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Structural Engineers Offer Insight On World Trade Center Collapse


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 the buildings, columns were spaced at 3’-3” on center, with 48”- deep plate girders at each floor.  At the third level, the columns transitioned in an arch-like formation to a 10’-0” spacing for the lower story.  Floors were supported by steel trusses spanning 60’, from the core to the perimeter wall, on each side of the building.  The buildings are also thought to have been the first buildings to use non-asbestos fireproofing.  The fibers of the spray-on fireproofing product were reportedly ceramic rather than asbestos.


NCSEA has contacted FEMA and will coordinate and make available structural engineers in the New York and Washington D.C. areas. NCSEA will also coordinate and provide the services of Member Structural Engineering Associations throughout the U.S., as needed.  


The National Council of Structural Engineers Associations is extremely saddened with the day’s news, including the collapse of the World Trade Center in New York City. Our hearts and prayers go out to all the victims and their families.


For additional information, contact the NCSEA Officers and Directors:


President:  Greg Schindler  (206) 622-5822

Vice President:  Mike Tylk  (312) 341-0055 x29

Treasurer:  Sanjeev Shah  (305) 500-9390

Secretary:  John Joyce  (405) 848-4093

Director:  Ron Hamburger  (510) 817-3100

Director:  Jim DeStefano  (203) 254-7131

Past President/Director:  Marc Barter  (251) 473-8354

Executive Director:  Jeanne Vogelzang  (312) 372-5708