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Earthquake Engineering goes High Tech

For homeowners in California and other earthquake-prone regions, seismic safety has not exactly been rocket science. Retrofitting measures typically are limited to properly securing anchor bolts to foundations and nailing and connecting wood shear walls to a structure's ground floor.

But residential earthquake engineering is about to get a boost from, well, rocket science.

A technology first used during the Cold War to isolate ballistic missile silos from vibrations will undergo its first test in a full-scale, wood-frame townhouse in the University at Buffalo's Structural Engineering and Earthquake Simulation Laboratory (SEESL) on July 6.

The goal of the project is to find out if these fluid seismic dampers, manufactured by Taylor Devices in North Tonawanda, would minimize earthquake damage to wood-frame homes.

The test townhouse at UB was constructed this spring as part of NEESWood, a four-year, $1.24 million National Science Foundation-funded consortium project.

The goal of NEESWood is to develop a better understanding of how wooden structures react to earthquakes, so that larger and taller structures can be safely built in seismic regions worldwide.

Wood-frame construction accounts for an estimated 80-90 percent of all structures in the United States and 99 percent of all residences in California.

"The idea with this test is to apply dampers in a real-life situation," explained Andre Filiatrault, Ph.D., UB professor of civil, structural and environmental engineering and the leader of the NEESWood experiments at UB. "We want to find out if incorporating these dampers in a wood-frame residence is feasible from all practical perspectives, including construction, performance and economics."

Michael Symans, Ph.D., associate professor of civil and environmental engineering at Rensselaer Polytechnic Institute in Troy, N.Y., who holds three degrees from UB's School of Engineering and Applied Sciences, will supervise the damper tests at UB.

If they prove successful, Taylor Devices, whose business is half military and half seismic applications as the result of a two-decades-old research partnership with UB, now will be poised to enter the residential market as well.

"It will be a brand new market for us," said Douglas P. Taylor, chief executive officer of Taylor Devices and a UB alumnus. "And if it works, this will be a double crossover technology," he said, noting that this actually would be the technology's third incarnation, since making the leap from missile silos to seismic applications in the 1980s.

Currently, the Taylor Devices seismic dampers have been installed in 180 commercial buildings and bridges worldwide, ranging from the Petronas Twin Towers in Malaysia and the Beijing Railway Station in China to California's San Francisco-Oakland Bay Bridge and the Triborough Bridge in New York City.

But they have never been used in a wood-frame residence.

In the UB test, a total of four seismic dampers will be installed within the perimeter walls on both floors of the house. Once the walls are sheathed in plywood and gypsum, the dampers will be invisible.

The testing will subject the 73,000-lb., 1,800-square foot townhouse to a simulation of the magnitude 6.9 1994 Northridge earthquake on UB's twin, movable shake tables. The tables are capable of reproducing with high precision and synchronization the ground motions recorded during the 1994 earthquake.

The shaking for the test will be exceeded only during the final test of the house in November when it will be shaken vigorously to simulate a far more powerful earthquake.

"Our computational analyses indicate that the four dampers will substantially reduce the deformations and thus reduce damage within the wood framing system," said Symans.

Each silicon-fluid-filled damper, measuring approximately 20 inches long and 3.5 inches in diameter, can dissipate about 10,000 pounds of force.

"That's equivalent in capacity to about 20 automotive shock absorbers," said Taylor, noting that the average car has only four.

The dampers will take the energy of the earthquake and convert it into heat, removing it from the structure, explained Taylor.

The heat then dissipates into the atmosphere, temporarily boosting the dampers' temperature as high as 200-degrees Fahrenheit; the temperature typically returns to normal in about 15 minutes.

"We expect to be able to subject the house to much stronger shaking with the dampers and have the same response in terms of damage sustained that we did at much lower levels of shaking before the dampers were installed," explained Filiatrault.

Successful results could pave the way toward eventual use of the dampers in homes, Taylor said.

"While it's too early to predict yet what the cost would be to purchase dampers for an average home, surveys we have done of homeowners in California show that if we charged about $15,000 to install dampers to minimize damage, consumers would be more than willing to pay it," he said.

The seismic damping test at UB is the second of five different tests that will take place in the first year of the NEESWood project. In November, the furnished, three-bedroom, two-bathroom townhouse will be subject to the most violent shaking possible in a laboratory -- mimicking what an earthquake that occurs only once every 2,500 years would generate.

The UB tests are the first step in moving toward performance-based design for wood-frame structures. NEESWood will culminate with the validation of new design processes using a six-story, wood-frame structure that will be tested on the world's largest shake table in Miki City, Japan, early in 2009.

NEESWood is a consortium of researchers led by John W. van de Lindt, Ph.D., professor of civil engineering at Colorado State University. The co-principal investigators are Rachel Davidson, Ph.D., assistant professor of civil and environmental engineering at Cornell University; Filiatrault of UB; David V. Rosowsky, Ph.D., professor and head of the department of civil engineering at Texas A&M University, and Symans at Rensselaer Polytechnic Institute.

The NEESWood project is supported by the National Science Foundation under Grant No. CMS-0529903 (NEES Research) and CMS-0402490 (NEES Operations).

The University at Buffalo is a premier research-intensive public university, the largest and most comprehensive campus in the State University of New York.

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