The Effect of Wind Induced Vibrations on Highway Lighting Bulbs

This study was initiated to investigate the possible causes for 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 feet (36.6 meters) high and the luminaries are attached to a ring assembly that can be lowered for lamp replacement. The study consisted of two methods of analysis. The first step was to analyze numerically the complete system by employing a finite element code and to compute the motions of the complete system under typical wind conditions at the site (wind velocities between 5 to 60 mph). The second phase of the study consisted of an experimental effort during which one of the illumination towers was instrumented and motion data was 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 acescent of modal effects, and comparisons between experimental and numerical results.