Failure Characteristics of Transmission Towers Subjected to Downbursts

Abstract

Downbursts are recognized as a significant threat to safety of transmission towers. The difference between downburst and boundary layer wind profiles will lead to different failure modes and regions of damage of a transmission tower. To account for differences of wind profiles and failure modes, the different design wind loads are proposed, and a novel analytical framework is formulated for checking the section wind-resistance capability. The framework is useful for checking strength of transmission towers under downbursts. It has been found that the peak values of section moments exceed the ultimate section moment capability at about a third of the tower height under downbursts, while failure occurs in the bottom panel of tower under boundary layer winds. The results are consistent with the fact that regions of damage for most collapsed high-rise transmission towers under downbursts were indeed in lower-middle height of tower.