Comparison of microburst-wind loads on low-rise structures of various geometric shapes

Abstract

Microburst can produce downdraft and strong divergent outflow wind, whose characteristics are distinct from the atmospheric boundary layer (ABL) wind. In the present study, microburst-wind loading effects on low-rise structures − a cubic-shaped building, a grain bin and two gable-roofed buildings – are evaluated and compared by performing laboratory tests on scaled models using a microburst simulator at Iowa State University. Velocity and turbulence intensity profiles at selected locations were studied. The distribution of mean and root-mean-square pressure coefficients for the models are shown for selected cases and compared with those obtained in the ABL wind. Results suggest that wind loads change significantly as the radial location, orientation and geometric shape of the structures vary. It was observed that at or near the center of the microburst, high external pressures occur for all structures, resulting in a large downward force on the roof. In the outburst region, the distribution of pressure coefficients on the structure envelope was found to be similar to those in the ABL wind, although actual wind load magnitudes may be much larger in the microburst wind. Different roof slopes and its cross-section resulted in different pressure distribution and overall wind loads on the models located in the outburst region. The low-angle gable roof and conical-shaped roof experience lower drag but larger uplift in the outburst region compared to buildings with flat roof and high-angle gable roof. The geometric parameters of the roof did not influence the wind loads at or near the center of the microburst where high positive static pressures govern the wind loads. Finally, it is found that the effect of geometric scale of a model on the mean wind loads in the outburst region is minor when it is within a blockage ratio of 3% as tested in the present study.