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Constructed by the Port Authority of New York and New Jersey in the early 1970s, the World Trade Center towers were, for their
time, the best known examples of tube buildings. Tube buildings are strengthened by closely spaced columns and beams in the
outer walls. The closely spaced columns and beams in each tower formed a steel tube that, together with an internal core,
withstood the tremendous wind loads that affect buildings this tall.
At the time of their completion in 1973, the World Trade Center towers were the two tallest buildings in the world. Two years
later, the Sears Tower in Chicago seized the coveted title.
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Vital Statistics:
Location: New York, New York, USA
Completion Date: 1972 (Tower One), 1973 (Tower Two); destroyed
2001
Cost: $400 million
Height: 1,368 feet (Tower One), 1,362 feet (Tower Two)
Stories: 110
Misc:
Materials:
Steel
Facing Materials: Aluminum, steel
Engineer(s): Skilling, Helle, Christiansen & Robertson
Aside from withstanding enormous wind loads, the World Trade Center towers were also constructed to withstand settlement loads.
Because the towers were built on six acres of landfill, the foundation of each tower had to extend more than 70 feet below
ground level to rest on solid bedrock.
The two towers were unable to survive the effects of a direct hit by two hijacked commercial jetliners during terrorist attacks
on the morning of September 11, 2001. Although they were in fact designed to withstand being struck by an airplane, the resultant
fires weakened the infrastructure of the building, collapsing the upper floors and creating too much load for the lower floors
to bear. Shortly after the attack, both towers collapsed.
Fast Facts:
Each tower had 104 passenger elevators, 21,800 windows, and roughly an acre of rentable space on each
floor.
From the observation deck on Two World Trade Center it was possible to see 45 miles in every direction.
Each tower swayed approximately three feet from true center in strong wind storms.
If all the glass used
in the construction of both towers were melted into a ribbon of glass, 20 inches wide, it would have run 65 miles long.
On Friday, February 26, 1993, a bomb exploded in the underground garage of One World Trade Center, creating a 22-foot-wide,
five-story-deep crater. Six people were killed and more than 1,000 were injured. The towers were cleaned, repaired, and reopened
in less than one month.
On Tuesday, September 11, 2001, a second terrorist attack destroyed both towers.
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