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2018 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 892 Guidelines for Shielding Bridge Piers Malcolm H. Ray Christine E. Carrigan Chuck A. Plaxico Roadsafe LLC Canton, ME Subscriber Categories Bridges and Other Structures â¢ Design 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 is the most effective way to solve 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 results in increasingly complex problems of wide inter- est to highway 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, United States Department of Transportation. 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 identified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the Federal Highway Administration. 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 http://www.national-academies.org and then searching for TRB Printed in the United States of America NCHRP RESEARCH REPORT 892 Project 12-90 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-47995-0 Library of Congress Control Number 2018960155 Â© 2018 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, FRA, FTA, Office of the Assistant Secretary for Research and Technology, PHMSA, 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; 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. C. D. Mote, Jr., 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.national-academies.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 increase the benefits that transportation contributes to society by providing leadership in transportation innovation and progress through research and information exchange, conducted within a setting that is objective, interdisciplinary, and multimodal. The Boardâs varied committees, task forces, and panels 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 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 CRP STAFF FOR NCHRP RESEARCH REPORT 892 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Waseem Dekelbab, Senior Program Officer Megan Chamberlain, Senior Program Assistant Eileen P. Delaney, Director of Publications Natalie Barnes, Associate Director of Publications Doug English, Senior Editor NCHRP PROJECT 12-90 PANEL Field of DesignâArea of Bridges Keith R. Fulton, Wyoming DOT, Cheyenne, WY (Chair) Arielle L.G. Ehrlich, Minnesota DOT, Oakdale, MN Paul B. Fossier, Louisiana DOTD (retired), Baton Rouge, LA Don J. Gripne, Trinity Highway Products, LLC, Olympia, WA Rodney D. Lacy, Burns & McDonell, Kansas City, MO Peter C. McCowan, New York State DOT, Albany, NY Richard G. Sarchet, DiExSys, LLC, Fruita, CO William P. Longstreet, FHWA Liaison Stephen F. Maher, TRB Liaison
F O R E W O R D By Waseem Dekelbab Staff Officer Transportation Research Board This report provides proposed load and resistance factor design (LRFD) bridge design pier protection specifications and proposed occupant protection guidelines to update the AASHTO LRFD Bridge Design Specifications and AASHTO Roadside Design Guide, respectively. The proposed specifications and guidelines are based on a comprehensive analytical program that used a risk-based approach for investigating the effects of a heavy truck hitting one or more bridge columns or piers. The report also includes four examples that illustrate the use of the proposed specifications and guidelines for shielding bridge piers. The material in this report will be of immediate interest to bridge and safety engineers. Bridge piers are generally close to the travelway to minimize bridge lengths. As a con- sequence, barriers are normally placed around piers to reduce the potential of vehicle crashes damaging the piers. However, the design and placement of the barriers may not have taken into consideration the possibility that vehicles, particularly large trucks, might still impact the pier. The AASHTO LRFD Bridge Design Specifications require piers that were not designed to withstand large impact loads to be protected by a 54-in.-high structurally independent barrier if the barrier is within 10 ft of the pier. If the barrier is more than 10 ft from the pier, a 42-in.-high barrier is specified. There is no consideration of the risk of a high-speed impact, traffic volume, truck usage, operating speeds, facility type, or other factors in the bridge specifications. In addition, while the bridge specifications specify a barrier height, they do not specify a barrier length in advance of the pier. The specifications also do not specify the transition that might be appropriate. The requirement for protecting bridge piers from truck impacts may have a significant effect on passenger car safety. Rigid barriers are generally believed to cause more injuries and fatalities than semi-rigid and flexible barrier systems. In addition, having barriers close to the travelway may significantly increase the number of passenger car crashes. Crashes involving heavy trucks hitting bridge piers are rare, and a barrier designed to protect a bridge pier from impact may create a new hazard especially for passenger vehicles. In the aggregate, the personal cost in lives and property to drivers who hit barriers is more than the cost of repairing bridge piers damaged by heavy trucks. Further, there are operational concerns associated with the use of tall concrete barriers near the travelway. Concrete barriers are much more likely to produce deep snow drifts than are other more open barriers. Drifting is also a problem during severe sand storms. The increase in snow and sand drifting will increase operational costs since highway agencies are forced to make more frequent passes with snow-plowing equipment to keep highways open. Also, tall concrete barriers placed near interchanges can adversely affect sight distances.
In fact, most of the issues mentioned here result from following a one-size-fits-all approach in protecting bridge piers without quantifying when and how the bridge pier protection should be applied. States are spending significant funding on projects that may not provide the expected benefits, particularly on lower traffic volume or functional class bridges. Under NCHRP Project 12-90, Roadsafe LLC was asked to develop (1) risk-based guide- lines that quantify when bridge piers should be investigated for vehicular collision forces per AASHTO LRFD Bridge Design Specifications or be shielded with a longitudinal barrier, considering as a minimum: site condition, traffic, bridge design configurations, geometry of the roadway section passing beneath a bridge, operation characteristics, and benefit/cost and (2) guidelines for barrier selection, length-of-need, and placement for shielding bridge piers and protecting the traveling public. A number of deliverables, provided as appendices, are not published in this report but are available at the NCHRP Project 12-90 web page (https://apps.trb.org/cmsfeed/ TRBNetProjectDisplay.asp?ProjectID=3170): â¢ Appendix A: Proposed LRFD Bridge Design Pier Protection Specifications â¢ Appendix B: Proposed RDG Occupant Protection Guidelines â¢ Appendix C: Survey of Practice â¢ Appendix D: Lateral Impact Loads on Pier Columns â¢ Appendix E: Nominal Resistance to Lateral Impact Loads on Pier Columns â¢ Appendix F: Heavy-Vehicle Traffic Mix and Properties
C O N T E N T S 1 Chapter 1 Introduction 3 Chapter 2 Literature Review 3 2.1 Guidelines and Specifications 6 2.2 Capacity, Design, and Impact Loading of Bridge Piers 9 2.3 Barrier Crash-Testing Guidelines 10 2.4 Crash Data Studies 10 2.5 Exemplar Bridge Pier Crashes 18 2.6 Bridge Pier Risk Analysis 20 2.7 Benefit/Cost Versus Risk 21 2.8 Summary 22 Chapter 3 Discussion of Proposed LRFD Bridge Design Pier Protection Guidelines 22 3.1 Defining Bridge Collapse 29 3.2 Design Choice Is Structural Resistance 37 3.3 Design Choice Is Shielding with a Barrier 54 Chapter 4 Discussion of Proposed RDG Occupant Protection Guidelines 54 4.1 Proposed RDG Guidelines 54 4.2 Proposed Preliminary RDG Guideline Development 68 Chapter 5 Verification and Validation 68 5.1 Example #1: Two-Lane Undivided Rural Collector with Three Pier Columns 74 5.2 Example #2: Four-Lane Divided Rural Primary with Three Pier Columns on a Skew in the Median 78 5.3 Example #3: Six-Lane Divided Urban Primary with Four Pier Columns Offset in the Median 83 5.4 Example #4: Six-Lane Rural Primary with Two Columns in a Gore of an Off-Ramp 90 Chapter 6 Implementation Strategy 90 6.1 Products 90 6.2 Audience 90 6.3 Impediments 90 6.4 Leadership 90 6.5 Activities 91 6.6 Criteria
92 Chapter 7 Conclusion 93 References 97 Appendices 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.