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PROCEEDINGS OF THE THIRTEENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING
Edited by: B.H.V. Topping and Y. Tsompanakis
Failure Analysis of Transmission Towers subject to Downbursts
W. Qu1, Y.-L. Pi2 and M.A. Bradford3
1Hubei Key Laboratory of Roadway Bridge and Structure Engineering, Wuhan University of Technology, China
W. Qu, Y.-L. Pi, M.A. Bradford, "Failure Analysis of Transmission Towers subject to Downbursts", in B.H.V. Topping, Y. Tsompanakis, (Editors), "Proceedings of the Thirteenth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 48, 2011. doi:10.4203/ccp.96.48
Keywords: downbursts, wind-resistance capability, section moment capability, failure.
Failures of lattice transmission towers induced by winds have been reported from time to time throughout the world [1,2]. Because of their high flexibility and low damping, transmission towers are prone to wind excitations and may fail under strong wind events, which may lead to adverse economical and social consequences.
Many of wind-related failures of transmission lines are caused by downbursts. An investigation of the collapse of transmission towers due to downbursts  has shown that damage of the members in the second and third panels above the bottom was quite significant, but no damage was observed in the bottom panel of the tower. This indicates that the failure mode and damage zones in transmission towers due to downbursts are quite different from those caused by boundary layer winds. Therefore, investigations are much needed to prevent transmission tower failure caused by downbursts, and appropriate methods for designing transmission towers subject to downbursts need to be developed.
Downbursts occur often in association with thunderstorms where the weight of the precipitation and the cooling arising from microphysical processes act together to accelerate the air downwards. They are characterised by a strong localised down-flow and an outburst of strong winds near the surface as the downdraft air is forced to spread horizontally near the ground level.
This paper proposes a novel computational analytical framework for both determining the section wind-resistance capability of transmission towers and for investigating the possible damage zones in the tower subject to downbursts and boundary layer wind loads. A model for the ultimate section moment capacity is proposed and the wind-induced section moments along the tower height are analysed by considering the influence of non-linear deformations of the transmission lines. The section moments produced by downbursts and boundary layer wind loads are compared with the ultimate section moment capacity to examine the structural safety of the tower against failure, and thereby to determine the extent of the zones of damage. From these findings, it can be concluded that the downburst wind loads should to be considered in the strength check of transmission towers.
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