Doctor of Philosophy
Civil and Environmental Engineering
One of the most crucial research areas in wind engineering is tornadoes due to the widespread damages to infrastructure and the environment in North America and other parts of the world. The proper scaling of tornadoes in experimental facilities, generating tornado-like vortices (TLVs) is, therefore, an essential part of evaluating tornado-indued damages on engineered buildings. The capability of producing TLVs of length scales in the range between 1:300 and 1:150 inside the Wind Engineering, Energy and Environment (WindEEE) Dome at Western University has already been demonstrated using only one mode of the full potential of this simulator. A new mode of function of the WindEEE Dome in order to generate larger-scale TLVs in the geometric scaling of approximately 1:50 is investigated and calibrated against an actual tornado. This, never achieved before, large experimental TLV facilitates the study of tornadic actions on buildings, especially on examining an aeroelastic model against TLV-structure interactions.
On the other hand, while studies of tornado-induced structural damages tend to focus mainly on low-rise residential buildings, the current rapid expansion of city centers and the development of large-scale building complexes increase the risk of tornadoes impacting tall buildings. It is, therefore, important to determine how tornado-induced load affects tall buildings compared with those based on synoptic boundary layer winds. A 1:200 scaled model of the Commonwealth Advisory Aeronautical Research Council (CAARC) building was built and equipped with pressure taps. This model is used to compare the pressure distributions induced by Atmospheric Boundary Layer (ABL) and TLV wind flows. A new way of defining pressure coefficients for TLV flows is advanced providing a compatible way to compare ABL and TLV induced pressures on high-rise buildings. Mean and peak surface pressures are reported and compared between TLV and ABL cases. By using the newly proposed pressure coefficient approach it is shown that the mean pressure distribution becomes similar while the fluctuating pressure coefficients are different but similar in trend. The mean and 3-sec pressures induced by ABL are found to be dominant over the ones induced by TLV. These findings are expected to provide a way forward towards future code implementations.
Summary for Lay Audience
Tornadoes can cause enormous destruction to life and properties. Due to the rise in tornadic wind damage during the last decades, the study related to the behavior of tornadoes has become a crucial subject in civil and wind engineering. It is essential to understand their structure and damage impact near the ground where most engineered structures are built. However, this is almost impossible based on full-scale studies. In this regard, physical simulation of scaled-down tornadoes inside laboratories provides a huge benefit to explore them in a safe and repetitive environment. In this thesis, two important aspects of tornadoes are discussed. First, examining a new experimental simulation of tornadoes to facilitate the study of the interaction of tornado-induced winds on structures (aeroelastic model) inside the simulator. Second, exploring the pressure effects generated by tornadoes on a standard high-rise model building and comparison with straight wind pressure coefficients. The findings of this study are expected to provide a way to implement tornado effects in future building codes.
Ashrafi, Arash, "Experimental simulation of tornado-like vortices and their impact on high-rise buildings" (2021). Electronic Thesis and Dissertation Repository. 8216.