Creative Speculation

... but since floor sagging was observed, that IS justification for thinking that model is more accurate. My point was that the NIST collapse scenario does not require hot columns because the core couldn't halt the collapse after the top started tilting, even without heat weakening. I believe it is possible to demonstrate that with a simple diagram showing how the tilt would move the center of mass until the entire weight of the upper building was bearing on just the columns closest to the perimeter wall that buckled. Even if we assume those columns could support three times the load that was normally on them, there is no way they could carry the entire top of the building, even if they were stone cold. Getting back to where this started, you brought up the fact that no columns were tested that showed effects of temperatures of 600 degrees C and implied that was a good reason to doubt the NIST collapse hypothesis. My response was that in addition to the fact that no columns from the collapse initiation area were tested, the NIST collapse hypothesis doesn't really require columns that hot, anyway, so that's a strawman. If you still think your original point has any validity, then I can't stop you from dragging it out again, but I think we've beat it to death for now.

But now the topic now seems to have moved to the general usefulness and applicability of FEA models in the first place. I asked above in a different subthread how any conceivable FEA model could "demonstrate that there weren't other factors"; the point being the general impossibility of logically proving non-existence. I guess I wasn't clear, if you still say this:

> NIST's findings are also consistent with a theory that it was their "middle" model that was the more accurate one and that rather than boost temperatures to make it collapse what they actually needed to do was to factor in additional help (from therm*te or other). This latter explanation is consistent with all their findings so they haven't ruled it out.

That's correct; therm*te was not "ruled out" by the NIST study, but I don't see anybody claiming it was, given the general impossibility of doing that. (Nor, as OTOH pointed out, is that remotely similar to the actual intent of the study.) But my claim is that, unless you can give me some cogent reason to doubt the physical modeling in that analysis or the input parameters used, then the analysis does in fact demonstrate that crash damage and fire alone could have caused the collapses, so there is no need to imagine "other factors" for which you have no evidence. And that IS a significant demonstration if the reason for imagining "other factors" is the claimed impossibility of such collapses without them. No, the analysis does not prove that crash damage and fire alone caused the collapses, nor will any such analysis ever be able to prove that, nor was that the intent, nor is it really necessary.