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 in the book. 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; and • APPENDIX I–Aerodynamic Pressure and Hotwire Data. (Author/publisher)
Samenvatting