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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
OCR for page R2
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
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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
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possesses avenues of communications and cooperation with federal,
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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
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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
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The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of
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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.
