[Lonesome in Massachussets]

The idea is that a structure stands for its rated life, during which time it is periodically imspected and maintained. After its rated life it is reevaluated to see if its life can be extended.

The whole idea is that a properly maintained structure, within its rated life, has a very small probability of catastrophic failure.

That it failed indicates that it either was not maintained properly or it was poorly designed.

Still Going Strong 124 Years On

[concretebob]

I don't think the total load at time of failure is being calculated.
IIRC that bridge was undergoing repair at the time of collapse, with live traffic loads.
The combination of static and dynamic loading is what caused this bridge to fail when it did.
Had no repairs been underway, I think this bridge would still be standing.
If traffic had been re-routed during repairs, I think the bridge would still be standing.