Measurements of shear stress distribution over a flat roof as a function of parapet height, wind direction, and roof roughness

A series of first-of-their-kind large-scale wind tunnel tests were conducted to measure the surface shear stress distribution on a flat roof of a square-plan building. Data were collected for a broad range of parapet heights and wind angles and for both smooth impermeable roofs and roofs covered with loose-laid permeable gravel. Mean and peak shear stress contours are presented for nine different wind angles between 0 o and 45 o and seven parapet heights. For cornering winds, the typical V-shaped contours are seen as typical of pressure coefficient contours though the angle of the V is narrower for the shear stress contours. However, unlike prior pressure coefficient measurements for cornering winds, there is no significant increase in loading as the parapet increases from no parapet to a small circumferential parapet. In fact, for the measurements made over a gravel roof surface, the shear stress coefficient decreases monotonically with parapet height. While this is inconsistent with pressure measurements, it is consistent with measurements of the wind speed required to produce roof gravel scouring. The implications of these results for gravel motion initiation are discussed. The data used in this paper is published on the DesignSafe-CI data repository ( Kaye et al., 2024a , Kaye et al., 2024b ).