Also known as the Roman arch, the Semicircular Arch forms a half-circle and is a major feature of all Roman architecture. A strong structure, this arch is often found in bridges and aqueducts. It appears to be a simple arch to manufacture, as each voussoir is identical in taper to its neighbor. The only variable is the length of the stiles or sides of the arches, which determine the height of the bridge or building that uses them.
The semi-circular arch is formed by two opposite arcs meeting at a point. This point is called the center of the arch. The radius of the inner arc is equal to the radius of the outer arc. They form a half-circle with the center of their intersection being the center of the arch. Because both arcs are of the same size, the distance between their centers is always the same and equals one-half the width of the arch. The faces of the voussoirs that define the arch are usually not perpendicular, but tend to be more angled. However, because they are flat surfaces, they can be made perfectly horizontal if needed.
Because of its strength and reliability, the semi-circular arch is used in many structures where appearance is not important. These include gates, doors, and windows. It is also common in bridges and buildings whose function is not related to movement of people or goods.
The Romans employed stone arches with round tops, known as "rounded arches." An arcade is a sequence of parallel rounded arches. The word comes from Latin and means "a row of arches." In architecture, an arcade is a series of columns or other structural members forming a roof or wall support. The term can also refer to the enclosed space formed by such columns or beams.
In classical architecture, the arcade was the usual name for a sequence of four columns (two on each side) supporting a flat ceiling or plenum above. The term is still used in this sense in English-speaking countries. But in France and Italy, where the original examples have been preserved, the term "arcement" (French for "arch") has replaced "classical arcade" (which actually describes only one type of arcade in French architecture). The arch itself is now called an "entablature" (from the Greek words for "table" or "baseboard").
Arches were used extensively in Rome during the Empire, but already known and respected before that. They appear often in the writings of the architects who designed buildings for the Emperors.
There are two types of arches: semicircular and pointed.
The circular arch is the most common form of vaulting in Europe and America. It can be used to create rooms as large as churches, with a height up to 100 feet (30 m). The key feature of this type of vault is that it has no flat surface inside the room - instead, there are a number of steps leading up to a central point where the vault meets the ceiling.
The term "Voussoir" comes from the French word "vouzoir", which means "to strike against". This refers to the role voussoirs play in supporting the arches they connect to prevent them from spreading too far and hitting the roof.
Inside a church with a circular vault, the diameter of the circle is equal to two times the height of the room. For example, if the room is 20 feet high (6 m), then the vault's diameter will be 40 feet (12 m).
There are several types of circular arches, depending on which part of the vault they support: pendentives, domes, or concaves.
Arches are semicircular or segmental (in the Mannerist style). Arches are frequently used in arcades, where they are supported by piers or columns with capitals. There might be an entablature segment between the capital and the arch's springing. Alberti was among the first to employ the arch on a grand scale, at the St. Peter's in Rome.
The arch is said to have been invented by Phoenician sailors who made use of the natural curve of timber when building their ships. The Egyptians also employed it but mainly for religious purposes. They built temples in which a central hall had double doors leading into smaller rooms called "apartments". Through these entrances, priests could pass from one room to another without being seen by worshippers outside the temple walls. The Romans adopted the arch and used it extensively in their buildings. It is said that they even transported some ancient arches across Europe before they built roads anywhere near as good as the ones in Italy.
In medieval architecture, arches were often used instead of windows because glass was rare and expensive. Arches provided an alternative means of light and ventilation. They were also useful in connecting one room to another without having to build all the way through. A doorway formed by two arches is called a triforium. The word "triforium" comes from the Latin meaning "through the door". In churches, the triforium usually contains offices or storage spaces for priests.
The majority of today's memorial arches are based after the early arches of ancient Rome. An example of an old Roman arch is the Arch of Constantine. It may be located in Rome, Italy, near the Colosseum. The arch can also be seen in a variety of domestic architectural styles. For example, it is found in English country houses in the 16th and 17th centuries.
Other examples include: the Arches of Septimius Severus in North Africa; the Ludi Aureli in Rome; and the Arc de Triomphe in Paris. All three were built to commemorate specific events.
The word "arch" comes from Latin arcus, meaning "bow". Thus, an arch consists of two supports with space between them which has been bent or shaped into a bow-like form. The term applies to both flat and round structures.
An example of a flat arch is the Pantheon in Rome. This 19th-century building has become synonymous with European architecture because of its use of classical elements. The name "Pantheon" means "all god's temple" in Greek. Flat arches were commonly used in ancient Greece and Rome. They are still used today in buildings that require light weight construction or large spans (such as bridges and tunnels).
A round arch has four sides instead of two for a flat arch.
The weight of all of an arch's parts holds it together, making building difficult. One solution is to construct a frame (historically, of wood) that precisely matches the shape of the arch's bottom. This is referred to as the "centre" or "centring." The frame is then filled with concrete, leaving only four openings for light and air.
An arch has two main forms: the half-dome and the pointed arch. In both cases, the weight of the structure above forces the members down into the ground or supports. If the members were not restrained from rising up out of the ground, they would collapse the arch itself.
Half-domes and elliptical arches tend to be more stable than pointed arches because there is more surface area connecting the top and bottom of the structure. This means less stress on any one part of either form of arch.
Pointed arches have a very slender base and tall point, where they connect to the wall surfaces below. Because there is no horizontal support beneath the points, they tend to be less stable than other shapes. However, if the points were to touch the ground or some other horizontal support, they could remain upright without collapsing.
Domed arches have a floor or base under them where the depth of the floor or base equals the height of the arch.
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