{{about|the structure|the card game|Contract bridge|other uses|Bridge (disambiguation)|and|Bridges (disambiguation)}}

{{refimprove|date=May 2015}}

{{Use mdy dates|date=January 2015}}

[[Image:Akashi-kaikyo bridge3.jpg|thumb|right|250px|The [[Akashi Kaikyō Bridge]] in [[Japan]], currently the world's longest suspension span.]]

[[Image:Sio se pol.jpg|thumb|right|337px|The [[Siosepol]] bridge over [[Zayandeh River]] is an example of [[Safavid dynasty]] (1502–1722) bridge design. [[Esfahan]], [[Iran]]]]

{{Public Infrastructure}}

A '''bridge''' is a [[nonbuilding structure|structure]] built to [[span (engineering)|span]] physical obstacles without closing the way underneath such as a [[body of water]], [[valley]], or [[road]], for the purpose of providing passage over the obstacle. There are many different designs that each serve a particular purpose and apply to different situations. Designs of bridges vary depending on the function of the bridge, the nature of the [[terrain]] where the bridge is constructed and anchored, the material used to make it, and the funds available to build it.

==Etymology==

The ''[[Oxford English Dictionary]]'' traces the origin of the word ''bridge'' to an [[Old English]] word ''brycg'', of the same meaning.<ref>{{cite book|publisher=Oxford University Press|author=Fowler|title=The Concise Oxford Dictionary|date=1925|page=102}}</ref> The word can be traced directly back to Proto-Indo-European ''*bʰrēw-.'' The word for the [[Contract bridge|card game of the same name]] has a different origin.

==History==

The first bridges made by humans were probably spans of cut wooden logs or planks and eventually stones, using a simple support and [[crossbeam]] arrangement. Some early Americans used trees or [[bamboo]] poles to cross small caverns or wells to get from one place to another. A common form of lashing sticks, logs, and [[deciduous]] branches together involved the use of long reeds or other harvested fibers woven together to form a huge rope capable of binding and holding together the materials used in early bridges.{{citation needed|date=May 2015}}

[[File:Pont mycénien de Kazarma 2.jpg|thumb|left|The [[Arkadiko Bridge]] in [[Greece]] (13th century BC), one of the oldest [[arch bridge]]s in existence]]

The [[Arkadiko Bridge]] is one of four [[Mycenean Greece|Mycenaean]] [[corbel arch]] bridges part of a former network of roads, designed to accommodate [[chariot]]s, between [[Tiryns]] and [[Epidauros]] in the [[Peloponnese]], in [[Greece]]. Dating to the Greek [[Bronze Age]] (13th century BC), it is one of the oldest arch bridges still in existence and use.

Several intact arched stone bridges from the [[Hellenistic age|Hellenistic era]] can be found in the [[Peloponnese]] in southern [[Greece]]<ref>{{cite book|author1=Kutz, Myer|title=Handbook of Transportation Engineering, Volume II: Applications and Technologies, Second Edition.|year=2011|publisher=McGraw-Hill Professional|isbn=978-00-7161-477-1}}</ref>

The greatest bridge builders of antiquity were the [[Roman Engineering|ancient Romans]].<ref>{{cite web|url=http://www.icomos.org/studies/bridges.htm |author=DeLony, Eric |title=Context for World Heritage Bridges |publisher=Icomos.org |year=1996 |deadurl=yes |archiveurl=https://web.archive.org/web/20050221084235/http://www.icomos.org/studies/bridges.htm |archivedate=February 21, 2005 }}</ref> The Romans built [[arch bridges]] and [[aqueduct (bridge)|aqueducts]] that could stand in conditions that would damage or destroy earlier designs. Some stand today.<ref name=historyworld>{{cite web| url=http://www.historyworld.net/wrldhis/PlainTextHistories.asp?historyid=ab97 |title=History of BRIDGES |publisher=Historyworld.net |date= |accessdate=January 4, 2012}}</ref> An example is the [[Alcántara Bridge]], built over the river [[Tagus]], in [[Spain]]. The Romans also used [[cement]], which reduced the variation of strength found in natural stone.<ref>{{cite web|url=http://www.pubs.asce.org/WWWdisplay.cgi?0103045 |title=Lessons from Roman Cement and Concrete |publisher=Pubs.asce.org |date= |accessdate=January 4, 2012}}</ref> One type of cement, called [[pozzolana]], consisted of water, [[lime (material)|lime]], sand, and [[volcanic rock]]. [[Brick]] and [[Mortar (masonry)|mortar]] bridges were built after the Roman era, as the technology for cement was lost then later rediscovered.

