I have not laid out the drawings and all the after photographs in order to agree or disagree with some of what you said. Specifically:
1) Obvious. Another report I have been reading identifies 52 different members between the two support piers (26 on each side of centerline) that would cause complete collapse if any ONE of them broke.
2) Don’t know for sure. I have not studied or laid out the available information in enough detail to agree or disagree.
3) Don’t know for sure.
4) Don’t know for sure.
5) Don’t know for sure.
6) Yes. Straight from the report.
7) Yes.
8) Yes.
9) Yes.
10) Yes.
11) Don’t know for sure.
> “In my experience, major failures occur because of multiple, additive causes, and that very often, these causes are known well in advance of failure.”
That is also my experience.
I have just about exhausted what I can say on this. I made several general statements that I believe will hold up in the final report. I did not get specific enough to identify exactly which structural member failed first and will not do so. To speculate to that detail without being there and physically inspecting the debris that comes out of the river and studying EVERY photograph taken would be irresponsible on my part and could be cause for someone to come after my PE.
It is sufficient to say that this bridge was an accident waiting to happen. The trigger that caused one of the 52 critical members to fall was probably the sum of several things. However, the mere fact that it was being redecked means that someone in MNDOT thought that that bridge would last another 10 or 15 years. How that conclusion was reached must be identified and corrected. I think that conclusion was totally irresponsible. If it did not collapse last week, there is absolutely no question in my mind that it would have collapsed before the new deck wore out.
BTW, I saw a news article in the local paper they weekend that tells me we are not going to get a truthful report. The head of the MNDOT was identified as a Republican several times. Case closed.
I’d be willing to lay the imagery out for you here, (have already done so in various other threads) in support for the contentious items on the list, but I understand your position in the engineering community and respect your professionalism and sense of responsibility in abiding by the conventions of same.
I’m not restricted by any of that, but I do hope I’ve been able to convey that my speculations are just that, best guesses, based on the admittedly limited pool of available data, not conclusive by any means.
Although I’m reasonably confident your posted material on the political claims that we won’t see a conclusive report was done so tongue in cheek, it wouldn’t be the first time a final report missed some aspect of a catastrophe. This has little to do with politics, it’s the nature of the situation. The investigating authorities do not have carte blanche, and are not freed from other duties and projects to concentrate solely on this one accident. Inspection time, analysis time, even processing time on large computers in simulation are all finite and limited resources.
Both the FEMA and NIST reports on the WTC collpase were less than perfect and missed some significant connections that were available. In plotting the available O2 budget for the fires, they failed to consider supplies located on floors away from the impact zone, even though burned victims in those areas make it clear that the initial fireball opened those areas to venting which could and probably did affect the overall thermal loads.
A significant collapse of several stories worth of floor systems on the northwest corner of Tower One several minuites before the onset of progressive collapse was not thoroughly analyzed in the dynamics of gravity load transfers which, along with the buckling of the Vierendiel truss structure of the south perimeter wall, led to the upper section settling almost wholly onto a very few core columns and initiating the pancake sequence.
The ASCE reports on the Louisiana Hurricane Protection levees spectacularly omitted the direct role subsidence played in the breaching of the St. Bernard Primary Protection systems.
These elements were not omitted (or concealed) for political reasons, they necessarily would have been speculative to some extent, and there was simply a limited budget that did not permit unlimited, open-spectrum analysis.
If the final report on the I35W bridge collpase does not fully answer all of our questions, it will be for similar reasons, and I fully expect that there will be enough data included in the report for us to satisfy all of our curiosities.
As to whether or not specific nodes of failure within the systems designed to prevent such disasters are identified and successfully addressed, I will await further developments and just see what happenes.
Thanks for sharing your well situated point of view in the alanysis we have cinducted here, and for some stimulating discussion, and all the best to you in the future.
Next time we cross paths, hoopefully, it will be under better circumstances.