Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Kopp, Gregory A.

Abstract

During extreme wind events, roofing failures may lead to damage of the whole structure. In order to alleviate the effect, surface pressure coefficients on the roofs have been extensively investigated. This research aims to determine the roof pressures acting on low-rise buildings with consideration of the effects of turbulence (terrain). Pressure measurements, as well as wind speed data, were taken at the Boundary Layer Wind Tunnel Laboratory (BLWTL) of the University of Western Ontario (UWO) to examine the influence of turbulence level (i.e., terrain condition) on the critical wind directions corresponding to the largest surface roof pressure coefficients for various upstream boundary layer conditions. In addition, plan dimensions and eave heights of the building were also varied. Generally, corner vortices play a vital role in generating larger suction pressures on the roof surface in flat terrain. Moreover, separation bubble at the leading edge of low-rise buildings is also significant to take into consideration for winds normal to the walls. Our objective is to examine these points in terms of area-averages used in design. The results indicate that corner vortices control larger area on the roof surface among all angles of attack in lower turbulence flow (i.e., flat terrain), whereas this effect is reduced in higher turbulence level (i.e., suburban terrain) for all plan shapes. In addition, the size of the corner vortices along both edges of the roof increases with building height for low-rise buildings, consistent with the new requirements in ASCE 7 – 16. It is also found that the critical wind directions depend significantly on the turbulence level and building height. The critical wind directions for the corner zones of low-rise building roofs are primarily due to oblique angles (i.e., corner vortices), while they are normal wind directions (i.e., bubble separation) for the edge, and interior zones, when the tributary areas are small. The magnitude of peak pressure coefficients, GCp, depend more on the integral length scales compared to the turbulence intensity, which may be important in some design scenarios.

Available for download on Monday, October 01, 2018


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