What’s backward about the tornado damage at this site, and how did this happen? Please stop and ponder this for a few moments, then continue. The garage door of this small, open-span metal structure tells all you need to know. The force responsible had to come from within, and the only other entry point for the needed blast of air is the missing roof. [The wall unseen at right was intact, as were all others.] This means the roof went first. The tornado approached from right to left, meaning its cyclonic flow aimed toward you as you look straight into the image. The vortex blew the roof off, thereby applying wind load against the inside of the garage door, which was least secure at its bottom. This flipped it out and over the area where the roof was. All of that occurred in just a few seconds, at most, before the vortex passed and the flow direction reversed. By that time, the tornado winds had a more typical path through the building: where the garage door should be, then up through the roof location, except neither was in place anymore. Garage doors quite often are the first parts of houses and detached garages to fail, applying bottom-up pressure to the roof, for which it isn’t designed, and the roof pops loose. In this case, the process unfolded the opposite way!
4 SW Farmersville TX (16 Jan 16) Looking E
33.115, -96.4092Backwards Damage Process
What’s backward about the tornado damage at this site, and how did this happen? Please stop and ponder this for a few moments, then continue. The garage door of this small, open-span metal structure tells all you need to know. The force responsible had to come from within, and the only other entry point for the needed blast of air is the missing roof. [The wall unseen at right was intact, as were all others.] This means the roof went first. The tornado approached from right to left, meaning its cyclonic flow aimed toward you as you look straight into the image. The vortex blew the roof off, thereby applying wind load against the inside of the garage door, which was least secure at its bottom. This flipped it out and over the area where the roof was. All of that occurred in just a few seconds, at most, before the vortex passed and the flow direction reversed. By that time, the tornado winds had a more typical path through the building: where the garage door should be, then up through the roof location, except neither was in place anymore. Garage doors quite often are the first parts of houses and detached garages to fail, applying bottom-up pressure to the roof, for which it isn’t designed, and the roof pops loose. In this case, the process unfolded the opposite way!
4 SW Farmersville TX (16 Jan 16) Looking E
33.115, -96.4092