Sears Tower

Sears Tower, skyscraper in Chicago, Illinois, that when it was built was the tallest inhabited building in the world. It lost its title in 1998 to the Petronas Towers in Kuala Lumpur, Malaysia. At 442 m (1,450 ft) and 110 storeys in height, the Sears Tower remains the tallest building in the United States.

The skyscraper was designed by Bruce Graham of the architectural firm Skidmore, Owings, & Merrill for Sears, Roebuck, & Company, the world’s largest retailer at the time. Construction began in 1970 and the modern, geometrically shaped building stretching the length of two blocks opened in 1974, having cost more than US$150 million to build.

Graham and engineer Fazlur Khan used the “bundled tube” concept, which had only recently made exceptionally tall buildings economically feasible. The design uses a steel frame clad with stainless aluminium and bronze-tinted glass. Nine 23 m (75 ft) square columns rise up together from the base, each one attaining a different height. Staggering the column heights not only helped the problem of overcoming wind resistance faced by the tall structure in a metropolis nicknamed “the windy city”, but also allowed Sears, Roebuck, & Company a choice of different sized office spaces for their operations. In the mid-1980s some adjustments were made to the lobby and commercial areas, and the communications tower was extended.

More than 100 lifts operate in the building. A system of double-deck express lifts transports passengers up to either of two skylobbies, where people transfer to single local lifts serving individual floors.