Congratulations on your study of this collapse. I am a retired structural engineer and worked on a lot of those bridges in the forties and fifties. I’m too lazy to study your analysis of the failure, but it looks like you have nailed it. Thank you.
Thank you for your comments. Professional agreement, even ex-professional agreement, is always welcome.
I’m of two minds in one critical area of the failure.
On one hand, U10 east failed, U10 east looked different before the collapse, and U10 east was, along with U10 west, and 6 other corresponding similar points, one of the eight most important details on the bridge. Way too much coincidence to gloss over with a ‘design flaw’ final report, especially the similarity between the discoloration and the fracture lines in U10 east.
On the other hand, the discoloration doesn’t appear to be rust or corrosion, and repair paint doesn’t explain such a fracture.
The best I can come up with is that the odd paint covered graffiti, AND SLIGHTLY more corrosion effect than U10 west and the other reversal points. If all those points were close to failure, and the post collapse images show that all four mainspan reversal points did let go at or during failure, then perhaps U10 only let go milliseconds before the rest would have gone anyway.
But that still doesn’t explain the coincidence between the outlines of the discoloration and the fracture lines visible in the post collapse imagery.
So then next step then, looks to...human engineering. Suppose U10 east showed corrosion similar to the last image in my original post. One side or the other of the deck truss above U10 sheds more water, just as in that other image, and the south side of U10 is heavily corroded, perhaps even cracked along the bolt lines. The graffiti artist completes his work, and the repair guy, armed with a spray can or cans, covers up not only the graffiti, but also the ugly corrosion, after all, he’s right there with paint, tasked with improving the bridge’s appearance.
Thoughts?
Other possibilities that would explain the correlation between discoloration and fracture line placement?