Occurrence of peak lift on a large cantilevered roof

A rigid model of a horizontal grandstand roof was tested in the wind tunnel to investigate the generation mechanism of wind pressures and lift forces on large cantilevered roofs. The roof model is 960 mm long and 180 mm wide. Wind pressures were measured simultaneously at 96 taps covering both surfaces of the roof with an electronic pressure scanning system. The conditional sampling technique was employed to extract the patterns of net wind pressure and of the lower and upper roof surface pressures when a large total uplift was occurring on the roof. It was found that the occurrences of peak lift are connected with large lifting actions on both roof surfaces. Some differences between the conditionally sampled pressure pattern and the time-average mean pressure pattern were observed. Wind forces on the roof surfaces and on narrow panels of the roof were obtained from the simultaneous pressure signals. These force signals were analysed statistically to investigate the mechanism of peak lift forces.