"Shock Absorbers" Can Minimize Quake Damage - Brief Article

USA Today (Society for the Advancement of Education), June, 2000

SEISMOLOGY

Devastating earthquakes in Turkey, Greece, and Taiwan point out the need for structural controls in buildings that could reduce the impact seismic events have on structures. Such controls could possibly save a number of lives and millions of dollars from building and infrastructure damage.

Shirley Dyke, professor of civil engineering, Washington University in St. Louis (Mo.), has tested a new device on a model building set atop an earthquake-simulating "shake table" that shows promise in minimizing earthquake damage. Using an earthquake-damping device called a magnetorheological (MR) damper on a six-foot-tall metal structure and utilizing data from a 1940 El Centro, Calif., earthquake, she applied the force parameters of that tremor to reproduce the effects on the model. Dyke compared the test results of the structure without the MR dampers, then with them. Measuring responses on every floor of the building, she found that the MR dampers reduce the peak acceleration by 50%.

The MR damper is a device that can act like a shock absorber on a structure. Three horizontal metal plates are sandwiched together, with the outer two plates connected to one end of the building and the middle one connected to the other end. When the shake table's hydraulic system moves the building, the middle plate slides back and forth between the two outer ones. Sensors are attached to the building's floors to measure the swaying when the shaking occurs. The data is relayed immediately to a computer that calculates where to turn the power on and put the dampers to work to lessen the shaking.

A MR fluid coats the middle plates and turns into a solid when a small electrical current is applied from a battery. This makes the three plates stick together, reducing the shaking. The liquid turns into a solid because the iron particles in the fluid join together from a magnetic field created by the electrical current. The entire process happens in fractions of a second. When the current is removed, the solid turns back to liquid. The process thus dampens the vibration so that it cannot accelerate through and up the floors of a building or structure.

The damper in the model building fits in the palm of the hand. In a real building, it would be about the size of a cardboard packing box and would be inserted inside the wall of the structure.

The MR damping technology is inexpensive and will operate on just 20-50 watts of power--the amount used by a household lightbulb. If electricity is cut off in a major quake, the device would still work because it is powered by a battery.