The ''[[Arthashastra]]'' of [[Kautilya]] mentions the construction of dams and bridges.<ref>Dikshitar, V. R. R. Dikshitar (1993). ''The Mauryan Polity'', Motilal Banarsidass, p. 332 ISBN 81-208-1023-6.</ref> A [[Mauryan]] bridge near [[Girnar]] was surveyed by [[James Prinsep|James Princep]].<ref name=Dutt/> The bridge was swept away during a flood, and later repaired by Puspagupta, the chief architect of emperor [[Chandragupta I]].<ref name=Dutt/> The bridge also fell under the care of the [[Yavana]] Tushaspa, and the [[Satrap]] Rudra Daman.<ref name=Dutt>Dutt, Romesh Chunder (2000). ''A History of Civilisation in Ancient India: Vol II'', Routledge, p. 46, ISBN 0-415-23188-4.</ref> The use of stronger bridges using plaited bamboo and iron chain was visible in India by about the 4th century.<ref>"suspension bridge" in Encyclopædia Britannica (2008). 2008 Encyclopædia Britannica, Inc.</ref> A number of bridges, both for military and commercial purposes, were constructed by the [[Mughal Empire|Mughal]] administration in India.<ref>Nath, R. (1982). ''History of Mughal Architecture'', Abhinav Publications, p. 213, ISBN 81-7017-159-8.</ref>

Although large Chinese bridges of wooden construction existed at the time of the [[Warring States]], the oldest surviving stone bridge in China is the [[Zhaozhou Bridge]], built from 595 to 605 AD during the [[Sui Dynasty]]. This bridge is also historically significant as it is the world's oldest open-[[spandrel]] stone segmental arch bridge. European segmental arch bridges date back to at least the [[Alconétar Bridge]] (approximately 2nd century AD), while the enormous Roman era [[Trajan's Bridge]] (105 AD) featured open-spandrel segmental arches in wooden construction.{{citation needed|date=May 2015}}

[[Inca rope bridge|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 16th century.

During the 18th century there were many innovations in the design of timber bridges by Hans Ulrich, [[Johannes Grubenmann]], and others. The first book on bridge engineering was written by [[Hubert Gautier]] in 1716. A major breakthrough in bridge technology came with the erection of [[the Iron Bridge]] in [[Coalbrookdale]], England in 1779. It used [[cast iron]] for the first time as arches to cross the [[river Severn]].{{citation needed|date=May 2015}}

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]].{{citation needed|date=May 2015}}

In 1927 [[welding]] pioneer [[Stefan Bryła]] designed the first welded road bridge in the world, the [[Maurzyce Bridge]] which was later built across the river [[Słudwia River|Słudwia]] at Maurzyce near [[Łowicz]], Poland in 1929. In 1995, the [[American Welding Society]] presented the Historic Welded Structure Award for the bridge to Poland.<ref>{{cite web|url=http://www.weldinghistory.org/whistoryfolder/welding/wh_1900-1950.html |title=Welding Timeline 1900–1950 |last=Sapp |first=Mark E. |date=February 22, 2008 |publisher=WeldingHistory.org |accessdate=April 29, 2008 |deadurl=yes |archiveurl=https://web.archive.org/web/20080803060938/http://www.weldinghistory.org/whistoryfolder/welding/wh_1900-1950.html |archivedate=August 3, 2008 }}</ref>

==Types of bridges==

Bridges can be categorized in several different ways. Common categories include the type of structural elements used, by what they carry, whether they are fixed or movable, and by the materials used.

