Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

El Damatty, Ashraf

Abstract

Tornadoes, as a form of high intensity wind (HIW) events, represent major threats to transmission line systems in many regions around the globe. Transmission line systems are among the most vulnerable structures to tornadoes due to their expansion over hundreds of kilometers and, therefore, increased exposure to such localized wind events. A comprehensive research project has been developed over the past two decades at Western University to study this problem. The research conducted in this thesis provides a significant development to the advancement of knowledge in this area through achieving three main objectives. The first objective is to assess and quantify the contribution of dynamic resonant component to the peak responses of the transmission line towers and conductors. For this purpose, a set of aeroelastic tests on multi-span transmission line and transmission tower under laboratory-simulated tornadoes is conducted and using proper instrumentations the responses of the models are measured. Such aeroelastic testing of transmission line subjected to tornadoes has not been reported previously in the literature. The second objective is to validate the numerical model previously developed in-house at Western University using the experimental measurements. The third objective is to numerically assess the effect of the variation of the tornado wind fields within the same Fujita scale on the response of transmission line structures. Finally, a comparison is carried out between the structural responses due to numerically simulated real tornado events, when normalized to the maximum velocity range of F2 tornadoes, and those estimated through the application of the load cases recently implemented in the guidelines of transmission line loading of the American Society of Civil Engineers.

Summary for Lay Audience

Tornadoes are localized wind events affecting relatively narrow paths. Considering the extensive tornado wind damages to the structures in recent years, the research related to tornado-like vortices has become a major subject in wind and structural engineering. Due the possibility of occurrence for such localized events, most structures are not designed to withstand the tornado-induced wind loads. However, for transmission line structures that are responsible for conducting electrical power from a generation source to cities with significant exposure to tornadoes, such loading should be considered. A complete self-supported transmission line system consists of supporting towers, conductors to carry the electricity, ground wires to protect direct incidence of lighting strokes, and insulators to provide a safe distance between the conductors and the towers’ cross-arms. Therefore, to fully understand the overall behaviour of such structures, multi-span lines, as well as towers, should be studied. In this thesis, an extensive study in order to analyze the static and dynamic responses of the transmission lines is carried out. Through conducting separate aeroelastic tests on isolated tower model and multi-span lines, the dynamic contribution is quantified. Also, the previously developed numerical model is validated using the test measurements. Eventually, using numerical tools, the effect of various tornadoes within the same scale on transmission lines is investigated. The results are used to compare the variation of responses to the load cases recently implemented in the guidelines of transmission line loading of the American Society of Civil Engineers.

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