Thank you for breaking it down like this. As someone without an engineering background, your explanation (along with some Googling for terms and definitions) really helped me grasp what happened.
You got me wondering:
> the whole bridge failed because the impact didn't exceed the impact strength of the bridge's material
When I first read this, it initially threw me off. The cargo ship's impact not exceeding the strength of the bridge sounds like a positive thing, but upon closer reading of your comment, it sounds as if it was the catalyst to the entire bridge collapsing.
So, how do engineers balance these properties of impact strength and tensile strength, especially considering large ships channel through these bridges near their pylons frequently? How much engineering goes into the possibility of large structures hitting their pylons?
> The cargo ship's impact not exceeding the strength of the bridge sounds like a positive thing, but upon closer reading of your comment, it sounds as if it was the catalyst to the entire bridge collapsing.
I had intended to add that exceeding the impact strength typically results in a local failure near the impact point. A tensile strength failure could happen far from the load and so could be more catastrophic.
I'm not sure if it would have made a difference in this case though, as destroying a main pillar by exceeding impact strength would have by itself transmitted most of the full bridge load to the remaining pillars and that alone may have been enough to exceed the safety margins on the tensile strength that are built into all structures. Unclear without more data, but there was a chance it could have survived in that case, but no chance with the ship consistently applying more and more shearing load.
> How much engineering goes into the possibility of large structures hitting their pylons?
Good questions, I'm not familiar enough with it to provide any further insight, except to say that I believe this bridge was designed long before these huge container ships existed. If they factored ship collisions into the bridge's design constraints at the time, they've no doubt been dramatically exceeded with these huge ships.
I don't think impact strength is factored very much into static structures, tensile strength is more important. It only comes up in very unusual situations like this or 9/11.
Bridges were not designed for being hit. They were designed to span. If those designing and engineering it had considered an impact, the design would not be catastrophic but rather sectional. If sectional, each span would remain standing rather than collapse like dominoes. It takes 3 miles to stop a 100k ton stacked container ship. The things nobody has mentioned are: Current direction and speed. Wind direction and speed. The entry of the vessel in relation to the bridge. The fact that dragging anchor would have on the starboard side pulled the bow right into the pilon, the worst case.
You got me wondering:
> the whole bridge failed because the impact didn't exceed the impact strength of the bridge's material
When I first read this, it initially threw me off. The cargo ship's impact not exceeding the strength of the bridge sounds like a positive thing, but upon closer reading of your comment, it sounds as if it was the catalyst to the entire bridge collapsing.
So, how do engineers balance these properties of impact strength and tensile strength, especially considering large ships channel through these bridges near their pylons frequently? How much engineering goes into the possibility of large structures hitting their pylons?