For Homes To Survive Tornadoes, Engineers Say Building-Design Standards Need To Change | KBIA

For Homes To Survive Tornadoes, Engineers Say Building-Design Standards Need To Change

May 30, 2019
Originally published on May 31, 2019 5:42 pm

Among the volunteers and workers moving furniture, broken lumber and fallen trees at Hawthorne Park apartments in Jefferson City last weekend, three engineers with a large remote control watched a drone fly over a building that was missing a chunk of its roof.

A team of engineering professors and students from the Missouri University of Science and Technology began inspecting damages after a violent tornado struck parts of the state capital last Wednesday. For several years, some have been studying ways to design houses in Tornado Alley states like Missouri to withstand extreme weather events.

If the apartment buildings at Hawthorne Park were built to withstand tornadoes, it’s possible some buildings could have kept their roofs, said Grace Yan, director of Missouri S&T’s Wind Hazards Mitigation Laboratory.

“We wish in the future that if this intensity of tornado comes, the damage we want to see mainly only occurs on some siding, some shingles,” Yan said.

The tornado that hit Jefferson City last week brought 160 mile-per-hour winds, making it an EF-3 tornado. It would be too expensive to build homes that would protect homes against more intense tornadoes, but a lot of costs could be saved from building homes to withstand lower-level tornadoes, Yan said.

Many residential buildings across the country are built according to the International Residential Code and standards set by the American Society of Civil Engineers. The code, for example, requires corrosion-resistant clamps or nails to hold down roofs, which can protect buildings against straight-line winds, or winds caused by thunderstorms.

But the standards don’t consider the how stronger, rotating winds from tornadoes damage buildings. By documenting the destruction in Jefferson City, Yan wants recommend improvements to the American Society of Civil Engineers’ criteria.

“[In civil engineering] everything’s about advancing the material, advance the construction approach,” Yan said. “But in front of a tornado, everything is fragile. As a civil engineer, I think we need to do something about this.”

The spinning air column causes air to flow out, creating low pressure inside the tornado. When it comes in contact with a house, which has higher air pressure, the tornado acts like a suction, tearing off roofs and other objects along its path.

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“You’ll see that the roofs have been lifted off; some of the walls have come down. That’s the most common things we’ve seen,” said Troy Arnold, a vice president of Haley Residential, an Omaha, Nebraska-based property-management company.

Haley Residential owns the 240 units at Hawthorn Park, built in the 1960s and 1970s. The company likely will rebuild the apartments according to Jefferson City’s current building code, Arnold said. The city uses the 2015 International Residential Code, which has some provisions that require wind-resistant design. That includes installing metal ties, or hurricane clips, to connect the roof with the rest of the building.

But the 2015 version of the code doesn’t necessarily protect homes against tornadoes, said Dan Vandevoorde, plans examiner for Jefferson City.

“When we had a Category 3 [tornado] with 160 mph winds, there isn’t a whole lot that could withstand that unless you went way above,” Vandevoorde said. “Everyone has to keep in mind, the building code is the minimum standard. So even at the minimum standard, it does offer protection, but it doesn’t take into account for, you know, tornadoes.”

Builders often want requirements to be minimal in order to keep costs low. That, along with the unpredictable nature of tornadoes, make it difficult to change building codes to better protect communities against tornadoes, said Kishor Mehta, a civil engineering professor at Texas Tech University.

“Even though the [additional] cost is not high, builders prevail in local communities to keep the costs down as much as possible,” Mehta said.

Installing metal ties to make a house tornado-resistant would increase construction costs for new buildings by no more than 1% and for existing buildings, no more than 2%, Yan said. The American Society of Civil Engineers is developing new standards to be established in 2022, which will likely account for wind speeds and pressure that come from tornadoes.

Throughout the inspection at Hawthorne Park, Yan and a structural engineering professor, Mohamed ElGawady, discussed the materials at destroyed buildings. ElGawady often pointed out the condition of the brick veneer that covered most of the buildings, noting that it needs to be reinforced and more connected to the frame of the structure.

“Do you think instead of brick, we could use something different here, like siding?” Yan said.

“Well, the veneer is very beautiful. It’s very nice,” ElGawady said. “I think it’s better to think about how to make it perform better, have better connections.”

He then pointed at another building, where the veneer had collapsed in one large piece. Next to it was a staircase that had twisted off of the building.

“Imagine if someone tried to run away — that’s scary, right?” Elgawady said, then looked back at the collapsed veneer. “I’d never seen something like that, that came out a single piece.”  

It wasn’t Yan’s first time inspecting destruction from a tornado, but it’s tough to see the damages, she said.

“When I see this, I was very emotional; I even cried on the site,” Yan said. “I think as civil engineers, we did not do a good job.”  

But she’s hopeful that building standards will improve. This summer, she and her colleagues expect to finish building a 21-foot tornado simulator chamber at Missouri S&T that will model how storms destroy houses. By doing that research, Yan is optimistic that her research will lead homebuilders to use materials and methods that make houses more resistant to extreme weather.

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