Researchers at Clemson University will simulate a tree falling on a house as part of a project to help develop practical cost-effective tornado "safe rooms" in homes.
The research, funded with an approximately $73,000 grant from the Federal Emergency Management Agency, will specifically investigate affordable ways in which interior rooms such as bathrooms and bedrooms can be reinforced to prevent damage by wind-blown debris and falling trees. The project looks at ways rooms can be strengthened during the initial construction or, in existing homes, be retrofitted.
"This valuable research being done by Clemson will provide common-sense practical solutions to homeowners so they can have some piece of mind and, if they are in a tornado, they can be a degree safer," said John B. Copenhaver, director for FEMA's eight-state regional office based in Atlanta.
To test what structural components work best against falling trees, researchers engineered what they call the "The Drop Zone," a 24-foot-tall truck-mounted device that can winch columns weighing up to 1,500 pounds into place and then drop them, ax-like, onto the structure being tested. Researchers are now evaluating damage from 6-inch diameter pine trees by using a 20-foot-long metal column weighing a quarter of a ton. Poles approximating the effect of a larger tree - for example, a large pine or small oak - will also eventually be tested.
Early tests show that the dropped column crunches half-way through a typical 6x8-foot wall panel made of wood studs and fiberboard sheathing. The same column barely takes a bite out of a metal-reinforced panel. For a person asleep in a bed, that three-foot differential could mean the difference between life and death.
Roofs and other components will, of course, give additional levels of protection and will be factored into the final recommendations.
"But if the tree were to fall between the roof structural members and impact the plywood roof sheathing, the roof wouldn't make much of a difference anyway," warned Ed Sutt, a Ph.D student who is helping with the research. "And keep in mind, we're only seeing the effects of a six-inch pine at this point. Larger trees could have far more devastating consequences."
To simulate wind-borne debris, researchers use an air cannon to fire 2x4's and other materials against wall sections at speeds up to and exceeding 100 mph.
The Clemson research will concentrate on identifying inexpensive techniques that could be used by a construction-savvy homeowner. Research findings will be used to develop technical guidance for contractors and practical application material for homeowners.
Low-tech fixes under study include installation of wood-reinforced wall panels, addition of a layer of metal decking under the wall panel, different combinations of plywood or common insulation foams.
Also under study are various high-tech methods.
"This won't lead to code changes, but we will come up with inexpensive suggestions that we think homeowners will want to include, particularly, in new construction," said Sutt, whose own research has led to a patented structural molding that will help "hold together" homes in tornadoes, hurricanes and even earthquakes.
"We need to break the cycle of thinking that says that tornadoes and hurricanes are acts of God and that nothing can be done," said Ben Sill, Alumni Distinguished Professor of Civil Engineering at Clemson and one of the founders of Clemson's wind research program. "Although some tornadoes or hurricanes will be so strong that extensive damage would be expected, it is not unrealistic to expect that most buildings should successfully withstand severe storms - very frequently, though, that's not the case."
Clemson has one of the top research facilities in the nation designed specifically to study and mediate the effects of high winds on low-rise structures such as homes and schools.