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NATIONAL NCHRP REPORT 675 COOPERATIVE HIGHWAY RESEARCH PROGRAM LRFD Metal Loss and Service-Life Strength Reduction Factors for Metal-Reinforced Systems
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TRANSPORTATION RESEARCH BOARD 2011 EXECUTIVE COMMITTEE* OFFICERS CHAIR: Neil J. Pedersen, Administrator, Maryland State Highway Administration, Baltimore VICE CHAIR: Sandra Rosenbloom, Professor of Planning, University of Arizona, Tucson EXECUTIVE DIRECTOR: Robert E. Skinner, Jr., Transportation Research Board MEMBERS J. Barry Barker, Executive Director, Transit Authority of River City, Louisville, KY Deborah H. Butler, Executive Vice President, Planning, and CIO, Norfolk Southern Corporation, Norfolk, VA William A.V. Clark, Professor, Department of Geography, University of California, Los Angeles Eugene A. Conti, Jr., Secretary of Transportation, North Carolina DOT, Raleigh James M. Crites, Executive Vice President of Operations, Dallas-Fort Worth International Airport, TX Paula J. Hammond, Secretary, Washington State DOT, Olympia Adib K. Kanafani, Cahill Professor of Civil Engineering, University of California, Berkeley Susan Martinovich, Director, Nevada DOT, Carson City Michael R. Morris, Director of Transportation, North Central Texas Council of Governments, Arlington Tracy L. Rosser, Vice President, Regional General Manager, Wal-Mart Stores, Inc., Mandeville, LA Steven T. Scalzo, Chief Operating Officer, Marine Resources Group, Seattle, WA Henry G. (Gerry) Schwartz, Jr., Chairman (retired), Jacobs/Sverdrup Civil, Inc., St. Louis, MO Beverly A. Scott, General Manager and CEO, Metropolitan Atlanta Rapid Transit Authority, Atlanta, GA David Seltzer, Principal, Mercator Advisors LLC, Philadelphia, PA Lawrence A. Selzer, President and CEO, The Conservation Fund, Arlington, VA Kumares C. Sinha, Olson Distinguished Professor of Civil Engineering, Purdue University, West Lafayette, IN Daniel Sperling, Professor of Civil Engineering and Environmental Science and Policy; Director, Institute of Transportation Studies; and Interim Director, Energy Efficiency Center, University of California, Davis Kirk T. Steudle, Director, Michigan DOT, Lansing Douglas W. Stotlar, President and CEO, Con-Way, Inc., Ann Arbor, MI C. Michael Walton, Ernest H. Cockrell Centennial Chair in Engineering, University of Texas, Austin EX OFFICIO MEMBERS Peter H. Appel, Administrator, Research and Innovative Technology Administration, U.S.DOT J. Randolph Babbitt, Administrator, Federal Aviation Administration, U.S.DOT Rebecca M. Brewster, President and COO, American Transportation Research Institute, Smyrna, GA Anne S. Ferro, Administrator, Federal Motor Carrier Safety Administration, U.S.DOT John T. Gray, Senior Vice President, Policy and Economics, Association of American Railroads, Washington, DC John C. Horsley, Executive Director, American Association of State Highway and Transportation Officials, Washington, DC David T. Matsuda, Deputy Administrator, Maritime Administration, U.S.DOT Victor M. Mendez, Administrator, Federal Highway Administration, U.S.DOT William W. Millar, President, American Public Transportation Association, Washington, DC Tara O'Toole, Under Secretary for Science and Technology, U.S. Department of Homeland Security, Washington, DC Robert J. Papp (Adm., U.S. Coast Guard), Commandant, U.S. Coast Guard, U.S. Department of Homeland Security, Washington, DC Cynthia L. Quarterman, Administrator, Pipeline and Hazardous Materials Safety Administration, U.S.DOT Peter M. Rogoff, Administrator, Federal Transit Administration, U.S.DOT David L. Strickland, Administrator, National Highway Traffic Safety Administration, U.S.DOT Joseph C. Szabo, Administrator, Federal Railroad Administration, U.S.DOT Polly Trottenberg, Assistant Secretary for Transportation Policy, U.S.DOT Robert L. Van Antwerp (Lt. Gen., U.S. Army), Chief of Engineers and Commanding General, U.S. Army Corps of Engineers, Washington, DC Barry R. Wallerstein, Executive Officer, South Coast Air Quality Management District, Diamond Bar, CA *Membership as of March 2011.
