Stephen L. Keeling

Institute for Mathematics and Scientific Computing
Karl-Franzens University of Graz
A-8010 Graz, Austria

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An Interactive Simulation Comparing Models of the Fall of the World Trade Center Towers

This is an easy-to-use interactive simulation using Netlogo, a software available here from Northwestern University free of charge. With this software, one can run the following Netlogo-program, wtc.nlogo:

in which a free fall of a world trade center tower is compared with a collapse, since the recorded fall times for the world trade center buildings correspond to a free fall, while the falls have been explained officially as a pancake type of collapse. In the simulation shown here, there are two mechanisms by which a collapse is retarded. First, the fall is retarded in a somewhat passive way by the presence alone of stationary mass in lower floors which opposes the momentum of the falling mass. Second, the fall is retarded in a somewhat active way, for example, by the fastening of each floor or by the bonds within materials which require energy for pulverization. The user may examine these effects by controlling how much mass is turned to dust and how strong the floors are. These effects may be controlled by selecting pulverization and floor strength which seem natural as well as by raising supplemental factors which enhance pulverization and which weaken floors. It remains for the user to decide whether the pancake collapse theory agrees with the recorded free fall times.

For basic information about the simulation for the interested user, see this description.

For a detailed mathematical basis of the simulation, see this derivation.

For matlab users see wtc.m. For excel users see wtc.xls.

For the fall of WTC1, see
For the fall of WTC2, see wtc2.mpg.
For the seldom seen fall of WTC7, see wtc7.wmv.

See other discussions of scientific interest in the film Improbable Collapse with homepage here and viewable directly here.