Revealing the influence of wind vortex shedding on the stressed-strained state of steel tower structures with solid cross-section

Abstract

This work investigated the effect of vortex shedding during the action of wind on tower structures with a solid cross-section. Failure to take into account this influence, together with the manifestation of the phenomena of physical wear of structures during long-term operation, can lead to building accidents. The object of the research are tower structures with a solid cross-section, which are widely used in modern infrastructure ‒ advertising pylons with a transparent advertising structure with a height of about 12, 22, 25 m, and a flagpole with a height of 48 m. The most frequent manifestations of oscillations according to the first natural frequency and shape have been considered, which occur even with moderate winds and when a large number of oscillation cycles occur. In this work, the number of oscillating cycles per year was determined and estimated based on the archive of meteorological observations. It was found that the number of oscillating cycles due to the action of wind excitation for the example of the structures under study is from 2.6 to 14.4 million per year, which requires the mandatory limitation of stresses in the parts of structures during the design to enable their durability. The magnitude of forces from vortex shedding for the studied structures ranges from 2.9 to 43.5 % of the forces caused by the influence of the frontal wind, depending on the height of the structure. Thus, it was found that the influence of vortex shedding is very insignificant for structures up to 12–15 m high and increases for structures 20 m and higher. Rational forms of the cross-sections of structures were established to reduce the influence of vortex shedding ‒ these are cross-sections of a circular and a cross-section close to it. In a general formulation, these are sections for which peak stresses relative to forces in one plane fall into the neutral zone for stresses from forces in another plane. Recommendations have been also given on the simultaneous consideration of forces from the action of frontal wind on the structure and vortex shedding since both manifestations of wind action on tower structures cannot be separated