Behaviour of guyed transmission line structures under tornado wind loading

Localized severe wind events, in the form of downbursts and tornadoes, are responsible of the majority of transmission line structures failures in many regions around the globe. The wind profiles associated with these events are different than the conventional boundary layer wind profile that is typically used to design the supporting towers. A comprehensive study is presented in this paper to assess and understand the performance of transmission line structures under tornado loading. The study is conducted numerically using a three-dimensional finite-element model and incorporates velocity fields for various tornado scales, which are based on a computational fluid dynamics analysis. The numerical model accounts for the nonlinear behaviour of the conductors, ground-wires, and supporting guys. An extensive parametric study is conducted by varying the location of F4 and F2 tornadoes relative to the transmission line system. The study investigates the variation of the tower members’ internal forces with the tornado locations. It also provides an insight about the structural response of the towers under tornado wind loads. The dynamic effect associated with the translation motion of the tornado is assessed. Finally, the results of the parametric study are used to assess the sensitivity of the members’ peak forces with the parameters defining the location of the tornado relative to the line.