Understanding Tornadic Wind Effects on Manufactured or Mobile Homes through High-Fidelity CFD Simulations

Abstract

Tornado fatality rates in the southeastern United States are higher than those in Tornado Alley, despite Tornado Alley having a higher frequency of tornadoes. A major contributing factor is the large number of mobile and manufactured homes (MMHs) in the southeastern states. Forensic engineering assessments of tornado damage have consistently shown that inadequate anchoring of MMHs or the absence of proper anchoring has been the primary cause of structural failure. To properly design a MMH anchorage system to resist tornadic winds, it is imperative to have accurate knowledge of the tornadic wind effects on the MMH systems. In this study, tornado–MMH interactions are investigated using high-fidelity numerical simulations. The pressure distribution on the MMH surface and the total forces/moments on the entire MMH induced by tornadic winds are obtained. In addition, simulations are conducted to reveal (1) the difference in tornadic wind effects between a MMH and its associated permanent home (home with classical on-site construction), and (2) the difference in wind effects between tornadic winds and the equivalent straight-line winds. The latter of these comparisons is intended to provide information on the unconservative use of straight-line wind loading for MMHs. The simulation results (peak wind pressure and total forces/moments on the MMH) are compared between the tornadic wind field and straight-line wind field. The comparison indicates that the results caused by the tornado are higher. Under a tornadic wind field, compared with the permanent home (PH), the peak pressure and horizontal forces on the MMH are smaller because of the existence of open space under the MMH. Although the research findings here demonstrate the limitation of US code for MMHs, a great number of simulation cases with the related uncertainties involved will be needed to be run to improve the US code.