vault

In building construction, an arched structure forming a ceiling or roof. The masonry vault exerts the same kind of thrust as the arch, and must be supported along its entire length by heavy walls with limited openings. The basic barrel vault, in effect a continuous series of arches, first appeared in ancient Egypt and the Middle East. Roman architects discovered that two barrel vaults intersecting at right angles (a groin vault) could, when repeated in series, span rectangular areas of unlimited length. Because the groin vault's thrusts are concentrated at the four corners, its supporting walls need not be massive. Medieval European builders developed the rib vault, a skeleton of arches or ribs on which the masonry could be laid. The fan vault, popular in the English Perpendicular style, used fan-shaped clusters of tracery-like ribs springing from pendants or columns. The 19th century saw the use of large iron skeletons as frameworks for vaults of lightweight materials (see Crystal Palace). An important modern innovation is the reinforced-concrete shell vault, which, if its length is three or more times its transverse section, behaves as a deep beam and exerts no lateral thrust.

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