benthamitemetric
Senior Member
Your example is wrong because it goes to an extreme: it assumes the falling floors were reduced very small pieces, which we know isn't the case based on both common sense and, more importantly, the debris field. But, even if the floors were powderized, it's not a foregone conclusion that the collapse would not ensue, it just gets much more complicated to calculate the forces at each stage. After all, if you drop 300 lbs of sand on yourself from 20 ft, it could kill you just as a 300 lbs piano could, and we all know the devastation that water can do in a tsunami or flood. The truth of the tower floor collapses is somewhere in between: fully rigid floors were broken to an extent, but its hard to imagine the mass of those concrete slabs and steel trusses acting more like sand than like rigid structures when compacted together with other failed floors in the debris wave. Remember we know the floors were sheered from the perimeter at the truss connections because that was observed and documented in the debris (see, e.g., NIST NCSTAR 1-3C).How is my example of a brick wrong, though? A brick weighs about 2kg, and the same brick chopped up into pieces will weigh the same. Yet it's obvious which one you would rather have dropped on your head.
I think Bazant understood this problem, which is why he insisted the upper block stayed intact during the "crush-down" phase, and then got crushed itself during the "crush-up" phase... Like a car crash where one car becomes deformed first, and then the other one, haha.
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