Occurence of peak lifting actions on a large horizontal cantilevered roof

Wind tunnel tests are performed on a rigid model of a horizontal grandstand roof. The objective is to investigate the generation mechanism of wind pressure and peak lifting actions on a large cantilevered roof. The roof model is 780 mm wide, 150 mm deep and is equipped with 78 pairs of pressure taps covering both roof surfaces. With an electronic pressure scanning system, wind pressures at these 156 taps are measured in a near-simultaneous manner. Time histories of the wind forces on both roof surfaces and of the net wind force on the entire roof are obtained from the simultaneous pressure signals. These force signals are analyzed statistically to investigate the mechanism of peak lift forces. The conditional sampling technique is used to extract the wind pressure pattern on the lower and upper roof surfaces when a large total uplift is occurring on the roof. It is found that the occurences of peak lift and peak moments on the roof are connected with large lifting actions on both roof surfaces. Differences between the conditionally sampled pressure pattern and the time-averaged mean pressure pattern are observed and discussed. A study is made on the overestimation of net roof pressure if it is assumed to be the worst combination of peak pressures simultaneously occuring on both roof surfaces.