arch. is a curved structure capable of spanning a space while supporting significant weight (e.g. a doorway in a stone wall).

An arch requires all of its elements to hold it together. This raises the interesting question of how an arch is actually constructed. One simple answer is to build a frame (historically, of wood) which exactly follows the form of the underside of the arch. This is known as a centre or centring. The voussoirs are laid on it until the arch is complete and self-supporting. For an arch higher than head height, scaffolding would in any case be required by the builders, so the scaffolding can be combined with the arch support. Occasionally arches would fall down when the frame was removed if construction or planning had been incorrect. The interior and lower line or curve of an arch is known as the intrados.

TYPES:

  • Vault: An application of the arch extended horizontally in two dimensions; the groin vault is the intersection of two vaults.
  • Dome: A three-dimensional application of the arch, rotated about the center axis. Igloos are notable early structures making use of domes.
  • Special form of the Arch: The triumphal arch, usually built to celebrate a victory in war. The most famous example is the Arc de Triomphe in Paris, France.
  • Natural rock Formations: May also be referred to as arches. These natural arches are formed by erosion rather than being carved or constructed by man.

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