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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2011. A Comparison of AASHTO Bridge Load Rating Methods. Washington, DC: The National Academies Press. doi: 10.17226/22874.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2011. A Comparison of AASHTO Bridge Load Rating Methods. Washington, DC: The National Academies Press. doi: 10.17226/22874.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2011. A Comparison of AASHTO Bridge Load Rating Methods. Washington, DC: The National Academies Press. doi: 10.17226/22874.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2011. A Comparison of AASHTO Bridge Load Rating Methods. Washington, DC: The National Academies Press. doi: 10.17226/22874.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2011. A Comparison of AASHTO Bridge Load Rating Methods. Washington, DC: The National Academies Press. doi: 10.17226/22874.
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TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2011 www.TRB.org N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP REPORT 700 Subscriber Categories Bridges and Other Structures A Comparison of AASHTO Bridge Load Rating Methods Mark Mlynarski MICHAEL BAKER JR. INC. Moon Township, PA Wagdy G. Wassef MODJESKI AND MASTERS Mechanicsburg, PA Andrzej S. Nowak UNIVERSITY OF NEBRASKA Lincoln, NE Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the 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 cooperative research. In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by funds from participating member states of the Association and it receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. 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 modern research practices. The Board is uniquely suited for this purpose as it maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; it possesses avenues of communications and cooperation with federal, state and local governmental agencies, universities, and industry; its relationship to the National Research Council is an insurance of objectivity; it maintains a full-time research correlation staff of specialists in highway transportation matters to bring the findings of research directly to those who are in a position to use them. The program is developed on the basis of research needs identified by chief administrators of the highway and transportation departments and by committees of AASHTO. Each year, specific areas of research needs to be included in the program are proposed to the National 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 NCHRP REPORT 700 Project 12-78 ISSN 0077-5614 ISBN 978-0-309-21344-8 Library of Congress Control Number 2011935078 © 2011 National Academy of Sciences. All rights reserved. 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, FMCSA, FTA, or Transit Development Corporation 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. NOTICE 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 the Governing Board of the National Research Council. The members of the technical panel selected to monitor this project and to review this report were chosen for their special competencies and with regard for appropriate balance. 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 by the Governing Board of the National Research Council. The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board, the National Research Council, or the program sponsors. The Transportation Research Board of the National Academies, the National Research Council, 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 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

CRP STAFF FOR NCHRP REPORT 700 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs Waseem Dekelbab, Senior Program Officer Danna Powell, Senior Program Assistant Eileen P. Delaney, Director of Publications Margaret B. Hagood, Editor NCHRP PROJECT 12-78 PANEL Field of Design—Area of Bridges Matthew Farrar, Idaho Transportation Department, Boise, ID (Chair) Timothy A. Armbrecht, Illinois DOT, Springfield, IL George A. Christian, AECOM, Latham, NY George H. Conner, Alabama DOT, Montgomery, AL William R. “Randy” Cox, American Segmental Bridge Institute, Driftwood, TX Rebecca Curtis, Federal Highway Administration, McLean, VA Arthur W. D’Andrea, Louisiana DOTD, Baton Rouge, LA Murugesu Vinayagamoorthy, California DOT, Sacramento, CA Pe-Shen Yang, Arizona DOT, Phoenix, AZ Firas I. Sheikh Ibrahim, FHWA Liaison Stephen F. Maher, TRB Liaison AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 12-78 by Michael Baker Jr., Inc., Modjeski and Masters, Inc., and the University of Nebraska. Michael Baker Jr., Inc. was the contractor for this study. The work undertaken by Modjeski and Masters, Inc. and the University of Nebraska was under a subcontract with Michael Baker Jr., Inc. Mark Mlynarski, Project Manager, Michael Baker Jr., Inc., and Wagdy G. Wassef, Ph.D., Modjeski and Masters, Inc. were the co-principal investigators. The other authors of this report were Andrzej S. Nowak, Ph.D., Professor of Engineering, University of Nebraska, and Vanessa L. Storlie, Modjeski and Masters, Inc. The work was performed under the general supervision of Mr. Mlynarski and Dr. Wassef. The software development and data extraction work at Michael Baker Jr., Inc. was performed under the supervision of Mr. Mlynarski with the assistance of Mehrdad Ordoobadi, Technical Manager-Bridge Software, and Scott Peterson, Programmer/Database Specialist. The work at Modjeski and Masters was performed under the supervision of Dr. Wassef with the assistance of Vanessa Storlie in all tasks of the project and Mr. Chad Clancy in the solicitation and review of state legal and permit vehicles. The development of the statistical parame- ters used in the calculation of the reliability index factors was performed at the University of Nebraska under the supervision of Dr. Nowak with the assistance of Piotr Paczkowski and Przemyslaw Rakoczy. Special thanks to Brian Goodrich of BridgeTech, Inc. and the Wyoming Transportation Department for modifications made to the BRASS software to allow the research team to extract additional data in NCHRP Process 12-50 format needed for reviewing the permit live loading results. 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

This report documents an analysis of 1,500 bridges that represent various material types and configurations using AASHTOWare™ Virtis® to compare the load factor rating to load and resistance factor rating for both moment and shear induced by design vehicles, AASHTO legal loads, and eight additional permit/legal vehicles. The report includes pro- posed revisions to the AASHTO Manual for Bridge Evaluation based on a review of the analysis results. The material in this report will be of immediate interest to bridge engineers. The Guide Manual for Condition Evaluation and Load and Resistance Factor Rating (LRFR) of Highway Bridges, 1st Edition and 2005 Interim, was developed under NCHRP Project 12-46. Before the Guide Manual was endorsed by the AASHTO Highway Subcom- mittee on Bridges and Structures (HSCOBS), some additional research was requested to explain differences between the new manual and the established load factor rating (LFR) requirements. NCHRP 20-07/Task 122 provided explicit comparisons between ratings produced by the LRFR methods of the Guide Manual and the load factor ratings from the latest edition of the AASHTO Manual for Condition Evaluation of Bridges. Nevertheless, because the Task 122 scope was limited to flexural ratings and the number of structures rated was small, HSCOBS wanted more bridges rated and LRFR/LFR comparisons made for moment and shear induced by a variety of loads. The choice of load rating method may affect the transportation of goods and services over the nation’s highways by restricting routes that were previously unrestricted. Additional comparisons of LRFR and LFR ratings were needed to (1) develop refinements to the load rating process that maintain an acceptable level of bridge reliability without unnecessary restrictions on commerce and (2) explain changes in truck weight restrictions to the public. The research was performed under NCHRP Project 12-78 by Michael Baker Jr., Inc, with the assistance of Modjeski and Masters, Inc., and the University of Nebraska. The objectives of NCHRP Project 12-78 were to propose refinements to the LRFR methods in the AASHTO Manual for Bridge Evaluation and to explain potential changes in truck weight restrictions of existing bridges. A number of deliverables are provided as appendices. These are not published herein but are available on the TRB website at http://www.trb.org/Main/Blurbs/165576.aspx. The appendices are: • Appendix A—Final Bridge/Girder List • Appendix B—Simple Span Steel Girder Bridges • Appendix C—Simple Span Prestressed I-Girder Bridges • Appendix D—Simple Span Prestressed Box Girder Bridges F O R E W O R D By Waseem Dekelbab Staff Officer Transportation Research Board

• Appendix E—Simple Span Reinforced Concrete T-Beam Bridges • Appendix F—Simple Span Reinforced Concrete Slab Bridges • Appendix G—Steel I-Girder Continuous Span Bridges • Appendix H—Continuous Reinforced Concrete Slab Bridges • Appendix I—Continuous Prestressed I-Girder Bridges • Appendix J—Calculated Reliability Indices • Appendix K—Effect of Permit Type and ADTT on LRFR Ratings • Appendix L—Effect of LRFR Rating on Operating Rating • Appendix M—Effect of LRFR on Rating Using Proposed Load Factors • Appendix N—MBE Examples • Appendix O—Review of the NBI/Virtis Databases • Appendix P—Final Survey • Appendix Q—Changes required for NCHRP 12-50/Software Documentation • Appendix R—Format of CSV output produced by RIO software

