Constructing Stronger Buildings for Spring Tornado Season

For schoolchildren, office workers, and homeowners who all live in tornado-prone regions of the country, crouching in hallways for tornado drills is an annual ritual. According to a recent report in Scientific American, tornado season is occurring earlier in the spring than it used to – with May, June, and July being the most likely months for tornado touchdowns. The United States sees about 1,200 tornadoes each year, most commonly across the prairies of the Great Plains states situated in “Tornado Alley.”

Researchers at Iowa State University have been searching for answers about how tornadoes interact with buildings and how to prevent weather phenomena from turning into widespread disaster scenes. To test their theories, the university has a tornado simulator that creates a funnel cloud over a model town. Around 90 percent all tornadoes are categorized with an intensity level of EF3 or less, but even those have top wind speeds of 165 mph. EF5 tornadoes can produce winds over 200 mph.

“In the long run,” the researchers wrote in their summary, “the research is expected to contribute to methods and strategies that can be implemented for preventing tornado hazards from becoming disasters.”

Partha Sarkar, who designed Iowa’s tornado simulator over 10 years ago, studies the loads and pressures caused by simulated storms passing over models of homes and buildings with his students. And he’s concluded that there are things about tornadoes that many engineers still don’t understand.

These are some of the questions that engineers must ask themselves when constructing a new building to withstand tornadoes:

-How do nearby buildings and lands affect tornado winds?
-How does the age of a building impact tornado damage?
-Which structure shapes are best suited to withstand tornadoes?
-What roof types are best for tornado-prone areas?
-What types of trusses, walls, and nails are best for strong tornado winds?
-How do internal pressures inside buildings affect tornado damage?
-How can building codes reinforce safety in tornado zones?

And these are some of the features of an EF-rated building that stands the best chance to weather tornado storms:

-Glued laminated timber (“glulam”) double-wall system with steel tube linking struts
-Glulam girder, buttresses and rafters
-Steel tie rods from footings to roof
-Roof panels with internal reinforcement at up-lift points
-Sufficient mass to resist overturning

Sarkar’s team and a Texas Tech University team received two three-year $250,000 collaborative research grants to help answer these questions and make their findings known to engineers who work in tornado-prone areas. But it’s important to remember that tornadoes know no geographic boundaries and can happen anywhere at any time.

In the U.S., there’s a second tornado season that hits in the fall, around early November when the weather patterns begin to shift. Tornadoes have been well-documented in the United States, but are also likely to occur in Canada’s prairie provinces, northeastern Mexico, northern Argentina, southern Brazil, Britain, Bangladesh, and southern Russia. And unlike hurricane season, which can often be forecasted in advance, tornadoes are dependent upon atmospheric patterns that are unpredictable and can form quickly without much warning.

Photo credit: Jmos® and Barry Lenard via Flickr