Some Misunderstandings Related to WTC Collapse Analysis

[Lauren Johnson]

Jeffrey, moving on. I continue to study your Top Down cartoon. You have agreed that it is meant to show graphically how the load from the damaged core was redistributed via the hat truss system into the perimeter columns which caused sagging and slippage and eventually pulled down the core columns. The runaway collapse ensued.

I asked both you and Tony to engage me in my thought experiment of an instantaneous disappearance of one floor's worth of core columns. Tony said that if that happened, it would require the instantaneous disappearance of five floors to allow enough momentum to begin the cascading collapse. You said one floor would be enough. In fact, I didn't ask you, but I should have asked is there a minimum threshold of the disappearance of core columns that would not lead to the collapse of the building. So I guess I will ask that question. If only one meter vanished, would there have been no collapse? Two meters? Etc.

But the key to this your assertion that the collapse is caused in all cases by the re-distribution of the load to the perimeter columns.

The reason I ask you to humor my request, in the Case of the Disappearing Columns is my way understanding you cartoon by taking it to the limiting condition.