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2021 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 RESEARCH REPORT 962 Proposed Modification to AASHTO Cross-Frame Analysis and Design Matthew Reichenbach Joshua White Sunghyun Park Esteban Zecchin Matthew Moore Yangqing Liu Chen Liang BalÃ¡zs KÃ¶vesdi Todd Helwig Michael Engelhardt Robert Connor Michael Grubb Ferguson structural engineering laboratory the university oF texas at austin Austin, Texas Subscriber Categories Bridges and Other Structures 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, 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 transporta- tion results in increasingly complex problems of wide interest to high- way 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 ini- tiated an objective national highway research program using modern scientific techniquesâthe 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 Agree- ment No. 693JJ31950003. The Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine was requested by AASHTO to administer the research program because of TRBâs recognized objectivity and understanding of modern research practices. TRB is uniquely suited for this purpose for many reasons: TRB maintains an extensive com- mittee structure from which authorities on any highway transportation subject may be drawn; TRB possesses avenues of communications and cooperation with federal, state, and local governmental agencies, univer- sities, and industry; TRBâs relationship to the National Academies is an insurance of objectivity; and TRB maintains a full-time staff of special- ists in highway transportation matters to bring the findings of research directly to those in a position to use them. The program is developed on the basis of research needs iden- tified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the FHWA. Topics of the highest merit are selected by the AASHTO Special Committee on Research and Innovation (R&I), and each year R&Iâs recommendations are proposed to the AASHTO Board of Direc- tors and the National Academies. Research projects to address these topics are defined by NCHRP, and qualified research agencies are selected from submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Academies and TRB. The needs for highway research are many, and NCHRP can make significant contributions to solving 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 research 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 by going to https://www.nationalacademies.org and then searching for TRB Printed in the United States of America NCHRP RESEARCH REPORT 962 Project 12-113 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-67373-0 Library of Congress Control Number 2020952857 Â© 2021 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, 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. NOTICE The research 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 National Academies of Sciences, Engineering, and Medicine. 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 Academies of Sciences, Engineering, and Medicine; the FHWA; or the program sponsors. The Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; and the sponsors of 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 the report.
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 Boardâs 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 AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 12-113 by the Department of Civil, Architectural, and Environmental Engineering at the University of Texas at Austin (UT Austin). UT Austin was the contractor for this study. The Texas Department of Transportation (TxDOT) provided substantial assistance to the research team throughout the field experimental program. TxDOT organized lane closures and provided dump trucks for controlled live load tests as well as general traffic control to assist in the instrumentation of the bridges. The research team specifically acknowledges Dr. Ken Lin, Lynn Champagne, Chris Baker, David Jeffreys, Adam Galland, Melody Galland, Maria Aponte, Ray Castillo, Jaime Castaneda, and Larry Whittington for their contributions to the field studies. Significant assistance was also provided by Jamie Farris, Dennis Johnson, and Walter Fisher in identifying bridges for possible instrumentation. Texas Advanced Computing Center (TACC) provided computing resources to conduct the extensive parametric studies associated with this research. The research team specifically acknowledges Bob Garza and Dr. Ritu Arora for their assistance throughout the process. The research team thanks Dr. Tom Murphy, Dr. John Kulicki, and Dr. Andrzej Nowak for informa- tion provided from the SHRP 2 R19B study that was invaluable for understanding weigh-in-motion data gathered and related reliability studies. CRP STAFF FOR NCHRP RESEARCH REPORT 962 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Waseem Dekelbab, Senior Program Officer Tyler Smith, Senior Program Assistant Eileen P. Delaney, Director of Publications Natalie Barnes, Associate Director of Publications Janet M. McNaughton, Senior Editor NCHRP PROJECT 12-113 PANEL Field of DesignâBridges Norman L. McDonald, Ames, IA (Chair) Xiaohua Hannah Cheng, New Jersey Department of Transportation, Trenton, NJ Domenic A. Coletti, HDR, Raleigh, NC Karl H. Frank, Consultant, Austin, TX John S. Hastings, National Steel Bridge Alliance (NSBA), Nashville, TN Thomas P. Macioce, Pennsylvania Department of Transportation, Harrisburg, PA Michelle Lauren Romage-Chambers, Texas Department of Transportation, Austin, TX Dayi Wang, FHWA Liaison Stephen F. Maher, TRB Liaison
