Forms of arches
There are many shapes of arches. These are mainly characterized by the curve of the intrados and the ratio of height to span. Most arches are connected to the wall by the extrados. The corbel arch, built using courses gradually jutting further out, and monolithic arches, whether poured, tamped or cut out, have no extrados and continue directly on from the wall.
Varied uses of arches
The main function of an arch is to bridge an opening in a wall. By juxtaposing and repeating arches resting on pillars, one can obtain arcades ( 1 ), which allow one to create very open covered spaces. Arcature, or blind arches (2), can be used to lighten the masonry structure or simply for decorative purposes.
A partition arch (3) serves as a load-bearing element in a large room by supporting roofing elements of restricted length, joists, purloins or even vaults or cupolas. An arch can serve directly as the springer of a cupola (4). In this ease the forms of the arch and of the cupola are closely interlinked.