Considerations for the Tornado-Resilient Structural Design of Low-Rise Buildings
Abstract
Building codes and standards have begun to incorporate tornado-specific loads to help protect community infrastructure against these potentially devastating storms, with a specific focus on low-rise buildings. The current tornado design loads are derived from atmospheric boundary layer (ABL) winds, even though it is relatively unclear to what extent tornado and ABL wind loads are equivalent for a given intensity. This research focuses on the tornado-resilient design of the main wind force resisting system (MWFRS) and component and cladding (C&C) elements of a low-rise gable roof building. Tornado loads derived from the results of experiments completed in a vortex simulator are compared to those obtained from both ABL wind tunnel tests and the proposed tornado-specific design provisions in the upcoming ASCE 7-22 standard. The external pressure datasets from the tornado and ABL wind tests are supplemented by a numerical model for internal pressure to represent enclosed and partially enclosed opening conditions. The analysis demonstrates the impact of the atmospheric pressure drop on enhancing the external tornado-induced MWFRS and C&C loads while showing that the tornado and ABL-induced loads are comparable once internal pressures are considered. Local variations attributed to increased tornado suction loads in high flow separation regions are also highlighted for the MWFRS and C&C. For the building geometry and simulated tornado studied, the peak normalized uplift forces, bending moments, and C&C pressures are found to be effectively enveloped by the ASCE 7-22 tornado design loads for the enclosed building configuration but generally exceed the ASCE loads for the perfectly sealed and partially enclosed cases. The lateral load coefficients computed from ASCE 7-22 are also found to be slightly unconservative irrespective of the opening condition. Further refinements in the internal and external pressure design values as well as the C&C loading zones may be required to better represent the tornado load conditions. Key uncertainties and limitations of the tornado data used in this study are outlined and discussed.