Controlled Demolition Theory
Officially, in accordance to the 9/11 Commission report, the World Trade Centre towers collapsed because of a combination of the planes hitting them, and the resulting fires melting the inner steel structures.
Many engineers have analysed the collapse of the WTC towers, and come to the conclusion that a fire could not have possibly melted the inner steel structure. Steel has a higher melting point (3000°C) than burning aviation fuel, which was burning at 12-1400°C in this situation. The fire resistant concrete reinforcing that enclosed the steel core also added to its stability. According to the architect Richard Gage, the WTC 7 should not have collapsed. It wasn't hit by a plane and only 8-10 small fires burned in the building. A possible reason for it collapsing was that bombs were exploded in it. Gage thought that the normal drop of a collapsing building would have been slowed down by crushing through the inner steel structure, but the speed of the WTC 7 collapse suggests that the central core had already been removed (by bombs).
Gage also noted that the planes that caused the collapse were only from one side, but the debris that was omitted from the building went in a symmetrical diametre, which points towards explosions in the building being set off at the same time as the planes hit the tower.
It has been mentioned by Gage and also other scientists that no other steel framed high rise building in history has ever collapsed due to fire, and other buildings of similar design, and in much more extreme conditions have managed to withstand the fire. So why did this one collapse?
Officially, in accordance to the 9/11 Commission report, the World Trade Centre towers collapsed because of a combination of the planes hitting them, and the resulting fires melting the inner steel structures.
Many engineers have analysed the collapse of the WTC towers, and come to the conclusion that a fire could not have possibly melted the inner steel structure. Steel has a higher melting point (3000°C) than burning aviation fuel, which was burning at 12-1400°C in this situation. The fire resistant concrete reinforcing that enclosed the steel core also added to its stability. According to the architect Richard Gage, the WTC 7 should not have collapsed. It wasn't hit by a plane and only 8-10 small fires burned in the building. A possible reason for it collapsing was that bombs were exploded in it. Gage thought that the normal drop of a collapsing building would have been slowed down by crushing through the inner steel structure, but the speed of the WTC 7 collapse suggests that the central core had already been removed (by bombs).
Gage also noted that the planes that caused the collapse were only from one side, but the debris that was omitted from the building went in a symmetrical diametre, which points towards explosions in the building being set off at the same time as the planes hit the tower.
It has been mentioned by Gage and also other scientists that no other steel framed high rise building in history has ever collapsed due to fire, and other buildings of similar design, and in much more extreme conditions have managed to withstand the fire. So why did this one collapse?
The architect of the WTC buildings, Minoru Yamasaki, designed these towers to be able to withstand a Boeing 707 crashing into it. These buildings were prepared for such an attack, and the Boeing 767 planes hit the towers with only slightly more force than they was designed to withstand. The hollow tube in the middle of the core was tightly packed with steel rods that increased the strength and stability of the building, enabling them to withstand higher wind forces, and other forces coming from a horizontal angle, like aeroplanes.