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    A bridge is a structure built to span a gorge, valley, road, railroad track, river, body of water, or any other physical obstacle. Designs may be built higher than otherwise needed in order to allow other traffic (particularly ship traffic) beneath.

    The purpose of a bridge is to allow people or cargo easy passage over an obstacle by providing a route that would otherwise be uneven or impossible.


        Bridge
            History
            Etymology
            Types of bridges
                By use
                Decorative and ceremonial bridges
                Index to types of bridges
                Index to bridge related topics
            Bridge structural and evolutionary taxonomy
            Efficiency
            Notable bridges
            Special Installations
            Catastrophic collapses
            See also

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    History





    The first bridges were spans made of wooden logs or planks and eventually stones, using a simple support and crossbeam arrangement.

    The arch was first used by the Roman Empire for bridges and aqueducts, some of which still stand today. The Romans also used cement, which reduced the variation of strength found in natural stone. Brick and mortar bridges were built after the Roman era, as the technology for cement was lost then later rediscovered.

    Rope bridges, a simple type of suspension bridge, were used by the Inca civilization in the Andes mountains of South America, just prior to European colonization in the 1500s.

    During the 18th century there were many innovations in the design of timber bridges by Hans Ulrich, Johannes Grubenmann, and others. The first engineering book on building bridges was written by Hubert Gautier in 1716.

    With the Industrial Revolution in the 19th century, truss systems of wrought iron were developed for larger bridges, but iron did not have the tensile strength to support large loads. With the advent of steel, which has a high tensile strength, much larger bridges were built, many using the ideas of Gustave Eiffel.


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    Etymology
    The Oxford English Dictionary traces the origin of the word bridge to an Old English word brycg, of the same meaning, derived from a hypothetical Proto-Germanic root brugjō. There are cognates in other Germanic languages (for instance Brücke in German, brug in Dutch or bro in Danish and Swedish).

    The word for the Pope, pontiff, comes from the Latin word pontifex meaning "bridge builder".

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    Types of bridges

    There are four main types of bridges: beam bridges, cantilever bridges, arch bridges and suspension bridges.

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    By use
    A bridge is designed for trains, pedestrian or road traffic, a pipeline or waterway for water transport or barge traffic. In some cases there may be restrictions in use. For example, it may be a bridge carrying a highway and forbidden for pedestrians and bicycles, or a pedestrian bridge, possibly also for bicycles.

    An aqueduct is a bridge that carries water, resembling a viaduct, which is a bridge that connects points of equal height.

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    Decorative and ceremonial bridges
    To create a beautiful image, some bridges are built much taller than necessary. This type, often found in east-asian style gardens, is called a Moon bridge, evoking a rising full moon.

    Other garden bridges may cross only a dry bed of stream washed pebbles, intended only to convey an impression of a stream.

    Often in palaces a bridge will be built over an artificial waterway as symbolic of a passage to an important place or state of mind. A set of five bridges cross a sinuous waterway in an important courtyard of the Forbidden City in Beijing, the People's Republic of China. The central bridge was reserved exclusively for the use of the Emperor, Empress, and their attendants.

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    Index to types of bridges


    Image:NagasakiMeganebashi.jpg|
    Arch bridge

    Image:UniversityBridge-1Clip.jpg|
    Bascule bridge

    Image:Small footbridge.jpg|
    Beam bridge


    Image:Saltashrab.jpg|Brunnel Truss bridge
    Image:Concrete box girder bridge.JPG|
    Box girder bridge

    Image:Baumgardener's Covered Bridge Inside Center 3008px.jpg|
    Burr Arch Truss

    Image:ThreeTwrBrCenter.jpg|
    Cable-stayed bridge

    Image:ForthBridgeEdinburgh.jpg|
    Cantilever bridge

    Image:Puente del Alamillo.jpg|
    Cantilever spar cable-stayed bridge

    Image:Tarr steps clapper bridge.jpg|
    Clapper bridge

    Image:Australia sydney-404.jpg|
    Compression arch suspended-deck bridge

    Image:CurlingBridgeClip.jpg|
    Rolling, or curling bridge

    Image:Fort ticonderoga drawbridge to demilune.jpg|
    Drawbridge

    Image:NoImageYetRectFramed.png|
    Extradosed bridge

    Image:EastbankEsplanade.jpg|
    Floating bridge

    Image:Hoernbruecke.jpg|
    Folding bridge

    Image:GirderBridge2.jpg|
    Girder bridge

    Image:Guilford vermont bridge covered bridge interior 20040820.jpg|
    Lattice bridge

    Image:BNSFBridgeClip.jpg|
    Lift bridge

    Image:Vallorcine footpath bridge 2003-12-13.jpg|
    Log bridge

    Image:PlateGirderUnderTracks.jpg|
    Plate girder bridge

    Image:ArmyPontoonBr.jpg|
    Pontoon bridge

    Image:Uppsala Ultunabron02 2005-06-16.jpg|
    Retractable bridge
    (Thrust bridge)

