What would happen if you cut the cables on the Golden Gate Bridge?

Would it collapse? Are those vertical cables used to actually hold up the road portion or are they just for decoration?

If they’re actually structural, does that mean those two horizontal cables actually hold up the entire bridge? That’s amazing…

Yes, the cables hold up the entire roadway. If you cut the cables anywhere along their length, the entire roadway will fall into the water. (This is something that movies nearly always get wrong).

Are you claiming that if one vertical cable were cut the entire roadway would collapse? Unless the cables are looped so there’s really only one (which I doubt), this sounds liek a sever under-design on the bridge. It’s been a long time since I studied engineering, but as I recall bridges are designed with safety factors over 2. Certainly one missing cable wold be more than adequately compensated for by its neighbors.

I think he was referring to the long, horizontal cables that run from shore to shore. Not the vertical ones that hang the roadway from the cables.

The east and west sides have horizontal cables that run from one end of the bridge to the other. They are not really horizontal, but curved. Two of them. They are about 3 feet in diameter. There are lots of vertical cables about 2 inches in diameter from the roadbed to the thick cables. The loss of a few vertical cables would not be catastrophic. The loss of either of the 3 foot cables would pull apart the whole bridge.

The two horizontal main cables hold up everything. What you see is actually a casing, inside are 27,000 smaller cables. They were made by spinning cable from one end to the other, over and over again, for six months.

The vertical cables which connect the road to the main cables are called suspender cables, and they more or less just connect the road to the main cables. You could probably cut a few of them and not collapse the roadway. They’ve all been replaced before, one at a time I’d imagine.

Can you rephrase this? One cable, like a humongous spider’s web thread? That can’t be, so I’m totally misunderstanding the technique.

Great photo, BTW.

Think of a thick hemp rope – a thick rope made of thinner strands twisted around each other for the length of the rope. The huge thick catenary cables (the curved ones) actually consist of a bundle of thinner cables. (And I’m not sure any more, if the thinner cables each consist of a bundle of even thinner wires, or if they are solid.)

At the south end of the bridge (the San Francisco end) is a small park and visitor center. There is a section of the cable on public display there.

ETA: Link to some pictures

If just decoration, it was mighty expensive decoration as a significant portion of the world’s steel production those years went for just those cables! The horizontal cables are anchored at each end in concrete boxes, whose dimensions are also amazing.

I watched a TV documentary (History Channel?) about the bridge with several interesting topics. I’d guess there are excerpts on Youtube, but the first to turn up for me is an old 26-minute Bethlehem Steel film which, I’ll guess, contains some of the same footage as the documentary I watched.

How else would the bridge be held up? The roadway is certainly not rigid enough to be cantilevered out from the bridge supports. Suspension bridges are a rather elegant and efficient design, taking advantage of the high tensile strength of steel cables.

The weight of the bridge is ultimately held by the anchors where the cables are attached at either end. (In many bridges these go directly into the bedrock, but the Golden Gate bridge has massive concrete anchor towers.)

I guess I just never really thought about it. Like skyscrapers, bridges are just one of those feats of engineering that I’ve taken for granted, but when I really pause and consider how they were built… nothing short of astonishing.

I’ll probably check out one of those documentaries :slight_smile:

If you cut all the vertical cables, the horizontal cables would change from a (mostly) parabolic shape to a (mostly) catenary shape.

And of course, the roadway would fall and drown the motorists, but that’s of little consequence compared to the mathmatics!

You would be arrested for terrorism.

But how would they get to you?

It has happened that a horizontal cable (or rather in this case an eyebar rather than a cable) failed. The Silver Bridge wound up in the Ohio River along with 46 people in 1967.

I’m not sure what you’re asking. Are you asking whether they spun one cable back and forth 27,000 times? I should have worded is differently, I think it was 27,000 different cables. Then they took a machine that wrapped itself around the cables and squeezed, compacting them really tight and forming them into a near perfect circle. Then then they put a casing around it, which you can see in the photo I posted earlier.

For anyone REALLY interested in this stuff I recommend this book about the construction of the Brooklyn Bridge - which goes into great detail about not only the way the cables were laid but the (perhaps even more technically interesting) underwater construction of the tower bases - as well as the dramatic personal stories of the family the family that designed and built the bridge, the politics of the time and the questionable wheeling and dealing involved in the planning and financing, etc.

That was all down the Mothman, though, wasn’t it?

Here’s the Bethlehem video, fast-forwarded to the cable spinning. (The History Channel documentary is much more interesting than the Bethlehem video, IMO.)

I think it was on an episode of Dirty Jobs where Mike was painting the Mackinac Bridge that he showed that the roadway is not even connected to the towers. The towers hold up the main cables, the main cables hold up the suspender cables, the suspender cables hold up the road. It’s not all just for looks.

I did a web search for a good diagram of the cable anchorage and found this one that shows how the strands of cable spread out so they can withstand the tension.

Where did I find that link? straightdope.com, in this thread about whether the Brooklyn Bridge could collapse if one of the cables failed.