Laboratory Simulation of Steady Tornadic Wind Loads on Structures

摘要

Using the University of Oklahoma modified tornado simulator, the interaction of tornadic flowfields with structures has been examined empirically. Measurements with and without swirl have been made of the pressure on the surface of a cyclindrical model and a rectangular model placed in the simulator. Results are presented for the surface pressure coefficient and the total force moments coefficients for imposed swirl angles of 0 degrees and 45 degrees, with the models placed at three locations within the simulator: (1) the convergent zone, (2) the boundary of the convergent zone and convection zone, (3) the convection zone. The measurements on the cyclindrical model show that in the swirling flow case, the nonuniform flow due to the tornado-like vortex induces a side-force, reckoned with respect to the local wind direction, that increases as the distance between the model and vortex decreases. The magnitude of both the force coefficients and overturning moment on the structure increase with swirl. The data for the rectangular model shows that the effects of the imposed swirl can be dramatic and important. Increases in the horizontal force coefficient and overturning moment coefficient by a factor of four over the zero swirl values can occur when the model is at the boundary of the convergent and convection zones. The vertical force on the roof can more than double. These results show that the tornadic windloads on stsructures cannot always be accurately estimated from the loads caused by boundary-layer-type winds.