Yep, It's Thermite! So Much for the "Oxygen" Excuse, page 31

For a chaser, there is a definitive book on skyscraper fires “Fire in the Skyscraper” by Arthur Scheuerman, previously Batallion Chief of the New York Fire Dept.

No dramatic Youtube, but he summarizes his findings re WTC here:

extruther.blogspot.com...

NIST did not examine the Tower’s collapses after the point of collapse initiation because after the exterior walls began buckling and the top of the buildings began tilting when the buckling spread to the core and remaining perimeter columns allowing the building top to begin falling straight down, the chaotic impacts of heavy floors and walls colliding could not possibly have been accurately predicted by even the most powerful computers. NIST only examined the collapses to the point where progressive collapse would have been inevitable and this took intense computer work.

Those WTC Tower buildings were built with long span, bar joist floor trusses which can collapse into catenaries (cables in suspension) from the expansion effects of heat on the steel truss components. Steel expands immediately when heated. NIST found that the differential expansion effects between the composite steel and concrete in the floors causes separation of the concrete and steel trusses and buckling of the diagonal struts in the trusses. This catenary effect starts at low temperatures of 4000 C to 5000 C before the steel itself even begins to weaken. This collapse the trusses into catenaries over several floors along with the additional ‘thermal bowing’ effect in some of the trusses, caused ‘pull-in’ forces on the exterior wall columns. Thermal bowing is caused by the bottom chords of the trusses expanding faster than the top. This allows the top chord to go into suspension exerting immediate increasing ‘pull-in’ forces on the exterior walls. Photos taken by the Police helicopters showed the exterior column walls in the Towers to be bowing inward, on the long span sides of both buildings well before the buildings started to collapse.

Added to the thermal weakness of the ‘long span’ trusses present in the Tower’s design was the absence of diagonal bracing in the core, the weak column splices in both the perimeter and core columns, one bolt connections of the truss to core columns, missing bolts in the exterior column splices, large open areas allowing extensive fire growth and enabling large areas of the buildings to be affected by heat, weak plaster board enclosures for stairways and elevator shafts, etc., etc.

Building 7 had all the same deficiencies present in the Towers except that the bar joist, trusses were replaced with long span I beams. There were large growing fires on several floors as well as damage from the exterior columns of Tower 1 which pealed away during its collapse and hit the southwest corner and the middle of the south side of building 7, gouging out large sections. In addition to this damage, there were problems with water supply and the Fire Department decided not to fight these fires and ordered every one out of the building and out of the collapse zone (which was a large area including buildings and streets around building 7) as is the procedure when discontinuing interior firefighting operations at an uncontrolled fire. The anticipation of collapse was a brilliant conclusion and no lives were lost when the 47 story building collapsed about an hour and a half after the evacuation order was given. The BBC somehow misheard the orders to evacuate the collapse zone and reported the building had already collapsed well before it actually did.

Arthur Scheuerman,
Retired Battalion Chief, FDNY

[edit on 8-7-2009 by mmiichael]

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