Tower

Atoweris a tallstructure,taller than it is wide, often by a significant factor. Towers are distinguished frommastsby their lack ofguy-wiresand are therefore, along with tall buildings, self-supporting structures.

Towers are specifically distinguished frombuildingsin that they are built not to be habitable but to serve other functions using theheightof the tower. For example, the height of aclock towerimproves the visibility of the clock, and the height of a tower in a fortified building such as acastleincreases the visibility of the surroundings for defensive purposes. Towers may also be built forobservation,leisure, ortelecommunicationpurposes. A tower can stand alone or be supported by adjacent buildings, or it may be a feature on top of a larger structure or building.

Etymology[edit]

Old Englishtorris fromLatinturrisviaOld Frenchtor.The Latin term together withGreekτύρσις was loaned from a pre-Indo-European Mediterranean language, connected with theIllyriantoponym Βου-δοργίς. With theLydiantoponyms Τύρρα, Τύρσα, it has been connected with the ethnonymΤυρρήνιοιas well as withTusci(from*Turs-ci), the Greek and Latin names for theEtruscans(Kretschmer Glotta 22, 110ff.)

History[edit]

Towers have been used by humankind since prehistoric times. The oldest known may be the circular stone tower in walls ofNeolithic Jericho(8000 BC). Some of the earliest towers wereziggurats,which existed inSumerian architecturesince the 4th millennium BC. The most famous ziggurats include the SumerianZiggurat of Ur,built in the 3rd millennium BC, and theEtemenanki,one of the most famous examples ofBabylonian architecture.

Some of the earliest surviving examples are thebrochstructures in northernScotland,which are conicaltower houses.These and other examples fromPhoenicianandRomancultures emphasised the use of a tower in fortification and sentinel roles. For example, the name of the Moroccan city ofMogador,founded in the first millennium BC, is derived from the Phoenician word forwatchtower('migdol'). The Romans utilised octagonal towers^[1]as elements ofDiocletian's PalaceinCroatia,which monument dates to approximately 300 AD, while theServian Walls(4th century BC) and theAurelian Walls(3rd century AD) featured square ones. The Chinese used towers as integrated elements of theGreat Wall of Chinain 210 BC during theQin dynasty.Towers were also an important element ofcastles.

Other well known towers include theLeaning Tower of PisainPisa, Italybuilt from 1173 until 1372, theTwo TowersinBologna, Italybuilt from 1109 until 1119 and theTowers of Pavia(25 survive), built between 11th and 13th century. TheHimalayan Towersare stone towers located chiefly inTibetbuilt approximately 14th to 15th century. ^[2]

Mechanics[edit]

Up to a certain height, a tower can be made with the supporting structure with parallel sides. However, above a certain height, the compressive load of the material is exceeded, and the tower will fail. This can be avoided if the tower's support structure tapers up the building.

A second limit is that of buckling—the structure requires sufficient stiffness to avoid breaking under the loads it faces, especially those due to winds. Many very tall towers have their support structures at the periphery of the building, which greatly increases the overall stiffness.

A third limit is dynamic; a tower is subject to varying winds, vortex shedding, seismic disturbances etc. These are often dealt with through a combination of simple strength and stiffness, as well as in some casestuned mass dampersto damp out movements. Varying or tapering the outer aspect of the tower with height avoids vibrations due to vortex shedding occurring along the entire building simultaneously.

Functions[edit]

Although not correctly defined as towers, many modernhigh-rise buildings(in particularskyscraper) have 'tower' in their name or are colloquially called 'towers'. Skyscrapers are more properly classified as 'buildings'. In theUnited Kingdom,tall domestic buildings are referred to astower blocks.In theUnited States,the originalWorld Trade Centerhad the nickname the Twin Towers, a name shared with thePetronas Twin TowersinKuala Lumpur.In addition some of the structures listed below do not follow the strict criteria used atList of tallest towers.

Strategic advantages[edit]

The tower throughout history has provided its users with an advantage in surveying defensive positions and obtaining a better view of the surrounding areas, including battlefields. They were constructed ondefensive walls,or rolled near a target (seesiege tower). Today, strategic-use towers are still used at prisons, military camps, and defensive perimeters.

Potential energy[edit]

By using gravity to move objects or substances downward, a tower can be used to store items or liquids like astorage siloor awater tower,or aim an object into the earth such as adrilling tower.Ski-jump rampsuse the same idea, and in the absence of a natural mountain slope or hill, can be human-made.

Communication enhancement[edit]

In history, simple towers likelighthouses,bell towers,clock towers,signal towersandminaretswere used to communicate information over greater distances. In more recent years,radio mastsand cell phone towers facilitate communication by expanding the range of the transmitter. TheCN TowerinToronto, Ontario,Canada was built as a communications tower, with the capability to act as both a transmitter and repeater.

Transportation support[edit]

Towers can also be used to support bridges, and can reach heights that rival some of the tallest buildings above-water. Their use is most prevalent insuspension bridgesandcable-stayed bridges.The use of the pylon, a simple tower structure, has also helped to build railroad bridges, mass-transit systems, and harbors.

Control towersare used to give visibility to help direct aviation traffic.

Other[edit]

To access tall or high objects:launch tower,service tower,service structure,scaffold,tower crane
To access atmospheric conditions aloft:wind turbine,meteorologicalmeasurement tower,tower telescope,solar powerstation
To lift high tension cables for electrical power distributiontransmission tower
To take advantage of the temperature gradient inherent in a height differential:cooling tower
To expel and disperse potentially harmful gases and particulates into the atmosphere:chimney
To protect from exposure:BREN Tower,lightning rod tower
For industrial production:shot tower
For surveying: Survey tower
To drop objects:Drop tube(drop tower),bomb tower,diving platform
To test height-intensive applications:elevator test tower
To improve structural integrity:thyristor tower
To mimic towers or provide height for training purposes:fire tower,parachute tower
As art:Shukhov Tower
For recreation:rock climbing tower
As a symbol:Tower of Babel,The Tower (Tarot card),church tower

The term "tower" is also sometimes used to refer to firefighting equipment with an extremely tall ladder designed for use in firefighting/rescue operations involving high-rise buildings.