Fatigue Loading and Design Methodology for High-Mast Lighting Towers (2012)

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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 718 Fatigue Loading and Design Methodology for High-Mast Lighting Towers Robert J. Connor Steven H. Collicott Allen M. DeSchepper Ryan J. Sherman Jaime A. Ocampo Purdue university West Lafayette, IN Subscriber Categories Highways • Bridges and Other Structures TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2012 www.TRB.org  Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

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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 documented in this report was performed under NCHRP Project 10-74 by the School of Civil and Environmental Engineering at Purdue University in West Lafayette, Indiana. Purdue University is the prime contractor for this study with Dr. Robert J. Connor, associate professor of civil engineering at Purdue, as the project director and principal investigator. The co-principal investigator of this report is Dr. Steven H. Collicott from the School of Aeronautics and Astronautics at Purdue University. The other authors of this report are Allen M. DeSchepper, research assistant at the School of Civil Engineering at Purdue University, Ryan J. Sherman, research engineer at the Bowen Laboratory for Large- Scale Civil Engineering Research at Purdue University, and Jaime A. Ocampo, research assistant at the School of Aeronautics and Astronautics at Purdue University. Special thanks are extended to Joe Mueller, field and lab engineering technician at the Bowen Laboratory, for his assistance in implementing the field monitoring program. CRP STAFF FOR NCHRP REPORT 718 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs Waseem Dekelbab, Senior Program Officer Danna Powell, Senior Program Assistant Eileen P. Delaney, Director of Publications Hilary Freer, Senior Editor NCHRP PROJECT 10-74 PANEL Field of Materials and Construction—Area of Specifications, Procedures, and Practices Gregg C. Fredrick, Wyoming DOT, Cheyenne, WY (Chair) Ahmad Abu-Hawash, Iowa DOT, Ames, IA Fouad H. Fouad, University of Alabama – Birmingham, Birmingham, AL Carl J. Macchietto, Valmont Industries, Inc., Valley, NE Christopher E. Meyer, Kansas DOT, Topeka, KS Justin M. Ocel, FHWA, McLean, VA Andre V. Pavlov, Florida DOT, Tallahassee, FL Bryan Spangler, Michael Baker Jr. Inc., Harrisburg, PA Scott J. Walton, Lower Colorado River Authority, Austin, TX Gary Moss, FHWA Liaison Stephen F. Maher, TRB Liaison

This report provides criteria for the fatigue design of high-mast lighting towers (HMLTs). The report also includes a series of proposed revisions with associated commentary to the fatigue design provisions of the AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals. In addition, to ensure the fatigue design provisions are properly implemented into practice, design examples are also provided. The material in this report will be of immediate interest to highway design engineers. Failures of high-mast lighting towers (HMLTs) in several states have raised questions as to the robustness and safety of the existing inventory of these structures. Fatigue failures have occurred at the base plate-to-column weld, handhole detail, and anchor rods. Several of the failed poles had been in service for less than 5 years. Based on field observations and forensic analysis of high-mast lighting poles, it is believed that wind-induced vibrations have a significant influence on the fatigue life. Neither the magnitude of the loads or the frequency of the application is understood. The current AASHTO specification does not adequately address these topics. Research was performed under NCHRP Project 10-74 by Dr. Robert Connor, the School of Civil Engineering at Purdue University in West Lafayette, IN. The objectives of NCHRP Project 10-74 were to develop (1) loading and analysis criteria for use in the fatigue design of high-mast lighting towers, (2) a design method and proposed specifications for high- mast lighting towers, and (3) design examples. These research objectives were achieved by laboratory testing to investigate the effects of wind gusts (i.e., buffeting), vortex shedding, and associated dynamic oscillations; and a long-term field monitoring study gathered wind and strain gage data from eleven different HMLTs over the course of 2 years. Fourteen additional HMLTs were tested to determine their dynamic properties. Additionally, wind tunnel tests were completed to examine flow separation and wake characteristics of various multi-sided, tapered, tube geometries. A number of deliverables are provided as appendices. Only Appendix A—HMLT Fatigue Design Examples and Appendix B—Proposed Specification and Commentary are published herein. Other appendices are not published but are available on the TRB website and can be found by searching on the title of the report. These appendices are titled as follows: • APPENDIX C—Stress Range Histogram Data and Regression • APPENDIX D—Wind Rosettes for Percent Occurrence and Mean Wind Speed • APPENDIX E—Site Specific Instrumentation Plans • APPENDIX F—Across Wind Excitation Algorithm • APPENDIX G— HMLT Modal Frequency Algorithm • APPENDIX H—HMLT Fatigue Life Evaluation • APPENDIX I—Aerodynamic Pressure and Hotwire Data F O R E W O R D By Waseem Dekelbab Staff Officer Transportation Research Board

1  Summary 2 Chapter 1  Background 2 1.1 Problem Statement 2 1.2 Objectives 3 1.3 Notes and Nomenclature 4 Chapter 2  Research Approach 4 2.1 Field Monitoring Program 10 2.2 Aerodynamic Testing Program 15 2.3 Factors Affecting Fatigue Loading of HMLTs 28 2.4 Fatigue Wind Load Methodology 34 Chapter 3  Findings and Applications 34 3.1 Results of Field Tests 47 3.2 Results of Aerodynamic Tests 56 3.3 Development of Proposed Specification 64 3.4 Large-Amplitude Oscillation 65 3.5 Fatigue Life Evaluation of Existing HMLTs 70 Chapter 4  Conclusions and Recommendations 70 4.1 Conclusions 71 4.2 Suggested Research 72  References A-1 Appendix A  HMLT Fatigue Design Examples B-1 Appendix B  Proposed Specification and Commentary C O N T E N T S Note: Many of the photographs, figures, and tables in this report 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.