Arch bridge

Arch Bridge
Double arch stone bridge, Japan
Ancestor:	Clapper bridge
Related:	None
Descendant:	Truss arch bridge, moon bridge (masonry)
Carries:	Pedestrians, vehicles, light rail, heavy rail, water
Span range:	short, but often set end-to-end to form a large total length
Material:	masonry, concrete, wrought iron, cast iron, timber, structural steel
Movable:	No
Design effort:	Low
Falsework required:	Yes

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. A viaduct (a long bridge) may be made from a series of arches, although other more economical structures are typically used today.

History

The Alcántara Bridge, Spain (built 103-106 AD)

Possibly the oldest existing arch bridge is the Mycenaean Arkadiko bridge in Greece from about 1300 BC. The stone corbel arch bridge is still used by the local populace.^[1] Although true arches were already known by the Etruscans and ancient Greeks, the Romans were - as with the vault and the dome - the first to fully realize the potential of arches for bridge construction.^[2]

A list of Roman bridges compiled by the engineer Colin O'Connor features 330 Roman stone bridges for traffic, 34 timber bridges and 54 aqueduct bridges, a substantial part still standing and even used to carry vehicles.^[3]

Roman arch bridges were usually semicircular, although a few were segmental (such as Alconétar Bridge).The advantages of the segemental arch bridge were that it allowed great amounts of flood water to pass under it, which would prevent the bridge from being swept away during floods and the bridge itself could be more lightweight ^[4]. Generally, Roman bridge featured wedge-shaped primary arch stones (voussoirs) of the same in size and shape. The Romans built both single spans and lengthy multiple arch aqueducts, such as the Pont du Gard and Segovia Aqueduct. Their bridges featured from an early time onwards flood openings in the piers, e.g. in the Pons Fabricius in Rome (62 BC), one of the world's oldest major bridges still standing.

Segovia Aqueduct (ca. 100 AD)

Roman engineers were the first and until the industrial revolution the only ones to construct bridges with concrete, which they called Opus caementicium. The outside was usually covered with brick or ashlar, as in the Alcántara bridge.

Although rarely built, the Romans also introduced segmental arch bridges into bridge construction. The 330 m long Limyra Bridge in southwestern Turkey features 26 segmental arches with an average span-to-rise ratio of 5.3:1,^[5] giving the bridge an unusually flat profile unsurpassed for more than a millennium. Trajan's bridge over the Danube featured open-spandrel segmental arches made of wood (standing on 40 m high concrete piers). This was to be the longest arch bridge for a thousand years both in terms of overall and individual span length, while the longest extant Roman bridge is the 790 m long Puente Romano at Mérida. The late Roman Karamagara Bridge in Cappadocia may represent the earliest surviving bridge featuring a pointed arch.^[6]

Devil's bridge, Céret, France (1341)

In medieval Europe, bridge builders improved on the Roman structures by using narrower piers, thinner arch barrels and lower span-rise ratios on bridges. Gothic pointed arches were also introduced, reducing lateral thrust, and spans increased as with the eccentric Puente del Diablo (1282).

The 14th century in particular saw bridge building reaching new heights. Span lengthes of 40 m, previously unheard of in the history of masonry arch construction, were now reached in places as diverse as Spain (Puente de San Martín), Italy (Castelvecchio Bridge) and France (Devil's bridge and Pont Grand) and with arch types as different as semi-circular, pointed and segmental arches. The bridge at Trezzo sull'Adda, destroyed in the 15th century, even featured a span length of 72 m, not matched until 1796.^[7]

The Ponte Vecchio, Florence, Italy (1345)

Constructions such as the acclaimed Florentine segmental arch bridge Ponte Vecchio (1345) combined sound engineering (span-to-rise ratio of over 5.3 to 1) with aesthetical appeal, while the three elegant arches of the Renaissance Ponte Santa Trinita (1569) constitute the oldest elliptic arch bridge worldwide. Such low rising structures required massive abutments, which at the Venetian Rialto bridge and the Fleischbrücke in Nuremberg (span-to-rise ratio 6.4:1) were founded on thousands of wooden piles, partly rammed obliquely into the grounds to counteract more effectively the lateral thrust.

