Supertall

From Wikipedia, the free encyclopedia

Supertall is a term that refers to an extremely tall skyscraper.

Although no official definition exists, a height of approximately 300 meters or 1,000 feet is a generally agreed minimum of architecture enthusiasts for a skyscraper to qualify as supertall. The term also applies to proposed structures over 1 kilometer (1000m/3281ft) or 1 mile (5280ft/1609m) in height — designs which have never advanced beyond the concept or planning stages. Additionally, the term may be used for a structure of any type taller than 300 meters such as free-standing towers, guyed masts, chimneys or bridge pillars. Most supertall structures rank among the top 10 in a particular category of height records.

Of the approximately 1150 existing supertall structures, most are guyed masts for FM radio and television broadcasting in the United States. This stems from the country having expansive flat areas where individual TV stations can build towers to service a wide area or population center. Other supertall structures are guyed masts for TV-broadcasting; longwave, mediumwave and VLF-transmission; scientific research; and free-standing TV-towers free-standing chimneys and skyscrapers. Located in Toronto, Ontario, Canada, the CN Tower is the world's tallest freestanding structure on land at a height of 553.3 metres (1,815 ft 5 in). Other noable supertall structures include the partially guyed TV-towers Gerbrandy Tower and Zendstation Smilde, two electricity pylons of the Yangtze River Crossing, the (Millau Viaduct) and the (Nurek Dam).

Contents 1 Structures 1.1 Challenges 1.2 Buildings 1.3 Radio towers 1.4 Chimneys 1.5 Pylons 1.6 Bridges 1.7 Other structures 2 See also

[edit] Structures

[edit] Challenges

Conceptual supertall designs, such as The Illinois by Frank Lloyd Wright (image, right), X-Seed 4000, and Sky City 1000 are probably technologically and architecturally feasible, but are considered by some to be simply too tall to be of any particular use. These designs tend to be bold and visionary, portending a shift in the nature of urban living towards multi-layered cities, and reflective of the human impulse to always build bigger and taller structures.^{[citation needed]} Although building supertall structures is often a way of showing prestige, their construction brings many technical challenges.

Building supertall structures of any kind is expensive, because the erection costs do not grow in direct proportion to height of structure, but grow faster. So a 1000 ft (305 m) radio mast in the USA costs between $0.7 and $1.1 million to build, while a 2000 ft (610 m) radio mast in the USA costs $2.4 to $4 million to build. In opposite to guyed masts, the erection costs for free-standing structures escalate almost exponentially with their height, which set their height in most cases an economical limit.

Supertall structures of all kinds have to withstand greater wind forces than smaller structures of the same type, requiring various structural engineering measures to handle them. Further, the construction site must be approved by flight safety authorities.

[edit] Buildings

Supertall skyscrapers save land by housing a large number of residents and/or workers on a relatively small footprint. However, fire safety and rapid evacuation problems increase with building height and the number of people the building is designed to serve. In addition, water and sewage networks become more expansive as buildings get taller, especially when they must handle the needs of many people. Many skyscrapers have observation decks open to tourists.

Chicago, Illinois has several supertall buildings, including the Sears Tower, the John Hancock Center and the Aon Center. The Trump Tower and Waterview Tower, both currently under construction, will be multi-use supertall towers. The proposed Chicago Spire will be primarily for residential use.

[edit] Radio towers

Supertall radio masts and towers for UHF-/VHF-transmission allow a wide area of reception. Because of reflections, which disturb radio wave propagation, their erection is only sensible in flatter areas, without single higher mountains. Therefore nearly all very high radio towers (height more than 300 meters) are situated in flat areas.

Supertall mast radiators, e.g. half-wave radiators for longwave radio allow larger areas of fading-free reception, because in opposite to shorter mast radiators, the ratio of skywave and groundwave radiation is much smaller, so fading occurs in areas much further away from the transmission tower than using a shorter mast radiator. However, because nowadays the range of longwave transmitters is more determined by jamming from other stations working in the same channel, using halfwave mast-radiators do not greatly improve longwave reception in greater distance of the transmission antenna. The only realized half-wave mast radiator for longwave was the Warsaw Radio Mast. The usage of supertall mast radiators and antenna structures with heights between 300 and 450 meters is however very sensitive for high power longwave radio stations with greater bandwidth requirement like longwave broadcasting or LORAN-C, because these antenna structures require for the realization of a quarter-wave length radiator no or only few electrical lengthening, which reduces beside bandwidth also antenna efficiency and which increases antenna voltage.

