Short clip of my full case study regarding WTC 1 that can be found here:
http://www.youtube.com/watch?v=4_J7ak_IZXk

Demo video of the development of the Demolition feature for Blender 2.5x/2.6.
The main purpose of this video is to prove the capabilities of my physics system development, if any. It is not intended to prove or disprove 9/11 conspiracy theories. I'm deleting comments that include hate speech, so you better think twice before starting an argument about the reasons of 9/11 here. Instead, I recommend to read a neutral source like: https://en.wikipedia.org/wiki/9/11_conspiracy_theories to get some pros and cons instead of watching videos on YouTube like mine to come to a realistic conclusion about what has happened that day.

This test case scenario needed 10 minutes per frame to calculate geometry deformations and additional 5 minutes to render the image. The test system was an Intel Core i7-980X Extreme Edition with 3,33 GHz, 12 virtual cores and 12 GB of RAM.

Check here for the complete case study video:
https://www.youtube.com/watch?v=4_J7ak_IZXk

For more information see:
http://blenderartists.org/forum/showthread.php?t=207866

WTC7 Simulation:
https://www.youtube.com/watch?v=MSlIFXw3EGg

http://kaikostack.com

FAQ:

Q: Is the core missing in your model?
A: No, it's just hardly visible because of the low camera angle.

Q: Why did the tower not tip over?
A: If one part of the supporting structure fails then a progressive process starts which makes neighbor supports failing as well due to increased load they have to bear and so on. This happens within seconds so that the building has literally no time to tip over. The larger a building the more immovable is it due to inertia.

Q: But I saw lots of demolition videos where high buildings tipped over, what now?
A: Reinforced concrete buildings with solid load bearing walls are not comparable to lightweight steel structures like the Twin Towers were. Also most certainly none of them were even half as high.

Q: The debris obviously didn't choose the way of least resistance by falling through the still intact structure, how is this even possible?
A: With the debris mass accumulating and accelerating over time also the momentum increases. It increases much faster than the resistance of the still intact structure could slow it down. In this case also the energy required to redirect the momentum to a path of less resistance would be much greater than keeping the original motion path throughout the intact structure. So it depends on the direction of momentum if the path of least resistance would actually be the most energy efficient way to go.

Q: What about Newton's third law? The collapse doesn't match up with my school physics calculations.
A: Classical Mechanics describes the behavior of idealized non-deforming objects, but steel isn't. In fact no known material in the universe is. You cannot reduce complex problems to simple formulas without iterative process, that's why we use computer simulations to understand the behavior of building collapses.

Q: I don't see my comment (anymore), do you censor?
A: No. YouTube automatically marks comments as possible spam if they contain certain keywords such as bad language, links to unknown websites, or when they basically got reported by other users. Then I need to manually accept them in order to make them visible again. I usually do this for most marked comments periodically and sometimes it takes a while until I see them.