ROBERT SIEGEL, host:
It's hard to imagine a building that could withstand a tornado like the one that hit Joplin with the winds close to 200 miles an hour, but there are things that can be done to mitigate tornado damage and make buildings safer in case one does touch down.
And we turn now to John van de Lindt. He's an engineer who's been consulting with FEMA officials about how to do just that. He's also in Tuscaloosa at the University of Alabama, and that is, of course, the site of another deadly tornado just a couple of weeks ago.
Welcome to the program.
Dr. JOHN VAN DE LINDT (Professor of Structural Engineering, University of Alabama): Hi. Thank you.
SIEGEL: And tell me, is there any such thing as a building that is tornado proof?
Dr. VAN DE LINDT: Well, there really isn't a tornado-proof building. There are certainly shelters that are tornado proof. The buildings themselves will sustain some level of damage. So tornado proof, no. Tornado resistant, certainly.
SIEGEL: And from what you've been looking at in the damage in Tuscaloosa, what have you been learning about how one could protect lives if we design or built things with tornados in mind?
Dr. VAN DE LINDT: Well, one thing we've been learning is that there needs to be a certain number of interior walls in a building in order to have a safe place to go, but for an EF4, that's enhanced Fujita level four or five tornado, there definitely needs to be a safe room, either underground or an actual shelter or a room aboveground made out of reinforced concrete, steel or masonry-reinforced block.
SIEGEL: Is there anything that there really shouldn't be in a structure that makes it more vulnerable in a tornado?
Dr. VAN DE LINDT: In many structures, one thing that's very, very important in residential structures is what's called a continuous load path, and so they need to be bolted to the foundation with anchor bolts, and then they need metal hardware that basically goes up and connects all the wood going all the way up to the roof. And the idea is to hold the roof on and keep the building envelop intact. And though it may be possible certainly for EF0, EF1, EF2, maybe even EF3. But at the EF4 and 5 levels, then it becomes purely a life safety issue taking cover.
SIEGEL: You're saying 200 miles an hour winds, and the roof is going to fly off.
Dr. VAN DE LINDT: Correct. You're really not going to hold a wood roof on. Now, reinforced concrete is certainly a different story. That can be held on.
SIEGEL: Now, here I'm working at a sturdy eight-story Washington D.C. office building. If some tornado got loose out of Tornado Alley and came down Massachusetts Avenue instead, it will blow all the windows out of the building if it were a 200-mile tornado? Would it knock the building down? Would it break through walls? What would happen?
Dr. VAN DE LINDT: In general, it would certainly knock all the windows out. There would be large amounts of debris flying around in the building. It would probably not knock it down for reinforced concrete. Steel buildings are a different story. I mean, certainly, we saw steel buildings come down in Tuscaloosa, and that can happen. But for reinforced concrete, you generally won't blow a building over.
SIEGEL: We assume that the damage that a tornado can do to the sturdiest building is to the windows. Some people say when there's a tornado warning, you should open the windows. Of course, a lot of us work in buildings where you can't open the windows.
Dr. VAN DE LINDT: Yeah. The - as far as opening the windows, it used to be an old belief that in your house, you should open the front and back door, but that's actually not the correct thing to do because your roof is being sucked off by the wind as well as the suction or the vertical uplift force of the tornado from the outside.
And if you allow the inside to pressurize, then it's actually being pushed from underneath as well. And so it increases the forces by almost 50 percent. So at all costs, if you can, you want to keep what's called the building envelop intact, and that's keeping everything closed and tight.
SIEGEL: Closed? It's a direct contradiction of what the old folk wisdom was about...
Dr. VAN DE LINDT: That's correct.
SIEGEL: ...about tornadoes.
Well, professor van de Lindt, thank you very much for talking with us today.
Dr. VAN DE LINDT: OK. Thank you.
SIEGEL: That's John van de Lindt. He's an engineering professor at the University of Alabama. He is part of a team of researchers who are looking at how to make buildings safer in tornadoes.
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