OneWhiteEye wrote:A drop height of 0.5m or about 20 inches is ridiculous.
No, it's not. A freefall drop of 12 feet is not conservative towards survival and is not representative of the initial descent. It bounds the solution to one extreme, my suggestion was to bound the problem at the other extreme, Bazant's criteria, as you note later.You can't use that to determine whether or not a jolt should have been noticeable at the roof in the real situation where the upper section had to drop a full story before an impact would occur.
Not everything is about jolts!We aren't trying to determine if Bazant's conjecture, that even a 0.5m drop would cause collapse, here.
Speak for yourself. It may have been Enik's purpose to examine for jolts (none), but a lot more comes out of it than that. The FEA indicates jolts is a non-issue, as I already know, so I'm concerned with issues that have some relevance. Bazant, who assumes single story failure, puts the threshold at 0.5m freefall drop. Simply doubling it for comparable destruction above and below is 1.0m. Thus the test points make a whole lot of sense, and are an attempt to advance understanding rather than allow it to keep wallowing in the mire of muddy physics.A drop of about 9 feet or 3 meters would be realistic given how a 12 foot column would bifurcate when buckling and the simulation should have buckled columns with three hinge points.
No period of free fall in initial descent was observed, so apparently conditions were not as you assumed. Another reason to tone down the drop a little if something realistic is to be tested.The real test would be to model all 236 perimeter columns 12 stories tall with their 52 inch deep spandrels every story with lateral support every 12 feet in the axis orthogonal to the spandrels and have a buckled column drop on its lower end which is the top of 97 stories of the same 236 columns with the same constraints but increasing wall thickness of both the columns and spandrels.
Of course, but this beats the crap out of anything I've seen done on this aspect of the collapse. One can learn from the results of simplified models before adding complexity beyond that which has any hope of being validated if done in isolation.
I can't help but sense that it sounds as though you and femr2 are hedging your bets as you aren't advocating doing the analysis based on observation. A 0.5 meter drop is not what happened and the north face of the upper section of WTC 1 was moving at about 19 ft./second after 9 feet of fall.