Continued from here.
The NISTers have, of course, not provided an example of something crushing through a larger something of the same material and density via gravity alone other than the Twin Towers, yet, because there isn't one.
The NIST/Bazant hypothesis describes an upper block of storeys that "crushes down" through the larger intact building then gets "crushed up" by the pile of rubble (never mind that it has been crushing against this pile of rubble throughout the collapse) at the end, all in the space of 13 seconds:
The Twin Towers were constructed with 240 perimeter structural steel box columns and 47 larger core box columns, ranging from 36" x 16" to 52" x 22", forming a dense core structure which, alone, comprised 25% of the total area in the buildings' horizontal span.
The NIST supporters have yet to address four gaping flaws in their theory. Not sure if they'll do it in this thread, or if they will just run away:
1) a step-by-step explanation of events after the collapse initiation
2) evidence of the existence of the upper blocks through the collapse progression
3) an example of top-driven gravitational collapse, and/or the law of physics that would explain it, and
4) math that accounts for what actually occurred, rather than what is hypothesized, and that is supported by accepted physical principles.