Reply #90: "It doesn't fall over to the south but it does tilt or slump enough"

[Bolo Boffin]

It was only a factor in the collapse as it was happening. If you read the NIST report:

http://wtc.nist.gov

You'll see that they conducted several test scenarios with their computer model. The damage caused by the debris did not contribute to collapse initiation. In fact, one test was run with the documentable fires but without the documentable damage and the building fell anyway. One test was run with Column 79 removed from floors 11-13 only, and the building fell. Both fell in notably different progressive sequences, but down they went.

The main reasons the building fell were the unusual dependence of the structure on column 79 and the long floor beams in the east of the building. They weren't cantilevered, but they were stretching over the ramp that supplied the entire WTC complex. It was their thermal expansion that kicked an important girder loose between 79 and the perimeter, started a localized collapse. That removed support from 79 for about seven or eight floors. The cantilevered girders in the northwest played their part in the ensuing collapse, though.