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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2023. Risk-Based Inspection and Strength Evaluation of Suspension Bridge Main Cable Systems. Washington, DC: The National Academies Press. doi: 10.17226/26861.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2023. Risk-Based Inspection and Strength Evaluation of Suspension Bridge Main Cable Systems. Washington, DC: The National Academies Press. doi: 10.17226/26861.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2023. Risk-Based Inspection and Strength Evaluation of Suspension Bridge Main Cable Systems. Washington, DC: The National Academies Press. doi: 10.17226/26861.
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NCHRP Web-Only Document 353 Risk-Based Inspection and Strength Evaluation of Suspension Bridge Main Cable Systems Blaise Blabac Thomas Murphy Barney Martin Modjeski and Masters, Inc. Mechanicsburg, PA Raimondo Betti George Deodatis Columbia University New York, NY Peter Sluszka John Svensson WSP New York, NY Conduct of Research Report for NCHRP Project 12-115 Submitted October 2022 © 2023 by the National Academy of Sciences. National Academies of Sciences, Engineering, and Medicine and the graphical logo are trademarks of the National Academy of Sciences. All rights reserved. NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed, and implementable research is the most effective way to solve many problems facing state departments of transportation (DOTs) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation results in increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 initiated an objective national highway research program using modern scientific techniques—the National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration (FHWA), United States Department of Transportation, under Agreement No. 693JJ31950003. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FTA, GHSA, NHTSA, or TDC endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. DISCLAIMER The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research. They are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; the FHWA; or the program sponsors. The Transportation Research Board does not develop, issue, or publish standards or specifications. The Transportation Research Board manages applied research projects which provide the scientific foundation that may be used by Transportation Research Board sponsors, industry associations, or other organizations as the basis for revised practices, procedures, or specifications. The Transportation Research Board, the National Academies, and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the object of the report. The information contained in this document was taken directly from the submission of the author(s). This material has not been edited by TRB.

The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non- governmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president. The National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. John L. Anderson is president. The National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president. The three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. The National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine. Learn more about the National Academies of Sciences, Engineering, and Medicine at www.nationalacademies.org. The Transportation Research Board is one of seven major programs of the National Academies of Sciences, Engineering, and Medicine. The mission of the Transportation Research Board is to provide leadership in transportation improvements and innovation through trusted, timely, impartial, and evidence-based information exchange, research, and advice regarding all modes of transportation. The Board’s varied activities annually engage about 8,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. Learn more about the Transportation Research Board at www.TRB.org.

C O O P E R A T I V E R E S E A R C H P R O G R A M S CRP STAFF FOR NCHRP WEB-ONLY DOCUMENT 353 Christopher J. Hedges, Director, Cooperative Research Programs Waseem Dekelbab, Deputy Director, Cooperative Research Programs, and Manager, National Cooperative Highway Research Program Sid Mohan, Associate Program Manager, Implementation and Technology Transfer, National Cooperative Highway Research Program Ahmad Abu-Hawash, Senior Program Officer Sheila A. Moore, Program Associate Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications Jennifer Correro, Assistant Editor NCHRP PROJECT 12-115 PANEL Field of Design—Area of Bridges Sreenivas Alampalli, Stantec, Albany, NY (Chair) Lubin Gao, FHWA Liaison Brandon W. Chavel, Michael Baker International, Inc., Rocky River, OH Ken Brown, State of California, Oakland, CA Shinae Jang, University of Connecticut, Storrs, CT Ross Hammock, Florida Department of Transportation, Lake City, FL Kim Nowack, Michigan Department of Transportation, Saint Ignace, MI William N. Pines, Maryland Department of Transportation, Nottingham, MD Shekhar Scindia, Delaware River and Bay Authority, New Castle, DE James W. Bryant, Jr., TRB Liaison ACKNOWLEDGMENTS This research report was prepared under NCHRP Project 12-115 by a research team led by Modjeski and Masters, Inc., with Mr. Blaise Blabac as the Principal Investigator, supported by Dr. Thomas Murphy, Dr. Barney Martin, Dr. Maria Lopez, Sean Casey and Diane Long. The team consisted of Dr. Raimondo Betti and Dr. George Deodatis of Columbia University (supported by Mengyao Shen), and Mr. Peter Sluszka and John Svensson of WSP. The research team would like to acknowledge and thank the panel led by Dr. Sreenivas Alampalli (formerly of NYSDOT) and panel members Mr. Ken Brown of Caltrans, Mr. Brandon Chavel of the Michael Baker International, Inc., Ms. Kim Nowack of the Mackinac Bridge Authority (MBA), Mr. William Pines of the Maryland DOT (MDTA), Mr. Shekhar Scindia of the Delaware River and Bay Authority (DRBA), Lubin Gao of the FHWA, Shinae Jang and Ross Hammock. The team would also like to thank the Senior Program Officer Mr. Ahmad Abu-Hawash and Dr. Waseem Dekelbab for their help and support during the project.

