Regarding the official bridge labelling scheme, you are correct. The drawing I based my assumptions on is a poor one but the text, on deeper investigation, does indicate the correct labelling scheme, and I apologize for any confusion in this area.
I also note that an earlier poster’s scheme actually is correct.
I pity the efforts you had to go through to make sense of my analysis in this respect. It’s hard enough to understand when the numbers line up.
As you note, a different scheme doesn’t change the basic conclusions, though I would clearly state, it moves the suspected problem area to the U10 connection point of the east truss.
This opens the door for some new data, and I am still working on other areas of analysis, including construction traffic and further identification of structural members in post collapse imagery.
I doubt these avenues of analysis will lead to concrete conclusions, and have to decide whether to publish sheer speculation or let important, but unresolved, issues lie unmentioned.
I note with interest your assessment that other scenarios are possible. I have looked at some of these, and for the most part, found one or more conflicting datapoints that appear to rule them out, though U have not and will not do so categorically.
I’d be interested in your read of other failure mechanisms that remain possible, given the available pool of empirical evidence.
I believe that posting them, even as speculation, yields more benefit then harm, and opens the door for further discussion.
Thanks for responding. I was afraid everyone had finally left this discussion! I think it’s important to realize there is a line between what we know or can logically infer, and rank speculation. As long as we maintain an awareness of that distinction I think it’s reasonable to postulate and conjecture.
Your fine detective work on identifying the steel members of the structure post-collapse is 100% valid IMO. It may be too much to ask that we’ll see hi-res pictures of the scene as the rubble is removed. I would think they would remove the concrete and rebar first, exposing the steel underneath. There’s a lot under there we’ll never see.
Regarding alternative collapse sequences, my thoughts on that come from reading the URS bridge analysis report. They identified 52 critical beams that, if one of them failed, would cause others to fail like dominoes. They listed them in their report but I need to go back and read it again. IIRC they identified secondary failures in some members that were not in close proximity to the initial failed member. That stood out when I first read it and I must read it again. Their study, of course, is predicated on certain assumptions that may turn out to be invalid. Garbage in, garbage out. If there initial data was bad then the results are suspect.
My model is not a finite-element model. It’s visual only so right now I don’t envision plugging it into any stress analysis software to analyze. Speaking of the picture I posted above, it occurs to me that perhaps the deck had already begun to fall in the first frame of that video. That could potentially explain the “curvature” of the roadway that I cannot replicate with the intact model. And speaking of video, I read yesterday that someone thought the camera wasn’t a video camera at all, but rather one that snaps still pictures in sequence, either at timed intervals or triggered by motion detectors. I don’t want to speculate further on that without knowing more about the actual camera system they use.
Glad you’re still here.