A massive simulated earthquake will rock a six-story wooden condominium to the brink of collapse Tuesday, during one of the largest shake-table experiments undertaken to date.



The simulation, which will be webcast live July 14 at 11 a.m. EDT on the National Science Foundation website, is designed to test how a mid-rise wood-frame building would stand up to shaking from an earthquake around magnitude 7.5.

Update: This post was updated Wednesday morning to include video from the shake experiment, below.

“We’re taking it to an earthquake level that’s associated with being on the verge of collapse,” said civil engineer Michael Symans of Rensselaer Polytechnic Institute, who helped design the test building. “We don’t expect it to collapse, but we expect it to be very vulnerable to a strong aftershock that could cause it to collapse.”

The 23-unit condo building currently sits on the world’s largest shake table, a 50-by-60-foot structure in Miki, Japan. The table will simulate the motions of the 1994 earthquake in Northridge, California, amplified about 1.5 times. Sensors on each floor of the building will record motion and detect internal damage, generating valuable data about how wooden structures perform in a quake.

Although wooden buildings are cheaper and faster to construct than those made of steel, very few mid-rise structures in the United States are currently built of wood. “Even in seismically vulnerable parts of the West Coast, there just isn’t much of an understanding of how taller wood structures will behave under ground shaking,” Symans said. “It might be desirable to build in wood, but at this point that’s not an option from a building-code point of view, partially because we just don’t know what will happen in an earthquake.”

The test marks the final experiment in a four-year collaboration called the Network for Earthquake Engineering Simulation Wood project, funded by a $1.4 million grant from NSF and donated materials from the industrial manufacturer Simpson Strong-Tie.

The project’s first experiment subjected a two-story wooden house to a magnitude 6.7 earthquake, which severely damaged the structure. The engineers determined that homes built to current building standards might not topple during a large earthquake, but they’d likely never be livable again.

For the current test, they experimented with new design principles meant to help the condominium withstand shaking.

“Basically, what happens during an earthquake in multiple-story building is something called a ‘soft story,'” said civil engineer John van de Lindt of Colorado State University, who led the condo design. “It’s not as stiff as the story above it, and the earthquake demands more stiffness from the lower story. This can develop into a pancake collapse, which damages the building and can kill people.”

The new design distributes the stiffness vertically throughout the height of the building, van de Lindt said, to reduce the chance of a soft-story collapse.

On June 30 and July 6, engineers subjected the condo to preliminary testing, seen in the video below.

In the two smaller earthquake simulations, the building sustained very little damage. “So far, it looks like it’s working like a charm,” he said. “If there were families living in this condo, they wouldn’t even have to move out.”

Tuesday’s quake may be a different story. Numerical models predict a 3 percent drift, which means that each story of the building will shift over about three inches — enough to cause significant damage, but not enough to cause collapse. The only way to validate the computer models is to do a full-scale simulation, and that’s something that’s never been done before on such a large building.

“The reality is that we really don’t know what will happen,” Symans said.

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Image: Simspon-Strong Tie.