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21. I Was At Chrissy Field... But You Must Have Enjoyed This...

The day the Golden Gate Bridge flattened
By Stephen Tung [e-mail]
Posted: 05/23/2012 08:24:38 PM PDT
Updated: 05/24/2012 06:28:26 AM PDT



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Picture this: Hundreds of thousands of people are crammed shoulder to shoulder on the Golden Gate Bridge when suddenly the bridge's gentle arch begins to flatten out. A metal groan then echoes across San Francisco Bay as the majestic towers begin tilting toward each other.
As the towers hit their breaking point, the 3-foot-thick main suspension cables slacken and the roadway splits open, dropping waves of pedestrians more than 200 feet to their deaths.

That almost happened 25 years ago today, at least according to urban legend.

On May 24, 1987, 300,000 people were stuck in human gridlock for hours while getting a rare chance to cross the 1.7-mile bridge en masse on foot to celebrate the bridge's golden anniversary. Officials quickly closed the bridge, so a half-million other people waiting to cross never got the chance. Still, the enormous, unprecedented weight caused the middle of the bridge to sag 7 feet.

"I'm grateful because if the others had gotten out there, maybe the bridge would have fallen down," Gary Giacomini, then president of the bridge district's board, told The Associated Press at the time.

But engineers said afterward that the bridge was never in danger of collapsing. And bridge officials insist that the reason the bridge district isn't permitting pedestrians to swarm over the Golden Gate for the 75th anniversary Sunday has nothing to do with the threat of collapse and everything to do with the threats of overcrowding and terrorism in a post-9/11 world.

"It's just not wise," said Ewa Bauer, chief engineer of the bridge district.

Independent engineers agree with Bauer that structurally the bridge was safe during the Golden Gate's last big celebration.

"It was probably the biggest load the bridge had ever seen," said Mark Ketchum, a San Francisco bridge engineer who studied the Golden Gate Bridge from 1989 to 1991. "But it did not exceed the design load capacity of the bridge."

On fully loaded suspension bridges the size of the Golden Gate, it's normal to have "deflections" of up to 10 feet, said Greg Deierlein, a Stanford University professor of civil and environmental engineering.

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More: http://www.contracostatimes.com/breaking-news/ci_20695953/day-golden-gate-bridge-flattened