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Abarrel vault, also known as atunnel vault,wagon vault orwagonhead vault, is an architectural element formed by the extrusion of a single curve (or pair of curves, in the case of a pointed barrel vault) along a given distance. The curves are typically circular in shape, lending a semi-cylindrical appearance to the total design. The barrel vault is the simplest form of avault: effectively a series ofarches placed side by side (i.e., one after another). It is a form ofbarrel roof.
As with allarch-based constructions, there is an outward thrust generated against the walls underneath a barrel vault. There are several mechanisms for absorbing this thrust. One is to make the walls exceedingly thick and strong – this is a primitive and sometimes unacceptable method. A more elegant method is to build two or more vaults parallel to each other; the forces of their outward thrusts will thus negate each other. This method was most often used in construction of churches, where several vaultednaves ran parallel down the length of the building. However, the outer walls of the outermost vault would still have to be quite strong or reinforced bybuttressing. The third and most elegant mechanism to resist the lateral thrust was to create an intersection of two barrel vaults at right angles, thus forming agroin vault.
Barrel vaults are known from theAncient Iran (Elam), IndianIndus Valley Civilization andAncient Egypt, and were used extensively inRoman architecture. They were also used to replace theCloaca Maxima with a system of underground sewers. Other early barrel vault designs occur in northernEurope,Turkey,Morocco, and other regions. Inmedieval Europe, the barrel vault was an important element of stone construction inmonasteries,castles,tower houses and other structures. This form of design is observed incellars,crypts, longhallways,cloisters and evengreat halls.
Barrel vaulting was known and utilized by early civilizations, includingancient Egypt andMesopotamia. However, it apparently was not a very popular or common method of construction within these civilizations. The Persians and the Romans were the first to make significant architectural use of them. The technique probably evolved out of necessity to roof buildings with masonry elements such as bricks or stone blocks in areas where timber and wood were scarce. The earliest known example of a vault is atunnel vault found under theSumerianziggurat atNippur inBabylonia, ascribed to about 4000 BC, which was built from fired bricks amalgamated withclaymortar. The earliest tunnel vaults in Egypt are found atRequagnah andDenderah, from around 3500 BC in thepredynastic era. These were built withsun-dried brick in three rings over passages descending totombs with aspan of only two metres.[1] In these early instances, the barrel vault was chiefly used for underground structures such as drains andsewers, though several buildings of the great Late Egyptianmortuarypalace-temple ofRamesseum were also vaulted in this way.[2] Recentarchaeological evidence discovered at theMorgantina site (in the province ofEnna) shows that the aboveground barrel vault was known and used in HellenisticSicily in 3rd century BC, indicating that the technique was also known toancient Greeks.
The vaulted roof of an early Harappan burial chamber has been noted fromRakhigarhi.[3]S.R Rao reports vaulted roof of a small chamber in a house fromLothal.[4] Barrel vaults were also used in the Late HarappanCemetery H culture dated 1900 BC-1300 BC which formed the roof of the metal working furnace, the discovery was made byVats in 1940 during excavation atHarappa.[5][6][7]
Ancient Romans most probably inherited their knowledge of barrel vaulting fromEtruscans and the Near East. Persians and Romans were the first to use this building method extensively on large-scale projects and were probably the first to usescaffolding to aid them in construction of vaults spanning over widths greater than anything seen before. However, Roman builders gradually began to prefer the use ofgroin vault; though more complex to erect, this type of vault did not require heavy, thick walls for support (see below), and thus allowed for more spacious buildings with greater openings and much more light inside, such asthermae.
After the fall of theRoman Empire, few buildings large enough to require much in the way of vaulting were built for several centuries. In the earlyRomanesque period, a return to stone barrel vaults was seen for the first great cathedrals; their interiors were fairly dark, due to thick, heavy walls needed to support the vault. One of the largest and most famous churches enclosed from above by a vast barrel vault was the church ofCluny Abbey, built between the 11th and 12th centuries.
In 13th and 14th centuries, with the advance of the newGothic style, barrel vaulting became almost extinct in constructions of great Gothic cathedrals;groin vaults reinforced by stone ribs were mostly used in the beginning, and later on various types of spectacular, ornate and complex medieval vaults were developed. However, with the coming of theRenaissance and theBaroque style, and revived interest in art and architecture of antiquity, barrel vaulting was re-introduced on a truly grandiose scale, and employed in the construction of many famous buildings and churches, such asBasilica di Sant'Andrea di Mantova byLeone Battista Alberti,San Giorgio Maggiore byAndrea Palladio, and perhaps most glorious of all,St. Peter's Basilica in Rome, where a huge barrel vault spans the 27 m (89 ft)-wide nave.[8]
With a barrel vault design the vectors of pressure result in a downward force on the crown while the lower portions of the arches realise a lateral force pushing outwards.[9] As an outcome this form of design is subject to failure unless the sides are anchored or buttressed to very heavy building elements or substantial earthwork sidings. For example, atMuchalls Castle inScotland, adjacent walls to the barrel vaulted chambers are up to 4.6 m (15 ft) thick, adding the buttressing strength needed to secure the curved design.
The inherent difficulty of adequately lighting barrel vaulted structures has been widely acknowledged.[10] The intrinsic engineering issue is the need to avoidfenestration punctures in stonework barrel vaults. Such openings could compromise the integrity of the entire arch system. Thus the Romanesque medieval builders had to resort to techniques of small windows, large buttresses, or other forms of interior wall cross-bracing to achieve the desired lighting outcomes. In many of the monasteries, a natural solution was cloisters which could have high barrel-vaulted construction with an open courtyard to allow ample lighting.
Since 1996structural engineers have appliedNewtonian mechanics to calculate numeric stress loads for ancient stonework barrel vaults.[11] These analyses have typically used afinite element algorithm to calculate gravity induced stresses from the self weight of an arched system. In fact, for structural engineers, analysis of the barrel vault has become a benchmark test of a structural engineeringcomputer model "because of the complex membrane and inextensional bending states of stress" involved.
In terms of comparison to other vaulting techniques, the barrel vault is inherently a weaker design compared to the more complexgroin vault. The barrel vault structure must rest on long walls creating less stable lateral stress, whereas the groin vault design can direct stresses almost purely vertically on the apexes.[12]
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There are numerous contemporary examples of barrel vault design inVictorian andmodern architecture, including:
Beyond the classical use of the barrel vault in macro-architectural design (e.g. as a major structural roofing element), there are a variety of derivative applications clearly based on the original concept and shape of the barrel vault. These applications arise in the fields ofsurgery,skylight design, children's toys and microstructure design (such as bus shelters). While none of these applications rival the majesty of the ancient and Classical predecessors, they demonstrate the pervasiveness of the barrel vault as an architectural concept in contemporary times.
In the field of bone surgery the technique of a "barrel vault" shaped incision is not only a well-definedstate-of-the-art surgical procedure, but the namebarrel vault is given to this technique byorthopedicsurgeons.[15] The Wohlfahrt study cited documents results of this surgical procedure on the humantibia in 91 such operations.
One or more of the preceding sentences incorporates text from a publication now in thepublic domain: Spiers, Richard Phené (1911). "Vault". InChisholm, Hugh (ed.).Encyclopædia Britannica. Vol. 27 (11th ed.). Cambridge University Press. p. 956.
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