Vortices are a swirling motion or pattern of the wind. The most serious situation arises when the vortex-shedding frequency synchronizes with the natural period of vibration in the pole, which can ultimately fatigue the pole to structural failure.
Light Pole Design
Pole design requires consideration of field conditions such as wind speed (sustained/gusts), pole height, appendages and local conditions. Wind induced vibration is a local, site-specific condition that may be overlooked by those selecting a pole because it is difficult to predict accurately. Poles which perform satisfactory in many installations all across the country may experience destructive vibration at a select location for no apparent reason. Typically, poles are designed or selected based on AASHTO (American Association of State Highway and Transportation Officials) criteria. The standards and codes take into account direct wind pressures on the pole and luminaire, the associated bending, shear, axial and torsional stresses on the pole, secondary moment effects (the pole and fixture being off center of the pole base when the wind deflects the pole) and the effect of heat on the base material in the area adjacent to the weld.