The 9/11 Forum

I think everyone is familiar with the soda pop can analogy for the towers' demise. You balance on top of an empty soda can, tap the side of the can with your finger, and it immediately collapses. It seems that this collapse would be fairly easily modeled numerically -- the can has regular geometry, known strength parameters, etc., and the weight on the top and the sudden deformation provided by the finger tap could be adjusted until "global collapse ensued." A back of the envelope computation should be capable of demonstrating both why the can doesn't collapse immediately, and what size the deformation would have to be to initiate collapse.

Would it be possible to start with a model of this type, and work up the complexity to create something similar to the WTC 7 geometry? Then, one could remove interior members (or simulate other types of deformations) and/or add weight to the top until failure was induced.

I am a modeler, but not of the structural type. The process of working from simplicity to complexity is something I use quite often.

Un-hyphenated:

While I believe that models can be useful to illustrate some collapse behaviors - as in soda cans with or without dents or cuts on their sidewalls - physical models generally don't scale well with regard to relative mass-to-strength ratios. Indeed, a number of posters on this very forum have discussed and even built models (of the Twin Towers), but these models are all open to criticism when it comes to the failure behavior of the columns because they are especially hard to model. (See the thread I started back in October in the WTC 1 & 2 section of this forum.)

In the case of WTC 7 we are in even worse shape because information on the core and perimeter columns is not readily available so we would never know if a particular model was accurate.

Yes, I don't believe a physical model of the towers would be very easy to create. I am speaking only of numerical models. I would think that the soda pop can collapse would be relatively simple to numerically model, showing both the stability prior to tap, and the collapse inevitability after tap. A similar (but more complex) numerical model could be used to explore the sensitivity of the WTC 7 structure to loss of elements, etc.