Bridge

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This article is about the edifice (including an index to articles on specific bridge types). For other uses, see Bridge (disambiguation).

A log bridge in the French Alps near Vallorcine.

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.

1 History of bridges
2 Etymology
3 Types of bridges
4 Bridge structural and evolutionary taxonomy
5 Efficiency
6 Special Installations
7 See also
8 External links

[edit] History of bridges

The famous Si-o-se Pol bridge over Zayandeh rud river is the epitome of Safavid bridge design. Isfahan, Iran.

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. One type of cement, called pozzolana, consisted of water, lime, sand, and volcanic rock. 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.

[edit] 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, brúgv in Faroese or bro in Danish, Norwegian and Swedish).

The word for the Pope, pontiff, comes from the Latin word pontifex meaning "bridge builder".It can also mean just "builder".

[edit] Types of bridges

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

[edit] 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.

The area underneath several bridges have become makeshift shelters and homes to homeless people.

The undersides of bridges all around the world are spots of prevalent graffiti.

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

[edit] 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.

[edit] Index to types of bridges

Arch bridge	Bascule bridge	Beam bridge	Brunel Truss bridge or lenticular truss
Box girder bridge	Cable-stayed bridge	Cantilever bridge	Cantilever spar cable-stayed bridge
Clapper bridge	Compression arch suspended-deck bridge	Curling bridge	Drawbridge
Extradosed bridge	Floating bridge	Folding bridge	Girder bridge
Lift bridge	Log bridge	Plate girder bridge	Pontoon bridge
Retractable bridge (Thrust bridge)	Segmental bridge	Self-anchored suspension bridge	Side-spar cable-stayed bridge
Simple suspension bridge	Step-stone bridge	Stressed ribbon bridge	Submersible bridge
Suspension bridge	Swing bridge	Table bridge	Tied arch bridge (Bowstring bridge)
Tilt bridge	Transporter bridge	Trestle	Truss arch bridge
Truss bridge	Tubular bridge	Vierendeel bridge	Zig-zag bridge

[edit] Index to bridge related topics

Armoured vehicle-launched bridge	Aqueduct	Bailey bridge	Balsa wood bridge breaking under load
Bridge of boats	Bridges in art	Brown truss	Burr Arch Truss
Caisson	Covered bridge	Double decker bridge	Eyebar
Hoogholtje bridge	Inca rope bridge	Jetway	Lattice girder (laced strut or tie)
Lattice truss (Town's lattice truss)	Medium Girder Bridge	Moon bridge	Toll bridge
Water bridge	Weigh bridge	Viaduct

[edit] Bridge structural and evolutionary taxonomy

A bridge taxonomy showing evolutionary relationships

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 principal 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.

[edit] Efficiency

Charles Bridge in Prague

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 replacement, less the value of scrap and reuse of components. 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.

[edit] 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.

[edit] See also

Bridge related articles
Articles
Bridge (main article)
Moveable bridge
Types of bridges
Beam bridge
Cantilever bridge
Arch bridge
Suspension bridge
Lists of Bridges
All bridges
Notable bridges
By length
Largest suspension bridges
Largest cable-stayed bridges
Largest cantilever bridges
Arch bridges
Bridge disasters
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