“A steel member in a structure is typically designed to accommodate 40% more than its anticipated “dead” load and 70% more than its anticipated “live” load”
That may be what you require as an engineer, but as a steel detailer, I always design each end connections for 75% of the total uniform load. we always go further than what the engineer calls for. You are right this probably wasn’t terrorism, I just didn’t want people to think that traffic isn’t taken into consideration when designing a bridge. Or that crappy material would be used without many levels of checking. The engineers of this country and the AISC using ASD are the best in the world. I just don’t want people loosing faith in engineers.
I'm not sure, but I think a partial collapse on a Milwaukee bridge about 10 years ago was due to faulty materials. Ultimately they had to remove large sections of the bridge with explosives and rebuild.
A questions for the Civil Engineers & Designers out there. Is it possible that the combination of rush hour traffic (bumper to bumper maximizing the number of vehicles), lanes being closed (maximize the load to one side), years of potential neglect and the vibration of a passing freight train caused overstressing of a "weak point" that caused a cascading effect of popped rivets, etc. that would have led to catastrophic failure?