CORVALLIS - Some tried-and-true techniques of home construction may not be true after all, experts say, if people are interested in high quality homes that could not only protect their lives during a hurricane or earthquake, but also avoid massive repair bills.
As part of a new research program at Oregon State University, structural engineers in the College of Forestry are actually going to bring some of those hurricane force winds and violent earthquakes right into the laboratory, and re-evaluate construction concepts that have been accepted for decades - some of which may still be quite valid and others that have room for improvement.
With progress in this area, they say, it should be possible to create a new generation of housing and other wood structures in the United States that are more safe than those of the past, and can help prevent the catastrophic losses that now seem commonplace after every major natural disaster.
"Current U.S. building codes are minimum standards designed to protect life and safety," said Dave Rosowsky, holder of the Richardson Chair in Wood Engineering in the OSU Department of Wood Science and Engineering. "The first building code in the U.S. was created after the great fire that destroyed Chicago in 1871."
But in a modern world full of expensive houses that lie in the path of hurricanes, floods, tornadoes and earthquakes, Rosowsky said, minimal standards are inadequate to contain the enormous costs associated with structural damage, even though they may be effective at preventing loss of life.
"The Loma Prieta earthquake of 1989 caused $7 billion in damage, and the Northridge quake cost $15 billion," Rosowsky said. "Hurricane Andrew in 1992 cost about $27 billion, causing some insurance companies in South Florida to go out of business and others to stop writing policies for wind damage. It's clear that our codes might be good enough to protect lives, but they are not preventing costly damage."
People have a perception, Rosowsky said, that their homes and most other structures offer protection from hurricanes and earthquakes, and they often do. But it may be time to reconsider whether safety alone is an adequate standard, he said, and move towards a new concept called "performance design" that requires a structure to do much more than just remain standing after a big blow. Performance-based design requires that multiple requirements be met, including those that ensure damage levels are kept below pre-determined acceptable levels.
"We have to apply engineering principles to the design and construction of wood structures to improve their performance and resistance to natural hazards," Rosowsky said.
"In the process we'll also re-evaluate and, where necessary, update our codes, to see if time-honored techniques of construction are really adequate. For new construction, some of the changes may be quite small and incremental and might add only a few percent to the cost of building a new house."
For instance, scientists examined the effect of changing from a six-penny to bigger eight-penny nails to hold down roof sheathing that was exposed to gust wind speeds in excess of 100 miles per hour. Just the use of that slightly larger nail decreased the failure rate from 95 percent to 5 percent. Hurricanes and other strong storm winds pose the risk of wind uplift and water damage, Rosowsky said, which have led in recent years to the frequent use of "hurricane clips," sometimes called ties or straps, on roof rafters that are now part of newer building codes in high-wind regions. Performance based design limits are established by assessing what amount of deflection and movement in structures is considered acceptable before windows start to break, drywall starts to crack, roofs begin to leak or collapse and other major structural or non-structural damage is done that will be very expensive to repair, even if it doesn't pose an immediate threat to life or safety.
The earthquake risks facing California and the Pacific Northwest, Rosowsky said, will offer new challenges beyond his study of hurricane resistant structures at Clemson University in South Carolina. He was one of the principal investigators at the Wind Load Test Facility at Clemson.
"Earthquake shaking is a far more complex loading on a structure, is difficult to predict and poses a whole new set of challenges," Rosowsky said. "But some of our solutions may end up being as simple as improving the connections between various parts of the structure. Part of our challenge will be educating the public about the risks of earthquakes, as well as other natural hazards, to the point they insist on these construction features when purchasing a house."
Some good information that people can use as a reference, Rosowsky said, can be found on the web at www.homebase.org, or at www.fema.gov/impact.
Rosowsky's work is a little more colorful than that of most academics. He has used huge vacuums to suck the sheathing off of roofs, and fired 2x4s through walls with an air cannon made out of a beer keg. To see whether a structure could resist the impact of a tree falling on it, he and his Clemson colleagues created a "tree drop" experiment using a massive steel pipe to whack a house.
Another experiment seemed like it was right out of a tornado movie. The investigators were designing a "safe room" where people could seek shelter from a tornado or hurricane, and wanted to see what would happen if a car was thrown into the house. To simulate this, they used a crane to drop a car.
Rosowsky says his goal is to make the Department of Wood Science and Engineering at OSU into the nation's leading research program in structural reliability and performance-based design of wood structures, with a special emphasis on design for natural hazards.
In the process, he may have to crack, smash and destroy a few buildings by simulated hurricane forces and earthquake loads in OSU laboratories. But the result some day could be the creation of homes that will not only protect our lives, but our pocketbooks.