As I may be the only civil engineer here, I think you are referring to me. Thank you for saying I am renowned. Certainly. In this forum, that is!
The safety factor for designs are never more than 50% over the maximum expected load (that is, failure shouldnt' happen till then). The 10 times you say is probably the safety over the normal expected load, not maximum. Here, it seems about 400 or so people on the bridge (about 2 or so per square meter) may have been the maximum expected. If so, perhaps 200 people's load on one suspension cable, and 200 on the other, for maximum case - to put it in simplistic terms (it is not exactly that).
That means each cable would have been designed to fail only at 50% more load. That is 300 or so people's load per cable (so 600 total) as the failure load. These are approximate numbers I am guesstimating. But a normal load would be as little as 50 people on the bridge (so your 10 times is an acceptable mutliplier from "normal load" - but designs are always for maximum load, with 50% factor of safety). If I were running the bridge operation, I would certainly not let more than 200 or so on the bridge, if even that. More like 100 max.
I went frame by frame over the best videos from the deck that I could find of the few seconds before the failure. It seems like some sort of wind (even mild breeze enough) was causing the bridge to sway. In fact this bridge is known for the sway and people apparently walk on it just for that experience. A friend of mine (an IITM civil engrg classmate) just told me that he found earlier pictures which seem to show that they may have changed the safety net on either side to one with less perforation recently during maintenance. If so, the wind may have caused even more swaying of the bridge than in the past. The side-to-side sway will naturally cause the deck to twist a bit - ie, up and down on either side. From what I see in the video, it seems like at one point a lot of people were going to the right side net, just before the right cable snapped. Basically a much higher unbalanced load on the right side main suspension cable. My wild guess is some 75% of the people load (that is probably over 350 people's load, out of the 500 on the bridge -- over the cables maximum design load, as my guesstimate). Not sure if those main cables were ever replaced in 140 years. If not, they may no longer have the 50% extra safety capacity anymore, due to corrosion, metal fatigue etc. Probably ready to fail if 250 people's load and the deck-weight went to it. Disaster.
I think the problem here was that they gave a maintenance contract and allowed that company to collect tolls. I don't think replacing the main suspension cables was part of their contract. That is an extremely elaborate process that this company is certainly not equipped to handle. Plus it would need a year or two for this bridge, and typically people would consider building a new bridge instead! The key issue was the toll collection. It appears that there wasn't a strict maximum number they were allowed to let in on the bridge, in the contract. That is stupidity at it worst. Of course, the company was going to just let in as many people as would pay for it (Rs. 17 each, I believe) to make money. They did just that, at unfortunately a time with good wind swaying. That and the netting issue above caused an unbalanced load transfer to one cable, which may be 30% weaker after a century, and we have 150+ dead. This is where my thinking is. We will see what the forensic team finds out later.
Rather than blame the maintenance company, and act like they didn't do maintenance right, the people who gave them the contract to collect money without maximum stipulations should be jailed.
