LATEST FINDINGS from the US team investigating the World Trade Center disaster show that the twin towers could have survived the aircraft impacts if structural fireproofing had not been dislodged.
The US National Institute of Standards & Technology (NIST) released its conclusions late on Tuesday.
It said that while the towers suffered distinctively different damage when the two Boeing 767 aircraft slammed into them on 11 September 2001, both remained standing because loads were redistributed to undamaged columns.
Collapse did not occur until the fires started by exploding jet fuel caused core columns, shorn of their spray-applied fire protection, to soften and shorten.
This shortening caused the floor system to pull the crucial perimeter columns inwards, closer to the fire.
As the fire raged, unprotected perimeter columns were softened and subjected to high compressive loads due to restrained thermal expansion.
Collapse was triggered when sections of the softened, highly stressed columns finally buckled inwards.
NIST believes that WTC 2 failed more quickly than WTC 1 mainly because the floor trusses in the impact area lost more of their fire protection.
They sagged significantly, increasing buckling loads on the perimeter columns.
NIST intends to publish its draft final report for public comment by the end of the year.