iv TABLE OF CONTENTS SUMMARY Risk-Based Inspection & Strength Evaluation of Suspension Bridge Main Cable Systems .................................................................................................................... 1 CHAPTER 1 Introduction ........................................................................................................................ 2 Background .............................................................................................................................................. 2 Research Objectives ................................................................................................................................. 4 CHAPTER 2 Literature Review and Synthesis ...................................................................................... 5 Literature Review ..................................................................................................................................... 5 Purpose of Literature Review ............................................................................................................... 5 Literature Review Process .................................................................................................................... 5 Identification of Knowledge Gaps ....................................................................................................... 6 Synthesis of Survey .................................................................................................................................. 9 Purpose of Survey ................................................................................................................................ 9 Survey Process and Summary of Results ............................................................................................. 9 Observations and Identification of Knowledge Gaps ......................................................................... 33 CHAPTER 3 Review of NCHRP Research Report 534 Approach ..................................................... 35 Introduction ............................................................................................................................................ 35 General ................................................................................................................................................... 35 Inspection ............................................................................................................................................... 36 Classifying Corrosion Stage of Wire .................................................................................................. 37 Broken Wires ...................................................................................................................................... 38 Sample Wires ..................................................................................................................................... 38 Inspection Completed ......................................................................................................................... 39 Laboratory Testing ................................................................................................................................. 40 Tensile Tests ....................................................................................................................................... 40 Fractographic Examination of Suspect Wires .................................................................................... 41 Additional Testing .............................................................................................................................. 42 Evaluation of Field and Laboratory Data ............................................................................................... 42 Number of Wires per Corrosion Stage ............................................................................................... 42 Broken Wires ...................................................................................................................................... 43 Wire Properties ................................................................................................................................... 43 Assigning Sample Wires to Groups ................................................................................................... 44 Cracked Wires .................................................................................................................................... 45 Properties of Wire Groups .................................................................................................................. 45 Wire Redevelopment Length .............................................................................................................. 46 Estimation of Cable Strength ................................................................................................................. 47 Simplified Strength Model ................................................................................................................. 47 Brittle Wire Model ............................................................................................................................. 47 Limited Ductility Model ..................................................................................................................... 48 Recommended Report Content .............................................................................................................. 50 Maintenance Personnel Inspection ..................................................................................................... 50 Biennial Inspection ............................................................................................................................. 51 Internal Inspection .............................................................................................................................. 51

v CHAPTER 4 Development of the Guidelines- Probabilistic Approach for Strength Evaluation .... 53 Estimation of Strength ........................................................................................................................... 53 Discussion of the Random Field Method ............................................................................................. 53 Mapping of Corrosion Stage Variation ................................................................................................ 54 Cumulative Distribution Functions for Different Corrosion Stage Wires ............................................ 56 Simulating the Variation of the Wire Strength along the Effective Panel Length ............................ 58 Broken Wires in Effective Development Length ................................................................................. 60 Method 1 ........................................................................................................................................... 61 Method 2 ........................................................................................................................................... 62 Methods of Determining Cable Strength ............................................................................................ 63 Monte Carlo Simulations for the Estimation of the Overall Cable Strength. ..................................... 64 Predicted Factor of Safety ...................................................................................................................... 65 Comparison of Proposed Random Field Method with NCHRP 534 ..................................................... 67 Predicted Remaining Life ...................................................................................................................... 76 CHAPTER 5 Risk-Based Method for Determining Timing of Next Inspection ................................ 78 Introduction ............................................................................................................................................ 78 Risk-Based Inspection of the Suspension System.................................................................................. 78 Element Attributes ................................................................................................................................. 83 RBI Approach for Main Cables ............................................................................................................. 83 Main Cable Strands ................................................................................................................................ 83 Determining Occurrence Factor (OF) ................................................................................................ 84 Screening Attributes .......................................................................................................................... 84 Design Attributes .............................................................................................................................. 84 Loading Attributes ............................................................................................................................ 84 Condition Attributes .......................................................................................................................... 85 Determining Consequence Factor (CF) .............................................................................................. 86 Anchorage Eyebars ................................................................................................................................ 86 Suspender Ropes .................................................................................................................................... 86 Determining Occurrence Factor (OF) ................................................................................................ 87 Screening Attributes .......................................................................................................................... 87 Design Attributes .............................................................................................................................. 88 Loading Attributes ............................................................................................................................ 88 Condition Attributes .......................................................................................................................... 89 Determining Consequence Factor ...................................................................................................... 90 Cable Band Bolts ................................................................................................................................... 90 CHAPTER 6 Review of NDE/SHM Methods ........................................................................................ 91 General Discussion ................................................................................................................................ 91 NDE Inspection Techniques .................................................................................................................. 91 Magnetic Flux Leakage ...................................................................................................................... 91 Magnetostriction ................................................................................................................................. 93 Health Monitoring Techniques .............................................................................................................. 94 Acoustic Emission .............................................................................................................................. 94 Combination of Acoustic Emission and Magnetostrictive Technologies .......................................... 95 Sensors in the Interior of a Main Cable .............................................................................................. 96 Preventive Measures .............................................................................................................................. 97

