This is how Dr Bazant himself describes why crush up doesn't happen until the upper portion makes contact with the earth.
Please try to understand the assumptions behind your own mechanics. It is quite interesting.
From BL Review. Bazant's direct quotes in black, my comments in red.
5.
Why Can Crush-Up Not Begin Later? The discusser fur-
ther states that “it is difficult to imagine, again from a basic
physical standpoint, how the possibility of the occurrence of
crush-up would diminish as the collapse progressed.”
This was about the only thing James Gourley said correctly in the paper. It is pretty difficult to imagine why crush up cannot occur, no? Dr Bazant reassures us upper block C and the magic carpet of debris is real with the following logic:
Yet the discusser could have imagined it easily, even without calcu-
lations, if he considered the free-body equilibrium diagram
of compacted layer B, as in Fig. 2͑f͒ of the paper.
In figure 2f, shown below, Dr Bazant simplifies the complex process of crushing, column spearing, the outward splitting of whole perimeter walls and the bypassing of core columns like opposing spears as two "big blocks" with the following cartoon scenario:
For a reader that wants to understand why Dr Bazant mistakes the upper block C to be virtually indestructable, it is important to understand this diagram and to understand what Dr Bazant is doing in the following passages. He continues...
After including the inertia force, it immediately follows from this
diagram that the normal force in the supposed crush up front
acting upward onto Part C is
vB rapidly decreases because of mass accretion of zone B and
becomes much smaller than g, converging to g / 3 near the
end of crush down ͑Bažant et al. 2007͒. This is one reason
that Fc is much larger than FЈ. After the collapse of a few
stories, mass mc becomes enormous. This is a further reason
that the normal force FЈ in the supposed crush-up front be-
comes much smaller than Fc in the crush-down front.
When the compacted zone B hits the ground, vB suddenly drops to
zero, the force difference ⌬F suddenly disappears, and then
the crush-up phase can begin.
If you really believe that the complex interactions within WTC1 can be accurately represented by 2 big blocks and a magic buffer zone B, perhaps this seems to make sense.
The discussers’ statement that “the yield and deformation
strength of . . . Part C would be very similar to the yield and
deformation strength of . . . the lower structure” shows a
misunderstanding of the mechanics of failure. Aside from the
fact that “deformation strength” is a meaningless term ͑de-
formation depends on the load but has nothing to do with
strength͒, this statement is irrelevant to what the discussers
try to assert. It is the normal force in the upper Part C that is
much smaller, not necessarily the strength ͑or load capacity͒
of Part C per se.
No upper block C exists. No such single normal force exists.
Force FЈ acting on Part C upward can easily
be calculated from the dynamic equilibrium of Part C ͑see
Fig. 2g͒, and it is found that FЈ never exceeds the column
crushing force of the overlying story. This confirms again
that the crush-up cannot restart until the compacted layer hits
the ground.
This is how the upper block remains intact in Dr Bazants crush up, crush down mechanics. He believes that the "upward force" on the "upper block" never exceeds the column crushing force of the story above. To him, it is the strength of the upper columns, their inability to buckle upwards, that preserves the upper block from damage.
It is natural to wonder: Why don't the upper and lower column stubs just spear through rubble zone B, allowing upper and lower portions to penetrate each other and mutually destroy one another? In Bazant's view, the rubble zone B provides a cushion of debris on which the bottom column stubs of the upper portion can remain supported, thus shielding the upper block C from damage. I know that makes no sense, but that is what Dr Bazant's crush-up, crush-down mechanics is based on, just as he has described in this section.
Do you understand why crush up cannot happen before contact with earth? This is why "1-D buckle down, then buckle up mechanics" is a more correct way to describe your collapse progression model.
) no-one has shown me where I am wrong. The argument to convince me would need to be more sophisticated that what we have been engaging in recently.