In 1970, Sears Roebuck & Co., the world’s largest retailer, with annual sales around $50 billion (adjusted for inflation), broke ground on a new corporate headquarters building in Chicago’s financial district. In order to accommodate its 13,000 administrative employees, Sears informed the architectural firm Skidmore, Owings and Merrill that they needed a building with minimum 50,000 ft² per floor, with a total square footage of 3,000,000 ft². Sears imagined a boxy, low rise structure, but the architects saw an opportunity to make history and along with the real estate advisors and the city planning board, urged Sears to think more boldly, and build a skyscraper with residential space occupying the upper elevations.
Skyscrapers were a hot topic in 1970. Skidmore, Owings & Merrill had just completed the 100-floor John Hancock Center in Chicago, the world’s second tallest building until 1974, and in New York, the World Trade Center’s Twin Towers were under construction and projected to be the world’s tallest buildings. Once Sears decided they would erect a tower, they quickly became caught up in the glamour and prestige of tall buildings and the free publicity associated with setting global records. They announced to the press in July 1970 that they intended to build the tallest building in the world and that its height of 1,454 feet was the maximum allowed by the Federal Aviation Agency–anything higher would interfere with air traffic around O'Hare Airport.
Before the Sears Tower, height bore an inverse relationship to floor space—the taller the building the more support was needed to support great weights at great heights. Buildings like the Empire State Building had both a system of supports running through every floor and another in the perimeter wall. All those columns, ate up floorspace and greatly restricted design. While designing the John Hancock tower, Skidmore’s structural engineer Fazlur Khan had developed a new solution to the height/weight problem, which he was able to use for the first time on the Sears Tower. The “bundled tube” solution relied on the tensile strength of cylindrical structures to make the building stand up. A bundle of tubes bound together like the threads of a cable and placed at the core of the building, gave the structure the tensile strength to stand without any other supports punctuating the floors. This solution greatly reduced the weight of the structure and cleared the floor of supports, thus freeing up more floor space and removing all obstacles hampering design. The new system also meant that unlike previous skyscrapers, the curtain wall did not have to bear any of the load, allowing it to be much thinner and window size to be larger. Upon completion the Sears Tower weighed much less per square foot than the Empire State Building, yet it was much taller.
Architect Bill Graham treated Khan’s core as the central module in a grid plan and wrapped 8 squares of the same size around it. As the modular plan of 9 squares rises in height, individual squares drop off at different floors (at which floor and on which side being determined by wind sheer), creating set-offs for the remaining ones. Only 2 of the 9 squares rise all the way to the 110th floor, thus giving the building its distinctive staggered profile.
The obstacle that came closest to threatening Sears Tower was neither fire nor low-flying 747, but suburban TV watchers. In 1972, when construction of the building had reached the 50th floor, several municipalities filed injunctions against Sears, demanding that the tower be capped at 67 stories; anything taller, they argued, would block television signals from reaching houses in those areas, thus killing their resale values. Hard evidence proving that a) the building would block TV signals and b) that real estate values were closely tied to the ability to watch All in the Family being hard to come by, the Illinois Supreme Court and the FCC sided with Sears, thus allowing construction to continued upward.
When the Sears Tower was finished in 1974, overall floor space had increased from the planned 3,000,000 ft² to 4,500,000 ft², allocated over 110 stories. At 1,454 feet tall (1,707 feet with the TV antenna included), it was the tallest building on earth, having surpassed the Twin Towers by 100 feet. It held that record for over twenty years, until it was surpassed in 1998 by the vulgar Petronas Tower in Indonesia. Volumetrically, the Sears Tower is still the largest skyscraper in the world. In 1994, Sears sold the tower, and although they had completely vacated it by 1995, the new owners were legally bound to retain the name Sears Tower until 2003. In 2009, the building was officially renamed Willis Tower, the name being decided by the corporate tenant renting the largest amount of space.
2014 marks the 40th anniversary of the completion of the Sears Tower.
The subway entering a city traveling out of the ground, through wide empty spaces, running next to freight lines. A city developed on flat ground is “sectioned” by a railway line; thus showing, one after another, its parts like peeled layers, from outside to inside. When the buildings are still very sparse, the city presents itself with an image squashing those who live on the edge with the Downtown skyline on the very plane of the window glass: thus it may happen that a gigantic building, for many years the tallest skyscraper in the world, is only part of the background, not yet the undisputed protagonist of every urban scene, as later occurs in the city center.
El metro, al entrar en una ciudad, viaja fuera de la tierra, a través de grandes espacios vacìos, acercado a líneas de transporte de mercancías. Una ciudad que se desarrolla en el plano esta “seccionada” de una línea de ferrocarril; muestra así, una tras otra, como estratos sus capas, de afuera hacia adentro. Cuando los edificios son todavía muy escasos, la ciudad se presenta con una imagen que aplasta en el mismo piso del cristal de la ventana, los que viven en el borde junto con el skyline de la ciudad: asì puede suceder que un edificio gigantesco, durante muchos años el rascacielos más alto del mundo, es sólo una parte del fondo, no siendo todavia el protagonista indiscutible de cada escena urbana, como sucede más tarde en el centro de la ciudad.
La metropolitana entrando in una città viaggia fuori terra, attraverso ampi spazi vuoti, accostata a linee merci.
Una città che si sviluppa in piano è “sezionata” da una linea ferrata; mostra così, uno dopo l’altro, come sfoglie i suoi strati, da fuori a dentro.
Quando ancora gli edifici sono molto radi, la città si presenta con un’immagine che schiaccia, sullo stesso piano del vetro del finestrino, chi abita sul margine insieme allo skyline di Downtown: può accadere così che un edificio gigantesco, il grattacielo per molti anni più alto del mondo, sia solo parte dello sfondo, non ancora mattatore indiscusso di ogni scena urbana, come dopo accade nel centro città.