Skyscraper History, Design and Construction
A skyscraper is a very tall, continuously habitable building. There is no official definition or a precise cutoff height above which a building may clearly be classified as a skyscraper. However, as per usual practice in most cities, the definition is used empirically, depending on the relative impact of the shape of a building to a city's overall skyline. Thus, depending on the average height of the rest of the buildings and/ or structures in a city, even a building of 80 meters height (approximately 262 ft) may be considered a skyscraper provided that it clearly stands out above its surrounding built environment and significantly changes the overall skyline of that particular city. The word skyscraper originally referred to a nautical term tall mast or its main sail on a sailing ship. The term was first applied to buildings in the late 19th century as a result of public amazement at the tall buildings being built in Chicago and New York City. 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. Philadelphia's City Hall, completed in 1901, still holds claim as the world's tallest load-bearing masonry structure at 167 m (548 ft). The steel frame developed in stages of increasing self-sufficiency, with several buildings in Chicago and New York advancing the technology that allowed the steel frame to carry a building on its own. Today, however, many of the tallest skyscrapers are built almost entirely with reinforced concrete. Pumps and storage tanks maintain water pressure at the top of skyscrapers. A loose convention in the United States and Europe now draws the lower limit of a skyscraper at 150 meters (500 ft).[1] A skyscraper taller than 300 meters (984 ft) may be referred to as supertall. Shorter buildings are still sometimes referred to as skyscrapers if they appear to dominate their surroundings. The somewhat arbitrary term skyscraper should not be confused with the slightly less arbitrary term highrise, defined by the Emporis Standards Committee as "...a multi-story structure with at least 12 floors or 35 meters (115 feet) in height."[2] All skyscrapers are highrises, but only the tallest highrises are skyscrapers. Habitability separates skyscrapers from towers and masts. Some structural engineers define a highrise as any vertical construction for which wind is a more significant load factor than weight. Note that this criterion fits not only highrises 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.[3] HistoryModern skyscrapers are built with materials such as steel, glass, reinforced concrete and granite, and routinely utilize mechanical equipment such as water pumps and elevators. Until the 19th century, buildings of over six stories were rare, as having great numbers of stairs to climb was impractical for inhabitants, and water pressure was usually insufficient to supply running water above 50 m (164 ft). An early example of high-rise housing is the 16th-century city of Shibam in Yemen, which is regarded as one of the earliest example of urban planning based on the principle of vertical construction. Shibam was made up of over 500 tower houses, each one rising 5 to 9 storeys high, with each floor being an apartment occupied by a single family. The city was built in this way in order to protect it from Bedouin attacks.[4] Another early example of high-rise housing was in 17th-century Edinburgh, Scotland, where a defensive city wall defined the boundaries of the city. Due to the restricted land area available for development, the houses increased in height instead. Buildings of 11 stories were common, and there are records of buildings as high as 14 stories. Many of the stone-built structures can still be seen today in the old town of Edinburgh. The oldest iron framed building in the world is The Flaxmill (also locally known as the "Maltings"), in Shrewsbury, England. Built in 1797, it is seen as the "grandfather of skyscrapers” due to its fireproof combination of cast iron columns and cast iron beams developed into the modern steel frame that made modern skyscrapers possible. Unfortunately, it lies derelict and needs much investment to keep it standing. On 31 March 2005, it was announced that English Heritage would buy the Flaxmill so that it could be redeveloped. The first skyscraper was the ten-story Home Insurance Building in Chicago, built in 1884–1885. While its height is not considered unusual or very impressive today, the architect, Major William Le Baron Jenney, created the first load-bearing structural frame. In this building, a steel frame supported the entire weight of the walls, instead of load-bearing walls carrying the weight of the building, which was the usual method. This development led to the "Chicago skeleton" form of construction. After Jenney's accomplishment the sky was truly the limit as far as building was concerned. Sullivan's Wainwright Building building in St. Louis, 1890, was the first steel frame building with soaring vertical bands to emphasize the height of the building, and is, therefore, considered by some to be the first true skyscraper. The United Kingdom also had its share of early skyscrapers. The first building to fit the engineering definition, meanwhile, was the then largest hotel in the world, the Grand Midland Hotel, now known as St Pancras Chambers in London, opened in 1873 with a clock tower 82 metres (269 ft) in height. The 12-floor Shell Mex House in London, at 58 metres (190 ft), was completed a year after the Home Insurance Building and managed to beat it in both height and floor count. 