Tornado-induced wind loads on a low-rise building

The effects of wind loading on buildings due to straight line boundary layer type winds have been studied extensively in the past. Building code estimates are mainly based on these works. Little research has been, however, done to study the effect of tornado winds on built structures. This research work essentially deals with the study of the effects of tornado type wind loading on low-rise buildings. Extensive testing was performed on a scaled down low-rise gable roof building model (1:100) to understand the loading pattern. The vortex generated using the ISU tornado simulator agreed well with the Doppler radar data from the Spencer, South Dakota tornado of May 30, 1998 and the Mulhall, Oklahoma tornado of May 3, 1999. The building model was tested using tornado vortices with five different core radii. The tornado could be translated using a crane mechanism; this enables realistic recreation of the actual effects on the low-rise building due to a moving vortex (which is the case in real world). The building model was also tested for four different vortex translation speeds. The lowest speed cases invariably produced larger loads. The effect of building orientation was also investigated by testing the model at seven different angles of attack. The results showed higher wind loads for the smallest vortex core with lower translation speeds. The building orientation of 60 deg had a higher loading pattern. In general the force and moment coefficients were higher than current building code provisions. Further wind tunnel tests were also carried out to study the effects of different roof types and building heights.