Sorry for the three in a row but here's more info on steel, fire, and a link with this one as well.
"IT WAS THE FIRE THAT BUCKLED THE BUILDINGS: SAY ENGINEERS
"It was the fire that killed the buildings - nothing on Earth could survive those temperatures with that amount of fuel burning," said Structural
engineer Chris Wise. 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 tonnes from the upper floors alone. "It was as if the top of the
building was acting like a huge pile-driver, crashing down on to the floors underneath," said Chris Wise. "Only the containment building at a
nuclear power plant" is designed to withstand such an impact and explosion, says Robert S. Vecchio, principal of metallurgical engineer Lucius Pitkin
Inc., referring to the hijacked Boeing 767 airplanes, heavy with fuel, that slammed into each WTC tower. As the fires burned, the structural steel on
the breached floors and above would have softened and warped because of the intense heat, say sources. Fireproofed steel is only rated to resist 1,500
to 1,600° F. As the structure warped and weakened at the top of each tower, the frame, along with concrete slabs, furniture, file cabinets, and other
materials, became an enormous, consolidated weight that eventually crushed the lower portions of the frame below. When the stability was lost, the
exterior columns buckled outward, allowing the floors above to drop down onto floors below, overloading and failing each one as it went down, he says.
The good thing is that the two towers of the World Trade Centre, one stood for one hour and the other stood for one and three-quarter hours after
impact. The American Institute of Steel Construction, Inc. (AISC) has contacted FEMA and the leading structural engineering associations and is
forming a special task force to investigate the structural collapses of the World Trade Center buildings resulting from the terrorist attacks on
September 11, 2001. What is of some concern is the fact that newer skyscrapers in the United States and elsewhere were constructed using cheaper
methods and would collapse even quicker. See the full analysis at "
I know none of us much trust the government and thats why I turn to structural engineers, metallurgical engineers, and specialist in the field. These
people deal with these properties everyday. they live it, they test it in lab and in field.