Did the Golden Gate Bridge 'flatten' under the weight of 300,000 people in 1987?

Question

According to SFGate (and many other sources):

The May 24, 1987 event celebrating the bridge's 50th anniversary was organized by the "Friends of the Golden Gate Bridge," a group made up of five members of the bridge district board of directors. The group expected a crowd of 80,000 people, but instead received an estimated 800,000 people at the event.

...

The weight of the 300,000 people flattened the normally arched roadbed, although bridge engineers later said there was never any real danger.

"The Golden Gate Bridge, all 419,000 tons of it, groaned and swayed like an old wooden plank thrown across a ditch," Montgomery wrote. "Frightened and seasick people vomited on their shoes."

Is the above story true? Did the bridge actually flatten back in 1987? Unfortunately I can't find any conclusive evidence in Google search.

Answer 1

Yes, according to the 27 May 1987 Desert Sun article 250,000 jammed Golden Gate span’s deck Engineer: Bridge crowd not close to load limit:

[Engineer Dan] Mohn said the 250,000 people who packed onto the bridge on Sunday for the 50th anniversary celebration made up the heaviest load ever supported by the orange landmark, heavy enough to temporarily flatten out the arch of the bridge deck and to concern some bridge officials. The concerns led Mohn to do some rapid calculations during the bash to see how close the weight came to the capacity designed by Joseph Strauss and others 50 years ago. The designers built the bridge to support 7,700 pounds per linear foot during a combination of high winds and earthquake, Mohn said. He said his calculations showed that Sunday’s load reached about 5,400 pounds per linear foot where the crowd was thickest.

Mohn said he wasn’t surprised by the flattening out of the bridge deck in the center of the span, where the revelers were packed shoulder-to-shoulder. He said the distortion was five to six feet, about half the 11-foot vertical movement allowed in the design capacity.

“If the design load was even all the way across the roadway, the bridge would be not only flat from tower to tower, but it would have a one-foot sag in it,” he said.

So it flattened, in the sense that it became more flat, moving 5 to 6 feet relative to with no load, but not the 10 feet that would be needed to be completely flat on the main span.

Answer 2

A NYT article from two days after the event already contains the claim that "The bridge flattened out - its whole arch disappeared." That quote is from Gary Giacomini, president of the bridge district board. However, Giacomini doesn't strike me as a trustworthy source based on the other things he's quoted as saying in the same article (including that "maybe the bridge would have fallen down" if more people had been allowed on – an irresponsible thing for a public official to say, and never corroborated by any engineer to my knowledge), and no other source is mentioned in the article.

Here are a couple of photos of the bridge walk at what appears to be its height, from this slideshow:

In both you can see that the roadway between the towers is far from flattened, although small stretches of it do look straight.

Here's a photo of the bridge from a similar angle under light traffic for comparison: