U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000


Skip to content
FacebookYouTubeTwitterFlickrLinkedIn

Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

 
REPORT
This report is an archived publication and may contain dated technical, contact, and link information
Publication Number:  FHWA-HRT-14-093    Date:  December 2014
Publication Number: FHWA-HRT-14-093
Date: December 2014

 

Interlaboratory Variability of Slip Coefficient Testing for Bridge Coatings

PDF Version (8.63 MB)

PDF files can be viewed with the Acrobat® Reader®

FOREWORD

Bolted connections are a critical part of nearly every steel bridge. Individual components are assembled together in the field using high-strength bolts, and frictional connections are specified to ensure appropriate connection performance throughout the life of the bridge. The coatings used on the faying surface of the connections must demonstrate a predetermined friction coefficient for the overall connection to attain its required frictional resistance. This friction coefficient is defined by a test method governed by the Research Council for Structural Connections (RCSC). In recent years, there has been concern within the bridge engineering community that ambiguities within the test method might increase the variability of reported friction coefficients.

This report outlines the findings and recommendations from a round-robin laboratory study on slip coefficients of organic zinc-rich primers for steel bridges. Prior to this work, variability of slip coefficients attained for the same coatings were noted by coating manufacturers despite no changes in formulation. This study was conducted to quantify the variability and recommend changes to RCSC to reduce the variability. Overall, it was found that participating labs followed the RCSC procedure but were sometimes reporting very different slip coefficients for identical coatings. The major finding was the manner in which each lab measured slip displacement, which contributed to the greatest variability in frictional coefficient results. It is recommended that RCSC clarify its intended method for measuring slip deformation. Once implemented, it is anticipated that the revised test method will appropriately quantify coating frictional coefficients and thus ensure proper connection performance. This report would benefit those in charge of specifying and testing steel bridge coatings including coating manufactures, RCSC, State transportation departments, researchers, and design consultants.

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.

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-14-093

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

Interlaboratory Variability of Slip Coefficient Testing for Bridge Coatings

5. Report Date

December 2014

6. Performing Organization Code
7. Author(s)

Justin Ocel, Ph.D., P.E. (FHWA)
Robert Kogler
Mir Ali (FHWA)

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

Rampart, LLC
422 E Jefferson Street
Falls Church, VA 22046

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-10-D-00017-T-13004

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

Final Report
August 2013-July 2014

14. Sponsoring Agency Code

HRDI-40

15. Supplementary Notes

The work reported herein was conducted under subcontract to Professional Service Industries, Inc., of Herndon, VA, as part of FHWA’s Support Services for the Structures Laboratories contract. Justin Ocel (FHWA) provided technical oversight/assistance and drafted portions of the final report. The Contracting Officer’s Representative was Fassil Beshah, HRDI-40.

16. Abstract

All steel bridge systems need some type of a corrosion protection scheme to ensure a serviceable life. The most common approach is to use a multilayered paint system with a zinc-rich primer. In addition to corrosion performance, other factors need to be considered in the selection of the corrosion protection system. Steel bridges are usually fabricated in smaller components and assembled onsite using high-strength bolted connections with slip-critical connections. Slip-critical connections use the high clamping force of the bolt to develop frictional shear stresses in excess of the load demand such that slip within the connection would not be expected under service loads.

 

Primers used on faying surfaces of slip-critical connections must demonstrate a predetermined level of slip resistance in accordance with the Research Council of Structural Connections (RCSC). This study seeks to evaluate the details of the RCSC slip test specification as applied by four different laboratories. A commonly manufactured set of test panels spanning five typical organic zinc-rich primers was tested independently and in parallel by four laboratories. The data were compared, and subtle yet important variations in test approach taken by each lab are discussed. Recommendations are provided for revisions to the RCSC test protocol to reduce variability.

17. Key Words

Organic zinc, Steel bridges, Primer, Slip critical, Connections, High-strength bolts, Slip coefficients

