Posted by Karl Johnson on May 22, 2013
Related program: Resilient Oklahoma & Rebuild Moore
Additional reporting by Katherine Allen
This morning, the second following the massive and devastating tornado that ripped through Moore, authorities are completing their rescue efforts of the wreckage. The death toll stands at 24. It's widely understood the area will be clearing debris for months - FEMA has dedicated itself to immediate needs - and we think about the future of Moore and the surrounding area to recover from this storm, and consider resilient strategies to safely withstand future ones.
How Buildings Fail
"Funnel tornadoes are much more powerful than hurricanes," explains Eric Cesal. "It's easy for a building to fail in these conditions."
The first building failure in a tornado is typically the roof, which due to wind and relative air pressures is torn off by the storm. "Then the structure loses strength - the roof is a critical structural element to the rest of the building." Unsupported walls topple, as they did in hundreds of homes and several schools in Moore.
Safe Rooms are small underground private or community shelters that have demonstrably saved towns during tornadoes and severe storms. We've found a great investigative synopsis of this Oklahoma shelter type by the Rachel Maddow Show - a clip worth watching to understand this aspect of the discussion.
Currently Safe Rooms are privately manufactured for private or community purchase, and are not mandated per town by the State. It has been recommended that large Safe Rooms be required in strategic community locations. Every Oklahoma school, for instance, is required to have an evacuation plan to a safe area, but are not required to have a Safe Room.
Underground shelters and basements seem an easy solution, however the clay soil conditions of central and eastern Oklahoma make basement construction prohibitively expensive for contractors to build, and for homeowners to maintain. NPR explains in some detail why basements are so unpopular.
There are strengthening strategies
Which isn't to say that Oklahoma houses and building codes are doing as much as they can to recommend stronger and safer construction.
In an interview with NPR this morning, civil engineer and University of Alabama Professor Andrew Graettinger explains that installing hurricane clips (tying wall to roof) and hurricane straps (tying wall to foundation) in Midwest houses would help them withstand lower-wind-strength storms, and mentions shelters for the strongest storms.
Again, the shelters can protect life, not property.