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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM NCHRP REPORT 675 LRFD Metal Loss and Service-Life Strength Reduction Factors for Metal-Reinforced Systems Kenneth L. Fishman MCMAHON & MANN CONSULTING ENGINEERS, P.C. Buffalo, NY James L. Withiam D'APPOLONIA ENGINEERS Monroeville, PA Subscriber Categories Highways · Bridges and Other Structures · Geotechnology Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration TRANSPORTATION RESEARCH BOARD WASHINGTON, D.C. 2011 www.TRB.org
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NATIONAL COOPERATIVE HIGHWAY NCHRP REPORT 675 RESEARCH PROGRAM Systematic, well-designed research provides the most effective Project 24-28 approach to the solution of many problems facing highway ISSN 0077-5614 administrators and engineers. Often, highway problems are of local ISBN 978-0-309-15549-6 interest and can best be studied by highway departments individually Library of Congress Control Number 2011923669 or in cooperation with their state universities and others. However, the © 2011 National Academy of Sciences. All rights reserved. accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of COPYRIGHT INFORMATION cooperative research. Authors herein are responsible for the authenticity of their materials and for obtaining In recognition of these needs, the highway administrators of the written permissions from publishers or persons who own the copyright to any previously American Association of State Highway and Transportation Officials published or copyrighted material used herein. initiated in 1962 an objective national highway research program Cooperative Research Programs (CRP) grants permission to reproduce material in this employing modern scientific techniques. This program is supported on 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, a continuing basis by funds from participating member states of the FMCSA, FTA, or Transit Development Corporation endorsement of a particular product, Association and it receives the full cooperation and support of the method, or practice. It is expected that those reproducing the material in this document for Federal Highway Administration, United States Department of 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 Transportation. from CRP. The Transportation Research Board of the National Academies was requested by the Association to administer the research program because of the Board's recognized objectivity and understanding of NOTICE modern research practices. The Board is uniquely suited for this purpose as it maintains an extensive committee structure from which The project that is the subject of this report was a part of the National Cooperative Highway Research Program, conducted by the Transportation Research Board with the approval of authorities on any highway transportation subject may be drawn; it the Governing Board of the National Research Council. possesses avenues of communications and cooperation with federal, The members of the technical panel selected to monitor this project and to review this state and local governmental agencies, universities, and industry; its report were chosen for their special competencies and with regard for appropriate balance. relationship to the National Research Council is an insurance of The report was reviewed by the technical panel and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved objectivity; it maintains a full-time research correlation staff of by the Governing Board of the National Research Council. specialists in highway transportation matters to bring the findings of The opinions and conclusions expressed or implied in this report are those of the research directly to those who are in a position to use them. researchers who performed the research and are not necessarily those of the Transportation The program is developed on the basis of research needs identified Research Board, the National Research Council, or the program sponsors. by chief administrators of the highway and transportation departments The Transportation Research Board of the National Academies, the National Research and by committees of AASHTO. Each year, specific areas of research Council, and the sponsors of the National Cooperative Highway Research Program do not needs to be included in the program are proposed to the National endorse products or manufacturers. Trade or manufacturers' names appear herein solely because they are considered essential to the object of the report. Research Council and the Board by the American Association of State Highway and Transportation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Research Council and the Transportation Research Board. The needs for highway research are many, and the National Cooperative Highway Research Program can make significant contributions to the solution of highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or duplicate other highway research programs. Published reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from: Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet at: http://www.national-academies.org/trb/bookstore Printed in the United States of America