In China, the oldest existing bridge is the Zhaozhou Bridge of 605 AD (although bridges were built since the ancient Zhou Dynasty), which combined a very low span-to-rise ratio of 5.2:1, with the use of spandrel arches (buttressed with iron brackets). The Zhaozhou Bridge is the world's first wholly-stone open-spandrel segmental arch bridge.^[8]

Richmond Bridge, Oldest operational bridge in Australia (1825)

In more modern times, stone and brick arches continued to be built by many civil engineers, including Thomas Telford, Isambard Kingdom Brunel and John Rennie. A key pioneer was Jean-Rodolphe Perronet, who used much narrower piers, revised calculation methods and exceptionally low span-to-rise ratios. Different materials, such as cast iron, steel and concrete have been increasingly used in the construction of arch bridges.

Simple compression arch bridges

Falsework centering in the center arch of Monroe Street Bridge, Spokane, Washington. 1911.

Advantages of simple materials

Stone, brick and other such materials are strong in compression and somewhat so in shear, but cannot resist much force in tension. As a result, masonry arch bridges are designed to be constantly under compression, so far as is possible. Each arch is constructed over a temporary falsework frame, known as a centering. In the first compression arch bridges, a keystone in the middle of the bridge bore the weight of the rest of the bridge. The more weight that was put onto the bridge, the stronger its structure became. Masonry arch bridges use a quantity of fill material (typically compacted rubble) above the arch in order to increase this dead-weight on the bridge and prevent tension from occurring in the arch ring as loads move across the bridge. Other materials that were used to build this type of bridge were brick and unreinforced concrete. When masonry (cut stone) is used the angles of the faces are cut to minimize shear forces. Where random masonry (uncut and unprepared stones) is used they are mortared together and the mortar is allowed to set before the falsework is removed.

Traditional masonry arches are generally durable, and somewhat resistant to settlement or undermining. However, relative to modern alternatives, such bridges are very heavy, requiring extensive foundations. They are also expensive to build wherever labor costs are high.

Construction sequence

Workflow on the Roman Bridge at Limyra: the falsework was moved to another opening as soon as the lower arch rib had been completed

• Where the arches are founded in a stream bed the water is diverted and the gravels excavated to a good footing. From this the foundation piers are raised to the base of the arches, a point known as the springing.
• Falsework centering is fabricated, typically from timbers and boards. Since each arch of a multi-arch bridge will impose a thrust upon its neighbors, it is necessary either that all arches of the bridge be raised at the same time, or that very wide piers are used. The thrust from the end arches is taken into the earth by footings at the canyon walls, or by large inclined planes forming ramps to the bridge, which may also be formed of arches.
• The several arches are constructed over the centering. Once the basic arch barrel is constructed, the arches are stabilized with infill masonry between the arches, which may be laid in horizontal running bond courses. These may form two walls, known as the spandrels, which are then infilled with loose material and rubble.
• The road is paved and parapet walls protectively confine traffic to the bridge.

Types of arch bridge

Roman Pont-Saint-Martin	The three-story Roman Pont du Gard aqueduct	The Roman segmental arch Bridge at Limyra	Pointed arch of the Puente del Diablo in Spain
Ponte Vecchio, a medieval shop bridge	Late medieval Krämerbrücke supporting two rows of houses	Ponte Santa Trinita. First bridge with elliptic arches	A masonry moon bridge showing the buttressing approach ramps that take the horizontal thrust of the arch
These Harlem River bridges are all supported deck arch bridges.	The center span of the deck of the Fremont Bridge is suspended and the deck acts as a tie, while the side spans of the deck are supported.	Fredrikstad bridge in Fredrikstad, Norway	Bridgeport Lamp Chimney Company Bowstring Concrete Arch Bridge located in Bridgeport, West Virginia

