Architecture and design
Preliminary site plans for the World Trade Center's reconstruction. In orange are the new buildings (One World Trade Center is the square at upper left), and in blue is the 9/11 Memorial and Museum.
Many of Daniel Libeskind's original concepts from the 2002 competition were discarded from the tower's final design. One World Trade Center's final design consisted of simple symmetries and a more traditional profile, intended to compare with selected elements of the contemporary New York skyline. The tower's central spire draws from previous buildings, such as the Empire State Building and the Chrysler Building. It also visually resembles the original Twin Towers, rather than being an off-center spire similar to the Statue of Liberty.[124][125][126][127][128]
The building occupies a 200-foot (61 m) square, with an area of 40,000 square feet (3,700 m2), nearly identical to the footprints of the original Twin Towers. The tower is built upon a 185-foot (56 m) windowless concrete base, designed to protect it from truck bombs and other ground-level attacks.[129] Originally, the base was to be covered in decorative prismatic glass, but a simpler glass-and-steel façade was adopted when the prisms proved unworkable.[80] The current base cladding consists of angled glass fins protruding from stainless steel panels, similar to those on 7 World Trade Center. LED lights behind the panels illuminate the base at night.[130] Cable-net glass façades on all four sides of the building for the higher floors, designed by Schlaich Bergermann, will be consistent with the other buildings in the complex. The façades are 60 feet (18 m) high, and range in width from 30 feet (9.1 m) on the east and west sides, 50 feet (15 m) on the north side, and 70 feet (21 m) on the south side.[10] The curtain wall was manufactured and assembled by Benson Industries in Portland, Oregon, using glass made in Minnesota by Viracon.[131]
From the 20th floor upwards, the square edges of the tower's cubic base are chamfered back, shaping the building into eight tall isosceles triangles, or an elongated square antiprism.[132] Near its middle, the tower forms a perfect octagon, and then culminates in a glass parapet, whose shape is a square oriented 45 degrees from the base. A 408-foot (124 m) sculpted mast containing the broadcasting antenna – designed in a collaboration between Skidmore, Owings and Merrill (SOM), artist Kenneth Snelson (who invented the tensegrity structure), lighting designers, and engineers – is secured by a system of cables, and rises from a circular support ring, which contains additional broadcasting and maintenance equipment. At night, an intense beam of light is projected above the spire, being visible over 1,000 feet (300 m) above the tower.[133]
David Childs of SOM, the architect of One World Trade Center, said the following regarding the tower's design:[134]
We really wanted our design to be grounded in something that was very real, not just in sculptural sketches. We explored the infrastructural challenges because the proper solution would have to be compelling, not just beautiful. The design does have great sculptural implications, and we fully understand the iconic importance of the tower, but it also has to be a highly efficient building. The discourse about Freedom Tower has often been limited to the symbolic, formal and aesthetic aspects but we recognize that if this building doesn't function well, if people don't want to work and visit there, then we will have failed as architects.[134]