TERRE HAUTE —
Tornadoes produce greater uplift forces than hurricanes, which can flatten homes such as in Moore Okla., south of Oklahoma City.
Learning ways to construct and protect vital buildings such as hospitals, schools and power plants from damaging winds is part of research that Rose-Hulman Institute of Technology Mechanical Engineering Professor Fred Haan has been studying for more than 15 years.
Haan is working to establish new professional construction standards he hopes can be adopted and implemented, either through discounts from insurance companies or placed into building codes.
“We are looking at how tornadoes produces forces on buildings that are different than the way that straight line winds produce forces,” Haan said.
“The sideways forces are very similar between straight line winds and tornadoes, but it is the forces that act to lift the roof of a house, those are significantly higher in tornadoes.
“By significantly, I mean, depending on conditions, can be twice or three times as high,” Haan said.
That is a much higher force than buildings are currently designed to handle, he said. New buildings are being designed to handle a 90-mile wind in a straight line. “It is ignores this extra load that you can get from a tornado,” he said.
Research in the last decade on extreme winds has allowed Haan to better understand forces involved. It also comes down to a question of how strong do buildings need to be constructed.
Haan argues that hospitals, schools and power plants could be designed to stronger standards to better withstand tornadoes. “It is involves better connections between the roof and the walls, better connection between the walls and the foundation,” he said. “Right now a lot of connections are not designed for uplift. People basically assume gravity will hold things together and hold house where it is. Most of the time that is just fine, but tornadoes have a very significant uplift...which rip things apart pretty easily,” Haan said.
Haan said some solutions are not expensive. For example, steel brackets can be placed at the connections and still use wood to build a structure. “It can make a really significant difference. They are about $2, so for a few hundred dollars on a house, you make a real significant change in how resistant it is to having its roof torn off,” Haan said.
The idea is not as easy as it seems, he said, as people can bulk at extra costs. Contractors, homeowners, insurance companies and policy makers will have to be convinced that this should be recommended or required.
“Obviously I think it looks like a great idea and I think it is a pretty reasonable price. This is part of discussions that have to be made out of disasters,” Haan said, such as Oklahoma City or Joplin, Mo., where a tornado two years ago killed 158 people.
Haan said a single home can spread debris throughout a community, damaging other homes. “In general, it is important to raise the general resilience of a community in whole, not one person’s decision with one house,” Haan said.
Currently, Haan is working on professional standards through the American Society of Civil Engineers for wind load standards. “One thing being discussed now is how and if to put in some language about dealing with tornadoes,” Haan said.
Haan said changes in building codes in Florida after Hurricane Andrew in 1992 showed a significant resilience for new houses to wind loads. The change, however, was just a toenail connection with nails pounded in diagonally and is not as strong as a bracket connection.
“I think that there are a lot of things that we can do to improve things and I hope [new wind load standards] get implemented in some way,” Haan said.
Reporter Howard Greninger can be reached at 812-231-4204 or firstname.lastname@example.org.