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“Overdue” earthquake has New York engineers on alert

By Liana Grey

Over a hundred years ago, a magnitude 5.1 earthquake struck where JFK stands today. The tremor lasted no more than several seconds, but it managed to liquefy soil in Queens and Brooklyn, causing beach houses on Coney Island to tilt and chimneys to crumble. Home owners as far away as Pennsylvania reported cracked walls and fallen bricks.

New York may not sit on a fault line like, say, Japan or Christchurch, New Zealand, but every century or so, the city is at risk of a seismic disaster. “We are overdue for one,” said Sissy Nikolaou, an expert in seismic design at Mueser Rutledge Consulting Engineers, a New York-based firm.

Last week, Nikolaou and three other engineers shared information for quake-proofing the Big Apple at a conference hosted by the American Council of Engineering Companies. Ramon Gilsanz, a founding partner of the engineering firm Gilsanz Murray Steficek, said, “You have to know how to get out.”

Staircases, which serve in some buildings as diagonal bracing, are often prone to collapse. “Measures must be taken so stairs aren’t structural elements,” said Gilsanz, who was part of a team that investigated structural damage to the World Trade Center after 9/11.

In some ways, lessons from that day’s attacks carry over to earthquake protection. “The risk of the hazard is moderate, but the effects of the hazard can be significant,” said Nikolaou.

Beyond casualties and the displacement of hundreds of apartment dwellers, the damage would extend to the global economy; by 2025, New York’s GDP is expected to grow fastest among cities worldwide.

In 2005, the Brooklyn Bridge and other East River crossings were strengthened with steel girders during renovations, as part of a government mandate requiring important infrastructure to be shielded from shock waves.

Dampers and bearings are used to displace energy and prevent structures from collapsing. “Seismic isolation is a method of construction, applied to the base of a structure just above the foundation,” explained Michael Constantinou, a SUNY professor that has spent 30 years developing isolation hardware.

In the 1800s, in San Francisco, that meant placing houses on rollers. These days, buildings like the San Francisco General Hospital are fitted with triple friction pendulum bearings, one of the most advanced methods of seismic protection.  “It shifts, bounces, and stretches back and forth,” Constantinou said of the black tubes.

But, “Even if you do everything by the book, 10 percent of buildings will collapse,” said Gilsanz. Of surviving structures, nearly half would be rendered unusable by a major quake. “Suddenly, you’ve lost water, you’ve lost sanitation. You can’t inhabit that apartment,” he explained.

The extent of damage depends on where a building is located. Much of Manhattan is built on “the hardest rock you can find on Earth,” Nikolaou said, but Chinatown sits above an ancient lake that once supplied water to the city. Parts of lower Manhattan, including Battery Park City, were built on landfill that could crack in the event of a tectonic shift.

“The code doesn’t deal with soils that can collapse,” said Nikolau, who has advocated more stringent measures for earthquake protection, including thorough inspections of the rock layers beneath a construction site.

New York’s building code was last updated with latest seismic design measures in 2008 and will be revised again next year.

In other good news for a city of towering landmarks, height doesn’t seem to matter. When an earthquake struck Mexico City in 1985, buildings 10 to 20 stories high experienced the least damage.

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  1. Roert Brookes
    Jul 25, 2011 - 11:45 PM



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