. Supplementary Notes

The Contracting Officer's Technical Representative (COTR): 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 led to the incorporation of different types of mitigation measures on many cable-stayed bridges around the world. These measures included 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 modification of exterior cable surface effectively disrupts the formation of a water rivulet.

 

The objective of this study was to supplement the existing knowledge base on some of the outstanding issues of stay cable vibrations and develop technical recommendations that may be incorporated into design guidelines. Specifically, this project focused on identification of in-situ cable dynamic properties and performance of external viscous dampers on the Penobscot Narrows Bridge. Forced vibration tests were conducted on the stay cables during the latter stages of construction, just prior to and following installation of viscous dampers. Cable properties, such as vibration frequencies and damping levels, were established and compared with design targets.

17. Key Words

Cable-Stayed Bridges, Cables, Vibrations, Wind, Rain, Dampers, Hazard Mitigation

18. Distribution Statement

No restrictions. This document is available to the public through NTIS:
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

179

22. Price
Form DOT F 1700.7 Reproduction of completed page authorized

 

SI* (Modern Metric) Conversion Factors

 

TABLE OF CONTENTS

LIST OF FIGURES

LIST OF TABLES

 

LIST OF SYMBOLS

AnAmplitude of in-plane displacement due to the nth mode of vibration.
cViscous damping coefficient per unit length.
DDiameter of cable pipe.
HPretension of string or cable.
LLength of string or cable.
L1,2Chord length distance along cable to box 1 or 2.
mCable mass per unit length.
ScNon-dimensional Scruton number.
TdnDamped natural period of the nth mode of vibration.
tTime.
UWind speed.
UaveAverage wind speed.
UeqNormalized equivalent wind speed.
uTime-dependent part of transverse in-plane displacement due to vibration.
wTransverse in-plane displacement due to vibration.
xDistance.
αnPhase angle of time-dependent part of transverse in-plane displacement due to nth mode of vibration.
βInclination angle of the cable from horizontal.
δNon-dimensional logarithmic decrement ratio.
ζnNon-dimensional damping ratio of the nth mode of vibration.
θAngle of the wind direction normal to the vertical plane of the cable.
θaveAverage angle of the wind direction normal to the vertical plane of the cable.
ρMass density of air.
ωnNatural angular frequency of the nth mode of vibration.
ωdnDamped natural angular frequency of the nth mode of vibration.

 

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