| Popis: |
Internal pressures play a large role in the failure of wood-frame houses as the loss of the entire roof section becomes much more likely once the envelope of the building has been breached. Many studies have used internal pressure modelling to simulate internal pressures in structures from atmospheric boundary layer (ABL) winds, however, relatively little work has been done on this subject using tornadic winds. The objective of this study is to explore internal pressure modelling issues for tornadoes. The first part of the study uses a computational internal pressure model to simulate tornadic internal pressures of a low-rise structure; the second part uses the same model to estimate failure wind speeds of a flexible garage door, one of the critical failure modes of these structures. The internal pressure model is able to reasonably simulate measured internal pressures in tornadic winds, although not quite as well as in ABL winds. The modelled internal pressure coefficients are mostly within 0.1 of measured internal pressure coefficients, which is similar to uncertainty bounds. When comparing ABL and tornadic building pressures, some differences are found in the mean pressures at oblique directions and the pressure distributions for normal wind directions. An analysis of the spectra of the theoretical model equation terms reveals that a lack of internal volume scaling in the tornadic tests also contributes to the differences from ABL tests. The same theoretical model also shows that net loads on garage doors are typically reduced to 34-46% of the external pressure applied from the wind due to the internal pressure developed in the garage from the fluctuating opening size during loading. When these results are combined with experimental net pressures of garage door failures, the resulting range of expected failure wind speeds are 130-265 km/h. |
