Stress analysis of wood-framed low-rise buildings under wind loads due to tornados

摘要

Buildings in the \u22tornado alley\u22 of the United States, an area where tornados occur most frequently, are built to withstand 3-sec wind speeds of 90 mph, whereas 90% of the tornados reported generate anywhere from 40 to 157 mph. At the same time, these codes are based mostly on studying the effects of straight line winds and not on tornado type winds on buildings, especially on low-rise, wood framed buildings which make up the majority of structures in the United States. Previous research at Iowa State University (ISU) includes extensive testing on a scaled down low-rise gable roof building model (1:100) to understand tornado induced loading pattern as the tornado sweeps past the building. This study was performed using the ISU tornado simulator for various building models and orientations subjected to different tornado speeds and vortex cores. In this work Finite Element models were developed using ANSYS for full-scale numerical gable roof buildings with three different roof angles (13.40, 25.50 and 35.10). The tornado-induced wind loads recorded in the laboratory experiments were applied to the models to determine the detailed stress distribution over them. This numerical study was performed using the same parameter as in the laboratory experiments such as those listed earlier. In the next phase of this research work a routine was developed in ANSYS to incorporate a failure criterion for the building models to assess its damage potential and resulting debris formation. Composite movie sets were created showing the stress distribution over the buildings as the tornado goes past it and also the pattern of debris generation and the order in which the building gets damaged.