Japan A Leader İn Quakeproof Structures

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

The location of the earthquake, 130 kilometres 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 quake 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 MIT. “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 the engineering firm Simpson Gumpertz & Heger in San Francisco.

New buildings shorter than three stories require reinforced walls and foundation slabs of a certain thickness, meaning “there is not a whole lot of design to it,” Hamburger said.

Mid-rise buildings, those up to 30 metres, require much more intensive engineering, while designs for highrise 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 shakeproof innovations into selling points for new high-rises, drawing higher rents, Hamburger added.

Mid-rise buildings such as hospitals and laboratories in Japan, as well as on the west coast of the United States, often rest on huge rubber shock absorbers.

Although the shocks in a car bounce up and down, these larger absorbers slide back and forth, quickly dissipating lateral motion by turning it into heat.

“They allow quite a bit of movement,” said James Martin, director of the World Institute for Disaster Risk Management at Virginia Tech. Of course, designs must account for how far a building might shift left and right, to avoid banging into neighbouring structures.

However, one design expert said traditionally built houses nearest the epicentre 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.