After three years of study, the National Institute of Standards and Technology (NIST) finally released its report on the collapse of World Trade Center building 7.
The main conclusion is that the building came down due to fire, not due to debris damage or some conspiracy demolition team. The fire started pretty small after the collapse of WTC 1, but was left to burn several floors out completely. The important finding is that the collapse was triggered by thermal expansion of beams, which could detach asymmetrically loaded girders from the main columns. Some limited pancaking of floors then caused a lack of lateral support and buckling of a single column. This triggered the failure of the entire core of the building, which finally fell down as a single piece.
All documents can be found at NIST's WTC page, which read like a porn magazine for finite element junkies. Simulation movies are also available. And yes, they used Beowulf clusters to do the simulations, some of which lasted for several months.
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