The 9/11 Forum

I find these reductionists arguments of rigid blocks crushing each other is completely wrong. They were not rigid blocks, but they were structures of tens of thousands of structural members with connections designed for very specific load conditions. Will a wood frame house without the plywood sheathing and sub floor behave like a rigid block? No. With it with the sheathing and subloor behave like a rigid block? No but it will be stiffer than the unsheathed structure as the sheathing is acting like a membrane and distributing the loads to many members and providing diagonal bracing.

The floors spanned between the perimeter core columns and the facade panels which acted like columns. Each floor had the identical structural system. The core columns were not crushed from anything crushing down on them, nor were the perimeter columns crushed not the top crushing them. The floor system was overloaded so severely that it collapses down leaving the facade to fall away and the core to mangle itself which was quite hollow to begin with as the steel came crashing through it breaking off the lateral supporting beams and the columns then broke apart and collapsed.

Getting this all going mean releasing several floors from the core side and probably at the beam stubs. How'd they do that do you suppose?

Comments withdrawn.

My position is such models are a useful stepping stone to understanding collapse dynamics in general, and have limited applicability to most structures and definitely do not resemble the tower collapse mechanics. Any attempt to make such a model a narrative is out of place, it's merely an expediency. The only analytic and computational models I've seen are basically variants of the same 1D approach; one generalized coordinate or two, step-wise discrete or continuous. This sort of model is manageable and gives numeric solutions without a lot of hassle. Moreover, these solutions are shown to have reasonably good correspondence with the actual collapses if sensible parameters are used. That means something!

My opinion is it's better to have something to compute than nothing, which is about the situation if you throw up your hands and say it's too chaotic, too messy.

If nothing else, the model can be adjusted to represent only a vertical slice of a building and a composite of different cross sections in a real, heterogenous structure MIGHT be able to be successfully approximated.

OneWhiteEye wrote:This sort of model is manageable and gives numeric solutions without a lot of hassle. Moreover, these solutions are shown to have reasonably good correspondence with the actual collapses if sensible parameters are used. That means something!

I'll take any excuse to roll out some old leg-work

http://the911forum.freeforums.org/wtccs-spreadsheet-crush-down-model-t159.html
http://www.youtube.com/view_play_list?p=22FAFC72D202A6D7

If you haven't played with the spreadsheet SanderO, might provide some insights ?

http://femr2.ucoz.com/load/3-1-0-9 (Spreadsheet)