===Structure type===

Bridges may be classified by how the forces of [[tension (mechanics)|tension]], [[compression (physical)|compression]], [[bending]], [[torsion (mechanics)|torsion]] and [[Shear stress|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.{{citation needed|date=May 2015}}

{| class="wikitable"

|-

| align="center" |[[File:BeamBridge-diagram.svg|200px]]'''[[Beam bridge]]'''{{br}}

|Beam bridges are horizontal beams supported at each end by substructure units and can be either ''[[simply supported]]'' when the beams only connect across a single span, or ''continuous'' when the beams are connected across two or more spans. When there are multiple spans, the intermediate supports are known as [[bridge pier|piers]]. The earliest beam bridges were simple logs that sat across streams and similar simple structures. In modern times, beam bridges can range from small, wooden beams to large, steel boxes. The vertical force on the bridge becomes a [[Shear stress|shear]] and [[Bending|flexural]] load on the beam which is transferred down its length to the substructures on either side<ref name=beambridge>{{cite web | url=http://www.design-technology.org/beambridges.htm | title=Beam bridges | publisher=Design Technology | accessdate=May 14, 2008}}</ref> They are typically made of steel, concrete or wood. Beam bridge spans rarely exceed {{convert|250|ft|m}} long, as the flexural stresses increase proportional to the square of the length (and deflection increases proportional to the 4th power of the length).<ref>[http://www.engineersedge.com/beam_bending/beam_bending1.htm Structural Beam Deflection Stress Bending Equations / Calculation Supported on Both Ends Uniform Loading]. Engineers Edge. Retrieved on April 23, 2013.</ref> However, the main span of the [[Rio-Niteroi Bridge]], a box girder bridge, is {{convert|300|m|ft}}.{{citation needed|date=May 2015}}

The world's longest beam bridge is [[Lake Pontchartrain Causeway]] in southern [[Louisiana]] in the United States, at {{convert|23.83|mi|km}}, with individual spans of {{convert|56|ft|m}}.<ref>{{cite journal|date=May 28, 1956|title=A big prefabricated bridge|journal=[[Life (magazine)|Life]]|volume=40|issue=22|pages=53–60}}</ref> Beam bridges are the most common bridge type in use today.{{citation needed|date=May 2015}}

|-

| align="center" |[[File:TrussBridge-diagram.svg|200px]]'''[[Truss bridge]]'''{{br}}

| A truss bridge is a bridge whose load-bearing superstructure is composed of a truss. This truss is a structure of connected elements forming triangular units. The connected elements (typically straight) may be stressed from tension, compression, or sometimes both in response to dynamic loads. Truss bridges are one of the oldest types of modern bridges. The basic types of truss bridges shown in this article have simple designs which could be easily analyzed by nineteenth and early twentieth century engineers. A truss bridge is economical to construct owing to its efficient use of materials.

|-

| align="center" |[[File:CantileverBridge-diagram.svg|200px]]'''[[Cantilever bridge]]'''{{br}}

|[[Cantilever bridge]]s are built using [[cantilever]]s—horizontal beams supported on only one end. Most cantilever bridges use a pair of [[continuous span]]s that extend from opposite sides of the supporting piers to meet at the center of the obstacle the bridge crosses. Cantilever bridges are constructed using much the same materials & techniques as beam bridges. The difference comes in the action of the forces through the bridge.

Some cantilever bridges also have a smaller beam connecting the two cantilevers, for extra strength.

The largest cantilever bridge is the {{convert|549|m|adj=on}} [[Quebec Bridge]] in Quebec, Canada.

|-

| align="center" |[[File:ArchBridge-diagram.svg|200px]]'''[[Arch bridge]]'''{{br}}

|Arch bridges have [[abutments]] at each end. The weight of the bridge is thrust into the [[abutments]] at either side. The earliest known arch bridges were built by the Greeks, and include the [[Arkadiko Bridge]].

