The Progressive Collapse Challenge
You've heard that the Twin Towers pancaked, crushing themselves completely. The experts gave us a fancy-sounding term for this: progressive collapse . If you search with the phrase "progressive collapse" you will find numerous articles, most of them written since 9/11/01 about things like assessing and retrofitting existing structures against progressive collapse. It seems that the only examples of progressive total building collapses cited are the Twin Towers, Building 7, with most damage to the Murrah Federal Building in Oklahoma City being one of the few purported examples of progressive partial building collapses.
A TV documentary which purported to explain the collapses of the Twin Towers featured a demonstration in which a house-of-cards like structure representing one of the towers was supposed to collapse from the top down. The documentary showed only the beginning of this simulated building collapse, since the producers were apparently unable to achieve progressive total collapse. This raises the question: If this newly discovered mode of structural failure is so likely to happen, why is it so difficult to reproduce?
THE PROGRESSIVE COLLAPSE CHALLENGE
The challenge is in 5 parts, from the easiest to the most difficult.
All five require building a structure that will undergo top-down progressive total collapse -- i.e.: when disturbed near the top, it will collapse from the top down to the bottom, leaving no part standing. The disturbance can include mechanical force, such as projectile impacts, and fires, augmented with hydrocarbon fuels. Explosives and electromagnetic energy beams are not permitted.
Your structure can be made out of anything: straws, toothpicks, cards, dominoes, mud, vegetables, pancakes, etc.
The designers of the Twin Towers were able to meet all 5 challenges using steel and concrete.
Build a structure with a vertical aspect ratio of at least 2 (twice as tall as it is wide) and induce it to undergo top-down total progressive collapse.
Build a structure with a square footprint and a vertical aspect ratio of at least 6.5 (6.5 times as high as it is wide), and induce it to undergo top-down total progressive collapse.
Build a structure as required by CHALLENGE #2 which, in the process of collapsing, will throw pieces outward in all directions such that at least 80% of the mass of the materials ends up lying outside of the footprint, but their center of mass lies inside the footprint.
Build a structure as required by CHALLENGE #2 which is capable of remaining intact in 100 MPH cross wind.
Build a structure that meets the requirements of both CHALLENGES #3 and #4.