Nice little study, Unfit. You are correct, the cores survived, then fell. What could explain this? If all of the floors and perimeter sections "fell" down past the core, why would the core then disintegrate a few seconds later? It makes no sense.
It will make sense if you were to read and understand all of NIST and use real experts to help you understand the structure of the WTC towers.
Take a few years to study and you will start to understand.
Some of the previous post already have supplied information that can help.
