The Active Effect of the Low-Rise Building Chimney in Withstanding Tornadoes

Abstract

A tornado is essentially a low-pressure field that has the following characteristics: minimum pressure of 850-950 hPa, occurring in a small range (typically 50-300 m in diameter), develops within severe winds. It can, in cases of closed or partially vented structures, produce direct differential pressure loads, which is extremely dangerous to low-rise buildings, especially the roof. Recent theoretical and experimental studies showed that tornado-like vortices can generate load coefficients greater than those prescribed by ASCE 7-05 for straight-line wind over open terrain. In cases of closed buildings, vertical uplift coefficients were found to be two to three times the standard provisions due to the effect of a large negative static pressure generated at the core of the vortex. The latest experimental research shows that opening the vent to the outside can significantly reduce the differential pressure between inside and outside the building. In this paper, the authors present the solution to reduce the vertical uplift coefficients by creating a chimney-shaped opening in the roof of a low-rise building, and the calculation of vertical uplift coefficients from the ratio of chimney area to building volume.