vi CHAPTER 7 Illustrative Example ......................................................................................................... 99 Detailed Application of the Proposed Methodology .............................................................................. 99 Cable Inspection ..................................................................................................................................... 99 Cumulative Distribution Functions for Different Corrosion Stage Wires ........................................... 120 Simulating the Variation of the Wire Strength along the Effective Panel Length ............................... 127 Accounting for Broken Wires in the Inspected Panel and in the Panels in the Redevelopment Length ..................................................................................................................... 130 Iterative Procedure to Estimate the Cable Strength ............................................................................. 134 Monte Carlo Simulations for the Estimation of the Overall Cable Strength ........................................ 135 CHAPTER 8 Conclusions and Suggested Research ........................................................................... 137 Conclusions .......................................................................................................................................... 137 Implementation Plan ............................................................................................................................ 140 NCHRP-Sponsored Workshop ............................................................................................................ 140 Future Research .................................................................................................................................... 141 REFERENCES ........................................................................................................................................ 142 APPENDIX A: Annotated Bibliography and Questionnaire .............................................................. 142 Annotated Bibliography ............................................................................................................................. Questionnaire ............................................................................................................................................. APPENDIX B: Workshop Agenda ........................................................................................................ 157 Agenda ................................................................................................................................................. 157 List of Attendees .................................................................................................................................. 158

vii LIST OF FIGURES Figure 1. Period Bridges Opened to Traffic ................................................................................................ 10 Figure 2. Total Length of Bridge (in feet) .................................................................................................. 11 Figure 3. Length of Main Span (in feet) ..................................................................................................... 11 Figure 4. Length of Side Spans Supported by Main Cables (in feet).......................................................... 12 Figure 5. Bridge Width (in feet).................................................................................................................. 12 Figure 6. Cable Sag ..................................................................................................................................... 13 Figure 7. Sag Ratio versus Age ................................................................................................................... 14 Figure 8. Diameter of Cables (inches) ........................................................................................................ 14 Figure 9. Number of Wires in Parallel Wire Cables ................................................................................... 16 Figure 10. Mean Wire Strength by Corrosion Stage ................................................................................... 16 Figure 11. Bridges with Acoustic Monitoring ............................................................................................ 17 Figure 12. Year of Last Inspection .............................................................................................................. 18 Figure 13. Number of Times Cables Have Been Inspected ........................................................................ 19 Figure 14. Regular Inspections Performed? ................................................................................................ 19 Figure 15. Number of Panels Inspected ...................................................................................................... 20 Figure 16. Selection Criteria for Opening Panels ....................................................................................... 21 Figure 17. Number of Samples and Specimens .......................................................................................... 22 Figure 18. Factor of Safety as of Last Inspection ....................................................................................... 27 Figure 19. Age of Anchorage Dehumidification System ............................................................................ 29 Figure 20. Suspender Diameter versus Panel Length ................................................................................. 30 Figure 21. Cable Wedge Pattern ................................................................................................................. 37 Figure 22. Wire Corrosion Stages ............................................................................................................... 37 Figure 23. Wire Redevelopment ................................................................................................................. 46 Figure 24. Corrosion Map of Cable (with Broken Wire Locations) [Guidelines Figure B.3.3-2] .............. 56 Figure 25. Empirical Cumulative Distribution Function (CDF) for Corrosion Stage 3 Wire Specimens .. 57 Figure 26. How to Obtain the Values of σ_u from the CDF ....................................................................... 59 Figure 27. Redevelopment Length for the Inspected Panel (Panel 1) ......................................................... 61 Figure 28. Distribution of Cable Strength, Ru ............................................................................................ 65 Figure 29. Flow Chart for Calculation Procedure [Guidelines Figure 4.1-1] ............................................. 66 Figure 30. Inspection and Strength Evaluation Procedure Flowchart [Guidelines Figure 1.2.3-1] ............ 75 Figure 31. NCHRP 782 Process for Reliability-Based Bridge Inspection Practices .................................. 82 Figure 32. MMFM Bobbin Mounted on Cable Mock-up ........................................................................... 92 Figure 33. MMFM Bobbin Mounted on Main Cable of Manhattan Bridge .............................................. 92 Figure 34. MS System Tested on a Coiled 127-wire Strand ....................................................................... 94 Figure 35. MS System Tested on a Coiled 127-wire Strand ....................................................................... 96 Figure 36. Temperature and Relative Humidity Readings over 24 Hour Period from Winter to Summer. 97 Figure 37. Wire Corrosion Stage Data. Location 1 ................................................................................... 101 Figure 38. Wire Corrosion Stage Data. Location 2 ................................................................................... 102 Figure 39. Wire Corrosion Stage Data. Location 3 ................................................................................... 103 Figure 40. Empirical Cumulative Distribution Function for Group 3 Wire Specimens ........................... 127 Figure 41. Empirical Cumulative Distribution Function for Group 3 Wire Specimens ........................... 128 Figure 42. Redevelopment Length for the Inspected Panel (Panel 1) ....................................................... 130