NCHRP Research Report 962 presents proposed AASHTO bridge design specifications for the analysis and design of cross-frames in straight and curved steel I-girder bridges. The proposed specifications are based on comprehensive analytical and testing programs for investigating the effects of support skew on the cross-frame behavior, fatigue design forces, the strength and stiffness requirements for stability bracing, and the influence of cross-frame member end connection upon the cross-frame stiffness. This report will be of immediate interest to bridge engineers. Developments in bridge design and analysis in recent years have created the need for improvements to cross-frame analysis and design for steel girder bridges. In the past, the configuration of cross-frame systems was generally based upon standard designs in which member sizes and layouts were dependent upon geometry and minimum member cross- section requirements. The opportunities for improvements to cross-frame analysis and design cover a variety of topics including: (1) improved definition of fatigue loading for cross-frames in curved and/or severely skewed steel girder bridges, analyzed using refined analysis methods; (2) implementation of stability bracing strength and stiffness require- ments in the context of AASHTO Load and Resistance Factor Design (LRFD) bridge design; and (3) additional guidance for adjustment of the effective stiffness of cross-frame members in refined analysis models to reflect the influence of end connections on cross- frame member stiffness. Addressing these topics could result in a dramatic improvement in reliability and economy of cross-frames for steel I-girder bridges. Research was performed under NCHRP Project 12-113, âProposed Modification to AASHTO Cross-Frame Analysis and Designâ by the University of Texas at Austin and included: (1) controlled live load tests and measurement of in-service stress cycle counts for three steel I-girder bridges and (2) an extensive analytical parametric study. The results of the live load tests and analytical study were used to develop the proposed modifica- tion to the AASHTO specifications. Several deliverables, provided as appendices, are not included in the report itself but are available on the TRB website at trb.org by searching for NCHRP Research Report 962. The appendices are as follows: â¢ Appendix B: Cross-Frame Design Example (Straight Bridge) â¢ Appendix C: Cross-Frame Design Example (Curved Bridge) â¢ Appendix D: Phase I Summary â¢ Appendix E: Phase II Summary â¢ Appendix F: Phase III Summary F O R E W O R D By Waseem Dekelbab Staff Officer Transportation Research Board
1 Summary 4 Chapter 1 Background 4 1.1 Problem Statement and Current Knowledge 5 1.1.1 Best Practices for Cross-Frame Layout and Detailing 6 1.1.2 Cross-Frame Fatigue Behavior 7 1.1.3 Cross-Frame Analysis 7 1.1.4 Cross-Frame Stability Bracing Requirements 8 1.2 Research Objectives 10 1.3 Scope of Study 10 1.4 Organization of Report 12 Chapter 2 Research Approach 15 2.1 Industry Survey 16 2.2 Field Experimental Program and Model Validation 17 2.2.1 Instrumented Bridge Overview 17 2.2.2 Experimental Testing Program Overview 19 2.3 Fatigue Loading Study 20 2.3.1 General Methodology 28 2.3.2 AASHTO Design Loads 31 2.3.3 WIM Records 38 2.4 R-Factor Study (3D Analysis) 39 2.4.1 General Load-Induced Cross-Frame Behavior 40 2.4.2 Stiffness Modification Approach 41 2.4.3 Proposed Eccentric-Beam Approach 43 2.4.4 Parametric Study Overview 46 2.5 Commercial Design Software Study (2D Analysis) 47 2.5.1 General Modeling Assumptions 48 2.5.2 Equivalent Beam Approach for Cross-Frames 49 2.5.3 Approaches for Improving 2D Analyses 52 2.5.4 Parametric Study Overview 52 2.6 Stability Study 56 2.6.1 Buckling in the Composite Condition 57 2.6.2 Bracing Strength Study 59 2.6.3 Bracing Stiffness Study C O N T E N T S
60 Chapter 3 Findings and Applications 60 3.1 Field Experimental Program and Model Validation 61 3.1.1 Controlled Live Load Test and Model Validation 67 3.1.2 In-Service Monitoring 70 3.2 Fatigue Loading Study 71 3.2.1 Influence of Bridge Geometry 83 3.2.2 Cross-Frame-Specific Load Factors 89 3.2.3 Multiple Presence Study 92 3.2.4 Major Outcomes 94 3.3 R-Factor Study (3D Analysis) 94 3.3.1 Panel-Level Studies (Noncomposite) 96 3.3.2 System-Level Studies (Composite) 103 3.3.3 Major Outcomes 103 3.4 Commercial Design Software Study (2D Analysis) 104 3.4.1 Sample Influence-Line Results 106 3.4.2 Postprocessing Error 115 3.4.3 Parametric Study 118 3.4.4 Alternative 2D Postprocessing Procedure 119 3.4.5 Major Outcomes 120 3.5 Stability Study 120 3.5.1 Buckling in the Composite Condition 123 3.5.2 Bracing Strength Study 128 3.5.3 Bracing Stiffness Study 131 3.5.4 Consideration of Stability Forces in Design 133 3.5.5 Major Outcomes 134 Chapter 4 Conclusions and Suggested Research 134 4.1 Major Conclusions 138 4.2 Suggestions for Implementation 142 4.3 Future Research Needs 143 References A-1 Appendix A Proposed Modifications to AASHTO LRFD Note: Photographs, figures, and tables in this report may 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.