Some Misunderstandings Related to WTC Collapse Analysis

[Lauren Johnson]

The core did pull down the building, but it wasn't because of weakness. There is no physical evidence of high steel temperatures on core columns and the rapid acceleration through the first story of the fall is too high for heat weakening induced buckling.

There are two kinds of weakness: the kind caused by excessive heat and other caused by excessive explosives.

Of course, Jeffrey does admit the core went down first. His problem comes in when he attempts to say its load was transferred to the perimeter through the hat truss, which could not possibly do it, and the perimeter columns would not buckle under the addition of the core load as a purely vertical load.

NIST doesn't admit the core went down first, but say it had some level of failure due to heating causing it to expand and then buckle under the compression due to the heat caused expansion being constrained and causing partial load redistribution through the hat truss to the perimeter, which are nowhere near enough to cause perimeter failure. However, it isn't their primary failure mode. Theirs is truss sagging causing perimeter inward bowing leading to perimeter failure of the south wall, in the case of WTC 1. However, in that case the load redistribution wasn't enough to fail either the core or the adjacent perimeter walls. NIST seems to be trying to use a shotgun approach where everything fails a little bit, but they never do make a case where they have high enough combined redistributed loads to cause additional failures.

The reason both Jeffrey's and NIST's explanations are confusing is that they aren't real and there was nowhere near enough load redistribution to cause additional failure in their scenarios. In my opinion their scenarios are worse than your analogy of a stable human losing one leg instantly and would be more like a four legged animal suddenly losing one leg. There isn't enough overload to fail the other three legs.

The real failure was due to something causing the core to fall other than heat and the falling core pulling the perimeter walls in through the floors causing them to buckle. The late Danny Jowenko showed how to do it at a little after three minutes into the video here http://www.youtube.com/watch?v=k3DRhwRN06I

But Jeffrey did answer my interpretation of his Top Down cartoon below:

Jeffrey, As I understand your sketch entitled Top Drop Cartoon, the load supported by the compromised core columns was slowly transferred to the perimeter columns via the hat trusses. As the perimeter column exceeded their designed load capacity, they began to buckle and slip pulling the core columns down. The core detaches from the hat trusses. After that I am a little vague. But somehow this leads to a cascading collapse which Major Tom calls ROOSD, which stands for Runaway Open Office Space Destruction. Am I correct in interpreting your cartoon?

And responded:

Basically you are getting the gist of the diagram. It's meant to show what happens as the core columns are weakened. When the lose capacity the 12 floors of the core ... and there were only 2 elevator chafts in the core at that height... were hanging from the hat truss. And this include part of the weight of the floors outside the core as the 24 perimeter core columns support about 45% of the outside the core floor loads. When the core lost capacity all of the loads were moved over to the facade columns which buckled and in so doing there was lateral translation and the facades slipped past each other 2 side passed outside and 2 inside. But surely the facade wasn't able to carry the floor loads alone including those inside the core up there. This mass.. became the ROOSD mass driving through the inside of the tower down to the ground.

Based on Jeffrey's words and my burning through the bottles of Visene squinting at the Top Down cartoon, he seems to be saying that the load was transferred to the perimeter columns via the hat trusses. The initiation of the collapse was the failure of the perimeter columns as they exceeded their designed load capacity taking the core columns down. The floor joists loaded with cement disconnected and formed the ROOSD mass.

Jeffrey, it's your call.