See also: Bridge (homonymy)
A bridge is a Work of art, realization of the Civil engineering, intended to allow the crossing of an obstacle (River, transportation route…) while passing over. A bridge can support a road Chaussée, a Railway, a channel (Pont-canal) or a Canalisation (Oléoduc, Aqueduc, etc). It can be mobile (raising bridge, transporter bridge). A temporary bridge can also be made up by Bateau X specialized (bridge of boats). Dismountable metal viaducts, successors of the Bailey bridges make it possible to bring a temporary solution to the unevenness of a crossroads. The soldiers developed specific tools (bridges dépliables). More generally, it indicates a point of passage or transmission (of matter, energy, information) between two zones.
A bridge is in the beginning a construction connecting two banks of a river. As from the 19th century, the construction of bridges became essential to cross new transportation routes, insuperable in a simple way or dangerous for the vulnerable users (railways, Autoroute S).
A bridge can be carried out in Béton, in Maçonnerie, Métal (iron, steel or exceptionally aluminum) or in other materials for bridges low length: Wood, cord S, Bamboo S (bridges of monkeys). At the base, the structure of a bridge is the following one:
- a apron constitutes the part which supports the lanes,
- of the abutments are used as fulcrum at the ends of the apron,
- of the piles support the apron between the abutments, if the length of the apron requires it. They can support it in an indirect way, for example with a system of cables, as in the suspended bridges or directly by ties as in the stayed girder bridges.
The Romains built many bridges of masonry (in stone or brick S), by using arcs of semicircular arch: the section between two piles is supported by a vault in half-circle, which distributes the effort between the two adjacent piles.
Types of bridges
Stayed girder suspended bridge and bridgeA Suspended bridge is a bridge whose apron is literally suspended on the piles (one speaks then about pylons) by a system of cables. The pylons rise above the apron and support one or two cables principal, called cables carrying, which go from one abutment to the other, one on each side of the apron. These cables support the apron via a whole of vertical cables: suspending rods. The Golden Spoils Bridge or the Tacoma Narrows Bridge is of the bridges of this type.
Another version of suspended bridge consists in supporting the apron by a network of cables directly tended between the top (or a part close to the top) of the pylons and fixed at regular intervals on the sides of the apron. One speaks in this case about Bridge stayed girder . The Bridge of Normandy and the Viaduc of Millau are examples.
The suspended bridges have a mechanical operation, which within sight of materials employed, makes it possible to cross ranges even more important than the stayed girder bridges.
Pont- levis, raising bridge and tilting bridgeA drawbridge is a bridge of which the apron can be raised (by rotation around an axis located at an end), for defensive reasons (the bridge being the single access to a strong Château, above a ditch or a dry ditch; when it is raised, it constitutes moreover one additional barrier in front of the harrow which protects the entry from the fort) or practices (to allow the passage of a ship great height for example). In this last case, one speaks about tilting bridge (the Tower Bridge is a tilting bridge). When the apron of the bridge is raised by Translation, one speaks then about bridge raising (the Pont of Recouvrance to Brest is a raising bridge).
Pont revolvingA bridge swing is a bridge whose apron is assembled on a pivot, which makes it possible to make turn the apron horizontally to present it in the axis of the water way that it crosses: thus, a ship can circulate in the passage released by the rotation of the apron (the viaduct of Caronte, with Martigues (Rhone delta), is a bridge swing on a railway route).
AdvantagesThe advantages of this type of bridge on various other solutions to give access at the same time to the river transport and road are:
- As it does not require a counterweight like bridge-tilting, its construction is simpler and light;
- If the channel is rather broad, one can make pass the ships in the two directions at the time of its opening and it is used to separate them one from the other what adds to the safety of the traffic;
- During construction, the artificial island created for the axis of rotation can be used for manufacture of the bridge without harming the passages of the ships.
- the central pillar can be a danger with navigation in the event of bad atmospheric conditions;
- This pillar reduces the width of the channel and, according to the width of this one, can limit circulation to only one direction;
- When it is open, the bridge must be able to maintain its structure in Porte-à-faux but when it is closed, the weight of the cars requires supports under the span. There are thus forces of compression and tension which can be exerted alternatively at the same point of the bridge;
- a shock in edge of banks, by a ship with the drift for example, can make him carry out a beginning of rotation what will become a danger to circulation on the bridge.
Pont transporterA Transporter bridge has a metal structure with traditional suspension or stay. It makes it possible to make pass the vehicles and the people of a bank to the other in a nacelle suspended to a trolly crab under the apron.
Temporary bridgesMilitary engineering has capacity of creation of bridges on bridge floating or which launch out or unfold themselves with the top of small rivers.
The inhabited bridges were very widespread with the Moyen-âge since each bridge, in each town of Europe, was surmounted dwellings. At the origin of this construction of dwellings on the bridges, one finds two types of population, with only one and even motivation, the Fiscalité. It always acted on the one hand poorer, and on the other hand tradesmen seeking to withdraw itself from the taxable quota (payable with the owner of the ground), and from the toll like with the Octroi (payable with the feudal lord).
The fires, frequent on these bridges out of wooden, the many accidents of river transport, the risings, the reorganizations of the centres town and the construction of stone bridges caused the quasi total disappearance of these bridges. Only a handle of these inhabited bridges remains today in Europe.
the bridge of Rohan to Landerneau, which one finds trace as of 1336, was rebuilt out of stones in 1510 by Jean II of Rohan. The bridge then carried a mill, fisheries, a vault, a staff waiting room and a prison. At the 17th century, in fact dwellings are built above. This bridge, built with the mouth of the Élorn, is subjected to the tides.
the Krämerbrücke ( bridge of the grocers ) with Erfurt, out of wood in the beginning, was rebuilt hones in 1325 of it on the broad arm of. After the giant fire of 1472, the city decided to raise on the bridge 62 houses in which the tradesmen had shop and residence.
the Ponte Vecchio with Florence builds in 1345 to replace the antique Roman bridge on the Arno. It is in 1564 that Giorgio Vasari restructured the bridge on the order of the Large Duke Ferdinand I to make there pass the corridori connecting the Palazzo Vecchio to the Palais Pitti, and reserving the shops with the only jewellers and goldsmiths.
Pulteney Bridge with Bath, England, built in 1773 on the rivère Avon.
the bridge covered with Lovech or (Lowetch) in Bulgaria, was rebuilt twice, in 1874 and 1931, after being destroyed the first time by a rising then by a fire. It shelters 14 stores Voir.
(should be completed in 2007-2008) (largest maritime Pont in the world)
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