Actually, I think the bridge collapsed because of vibration, and how vibration affects tensile strength.
Along with other factors, there was a train trundling by, close, at the time.
Once, as a youngster, working with steel workers, I watched as a crane began to lift a stack of steel plates. The crane lifted it about half way up, and it began to tremble, and the operator eased it back down. The crew cut the load by half, removing half the stack.
When the crane had it high enough to swing, a steel worker above dropped a spud wrench, weighing about three pounds. When the spud wrench hit the lifted steel plates, the plates and the cable began to shake and hum loudly. Then the cable broke.
That simple dropped spud wrench issued more destructive threat than half the stack of steel.
