bridges

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.

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.

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".

Types of bridges

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

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.

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, China. The central bridge was reserved exclusively for the use of the Emperor, Empress, and their attendants.

Index to types of bridges

Index to bridge related topics

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.

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. 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.

Notable bridges

• Albert Edward Bridge - England, large single span cast iron railway bridge similar to Victoria Bridge
• Akashi-Kaikyo Bridge - Japan, suspension bridge with the longest section span of 1.9 km.
• Bosphorus Bridge - Turkey, connects Asia and Europe
• Brooklyn Bridge - connecting the New York City boroughs of Manhattan and Brooklyn.
• Charles Bridge - Czech Republic, famous 14th century bridge in Prague
• Chicago Skyway - USA, a 7.8-mile toll bridge bypassing much of the southwest of Chicago
• Confederation Bridge - Canada, world's longest bridge over waters that freeze.
• Forth Railway Bridge - Scotland, one of the most famous cantilever bridges in the world.
• Golden Gate Bridge - USA, one of the most famous suspension bridges in the world.
• Great Belt Fixed Link, Eastern Bridge - Denmark, second longest section span of 1.6 km
• Hercilio Luz Bridge - Florianopolis, Brazil, longest Brazilian suspension bridge, one of the 100 largest suspension bridges of the world and one of the oldest hanging bridges in the world.
• The Iron Bridge - England, the world's first iron bridge.
• Jamuna Bridge- Bangladesh, longest rail-road bridge in south asia , 2nd longest in world.
• Lake Pontchartrain Causeway - USA, spanning Lake Pontchartrain in south Louisiana, it is the longest bridge in the world at 23.87 miles (38.41 km).
• Lupu Bridge- China, longest single steel arch.
• Mackinac Bridge - USA, Opened to traffic in 1957, connecting the two peninsulas of Michigan; held the title of the world's longest two tower suspension bridge between anchorages until the 1990s.
• Mahatma Gandhi Setu - India, the longest river bridge in the world.
• Menai Suspension Bridge - Wales, first road suspension bridge in the world.
• Millau Viaduct - France, the tallest vehicular bridge in the world.
• Øresundbroen/Öresundsbron - Denmark - Sweden - Built year 2000. Connects Sweden with Denmark and Northern Europe with Europe
• Overtoun Bridge, - Scotland, dogs have leaped to their deaths from this bridge, leading to urban legends.
• Palace Bridge - St Petersburg, Russia, one of iconic images of the city
• Penang Bridge - Malaysia, longest bridge in Southeast Asia.
• Québec Bridge - Canada, largest cantilever bridge in the world.
• Rio-Antirio bridge - Greece, the longest cable-stayed bridge in the world.
• Rio-Niterói Bridge - Brazil, highest central span in the world.
• San Francisco-Oakland Bay Bridge - USA, especially for seismic retrofit and eastern span replacement.
• Sundial Bridge - USA, a dramatic single cantilever spar cable stayed span for pedestrians.
• 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.
• Sydney Harbour Bridge - Australia, arguably the best-known suspended-deck compression arch bridge, also the world's widest long span bridge (according to Guinness World Records).
• Tacoma Narrows Bridge - USA, famous for its collapse due to aerodynamic effects.
• Tatara Bridge - Japan, largest span cable-stayed bridge.
• Tower Bridge - London, England, and a symbol of this city.
• Trajan's bridge - Romania, ancient Roman bridge over the river Danube, only fragments visible.
• Tsing Ma Bridge - Hong Kong, the world's longest rail & road suspension bridge
• Tyne Bridge - England, one of Northern England's most iconic structures.
• Vasco da Gama Bridge - Portugal, the longest bridge in Europe at 17.2 km.
• Verrazano-Narrows Bridge - USA - longest suspension bridge in USA.
• Victoria Bridge - England large single span cast iron railway bridge similar to Albert Edward Bridge
• Victoria Falls Bridge - linking Zimbabwe to Zambia, built in 1905 as part of the projected Cape-Cairo railway.
• Zakim Bunker Hill Bridge - USA, built during Boston's Big Dig, the widest cable-stayed bridge.

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.

Catastrophic collapses

See also

• Architectural structure
• BASE jumping
• List of bridges
• List of bridges by length
• List of largest suspension bridges
• Moveable bridge
• List of bridge disasters

External links

• Structurae - International Database and Gallery of Structures with over 10 000 Bridges.
• American Society of Civil Engineers History and Heritage of Civil Engineering - Bridges
• Bridge Building — Art and Science Comprehensive explanations about bridges.
• Bridge Basics A guide to bridge terminology and styles
• Bridge disasters
• A dictionary of bridge terms
• Digital Bridge Library at Lehigh University
• Flickr Pictures tagged with Bridge by most interesting
• Bridges and Tunnels of Allegheny County and Pittsburgh, PA Details of over 2,000 bridges of 8 feet span or greater. Bridge engineers hold their conventions in Pittsburgh.
• Federal Highway Administration Bridge Technology
• Video on how bridges are made (Grade school level educational film by National Association of Manufactures.) Caution: Other links on this page may lead to politically biased material.