Effect of low-rise building geometry on tornado-induced loads

Despite the destructive effects of tornadoes, limited attempts have been made to quantify tornado-induced loading. The purpose of the study presented here was to investigate the effect of different building geometry on the forces and pressures that low-rise buildings would experience in a simulated tornado with a swirl ratio comparable to what has been measured and recorded for full-scale tornadoes. Measured force and pressure data were then used to judge whether tornado-resistant design for residential structures is feasible. The tornado-induced wind loads were measured on scaled models of buildings in a laboratory-simulated tornado with a core diameter (56 m) and relatively high swirl ratio (2.6) representing an EF3 tornado. The study found that the peak loads vary as a function of eave height, roof pitch, aspect ratio, plan area, and other differences in geometry such as the addition of a garage, roof overhang and soffit. The required strengths of the roof-to-wall and roof sheathing-to-rafter connections were calculated based on the measured loads and compared with their capacities to assess the possibility of failure. It appears that the design of the two critical roof connections in residential construction for tornado-resistant design up to and including EF3 tornadoes can ensure adequate safety cost-effectively by using currently available technology.