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TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2010 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 647 Subscriber Categories Highways ⢠Bridges and Other Structures Recommended Design Specifications for Live Load Distribution to Buried Structures D. Lee Petersen Charles R. Nelson Gang Li CNA CONSULTING ENGINEERS Minneapolis, MN Timothy J. McGrath Yasuo Kitane SIMPSON GUMPERTZ & HEGER INC. Waltham, MA 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 Boardâs 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 647 Project 15-29 ISSN 0077-5614 ISBN 978-0-309-11822-4 Library of Congress Control Number 2010922165 © 2010 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. Such approval reflects the Governing Boardâs judgment that the program concerned is of national importance and appropriate with respect to both the purposes and resources of the National Research Council. The members of the technical committee selected to monitor this project and to review this report were chosen for recognized scholarly competence and with due consideration for the balance of disciplines appropriate to the project. The opinions and conclusions expressed or implied are those of the research agency that performed the research, and, while they have been accepted as appropriate by the technical committee, they are not necessarily those of the Transportation Research Board, the National Research Council, the American Association of State Highway and Transportation Officials, or the Federal Highway Administration, U.S. Department of Transportation. Each report is reviewed and accepted for publication by the technical committee according to procedures established and monitored by the Transportation Research Board Executive Committee and the Governing Board of the National Research Council. The Transportation Research Board of the National Academies, the National Research Council, the Federal Highway Administration, the American Association of State Highway and Transportation Officials, and the individual states participating in the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturersâ names appear herein solely because they are considered essential to the object of this report.
CRP STAFF FOR NCHRP REPORT 647 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs David B. Beal, Senior Program Officer, Retired Waseem Dekelbab, Senior Program Officer Danna Powell, Senior Program Assistant Eileen P. Delaney, Director of Publications Hilary Freer, Senior Editor NCHRP PROJECT 15-29 PANEL Field of DesignâArea of General Design Brian G. Thompson, Pennsylvania DOT, Harrisburg, PA (Chair) Scott A. Anderson, Federal Highway Administration, Lakewood, CO Harry A. Capers, Jr., Arora and Associates, P.C., Lawrenceville, NJ Susan E. Hida, California DOT, Sacramento, CA Michael G. Katona, Washington State University, Gig Harbor, WA Roman J. Selig, III, Hanson Pipe & Precast, Birmingham, AL Amjad Waheed, Ohio DOT, Columbus, OH James L. Withiam, Ground Technology, Inc., Monroeville, PA Firas I. Sheikh Ibrahim, FHWA Liaison Stephen F. Maher, TRB Liaison 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 provides recommendations to revise the AASHTO LRFD Bridge Design Spec- ifications relating to the distribution of live load to buried structures. The report details the development of simplified design equations (SDEs) for structural response based on three- dimensional (3D) analysis of 830 buried culverts. In addition, the report provides guide- lines for conducting 2D and 3D modeling for design situations with conditions not covered by the SDEs. The material in this report will be of immediate interest to roadway and bridge designers. Much analytical and experimental work has been conducted to investigate the distribu- tion of surface loads through earth fills. The classic Boussinesq (1885) solution, and simple assumptions such as spreading a surface load over an area that is a linear function of depth, remain perhaps the most widely used calculation procedures. The approximate method for estimating the distribution of vehicular live loads through earth fill in the AASHTO Stan- dard Specifications has, over many years, produced designs that have performed acceptably. The AASHTO LRFD Bridge Design Specifications use a different approximation method that significantly increases live load pressures on buried structures compared with the Stan- dard Specifications. When combined with the increased dynamic load allowance prescribed in the LRFD Specifications, this increase is even greater. In addition, the basis of the approx- imation methods in both codes is neither well documented nor understood. The objective of this project was to develop (1) recommended revisions to the AASHTO LRFD Bridge Design Specifications relating to the distribution of live load to buried struc- tures and (2) refined methods for analyzing the distribution of live load to buried structures, including selection of an appropriate soil models. This research was managed by Charles R. Nelson and Lee Petersen, CNA Consulting Engineers, in Minneapolis, Minnesota, with the assistance of Timothy J. McGrath, Simp- son Gumpertz & Heger, Inc., in Waltham, Massachusetts. The report fully documents the research leading to the recommended design specifications for live load distribution to buried structures. Appendixes A through E from the research agencyâs final report are not published herein but are available on the TRB website. These appendixes are as follows: ⢠Appendix Aâ3-D Numerical Analysis of Live Load Distribution: Soil Constitutive Models, Load Factoring and Comparison with Field Measurements ⢠Appendix Bâ3-D Numerical Analysis of Live Load Distribution: Model Details and Results F O R E W O R D By Waseem Dekelbab Staff Officer Transportation Research Board
⢠Appendix CâRecommended Revision to AASHTO LRFD Bridge Design Specifications ⢠Appendix D.1âParametric Study MathCAD Calculation Sheets ⢠Appendix D.2âTabular Listings of Parametric Study Results ⢠Appendix EâRefined Analysis Guidelines
C O N T E N T S 1 Summary 6 Chapter 1 Introduction and Research Approach 7 1.1 Review and Evaluation of Relevant Experience 7 1.2 Soil Constitutive Models and Software 7 1.3 2D and 3D Modeling 8 1.4 Development of SDEs 8 1.5 Investigation of Effect of SDEs on Culvert Forces 8 1.6 Refined Analysis Guidelines 9 Chapter 2 Findings 9 2.1 Review and Evaluation of Relevant Experience 15 2.2 Selection and Development of Refined Analytical Models 21 2.3 Development of SDEs 36 2.4 Effect of SDEs on Culvert Forces 56 2.5 Guidelines for Use of Refined Analysis Methods 67 Chapter 3 Interpretation, Appraisal, and Applications 67 3.1 SDEs 70 3.2 Recommended Changes to the AASHTO LRFD Bridge Design Specifications 70 3.3 Overall Design and Reliability Margin 73 Chapter 4 Conclusions 75 References
