Doctor of Philosophy
Civil and Environmental Engineering
Ashraf El Damatty
The majority of worldwide weather-related transmission line failures have been attributed to High Intensity Wind (HIW) events in the form of tornadoes and downbursts. The research conducted in the current thesis presents a significant development in the understanding of the structural behaviour of transmission line systems under tornado loading. A comprehensive in-house numerical model that combines the data of computational fluid dynamic (CFD) simulations of tornado wind fields with three dimensional nonlinear structural analysis modelling is developed. A three dimensional four-nodded cable element is first formulated to simulate the nonlinear large deformation behaviour of the conductors. The support provided to the conductors through the towers and the insulators is modelled using a three dimensional nonlinear spring system with stiffness dependent on the rotation experienced by the insulators. This lines model is used to assess the importance of accounting for the flexibility of the insulators and supporting towers on the lines behaviour, the effect of the tornado loads acting on conductors on the overall response of transmission towers, and the behaviour of conductors under the most critical tornado configurations. The in-house model formulation is extended by including a simulation for members of the lattice towers using three dimensional nonlinear frame elements. By including a failure model, the numerical model is employed to predict the tornado velocities at which failure initiates and to describe the progress of collapse. The in-house numerical model provides a lot of flexibility, in term of computational efficiency and in term of implementation of various failure models. A sophisticated aeroelastic model of a three span transmission line system is designed and constructed to perform a boundary layer wind tunnel test. The results of the test are used to investigate the dynamic response of the transmission line system under boundary layer wind, and to validate the developed numerical model. Finally the numerical model is used to develop a set of load configurations simulating the critical effect of F2 tornado on Lattice transmission line structures that can be implemented in the codes of design and can be used by line design engineers.
Hamada, Ahmed, "Numerical and Experimental Studies of Transmission Lines Subjected to Tornadoes" (2014). Electronic Thesis and Dissertation Repository. 2479.