unkadug
Follower of "Saget"The Cult
Im not a Stress Analysis Engineer (although I have a friend on the site that could help shed some light), but from your list above, this is comparing apples to pears. They have the same inside (shape and purpose) but they are under different stresses. Also, I have seen programs about the yearly maintenance that goes into structures like the ESB and Statue of Liberty to keep the metal healthy.
One might ask, well SM is indoors away from rain etc, how could it rust. I do recall a picture in my collection that show a very rusty structure inside DL SM that includes actual track.
If they treated the listed above like this, im sure they would fail too.
Lastly, as stated, im not an engineer and could be WAY off base, just trying to figure it out logically and offering suggestions why one is and the other isnt. :wave:
Points taken, however some people seem to feel that they know that because supports aren't being replaced that doom and immediate failure is imminent.