Examination of gust effect factors and statistical characteristics of wind loads for components and cladding of low-rise building roofs

The traditional approach for predicting wind pressures on the components and cladding (C&C) of roofs in low-rise buildings relies on directly measured peak wind pressure coefficients obtained from wind tunnel testing, as outlined in ASCE 7 22 and NBCC 2020. In contrast, EN 1991-1-4 recommends a constant gust effect factor (structural factor CsCd) of 1.0 for C&C wind loads on roof elements, with mean external pressure coefficients defined based on the loaded area. However, the actual gust effect factors of C&C wind loads remain underexplored. This study evaluated the gust effect factors of wind loads on C&C of low-rise buildings' roofs by analyzing their statistical properties. Aerodynamic data from the NIST database, obtained from the Boundary-Layer Wind Tunnel II at the University of Western Ontario, is utilized for the analysis. This study examines a range of low-slope low-rise building configurations with different roof heights and plan dimensions. The analysis explores key statistical properties of wind pressure coefficients, including mean, standard deviation, skewness, kurtosis, and peak factor, considering varying tributary areas and roof zone locations. In addition, this study assesses the background response factor, which quantifies the relationship between wind load fluctuations and upstream turbulence, along with the gust effect factors. The results reveal that the mean and standard deviation of wind pressures on C&C follow similar trends with effective wind area as observed for the peak wind pressures in ASCE 7-22 and NBCC 2020. Non-Gaussian features of wind pressures, indicated by high skewness and kurtosis, lead to large peak factors. The gust effect factors for tributary areas of 9 ft2 at corner zone (Zone 3), and edge zone (Zone 2) of roofs are approximately 1.5 across various building configurations. However, in the internal zone (Zone 1'), the gust effect factors for effective wind area less than 100 ft2 exhibit significant variability ranging from 1.0 to 2.5. In addition, models for gust effect factors with effective wind area are proposed for different roof zones in this study.