9/3/13

Japan a leader in engineering earthquake-proof structures, helping to limit damage

Japan a leader in engineering earthquake-proof structures, helping to limit damage
By Brian Vastag
Washington Post Staff Writer
Friday, March 11, 2011; 10:52 PM

Huge 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 remained standing in the wake of the country's largest earthquake on record, construction experts said Friday.
The location of the earthquake, 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, a 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 and Heger in San Francisco.
New buildings shorter than three stories are required to have 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 100 feet, require much 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.
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 or fluid-filled shock absorbers.
While the shocks in your car bounce up and down, these larger absorbers slide side to side, quickly dissipating lateral motion and 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.
Other shorter and mid-rise buildings rest on Teflon-coated pegs embedded in the foundation. The weight of the structure anchors the building on the pegs, but when the ground shifts the entire building slides over the smooth surfaces. www.washingtonpost.com/wp-dyn/content/article/2011/03/11/AR2011031104541_pf.html

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9/3/13

Japan a leader in engineering earthquake-proof structures, helping to limit damage

This technique is one of many "base isolation" methods that decouple buildings from the ground beneath, rendering them subtly floating structures.
In the United States, such techniques grew in prevalence after the 1989 quake that hit the San Francisco Bay
Area. The historic, mid-rise city halls of San Francisco, Oakland and Los Angeles were all retrofitted to rest on giant shock absorbers.
Taller buildings employ more sophisticated measures, often in combination.
All modern skyscrapers are engineered to be strong yet flexible, so they sway in the wind - a discomfiting sensation felt on the observation decks of super-tall buildings such as the Willis Tower (formerly the Sears
Tower) in Chicago.
Designing extra flexibility into the tallest buildings is essential for earthquake-proofing, said John W. van de Lindt, a civil engineering professor at the University of Alabama.
Video filmed during the aftershocks that hit Tokyo on Friday shows high-rises doing exactly that - wavering dramatically without snapping.
"You will get shelves tipping over and copy machines running across the floor," said van de Lindt, but structural damage will be minimal, even when the top of the