ceiling over a room, formed in any one of a variety of curved shapes.
A vault is generally composed of separate units of material, such as bricks, tiles, or blocks of stone, so shaped or cut that when assembled they form a tightly wedged and stable construction whose weight can be concentrated upon the proper supports. Vaults are also formed in a homogeneous material, as when built in concrete. In modern work ceilings in the form of masonry vaults are often merely of plaster applied against a curved framework of wood or metal. Since antiquity vault surfaces have been enriched at various times in diverse ways—with coffers, carvings, plaster decorations, mosaics, or frescoes.
Vaults constructed of numerous blocks of material pressing against one another exert not only the accumulated downward weight of the material and of any superimposed load but also a side thrust or tendency to spread. To avoid collapse, adequate resistance against this thrust must thus be concentrated at the haunches (lower portions) of the vault. The resistance may take the form of thickened walls at the haunches; of buttresses placed at points of concentrated thrust as in Romanesque and Gothic architecture; or of vaults so placed that their thrusts oppose and counteract. This necessity has controlled the evolution of masonry vaulting and its use in buildings.
In ancient Egypt brick vaulting was used, chiefly for drains. The Chaldaeans and Assyrians used vaults for the same purpose but seem also to have made architectural use of high domes and barrel vaults. The Greeks made no use of vaults.
The vaulting technique of the Etruscans was absorbed by the Romans, who started in the 1st cent. A.D. the development of a mature vaulting system. Casting concrete in one solid mass, the Romans created vaults of perfect rigidity, devoid of external thrust, and requiring no buttresses. Thus vaults and domes could be easily erected over vast spaces, producing impressive and complex thermae, amphitheaters, and basilicas.
Roman vaults were the basis on which more complex and varied forms were developed in the Middle Ages. The tunnel (or barrel) vault spans between two walls, like a continuous arch. The cross, or groined, vault is formed by the intersection at right angles of two barrel vaults, producing a surface that has arched openings for its four sides and concentration of load at the four corner points of the square or rectangle. The semicircular arch was universally employed in Romanesque vaulting throughout Europe, and the Roman cross vault was the type used for covering square or rectangular compartments.
Ribs to strengthen the groins and sides of a cross vault were first employed in the Church of Sant'Ambrogio, Milan (11th cent.). When the system of using ribs to form a complete organic supporting skeleton was developed, it became one of the basic principles of perfected Gothic architecture. The use of ribs led to increasing complexity, beginning in the 12th cent., in vault forms.
The pointed arch, which was dominant in medieval architecture from the 13th cent. onward, helped to overcome the difficulties of vaulting oblong compartments exclusively with semicircular sections and to bring the various ribs of unequal spans to a crown at the same height. Some vaulting compartments or bays were divided by ribs into six segments and were known as sexpartite vaults, but the four-part vault generally prevailed. In England the multiplication of ribs for structural and decorative purposes culminated in the 15th cent. in the elaborate fan vault of the Perpendicular style.
The architects of the Renaissance and baroque periods abandoned Gothic methods and returned to Roman vault forms. New devices were added to these basic forms, including barrel vaults of semi-elliptical section, domes mounted on drums, and cross vaults with groins of elliptical section. In modern times reinforced concrete produces lightweight vaults devoid of thrust.
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