 A double-arch stone bridge inNagasaki, Japan | |
| Ancestor | Clapper bridge |
|---|---|
| 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 |
Anarch bridge is abridge withabutments at each end shaped as a curvedarch. Arch bridges work by transferring the weight of the bridge and itsloads partially into a horizontal thrust restrained by the abutments at either side, and partially into a vertical load on the arch supports. Aviaduct (a long bridge) may be made from a series of arches, although other more economical structures are typically used today.
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Possibly the oldest existing arch bridge is theMycenaeanArkadiko Bridge in Greece from about 1300 BC. The stonecorbel arch bridge is still used by the local populace.[1] The well-preservedHellenisticEleutherna Bridge has a triangular corbel arch.[2] The 4th century BCRhodes Footbridge rests on an earlyvoussoir arch.[3]
Althoughtrue arches were already known by theEtruscans andancient Greeks, theRomans were – as with thevault and thedome – the first to fully realize the potential of arches for bridge construction.[4] A list ofRoman bridges compiled by the engineer Colin O'Connor features 330Roman stone bridges for traffic, 34Roman timber bridges and 54Roman aqueduct bridges, a substantial part still standing and even used to carry vehicles.[5] A more complete survey by the Italian scholar Vittorio Galliazzo found 931 Roman bridges, mostly of stone, in as many as 26 countries (including formerYugoslavia).[6]
Roman arch bridges were usuallysemicircular, although a number were segmental arch bridges (such asAlconétar Bridge), a bridge which has a curved arch that is less than a semicircle.[7] The advantages of thesegmental 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.[8] Generally, Roman bridges featured wedge-shaped primary arch stones (voussoirs) of the same in size and shape. The Romans built both single spans and lengthy multiple archaqueducts, such as thePont du Gard andSegovia Aqueduct. Their bridges featured from an early time onwards flood openings in the piers, e.g. in thePons Fabricius in Rome (62 BC), one of the world's oldest major bridges still standing.
Roman engineers were the first and until theIndustrial Revolution the only ones to construct bridges withconcrete, which they calledOpus caementicium. The outside was usually covered with brick orashlar, as in theAlcántara Bridge.
The Romans also introduced segmental arch bridges into bridge construction. The 330 m-long (1,080 ft)Limyra Bridge in southwesternTurkey features 26 segmental arches with an average span-to-rise ratio of 5.3:1,[9] giving the bridge an unusually flat profile unsurpassed for more than a millennium.Trajan's bridge over theDanube featured open-spandrel segmental arches made of wood (standing on 40 m-high (130 ft) 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 (2,590 ft) longPuente Romano atMérida. The late RomanKaramagara Bridge inCappadocia may represent the earliest surviving bridge featuring a pointed arch.[10]
Inmedieval Europe, bridge builders improved on the Roman structures by using narrowerpiers, thinner arch barrels and higher span-to-rise ratios on bridges.Gothic pointed arches were also introduced, reducing lateral thrust, and spans increased as with the eccentricPuente del Diablo (1282). With more advanced design and bridge-building techniques, the alternative informal name ofDevil's Bridge became more widely used across Europe, because many people could not believe that these were man-made and capable of carrying the size of loads that they did.
The 14th century in particular saw bridge building reaching new heights. Span lengths of 40 m (130 ft), 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 andPont Grand) and with arch types as different as semi-circular, pointed and segmental arches. Thebridge at Trezzo sull'Adda, destroyed in the 15th century, even featured a span length of 72 m (236 ft), not matched until 1796.[11]
Constructions such as the acclaimedFlorentine segmental arch bridgePonte Vecchio (1345) combined sound engineering (span-to-rise ratio of over 5.3 to 1) with aesthetical appeal. The three elegant arches of theRenaissancePonte Santa Trinita (1569) constitute the oldest elliptic arch bridge worldwide. Such low rising structures required massiveabutments, which at theVenetianRialto Bridge (1591) and the Pegnitz orFleischbrücke (1598) inNuremberg (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 extant arch bridge is theZhaozhou Bridge of 605 CE, 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, with a length of 51 metres (167 ft) and span of 37.4 metres (123 ft), is the world's first wholly stone open-spandrel segmental arch bridge, allowing a greater passage for flood waters.[12] Bridges with perforated spandrels can be found worldwide, such as theBridge of Arta, (17th century) Greece andCenarth Bridge, (18th century) in Wales.
