I live by the Margaret Hunt Hill bridge and I can just look at it and see how the cables are holding up the bridge. But it’s not obvious to me how the cables help on a bridge like the golden gate bridge. Just visually it looks like the cables have so much slack they would weigh the bridge down even more.
In: Engineering
That’s actually an interesting phenomenon. See the cables actually aren’t very slack at all. However they are steel cables so they have to hold up their own weight as well, causing that bowing. See if you were to try and add more tension to the main cables, it would take astronomical amounts of force and actually put a lot more strain on the towers holding the cables up. So while yes they do have a distinct sag in them, they still have a lot of tension and are more than capable of transferring the load to the towers without issue.
Imagine hanging a loose piece of string between two posts. It forms a curve (called a catenary). Now hang a series of small pebbles on short lengths of string from the original string. You will see that the overall shape of the original string is still a curve (actually a parabola) but that it is made of lots of straight lines between the points where the vertical strings are tied on.
Now adjust the lengths of the vertical strings until all the pebbles are in line horizontally. The curved string is holding up all of those pebbles. Now imagine that instead of pebbles you tie a floppy stick to the bottom of the vertical strings. Clearly the curved string can hold this up, assuming it weighs the same as all the pebbles. The floppy stick is the bridge deck, and you have just made yourself a suspension bridge!
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