Characteristic wind actions on large flat roofed porous canopies

Large porous protection canopy construction has evolved in Australia over the past 30 years from modest small orchard canopies to large canopies over essential water storages to reduce evaporation and pollution, canopies over large numbers of vehicles for car importers and exporters, and horticultural canopies of over 40 hectares in area. The canopies have proved to be an effective economical method to protect increasing numbers and types of assets from exposure to sun, hail, wind, birds and insects. Canopy design and construction has evolved from the grass roots with initially no structural engineering design input. As the value of assets protected has increased, the request for structural engineering certification of the canopies has become common. To be able to certify the canopy's structure, the certifying engineer needs to confidently be able to predict the wind actions that may occur. In the past there has been limited structural engineering research undertaken into wind loads on porous structures. The aim of this study is to research the characteristic wind actions normal to large flat roof porous canopies and derive design pressure coefficients. Surface friction actions from wind drag across the surfaces are not researched in this thesis and remain a subject for future research. Four scale models of a typical porous protection canopy were constructed for testing in the wind tunnel at the Cyclone Testing Station (CTS), James Cook University, Townsville. The models are of identical geometry, but each of different porosity, 0%, 19%, 38% and 58%. The Models were placed in the CTS boundary layer wind tunnel and rotated through 360° at increments of 15°. At each 15° increment, three sets of pressure readings, each for 30 seconds, were taken at a series of pressure taps located on the Model externally and internally. The pressure readings were processed by the wind tunnel transducer into non dimensional pressure coefficients and then adjusted for the boundary layer speed at the height of the Model. The pressure ...