For VLF transmission the usage of supertall masts either as mast radiator (electrical enlengthed as an umbrella antenna) or as carrier of wire antennas is perhaps the best choice. However the erection costs grow taller than the height of the masts, which is also the case for the maintenance. So one tries to find out, if it is possible by using electrical lengthing to build the masts not unnecessarily tall. Because the bandwidth of most VLF-transmitters is very low, the usage of excessive electrical lengthing is possible without bigger problems. At VLF there is also nearly no skywave propagation, so there is no requirement for skywave suppression characteristics of the antenna. In opposite to the skywave propagation the groundwave propagation of VLF is very well and one can easy increase the range of the transmitter by increasing the power. It may be in this frequency range often cheaper to run a high power transmitter with a not extremely effective antenna using lower masts, than building and maintaining an antenna using extreme tall masts. So VLF transmitters use often very tall masts (height between 200 and 400 meters) for their transmitting antennas, but their masts belong not to the tallest ever built. In the Western hemisphere the masts of VLF transmitter Lualualei on Hawaii are the tallest structures used for transmission in this frequency range.

Nevertheless satisfactorily working VLF and LF transmitters can be built according to the works of the radio engineer Alexanderson without using supertall towers. Such antennas use Kalundborg longwave broadcasting transmitter and the SAQ-VLF transmitter in Grimeton, Sweden. There towers are approximately 120 meters tall.

For mediumwave-transmission supertall mast radiators are a bad choice, because they show high skywave emission, which result in excessive fading at night. However there are some special high-effective fading reducing antenna types for mediumwave broadcasting, which require supertall towers. Because of the high erection costs for the required towers, their usage is only sensitive for high power stations working on nearly interference free channels at the lower end of the mediumwave band. So only a few broadcasting stations like RKS Liblice 2 uses or used such antennas.

[edit] Chimneys

Historically, supertall chimneys were used to improve the dispersion of waste gases and heat from a factory or power generation station. However, tall chimneys did not eliminate toxic substances in the smoke -- it simply distributed a lower concentration of pollutants over an increased area, often over a population center. In many countries, recent enactment of stricter pollution laws has reduced simply dispersing exhaust with huge chimneys and requires emissions cleaning equipment to be installed. The regulations reduced the need for extremely tall chimneys, as the resulting polluting emissions are of a low concentration so that distribution over a wide area is no longer necessary. However, a supertall chimney may be appropriate for a factory or conventional thermal power station situated in a valley, exampled by the Trbovlje Chimney at Trbvolje Power Station in Slovenia, located in a deep valley.

[edit] Pylons

For power line crossings of sea narrows and wide rivers surrounded by flat terrain is possible by building supertall electricity pylons. However only one of such crossing, the Yangtze River Crossing in China was realized, because in most cases building an underground cable may be more practical. For long spans, the use of bundled conductors can result in wind-induced oscillations resulting in short circuits. Single conductors are thick enough to transport the same amount of electricity as bundled conductors but show more corona losses.^{[citation needed]} A more serious problem at such crossings, is that conductive materials of high tensile strength are required. Unfortunately these materials demonstrate a higher specific electrical resistance than standard conductors, resulting in higher losses.

[edit] Bridges

Supertall bridge towers must withstand enormous forces and are designed to support the weight of the bridge and vehicles crossing the bridge in addition to the dynamic structural loads caused by vehicle movement, which are especially considerable for railroad bridges. Bridges with supertall pillars may be built as suspension bridges or other types of bridges carried by cable. The only realized supertall bridge is Millau Viaduct, a suspension bridge for a motorway across a valley in France. The proposed Strait of Messina Bridge would have qualified as supertall, had it not been cancelled due to the depth of the strait making a bridge with pillars economically questionable.

Spans and bridges without supertall support structures that cross a valley higher than the height level defined as criteria for supertall structures at the point where the valley is deepest, should not be classified as supertall structures , because in these constructions the maximum height above the ground has minimal influence on the design.^{[citation needed]}

[edit] Other structures

Supertall dams require a deep canyon-like valley as a construction site. So far only one such dam (Nurek Dam in Tajikistan) was built and two further are under construction.

Solar chimneys in opposite have to be built as supertall structures, because this improves the efficiency of the facility.

A future use for supertall structures may be special towers with maglev tracks for launching spacecraft and space elevators.

