Rotation Limits for Elastomeric Bearings (2008)

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TRANSPORTATION RESEARCH BOARD 2007 EXECUTIVE COMMITTEE* OFFICERS CHAIR: Linda S. Watson, CEO, LYNX–Central Florida Regional Transportation Authority, Orlando VICE CHAIR: Debra L. Miller, Secretary, Kansas DOT, Topeka EXECUTIVE DIRECTOR: Robert E. Skinner, Jr., Transportation Research Board MEMBERS J. Barry Barker, Executive Director, Transit Authority of River City, Louisville, KY Michael W. Behrens, Executive Director, Texas DOT, Austin Allen D. Biehler, Secretary, Pennsylvania DOT, Harrisburg John D. Bowe, President, Americas Region, APL Limited, Oakland, CA Larry L. Brown, Sr., Executive Director, Mississippi DOT, Jackson Deborah H. Butler, Vice President, Customer Service, Norfolk Southern Corporation and Subsidiaries, Atlanta, GA Anne P. Canby, President, Surface Transportation Policy Partnership, Washington, DC Nicholas J. Garber, Henry L. Kinnier Professor, Department of Civil Engineering, University of Virginia, Charlottesville Angela Gittens, Vice President, Airport Business Services, HNTB Corporation, Miami, FL Susan Hanson, Landry University Professor of Geography, Graduate School of Geography, Clark University, Worcester, MA Adib K. Kanafani, Cahill Professor of Civil Engineering, University of California, Berkeley Harold E. Linnenkohl, Commissioner, Georgia DOT, Atlanta Michael D. Meyer, Professor, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta Michael R. Morris, Director of Transportation, North Central Texas Council of Governments, Arlington John R. Njord, Executive Director, Utah DOT, Salt Lake City Pete K. Rahn, Director, Missouri DOT, Jefferson City Sandra Rosenbloom, Professor of Planning, University of Arizona, Tucson Tracy L. Rosser, Vice President, Corporate Traffic, Wal-Mart Stores, Inc., Bentonville, AR Rosa Clausell Rountree, Executive Director, Georgia State Road and Tollway Authority, Atlanta Henry G. (Gerry) Schwartz, Jr., Senior Professor, Washington University, St. Louis, MO C. Michael Walton, Ernest H. Cockrell Centennial Chair in Engineering, University of Texas, Austin Steve Williams, Chairman and CEO, Maverick Transportation, Inc., Little Rock, AR EX OFFICIO MEMBERS Thad Allen (Adm., U.S. Coast Guard), Commandant, U.S. Coast Guard, Washington, DC Thomas J. Barrett (Vice Adm., U.S. Coast Guard, ret.), Pipeline and Hazardous Materials Safety Administrator, U.S.DOT Joseph H. Boardman, Federal Railroad Administrator, U.S.DOT Rebecca M. Brewster, President and COO, American Transportation Research Institute, Smyrna, GA Paul R. Brubaker, Research and Innovative Technology Administrator, U.S.DOT George Bugliarello, Chancellor, Polytechnic University of New York, Brooklyn, and Foreign Secretary, National Academy of Engineering, Washington, DC J. Richard Capka, Federal Highway Administrator, U.S.DOT Sean T. Connaughton, Maritime Administrator, U.S.DOT Edward R. Hamberger, President and CEO, Association of American Railroads, Washington, DC John H. Hill, Federal Motor Carrier Safety Administrator, U.S.DOT John C. Horsley, Executive Director, American Association of State Highway and Transportation Officials, Washington, DC J. Edward Johnson, Director, Applied Science Directorate, National Aeronautics and Space Administration, John C. Stennis Space Center, MS William W. Millar, President, American Public Transportation Association, Washington, DC Nicole R. Nason, National Highway Traffic Safety Administrator, U.S.DOT Jeffrey N. Shane, Under Secretary for Policy, U.S.DOT James S. Simpson, Federal Transit Administrator, U.S.DOT Carl A. Strock (Lt. Gen., U.S. Army), Chief of Engineers and Commanding General, U.S. Army Corps of Engineers, Washington, DC Robert A. Sturgell, Acting Administrator, Federal Aviation Administration, U.S.DOT *Membership as of October 2007.

TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2008 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 596 Subject Areas Bridges and Other Structures Rotation Limits for Elastomeric Bearings John F. Stanton Charles W. Roeder Peter Mackenzie-Helnwein Christopher White Colin Kuester Brianne Craig DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING UNIVERSITY OF WASHINGTON Seattle, WA 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. 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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 596 Project 12-68 ISSN 0077-5614 ISBN 978-0-309-09918-9 Library of Congress Control Number 2008920212 © 2008 Transportation Research Board COPYRIGHT PERMISSION 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. 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CRP STAFF FOR NCHRP REPORT 596 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs David B. Beal, Senior Program Officer Eileen P. Delaney, Director of Publications Margaret B. Hagood, Editor NCHRP PROJECT 12-68 PANEL Field of Design—Area of Bridges Ralph E. Anderson, Illinois DOT, Springfield, IL (Chair) Thomas K. Koch, North Carolina DOT, Raleigh, NC Brad J. Boehm, California DOT, El Dorado Hills, CA Timothy Bradberry, Texas DOT, Austin, TX Richard A. Bray, H.W. Lochner, Inc., Rocky Hill, CT Robert A. Burnett, New York State DOT, Albany, NY Ralph J. Dornsife, Washington State DOT, Tumwater, WA Neil M. Hawkins, University of Illinois - Urbana-Champaign, Urbana, IL Jose A. Lopez, New Jersey DOT, Trenton, NJ William Henry Pate, Tennessee DOT, Nashville, TN Hamid Ghasemi, FHWA Liaison Stephen F. Maher, TRB Liaison AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 12-68 by the Department of Civil and Environmental Engineering at the University of Washington (UW). Dr. John Stanton, Professor of Civil Engineering at UW, was the Project Director and co-Principal Investigator. The other authors of this report are Dr. Charles Roeder, Professor of Civil Engineering at UW and co-PI, Dr. Peter Mackenzie-Helnwein, Assistant Professor of Civil Engineering at UW and co- PI, Mr. Christopher White, Mr. Colin Kuester and Ms. Brianne Craig, all Graduate Student Assistants and MSCE recipients at UW. The work was done under the direction of Professors Stanton, Roeder and Mackenzie-Helnwein. The assistance with the laboratory work of Mr. Vince Chaijaroen, Laboratory Man- ager, Mr. Kevin Soderlund, Instrument Maker, and Mr. Kyle Twitchell, Undergraduate Assistant, is grate- fully acknowledged. The specialty test rig that made possible the extensive cyclic testing was based on a concept developed by Mr. Ken Olson and built by Mr. Tim Rodgers, both of whom received their MSCE degrees at UW. 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 elastomeric bearing design procedures suitable for adoption in the AASHTO LRFD Bridge Design Specifications. The report details the experimental and ana- lytical program used to develop the design procedures. The material in this report will be of immediate interest to bridge designers. Bridges experience translational movements and rotations caused by creep and shrink- age, thermal effects, traffic loading, initial construction tolerances, and other sources. Bridge bearings are designed and built to accommodate these movements and rotations while sup- porting required gravity loads and providing the necessary restraint to the structure. Elas- tomeric bearings accommodate movement and rotation by deformation of the elastomer. The bearing must be designed to control the strains and deformations in the elastomer to assure a long service life and good bearing performance. AASHTO’s current elastomeric bearing design limits were developed in NCHRP Project 10-20, but bearing rotation was not considered a high-priority issue for that project. As a result, virtually no experimental research on elastomeric bearing rotation was performed, and design provisions were developed based on conservative interpretation of past theoret- ical results. For example, the experiments used to validate the tension limits were done nearly 60 years ago and used very small laboratory samples, which are not at all similar to bridge bearings. The limits on lift off, uplift, and shear strain in the elastomer are known to be controlling criteria for elastomeric bearing rotation, but the equations used in the cur- rent AASHTO provisions have not been verified experimentally and are believed to be overly conservative. In particular, the load combination of low axial load plus high rotation that may be experienced during construction leads to potential lift-off. Under the 2005 LRFD Specifications, this load combination often unreasonably controlled the bearing design or prevented the use of an elastomeric bearing altogether. The present conservatism in the rotational design limits results in more expensive bearings and may limit their use. The increased bearing cost is due in part to additional elastomeric mate- rial and quality-assurance testing. In some cases, expensive high-load multi-rotational bearings must be used to satisfy the design requirements. For these reasons, it was important to re- evaluate rotational design limits and quality-assurance requirements for elastomeric bearings. The objective of NCHRP project 12-68 was to develop recommended provisions and commentary for rotational design capacity and quality assurance of elastomeric bearings suitable for inclusion in the AASHTO LRFD specifications. This objective has been accom- plished. This research was performed by the University of Washington, Seattle, Washing- ton. The report fully documents the experimental and analytical program used to develop the design procedures. F O R E W O R D By David B. Beal Staff Officer Transportation Research Board

C O N T E N T S 1 Summary 3 Chapter 1 Introduction and Research Approach 3 1.1 Bridge Bearings 3 1.2 Bearing Mechanics 4 1.3 Failure Modes, Analysis, and Design Criteria 7 1.4 Current Design Specifications 7 1.4.1 Method A 8 1.4.2 Method B 8 1.5 Motivation for this Study 9 1.6 Previous Studies 9 1.7 Survey of Practice 9 1.8 Goals, Scope, and Organization of Report 10 Chapter 2 Findings 10 2.1 Physical Testing 14 2.2 Finite Element Analysis 14 2.2.1 Objectives 15 2.2.2 Modeling Techniques 15 2.2.2.1 Geometry and Boundary Conditions 15 2.2.2.2 Materials 16 2.2.2.3 Loading 16 2.2.3 Analyses Conducted 16 2.2.4 Results 16 2.2.4.1 Evaluation and Validation of Stiffness Coefficients 20 2.2.4.2 Bearings with Rigid External Plates—Uplift 21 2.2.4.3 Significance of Nonlinear Effects—Superposition Error 23 2.2.5 Discussion 23 2.3 Development of Design Procedures 23 2.3.1 Computation of Shear Strains using the Linearized Theory 24 2.3.2 Shear Strain Capacity 27 2.3.3 Analysis of Rotation and Axial Force Demand 28 2.3.4 Evaluation of the Design Model 28 2.4 QA/QC Issues 28 2.4.1 Quality of Current Elastomeric Bearings 29 2.4.2 Test Requirements 30 2.4.3 Number of Tests Required 31 2.4.4 Material Test Requirements 32 2.4.5 Very Large or Unusual Bearings