Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
1 S U M M A R Y The objective of this research was to develop new specifications for structural supports for highway signs, luminaires, and traffic signals. The AASHTO load and resistance factor designâluminaires, traffic signals, and signs (LRFD-LTS) specifications were written to incorporate an LRFD approach to design. Survey results indicated that present designs were performing well, with the exception of fatigue where winds are persistently active. The LRFD-LTS specifications were calibrated using the AASHTO STD-LTS (standard LTS specifications) allowable stress design method as a baseline. The variabilities of the loads and resistances were considered in a rigorous manner. The wind loads have higher variabilities than the dead loads. Therefore, structures with a high wind-to-total-load ratio will require higher associated resistances compared to allowable stress design. This increase is on the order of 10% for high-mast structures. For structures with a wind-to-total-load ratio of approximately 0.5 (e.g., cantilever structures), the required resistance does not change significantly. The reliability index for the LRFD-LTS specifications is more uniform over the range of load ratios of practical interest than the current allowable stress designâbased specifications. This uniformity was one of the primary goals of this project. Characteristics and outcomes of the LRFD-LTS specifications are: 1. The organization has been reformatted so that all sections are consistent, 2. Variable definitions and nomenclature are located in a consistent manner, 3. Improved text in the STD-LTS for editorial changes, 4. Updated references, including ASCE/SEI (Structural Engineering Institute) 07-10 wind hazard maps, 5. Latest fatigue research, 6. Most recent U.S. specifications for steel and aluminum, 7. Rigorous calibration, 8. Improved uniformity of reliability over typical wind load to total load ratios, 9. New sections on fabrication, materials, and detailing, construction, inspection, and asset management, 10. New appendix on an alternate method for fatigue design/evaluation, 11. Core element system is defined in a new appendix, and 12. Smart flags and environmental definitions are defined to support the core elements. Development and Calibration of AASHTO LRFD Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals
2There are 16 example designs provided (in Appendix C, available on the TRB website by searching for NCHRP Report 796 at www.TRB.org) to demonstrate the LRFD-LTS speci- fications. These examples address the typical systems in use today, and are included for all materials. Finally, calibration is described in Appendix A. The interested reader and future specification committees should find this document to be of benefit.