1877 saw the opening of the Gothic revival style Manchester Town Hall by Alfred Waterhouse. Its 87-metre-high clock and bell tower dominated that city's skyline for almost a century. Most early skyscrapers emerged in the land-strapped areas of Chicago, London, and New York toward the end of the 19th century. London builders soon found building heights limited due to a complaint from Queen Victoria, rules that continued to exist with few exceptions until the 1950s; concerns about aesthetics and fire safety had likewise hampered the development of skyscrapers across continental Europe for the first half of the twentieth century (with the notable exceptions of the 26-storey Boerentoren in Antwerp, Belgium, built in 1932, and the 31-storey Torre Piacentini in Genoa, Italy, built in 1940). After an early competition between New York City and Chicago for the world's tallest building, New York took a firm lead by 1895 with the completion of the American Surety Building. Developers in Chicago also found themselves hampered by laws limiting height to about 40 storeys, leaving New York to hold the title of tallest building for many years. New York City developers then competed among themselves, with successively taller buildings claiming the title of "world's tallest" in the 1920s and early 1930s, culminating with the completion of the Chrysler Building in 1930 and the Empire State Building in 1931, the world's tallest building for forty years. From the 1930s onwards, skyscrapers also began to appear in Latin America (São Paulo, Caracas, Mexico City) and in Asia (Tokyo, Shanghai, Hong Kong, Singapore). Immediately after World War II, the Soviet Union planned eight massive skyscrapers dubbed "Stalin Towers" for Moscow; seven of these were eventually built. The rest of Europe also slowly began to permit skyscrapers, starting with Madrid, in Spain, during the 1950s. Finally, skyscrapers also began to appear in Africa, the Middle East and Oceania (mainly Australia) from the late 1950s and early 1960s. Still today no city in the world has more completed individual free-standing buildings over 492 ft. (150 m) than New York City.[5]. Hong Kong comes in with the most in the entire world,[6] if one counts individually the multiple towers that rise from a common podium (as Emporis does), in buildings that rise several stories as a single structure before splitting into two or more columns of floors. The number of skyscrapers in Hong Kong will continue to increase, due to a prolonged highrise building boom and high demand for office and housing space in the area. A new building complex in Kowloon contains several mixed-use towers (hotel-shops-residential) and one of them will be 118 stories tall. Chicago's skyline was not allowed to grow until the height limits were relaxed in 1960; over the next fifteen years many towers were built, including the massive 442-meter (1,451-foot) Sears Tower,[7] leading to its current number of buildings over 492 ft. Chicago is currently undergoing an epic construction boom that will greatly add to the city's skyline. Since 2000, at least 40 buildings at a minimum of 50 stories high have been built.[8][9] The Chicago Spire, Trump International Hotel and Tower (Chicago), Waterview Tower, Mandarin Oriental Tower, 29-39 South LaSalle, Park Michigan, and Aqua are some of the more notable projects currently underway in the city that invented the skyscraper. Chicago, Hong Kong, and New York City, otherwise known as the "the big three," are recognized in most architectural circles as having the most compelling skylines in the world. Other large cities that are currently experiencing major building booms involving skyscrapers include Shanghai in China and Dubai in the United Arab Emirates. Today, skyscrapers are an increasingly common sight where land is scarce, as in the centres of big cities, because of the high ratio of rentable floor space per area of land. Skyscrapers, like temples and palaces in the past, are considered symbols of a city's economic power. History of tallest skyscrapersAt the beginning of the 20th century, New York City was a center for the Beaux-Arts architectural movement, attracting the talents of such great architects as Stanford White and Carrere and Hastings. As better construction and engineering technology become available as the century progressed, New York became the focal point of the competition for the tallest building in the world. The city's striking skyline has been composed of numerous and varied skyscrapers, many of which are icons of 20th century architecture:
Momentum in setting records passed from the Unites States to other nations in 1997 with the opening of the Petronas Twin Towers in Kuala Lumpur, Malaysia. The record for world's tallest building remained in Asia with the opening of Taipei 101 in Taipei, Taiwan, in 2004. A number of architectural records will likely reside in the Middle East in 2008 or 2009 with the opening of the Burj Dubai in Dubai, UAE. With this geographical transition a change can be seen in the approach to skyscraper design. For much of the twentieth century large buildings such as the Sears Tower and World Trade Center (New York) took the form of simple geometrical shapes. They were designed as large boxes. This reflected the "international style" or modernist philosophy shaped by Bauhaus architects early in the century. By the 1990s skyscraper design began to exhibit postmodernist influences. The newest record setters, though modern, incorporate traditional architectural features associated with the part of the world where they stand. Taipei 101 recalls the traditions of Asian pagoda architecture even as the Burj Dubai incorporates motifs from traditional Arabic art. The result in each case is a building that does not look equally at home in any skyline in any city in the world, but a building that reflects its own continent and culture. For current rankings of skyscrapers by height, see List of skyscrapers. FutureThe following skyscrapers are either proposed, approved or due to be completed in the near future:
Quotations
Skyline ImageryWith tall, distinctive skyscrapers, these skyline images show how skyscrapers are able to affect, define and transform cities into skylines. 
