Tuesday, 11 September 2001 19:50 (ET)
DETROIT, Sept. 11 (UPI) -- A lead engineer who worked on New York's World Trade Center Towers expressed shock Tuesday that the 110-story landmarks in Lower Manhattan collapsed after each tower was struck by a hijacked passenger jetliner.
Constructed and operated by the Port Authority of New York and New Jersey, the 3.8 million square foot World Trade Center was built as a seven-building complex on 16 acres. The towers destroyed -- One and Two World Trade Center -- rose over 100 feet higher than the Empire State Building from the center of the complex.
Built without masonry, the towers were the first of such buildings to face problems from intense air pressure caused by high-speed elevators. To circumvent problems, a drywall system was attached to the reinforced steel core.
One of the towers had survived a 1993 attack by terrorists in an explosives-filled van that killed six people and injured more than 1,000 others.
Lee Robertson, the project's structural engineer, addressed the problem of terrorism on high-rises at a conference in Frankfurt, Germany, last week, Chicago engineer Joseph Burns told the Chicago Tribune.
Burns said Robertson told the conference, "I designed it for a (Boeing) 707 to hit it."
"Fire melts steel," Burns told the Tribune, speculating that the impact from the planes had damaged sprinkler systems in both towers.
"You never know in an explosion like that whether they get cut off," Burns said.
The World Trade Center was designed by architect Minour Yamasaki of the Rochester Hills, Mich., firm, Minoru Yamasaki and Associates, was known for its sweeping use of glass.
Because of the buildings' heights, engineers used tubular construction of tightly spaced steel columns. The floor trusses were built across to this central core.
Yamasaki, who died in 1986, also designed the McGregor Memorial Conference Center at Wayne State University, the Reynolds Aluminum building in Southfield, Mich., and the 30-story Consolidated Gas Co. Building in downtown Detroit.
Militants who carried out the 1993 attack on the symbol of America's financial prowess said they had wanted to bring the New York tower to the ground.
Near Washington, part of the 6.5 million-square-foot Pentagon collapsed after the nerve center of U.S. military forces was hit by a plane, causing a huge fire.
High rises, office buildings, courts, city halls, museums, sports stadiums and other public buildings were closed coast-to-coast as a precaution. The Mall of America in Bloomington, Minn., the largest shopping mall in the United States, was evacuated after the morning attacks.
"While we have not received any threats we believe this is a prudent precaution," said Maureen Bausch, vice president of marketing and business development.
The Fitzgerald Theater in Minneapolis canceled a Talking Volumes Book Club event featuring author Salmon Rushdie. Rushdie, who was marked for death by Islamic fundamentalists several years ago, was unable to travel because of the nationwide ground stop that halted commercial air traffic ordered by the Federal Aviation Administration.
Copyright 2001 by United Press International.
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