"......never has a building collapsed by fire i that way ever anywhere.....but here it happened 3 times ....3 prefect collapses......its the most amazing thing isn't it."
Accepting the fact that no building has ever collapsed because of a fire.
BUT
add to the heat of the fire the structual damage done by a 100,000kg odject hitting the building at 500km per hour (or what ever the speed was)
The planes hit the building 3/4 of the way up
the damage caused by the impact and the following fire weakened the buildings structual capability of supporting the 1/4 of the building above the impact area.
once the structual support weakened to the point of collapse the wieght of the building above the impact zone dropped onto the structure below the impact zone
buildings are designed to support the wieght of the structure adove a certain point
NOT to have the wieght of a part of the structure DROPPED onto a lower part of the structure.
Very simple
Fair simpler than the inpossible logistics of some how staging some controlled demolition of the buildings without anyone knowing or speaking out afterwards