viii LIST OF TABLES Table 1. Date of Suspender Removal/Testing ............................................................................................ 31 Table 2. Statistical parameters for tensile strength for different corrosion stages and selected cases. ....... 50 Table 3. Corrosion Stage Variation Along Observed Wire ........................................................................ 55 Table 4. Ultimate Stresses determined from CDF ...................................................................................... 60 Table 5. Redevelopment factors, Cdi ........................................................................................................... 61 Table 6. Comparison between NCHRP 534 and Proposed Guidelines....................................................... 67 Table 7. Simulated profiles along the length of all wires on the left side of the wedge. Sector 1 ............ 104 Table 8. Simulated profiles along the length of all wires on the right side of the wedge. Sector 1 .......... 105 Table 9. Simulated profiles along the length of all wires on the left side of the wedge. Sector 2 ............ 106 Table 10. Simulated profiles along the length of all wires on the right side of the wedge. Sector 2 ........ 107 Table 11. Simulated profiles along the length of all wires on the left side of the wedge. Sector 3 .......... 108 Table 12. Simulated profiles along the length of all wires on the right side of the wedge. Sector 3 ........ 109 Table 13. Simulated profiles along the length of all wires on the left side of the wedge. Sector 4 .......... 110 Table 14. Simulated profiles along the length of all wires on the right side of the wedge. Sector 4 ........ 111 Table 15. Simulated profiles along the length of all wires on the left side of the wedge. Sector 5 .......... 112 Table 16. Simulated profiles along the length of all wires on the right side of the wedge. Sector 5 ........ 113 Table 17. Simulated profiles along the length of all wires on the left side of the wedge. Sector 6 .......... 114 Table 18. Simulated profiles along the length of all wires on the right side of the wedge. Sector 6 ........ 115 Table 19. Simulated profiles along the length of all wires on the left side of the wedge. Sector 7 .......... 116 Table 20. Simulated profiles along the length of all wires on the right side of the wedge. Sector 7 ........ 117 Table 21. Simulated profiles along the length of all wires on the left side of the wedge. Sector 8 .......... 118 Table 22. Simulated profiles along the length of all wires on the right side of the wedge. Sector 8 ........ 119 Table 23. Generate Cumulative Distribution function (CDF) .................................................................. 121 Table 24. Ultimate Stresses determined from CDF .................................................................................. 129 Table 25. Redevelopment factors, Cdi ....................................................................................................... 131 Table 26. Estimated broken wires in the panels within the redevelopment length ................................... 132

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Most suspension bridges in use today have cables composed of thousands of steel wires and most of these bridges are aging and carry high volumes of traffic. Deterioration of the elements of the suspension system is a problem, replacement of these elements can be expensive and problematic, while failure could be catastrophic.

The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 353: Risk-Based Inspection and Strength Evaluation of Suspension Bridge Main Cable Systems helps develop guidelines for inspection and evaluation of suspension bridge main cable systems using probabilistic approaches.

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