Are skyscrapers structurally sound? Why did the World Trade Center buildings collapse?
From the National Council of Structural Engineers Association: September 11, 2001 According to one of the designers of the World Trade Center (WTC), the towers were originally designed to take the impact of a Boeing 707; and the impact of the aircraft this morning did not take the buildings down. In fact, WTC One stood for 1 hour and WTC Two stood for 1 3/4 hours after impact. Engineers familiar with the chain of events suspect that heat from the massive and extraordinary fires weakened the structures and initiated the progressive collapses. John Hooper, a structural engineer from Skilling, Ward, Magnusson, Barkshire, the structural engineering firm that evolved from Skilling, Helle, Christianson, Robertson, which was the structural engineering firm of record for the WTC, provided the following facts to NCSEA: WTC One was 1368′ tall, and WTC Two was 1362′ tall. Each 110-story tower had a floor plate that was 208′ by 208′. The central core of each was 86′ square. Around the perimeter of
