An arch is a structural opening whose top is shaped to pass loads to its supports. Arches are common features in building design and engineering because their curved form moves forces away from the center and toward supporting walls or piers.
Form and mechanics
The curved portion of an arch can take different geometries. It may follow part of a circle, producing a smooth rounded profile, or be composed of two circular arcs that meet at a point, creating a pointed shape. Traditional arches are assembled from many small wedge-shaped units such as stones or fired clay bricks. The central stone at the top, called the keystone, locks those units together so the arch acts as a single, stable structure.
Where arches are used
- Arches commonly span doorways and frame windows, providing both strength and an opening.
- Many kinds of bridges use arch forms. Some of these are specifically termed arch bridges, and modern examples may be built from materials like steel.
- A row of adjacent arches creates an arcade, often used in covered walkways or as an architectural motif.
Natural arches
Arches are not only man-made. In nature, openings that resemble architectural arches can develop when the erosion of rock removes softer material and leaves a curved span. This process frequently occurs in cliffs and other exposed rock formations, producing the natural arches seen in many landscapes.