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

61

22. Price

N/A

Form DOT F 1700.7 Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

LIST OF FIGURES

Figure 1. Illustration. Test plate
Figure 2. Illustration. RCSC compression slip test setup
Figure 3. Illustration. Lab 1 testing system
Figure 4. Illustration. Lab 2 testing system
Figure 5. Illustration. Lab 3 testing system
Figure 6. Illustration. Lab 4 testing system
Figure 7. Graph. Mean slip coefficient for each coating system tested at each test lab using existing RCSC failure criterion
Figure 8. Graph. Load versus slip displacement response of two LVDTs from lab 4 for specimen C2-1
Figure 9. Graph. Mean slip coefficient for each coating system tested at each test lab only using peak load response
Figure 10. Graph. Load versus slip displacement curves for lab 1 coating A1
Figure 11. Graph. Load versus slip displacement curves for lab 2 coating A1
Figure 12. Graph. Load versus slip displacement curves for lab 3 coating A1
Figure 13. Graph. Load versus slip displacement curves for lab 1 coating A2
Figure 14. Graph. Load versus slip displacement curves for lab 2 coating A2
Figure 15. Graph. Load versus slip displacement curves for lab 3 coating A2
Figure 16. Graph. Load versus slip displacement curves for lab 4 coating A2
Figure 17. Graph. Load versus slip displacement curves for lab 1 coating B1
Figure 18. Graph. Load versus slip displacement curves for lab 2 coating B1
Figure 19. Graph. Load versus slip displacement curves for lab 3 coating B1
Figure 20. Graph. Load versus slip displacement curves for lab 1 coating B2
Figure 21. Graph. Load versus slip displacement curves for lab 2 coating B2
Figure 22. Graph. Load versus slip displacement curves for lab 3 coating B2
Figure 23. Graph. Load versus slip displacement curves for lab 1 coating C1
Figure 24. Graph. Load versus slip displacement curves for lab 2 coating C1
Figure 25. Graph. Load versus slip displacement curves for lab 3 coating C1
Figure 26. Graph. Load versus slip displacement curves for lab 4 coating C1
Figure 27. Graph. Load versus slip displacement curves for lab 1 coating C2
Figure 28. Graph. Load versus slip displacement curves for lab 2 coating C2
Figure 29. Graph. Load versus slip displacement curves for lab 3 coating C2
Figure 30. Graph. Load versus slip displacement curves for lab 4 coating C2
Figure 31. Graph. Load versus slip displacement curves for lab 1 coating D1
Figure 32. Graph. Load versus slip displacement curves for lab 2 coating D1
Figure 33. Graph. Load versus slip displacement curves for lab 3 coating D1
Figure 34. Graph. Load versus slip displacement curves for lab 1 coating D2
Figure 35. Graph. Load versus slip displacement curves for lab 2 coating D2
Figure 36. Graph. Load versus slip displacement curves for lab 3 coating D2
Figure 37. Graph. Load versus slip displacement curves for lab 1 coating E1
Figure 38. Graph. Load versus slip displacement curves for lab 2 coating E1
Figure 39. Graph. Load versus slip displacement curves for lab 3 coating E1
Figure 40. Graph. Load versus slip displacement curves for lab 4 coating E1
Figure 41. Graph. Load versus slip displacement curves for lab 1 coating E2
Figure 42. Graph. Load versus slip displacement curves for lab 2 coating E2
Figure 43. Graph. Load versus slip displacement curves for lab 3 coating E2
Figure 44. Graph. Load versus slip displacement curves for lab 4 coating E2
Figure 45. Graph. Labs within material for h-statistic considering the 0.02-inch slip criterion
Figure 46. Graph. Materials within lab for h-statistic considering the 0.02-inch slip criterion
Figure 47. Graph. Labs within material for k-statistic considering the 0.02-inch slip criterion
Figure 48. Graph. Materials within lab for k-statistic considering the 0.02-inch slip criterion
Figure 49. Graph. Labs within material for h-statistic considering just the peak load criterion
Figure 50. Graph. Materials within lab for h-statistic considering just the peak load criterion
Figure 51. Graph. Labs within material for k-statistic considering just the peak load criterion
Figure 52. Graph. Materials within lab for k-statistic considering just the peak load criterion
Figure 53. Illustration. Overall view of modified slip measuring device mounted to a specimen
Figure 54. Illustration. Upper bracket detailing of modified slip measuring device
Figure 55. Illustration. Lower bracket detailing of modified slip measuring device
Figure 56. Graph. Comparison of slip behavior with cure time for coating A1
Figure 57. Graph. Comparison of slip behavior with cure time for coating A2
Figure 58. Graph. Comparison of slip behavior with cure time for coating B1
Figure 59. Graph. Comparison of slip behavior with cure time for coating B2
Figure 60. Graph. Comparison of slip behavior with cure time for coating C1
Figure 61. Graph. Comparison of slip behavior with cure time for coating C2
Figure 62. Graph. Comparison of slip behavior with cure time for coating D1
Figure 63. Graph. Comparison of slip behavior with cure time for coating D2
Figure 64. Graph. Comparison of slip behavior with cure time for coating E1
Figure 65. Graph. Comparison of slip behavior with cure time for coating E2

LIST OF TABLES

Table 1. Test matrix of coatings and labs
Table 2. Results of slip coefficient testing considering existing RCSC failure criteria
Table 3. Results of slip coefficient testing considering just peak load failure criteria
Table 4. Deviations from manufacturer’s recommended DFT
Table 5. h-statistic considering 0.02-inch failure criteria
Table 6. h-statistic considering just peak load failure criteria
Table 7. k-statistic considering 0.02-inch failure criteria
Table 8. k-statistic considering just peak load failure criteria
Table 9. Precision statistics considering 0.02-inch requirement
Table 10. Precision statistics considering just peak load
Table 11. Slip coefficient results of aging study
Table 12. Comparison of slip coefficients between 10-day and extended cure

 

Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000
Turner-Fairbank Highway Research Center | 6300 Georgetown Pike | McLean, VA | 22101