Evaluation of the Ultimate Collapse Load of a High-Voltage Transmission Tower under Excessive Wind Loads

Several high-voltage transmission towers failed under excessive wind loads in a mountainous and exposed area. This study discusses the efficient and reliable modeling of lattice towers dominantly loaded by wind, a scenario which led to a collapse cascade in a high-voltage transmission line. The ultimate load-bearing capacity had to be estimated and the failure positions identified. Finite Element Analysis was employed through static analyses, Linear Buckling Analyses (LBA) and RIKS analyses (Arc-Length method) in Abaqus 2021. With the purpose of improving the accuracy in the simulation of structural instabilities of complex lattice structures, the model sensitivity to superimposed geometrical imperfections and the joint stiffness of the truss connections were investigated in brace and lattice structure sub-assemblies. Afterwards, linear analyses and non-linear analyses with imperfections were performed on the single tower model. The analysis proved that solely excessive wind can cause such failure on the lattice structures, and the critical structural elements have been correctly identified. The investigation proved that the towers had not been under-designed with respect to the standards valid at the time of erection. However, they were not designed for this exceptional storm event, and evidence was provided that wind alone could bring about the collapse. It is nevertheless not recommended to increase the safety factors in general for the design of such structures, but to base the assumed loading on actual and local wind and service load measurements.

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