The Towers' Architecture
The Innovative Design of the World Trade Center Towers
The Twin Towers were the tallest buildings in the world when they were completed in 1972. The design, created by architect Minoru Yamaski, was innovative in several ways, including its elevator system, and its structural system. These innovations would be widely adopted in later skyscrapers.
A conventional elevator system would have taken up half the space of the lower floors. A novel system employing express and local elevators was developed by Otis Elevators. The express elevators took people to "sky lobbies" on the 44th and 78th floors, where they could board local elevators. (See this schematic.) This system halved the number of elevator shafts that would have been required in a conventional system, and resulted in shorter average transit times for tenants.
A March 2001 article in Elevator World describes contemporary work on the elevator system of the Twin Towers by Ace Elevator as "one of the largest, most sophisticated elevator modernization programs in the industry's history." 1
1 and 2 World Trade Center used the so-called tube within a tube architecture, in which closely-spaced external columns form the building's perimeter walls, and a dense bundle of columns forms its core. Tall buildings have to resist primarily two kinds of forces: lateral loading (horizontal force) due mainly to the wind, and gravity loading (downward force) due to the building's weight. The tube within a tube design uses a specially reinforced perimeter wall to resist all lateral loading and some of the gravity loading, and a heavily reinforced central core to resist the bulk of the gravity loading. The floors and hat truss completed the structure, spanning the ring of space between the perimeter wall and the core, and transmitting lateral forces between those structures.
The tube within a tube architecture was relatively new at the time the Twin Towers were built, but has since been widely employed in the design of new skyscrapers. In fact most of the world's tallest buildings use it, including:
- The Sears Tower (1450 ft)
- The World Trade Center Towers (1350 ft)
- The Standard Oil of Indiana Building (1125 ft)
- The John Hancock Center (1105 ft)
An 800- x 400-foot foundation box, 65 feet deep and with 3-foot-thick retaining walls -- the so-called bathtub -- was under more than half the World Trade Center complex, including the Twin Towers and the adjacent hotel. 2 3
2. , ENR, 7/9/64, page 36
3. World Trade Center 'Bathtub': From Genesis to Armageddon, nae.edu, [cached]