10-28-2009, 03:27 AM
Quote:Many of the vertical steel members buckled in an event called PLASTIC DEFORMATION.
The horizontal ones too -- they deformed and sagged enough to pull them away from their vertical supports, which were also deformed.
Really, this was the whole cause of the collapse. Take a straight section of a steel coat hangar and flex it a bit. It will return to the original "straitness" (assuming you don't apply too much force). That's called "elastic deformation", and is what load-bearing steel members in structures are carefully designed to withstand. Now add some heat to the coat hanger. Even a cigarette lighter for 30 seconds would probably do. Flex the hanger again with exact same force. It will make a permanent bend at the point where the heat was applied. That's "plastic deformation" due to heat, and is what happened in the WTC collapses.
The steel members in huge buildings are designed to withstand an enormous amount of force. One really has no idea until one gets into the math of it. A lower support member failing catastrophically is going to sound like a bomb went off. Multiple lower supports failing are going to sound like multiple bombs going off.