British Engineers Give Their Theory Taken from BBC:
The design of the World Trade Center saved thousands of lives by standing for well over an hour after the planes crashed into its twin towers, say structural engineers.
"It was the fire that killed the buildings - nothing on Earth could survive those temperatures with that amount of fuel burning" Structural engineer Chris Wise
But the towers' ultimate collapse was inevitable, as the steel cores inside them reached temperatures of 800C - raising questions why hundreds of rescue workers were sent into the doomed buildings to their deaths.
The steel and concrete structure performed amazingly well, said John Knapton, professor in structural engineering at Newcastle University, UK. "I believe tens of thousands of lives have been saved by the structural integrity of the buildings," he told BBC News Online. "They had a lot of their structure taken out, yet they remained intact for more than an hour, allowing thousands to escape."
But as fires raged in the towers, driven by aviation fuel, the steel core in each building would have eventually reached melting point - 800C. The protective concrete cladding on the cores would certainly have been no defense in these extraordinary circumstances.
"Nothing is designed or will be designed to withstand that fire" - World Trade Center construction manager.
"It was the fire that killed the buildings. There's nothing on Earth that could survive those temperatures with that amount of fuel burning," said structural engineer Chris Wise. "The columns would have melted, the floors would have melted and eventually they would have collapsed one on top of each other."
The building's construction manager, Hyman Brown, agreed that nothing could have saved it from the inferno. "This building would have stood had a plane or a force caused by a plane smashed into it," he said.
"I would have given the order to get out - you would have thought someone with technical expertise would have been advising them" Professor John Knapton, Newcastle University "But steel melts, and 24,000 gallons (91,000 liters) of aviation fluid melted the steel. Nothing is designed or will be designed to withstand that fire."
Once the steel frame on one floor had melted, it collapsed downwards, inflicting massive forces on the already-weakened floor below. From then on, the collapse became inevitable, as each new falling floor added to the downward forces. Further down the building, even steel at normal temperatures gave way under the enormous weight - an estimated 100,000 tones from the upper floors alone.
