WASHINGTON
UNIVERSITY TEAM TESTS QUAKE-DAMPING DEVICE
FLUID THAT TURNS SOLID COULD
SERVE AS SHOCK ABSORBER, SAVE LIVES
Byline William
Allen
Of the Post-Dispatch
Sept. 7, 1999
Edited by Virginia Baldwin Gilbert
If tests by Washington University researchers are successful, a technology developed to help save truck drivers' backs may one day be used to save lives in major earthquakes.
The technology is a kind of high-tech shock absorber containing a fluid that turns solid when a bit of electricity is applied.
"We're trying to develop these devices to reduce the devastating consequences of an earthquake," said Shirley Dyke, a civil engineering professor at the university.
The researchers are conducting experiments on the St. Louis region's first "shake table," a $100,000 earthquake simulator that Dyke designed and built in 1997.
Dyke and her students are using it to simulate the forces unleashed on a building in a quake. Their goal is to develop guidelines for design engineers who can use the quake-damping devices in new buildings and in old buildings that need retrofitting to better withstand an earthquake.
The work is part of the effort by scientists worldwide to find ways to lessen the damage to buildings and the subsequent loss of life in earthquakes. Already such methods include placing a building's main columns on huge rubber pads that isolate the structure from shaking. The new Monsanto Research Center at the Missouri Botanical Garden is the region's first building with that technology.
Scientists don't have enough information yet to know whether this knowledge would have been useful in the Aug. 17 quake in Turkey, Dyke said.
"But these techniques could be implemented there in some buildings to help prevent damage," she said.
The techniques could be just as important in Missouri and Southern Illinois, where the New Madrid Fault is a constant quake threat.
The fault got its name from New Madrid, Mo., a town where one of many powerful quakes in 1811-12 was centered. The New Madrid Fault zig-zags for more than 100 miles from northeastern Arkansas, through the Missouri Bootheel and into the southern tip of Illinois. Scientists say a major quake along the fault could cause damage hundreds of miles away.
The device now being tested at Washington University is called a magnetorheological damper, or an MR damper for short.
The damper works like a shock absorber. Put simply, it consists of three horizontal metal plates sandwiched together. The outer two plates are connected to one end of the building and the middle one is connected to the other end.
When the building begins to shake, the middle plate slides back and forth between the two outer plates.
A special oil-like fluid coats the middle plate, but the fluid turns into a solid when a small electrical current is applied from a battery. That causes the three plates to stick to each other, which reduces the shaking.
Key to this process is that the fluid contains iron particles. When the electrical current causes a magnetic field in the liquid, the iron particles line up and grab onto each other in a way that makes the liquid solid.
This occurs in only a few thousandths of a second. The solid returns to liquid just as quickly when the current is turned off.
Lord Corp. of Cary, N.C., developed the fluid as part of a project to dampen the vibrations that gradually wear on the backbones of long-distance truck drivers. Now it's used in exercise equipment, washing machines and other products.
And someday it will be used in earthquake-resistant buildings, if Dyke has her way.
Testing the technology
Dyke directs the university's Structural Control and Earthquake Engineering Laboratory, where the shake table is housed.
The base of the table is a 5 foot-by-5 foot plate of aluminum. That's considered medium-size.
Engineers at the Columbia and Rolla campuses of the University of Missouri work with medium shake tables, too. Engineers at the University of Illinois at Champaign-Urbana conduct experiments on a large shake table, which is roughly three times larger.
The tables are a fairly rare research device, with only a half-dozen large ones around the country and about 15 medium ones.
"To have three in one state is pretty amazing," Dyke said.
Researchers build various structures atop the tables. During a test, a hydraulic system moves the table back and forth to simulate the forces experienced in any of several earthquakes, including those in 1995 in Kobe, Japan, and 1994 in Northridge, Calif.
"When it's available, we'll reproduce the one in Turkey, too," she said.
The structure on the shake table last week was not exactly the Sears Tower. The 6-foot-tall naked frame with flat steel bars looked nothing like a real building. But it was fastened together in a way that simulated the natural behavior of a six-story steel building during an earthquake.
The structure was topped by a clear plastic tank filled with blue water, which sloshed around during the tests to indicate the severity of shaking.
Dyke pointed to the damping devices fastened to the frame on the first and second floors.
"You want to dampen out the vibration before it gets to the upper levels," she said. Vibrations are harder to control when they reach that high.
Sensors attached to each floor of the building measure the swaying when the shaking hits. This information shoots to a computer, which instantly calculates where to turn on the power and engage the dampers in the best way to counteract the shaking. "This is a 'smart building,' " Dyke said.
Preliminary results show that the new technique reduces by 50 percent a quake-struck building's acceleration - the name scientists use to describe the force that shakes the structure.
The work is funded by the National Science Foundation and Washington University.
The damping technology shows great promise for large buildings because it's cheap, simple and only needs the electricity provided by one or two car batteries, Dyke said. That means if electrical power is cut - a common occurrence in a major quake - the fluid would still work.
Dyke and her students plan to study bridges and other kinds of structures on the shake table. They also will measure the effects of a quake on buildings built next to each other.