Tornado-Induced Wind Loads on a Low-Rise Building

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 can occur during extreme weather 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 the provisions of building standards. Tornadoes were simulated in smooth, open terrain with vortex core diameters from roughly five to twelve times the plan dimension of the building model (0.46 to 1.06 m). A 1:100 scale model of a building with dimensions of 9.1 m x 9.1 m 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 tornado-like vortices can generate load coefficients greater than those prescribed by ASCE 7-05 for straight-line wind over open terrain. For lateral forces, these coefficients were found to be as much as 50% larger than the standard provisions. Vertical uplift coefficients were found to be two to three times the provisions most likely due to the effect of a large negative static pressure generated at the core of the vortex.