There is NO senario presented by NIST which says the building fell because of ONE piece of the puzzle.

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Probable Collapse Sequence for WTC 1

1.Aircraft Impact Damage:
•Aircraft impact severed a number of exterior columns on the North wall from floors 93 to 98, and the wall section above the impact zone moved downward.

•After breaching the building’s perimeter, the aircraft continuedto penetrate into the building, severing floor framing and core columns at the North side of thecore. Core columns were also damaged toward the center of the core and, to a limited extent on the South side of the core. Fireproofing was damaged from the impact area to the South perimeter wall, primarily through the center of WTC 1 and at least over a third to a half of the core width.

•Aircraft impact severed a single exterior panel at the center ofthe South wall between floors 94 and 96.

•The impact damage to the exterior walls and to the core resultedin redistribution of severed column loads, mostly to the columns adjacent to the impact zones. The hat truss resisted the downward movement of the North wall, and rotated about the East-West axis.

•As a result of the aircraft impact damage, the North and South walls each carried about 7 percent less gravity loads after impact, and the East and West walls each carried about 7 percent more loads. The core carried about 1 percent more gravity loads after impact.



2.Effects of Subsequent Fires and Impact Damaged Fireproofing:

A.Thermal Weakening of the Core:

•The undamaged core columns developed high plastic and creep strains over the duration the building stood, since both temperatures and stresses were high in the core area. The plastic and creep strains exceeded thermal expansion in the core columns.

•The shortening of the core columns (due to plasticity and creep)was resisted by the hat truss which unloaded the core over time and redistributed loads to perimeter walls.

•As a result of the thermal weakening (and subsequent to impact and prior to inward bowing of the South wall), the North and South walls each carried about10 percent more gravity loads, and the East and West walls each carried about 25 percentmore loads. The core carried about 20 percent less gravity loads after thermal weakening.

B.Thermal Weakening of the Floors:

•Floors 95 to 99 weakened with increasing temperatures over time on the long-span floors and sagged. The floors sagged first and then contracted due to cooling on the North side; fires reached the South side later, the floors sagged, and the seat connections weakened.

•Floor sagging induced inward pull forces on the South wall columns.

•About 20 percent of the connections to the South perimeter wall on floors 97 and 98 failed due to thermal weakening of the vertical supports.

C.Thermal Weakening of the South Wall:

•South wall columns bowed inward as they were subjected to high temperatures and inward pull forces in addition to axial loads.
•Inward bowing of the South wall columns increased with time.




3.Collapse Initiation
•The inward bowing of the South wall induced column instability, which progressed rapidly horizontally across the entire South face.

•The South wall unloaded and tried to redistribute the loads via the hat truss to the thermally weakened core and via the spandrels to the adjacent East and West walls.

•The entire section of the building above the impact zone began tilting as a rigid block (all four faces; not only the bowed and buckled South face) to the South (at least about 8º) as column instability progressed rapidly from the South wall along the adjacent East and West walls.

•The change in potential energy due to downward movement of building mass above the buckled columns exceeded the strain energy that could be absorbed by the structure. Global collapse then ensued.

Probable Collapse Sequence for WTC 2

1.Aircraft Impact Damage:

•Aircraft impact severed a number of exterior columns on the South wall from floors 78 to 84, and the wall section above the impact zone moved downward.

•After breaching the building’s perimeter, the aircraft continuedto penetrate into the building, severing floor framing and core columns at the Southeast corner of the core. Fireproofing was damaged from the impact area through the East half of the core up to the North and East perimeter walls. The floor truss seat connections over about 1/4to 1/2 of the East side of the core were severed on floors 80 and 81 and over about 1/3 of the East perimeter wall on floor 83.

•Aircraft impact severed a few columns near the East corner of the North wall between floors 80 and 82.

•The impact damage to the exterior walls resulted in redistribution of severed column loads, mostly to the columns adjacent to the impact zones. The impact damage to the core columns resulted in redistribution of severed column loads mostly to other intact core columns and the East exterior wall. The hat truss resisted the downward movementof the South wall, and rotated about the East-West axis.

•As a result of the aircraft impact damage, the core carried 6 percent less gravity loads after impact and the North face carried 10 percent less loads. The East face carried 24 percent more gravity load, while the West face and the South face carried 3 percent and 2 percent more gravity load, respectively.

•After impact, the core was leaning toward the East and South perimeter walls. The perimeter walls acted to restrain the core structure.



2.Effects of Subsequent Fires and Impact Damaged Fireproofing:

A.Thermal Weakening of the Core:

•Several of the undamaged core columns near the damaged and severed core columns developed high plastic and creep strains over the duration the building stood, since both temperatures and stresses were high in the core area. The plastic and creep strains exceeded thermal expansion in the core columns.

•The core continued to tilt toward the East and South due to the combination of column shortening (due to plasticity, creep, and buckling) and the failure of column splices at the hat truss in the Southeast corner.

•As a result of thermal weakening (and subsequent to impact), theEast wall carried about 5 percent more gravity loads and the core carried about 2 percent less loads. The other three walls carried between 0 and 3 percent less loads.

B.Thermal Weakening of the Floors:

•Floors 79 to 83 weakened with increasing temperatures over time on the long-span floors on the East side and sagged.

•Floor sagging induced inward pull forces on the East wall columns.

•About an additional 1/3 of the connections to the East perimeterwall on floor 83 failed due to thermal weakening of the vertical supports.

C.Thermal Weakening of the East Wall:

•East wall columns bowed inward as they were subjected to high temperatures and inward pull forces in addition to axial loads.
•Inward bowing of the East wall columns increased with time.

3.Collapse Initiation

•The inward bowing of the East wall induced column instability, which progressed rapidly horizontally across the entire East face.

•The East wall unloaded and tried to redistribute the loads via the hat truss to the weakened core and via the spandrels to the adjacent North and South walls.

•The entire section of the building above the impact zone began tilting as a rigid block (all four faces; not only the bowed and buckled East face) to the East (about 7ºto 8º) and South (about 3ºto 4º) as column instability progressed rapidly from the East wall along the adjacent North and South walls. The building section above impact continued to rotate to the East as it began to fall downward, and rotated to at least 20 to 25 degrees.

•The change in potential energy due to downward movement of building mass above the buckled columns exceeded the strain energy that could be absorbed by the structure. Global collapse then ensued.

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That doesn't matter a bit. Because the main point is it shows the columns being pulled in without anything ejecting out the windows before hand supporting the NIST hypothesis.