C O N T E N T S 1 Summary 3 Chapter 1 Background 3 1.1 Surveying/Soliciting Data 5 Chapter 2 Research Approach 5 2.1 Selection of Bridges 5 2.1.1 NBI/Virtis Data Review/Comparison with Virtis Data 6 2.1.2 Refinement of the Bridge Selections—Final Bridge Domain 9 2.2 Development of Live Load Vehicle List 9 2.2.1 Introduction 14 2.2.2 Conclusion 14 2.2.3 Vehicle Options 16 Chapter 3 Findings and Applications 16 3.1 Summary of Bridge Rating Analysis 16 3.1.1 Software Used for the Analysis/Data Gathering 16 3.1.2 Virtis/BRASS 17 3.1.3 Final Bridge Breakdown 18 3.1.4 Live Loads 20 3.2 Reliability Index Calculation Spreadsheet 24 3.2.1 Raw Data 24 3.2.2 Sorted Raw Data 24 3.2.3 Reliability Index Calculation 27 3.3 Rating Factor Comparison Spreadsheet 28 3.3.1 Data Analysis and Trends 28 3.3.2 Main Sources of Difference in Rating Factors Between LFR and LRFR 34 3.4 Effect of ADTT and Permit Type on Ratings 34 3.4.1 AASHTO Legal Vehicles 38 3.4.2 Routine Permit Vehicles 38 3.5 Special Permit Vehicles 47 3.6 Effect of LRFR Rating on Inventory Rating 47 3.6.1 Simple Span Steel Girder Bridges 48 3.6.2 Continuous Span Steel Girder Bridges 49 3.6.3 Simple Span Prestressed I-Girder Bridges 50 3.6.4 Simple Span Prestressed Box Girder Bridges 51 3.6.5 Simple Span Reinforced Concrete T-Beam Bridges 52 3.6.6 Simple Span Reinforced Concrete Slab Bridges 53 3.6.7 Continuous Span Reinforced Concrete Slab Bridges 53 3.6.8 Continuous Prestressed Concrete I-Girder Bridges 55 3.7 Comparison of Reliability Index to Live Load Factors 56 3.7.1 Design Vehicle 56 3.7.2 Routine Permit Vehicles

56 3.7.3 Special or Limited Crossing Permit Vehicles 56 3.7.4 AASHTO Legal Vehicles 58 3.7.5 Proposed Live Load Factors 58 3.8 Selection of Load Factors for Implementation in the MBE 71 3.9 Effect of Using Proposed Live Load Factors on Rating Factors 72 3.9.1 Simple Span Steel 74 3.9.2 Simple Span Prestressed I-Beams 75 3.9.3 Simple Span Prestressed Box Beams 75 3.9.4 Simple Span Reinforced Concrete T-Beams 76 3.9.5 Simple Span Reinforced Concrete Slabs 76 3.9.6 Continuous Span Steel Girders 76 3.9.7 Continuous Span Reinforced Concrete Slabs 76 3.9.8 Continuous Span Prestressed Concrete I-Beams 77 3.9.9 Average Ratio of Rating Factors for Existing and Proposed Live Load Factors 84 Chapter 4 Conclusions 84 4.1 Proposed Revisions to the MBE 92 4.2 Data Archiving 93 Appendices A through R 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.

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 700: A Comparison of AASHTO Bridge Load Rating Methods documents an analysis of 1,500 bridges that represent various material types and configurations using AASHTOWare™ Virtis® to compare the load factor rating to load and resistance factor rating for both moment and shear induced by design vehicles, American Association of State Highway and Transportation Officials (AASHTO) legal loads, and eight additional permit/legal vehicles.

The report includes proposed revisions to the AASHTO Manual for Bridge Evaluation based on a review of the analysis results.

The appendixes to NCHRP Report 700 are not part of the printed version of the report. The appendixes are available in a single electronic document and are listed below. Please note that this is a very large document and may take a number of minutes to download.

• Appendix A—Final Bridge/Girder List

• Appendix B—Simple Span Steel Girder Bridges

• Appendix C—Simple Span Prestressed I-Girder Bridges

• Appendix D—Simple Span Prestressed Box Girder Bridges

• Appendix E—Simple Span Reinforced Concrete T-Beam Bridges

• Appendix F—Simple Span Reinforced Concrete Slab Bridges

• Appendix G—Steel I-Girder Continuous Span Bridges

• Appendix H—Continuous Reinforced Concrete Slab Bridges

• Appendix I—Continuous Prestressed I-Girder Bridges

• Appendix J—Calculated Reliability Indices

• Appendix K—Effect of Permit Type and ADTT on LRFR Ratings

• Appendix L—Effect of LRFR Rating on Operating Rating

• Appendix M—Effect of LRFR on Rating Using Proposed Load Factors

• Appendix N—MBE Examples

• Appendix O—Review of the NBI/Virtis Databases

• Appendix P—Final Survey

• Appendix Q—Changes required for NCHRP 12-50/Software Documentation

• Appendix R—Format of CSV output produced by RIO software

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