In the 1930s, the middle of the bridge was designed to move 16 feet vertically and 27 feet from side to side without causing permanent damage, said Mary Currie, a spokeswoman for the bridge district.
Originally, the bridge was engineered to hold 4,000 pounds for every foot of bridge. And during the mid-1980s, concrete was replaced with a lighter steel framework, boosting that capacity to 5,700 pounds per foot, bridge engineers said during the 50th anniversary festivities.
No one knows the exact weight of the pedestrians on the bridge on that May day. But assuming the average person weighs about 150 pounds and occupies about 2.5 square feet in a crowd, there would have been about 5,400 pounds for every foot in length. That’s more than double the weight of cars in bumper-to-bumper traffic.
The difference between 5,400 and 5,700 pounds might sound too close for comfort. But bridge engineers emphasize that they routinely build in an additional “factor of safety” to account for unexpected loads put on a structure.
The designers of the Golden Gate over-engineered the bridge to accommodate at least an additional 150 percent weight, said chief engineer Bauer.
And even if the crowd 25 years ago had formed a massive human pyramid and exceeded that safety buffer, the deck would “deform” and not break, like a paper clip bending instead of snapping, said Abolhassan Astaneh, a UC Berkeley professor of civil engineering, structural engineering and bridge engineering.
What’s more, even if part of the bridge collapsed, not all of the roadway would have fallen into the bay, Astaneh said. Sections of the roadway are supported by the cables and not by each other, Astaneh said, so if one piece of the deck falls, it doesn’t bring others with it.
“They’re just swings, 50-foot-long swings next to each other,” he said of the roadway’s sections.
Most of the anxiety that day came when the crowds from San Francisco and Marin County met in the middle of the bridge. People were sandwiched together and couldn’t move.
“Then it got kind of scary, because we realized we were trapped,” said Barbara Schnur, a Foster City resident who was 25 at the time. “We were standing there, and then I said to my friend, ‘Dude, this bridge is moving.’ “
Indeed, winds were blowing as fast as 40 miles per hour, so the bridge was swaying from side to side.
“It was almost like you were walking drunk,” said San Francisco native Karl Watanabe, who was 32 at the time. He said he was also worried about the crowd panicking, causing “a mass exodus.”
Luckily, smartphones and Twitter didn’t yet exist, so many of the pedestrians were blissfully unaware the bridge had flattened until they saw the picture in the newspaper the next day.
BeaArthursGhost on September 20th, 2017 at 01:47 UTC »
I hope none of the folks in the middle were claustrophobic!
hazeleyedwolff on September 20th, 2017 at 01:54 UTC »
How do you determine the point of "almost collapse"?
DrRonny on September 20th, 2017 at 02:50 UTC »
In the 1930s, the middle of the bridge was designed to move 16 feet vertically and 27 feet from side to side without causing permanent damage, said Mary Currie, a spokeswoman for the bridge district.
Originally, the bridge was engineered to hold 4,000 pounds for every foot of bridge. And during the mid-1980s, concrete was replaced with a lighter steel framework, boosting that capacity to 5,700 pounds per foot, bridge engineers said during the 50th anniversary festivities.
No one knows the exact weight of the pedestrians on the bridge on that May day. But assuming the average person weighs about 150 pounds and occupies about 2.5 square feet in a crowd, there would have been about 5,400 pounds for every foot in length. That’s more than double the weight of cars in bumper-to-bumper traffic.
The difference between 5,400 and 5,700 pounds might sound too close for comfort. But bridge engineers emphasize that they routinely build in an additional “factor of safety” to account for unexpected loads put on a structure.
The designers of the Golden Gate over-engineered the bridge to accommodate at least an additional 150 percent weight, said chief engineer Bauer.
And even if the crowd 25 years ago had formed a massive human pyramid and exceeded that safety buffer, the deck would “deform” and not break, like a paper clip bending instead of snapping, said Abolhassan Astaneh, a UC Berkeley professor of civil engineering, structural engineering and bridge engineering.
What’s more, even if part of the bridge collapsed, not all of the roadway would have fallen into the bay, Astaneh said. Sections of the roadway are supported by the cables and not by each other, Astaneh said, so if one piece of the deck falls, it doesn’t bring others with it.
“They’re just swings, 50-foot-long swings next to each other,” he said of the roadway’s sections.
Most of the anxiety that day came when the crowds from San Francisco and Marin County met in the middle of the bridge. People were sandwiched together and couldn’t move.
“Then it got kind of scary, because we realized we were trapped,” said Barbara Schnur, a Foster City resident who was 25 at the time. “We were standing there, and then I said to my friend, ‘Dude, this bridge is moving.’ “
Indeed, winds were blowing as fast as 40 miles per hour, so the bridge was swaying from side to side.
“It was almost like you were walking drunk,” said San Francisco native Karl Watanabe, who was 32 at the time. He said he was also worried about the crowd panicking, causing “a mass exodus.”
Luckily, smartphones and Twitter didn’t yet exist, so many of the pedestrians were blissfully unaware the bridge had flattened until they saw the picture in the newspaper the next day.