An experimental study of flow fields and wind loads on gable-roof building models in microburst-like wind

Abstract

An experimental study was conducted to quantify the flow characteristics of microburst-like wind and to assess the resultant wind loads acting on low-rise, gable-roof buildings induced by violent microburst-like winds compared with those in conventional atmospheric boundary layer winds. The experimental work was conducted by using an impinging-jet-based microburst simulator in the Department of Aerospace Engineering, Iowa State University. Two gable-roof building models with the same base plan and mean roof height, but different roof angle, were mounted over a homogenous flat surface for a comparative study. In addition to measuring the surface pressure distributions to determine the resultant wind loads acting on the building models, a digital particle image velocimetry system was used to conduct flow field measurements to reveal the wake vortex and turbulence flow structures around the building models placed in the microburst-like wind. The effects of important parameters, such as the distance of the building from the center of the microburst, the roof angle of the building, and the orientation of the building with respect to radial outflow of the oncoming microburst-like wind, on the flow features such as the vortex structures and the surface pressure distributions around the building models as well as the resultant wind loads acting on the test models were assessed quantitatively. The measurement results reveal clearly that when the building models were mounted within the core region of the microburst-like wind, the surface pressure distributions on the building models were significantly higher than those predicted by ASCE 7-05 standard, thereby induced considerably greater downward aerodynamic forces acting on the building models. When the building models were mounted in the outflow region of the microburst-like wind, the measured pressure distributions around the building models were found to reach a good correlation with ASCE 7-05 standard gradually as the test models were moved far away from the center of the microburst-like wind. It was also found that both the radial and vertical components of the aerodynamic forces acting on the building models would reach their maximum values when the models were mounted approximately one jet diameter away from the center of the microburst-like wind, while the maximum pressure fluctuations on the test models were found to occur at further downstream locations. Roof angles of the building models were found to play an important role in determining the flow features around the building models and resultant wind loads acting on the test models. The flow field measurements were found to correlate with the measured surface pressure distributions and the resultant wind loads (i.e., aerodynamic forces) acting on the building models well to elucidate the underlying physics of flow-structure interactions between the microburst-like winds and the gable-roof buildings in order to provide more accurate prediction of the damage potentials of the microburst wind.