Last year I created a physical model to illustrate some aspects of the WTC Tower collapses. The basic structure was columns connected by floors. The floors supply lateral stability to the columns, so when the floors are removed the columns are very unstable. This worked out reasonably well, and I got this nice demonstration from it:
I'm currently re-creating my physical model as a virtual model using Blender physics to allow for a larger variety of experiments, and also to illustrate the difference that scale makes.
The first version I tried quite closely resembles the first physical model
The intent behind these models is to help people understand more about the actual mechanisms of the collapse speed of the Twin Towers. One of the reasons the 9/11 "Truth" movement has been relatively popular is the non-intuitive nature of the collapse where a smaller top block appeared to crush a much larger lower part at quite high speeds. This has led to some quite inaccurate "models" of the what happened, like this one from the organization "Architects and Engineers for 9/11 Truth"
The problem is that these things ignore the scale of the building, the internal structure of the building, and how it actually collapsed.
The collapse of the towers (once started) was a "zipper" progressive collapse. A wave of very fast falling debris stripped the horizontal members away from the columns, which eventually collapsed - rapidly in the case of the outer walls, and less rapidly in the case of the inner core. Any model of the collapse needs to reflect that reality, and that's what I'm trying to illustrate here.