Investigators working for the American government have ruled out design faults in the steel beams in New York's World Trade Centre as the cause of the twin towers' collapse on 11 September 2001.
Preliminary findings concluded that the beams met or exceeded their load-bearing requirements and did not contribute to the disaster.

Engineers have said that the towers collapsed because the steel beams melted in the intense heat of the explosions. With both jets carrying full fuel tanks on impact, the temperature of the fire has been estimated at up to 500°C.

The federal investigators confirmed that the beams exceeded the requirement to bear 16,300 kg per square inch and had in fact helped save thousands of lives by staying upright for more than an hour after the explosions.

However, with support columns damaged by the planes' impact, the weakened beams were unable to hold up the weight of the floors.