Corbel arch bridge

Corbel arch of the Mycenaean Arkadiko bridge

A corbelled arch with the masonry untrimmed

A corbel arch with the masonry cut into an arch shape

The corbel arch bridge is a masonry, or stone, bridge where each successively higher course (layer) cantilevers slightly more than the previous course.^[9] The steps of the masonry may be trimmed to make the arch have a rounded shape.^[10] The corbel arch does not produce thrust, or outward pressure at the bottom of the arch, and is not considered a true arch. It is more stable than a true arch because it does not have this thrust. The disadvantage is that this type of arch is not suitable for large spans.^[11]

Aqueducts and canal viaducts

• In some locations it is necessary to span a wide gap at a relatively high elevation, such as when a canal or water supply must span a valley. Rather than building extremely large arches, or very tall supporting columns (difficult using stone), a series of arched structures are built one atop another, with wider structures at the base. Roman civil engineers developed the design and constructed highly refined structures using only simple materials, equipment, and mathematics. This type is still used in canal viaducts and roadways as it has a pleasing shape, particularly when spanning water, as the reflections of the arches form a visual impression of circles or ellipses.

Supported deck arch bridge

This type of bridge comprises an arch which supports a deck by means of a number of vertical columns. The Alexander Hamilton Bridge is a supported deck arch bridge.

See also: Category:Deck arch bridges

Suspended deck arch bridge

See also: Category:Through arch bridges

This type of bridge comprises an arch which supports the deck by means of suspension cables or tie bars. The Sydney Harbour Bridge is a suspended deck arch bridge which uses a truss type arch.

These suspended deck bridges are in contrast to suspension bridges which use the catenary to which the aforementioned cables or tie bars are attached and suspended. While in fact all proper arches use predominantly the compressive strength of materials, this type of bridge is also referred to as the Compression arch suspended-deck bridge.

Tied arch bridge

This type of arch bridge incorporates a tie between two opposite ends of the arch. The tie is capable of withstanding the horizontal thrust forces which would normally be exerted on the abutments of an arch bridge.

Use of modern materials

Most modern compression arch bridges are made from reinforced concrete. This type of bridge is suitable where a temporary centering may be erected to support the forms, reinforcing steel, and uncured concrete. When the concrete is sufficiently set the forms and falseworks are then removed. It is also possible to construct a reinforced concrete arch from precast concrete, where the arch is built in two halves which are then leaned against each other.

Many modern bridges, made of steel or reinforced concrete, often bear some of their load by tension within their structure. This reduces or eliminates the horizontal thrust against the abutments and allows their construction on weaker ground. Structurally and analytically they are not true arches but rather a beam with the shape of an arch. See truss arch bridge for more on this type.

A modern evolution of the arch bridge is the compression arch suspended-deck bridge (through arch bridge). This has been made possible by the use of light materials that are strong in tension such as steel, reinforced concrete, and post-tensioned concrete.

See also

• List of arch bridges by length
• List of longest masonry arch bridge spans
• Truss arch bridge
• Compression arch suspended-deck bridge
• Tied arch bridge
• Roman bridge

Footnotes

References

• Galliazzo, Vittorio (1995), I ponti romani, Vol. 1, Treviso: Edizioni Canova, pp. 92, 93 (fig. 39), ISBN 88-85066-66-6 
• O’Connor, Colin (1993), Roman Bridges, Cambridge University Press, p. 129, ISBN 0-521-39326-4 

External links

• NOVA Online - Super Bridge - Arch Bridges
• Matsuo Bridge Co. - Arch Bridges
• Historic Bridges of the Midwest
• Historic Arch Railroad Bridges in Western Massachusetts

v • d • e Bridge-related articles Types of bridges Moveable bridge · Beam bridge · Cantilever bridge · Arch bridge · Suspension bridge (Simple, Underspanned, Suspended-deck, Stressed ribbon, Self-anchored) · Cable-stayed bridge · Truss bridge · Visual index to various types Lists of Bridges Notable bridges · By length · Longest suspension bridge spans · Largest cable-stayed bridges · Longest cantilever bridges · Longest continuous truss bridges · Arch bridges · Tallest · Bridge disasters