Skyscrapers

I Beam Sizes and Spans

• 12x5" beams allow 24' spans holding about 10 tons of weight. These beams are about 35 lb per foot.
• Compare Rebar Truss at 15 lb per foot.

Failure Modes

• Fire protective coating on floor beams, and flexible vertical columns were found in the WTC collapse, according to the official reports. [1]. Heat was from molten aluminum (20 tons of aluminum per plane) reacting with water. Molten aluminum in water are explosive. Lesson: do not build aluminum buildings [2].