A surly high school shop teacher was once heard admonishing his students not to store heavy items overhead.
“Things don’t fall up!” he growled.
Generally not. But as any tornado victim can tell you, there’s an occasional exception to the rule.
Indeed, a “rapid-response” structural engineering team based at the University of Kansas said as much. In a preliminary study of damage from the May 28 EF4 tornado that gouged Linwood, Kansas, and environs, the engineers documented houses utterly unprepared to withstand the upward surge a twister can produce.
In many cases, the report says, the walls simply were not adequately anchored to the foundation, or the roof to the walls. A “lack of anchorage and roof-to-wall straps were observed consistently with damaged wood-frame structures. Nailed connections were clearly not sufficient in resisting the uplift and lateral loads experienced by these structures. ...
“Many severely and completely damaged single-family wood-frame structures had insufficient load paths characterized by a typical gravity-based design ...”
In short, their construction ignored the fact that in a tornado, things do fall up. Then they fall sideways and down. Structures that are blown apart contribute to flying debris that becomes a danger to people and a hazard to surrounding properties.
The study also cites the complete destruction of the unreinforced masonry at the Building Blocks Daycare. Thankfully, the tornado struck after hours. Otherwise, the report notes, we’d be talking about injured or dead children.
And guess what the daycare center used to be? A school.
If you lived in hurricane land, wouldn’t you build to withstand them? Why shoot for any less in tornado territory? Consider: A Category 5 hurricane has sustained winds of 157 mph. The Linwood tornado’s were estimated at 170.
Since Hurricane Andrew in 1992, Florida has stiffened building codes, including for many existing homes. During certain remodeling in hurricane-susceptible regions, homeowners are now required to shore up roof-to-wall connections.
“The good news,” writes The Journal of Light Construction, “is that just tying roof framing to the wall plate will fix a weak point and make the house better able to survive a hurricane.”
Or, presumably, a tornado.
Credit to the 16-member engineering team, which was swiftly organized by KU assistant professor of engineering Elaina Sutley, included an engineer from the University of Missouri-Kansas City and was financed by the National Science Foundation’s Structural Extreme Events Reconnaissance Network. After the Tuesday tornado, the team was on the ground by Friday, assessing every third structure in dense areas until they’d surveyed 271 of them door to door.
Despite all the damage May 28, no one was killed, though 18 were injured. But state and county officials in the region should study the rapid-response team’s report and recommendations, which include creating the first public storm shelters in Douglas County; updating building regulations and inspections; making affordable housing safer; and abandoning or at least retrofitting unsafe school and daycare buildings.
Many unincorporated areas, such as in Leavenworth County, have no building codes to speak of, Sutley says, and existing ones need to be updated.
Not even structural engineers can know for certain what buildings might have survived the EF-4 twister. But they do know a little about uplift and lateral loads that can destroy homes.
Their report is a tornado siren of its own.