With the coming of theIndustrial Revolution, in the 18th and 19th centuries, stone and brick arches continued to be built by many prominent Britishcivil engineers, includingThomas Telford,John Rennie, and latterlyIsambard Kingdom Brunel. They also started the modern usage of different materials, such ascast iron — Telford designed the first bridge built of metal, completed in 1781,the Iron Bridge with a single arch of sections of cast iron constructed in traditional woodworking techniques — and thensteel andconcrete, which have been increasingly used in the construction of arch bridges, to almost the exclusion of other materials. A key pioneer wasJean-Rodolphe Perronet, who used much narrower piers, revised calculation methods, and exceptionally low span-to-rise ratios.
Stone, brick and other such materials are strong incompression and somewhat so inshear, but cannot resist much force intension. As a result, masonry arch bridges are designed to be constantly under compression, so far as is possible. Each arch is constructed over a temporaryfalsework frame, known as acentring. In the first compression arch bridges, akeystone 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 tosettlement or undermining. However, relative to modern alternatives, such bridges are very heavy, requiring extensivefoundations. They are also expensive to build wherever labor costs are high.
The corbel arch bridge is a masonry, or stone, bridge where each successively higher course (layer) cantilevers slightly more than the previous course.[13] The steps of the masonry may be trimmed to make the arch have a rounded shape.[14] Thecorbel arch does not produce thrust, or outward pressure at the bottom of the arch, and is not considered atrue arch. It is more stable than atrue arch because it does not have this thrust. The disadvantage is that this type of arch is not suitable for large spans.[15]
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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. Romancivil 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.
This type of bridge comprises an arch where the deck is completely above the arch. The area between the arch and the deck is known as thespandrel. If the spandrel is solid, usually the case in a masonry or stone arch bridge, the bridge is called aclosed-spandrel deck arch bridge. If the deck is supported by a number of vertical columns rising from the arch, the bridge is known as anopen-spandrel deck arch bridge. TheAlexander Hamilton Bridge is an example of an open-spandrel arch bridge. Finally, if the arch supports the deck only at the top of the arch, the bridge is called acathedral arch bridge.[16]
This type of bridge has anarch whose base is at or below the deck, but whose top rises above it, so the deck passes through the arch. The central part of the deck is supported by the arch via suspension cables or tie bars, as with atied-arch bridge. The ends of the bridge may be supported from below, as with a deck arch bridge. Any part supported from arch below may have spandrels that are closed or open.
TheSydney Harbour Bridge and theBayonne Bridge are a through arch bridge which uses a truss type arch.
Also known as a bowstring arch, this type of arch bridge incorporates a tie between two opposite ends of the arch. The tie is usually the deck and is capable of withstanding the horizontal thrust forces which would normally be exerted on the abutments of an arch bridge.
The deck is suspended from the arch. The arch is in compression, in contrast to a suspension bridge where it'scatenary arch is in tension. A tied-arch bridge can also be athrough arch bridge.
An arch bridge with hinges incorporated to allow movement between structural elements. A single-hinged bridge has a hinge at thecrown of the arch, a two-hinged bridge has hinges at both springing points and a three-hinged bridge has hinged in all three locations.[17]
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Most modern arch bridges are made fromreinforced concrete. This type of bridge is suitable where a temporary centring 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 fromprecast 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 nottrue arches but rather abeam with the shape of an arch. Seetruss arch bridge for more on this type.
A modern evolution of the arch bridge is the long-spanthrough arch bridge. This has been made possible by the use of light materials that are strong in tension such as steel and prestressed concrete.
With the span of 220 metres (720 ft), theSolkan Bridge over theSoča River atSolkan in Slovenia is the second-largest stone bridge in the world and the longest railroad stone bridge. It was completed in 1905. Its arch, which was constructed from over 5,000 tonnes (4,900 long tons; 5,500 short tons) of stone blocks in just 18 days, is the second-largest stone arch in the world, surpassed only by the Friedensbrücke (Syratalviadukt) inPlauen, and the largest railroad stone arch. The arch of the Friedensbrücke, which was built in the same year, has the span of 90 m (295 ft) and crosses the valley of theSyrabach River. The difference between the two is that the Solkan Bridge was built from stone blocks, whereas the Friedensbrücke was built from a mixture of crushed stone and cement mortar.[18]
The world's largest arch bridge is theChaotianmen Bridge over theYangtze River with a length of 1,741 m (5,712 ft) and a span of 552 m (1,811 ft). The bridge was opened 29 April 2009, inChongqing, China.[19]
"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."
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