In terms of virtual models: I am impressed by enik's work, OWE.
Glad you like it. It is top notch. It took a lot of time to set up those models and a surprisingly long time (~week) to run some of them. They're both more detailed and expansive than most of the scenarios involving large structure failure I've seen in published rags.
All the same, one of the things which was apparent as a result is the profound limitations of FEA when it comes to these simulations. Despite the substantial complexity, there was still important detail missing in some cases which adversely affected the result. Simply providing the requisite level of detail can sometimes make the model unworkable - either it takes literally forever to run, exhausts available resources, never achieves stability, or all of the above. Definitely not a panacea.
Example: in an enik floor collapse scenario, key connectors did not have fracture attributes supplied so were infinitely ductile. You had things like bolts stretching up to 10 feet. While some would take that as a complete deal-killer, I felt there were still some useful things that could be gleaned from it. The problem would be taking it (on the whole) as a realistic depiction of
what would happen. Naturally, a major demonstrable flaw casts doubt on the veracity; just because there's a flaw easily discerned doesn't mean there aren't other flaws hidden deeper.
It seems, in an (structural) engineering mind-set, there is deep seated tendency to declare something "good enough" after a certain amount of effort, whether it really is or not. Maybe in the world of static structures always near equilibrium, adding some factor of safety in calculations is in fact good enough. But in chaotic, non-linear systems far from equilibrium, that sort of thinking is inadequate. So there are qualified and competent engineers like enik, who have powerful tools and know how to use them inside their comfort zone, who then apply the same methodologies and standards they do in their everyday work to problems well outside that domain. And expect to run the sim and get a good answer.
enik definitely exhibited that trait; the connections didn't have fracture because it would've been "too much work". But, from my perspective (which I can argue is correct), the work that was invested was largely wasted because a critical element wasn't properly characterized. It probably was a perfectly good model for determining (some aspect of) behavior up to the onset of failure. His mistake was in thinking he could let it run past that point - indefinitely - and it would all be okay.
And so it goes with various aspects of most of them. As impressive as they look, there's only so much you can take away from them. One of things which cannot be determined is CD/not-CD... not a shred of doubt in my mind about that. Which brings us to the next comment.
Why do you think enik concluded gravity alone could not have caused the collapses, having put so much effort into creating models to investigate them?
I really don't know. It was a weird disconnect. On the one hand he's capable of constructing jaw-dropping models and running them, and willing to spend inordinate amounts of time doing so. On the other, he didn't seem to have a good awareness of what shortcomings there are in the models. No doubt he'd come to his conclusions before conducting the experiments. If he was inclined to accept the results as valid, it really should've pushed him the other way since nothing ever arrested.
An educated guess as to why he made this proclamation on a collapse model which
had not arrested at termination: he was indoctrinated in Bazantian thinking. There were some clues in things he said - and you pretty much have to take those "pennies from heaven" because he's a man of few words and many graphics and tables! I believe enik bought into the idea that exclusive crush down will occur, and further that exclusive crush down is required to perpetuate collapse. He made a point of how bidirectional crushing was demonstrated in his model and this proved Bazant wrong. I guess, by extension, he thought that meant Bazant was wrong about everything and, if Bazant was wrong, the collapse was not natural.
Funny, all enik had to do was look at his own model! If he took it seriously, and clearly he did, why didn't he notice that his model gave no indication of arrest? It crushed up and down simultaneously. Cool, that's good, that's realistic. Did it arrest? No.