https://files.wtc7report.org/file/public-download/A-Structural-Reevaluation-of-the-Collapse-of-World-Trade-Center-7-March2020.pdf
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Columns 79, 80, and 81 did not fail at the lower floors of the building. Instead, they needed to have failed at the upper floors of the building all the way to the penthouse. Yet there were no documented fires above Floor 30. Therefore, fire did not cause the collapse of Columns 79, 80, and 81 nor the collapse of the east penthouse.
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The hypothetical failure of Columns 79, 80, and 81 — the three easternmost core columns — would not trigger a horizontal progression of core column failures.
Therefore, the hypotheses of NIST, Arup/Nordenson, and Weidlinger that the buckling of Column 79 would trigger a progressive collapse of the entire building are invalid, and the collapse of Columns 79, 80, and 81 high in the building was a separate and distinct event
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Even if we assume the failure of Columns 79, 80, and 81 could lead to the failure of the next row of core columns, the hypothetical failure of Columns 76 to 81 would overload the exterior columns around the southeast corner of the building, rather than overloading the next row of core columns to the west, which would result in the building tipping to the southeast and not in a straight-down collapse.
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The simultaneous failure of all core columns over 8 stories followed 1.3 seconds later by the simultaneous failure of all exterior columns over 8 stories produces almost exactly the behavior observed in videos of the collapse. The collapse could have started at various floors starting at Floor 16 and below and produced the same behavior.
It is our conclusion that the collapse of WTC 7 was a global failure involving the near-
simultaneous failure of all columns in the building and not a progressive collapse involving the sequential failure of columns throughout the building.
Despite simulating a number of hypothetical scenarios, we were unable to identify any progressive sequence of failures that could have taken place on September 11, 2001, and caused a total collapse of the building, let alone the observed straight-down collapse with approximately 2.5 seconds of free fall and minimal differential movement of the exterior.