Reduction of Wind-Induced Vibrations in High-Mast Light Poles - FHWA-WY-10/02F
High-mast light poles are frequently used in areas where widespread illumination is required, such as along interstates and at major highway interchanges. The structures' heights are large relative to their cross-sectional dimensions, and, consequently, they are flexible and sensitive to wind loading. A number of failures of high-mast structures have occurred due to fatigue cracking. These failures have been linked to buffeting and vortex shedding loads.
The primary study objective is to characterize the dynamic effects of wind-induced vibrations on high-mast structures in Laramie, WY, and to propose several retrofits that increase the aerodynamic damping, thereby reducing vibrations. A 120-ft tall high-mast pole was monitored to determine its dynamic characteristics. The pole was then retrofitted with helical strakes, ribbon dampers, a perforated shroud, and surface roughness, and the difference in the dynamic response of the retrofitted and unretrofitted pole under similar wind conditions was examined. The perforated shroud covering approximately 13% of the pole prevented lock-in under the wind conditions tested.
A second pole was monitored and exhibited a drastically different response. It was observed that traffic vibrations exciting the pole at higher frequencies prevented lock-in from occurring. The phenomenon has not previously been observed as reported in the literature.