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