![]() Unfortunately, field data acquisition has not yet captured the turbulent flow quantities necessary to make precise estimates of aerodynamic loading. ![]() These general trends are consistent with velocity measurements in the ISU simulator ( Fleming et al., 2013) and lend credibility to simulator testing. Data from a vehicle-mounted anemometer ( Wurman et al., 2013) also showed velocities at 3.5 m above the ground to be greater than those aloft. Velocities at 4 m above ground level were 10–30% greater than those at 10 m. Kosiba and Wurman (2013) reported tornado boundary layer profiles that showed the highest velocity near the ground. Recent field research has also aided the study of tornado-induced loading. The VorTECH facility at Texas Tech and the WindEEE Dome at the University of Western Ontario ( Refan and Hangan, 2016) can simulate higher speed flows with larger diameters than the ISU simulator. While the ISU simulator was the largest of its kind when built, the future of research on tornado-induced loading includes even larger facilities and the promise of investigations at larger Reynolds numbers. Although internal pressure plays an important role in tornado-induced loading, this study’s focus was on identifying the behavior of external pressures induced by tornado vortices. Ground roughness was found to increase both internal and external pressures. (2013a, b) has used a tornado simulator to examine pressures on low-rise buildings with respect to ground roughness. They reported that the total uplift loading on a building can be reduced significantly depending on the size and orientation of holes in the building envelope. (2011) examined the role of internal pressure along with external pressure. The large difference between those vertical loads and ASCE 7 are part of the motivation for the present work. Integrated uplift loads were also reported and had values that were two to three times that predicted with ASCE 7 provisions. (2010) reported tornado-induced roof pressure coefficients that were 50–60% larger than ASCE 7 provisions. (2008) found significant differences in the character of the loading between straight-line boundary layer tests and tornado simulator tests. Chang (1971) and Jischke and Light (1983) were among the first to employ laboratory tornado simulators with building models to assess loading on buildings. Tornado-induced pressures on low-rise buildings have been studied by several researchers over the years. The specific goal of this work was to examine how peak pressures induced by a tornado vortex depend on the static pressure induced by the vortex and on the amount of time it takes for a vortex to pass over a building (duration effect). (2010) where the Iowa State University (ISU) tornado simulator was used to measure tornado-induced pressures on a low-rise building model. This study constitutes a continuation of the work reported in Haan et al. The largest pressure peaks were observed to occur in or near the vortex core, and profiles of vertical velocity and static pressure suggest that strong unsteady vertical gusting and strong static pressure fluctuations could play a role in creating these large peaks. Work like this could lead to factors to adjust tornado pressure coefficients for the effect of event duration. Results showed that peak pressure magnitudes could increase by factors of 1.1–1.4 depending on duration. To consider duration effects, translating and stationary vortex data were used with varying exposure times. While subtracting the static pressure from pressure time series and normalizing by a local horizontal velocity brought peak pressures closer to what one would expect from straight-line flows, and these data showed that some peaks could still be significantly larger than ASCE 7–10 provisions. ![]() ![]() This study showed that much but not all of this increase can be explained by the static pressure of the vortex. Past studies have suggested that peak pressures on buildings in tornadoes were up to 50% higher than straight-line atmospheric boundary layer values as provided by ASCE 7–10. Time-resolved velocity measurements were also made on the vortex to aid in the analysis. A tornado simulator was used to generate both translating and stationary vortices to measure pressure time series on a building model. This study investigated the role of duration and tornado-induced static pressure on peak pressures on a low-rise building. ![]() Engineering Department, Calvin College, Grand Rapids, MI, USA. ![]()
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