World Trade Center Towers

New York City
On the morning of 11 September 2001, terrorists targeted the World Trade Center in Manhattan, first crashing a hijacked commercial jetliner into the upper levels of One World Trade Center, one of its twin 110-story iconic skyscrapers. A few minutes later a second hijacked aircraft sliced through the middle levels of Two World Trade Center, the other tower. (A third airliner crashed into the Pentagon outside Washington, D.C., while a fourth crash landed in a field in Pennsylvania, its intended target undetermined.) The effects were predictably devastating: both buildings burned fiercely before totally collapsing in clouds of dust and rubble that darkened the sky above Manhattan. A third building in the complex, a forty-seven-story office block (Seven World Trade Center), damaged by flying debris, followed soon after. In an earlier raid in February 1993 Arab terrorists exploded a 1,200-pound (550-kilogram) truck bomb in the Centers parking garage, creating a 150-foot diameter (46-meter) crater. Six people died, and over 1,000 were injured. Floors were destroyed for three levels below the point of detonation, but because of the load-bearing exterior walls, the structural stability of the building was largely unaffected. Tenants returned to their offices by the end of March. The cost of repairs was $250 million. The World Trade Center occupied a 16-acre (6.5 hectare) site a few blocks from Wall Street at the southwestern tip of Manhattan Island, near the bank of the Hudson River. Designed by Minoru Yamasaki and Associates and supervised by Emery Roth and Sons, it was the core of an urban renewal scheme sponsored by the Port Authority of New York and New Jersey to attract international firms to downtown Manhattan.The surviving parts of the complex are a twenty-two story, 818-room hotel (Three World Trade Center); two nine-story office buildings (Four and Five World Trade Center); and an eight-story Customs House (Six World Trade Center). With the destroyed buildings, they were grouped around the 5-acre (2 hectare) landscaped Austin J. Tobin Plaza. Beneath it is The Mall, with about sixty specialty shops, banks, restaurants, and function spaces. Before the tragedy, about 500 international companies were located in the center, employing 50,000 people. It had its own subway stations and its own zip code. In March 1999 U.S. construction executives named the World Trade Center among the top ten construction achievements of the twentieth century. For a short while the One and Two World Trade Center towers, at around 1,353 feet (411 meters), were the worlds tallest buildings, but they were superseded in 1974 by the 1,442-foot (450-meter) Sears Tower in Chicago. In 1998 the Petronas Twin Towers in Kuala Lumpur, Malaysia, reached 1,483 feet (452 meters). Even higher buildings have been projected: for example, the Taipei Financial Center, to be completed in August 2002, will stand 1,660 feet (508 meters) tall and Hong Kongs Kowloon MTR Tower will be 1,903 feet (580 meters). As technically demanding as it is, great height does not qualify a building as an architectural feat. It was their structural system and the consequent creation of usable space that made the New York World Trade Centers towers remarkable. Ironically, it also was a contributor to their collapse. Yamasakis team was selected over a dozen other American architects. During the preliminary design phase, more than 100 proposals were reviewed, ranging from a single 150-story tower (its scale was far too large) to a series of lower towers (which looked too much like a housing project