Performance-Based Design of Transmission Line Structures Under Tornadoes and Downbursts

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Downbursts and tornadoes belong to a category of storms that are referred to as High Intensity Winds (HIW). The proposed research focuses on the effect of these extreme events on transmission line (TL) structures. Failure incidents of those structures during HIW events have been observed on an annual basis in Canada and amongst other countries, resulting in huge economic losses. Western has consistently taken the lead in research related to the effect of wind on structures. Its research capabilities have been augmented by the establishment of the WindEEE dome, a $30M facility representing the first chamber in the world for testing structures under large scale HIW. The HIW fields consist of a mean and a turbulent component, which are both dependent on whether the site terrain is open, suburban or urban. In his previous DG, the applicant focused on the effect of the mean component of the HIW fields on TLs in the case of open terrain. With the availability of HIW field data from the WindEEE, the research will be taken to a higher level. Numerical simulations will be conducted for TLs using HIW fields corresponding to different terrains, while varying the location of the event. Critical locations leading to peak forces in the tower members will be identified. The analyses will be conducted considering the dynamic effects resulting from turbulence. The outcome will take the form of load cases simulating the critical effects of the mean component of HIWs for various terrain conditions, together with gust response factors magnifying these loads to account for dynamic effects. When a transmission tower collapses, the de-attachment of the connected conductors leads to the creation of unbalanced longitudinal forces acting on subsequent towers causing a chain of tower failures. A novel nonlinear numerical model will be developed to simulate the progressive collapse of an entire line system, which will be validated experimentally through tests conducted at WindEEE. This experimental program will take wind testing to new horizons for failure investigation, benefiting from the availability of a large scale wind testing facility. Since a TL extends for hundreds of kilometers, it could be very expensive and impractical to design all the towers of a line to remain undamaged under extreme HIW events. A performance-based design procedure will be developed as described in this proposal. The desired performance criteria will involve the minimization of the effect and the duration of the interruption of electricity due to the failure of a portion of the line as well as the containment of such a failure. The research will lead to finding a sustainable solution to a worldwide problem, will set up a framework for a performance-based design of structures under wind loading, and will provide training for 6 graduate students in state-of-the-art numerical and experimental techniques, which will address a very practical and pressing problem.