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.
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. 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.
The engineer Colin O'Connor lists 330 Roman stone bridges for traffic, 34 timber bridges and 54 aqueduct bridges, a substantial part still standing and even used to carry vehicles.
Roman arch bridges were usually semicircular, although a few were segmental (such as Alconétar Bridge). 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.
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, 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.
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.
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.
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.
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 labour costs are high.
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.
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.
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