World Trade Center

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The World Trade Center was a complex of several buildings around a central plaza in New York City. It was designed by American architect Minoru Yamasaki, and was one of the most striking American implementations of the architectural ethic of Le Corbusier, as well as the seminal expression of Yamasaki's gothic modernist tendencies. Constructed in the early 1970s under the auspices of the semi-autonomous Port Authority of New York and New Jersey, the WTC consisted of 7 buildings, but its most notable features were the huge and characteristic twin towers. On any given day, some 50,000 people worked in the towers (for lists of the companies see /North Tower and /South Tower).

The towers collapsed in a terrorist attack on September 11, 2001, where two commercial jets crashed into the towers. For details on the terrorist attack see September 11, 2001 Terrorist Attack.

1993 World Trade Center bombing: On February 26, 1993, a bomb planted by terrorists exploded in the underground garage of the north tower. Six people were killed and over a thousand injured. Six Islamic extremist conspirators were convicted of the crime in 1997 and 1998 and given prison sentences of 240 years each.

The towers

Each of the towers had 110 stories. The height of the towers were 417 m (1368 feet) (tower one, the northern one with a huge antenna on top) and 415 m (1362 feet) (tower two, the southern one with a spectator platform). When the towers were completed in 1972 (tower one) and 1973 (tower two) they were the tallest buildings on earth, 100 feet taller than the Empire State Building. Their size was the subject of a joke during a press conference unveiling the landmarks. Minoru Yamasaki was asked: "Why two 110-story buildings? Why not one 220-story building?" His response was: "I didn't want to lose the human scale."

The towers held the height record only briefly. As the building neared completion, work had already begun on Chicago's Sears Tower, which would climb to 1,450 feet. Since their desctruction, the Empire State Building is again the tallest building in New York, after spending almost 30 years as the third-tallest.

To solve the problem of wind sway or vibration Yamasaki took a then unusual approach - instead of bracing the buildings corner-to-corner or using internal walls the towers were essentially hollow steel tubes. Each tower contained 240 vertical steel columns called Vierendeel trusses around the outside of the building, these were bound to each other using ordinary steel trusses. In additon, 10,000 dampers were included in the structure. With a strong shell such as this, the internal floors could be simply light steel and concrete with internal walls not needed for structural integrity, creating a tower that for its size was extremely light. This method of construction also meant that the twin towers had the world's highest load-bearing walls.

Of the 110 stories twelve were set aside for technical services, in four three floor areas evenly spread up the building. All the remaining floors were free for open-plan offices.

The role of asbestos in the contruction of the towers and collapse has been discussed by [1]. Basically, asbestos was used as a fire-retardant agent and insulation in the first 60 floors, but not for the entire building. This is thought to have contributed to the collapse because the structural material was not as impervious to heat without the asbestos coating. Cleanup of the wreckage has been hindered by asbestos content as well.

The excavation of the foundations of the building, located on the former Radio Row, was particularly complicated since there were two subway tubes close by needing protection without service interruption. A six-level basement was built in the foundations. Excavation of about 1 million cubic yards of earth and rock created a $90 million real estate asset for the project owner, the Port Authority of New York and New Jersey, which helped offset the enormous loss in revenues which came from the tax breaks given to the Trade Center itself. The spoil was used to create 23 acres of landfill in the Hudson river next to the World Trade Center site. It was developed as Battery Park City.

One of the world's largest gold depositories was stored underneath the World Trade Center, owned by a group of commercial banks. The 1993 bomb detonated close to the vault, but it withstood the explosion. One source estimates the 1993 value of the gold at one billion dollars, believed to be owned by Kuwaiti interests. That same source claims that when the World Trade Center was destroyed, the amount of gold "far exceed[ed] the 1993 levels." The gold remains buried under the rubble of the building. [as of 22 September 2001] [2], [3].


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http://www.wikipedia.com/images/NOAA_WTC.jpg
Image taken from the west (from NOAA in the public domain)