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The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. On the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Charles M. Vest is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, on its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. Charles M. Vest are chair and vice chair, respectively, of the National Research Council. The Transportation Research Board is one of six major divisions of the National Research Council. The mission of the Transporta- tion Research Board is to provide leadership in transportation innovation and progress through research and information exchange, conducted within a setting that is objective, interdisciplinary, and multimodal. The Board's varied activities annually engage about 7,000 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 individu- als interested in the development of transportation. www.TRB.org www.national-academies.org
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COOPERATIVE RESEARCH PROGRAMS CRP STAFF FOR NCHRP REPORT 675 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs Edward T. Harrigan, Senior Program Officer Melanie Adcock, Senior Program Assistant Eileen P. Delaney, Director of Publications Scott E. Hitchcock, Editor NCHRP PROJECT 24-28 PANEL Field of Soils and Geology--Area of Mechanics and Foundations Norman D. Dennis, Jr., University of Arkansas - Fayetteville, Fayetteville, AR (Chair) Richard M. Lane, Pembroke, NH Robert A. Gladstone, Association for Metallically Stabilized Earth, McLean, VA Mohammed A. Mulla, North Carolina DOT, Raleigh, NC Robert A. Reis, California DOT, Sacramento, CA Louis D. Taylor, Michigan DOT, Lansing, MI John J. Wheeler, Jr., New York State DOT, Albany, NY Masha B. Wilson, Nevada Department of Public Safety, Carson City, NV Thomas F. Zimmie, Rensselaer Polytechnic Institute, Troy, NY Michael Adams, FHWA Liaison G. P. Jayaprakash, TRB Liaison
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FOREWORD By Edward T. Harrigan Staff Officer Transportation Research Board NCHRP Report 675 presents the findings of research conducted to develop metal loss models for metal-reinforced systems that are compatible with the AASHTO LRFD (Load and Resistance Factor Design) Bridge Design Specifications. The report will be of immediate interest to engineers in state highway agencies and industry with responsibility for the construc- tion and maintenance of bridges and structures, with particular emphasis on mechanically stabilized earth (MSE) walls. Transportation agencies use a variety of metal-reinforced systems in geotechnical applica- tions, including soil and rock reinforcements, ground anchors, and tiebacks. These systems support retaining walls and soil and rock slopes, and they stabilize roadway cuts and fills. The precise conditions governing the deterioration of these systems are uncertain, but corrosion is known to have an impact on their service life. Engineers, faced with the task of allocating budgets to rehabilitate aging facilities, need reliable techniques for assessing corrosion and estimating metal loss. Service-life estimates for new systems need to be improved, and consid- eration of metal loss in their design needs to be consistent with the reliability-based approach adopted in the AASHTO LRFD Bridge Design Specifications. The objectives of this research were to (1) assess and improve the predictive capabilities of existing computational models for corrosion potential, metal loss, and service life of metal- reinforced systems used in retaining structures, highway cuts and fills, and other applications; (2) develop methodology that incorporates the improved predictive models into an LRFD approach for the design of metal-reinforced systems; and (3) recommend additions and revi- sions to the AASHTO LRFD specifications that incorporate the improved models and method- ology. The project was carried out by McMahon & Mann Consulting Engineers, P.C., Buffalo, New York, assisted by subcontractor D'Appolonia Engineers, Monroeville, Pennsylvania. The report fully documents the research leading to the following key products: (1) metal loss models for estimating sacrificial steel requirements for Type I metal-reinforced systems [mechanically stabilized earth (MSE) reinforcements], for which the AASHTO LRFD spec- ifications include metal loss as a specific part of the design; (2) recommended sampling and testing protocols needed for condition assessment and corrosion monitoring of MSE rein- forcements to develop input data for the metal loss models; and (3) an example problem demonstrating analysis and design of an MSE wall using LRFD and the corresponding metal loss models and resistance factors. The report also presents service-life estimates and exam- ple calibrations for a Type II metal-reinforced system (specifically, a rock bolt), for which metal loss is not incorporated in the LRFD design calculations. Three of seven appendices from the contractor's final report not contained in NCHRP Report 675 may be downloaded from the NCHRP Project 24-28 webpage at http://apps .trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=727.
