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Making earthquakes for science

Ben Schafer of the Johns Hopkins Department of Civil Engineering

Engineering researchers at the Johns Hopkins University plan to stir an earthquake this month, a temblor as powerful as the 1994 Northridge quake in Southern California — one of the costliest in U.S. history.

It will hit at the University at Buffalo, the State University of New York, inside a huge laboratory with a soaring ceiling, big enough to contain a two-story building set on a giant hydraulic "shake table." They know they will take their places in a control room, eyes on that building and an array of computer monitors, to watch the simulated Northridge earthquake unfold before them at the click of a computer mouse.


"It's awesome, it's the best project of my life," said Benjamin Schafer, professor and chair of Hopkins' department of civil engineering. He's leading the project, which includes shaking a full-size building with earthquake force to test the resilience of an increasingly popular construction material, cold-formed steel.

Schafer expects to be there in Buffalo when the final tests take place, probably Aug. 15 or 16. While his graduate research assistant Kara Peterman blogs from the Buffalo laboratory, he's been shuttling up and back for months keeping tabs on the project that could lead to safer buildings and construction standards that make more efficient use of materials.


"This is the first in the world test of cold-formed steel buildings" for earthquake resistance, Schafer said.

Cold-formed steel has become more prevalent in framing homes and especially commercial buildings since the 1990s, but it's been around since the 1920s. Unlike hot-rolled, or structural steel, this stuff starts out in sheets of thin metal and is shaped — at room temperature — into pieces of varying thickness used in construction. A common cold-formed steel piece used in framing, for instance, is comparable to a wood 2-by-4.

Larry Williams, executive director of the Steel Framing Industry Association, estimated that cold-formed steel holds only a 1 percent or 2 percent share in the single-family homebuilding market, perhaps 3 or 4 percent in residential apartments. In commercial construction, it's about 39 percent of the market, with slightly more use in load-bearing than non-load-bearing elements.

He called the Hopkins research "a very significant piece of work" that could provide information to "enable engineers to produce more efficient designs," potentially saving time and money.

Jay Larson of the American Iron and Steel Institute, which is helping to finance the research, said there's bound to be a benefit "whenever you can have a better understanding of the actual behavior of a building" under stress. "You can improve your designs; you can improve your detailing."

The National Science Foundation thought cold-formed steel's place in the universe of building materials was significant enough to award a three-year, $923,000 grant in 2010 to find out more about it. Specifically, how does it hold up in earthquakes? Could international construction standards be refined to reflect new information?

The foundation provided most of the money, and "their interest is structural safety" and how to "improve efficiency and sustainability of buildings," said Schafer, who is working on the project with several engineering firms and colleagues at four other universities.

Hopkins researchers can do laboratory work on small structures using a contraption made of blue I-beams in the basement of Latrobe Hall on the Homewood campus. For full-building scale testing, however, only a few places on the planet will do.


Buffalo is the only place in the United States where a building this size — 50 by 23 feet, or about the size of a small office building in a suburban strip mall — can be subjected to an ersatz earthquake

Peterman, who is working on her doctorate in civil engineering, has been in Buffalo since April, blogging on the details of creating and testing the two-story building. Using the shake table as a foundation, the work crew first built a skeletal version and was putting finishing touches on a second, more fleshed-out model, complete with interior walls, stairways, office cubicles and weatherproofing.

There will be no plumbing, heating or air conditioning, however. To make up for the weight of that stuff, plus furniture, and more closely replicate the specifications of a real building, the crew has added steel plates to the roof and concrete blocks inside. That brings the weight to about 77,500 pounds, Peterman said.

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About 100 tests have been performed, some replicating earthquake movement, some slower and less jarring. Members of the laboratory team sit in a control room equipped with an array of computer monitors, receiving information from 168 motion sensors and eight video cameras on the building, Peterman said.

The building has held up better than the researchers expected, Peterman said. Some plywood has torn away from its moorings in the steel, and a steel piece once bent at the edge, but that was because of a construction error rather than the motion impact, Peterman said.

For the earthquake simulations, researchers have used as a standard the seismic movement recorded at a station in Canoga Park, about 25 miles northwest of Los Angeles, during the Northridge quake shortly before dawn on Jan. 17, 1994.


Readings there for the ground acceleration rate were about 40 percent lower than those taken at two stations in Granada Hills, about eight miles to the northwest. Those higher readings were equal to a car accelerating from zero to 60 miles per hour in 3.25 seconds, "slightly faster than a Ferrari 458 Italia," Peterman said in an email.

In the final test, the fully built structure will be subjected for the first time for about 20 seconds — the duration of the Northridge quake — to the full impact of movement at both the Canoga Park and Granada Hills stations. It's bound to be bumpy and informative.

"Everything we learn is new," said Schafer. "That's the beauty of going first."