Researchers probe how strong buildings must be to survive tsunamis

Posted: March 12, 2012

Clay J. Naito started to feel woozy in his ninth-floor hotel room in Japan, then quickly realized the reason: The entire building was shaking.

It was not the earthquake that unleashed a deadly tsunami a year ago on March 11 - a surge of water that topped 60 feet in places - but a much smaller quake a few months later. Still, it rattled him, because he is a civil engineer and knows how a building can succumb to the might of the trembling earth.

"For me, it's worse than most people," said Naito, an associate professor at Lehigh University. "I know what can go wrong."

Naito was in Japan with a team researching how strong a building must be to withstand the destructive potential of a tsunami.

The forces from floodwaters alone are bad enough, but as Japan learned last year, a tsunami can pick up trucks, shipping containers, and even houses in its wake, slamming them into buildings where people have sought refuge.

Having surveyed the damage during their visit to Japan in June, Naito and his partners now are trying to re-create tsunami-like conditions in the lab.

At Lehigh, in a cavernous testing center that once was a Bethlehem Steel warehouse, engineers have suspended a 20-foot shipping container from sturdy cables. They use a hydraulic winch to pull it back and let it go, like a battering ram, to measure the resulting forces.

This summer, Naito's collaborators at Oregon State University plan to conduct more tests in water, in a wave pool longer than a football field. They will use scale models of shipping containers, measuring one-fifth normal size. Both studies will be used to tweak sophisticated computer models.

A Katrina connection

The idea for this study, funded by the National Science Foundation, arose after engineers saw the devastation wrought by Hurricane Katrina. The findings would apply to any sort of waterborne debris, and thus could be relevant in areas vulnerable to hurricanes and storm surges, such as the Jersey Shore.

The Japanese quake and tsunami, both named Tohoku after the affected region of the country, struck a few months after the research had begun. That further illustrated the power of debris, said project leader H. Ronald Riggs, a professor of civil engineering at the University of Hawaii.

"The Tohoku tsunami opened people's eyes to the threat," Riggs said.

In a tsunami, water rushes onto land in a hurry. There often is no time to get to higher ground, or there may not be any higher ground available - as is the case in parts of Japan. Of the 20,000 people killed by the Tohoku event, most drowned.

The answer is to have tall buildings serve as evacuation centers, but they must be strong enough.

Riggs said he did not know of any Japanese evacuation centers that failed as the result of debris. But the area has received little research, and current building codes and industry standards do not properly take the threat into account, he said.

A key goal would be to guard against the problem of progressive collapse, meaning that a building should be designed to remain standing even if one column is taken out, Riggs said.

Much work remains to be done, but one thing is clear so far. The research is loud.

Stress and strain

Last Monday at the Lehigh testing center, an engineer in a hard hat pulled a 21/2-ton shipping container back several feet in the air, using a winch.

When he let go, the container swung forward toward four circular "load cells" - instruments that measure force.

The impact echoed throughout the test center, a five-story structure on Lehigh's Mountaintop Campus in Bethlehem, Pa.

One of the cells recorded an impact of 10,000 pounds of force. Another registered 5,500 pounds, and a third recorded 4,500 pounds. The fourth cell was not struck at all.

Those results illustrated one of the difficulties in predicting how debris will behave. It can flex on impact and does not necessarily strike all at once.

In addition to measuring the forces, the engineers also recorded data from 20 strain gauges that were attached to the container, connected to nearby "data loggers" with white cables.

For these initial tests, the container was pulled back just one or two feet. In a few weeks, the Lehigh engineers plan to really let it rip, pulling back the container about 10 feet - far enough that the engineers expect it to crumple.

Early interest

Naito, whose office at Lehigh is lined with such kinetic-sounding titles as Shock and Vibration Handbook, said he became interested in civil engineering while growing up in Hawaii, watching his father work as a general contractor.

"Working with him over the holidays and summers, I developed an interest in how structures are able to stand," Naito said.

Naito met Riggs in 1993 at the University of Hawaii, when Riggs started teaching there and Naito was finishing his undergraduate degree. Riggs invited Naito to join the debris research in 2010.

When the tsunami struck Japan the following year, Naito already had some familiarity with the culture and spoke a few words of Japanese, as his paternal grandparents happened to be from Japan.

That came in handy when the smaller quake struck during his June visit. In a blog about his trip, Naito described how he rushed into his hotel hallway, suitcase in hand, once the shaking had stopped.

Encountering another hotel guest, Naito asked if everything was OK.

Daijoubu desu ka?

Hai, daijoubu. Yes, it's OK.

Naito estimates that the June quake was a magnitude of about 6 - hundreds of times weaker than Tohoku. But while in his room on the ninth floor, able to see electrical cables swaying outside, the engineer was troubled.

"Being a bit of an adrenaline junkie, I had always thought that an earthquake would not be too scary," Naito wrote afterward. "As the building shook under my feet, I quickly realized that I was mistaken."


Lehigh University researchers use a large shipping container to simulate the destruction of tsunami debris. Go to www.philly.com/tsunami


Contact Tom Avril at 215-854-2430 or tavril@phillynews.com.

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