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AUTHOR ACKNOWLEDGMENTS The authors gratefully acknowledge assistance and cooperation from various state DOTs and other gov- ernment agencies, universities, private consultants, and contractors, particularly with respect to data col- lection activities that comprised such an important part of this project. Caltrans Corrosion Technology Branch, Materials Engineering and Testing Services Unit provided access to sites in California and shared expertise with respect to corrosion monitoring including Messrs. Rob Reis, Doug Parks, Dave Castanon, Rudy Lopez, Joe Shanabrook, Charlie Sparkman, and Rich Sullivan. Ms. Kathryn Griswell, Caltrans Retaining Wall Specialist also assisted, and personnel from Caltrans Districts 1, 4, 7 and 8 assisted with site access and maintaining traffic control. NCDOT personnel including Messrs. Mohammed Mulla, Cecil Jones, Chris Peoples, Kelly Croft, and Dan Smith provided access, information, and assistance as necessary to collect data from sites in North Carolina. Messrs. Robert Burnett, JJ Wheeler Jr., and Joseph DiGrego- rio from NYSDOT provided access, information, and assistance as necessary to collect data from sites in New York. Messrs. Dennis S. Brown, Thomas Prestach, Kevin Nagy, Glenn Keiper (now with American Geotechnical & Environmental Services, Inc.) provided access, information, and assistance as necessary to collect data on ground anchors at the site along I-99 in Altoona, PA. Mr. Dave Weatherby from Schnabel Foundations, Inc., provided installation details from this site. Messrs. Craig Compton, Dennis R. Dolinar, and Paul K. Stefko facilitated access at the NIOSH SRCM. Mr. Richard Lane, Mr. Dave Merrill, and Ms. Krystle Pelham provided access, information and assistance as necessary to collect data from the site of the Barron Mountain Rock Cut in Woodstock, NH. Prof. Alberto Sagues from the University of South Florida, and Jean Marc Jailloux from Profactal Engineering and Consulting provided data from their cor- rosion monitoring activities in Florida and France, respectively. The FHWA provided use of their PR mon- itors for corrosion monitoring at selected sites. Use of the FHWA equipment is greatly appreciated and is also available from the FHWA to state DOTs on an as needed basis. Project consultants included Prof. Gregory Baecher from the University of Maryland, Mr. Peter Ander- son, Reinforced Earth Company (RECO), Dr. Barry Christopher (Consultant), and Mr. Louis Pinto (Con- sultant). Dr. James L. Withiam, P.E., from D'Appolonia was co-Principal Investigator for the project and other personnel from D'Appolonia including Mr. Vince Gusbar and Dr. Yasser Hegazy contributed to the project. Personnel from McMahon and Mann Consulting Engineers, P.C., including Ms. Suzanne George, and Messrs. Andrew Klettke, James Janora, Richard J. Bojarski, Vince LoVullo, and Andrew McMahon contributed to data collection activities, data analysis, and reliability studies.
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CONTENTS 1 Chapter 1 Background 1 Earth Reinforcements 1 Details of Type I Reinforcements 3 Details of Type II Reinforcements 3 Durability and Performance Issues for Earth Reinforcements 4 Type I Reinforcements 7 Type II Reinforcements 8 Test Protocol and Measurement Techniques 8 Measurement Techniques 9 Performance Database 9 Load and Resistance Factor Design (LRFD) 10 Resistance Factors for Design of Earth Reinforcements 12 Chapter 2 Research Approach 12 Tasks 12 Task 1--Literature Review and Survey 12 Task 2--Prepare Performance Database 12 Task 3--Estimate Reliability of Service-Life Models 12 Task 4--Develop Work Plan for Field Investigation 12 Task 5--Submit Interim Report 12 Task 6--Implement Field Investigation 12 Task 7--Identify Target Reliability Index for LRFD 13 Task 8--Recommend Revisions to AASHTO LRFD Specifications 13 Task 9--Submit Final Report 13 Test Protocol 13 Calibration of Resistance Factors for LRFD 14 Yield Limit State 15 Resistance Factor Calibration 18 Chapter 3 Findings and Applications 19 Type I--Measured Corrosion Rates 20 Bias of LPR Measurements 22 Trends 24 Metal Loss Models and Reliability 28 Calibration of Resistance Factors 28 Galvanized Reinforcements 32 Verification of Monte Carlo Analysis 34 Plain Steel Reinforcements 35 Marginal Fill Quality 36 Type II--Condition Assessment 38 Rock Bolts 41 Ground Anchors
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42 Chapter 4 Conclusions and Recommendations 43 Recommended Resistance Factors for LRFD 45 Recommendations for Asset Management 45 Performance Data 46 Maintenance, Rehabilitation, and Replacement 46 Update Experience with Different Reinforced Fills 46 Recommendations for Future Research 47 Type I Reinforcements 47 Type II Reinforcements 48 References 51 Appendix A Details of Metal Loss Models 56 Appendix B Test Protocols 69 Appendix C Performance Database 69 Appendix D Data Analysis 69 Appendix E Details of Monte Carlo Simulations and Reliability Analyses 70 Appendix F Example 99 Appendix G List of Symbols and Summary of Equations Note: Many of the photographs, figures, and tables in this report have been converted from color to grayscale for printing. The electronic version of the report (posted on the Web at www.trb.org) retains the color versions.