See also
References
External links
Skyscrapers are tall, internally supported structures where the majority of load bearing structure, outside of that providing structural support for dead load is specifically designed to provide for large free spaces between supporting elements while still providing structural support and the building utilities required for the densely populated structure that results. The problems posed in skyscraper design are considered among the most complex encountered given the balances required between economics, engineering, and construction management.
Basic design considerationsGood structural design is of importance in most building design, but especially among skyscrapers since even a small likelihood of catastrophic failure is unacceptable given the number of individuals served by skyscrapers and the resulting price of failure. This presents a paradox to civil engineers: the only way to assure a lack of failure is to test for all modes of failure, in both the laboratory and the real world. The only way to know of all modes of failure is to learn from previous failures. In this way, no engineer can be absolutely sure that a given structure will resist all loadings that could cause failure, but can only be sure, that given large enough margins of safety, that a sufficiently small percentage of the time will a failure ever occur. When buildings do fail, engineers question if the failure was due to some lack of foresight on their part or some unknowable factor that would have never been expected to have been designed for. Loading and vibration
The load a skyscraper experiences is largely from the force of the building material itself. In most building designs, the weight of the structure is much larger than the weight of the material that it will support beyond its own weight. In technical terms, the dead load, the load of the structure, is larger than the live load, the weight of things in the structure (people, furniture, vehicles, etc). As such, the amount of structural material required within the lower levels of a skyscraper will be much larger than the material required within higher levels. This is not always visually apparent, or borne out visually. The Empire State Building's setbacks are actually a result of the building code at the time, and were not required. On the other hand John Hancock Center's shape is uniquely the result of how it supports loads. Vertical supports can come in several types, among which the most common for skyscrapers can be categorized as steel frames, concrete cores, tube within tube design, and shear walls. The wind loading on a skyscraper is also considerable. In fact, the lateral wind load imposed on super-tall structures is generally the governing factor in the structural design. Wind pressure increases with height, so for very tall buildings, the loads associated with wind are larger than dead or live loads. Other vertical and horizontal loading factors come from varied, unpredictable sources Shear wallsA shear wall, in its simplest definition is a wall where the entire material of the wall is employed in the resistance of both horizontal and vertical loads. A typical example is a brick wall, or a cinderblock wall. Since the wall material is used to hold the weight, as the wall expands in size, it must hold considerably more weight. Due to the features of a shear wall, it is perfectly fine, and even ideal for small constructions such as suburban housing or a typical urban brownstone, because it requires low cost of material, low maintenance, and provides high reliability for small designs. In this way, shear walls typically in the form of either plywood and framing, brick, or cinderblock, is used for these structures. For skyscrapers though, as the size of the structure increases, so does the size of the supporting wall. Previous large structures such as castles and cathedrals could ignore these issues due to a large wall being advantageous (castles), or ingeniously designed around (cathedrals). Since skyscrapers seek to maximize the floor-space by consolidating structural support, shear walls tend to be used only in conjunction with other support systems. Steel frameThe classic concept of a skyscraper is a large steel box with many small boxes inside it. The genius of the steel frame is its simplicity. By eliminating the inefficient part of a shear wall, the central portion, and consolidating support members in a much stronger material, steel, a skyscraper could be built with both horizontal and vertical supports throughout. This method, though simple, has drawbacks. Chief among these is that as more material must be supported (as height increases), the distance between supporting members must decrease, which actually in turn, increases the amount of material that must be supported. Tube frame
After 1965 a new structural system of framed tubes appeared. Fazlur Khan and J. Rankine defined the framed tube structure as "a three dimensional space structure composed of three, four, or possibly more frames, braced frames, or shear walls, joined at or near their edges to form a vertical tube-like structural system capable of resisting lateral forces in any direction by cantilevering from the foundation."[1] Closely spaced interconnected exterior columns form the tube. Horizontal loads, for example wind, are supported by the structure as a whole. About half the exterior surface is available for windows. Framed tubes allow fewer interior columns, and so create more usable floor space. Where larger openings like garage doors are required, the tube frame must be interrupted, with transfer girders used to maintain structural integrity. Tube-frame construction was used in the DeWitt-Chestnut apartment building, and in the building of the World Trade Center. Further reading
References
External links
This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia Encyclopedia article "Skyscraper" |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
