Tornado resistant structures | Engineering Explained

Movies often show entire homes flying in the air, which is possible during extreme tornadoes. Don't stay in your car during a tornado. Unless you are Glen Powell. I'm Monica Arul, an assistant professor in the Department of Civil and Environmental Engineering at Virginia Tech. I study how tornadoes and downbursts interact with buildings. We use wind tunnel experiments and computer simulations to understand how wind forces flow through structures, and how we can strengthen them to mitigate damage. We also analyze damage after storms to see how buildings perform during actual extreme wind events. Yes, Virginia experiences tornadoes. On an average, Virginia experiences about ten tornadoes in a year. Historically, the southeastern and central parts of Virginia tend to have more tornado activity, and it's a myth that tornadoes don't happen in the mountain. One of the deadliest tornadoes to strike Virginia was the 1929 Rye Cove tornado in Scott County, and this was in the Appalachian Mountains. So yes, tornadoes can happen in the mountains. Tornado intensity is measured using the EF scale or the Enhanced Fujita Scale. And what most people don't realize is that we don't have reliable measurements of wind speed near the ground during a tornado. So what we do is we work backward and we use the damage to kind of estimate what the wind speeds should have been to cause such a damage. And that's the EF scale. A downburst is a powerful column of air that rushes down from the thunderstorm and then spreads outward upon hitting the ground, producing intense straight-line winds. It is such an underrated wind threat whose damage is often confused with that of damage from tornadoes. Matter of fact, for every one tornado damage report, we have ten downburst damage reports — that's how frequent they are. And yes, Virginia does experience downbursts, especially during summertime. Movies often show entire homes flying in the air, which is possible during extreme tornadoes. But most real-world failures start at weak connections. We cannot tornado-proof a home, but better anchoring and reinforced connections give us a continuous load path from the roof to the foundation, which mitigates damage and also improves life safety. Tornadoes form very quickly. The average warning time for tornadoes is anywhere between 13 and 15 minutes, which is not a lot of time. So the best time to prepare for a tornado is during a severe thunderstorm watch. If you know a storm is brewing, first you would clear your yard of any loose items, like patio furniture or your kid's trampoline, because these can become dangerous sources of debris. Second, you would secure your windows and doors — doors on the outside and doors on the inside — especially the garage doors, because they are the most vulnerable. Because when we have openings, air rushes in through the openings and tries to push the roof. Shut your door and save your roof. The safest place to take shelter during a tornado is ideally the lower level of a building or a basement. If you don't have a basement, go to a small interior room like a bathroom or closet, which is away from windows. So the goal here is to put as many walls between you and the outside. And it is very important that you think of the safe space well ahead of time, because when a tornado warning is issued, you won't have enough time to think.