> My concern WRT the conspiracy theories is in the way 3 WTC buildings > collapsed fairly squarely into thier footprints. It is quite difficult > to *make* this occur (in the sense that work must be done to garuantee > it), yet 3 WTC buildings did just that on their own and one was not > even hit by a plane. If I have any doubts about the "rational" > explanation it lies there.
At the Scientific American site we have this explaination: <quote> Kausel addressed the oft-asked question of why the towers did not tip over like a falling tree. "A tree is solid, whereas building is mostly air or empty space; only about 10 percent is solid material. Since there is no solid stump underneath to force it to the side, the building cannot tip over. It could only collapse upon itself." Robert McNamara said his failure mechanism theory "focuses on the connections that hold the structure together," but he cautioned that "we really need to wait for a detailed investigation, before we decide if we have to up the code ratings for these connections in signature structures <end quote> To make it tilt, one side of the building would have to hold for a significantly longer time than the other. If you watch the video of the south tower (I think it is the south tower), you will see some tilting at the beginning. After that, its more like a wave in a structure. In essence, by the time the wave got down 20 floors, the forces involved in stopping it were much greater than the design strength of the connections. They broke very quickly...so that even a 50% variation in breaking speed would not cause tilt. I think part of the problem in intuiting this is that our gut level experience is not with this type of collapse with this type of structure. Now, if the bottom collapsed, then we would expect tilt, but not the top. Dan M. _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
