Arch - AbsoluteAstronomy.com

An arch is a structure

Structure

Structure is a fundamental, tangible or intangible notion referring to the recognition, observation, nature, and permanence of patterns and relationships of entities. This notion may itself be an object, such as a built structure, or an attribute, such as the structure of society...

that spans

Span (architecture)

Span is the distance between two intermediate supports for a structure, e.g. a beam or a bridge.A span can be closed by a solid beam or of a rope...

a space and supports a load. Arches appeared as early as the 2nd millennium BC in Mesopotamia

Mesopotamia

Mesopotamia is a toponym for the area of the Tigris–Euphrates river system, largely corresponding to modern-day Iraq, northeastern Syria, southeastern Turkey and southwestern Iran.Widely considered to be the cradle of civilization, Bronze Age Mesopotamia included Sumer and the...

n brick architecture and their systematic use started with the Ancient Romans

Ancient Rome

Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

who were the first to apply the technique

Roman Architectural Revolution

The Roman Architectural Revolution, also known as the concrete Revolution, is a term used to describe the widespread use in Roman architecture of the previously little-used architectural forms of the arch, vault and dome...

to a wide range of structures.

Technical aspects

The arch is significant because, in theory at least, it provides a structure which eliminates tensile stresses in spanning an open space. All the forces are resolved into compressive stresses. This is useful because several of the available building materials such as stone

Rock (geology)

In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

, cast iron

Cast iron

Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...

and concrete

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

can strongly resist compression but are very weak when tension, shear

Shear stress

A shear stress, denoted \tau\, , is defined as the component of stress coplanar with a material cross section. Shear stress arises from the force vector component parallel to the cross section...

or torsional

Torsion (mechanics)

In solid mechanics, torsion is the twisting of an object due to an applied torque. In sections perpendicular to the torque axis, the resultant shear stress in this section is perpendicular to the radius....

stress is applied to them. By using the arch configuration, significant spans can be achieved. This is because all the compressive forces hold it together in a state of equilibrium. This even applies to frictionless surfaces. However, one downside is that an arch pushes outward at the base, and this needs to be restrained in some way, either with heavy sides and friction or angled cuts into bedrock or similar.

This same principle holds when the force

Force

In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...

acting on the arch is not vertical such as in spanning a doorway, but horizontal, such as in arched retaining wall

Retaining wall

Retaining walls are built in order to hold back earth which would otherwise move downwards. Their purpose is to stabilize slopes and provide useful areas at different elevations, e.g...

s or dam

Dam

A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...

s.

Even when using concrete, where the structure may be monolithic, the principle of the arch is used so as to benefit from the concrete's strength in resisting compressive stress. Where any other form of stress is raised, it has to be resisted by carefully placed reinforcement rods

Rebar

A rebar , also known as reinforcing steel, reinforcement steel, rerod, or a deformed bar, is a common steel bar, and is commonly used as a tensioning device in reinforced concrete and reinforced masonry structures holding the concrete in compression...

or fibres. (See Arch bridge

Arch bridge

An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side...

History

True arches, as opposed to corbel arch

Corbel arch

A corbel arch is an arch-like construction method that uses the architectural technique of corbeling to span a space or void in a structure, such as an entranceway in a wall or as the span of a bridge...

es, were known by a number of civilizations in the Ancient Near East

Ancient Near East

The ancient Near East was the home of early civilizations within a region roughly corresponding to the modern Middle East: Mesopotamia , ancient Egypt, ancient Iran The ancient Near East was the home of early civilizations within a region roughly corresponding to the modern Middle East: Mesopotamia...

, the Levant

Levant

The Levant or ) is the geographic region and culture zone of the "eastern Mediterranean littoral between Anatolia and Egypt" . The Levant includes most of modern Lebanon, Syria, Jordan, Israel, the Palestinian territories, and sometimes parts of Turkey and Iraq, and corresponds roughly to the...

, and Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

, but their use was infrequent and mostly confined to underground structures such as drains where the problem of lateral thrust is greatly diminished. A rare exception is the bronze age

Bronze Age

The Bronze Age is a period characterized by the use of copper and its alloy bronze as the chief hard materials in the manufacture of some implements and weapons. Chronologically, it stands between the Stone Age and Iron Age...

arched city gate of Ashkelon

Ashkelon

Ashkelon is a coastal city in the South District of Israel on the Mediterranean coast, south of Tel Aviv, and north of the border with the Gaza Strip. The ancient seaport of Ashkelon dates back to the Neolithic Age...

(modern day Israel

Israel

The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...

), dating to ca. 1850 B.C. An early example of a voussoir

Voussoir

A voussoir is a wedge-shaped element, typically a stone, used in building an arch or vault.Although each unit in an arch or vault is a voussoir, two units are of distinct functional importance: the keystone and the springer. The keystone is the center stone or masonry unit at the apex of an arch. A...

arch appears in the Greek

Ancient Greece

Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

Rhodes Footbridge

The Rhodes Footbridge is an ancient Greek arch bridge in the city of Rhodes, Greece. Dating to the 4th century BC or early Hellenistic period, the modest structure represents the oldest known Greek bridge with a voussoir arch.- Construction and location :...

