Taking the shake out of quakes

A technology first used during the Cold War to isolate ballistic missile silos from vibrations is to be tested on a full-scale, wood-frame townhouse subjected to a simulated 6.9 magnitude earthquake.

The experiment will take place in the University at Buffalo's Structural Engineering and Earthquake Simulation Laboratory (SEESL) on 6 July.  The goal of the project is to find out if fluid seismic dampers would minimise earthquake damage to wood-frame homes.

The test townhouse at University of Buffalo (UB) was constructed this spring as part of NEESWood, a four-year, $1.24 million National Science Foundation-funded consortium project, as reported on The Engineer Online.

"The idea with this test is to apply dampers in a real-life situation," said Andre Filiatrault, 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, associate professor of civil and environmental engineering at Rensselaer Polytechnic Institute, will supervise the damper tests at UB.

The dampers have previously been used in both military and seismic applications, having made the leap from missile silos to seismic applications in the 1980s. This will be their first trial on a residential building.

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 33,000kg, 167m² 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 synchronisation 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 51cm long and 9cm in diameter, can dissipate about 4,500 Newtons of force.

"That's equivalent in capacity to about 20 automotive shock absorbers," said Douglas Taylor, chief executive officer of Taylor Devices, who manufacture the dampers.

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

The heat then dissipates into the atmosphere, temporarily boosting the dampers' temperature as high as 93^oC. 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," said Filiatrault.