Technical Report Documentation Page 1. Report No. 2. Government 3. Recipient’s Catalog No. FHWA/TX-10/0-5706-1 Accession No. 4. Title and Subtitle 5. Report Date Impact of Overhang Construction on Girder Design November 2009; Revised May 2010 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Seongyeong Yang, Todd Helwig, Rich Klingner, Michael 0-5706 Engelhardt, and Jeremiah Fasl 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Center for Transportation Research 11. Contract or Grant No. The University of Texas at Austin 0-5706-1 1616 Guadalupe, Suite 4.202 Austin, Texas 78701-1255 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Texas Department of Transportation Technical Report Research and Technology Implementation Office September 2006–August 2009 P.O. Box 5080 Austin, TX 78763-5080 14. Sponsoring Agency Code 15. Supplementary Notes Project performed in cooperation with the Texas Department of Transportation and the Federal Highway Administration. 16. Abstract Economical constraints on the design of bridges usually necessitate the use of as few girders as possible across the bridge width. The girders are typically uniformly spaced transversely with the deck extending past the fascia girders, thereby resulting in an overhang. While designers commonly employ rules of thumb with regard to the geometry of the overhang, these rules of thumb generally address only the deck in-service strength and deflection requirements, and the effect due to construction load is not considered. In particular, the impact of the overhang on fascia girder behavior during construction is not well understood. Overhang construction often leads to a torsional load on the girder system that can lead to problems in steel and concrete girder bridges during construction. The main issue with concrete girder bridges is excessive lateral rotation in the fascia girder, which can cause potential problems of construction safety and maintenance. Field problems on concrete bridges have been reported in the state of Texas where the fascia girders experienced excessive rotation during construction. For steel girder bridges, the unbalanced overhang loading can lead to both local and global instability. Locally, the overhang brackets often exert a large force on the web plate that can distort the web and increase the magnitude of the plate imperfection. Global stability problems have occurred primarily on bridge widening projects where a few girders are added to an existing bridge system. The girders in the widening are usually isolated from the existing bridge and the unbalanced load from the overhang can cause excessive twist that intensifies the global stability of the girder system. The objective of this study was to improve the understanding of the bridge behavior due to the unbalanced loading from the overhangs and to identify critical factors affecting the girder behavior. The study was also aimed at developing simple design methodologies and design recommendations for overhang construction. The research included field monitoring, laboratory tests, and parametric finite element analyses. The data from the field monitoring and laboratory tests were used to validate finite element models for both concrete and steel girder bridges. Based on the validated models, detailed parametric studies were conducted to investigate the effects of the unbalanced loading. Results from the parametric studies were used to identify the geometries of girder systems that are prone to problems with the overhangs as well as to provide design suggestions. In addition, a closed-form solution for lateral rotation in the fascia girder in a concrete girder bridge was derived using a rigid-body model, and was used to develop design methodology and design recommendations for overhang construction. 17. Key Words 18. Distribution Statement I-girder, Curved Bridge, Lifting, Erection, Construction No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161; www.ntis.gov. 19. Security Classif. (of report) 20. Security Classif. (of this page) 21. No. of pages 22. Price Unclassified Unclassified 206 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized Impact of Overhang Construction on Girder Design Seongyeong Yang Todd Helwig Richard Klingner Michael Engelhardt Jeremiah Fasl CTR Technical Report: 0-5706-1 Report Date: November 2009; Revised May 2010 Project: 0-5706 Project Title: Impact of Overhang Construction on Girder Design Sponsoring Agency: Texas Department of Transportation Performing Agency: Center for Transportation Research at The University of Texas at Austin Project performed in cooperation with the Texas Department of Transportation and the Federal Highway Administration. Center for Transportation Research The University of Texas at Austin 1616 Guadalupe, Suite 4.202 Austin, Texas 78701-1255 www.utexas.edu/research/ctr Copyright (c) 2009 Center for Transportation Research The University of Texas at Austin All rights reserved Printed in the United States of America Disclaimers Author's Disclaimer: The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official view or policies of the Federal Highway Administration or the Texas Department of Transportation (TxDOT). This report does not constitute a standard, specification, or regulation. Patent Disclaimer: There was no invention or discovery conceived or first actually reduced to practice in the course of or under this contract, including any art, method, process, machine manufacture, design or composition of matter, or any new useful improvement thereof, or any variety of plant, which is or may be patentable under the patent laws of the United States of America or any foreign country. Engineering Disclaimer NOT INTENDED FOR CONSTRUCTION, BIDDING, OR PERMIT PURPOSES. Project Engineer: Todd Helwig Professional Engineer License State and Number: Texas PE # 94280 P. E. Designation: Research Supervisor v Acknowledgments The authors would like to thank the TxDOT Project Director, Lewis Gamboa, and the other members of the project monitoring committee for their assistance and direction including John Holt, Yuan Zhao, and Wade Odell. The advice on commonly-used details and construction practices was very useful throughout the life of the project. vi Table of Contents Chapter 1. Introduction.................................................................................................................1 1.1 Overview ................................................................................................................................1 1.2 Scope ......................................................................................................................................2 1.3 Organization ...........................................................................................................................3 Chapter 2. Background .................................................................................................................5 2.1 Overhang Construction ..........................................................................................................5 2.1.1 Definition of Overhang ...................................................................................................5 2.1.2 Overhang Bracket ...........................................................................................................5 2.1.3 Construction Loads .........................................................................................................6 2.1.4 Balanced and Unbalanced Loads ....................................................................................7 2.2 Bracing for Concrete Girder Systems ....................................................................................8 2.3 Fundamentals of Overturning for Concrete Girder ..............................................................10 2.3.1 Body on Rigid Support under Pure Torque ..................................................................11 2.3.2 Body on Rigid Support under Eccentric Load ..............................................................11 2.4 Global Buckling of Steel Twin-Girder System ....................................................................13 2.5 Literature Review ................................................................................................................15 2.5.1 Overhang-Related Laboratory Studies ..........................................................................15 2.5.2 Bearing Pad Studies ......................................................................................................15 2.5.3 Overhang Design Guidelines ........................................................................................16 2.5.4 Computer Design Tool ..................................................................................................18 2.5.5 FEA modeling ...............................................................................................................18 2.6 Case Studies .........................................................................................................................19 Chapter 3. Experimental Program .............................................................................................23 3.1 Overview ..............................................................................................................................23