[edit] See also

• Megastructure
• World's tallest structures
• List of world's tallest structures
• List of masts
• List of towers
• List of chimneys
• List of skyscrapers
• Skyscraper

v • d • e Supertall structures (at least 300 meters in height - Other proposed structures)
Antennas:	Alma-Ata Tower • Azeri TV Tower • Emley Moor • Europaturm • Fernsehturm Berlin • Gerbrandy Tower • Kiev TV Tower • Mumbai Television Tower • Saint Petersburg TV Tower • Sumida Tower (proposed) • TV Tower Yerevan • WITI TV Tower • Zendstation Smilde
Bridges:	Millau Viaduct
Dams:	Rogun Dam (construction) • Nurek Dam • Jinping 1 Hydropower Station (construction)
Electricity pylons:	Yangtze River Crossing
Oil platforms:	Petronius Platform • Baldpate Platform • Bullwinkle Platform • Troll Platform • Gullfaks C

v • d • e Supertall skyscrapers
Current:	Aon Center (Chicago) • AT&T Corporate Center • Baiyoke Tower II • Bank of America Plaza • Bank of China Tower • Burj al-Arab • Central Plaza • Chrysler Building • CITIC Plaza • Emirates Office Tower • Emirates Towers Hotel • Empire State Building • Eureka Tower • First Canadian Place • International Finance Centre • JPMorgan Chase Tower • Jin Mao Building • John Hancock Center • Kingdom Centre • Kuala Lumpur Tower • Menara Telekom • Nina Tower I • Petronas Twin Towers • Q1 • Sears Tower • Shimao International Plaza • Shun Hing Square • Taipei 101 • The Center • Tuntex Sky Tower • Two Prudential Plaza • U.S. Bank Tower
Under construction:	23 Marina • Abraj Al Bait Towers • Ahmed Abdul Rahim Al Attar Tower • Airlangga Residences • Al Durrah Tower II • Al Hamra Tower • Al Rajhi Tower • Al Yaquob Tower • Almas Tower • Bank of America Tower • Burj Dubai • Burj Dubai Lake Hotel & Serviced Apartments • Busan Lotte Tower • Chicago Spire • City Hall and City Duma • Federation Tower • Freedom Tower (World Trade Center Tower 1) • The Index • Ice Tower • Guangzhou Twin Towers West Tower • Dubai Towers Doha • Sky Tower Dubai • Elite Residence • JW Marriott International Finance Centre • Ocean One • Square Capital Tower • International Commerce Centre • Jakarta Tower • Mercury City Tower • New York Times Building • Northeast Asia Trade Tower • Ocean Heights 1 • Ocean Heights 2 • Marina 101 • One Island East • Parcel 12 • Princess Tower • Rose Rotana Suites • Shanghai World Financial Center • The Torch • Trans National Place • Trump International Hotel and Tower (Chicago) • Trump International Hotel and Tower (Toronto) • Waterview Tower • Tianjin International Trade Centre • Mag 218 Tower • Torre Gran Costanera • China World Trade Center Tower 3 • Pearl River Tower • Shenzhen Nikko Tower • Wenzhou World Trade Center • Gate of Kuwait • Doha Sport City Tower • Faros del Panamá
In development:
Former:	World Trade Center
Construction suspended:	Ryugyong Hotel • Dalian International Trade Center • Xiamen Post & Telecommunications Building • Najd Tower • 868 Towers Offices and Hotel • Tianlong Hotel • BDNI Center 1 • Infinity Tower • Marina Gardens • Skycity • Plaza Rakyat

v • d • e Supertall proposed skyscrapers (at least 300m tall)
Proposed:	Chicago Spire • 175 Greenwich Street • 200 Greenwich Street • Al Burj • Signature Tower • Las Vegas Tower • Burj al Alam • Mubarak al-Kabir Tower • Plaza Rakyat • Russia Tower • Shard London Bridge • Empire World Towers • AIG Main Tower • Incheon Tower • International Business Center • Suyong Bay Tower • San Francisco Transbay Supertalls • Lotte Super Tower • Dubai Towers Istanbul • Phare Tower • Trans National Place • One Bayfront Plaza • India International Trade Center • Port tower complex •
Cancelled:	7 South Dearborn • Grollo Tower • Chicago World Trade Center • Project 2000 • Miglin-Beitler Skyneedle • Palace of Soviets • Park Square Tower • Larkin Building • Hotel Attraction • South Ferry Plaza • 1 New York Place • Hankang City Tower • Torre Generali • Sapphire Tower • Eaton's / John Maryon Tower • Lotte World II Hotel • Ryugyong • Palacio de la Bahía
Visions:	Pyramid City • Sky City 1000 • The Illinois • X-Seed 4000 • Aeropolis 2001 • Kostabi World Trade Center • Center of India Tower