Reply #60: Well thanks for the link,but

[LARED]

I was not looking for advice or instruction. I was trying to tell you that the conservation of angular momentum has nothing to do with why or why not the top collapsed.

Your mistake is assuming the top section continued to be a solid body as it started to rotate. See, without the core steel and perimeter steeel in the top section maintaining its connection to the structure it cannot be considered a rigid body. Look up building drift.

If you need additional info, PM me and I'll try to help.

Regards