But that didn't happen. They collapsed from the basement.It’s like vertical dominoes. The top stories collapse due to weakened support structure. The shock load of one floor collapsing upon the next intensifies exponentially all the way down. Even floors with no fire damage (even though fuel and fire were burning all the way down through elevator shafts which were located in the center support structure) cannot support the shock load of all the floors above pancaking down one on top of another.