'It's Definitely Easier To Engineer For An Earthquake' Than Tornadoes

May 24, 2011
Originally published on May 24, 2011 5:14 pm

Can homes, schools, hospitals and office buildings be built to be tornado-proof?

After the death and destruction we've seen in recent weeks in Joplin, Mo., Tuscaloosa, Ala., and other parts of the nation where tornadoes have struck, that is likely on many minds.

This afternoon, All Things Considered host Robert Siegel put the question to John W. van de Lindt, a civil engineering professor at the University of Alabama (in Tuscaloosa), who has extensively studied the effects of tornadoes on structures.

Looking at the damage in Tuscaloosa, van de Lindt said it was apparent that buildings constructed with a "continuous load path" (in which structures are bolted to their foundation and metal hardware goes all the way up and connects to the roof) fared better. But the most powerful tornadoes, with winds up to 200 mph, will rip off almost any wooden home's roof, he said. Once that happens, "the building is no longer stable and it blows the walls down."

By the way, it's also a myth, he said, that you should open your windows. That will only increase the upward pressure on a roof.

It's critical, van de Lindt said, that residents have — or can get to — storm shelters or an "inner core" where there's a closet or a bathroom that offers some protection.

And it's especially critical, he added, that they not wait to actually see the funnel cloud. By then, it's way too late and the twister may be headed in their direction "at about the speed of a car on the highway."

Unfortunately, van de Lindt noted, many of the people in Alabama (and, it's likely, in other places) wanted to stay home until what they thought was the last possible moment in case the tornado passed them by.

As for the forces that tornadoes can bring to bear on a building, van de Lindt said "it's definitely easier to engineer for an earthquake."

"A tornado works from the top down," he said. And it's especially difficult to keep a roof attached to a typical house if a major tornado hits it. An earthquake works from the bottom up, and a foundation can be built to withstand great force.

Much more from Robert's conversation with van de Lindt will be on today's edition of All Things Considered. We'll add the as-broadcast version of the interview to this post later.

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Welcome to the program.

JOHN VAN DE LINDT: Hi. Thank you.

SIEGEL: And tell me, is there any such thing as a building that is tornado proof?

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?

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?

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.

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?

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.

VAN DE LINDT: 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...

VAN DE LINDT: That's correct.

SIEGEL: Well, professor van de Lindt, thank you very much for talking with us today.

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. Transcript provided by NPR, Copyright NPR.