1. 9/11: Why The Towers Collapsed

2. Theory A previous article written in 2007 by William Rice, a civil engineer on the twin towers discussed the low chances of a collapse of the twin towers. Mr. Rice talks in his article about how an plan impact would do tons of damage, however, the towers were built for it. The entry below is an important part of his article discussing the tower and how it would deal with an impact: “The prevailing theory for the collapse of the 110-story, award-winning Twin Towers is that when jetliners flew into the 95th and 80th floors of the North and South Towers respectively, they severed several of each building’s columns and weakened other columns with the burning of jet fuel/kerosene (and office combustibles). However, unlike concrete buildings, structural steel buildings redistribute the stress when several columns are removed and the undamaged structural framework acts as a truss network to bridge over the missing columns. After the 1993 car bomb explosion destroyed columns in the North Tower, John Skilling, the head structural engineer for the Twin Towers, was asked about an airplane strike. He explained that the Twin Towers were originally designed to withstand the impact of a Boeing 707 (similar in size to the Boeing 767). He went on to say that there would be a horrendous fire from the jet fuel, but “the building structure would still be there.” -William Rice

3. Structure The twin towers are composed of steel and concrete. The middle of the building is made of reinforced steel center (called tube in tube structure). Each tower had 244 columns in the center.

4. The planes impact When the plans hit, 10,000 gallons of fuel burned, which can bur between 800 and 1,500 degrees Celsius. This would not melt steel, however, at 1,200 degree Celsius plus the impact would cause the steel to loose half its strength. The steel in the impact area would also distort due to a non-uniform temperature across the tower floors.

5. Conspiracy of Controlled Demolition Many believe they saw white smoke and heard explosions coming from the area under the tower where the supports for the structure are. There is evidence of this, however, there is no solid evidence of this, except pictures which can be mistaken for pressurized explosions from the impact

6. Conclusion The towers both collapsed shortly after the impact of the two planes. Many believe it was planned and there was a controlled demolition, and many believe it was completely from the planes impact. There is evidence that supports both sides, ranging from eye witnesses and pictures, to understanding the actual structure and statistics.

7. Work Cited Rice, William. "Why the towers fell: Two theories." Vermont Guardian | For The Independent Mind. N.p., n.d. Web. 20 Jan. 2012. <http://www.vermontguardian.com/commentary Craven, Jackie. "Why the World Trade Center Twin Towers Fell." Architecture and House Styles and Building Design. N.p., n.d. Web. 23 Jan. 2012. <http://architecture.about.com/od/disastersandc ollapses