Regarding the cables on the Brooklyn Bridge, it is of interest to note that when the main cables were well along in the spinning process, it was found that the contractor supplying the wire was not meeting the strength specifications by a considerable amount (I forget just how much it was, but it was not insignificant). The bridge authorities decided that since the original factor of safety was so high that even with this reduction, the bridge would still be perfectly safe. So the substandard wire was allowed to stay in the cables, and better wire used to finish the job.
Since the bridge is still standing after over a century, this could be considered to be a good decision.
I read the above mentioned book by David McCullough. As I recall Roebling’s design had a safety factor of ten(!), but because of the inferior wire (which was only used because of political pressure to not have Roebling’s company get the contract for it) the bridge has a safety factor of ‘only’ six.
Every time I see modern ‘cable-stayed’ bridges I can’t help but think how flimsy they look! Like a discount suspension bridge…
I saw a documentary that discussed the Forth Road Bridge just north of Edinburgh. They have attached microphones to the main cables and are recording the sounds of individual cables snapping. I wonder if the same thing is being used to monitor the Golden Gate.