Wind loading of porous fabric roofs

Vitale, Andrew Michael. (2001). Wind loading of porous fabric roofs PhD Thesis, School of Engineering, The University of Queensland.

       
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Author Vitale, Andrew Michael.
Thesis Title Wind loading of porous fabric roofs
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 2001
Thesis type PhD Thesis
Supervisor Chris Letchford
Faris Albermani
Total pages 283
Language eng
Subjects 870299 Construction Design not elsewhere classified
290201 Aerodynamics
Formatted abstract

Porous fabric roofs are a cost-effective means of protecting outdoor areas from the destructive influences of sun and hail. Sun protection is an important part of community planning, particularly in areas that experience a high exposure to ultra-violet radiation due to the degradation of the atmospheric ozone layer. Australia has the highest incidence of skin cancer in the world and it is estimated that two out of three Australians will be treated for skin cancer in their lifetime. Aside from humanitarian benefits, the economic benefits of using porous fabric roofs to provide sun and hail protection are now being realised in a number of agricultural and commercial applications, such as feedlots, horticulture and car sales yards. 

The two main types of porous fabric roof are the pitched canopy roof and the flat profile roof. Since these structures are lightweight and non-trafficable, wind is the dominant loading mechanism. To date, there have been very few wind loading studies of porous fabric roofs and accordingly there is a lack of reliable wind loading information available to designers of these structures. In this work, wind loading and response information is obtained for pitched fabric canopy roofs and flat profile fabric roofs. 

A rigid model wind tunnel study of pitched canopy roofs is described. Mean wind loading coefficients are presented for different types, pitches and porosities of canopy roof. These results indicate that while a porous roof experiences reduced wind loading in leeward areas compared to an impervious roof, wind loads are actually increased on windward faces for a porous roof. Full-scale wind testing of a pitched fabric canopy roof confirms that these mean wind loading coefficients can be combined with the quasi-steady design approach to predict peak design loads for this class of porous fabric structure. 

A sectional model wind tunnel study of flat profile fabric roofs identifies two possible types of wind-induced response: a static response which is exhibited by impervious fabrics only and a dynamic response which is exhibited by both impervious and porous fabrics. It is found that the wind-induced fabric tensions for the static response are an order of magnitude greater than for the dynamic response and thus fabric porosity is responsible for causing a significant reduction in wind loading for flat profile fabric roofs. 

Classical potential flow theories for wind flow around aerofoils and sails are reviewed and extended to allow prediction of the wind loading and response of flat profile fabric roofs. Comparison with the experimental results demonstrates that these analytical methods facilitate a reasonable prediction of the static response characteristics, but provide a poor theoretical model for the dynamic response. The main limitation of the theory is the assumption of no flow separation from the surface of the fabric. 

Keyword Awnings
Roofs -- Aerodynamics
Roofs -- Design and construction

 
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