HIGH-RISE BUILDING

also called High-rise, a multistory building tall enough to require the use of a system of mechanical vertical transportation such as elevators. The skyscraper (q.v.) is a very tall high-rise building. The first high-rise buildings were constructed in the United States in the 1880s. They arose in urban areas where increased land prices and great population densities created a demand for buildings that rose vertically rather than spread horizontally, thus occupying less precious land area. High-rise buildings were made practicable by the use of steel structural frames and glass exterior sheathing. By the mid-20th century, such buildings had become a standard feature of the architectural landscape in most countries in the world. The foundations of high-rise buildings must sometimes support very heavy gravity loads, and they usually consist of concrete piers, piles, or caissons that are sunk into the ground. Beds of solid rock are the most desirable base, but ways have been found to distribute loads evenly even on relatively soft ground. The most important factor in the design of high-rise buildings, however, is the building's need to withstand the lateral forces imposed by winds and potential earthquakes. Most high-rises have frames made of steel or steel and concrete. Their frames are constructed of columns (vertical-support members) and beams (horizontal-support members). Cross-bracing or shear walls may be used to provide a structural frame with greater lateral rigidity in order to withstand wind stresses. Even more stable frames use closely spaced columns at the building's perimeter, or they use the bundled-tube system, in which a number of framing tubes are bundled together to form exceptionally rigid columns. High-rise buildings are enclosed by curtain walls; these are non-load-bearing sheets of glass, masonry, stone, or metal that are affixed to the building's frame through a series of vertical and horizontal members called mullions and muntins. The principal means of vertical transport in a high-rise is the elevator (q.v.). It is moved by an electric motor that raises or lowers the cab in a vertical shaft by means of wire ropes. Each elevator cab is also engaged by vertical guide tracks and has a flexible electric cable connected to it that provides power for lighting, door operation, and signal transmission. Because of their height and their large occupant populations, high-rises require the careful provision of life-safety systems. Fire-prevention standards should be strict, and provisions for adequate means of egress in case of fire, power failure, or other accident should be provided. Although originally designed for commercial purposes, many high-rises are now planned for multiple uses. The combination of office, residential, retail, and hotel space is common. See also building construction.