Heat from fires causes columns to lose most of their strength
precipitating a progressive collapse.
Endorsed in a paper
Why Did the World Trade Center Collapse?-Simple Analysis
by Bazant and Zhou.
Uses elastic dynamic analysis
to conclude:
"The structural resistance is found to be an order of magnitude
less than necessary for survival."
Reveals authors' ignorance of
structural engineering,
and of the towers' design. "[... if the] majority of columns of a single floor were to lose
their load carrying capacity, the whole tower was doomed."
Described as "simple and approximate,"
yet no other papers have quantitatively analyzed collapses.
Endorsed by Silverstein insurance claim investigation
conducted by Weidlinger Associates Inc.