Huge Earthquake Strikes Single Building in 'Shake Test'

At midnight in Japan on Tuesday, July 14, one of the worst earthquakes in human history took place in Miki City.

But the massive quake — which measured a 7.5 on the Richter scale — only struck one building, a seven-story wooden structure exposed to a simulated earthquake inside a Japanese laboratory. Happily for the U.S. engineers who designed the building, it did not fall down.

The full-scale building sat on a metal shake table that rocked it violently back and forth.

The table, designed to hold up to 2.5 million pounds, reproduced forces based on those recorded at a 1994 earthquake at Northridge, Calif., but scaled up by 180 percent to simulate an earthquake so violent it would only occur on average once every 2,500 years.

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The goal of this shake-table experiment, the largest ever, was to challenge building regulations that currently prohibit buildings of seven stories or more in quake-prone regions of the United States such as the Pacific Northwest.

"We're trying to demonstrate that if you use performance-based design, this building will perform very well in a very large earthquake," said John Van de Lindt, an engineer at Colorado State University in Fort Collins.

He is working with a team of engineers on a top-down way of designing buildings that focused on the building as a whole, as opposed to a bottom-up approach that starts with the individual components.

Van de Lindt was involved with similar test on a small two-story house in 2006, using a smaller shake table at the University of Buffalo in upstate New York.

The results from that test suggested that drywall is more important for structural stability than previously thought, and that steel support beams called sole plates should be an inch wider than those commonly used.

The seven-story condo constructed for the test contains 1,400 square feet of living space in 23 units and uses a new design that stacks six residential stories made of wood on top of a reinforced first story made of steel and intended for commercial shops.

The Japanese test is the culmination of a series of seismic tests known as the Network for Earthquake Engineering Simulation, funded by a $1.4 million grant from the National Science Foundation.

As the building swayed from side to side in Tuesday's test, a variety of instruments inside the structure measured the stretch and strain of individual components. High-speed cameras watched the horizontal motion of lights bolted to the outside of the building to check its sway.

The team will spend months analyzing the data to see how much structural damage was caused by the shaking and the likelihood of a person in the building being injured or killed.

"We're checking how far did the roof move relative to the first floor," said Steve Pryor, development manager for Simpson Strong-Tie, the California-based company that makes the metal connectors that helped hold the building together. "Our cut-off displacement is a few inches of movement per story."

Most buildings this tall are built of concrete or steel.

"This is first time that there have been any major development for wood," said Van de Lindt, who predicts that more designs made out of wood will be used in the coming years.

Provided by Inside Science News Service, http://www.aip.org/isns.