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The image is from:
https://www.metabunk.org/threads/the-uniqueness-of-the-wtc7-collapse.1972/page-5
"The Uniqueness of the WTC7 [World Trade Center Building 7] Collapse"
Text from:
http://en.wikipedia.org/wiki/Collapse_of_the_World_Trade_Center#Collapse_initiation
“In November 2008, NIST (National Institute of Standards and Technology] released its final report on the causes of the collapse of 7 World Trade Center.[31] This followed their August 21, 2008 draft report which included a period for public comments.[37] In its investigation, NIST utilized ANSYS to model events leading up to collapse initiation and LS-DYNA models to simulate the global response to the initiating events.[81] NIST determined that diesel fuel did not play an important role, nor did the structural damage from the collapse of the twin towers, nor did the transfer elements (trusses, girders, and cantilever overhangs). But the lack of water to fight the fire was an important factor. The fires burned out of control during the afternoon, causing floor beams near Column 79 to expand and push a key girder off its seat, triggering the floors to fail around column 79 on Floors 8 to 14. With a loss of lateral support across nine floors, Column 79 soon buckled – pulling the East penthouse and nearby columns down with it. With the buckling of these critical columns, the collapse then progressed east-to-west across the core, ultimately overloading the perimeter support, which buckled between Floors 7 and 17, causing the entire building above to fall downward as a single unit. From collapse timing measurements taken from a video of the north face of the building, NIST observed that the building's exterior facade fell at free fall acceleration through a distance of approximately 8 stories (32 meters, or 105 feet), noting ‘the collapse time was approximately 40 percent longer than that of free fall for the first 18 stories of descent.’ [82] The fires, fueled by office contents, along with the lack of water, were the key reasons for the collapse.[31]”
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