Development of a Semiprescriptive Selection Procedure for Reliability-Based Fatigue Design of High-Mast Lighting Structural Supports

High mast lighting structures are being used to provide illumination for large intersections, particularly for highways located in rural areas. These structures, ranging from approximately $15–40\mathrm{m}$ $(50–130\mathrm{ft})$ in height, are exposed to high wind forces that in turn produce a tremendous number of loading cycles each year. A recent high mast lighting structural support failure in the high plains of Colorado near Denver International Airport provided the impetus for this study. These high-mast structures are less than one meter $\left(3.28\mathrm{ft}\right)$ in diameter and are quite flexible relative to many civil engineering structures. This flexibility results in large deformations when compared to their diameter, i.e., when combined with the height of these structures. Furthermore, large forces and moments at the base are produced that result in large stresses and stress reversals during multimode excitation. This paper presents the process and results for the development of a reliability-based design procedure for high-mast lighting structural supports based on fatigue life. The resulting procedure is prescriptive in that a series of design charts result from full nonlinear finite element analysis. The loading on the slender body is characterized by Morison’s equation, essentially providing the nonlinear loading relationship for the wind on the moving structure. Then, a well-known random vibrations approach was coupled with Miner’s rule to estimate the fatigue life of the structural support. Several illustrative design examples are presented and shown to compare very well with full simulations.