Characteristics of fluctuating pressures on a cantilevered roof
Abstract of thesis entitled
CHARACTERISTICS OF FLUCTUATING PRESSURES ON A CANTILEVERED ROOF
for the degree of Master of Philosophy
at The University of Hong Kong
in May 2001
Wind tunnel tests were carried out on a rigid model of a horizontal grandstand roof. The model consists a grandstand roof model and a stepped grandstand. The roof model was 780 mm long, 150 mm wide and 6 mm thick and was cantilevered at its rear edge at a height of 180 mm above the wind tunnel floor. The roof was equipped with 78 pairs of pressure taps covering both the upper and lower roof surfaces. Wind pressures at these 156 taps were measured in a near-simultaneous manner with an electronic pressure scanning system. The objective of the study was to investigate the generation mechanism of wind pressure and peak lifting actions on a large cantilevered roof.
The mean, standard deviation and peak values of fluctuating wind pressure distributions on the roof are presented as contour maps. The conditional sampling technique was used to extract the wind pressure pattern on both roof surfaces when a peak total uplift or a total net moment was occurring on the roof. It was
found that the occurrence of peak uplift and peak moment on the roof were connected with large lifting actions on both roof surfaces. An evaluation was made on the degree of over-estimation in peak net pressure if the separately obtained peak pressure values on the upper and lower roof surfaces were combined to form the worst situation.
Spectral characteristics, probability distribution and correlation of the
pressures on the roof were analyzed. The pressure power spectra show that a
significant portion of the fluctuating pressure energy was contained at low
nD frequencies below = 0.3. The PDFs of the normalized pressure coefficients at U
the tappings in the separation regions show that the probability distribution
departs from the Gaussian distribution with significant deviations at the negative
Time histories of the wind forces on both roof surfaces and of the net force on the entire roof were obtained from an integration of the simultaneous pressure signals. These force signals were analyzed statistically to investigate the mechanism of peak lift forces. Correlation and conditional sampling analysis shows that the occurrence of peak total roof lift is connected with simultaneous large lifting actions on both roof surfaces, with more significant contribution from the upper roof surface.
Effect of roof inclination angle on the pressure pattern and on the wind forces was investigated by repeating the wind tunnel measurements on three sloping roof models. Higher and larger suction pressure regions were found on the up-sloping roofs compared with the horizontal roof.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:wind pressure roofs
Date of Publication:01/01/2002