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Re: Nova program on World Trade Tower Collapse

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On Mar 28, 2006, at 10:01 AM, Paul Feather wrote:

There were a lot of things that struck me as incorrect in the Nova special, especially the entire two bolt fallacy. Overall Nova specials are usually really well put together and always a good effort, but I thought this one was a little premature and some of the "experts" were too quick with the spotlight and too slow with their facts.
I've only read the executive summary of the draft report but it seems to me that the NOVA program and NIST agreed that the proximate cause of the collapse was the lateral loading produced by the floor truss sag:
In WTC 1, the fires weakened the core columns and caused the floors on the south side of the building to sag. The floors pulled the heated south perimeter columns inward, reducing their capacity to support the building above. Their neighboring columns quickly became overloaded as columns on the south wall buckled. The top section of the building tilted to the
south and began its descent.
and
In WTC 2, the core was damaged severely at the southeast corner and was restrained by the east and south walls via the hat truss and the floors. The steady burning fires on the east side of the building caused the floors there to sag. The floors pulled the heated east perimeter columns inward, reducing their capacity to support the building above. Their neighboring columns quickly became overloaded as columns on the east wall buckled. The top section of
the building tilted to the east and to the south and began its descent.

Both of the above are taken from Sub-part E3 of the NIST report. The NOVA program also reported that the collapse would have at least been delayed had the floor trusses not been weakened by heat after the insulation blew off.


Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw/


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