    Image:SegmentalBridgeFtLauderdale.jpg|
    Segmental bridge

    Image:ProposedSFOBBEasternSpan.jpg|
    Self-anchored suspension bridge

    Image:WinnepegBridge.jpg|
    Side-spar cable-stayed bridge

    Image:CapilanoBridge.jpg|
    Simple suspension bridge

    Image:StepStoneBridge.jpg|
    Step-stone bridge

    Image:Holzbrücke bei Essing 1.jpg|
    Stressed ribbon bridge

    Image:BridgeSubmerging4.jpg|
    Submersible bridge

    Image:suspension.bridge.bristol.arp.750pix.jpg|
    Suspension bridge

    Image:Railway swing bridge.jpg|
    Swing bridge

    Image:Tournai Pont levant Notre Dame 20040520-014.jpg|
    Table bridge

    Image:FortPittBridge.jpg|
    Tied arch bridge
    (Bowstring bridge)

    Image:Millenium_bridge_close.jpg|
    Tilt bridge

    Image:Newport.transporter.750pix.jpg|
    Transporter bridge

    Image:AlhambraTrestle.jpg|
    Trestle

    Image:Eastbound_over_SCB.jpg|
    Truss arch bridge

    Image:LittleManateeRiver.jpg|
    Truss bridge

    Image:Conwy Castle 2.jpg|
    Tubular bridge

    Image:Grammene-vierendeelbridge 20030618.jpg|
    Vierendeel bridge

    Image:BoxerwoodDotComZigZag.jpg|
    Zig-zag bridge




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    Index to bridge related topics


    Image:Titanbridger.jpg|
    Armoured vehicle-launched bridge

    Image:Pont_du_gard.jpg|
    Aqueduct

    Image:PontBailey800px.jpg|
    Bailey bridge

    Image:BalsaBridge_Break.jpg|
    Balsa wood bridge breaking under load

    Image:WWI bridge of boats Scheldt.jpg|
    Bridge of boats

    Image:Claude Monet-Waterlilies.jpg|
    Bridges in art

    Image:CaissonSchematic.jpg|
    Caisson

    Image:Guilford vermont covered bridge 20040820.jpg|
    Covered bridge

    Image:IRBSideViewClip.jpg|
    Inca rope bridge

    Image:JetwayAtVancouverBC.jpg|
    Jetway

    Image:16 Bay With Link 4.jpg|
    Medium Girder Bridge

    Image:SFTGMoonBridge.jpg|
    Moon bridge

    Image:Paying Toll on passing a Bridge From a Painted Window in the Cathedral of Tournay Fifteenth Century.png|
    Toll bridge

    Image:Trogbrücke_Magdeburg.JPG|
    Water bridge

    Image:WeighBridge5500.JPG|
    Weigh bridge

    Image:Toronto-bloorviaduct.jpg|
    Viaduct



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    Bridge structural and evolutionary taxonomy





    Bridges may be classified by how the four forces of tension, compression, bending and shear are distributed through their structure. Most bridges will employ all of the principle forces to some degree, but only a few will predominate. The separation of forces may be quite clear. In a suspension or cable-stayed span, the elements in tension are distinct in shape and placement. In other cases the forces may be distributed among a large number of members, as in a truss, or not clearly discernible to a casual observer as in a box beam. Bridges can also be classified by their lineage, which is shown as the vertical axis on the diagram to the right.


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    Efficiency





    A bridge's structural efficiency may be considered to be the ratio of load carried to bridge weight, given a specific set of material types. In one common challenge students are divided into groups and given a quantity of wood sticks, a distance to span, and glue, and then asked to construct a bridge that will be tested to destruction by the progressive addition of load at the center of the span. The bridge taking the greatest load is by this test the most structurally efficient. A more refined measure for this exercise is to weigh the completed bridge rather than measure against a fixed quantity of materials provided and determine the multiple of this weight that the bridge can carry, a test that emphasizes economy of materials and efficient glue joints (see ''balsa wood bridge'').

    A bridge's economic efficiency will be site and traffic dependent, the ratio of savings by having a bridge (instead of, for example, a ferry, or a longer road route) compared to its cost. The lifetime cost is composed of materials, labor, machinery, engineering, cost of money, insurance, maintenance, refurbishment, and ultimately, demolition and associated disposal, recycling, and reuse. Bridges employing only compression are relatively inefficient structurally, but may be highly cost efficient where suitable materials are available near the site and the cost of labor is low. For medium spans, trusses or box beams are usually most economical, while in some cases, the appearance of the bridge may be more important than its cost efficiency. The longest spans usually require suspension bridges.


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    Notable bridges


      Chicago Skyway - USA, a 7.8-mile toll bridge bypassing much of the southwest of Chicago
      Sunshine Skyway Bridge - USA, longest cable-stayed concrete bridge in the world. Replaced a cantilever truss structure which partially collapsed in 1980 as a result of collision by a freighter.

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    Special Installations
    Some bridges carry special installations such as the tower of Nový Most bridge in Bratislava which carries a restaurant. On other suspension bridge towers transmission antennas are installed.

    A bridge can carry overhead powerlines as the Storstrøm Bridge.

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    Catastrophic collapses




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    See also


     
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    Scientus.org Dictionary (Yet Another Wiki) RC : 1.39
    This article is licensed under the GNU Free Documentation License [copyleft]. It uses material from the Wikipedia article "Bridge". link