WORLD TRADE CENTER, NEW YORK

The World Trade Center was planned in 1960 as a seven-building complex to form the economic center of New York City, but the buildings went on to symbolize a broader image of American prosperity. The idea for the center was initiated by David and Nelson Rockefeller, and Minoru Yamasaki was hired to design the towers. The lower Manhattan site was ideal, given that this part of the island has deep bedrock deemed adequate to support the 110-story "twin towers" that formed the centerpiece of the complex. Construction began in 1966, and Tower 1 (to the north) was completed in 1970, while Tower 2 (to the south) was finished in 1972. For one year, the twin towers were the tallest structures in the world, standing at 1,368 and 1,362 feet tall respectively, but they were surpassed in height in 1973 by the Chicago Sears Tower, built by the firm ofSkidmore,Owings&Merrill. Structurally innovative, the twin towers were some of the earliest "super-tall" skyscrapers in the world.

When construction began, aconcretewall was built underground as a slurry wall to keep water from the Hudson River out of the foundations of the buildings. Then a six-level basement was completed in each of the "twin towers." The soil displaced from these foundations was added to the landfill used to create Battery Park. The towers were designed assteel-framed cubes, with each floor a self-supporting unit. Steel piers lining the perimeter of the buildings, as well as a strong central core of piers, supported the outer lateral loads and the force of gravity. The central core was used for the elevator shafts, stairwells, restrooms, and utility rooms, while unencumbered office space filled the rest of each floor. The buildings were conceived of as hollow tubes surrounding a strong central core.The intended result was a wind sway minimal enough to be absorbed by the lightweight outer walls, a significant improvement over previous curtain wall structures. The floors were constructed of four-inch-thick concrete slabs laid on steel decks with floor trusses between the piers. The windows on each floor were relatively narrow, at 18 inches wide, intended by Yamasaki to help enclose the space to limit any fear of heights or sense of vertigo that might plague the inhabitants of the higher-level offices. Nevertheless, the narrow windows, along with the great height of the buildings, were considered too impersonal. Lewis Mumford argued that the large scale had no real function aside from what he termed "technological exhibitionism." Indeed, the towers were initially difficult to fill with renters, and only in the 1980s were they considered fully occupied.

After one relatively small accidental fire and one prior bombing attempt, on September 11, 2001, Al Qaeda suicide hijackers flew planes into the twin towers, resulting in their total collapse. The other buildings in the complex were also affected. WTC 7 collapsed, WTC 3 was crushed by the weight of these structures, and WTC 4, 5, and 6 were subsequently demolished. The official death total currently numbers 2,750, which was a challenging figure to reconstruct given the dearth of human remains found at the obliterated site. After eight and a half months of clearing debris 24 hours a day, the Lower Manhattan Development Corporation was given the task of selecting the future construction on this valuable piece of real estate. Hoping to balance the use of the site as a historical memorial and a future economic center, the advisory committee selected the overall site design created by the Polish-born American architect Daniel Libeskind, whose Jewish Museum in Berlin, constructed in 1999 in the style ofDeconstructivism, provided him international recognition. Libeskind planned five buildings and a memorial clustered around a sunken field that maintains the foundations of the destroyed twin towers and the original slurry wall. This central area is to feature a museum and a memorial titled Reflecting Absence, selected in 2004 from a competition design submitted by Michael Arad and Peter Walker. The office towers, three of which are to be designed by Norman Foster, Richard Rogers, and Fumihiko Maki, all known for theirHigh-Tech architecture, are clustered around Libeskind's Freedom Tower, which rises 1,776 feet, in reference to the date of American Independence. Seventy stories would be used for offices space, restaurants, and shops, while the top 30-story spire is to have gardens. The three currently planned glass office towers will range in height from 946 to 1,254 feet tall, and will be completed in 2011-2012, while a fifth building is now being designed. WTC 7, not part of Libeskind's project, has already been rebuilt by the firm of Skidmore, Owings & Merrill.