Master of Engineering Science
Civil and Environmental Engineering
Kopp, Gregory A.
Internal pressures play a large role in the failure of wood-frame houses as the loss of the entire roof section becomes much more likely once the envelope of the building has been breached. Many studies have used internal pressure modelling to simulate internal pressures in structures from atmospheric boundary layer (ABL) winds, however, relatively little work has been done on this subject using tornadic winds. The objective of this study is to explore internal pressure modelling issues for tornadoes. The first part of the study uses a computational internal pressure model to simulate tornadic internal pressures of a low-rise structure; the second part uses the same model to estimate failure wind speeds of a flexible garage door, one of the critical failure modes of these structures.
The internal pressure model is able to reasonably simulate measured internal pressures in tornadic winds, although not quite as well as in ABL winds. The modelled internal pressure coefficients are mostly within 0.1 of measured internal pressure coefficients, which is similar to uncertainty bounds. When comparing ABL and tornadic building pressures, some differences are found in the mean pressures at oblique directions and the pressure distributions for normal wind directions. An analysis of the spectra of the theoretical model equation terms reveals that a lack of internal volume scaling in the tornadic tests also contributes to the differences from ABL tests.
The same theoretical model also shows that net loads on garage doors are typically reduced to 34-46% of the external pressure applied from the wind due to the internal pressure developed in the garage from the fluctuating opening size during loading. When these results are combined with experimental net pressures of garage door failures, the resulting range of expected failure wind speeds are 130-265 km/h.
Summary for Lay Audience
Tornadoes and other severe wind events pose a significant threat to residential structures across the globe, and are a prominent issue in Canada and the United States. Although the majority of the costs of damages from these events are to houses, they are not designed for them. When it comes to severe wind, the most crucial part of a residential building in terms of structural and economic integrity is its roof. The loss of a house’s roof exposes the interior to wind and rain, resulting in the destruction of contents, unsalvageable damage to the structure, and a significant threat to human life.
Wind causes pressures that push and pull on various elements of a structure. When the structure is breached by severe winds, often due to debris damage to doors and windows, or the inward collapse of a garage door, these pressures enter the building and become internal pressures that push up on the roof and out on the walls. Therefore, these openings greatly increase the chance of the loss of a house’s roof in these events. The goal of this thesis is to understand these internal pressure, and how they differ in tornadoes versus “straight-line” wind.
This thesis contains two parts. The first part examines and simulates the internal pressures in a residential structure model from a tornadic wind-tunnel test. A comparison is then made between results from tornadic and straight-line wind tunnel tests. The second part of the thesis examines the failure wind speeds of garage doors in severe wind events. This is done by combining past experimental testing of the wind-resistance of garage doors, with the theoretical model that was used to simulate internal pressures in the first part of the thesis.
This study concludes that internal pressures can be simulated in tornadic winds, despite the differences from straight-line winds. The study also gives failure wind speeds of several garage door models, which mostly align with the Enhanced Fujita Scale, the primary way of assessing damaging winds in North America. The conclusions from both parts of this thesis lead to a better understanding of the behaviour of internal pressures in tornadoes and other severe wind events. Research such as this will aid in designing more wind resilient structures for the future.
Jaffe, Aaron L., "Internal Pressure Modelling for Low-Rise Buildings in Tornadic Winds" (2020). Electronic Thesis and Dissertation Repository. 7063.
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