Thesis Format
Integrated Article
Degree
Doctor of Philosophy
Program
Civil and Environmental Engineering
Supervisor
Hangan, Horia
Affiliation
Ontario Tech University
2nd Supervisor
Hong, Han-Ping
Affiliation
Harbin Institute of Technology
Co-Supervisor
3rd Supervisor
Zhou, Wenxing
Co-Supervisor
Abstract
Low-rise wood-frame residential buildings, which constitute most buildings affected by tornadoes, are highly vulnerable to tornado-induced damage. Evidence indicates that the wind velocities impacting these buildings during tornadoes are often comparable to hurricane winds, for which effective design provisions and mitigation measures exist. In this research, pressures were measured at the WindEEE Dome during interactions of tornado-like vortices (TLVs) with a scaled model of part of the Dunrobin community, struck by an EF3 tornado in September 2018. Three swirl ratios were tested with TLVs moving along various paths and translation velocities. Measured loads were compared with design loads specified in Chapter 32 of ASCE/SEI 7-22 for different internal pressure scenarios simulated using the multiple discharge equations (MDE). An iterative method was developed to estimate tornado-velocity gust factors from wind tunnel data. Results showed that uplift forces on the entire roof in scenarios with one dominant opening were 44\% to 63\% higher than in the distributed leakage scenario, emphasizing the importance of maintaining the envelope's integrity. Revised values for internal and external pressure coefficients or correction factors could enhance the standard’s ability to provide safer design loads. ASCE/SEI 7-22 uses pressure coefficients from atmospheric boundary layer (ABL) wind tunnels to evaluate tornado-induced loads. This approach is not supported by evidence, as most studies suggest pressure distributions differ between tornadoes and straight-line winds. However, this study's comparison of ABL and TLV-induced pressure coefficients revealed that for radial distances larger than 0.6 times the core radius, TLV-induced peak pressure coefficients are lower in absolute value than those from ABL winds. A 1.4 safety factor applied to ABL coefficients sufficiently accounts for most loading scenarios at these distances. Finally, a method was developed to stochastically simulate the pressure field induced by TLVs on the model buildings. This approach could reduce testing costs by enabling data extrapolation for Monte Carlo simulations. While the method shows promise in predicting the empirical extreme value distribution (EEVD) of minimum pressures, further work is required to validate and improve it.
Summary for Lay Audience
Tornadoes can cause severe damage to homes, especially low-rise, wood-frame buildings, which are the most commonly affected. Traditionally, tornadoes were thought to be too rare and powerful to justify specific design considerations. However, recent evidence shows that the wind speeds most homes experience during tornadoes are similar to those in hurricanes, where simple, effective design measures have been implemented. To better understand tornado impacts, we recreated tornado winds at a reduced scale in a specialized facility and tested their effects on a model of a neighborhood struck by a tornado in 2018. We studied how different tornado paths and wind characteristics affected pressures on the model buildings. A key finding was that when a building had a broken window or door, the upward forces on the roof could be up to 63\% higher than when the structure was intact. This highlights the importance of protecting windows and doors from flying debris during tornadoes. Adjustments to U.S. building codes could make homes safer in tornado-prone areas. Unlike common straight-line winds, tornado winds have a curved flow. This difference complicates the use of current design techniques based on straight-line winds, which remain common due to their simplicity. Our research found that while tornado wind pressures are distinct when a tornado is close, beyond a certain distance from its center, the forces are actually smaller than those caused by straight-line winds. Adding a safety factor to current standards could improve their applicability to tornado conditions. Finally, we developed a new method to simulate tornado pressures on buildings using a small number of experiments. This method can reduce testing costs by generating artificial experiments and is a promising tool for future research and design. However, further refinement is needed to ensure its accuracy.
Recommended Citation
Narancio, Edmundo G., "Tornado Impacts on Communities" (2025). Electronic Thesis and Dissertation Repository. 10804.
https://ir.lib.uwo.ca/etd/10804
Creative Commons License
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