A skyscraper is a tall, continuously habitable building of over 40 floors, mostly designed for office, commercial and residential uses. A skyscraper can also be called a high-rise, but the term skyscraper is often used for buildings higher than . For buildings above a height of , the term ''Supertall'' can be used, while skyscrapers reaching beyond are classified as ''Megatall''.
One common feature of skyscrapers is having a steel framework that supports curtain walls. These curtain walls either bear on the framework below or are suspended from the framework above, rather than load-bearing walls of conventional construction. Some early skyscrapers have a steel frame that enables the construction of load-bearing walls taller than of those made of reinforced concrete. Modern skyscrapers' walls are not load-bearing and most skyscrapers are characterized by large surface areas of windows made possible by the concept of steel frame and curtain walls. However, skyscrapers can have curtain walls that mimic conventional walls and a small surface area of windows. Modern skyscrapers often have a tubular structure, and are designed to act like a hollow cylinder to resist lateral loads (wind, seismic, etc.). To appear more slender, allow less wind exposure and to transmit more daylight to the ground, many skyscrapers have a design with setbacks.
A relatively big building may be considered a skyscraper if it protrudes well above its built environment and changes the overall skyline. The maximum height of structures has progressed historically with building methods and technologies and thus what is today considered a skyscraper is taller than before. The Burj Khalifa is currently the tallest building in the world.
High-rise buildings are considered shorter than skyscrapers. There is no clear definition of any difference between a tower block and a skyscraper though a building lower than about thirty stories is not likely to be a skyscraper and a building with fifty or more stories is certainly a skyscraper.
The term "skyscraper" was first applied to buildings of steel framed construction of at least 10 stories in the late 19th century, a result of public amazement at the tall buildings being built in major cities like Chicago, New York City, Philadelphia, Detroit, and St. Louis.〔(For more on the origins of the term skyscraper, see "Skyscrapers," ''Magical Hystory Tour: The Origins of the Commonplace & Curious in America'' (1 September 2010) ) 〕 The first steel frame skyscraper was the Home Insurance Building (originally 10 stories with a height of ) in Chicago, Illinois in 1885. Some point to Philadelphia's 10-story Jayne Building (1849–50) as a proto-skyscraper, or to New York's seven-floor Equitable Life Assurance Building, built in 1870, for its innovative use of a kind of skeletal frame, but such designation depends largely on what factors are chosen. Even the scholars making the argument find it to be purely academic.
The structural definition of the word ''skyscraper'' was refined later by architectural historians, based on engineering developments of the 1880s that had enabled construction of tall multi-story buildings. This definition was based on the steel skeleton—as opposed to constructions of load-bearing masonry, which passed their practical limit in 1891 with Chicago's Monadnock Building.
:::—Louis Sullivan's ''The Tall Office Building Artistically Considered'' (1896)
The Emporis Standards Committee defines a high-rise building as "a multi-story structure between 35–100 meters tall, or a building of unknown height from 12–39 floors"〔(Data Standards: high-rise building (ESN 18727) ), Emporis Standards, accessed on line 16 October 2009.〕 and a skyscraper as "a multi-story building whose architectural height is at least ."〔(Data Standards: skyscraper (ESN 24419) ), Emporis Standards, accessed on line 16 October 2009.〕 Some structural engineers define a highrise as any vertical construction for which wind is a more significant load factor than earthquake or weight. Note that this criterion fits not only high-rises but some other tall structures, such as towers.
The word ''skyscraper'' often carries a connotation of pride and achievement. The skyscraper, in name and social function, is a modern expression of the age-old symbol of the world center or ''axis mundi'': a pillar that connects earth to heaven and the four compass directions to one another.
A loose convention of some in the United States and Europe draws the lower limit of a skyscraper at .
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