Moderator note: It appears that a debate on this topic was started without clear agreement as to the debate format. Readers are warned that the resulting debate does not really fit the format of the Formal Debates forum. It is retained here for those who are interested, although the discussion thread is closed. [thread=90058]Proposal thread[/thread]. [thread=90071]Debate thread[/thread]. [thread=90070]Discussion thread[/thread] ------------ Scott and I have agreed to the rules. He has graciously given me the floor first. I will use this opportunity to repost my position given in the proposal thread. (MacGyver stands behind the podium) How did the WTC towers collapse? It's because of this: (MacGyver produces a standard wooden meter stick from behind the podium, much like this) Please Register or Log in to view the hidden image! No..I don't think a meter stick brought down the twin towers, but I would like to use it as example of what happens to a long, light-weight structure when under compression, with no external support. (Macgyver then holds the meter stick at both ends and pushes inward..causing the meter stick to bow in the center) It bows! Light weight structures, like this meter stick perform very poorly under compression...BUT! (points one finger in the air dramatically) (Macgyver holds meterstick vertically) If you add horizontal supports, in tension, evenly along its length, to this flimsy vertical member, that prevent it from bowing, the compression strength of the member greatly increases...and the meter stick can hold much more weight. I would like to propose that the collapse of the twin towers was initially caused by failure of the light weight floor joists, who's job it was to prevent the perimeter columns from bowing under load, (like our meter stick). I would like to submit this stock photo (arrows added my me) of a WTC floor joist and it's connection to the perimeter columns as Reference picture #1. Please Register or Log in to view the hidden image! We can clearly see in the photograph, the delicate construction of each individual joist. The joist is made up of a top rail (indicated by the blue arrow) and the bottom rail (pink arrow). These two rails were supported and kept rigid, by a long steel rod, bent in a continuous "M" shape, and welded at the top and bottom (green arrow). It is my opinion that this steel rod was the first component to fail in the system. The steel structure was protected by blown on fire-proofing. These metal rods presented a small diameter, and little surface area for that type of blown on insulation to stick to. When the massive plane struck the perimeter columns and shattered, many of these key floor joists were damaged or destroyed in the initial impact. Others had their fireproofing stripped from them by high-speed, flying debris. Thousands of gallons of jet fuel instantly ignited a fire across many floors. These small diameter rods were exposed to temperatures that allowed them to soften to begin to lose their strength. When the rods began to fail, it allowed the top and bottom rail to sag in their center, pulling on the connections at the perimeter wall (yellow arrows) Eventually, the joist would sag enough to cause the connections to the wall to fail, causing the joist to fall to the next floor. When enough of these joists became dislodged, it allowed the perimeter columns to bow (like our meter stick) and fail. These columns were already under more than their designed load, due to the massive hole in the side of the building. The perimeter columns initially were successful in transferring the load around the hole, immediately after the impact...but with a lack of horizontal support to keep them from buckling, they failed. At that point gravity took over. And that is what I believe caused the twin towers to collapse. Thank you. Scott, you can either respond to this, or present your own position on "Why the WTC buildings collapsed".