Tuesday, January 23, 2007

Someone Else's Attempt at Modeling

Described here.

This part is cool-- he loads it with charcoal and burns his tower.

Here he uses a blowtorch on it

The Progressive Top Down 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 collapse of buildings cited are the Twin Towers, Building 7, and the Murrah Federal Building in Oklahoma City.

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 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.

There IS no precedent for what happened on 9/11 to the twin towers.

So why are so many people here so god-danged bent on declaring it a pure structural-failure "collapse"?


Wednesday, January 03, 2007

Single Columns

I wondered if I used single wire columns, without cross-bracing, if that would subtract a factor of 2 from the strength, making the model only 28 times as strong, relatively compared to my calculation of 55 times stronger). Thus if I used one column at each corner, and six "core" columns, this would lead to rough strength equivalence.

I tried a simple model of two floors using only 10 single wire columns (no cross-bracing)in between, but preliminary tests suggest this arrangement was quite weak. This indicates that the wire columns are not as strong as I calculated.

I still am very interested in trying to model a progressive collapse. The idea is to get the proper column arrangement such that when an upper set of floors falls, the next floor down will fail, then the next, and so forth.