An Examination of Static Pressure and Duration Effects on Tornado-Induced Peak Pressures on a Low-Rise Building

Fred L Haan

doi:10.3389/fbuil.2017.00020

Abstract

This study investigated the role of duration and tornado-induced static pressure on peak pressures on a low-rise building. A tornado simulator was used to generate both translating and stationary vortices to measure pressure time series on a building model. Time-resolved velocity measurements were also made on the vortex to aid in the analysis. Past studies have suggested that peak pressures on buildings in tornadoes were up to 50% higher than straight-line atmospheric boundary layer (ABL) values as provided by ASCE 7-10. This study showed that much but not all of this increase can be explained by the static pressure of the vortex. 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, the data showed that some peaks could still be significantly larger than ASCE 7-10 provisions. To consider duration effects, translating and stationary vortex data were used with varying exposure times. Results showed that peak pressure magnitudes could increase by factors of 1.1 to 1.4 depending on duration. Work like this could lead to factors to adjust tornado pressure coefficients for the effect of event duration. 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.

Highlights

This study constitutes a continuation of the work reported in Haan et al (2010) where the Iowa State University (ISU) tornado simulator was used to measure tornado-induced pressures on a low-rise building model
This study investigated the role of tornado-induced static pressure and duration on peak pressures on a low-rise building
Past studies have suggested that peak pressures on buildings in tornadoes were up to 50% higher than straight-line atmospheric boundary layer (ABL) values (Haan et al, 2010)

Summary

Introduction

This study constitutes a continuation of the work reported in Haan et al (2010) where the Iowa State University (ISU) tornado simulator was used to measure tornado-induced pressures on a low-rise building model. Tornado-induced pressures on low-rise buildings have been studied by several researchers over the years. Chang (1971) and Jischke and Light (1983) were among the first to employ laboratory tornado simulators with building models to assess loading on buildings. Mishra et al (2008) found significant differences in the character of the loading between straight-line boundary layer tests and tornado simulator tests. Haan et al (2010) reported tornado-induced roof pressure coefficients that were 50–60% larger than ASCE 7

Objectives

Results

Conclusion