March 12, 2011

Japan's quake-resistant buildings withstand temblor

Huge rubber shock absorbers, walls that slide and Teflon foundation pads that isolate buildings from the ground all help explain why medium- and high-rise structures in Japan remain standing in the wake of the country's largest earthquake on record, construction experts said Friday.

The location of the quake, 80 miles offshore, might also explain why most of the structural damage reported appears to be from the tsunami that followed the quake rather than the shaking itself.

Since the devastating Kobe temblor in 1995, Japan has become a world leader in engineering new structures and retrofitting old ones to withstand violent shaking.

"The Japanese are at the forefront of seismic technology," said Eduardo Kausel, professor of civil and environmental engineering at the Massachusetts Institute of Technology. "All modern structures have been designed for earthquakes."

Strong Japanese building codes specify rules for short, medium and tall buildings, said Ron Hamburger, senior principal at Simpson, Gumpertz and Heger, an engineering firm in San Francisco.

New buildings shorter than three stories require reinforced walls and foundation slabs of a certain thickness.

Midrise buildings, those up to 100 feet, require more-intensive engineering, while designs for high-rise structures often employ innovative earthquake-resistant designs that undergo rigorous review by the country's top structural engineers.

The omnipresent threat of large quakes has turned shake-proof innovations into selling points for new high-rises, drawing higher rents, Hamburger added.

Midrise buildings in Japan often rest on huge rubber shock absorbers.

These large absorbers slide back and forth, quickly dissipating lateral motion by turning it into heat. Designs must account for how far a building might shift left and right to avoid banging into neighboring structures.

However, one design expert said traditionally built houses nearest the epicenter probably fared much worse.

"My strong feeling is that there are collapsed wooden buildings in the hills and rural areas over there that we don't know about yet," said John W. van de Lindt, a civil-engineering professor at the University of Alabama who has tested new methods in Japan to help prevent such collapses.

About 2,200 people died in small wooden buildings during the Kobe earthquake, he added. That toll prompted the Japanese government to launch an intensive retrofitting program called Dai-Dai-Toku (roughly translated: "very, very special") to prevent a similar catastrophe.

It remains unclear how the fruits of the program, which included insurance and government assistance to retrofit buildings, performed Friday, but van de Lindt and a team of National Science Foundation-funded researchers will find out soon enough. The agency will send several rapid-response teams to Japan to evaluate the damage and gather data from collapsed structures, which will be used to improve construction methods.

by Brian Vastag Washington Post Mar. 12, 2011 12:00 AM

Japan's quake-resistant buildings withstand temblor

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