26

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.

9
  • 17
    People underestimate how stretchy large amounts of any material is. Giant structures can bend a lot before breaking (more so in earthquake areas where they are designed to flex). The Tacoma narrows bridge twisted the road to almost vertical before it finally gave out. Commented Apr 29, 2023 at 6:05
  • 1
    Given the height of the road deck and the subtle swaying from wind, one might consider vertigo to cause nausea amongst some attendees.
    – Criggie
    Commented Apr 29, 2023 at 6:08
  • 3
    Isn't this off topic by definition here? Honest question, I don't really know the scope that well. I ask because you are already providing several reputable sources to back the claim in the question itself and any answer would just be more of the same. Haven't you already proven, by the standards of this site, that the claim is true and, if so, isn't this question off topic because it includes its own answer?
    – terdon
    Commented Apr 29, 2023 at 14:12
  • 4
    @terdon I can find hundreds of sources for the story about Albert Einstein and his driver attending a lecture together. Doesn't mean it actually happened. Commented Apr 29, 2023 at 18:14
  • 1
    @KevinKostlan almost vertical? looks more like 30 degrees to me. Still a lot of flexing Commented May 5, 2023 at 1:42

2 Answers 2

53

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.

6
  • 3
    I'm not quite sure the quotes support your last statement. If the design is to be able to support going from an arch of +6 to a sag of -6, then flattening it by 6 feet would, in fact, make it completely flat.
    – Bobson
    Commented May 1, 2023 at 15:03
  • 3
    @Bobson that's not the design. The design is +10 to -1 feet.
    – DavePhD
    Commented May 1, 2023 at 16:35
  • "about 5,400 pounds per linear foot" I might be struggling with converting American units, but maybe someone could make a similar calculation for a heavy loaded truck carrying some 30-50 metric tons. Because I can't quite grasp how humans no matter how tightly packed or piled on top of each other can ever weigh more than a truck hauling something like construction machinery. Or maybe such heavy haulage trucks are not allowed to use the bridge?
    – Lundin
    Commented May 9, 2023 at 13:21
  • 1
    @Lundin those trucks are about 72 feet long and 72,000 pounds, so only 1000 pounds per linear foot of bridge (for trucks touching end to end the all along the bridge in one lane). If all 6 lanes were covered with trucks end to end with no spacing it would be about 6000 pounds per linear foot of bridge.
    – DavePhD
    Commented May 9, 2023 at 13:38
  • Still, how could you get 5400 pounds into a linear foot by using humans? Doesn't that mean you'd have to pack like ~25 big men into that linear foot...
    – Lundin
    Commented May 9, 2023 at 13:56
21

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:

11
  • 29
    The photos are hard to interpret without comparisons from similar angles to see how curved it normally is. I don't think "flattened" necessarily means "completely flat", only "flatter than normal".
    – IMSoP
    Commented Apr 29, 2023 at 9:33
  • @IMSoP: True, though I think it's more important to note that arch shape of the road surface does not serve as any kind of compression arch. Many bridge surfaces and roof are designed to be slightly arched up in the middle for practical reasons (e.g. minimizing the amount of force required to remove a heavy vehicle whose engine fails while it's on the bridge), but from a structural standpoint woudln't care about whether they were bowed up or down.
    – supercat
    Commented Apr 29, 2023 at 17:51
  • 4
    @IMSoP The use of "flattened" in the question is a bit vague, but I linked an article showing that even immediately after the event there were notable (NYT quoting a named official) claims that it had flattened completely, not just locally ("its whole arch disappeared"). I'd guess that at least some subsequent mentions of flattening are linked to that early claim. So it seems relevant that it didn't flatten to that extent.
    – benrg
    Commented Apr 29, 2023 at 22:16
  • 1
    @IMSoP: If one were to place a bowed piece of material on the floor and step on it, there would be a qualitative difference between being heavy enough to flatten it "completely", versus flattening it to a lesser degree. With something like a suspension bridge, there would likely be a level of loading at which it would be closest to being flat (though it would most likely some parts that were concave up and some that were concave down), and additional loading would cause the bridge to be less flat. Thus, the adjective "completely" wouldn't really have a well defined meaning.
    – supercat
    Commented Apr 30, 2023 at 16:17
  • 1
    @Evargalo I rehosted it.
    – benrg
    Commented May 2, 2023 at 6:50

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .