The present study was initiated to investigate the possible causes of excessive lamp failure rates on high-mast illumination towers in the state of Minnesota. This type of highway illumination system consists of high masts on which there are either three or four luminaires. The masts are 120 ft high and the luminaires are attached to a ring assembly that can be lowered for lamp replacement. The study consisted of two methods of analysis that were combined for obtaining information on the motion of the towers and the luminaires. The first step was to analyze numerically the complete system by employinga finite element code and to compute the motions of the complete system under typical wind conditions at the site (wind velocities between 5 and 60 mph). The numerical results provided information about lamp accelerations and the frequencies of motion. The second phase of the study conisted of an experimental effort during which one of the illumination towers was instrumented and motion data were collected for various wind conditions. The final phase of the study included the evaluation of the numerical as well as the experimental data that had been obtained from the preceding steps. This evaluation included the identification of modes of vibration in the frequency domain, filtering of data for assessment of modal effects, and comparisons of experimental and numerical results.(A).
Abstract