What is an Arch?

An arch is a structure constructed in curved shape with wedge-shaped units - either bricks or stones, which are joined together with mortar, and provided at openings to support the weight of the wall above it along with other superimposed loads. Due to its shape, the loads from above get distributed to supports - either the pier or abutment.

The common terms used in arches are

• Keystone: A keystone (or capstone) is a wedge-shaped stone at the apex of a masonry arch or typically round-shaped one at the apex of a vault.

• Voussoir: A voussoir is a wedge-shaped stone used in building arches and vaults.

• Impost: An impost or impost block is a projecting block resting on top of a column or embedded in a wall, serving as the base for the springer or lowest voussoir of an arch.

The different types of arches are:

1. Round Arch

Also known as a semi-circular arch, this is formed in a continuous curve and was developed by the Romans. They were often used side by side in a series to create an arcade. The ancient Romans often used circular or rounded arches to build bridges, large buildings, and aqueducts.

Illustrations: Sonali

2. Segmental Arch

A segmental arch is a type of arch with a circular arc of less than 180 degrees. The segmental arch is one of the strongest arches because it can resist thrust. The flatter segmental shape has long been used for bridges. With the segmental arch, the flatter it gets the more of its thrust is delivered sideways to the abutments or embankments at each end of the bridge.

Illustrations: Sonali

3. Flat Arch

A spanning member constructed of mutually supporting voussoirs and having straight or almost straight horizontal intrados and extrados. The flat arch generates an equilateral triangle within Intrados as a basis at an angle of 60° degrees. The flat arch is commonly used for building structures with minimum weight requirements.

Illustrations: Sonali

4. Triangular Arch

Two flat stones set at an angle of 45° or thereabouts, mitered at the top, and touching each other at the apex of a triangular-headed opening. Triangular arches are strong and stable, and they can support a lot of weight. They are also relatively easy to build, which makes them a popular choice for architects and builders. 

Illustrations: Sonali

5. Rounded horse-shoe Arch

Also called the Moorish arch and the keyhole arch, is a type of arch in which the circular curve is continued below the horizontal line of its diameter so that the opening at the bottom of the arch is narrower than the arch's full span. In addition to their use across the Islamic world, horseshoe arches became popular in Western countries in Moorish Revival architecture, which became fashionable in the 19th century. They were widely used in Moorish Revival synagogues.

Illustrations: Sonali

6. Multifoil Arch

A multifoil arch, also known as a cusped arch, polylobed arch, or scalloped arch, is an arch characterized by multiple circular arcs or leaf shapes that are cut into its interior profile or intrados. Rounded multifoil arches are often used in Islamic architecture, and they can be found in many mosques and other religious buildings. They are also used in some secular buildings, such as palaces and tombs. Rounded multifoil arches are known for their beauty and their intricate design.

Illustrations: Sonali

7. Trefoil Arch

A trefoil arch, or three-foiled cusped arch, is an arch incorporating the shape or outline of a trefoil – three overlapping circles. It has been widely used for its symbolic significance in Christian architecture. Trefoil arches are common in Gothic architecture for portals and decoration. It was adopted as ornamentation to churches during the Middle Ages.

Illustrations: Sonali

8. Ogee four-centered Arch

A four-centered arch is a low, wide type of arch with a pointed apex. Its structure is achieved by drafting two arcs which rise steeply from each springing point on a small radius, and then turning into two arches with a wide radius and much lower springing point. It is a pointed sub-type of the general flattened depressed arch. This type of arch uses space efficiently and decoratively when used for doorways.

Illustrations: Sonali

9. Pointed trefoil Arch

The pointed trefoil arch is a distinctive architectural form that has been used in the construction of many structures throughout history. This particular form of arch is composed of three lobes that are connected at the peak of the arch. The lobes of the arch are slightly pointed and typically built from stone or brick. This form of arch is often used in Gothic architecture and is particularly suited to the construction of vaults and ceilings.

Illustrations: Sonali

10. Lancet Arch

The lancet arch is a variety of pointed arch in which each of the arcs, or curves, of the arch have a radius longer than the width of the arch. It takes its name from being shaped like the tip of a lance. The lancet window is one of the typical features of the Early English 13th century in Gothic architecture.

Illustrations: Sonali

11. Tudor Arch

A four-centered arch, the inner pair of curves having a radius much greater than that of the outer pair. The Tudor arch was especially used for doorways, where it gives a wide opening without taking too much space above, compared to a more pointed Gothic arch. In Tudor architecture of the grander sort, it is so used when the window openings are rectangular, for example at Hampton Court Palace.

Illustrations: Sonali

12. Inflexed Arch

An inflexed or reversed ogee arch is a unique design that takes the arcs of a pointed arch and inverts them to create two bows in the opening. The inverted design of the apex of the archway creates a serpentine appearance, adding architectural appeal and style. This arch design is a common aesthetic feature in architecture, and modern design incorporates the inflexed arch for a variety of building applications.

Illustrations: Sonali

FAQs

1. What is the purpose of keystones in an arch?

- Keystones serve as the central, wedge-shaped stone at the apex of a masonry arch. They distribute pressure and help hold the other stones in place, providing structural integrity to the arch.

2. Why is a segmental arch considered one of the strongest arch types?

- A segmental arch is strong because it can resist thrust effectively due to its circular arc, which is less than 180 degrees. This shape ensures that more of its load is delivered sideways to the abutments.

3. What distinguishes the lancet arch from other pointed arches?

- The lancet arch features a longer arc radius compared to the width of the arch, giving it a slender, lance-like appearance. It is commonly associated with Early English Gothic architecture.

4. How does the multifoil arch enhance architectural design?

- Multifoil arches are characterized by multiple circular arcs or leaf shapes within the arch's profile. They add intricate and decorative designs, often found in mosques, religious buildings, and some secular structures like palaces.

These were some of the important points to remember while learning about arches in buildings. Stay tuned for more information on other important topics in the AEC industry and follow Kaarwan for such detailed guides!