. In 2010, a robot discovered a long arch-roofed passageway underneath the Pyramid of Quetzalcoatl which stands in the ancient city of Teotihuacan

Teotihuacan

Teotihuacan – also written Teotihuacán, with a Spanish orthographic accent on the last syllable – is an enormous archaeological site in the Basin of Mexico, just 30 miles northeast of Mexico City, containing some of the largest pyramidal structures built in the pre-Columbian Americas...

north of Mexico City

Mexico City

Mexico City is the Federal District , capital of Mexico and seat of the federal powers of the Mexican Union. It is a federal entity within Mexico which is not part of any one of the 31 Mexican states but belongs to the federation as a whole...

, dated to around 200 AD.

The ancient Romans

Roman architecture

Ancient Roman architecture adopted certain aspects of Ancient Greek architecture, creating a new architectural style. The Romans were indebted to their Etruscan neighbors and forefathers who supplied them with a wealth of knowledge essential for future architectural solutions, such as hydraulics...

learned the arch from the Etruscans, refined it and were the first builders to tap its full potential for above ground buildings:

The Romans were the first builders in Europe, perhaps the first in the world, fully to appreciate the advantages of the arch, the vault and the dome.

Throughout the Roman empire

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

, their engineers erected arch structures such as bridges

Roman bridge

Roman bridges, built by ancient Romans, were the first large and lasting bridges built. Roman bridges were built with stone and had the arch as its basic structure....

, aqueducts

Roman aqueduct

The Romans constructed numerous aqueducts to serve any large city in their empire, as well as many small towns and industrial sites. The city of Rome had the largest concentration of aqueducts, with water being supplied by eleven aqueducts constructed over a period of about 500 years...

, and gates. They also introduced the triumphal arch

Triumphal arch

A triumphal arch is a monumental structure in the shape of an archway with one or more arched passageways, often designed to span a road. In its simplest form a triumphal arch consists of two massive piers connected by an arch, crowned with a flat entablature or attic on which a statue might be...

as a military monument. Vault

Vault (architecture)

A Vault is an architectural term for an arched form used to provide a space with a ceiling or roof. The parts of a vault exert lateral thrust that require a counter resistance. When vaults are built underground, the ground gives all the resistance required...

s began to be used for roofing large interior spaces such as halls and temples, a function which was also assumed by domed structures from the 1st century BC onwards.

The segmental arch was first built by the Romans who realized that an arch in a bridge did not have to be a semicircle, such as in Alconétar Bridge

Alconétar Bridge

The Alconétar Bridge , also known as Puente de Mantible, was a Roman segmental arch bridge in the Extremadura region, Spain. The ancient structure, which featured flattened arches with a span-to-rise ratio of 4–5:1, is one of the earliest of its kind...

or Ponte San Lorenzo

Ponte San Lorenzo

The Ponte San Lorenzo is a Roman segmental arch bridge over the river Bacchiglione in Padua, Italy. Constructed between 47 and 30 BC, it is one of the very earliest segmental arched bridges in the world...

. They were also routinely used in house construction as in Ostia Antica

Ostia Antica

Ostia Antica is a large archeological site, close to the modern suburb of Ostia , that was the location of the harbour city of ancient Rome, which is approximately 30 km to the northeast. "Ostia" in Latin means "mouth". At the mouth of the River Tiber, Ostia was Rome's seaport, but, due to...

(see picture).

The semicircular arch was followed in Europe by the pointed Gothic arch

Gothic architecture

Gothic architecture is a style of architecture that flourished during the high and late medieval period. It evolved from Romanesque architecture and was succeeded by Renaissance architecture....

or ogive

Ogive

An ogive is the roundly tapered end of a two-dimensional or three-dimensional object.-Applied physical science and engineering:In ballistics or aerodynamics, an ogive is a pointed, curved surface mainly used to form the approximately streamlined nose of a bullet or other projectile.The traditional...

whose centreline more closely followed the forces of compression and which was therefore stronger. The semicircular arch can be flattened to make an elliptical

Ellipse

In geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...

arch as in the Ponte Santa Trinita

Ponte Santa Trinita

The Ponte Santa Trìnita is a Renaissance bridge in Florence, Italy, spanning the Arno. The Ponte Santa Trìnita is the oldest elliptic arch bridge in the world, the three flattened ellipses giving the structure its celebrated elegant appearance...

. Both the parabolic

Parabola

In mathematics, the parabola is a conic section, the intersection of a right circular conical surface and a plane parallel to a generating straight line of that surface...

and the catenary

Catenary

In physics and geometry, the catenary is the curve that an idealised hanging chain or cable assumes when supported at its ends and acted on only by its own weight. The curve is the graph of the hyperbolic cosine function, and has a U-like shape, superficially similar in appearance to a parabola...

arches are now known to be the theoretically strongest forms. Parabolic arches were introduced in construction by the Spanish architect

Spanish architecture

Spanish architecture refers to architecture carried out in any area in what is now modern-day Spain, and by Spanish architects worldwide. The term includes buildings within the current geographical limits of Spain before this name was given to those territories...