With the span of {{convert|220|m}}, the [[Solkan Bridge]] over the [[Soča]] River at [[Solkan]] 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 {{convert|5000|t}} of stone blocks in just 18 days, is the second largest stone arch in the world, surpassed only by the Friedensbrücke (Syratalviadukt) in [[Plauen]], and the largest railroad stone arch. The arch of the Friedensbrücke, which was built in the same year, has the span of {{convert|90|m|0|abbr=on}} and crosses the valley of the [[Syrabach]] 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.<ref>{{cite conference |url=http://books.google.com/books?id=E7ywmb24EQMC&lpg=PA121&dq=%22world%20famous%20arch%20bridges%20in%20slovenia%22&pg=PA121#v=onepage&q=%22world%20famous%20arch%20bridges%20in%20slovenia%22&f=false |title=World Famous Arch Bridges in Slovenia |language=English, French |author=Gorazd Humar |date=September 2001 |publisher=Presses des Ponts |booktitle=Arch'01: troisième Conférence internationale sur les ponts en arc Paris: |editor=Charles Abdunur |pages=121–124 |location=Paris |ISBN=2-85978-347-4}}</ref>

The world's current largest arch bridge is the [[Chaotianmen Bridge]] over the [[Yangtze River]] with a length of {{convert|1,741|m|ft|0|abbr=on}} and a span of {{convert|552|m|ft|0|abbr=on}}. The bridge was opened April 29, 2009 in [[Chongqing]], China.<ref name=Chaotianmen >{{cite web | url=http://www.guinnessworldrecords.com/records-1/longest-bridge-steel-arch-bridge/# | publisher=Guinness World Records | accessdate=February 18, 2013 | title=Longest bridge, steel arch bridge }}</ref>

|-

| align="center" |[[File:TiedarchBridge-diagram.svg|200px]]'''[[Tied arch bridge]]'''{{br}}

|Tied arch bridges have an arch-shaped superstructure, but differ from conventional arch bridges. Instead of transferring the weight of the bridge and traffic loads into thrust forces into the abutments, the ends of the arches are restrained by tension in the bottom chord of the structure. They are also called bowstring arches.

|-

| align="center" |[[File:SuspensionBridge-diagram.svg|200px]]'''[[Suspension bridge]]'''{{br}}

|Suspension bridges are suspended from cables. The earliest suspension bridges were made of ropes or vines covered with pieces of bamboo. In modern bridges, the cables hang from towers that are attached to caissons or cofferdams. The caissons or cofferdams are implanted deep into the floor of a lake or river. Sub-types include the [[simple suspension bridge]], the [[stressed ribbon bridge]], the [[underspanned suspension bridge]], the [[suspended-deck suspension bridge]], and the [[self-anchored suspension bridge]]. There is also what is sometimes called a "semi-suspension" bridge, of which the [[Ferry Bridge Burton|Ferry Bridge]] in Burton-upon-Trent is the only one of its kind in Europe.<ref>A.O.P. Guide to Burton-on-Trent, 1911, p.13</ref> This is a three-span footbridge totalling 240 feet in length, the suspension consisting of flat bar-iron riveted to the main girders, not anchored at a distance. It was designed and constructed by a local firm, Thornewill and Warham.

The longest suspension bridge in the world is the {{convert|3909|m|0|abbr=on}} [[Akashi Kaikyō Bridge]] in Japan.<ref name=suspension>{{cite news | url=http://www.constructionequipmentguide.com/story.asp?story=8153&headline=The%20Mighty%20Mac:%20A%20Sublime%20Engineering%20Feat | title=The Mighty Mac: A Sublime Engineering Feat | first=Pete | last=Sigmund | publisher=Construction Equipment Guide | date=February 7, 2007 | accessdate=May 14, 2008}}</ref>

|-

| align="center" |[[File:CableStayedBridge-diagram.svg|200px]]'''[[Cable-stayed bridge]]'''{{br}}

