Tornado-Induced Wind Loads on a Low-Rise Building

Abstract

Current design wind loads for buildings and other structures are based upon model tests in low-speed boundary-layer wind tunnels that generate straight-line winds. Winds resulting from tornadoes that could occur during storm events such as thunderstorms or hurricanes differ greatly from conventionally-conceived atmospheric boundary-layer winds. This paper presents transient wind loads on a one-story gable-roofed building in a laboratory-simulated tornado and compares them with building code estimates. Tornadoes were simulated in smooth open terrain with vortex core diameters from 0.46 m to 1.06 m. A 1:100 scale model of a building with dimensions of 9.1m x 9.1m x 6.6 m and gable roof angle of 35° was used for this study. Comparisons of peak loads measured in this study showed that tornadoes of F2 strength would generate loads significantly greater than those prescribed by ASCE 7-05 for 40 m/s (90 mph), 3-sec gust, straight-line wind over open terrain.

Development of Empirically-Based Fragilities of Residential Damage in the 2011 Joplin, Missouri, Tornado

“…In addition, the rapid pressure drop associated with the tornado vortex is not present in straightline winds, although its effect on building loads is limited when building leakage is present to equilibrate external and internal pressures. These factors may enhance tornado loads and cause buildings to fail at lower wind speeds than in a straightline wind event Haan et al, 2010). However, tornadoes are also typically of much shorter duration than hurricanes, and therefore during the passage of a tornado, buildings may experience fewer damaging gusts and thus less damage.…”

“…In the Amini et al (2013) study, tornado loads were estimated by using ASCE 7-10 pressures for straightline winds and amplifying them using factors between 1.8 and 3.2. These amplification factors were based upon the experimental results from Haan et al (2010), which were obtained by passing a laboratory-simulated, translating vortex directly over an instrumented building model. However the building model used in this study was fully sealed, maximizing the effect of the pressure drop associated with the vortex.…”

“…A significant body of work exists for the determination of analytically-derived fragility curves for wood-frame structures and their structural components in hurricane winds (Amin and van de Lindt, 2013;Ellingwood et al 2004;Li and Ellingwood 2006;, but fragility relationships for wood-frame structures in tornadoes have only recently been developed. Amini et al (2013) performed a probabilistic assessment of sheathing and roof-to-wall connection failures assuming a fully sealed, wood-frame structure during a tornado using wind pressures from ASCE 7-10, modified for tornado loads using simple amplification factors based upon Haan et al (2010). As of yet however, no studies have provided empirical results for comparison to this and any future models, as the spatial distribution of near-surface wind speeds in tornadoes, necessary for comparison to observed damages, is difficult to obtain.…”

Systematic Study of the Failure of a Light-Frame Wood Roof in a Tornado

“…The effect of straight line winds on structures has been studied extensively and has led to the development of the current design provisions [14]. However, research has been less robust in terms of understanding the effects of tornadoes on structures with only a limited number of studies conducted on this topic [13,[15][16][17]. Many of these studies present a combination of theoretical and experimental work with the main purpose of comparing the effects of tornadoes versus straight line winds.…”

“…Therefore, buildings in the U.S. are typically designed using loads from ASCE Standard 7 which were developed for straight line winds. However, tornadoes have been shown to produce uplift pressures that are significantly higher than straight line winds [13].…”