Antoni Gaudí

Antoni Gaudí i Cornet was a Spanish Catalan architect and figurehead of Catalan Modernism. Gaudí's works reflect his highly individual and distinctive style and are largely concentrated in the Catalan capital of Barcelona, notably his magnum opus, the Sagrada Família.Much of Gaudí's work was...

, who admired the structural system of Gothic style, but for the buttresses, which he termed “architectural crutch

Crutch

Crutches are mobility aids used to counter a mobility impairment or an injury that limits walking ability.- Types :There are several different types of crutches:...

es”. The catenary and parabolic arches carry all horizontal thrust to the foundation and so do not need additional elements.

The horseshoe arch is based on the semicircular arch, but its lower ends are extended further round the circle until they start to converge. The first known built horseshoe arches are known from Aksum (modern day Ethiopia

Ethiopia

Ethiopia , officially known as the Federal Democratic Republic of Ethiopia, is a country located in the Horn of Africa. It is the second-most populous nation in Africa, with over 82 million inhabitants, and the tenth-largest by area, occupying 1,100,000 km2...

and Eritrea

Eritrea

Eritrea , officially the State of Eritrea, is a country in the Horn of Africa. Eritrea derives it's name from the Greek word Erethria, meaning 'red land'. The capital is Asmara. It is bordered by Sudan in the west, Ethiopia in the south, and Djibouti in the southeast...

) from around the 3rd–4th century, around the same time as the earliest contemporary examples in Roman Syria, suggesting either an Aksumite or Syrian origin for the type of arch.

Construction

An arch requires all of its elements to hold it together, raising the question of how an arch is constructed. One 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

Centring

Centring , or centering , is the structure upon which the stones of arches or vault are laid during construction. Once the arch is complete, it supports itself, but until the keystone is inserted, it has no strength and needs the centring to keep the voussoirs in their correct relative...

. The voussoir

Voussoir

s 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 A85

A85 road

The A85 is a major road in Scotland. It runs east from Oban along the south bank of Loch Etive, through Lochawe and Tyndrum, Crianlarich, Lochearnhead, St Fillans and Crieff before passing through Perth, where it crosses the River Tay via Perth Bridge. Its name between the latter two locations is...

bridge at Dalmally, Scotland suffered this fate on its first attempt, in the 1940s). The interior and lower line or curve of an arch is known as the intrados.

Old arches sometimes need reinforcement due to decay of the keystones, forming what is known as bald arch
Bald Arch
Bald arch is a technical term used by engineers to describe the decay of the crucial keystones in medieval buildings, particularly churches and cathedrals.- Causes and symptoms :...

.

The gallery shows arch forms displayed in roughly the order in which they were developed.

Construction of Adobe Arches

Below a set of pictures of various stages of construction of Arches made of adobe- mud- bricks using local materials and local labor in Merzouga, Morocco

Morocco

Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...

. They rest upon concrete pillars and have a concrete bar across them for strength.

Other types

A blind arch

Blind arch

A blind arch is an arch found in the wall of a building which has been infilled with solid construction so it cannot serve as a passageway, door, or window. The term is most often associated with masonry wall construction, but is also found in other types of construction such as light frame...

is an arch infilled with solid construction so it cannot function as a window, door, or passageway.

Natural rock formations may also be referred to as arches. These natural arch

Natural arch

A natural arch or natural bridge is a natural geological formation where a rock arch forms, with an opening underneath. Most natural arches form as a narrow ridge, walled by cliffs, become narrower from erosion, with a softer rock stratum under the cliff-forming stratum gradually eroding out until...

es are formed by erosion

Erosion

Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

rather than being carved or constructed by man. See Arches National Park

Arches National Park

Arches National Park is a U.S. National Park in eastern Utah. It is known for preserving over 2000 natural sandstone arches, including the world-famous Delicate Arch, in addition to a variety of unique geological resources and formations....

for examples.

A special form of the arch is the triumphal arch

Triumphal arch

, usually built to celebrate a victory in war. A famous example is the Arc de Triomphe

Arc de Triomphe

-The design:The astylar design is by Jean Chalgrin , in the Neoclassical version of ancient Roman architecture . Major academic sculptors of France are represented in the sculpture of the Arc de Triomphe: Jean-Pierre Cortot; François Rude; Antoine Étex; James Pradier and Philippe Joseph Henri Lemaire...

in Paris

Paris

Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

, France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

External links

DIYinfo.org's Constructing Brick Arches Wiki - A wiki on how to construct brick arches around the house
DIYinfo.org's Constructing Timber Framed Arches Wiki - Similar to the brick arches but extra information for timber arches