|[[Cable-stayed bridge]]s, like suspension bridges, are held up by cables. However, in a cable-stayed bridge, less cable is required and the towers holding the cables are proportionately higher.<ref name=cable>{{cite web | url=http://www.newton.dep.anl.gov/askasci/eng99/eng99373.htm | title=Cable Stay vs Suspension Bridges | first=Andy | last=Johnson | publisher=U.S. Department of Energy}}</ref> The first known cable-stayed bridge was designed in 1784 by C. T. (or C. J.) Löscher.<ref>[http://books.google.ca/books?id=AhSgrMcT4sgC&pg=PA5&lpg=PA5&dq=loescher+cable-stayed&source=bl&ots=Ldmb12QZ67&sig=Au-TF0YlWc2pQOrtw7CmDufITds&hl=en&sa=X&ei=LfenUZXOLqri0QGCtoFo&ved=0CCwQ6AEwAA#v=onepage&q=loescher%20cable-stayed&f=false Earliest cable-stayed bridge]</ref><ref>[http://www.contech.co.nz/uploaded/Marcel%20Poser%20-%20Cable%20Stayed%20Structures%20and%20Stay%20Cable%20Technology.pdf Earliest cable-stayed bridge]</ref>

The longest cable-stayed bridge since 2012 is the [[Russky Bridge]] in [[Vladivostok]], [[Russia]].<ref>{{cite news|publisher=The Guardian|date=2 July 2012|author=Elder, Miriam|title=Russian city of Vladivostok unveils record-breaking suspension bridge|url=http://www.theguardian.com/world/2012/jul/02/russian-vladivostok-record-suspension-bridge|accessdate=3 February 2016}}</ref>

|}

===Fixed or movable bridges===

[[File:Moving a Bloomingdale Trail bridge from Ashland to Western on a Saturday in Chicago.webmhd.webm|thumb|Moving a [[Bloomingdale Trail]] bridge from Ashland to Western in [[Chicago]].]]

Most bridges are fixed bridges, meaning they have no moving parts and stay in one place until they fail or are demolished. Temporary bridges, such as [[Bailey bridge]]s, are designed to be assembled, and taken apart, transported to a different site, and re-used. They are important in military engineering, and are also used to carry traffic while an old bridge is being rebuilt. [[Movable bridge]]s are designed to move out of the way of boats or other kinds of traffic, which would otherwise be too tall to fit. These are generally electrically powered.{{citation needed|date=May 2015}}

===Double-decked bridges===

[[File:George Washington Bridge from New Jersey-edit.jpg|thumb|right|200px|The double-decked [[George Washington Bridge]], connecting [[New York City]] to [[Bergen County]], [[New Jersey]], USA, is the world's busiest bridge, carrying 102 million vehicles annually.<ref name="panynj.gov">{{cite web |url=http://www.panynj.gov/bridges-tunnels/george-washington-bridge.html |accessdate=September 13, 2013 |title=Port Authority of New York and New Jersey - George Washington Bridge|publisher= The Port Authority of New York and New Jersey}}</ref><ref name=abcgwb>{{cite web|url=http://abcnews.go.com/US/george-washington-bridge-painters-dangerous-job-top-worlds/story?id=17771877|title=GW Bridge Painters: Dangerous Job on Top of the World's Busiest Bridge|author1=Bod Woodruff |author2=Lana Zak |author3=Stephanie Wash |last-author-amp=yes |publisher=ABC News|date=November 20, 2012|accessdate=September 13, 2013}}</ref>]]

{{See also|List of multi-level bridges}}

Double-decked (or double-decker) bridges have two levels, such as the [[George Washington Bridge]], connecting [[New York City]] to [[Bergen County]], [[New Jersey]], USA, as the world's busiest bridge, carrying 102 million vehicles annually;<ref name="panynj.gov"/><ref name=abcgwb/> [[truss]] work between the roadway levels provided stiffness to the roadways and reduced movement of the upper level when the lower level was installed three decades after the upper level. The [[Tsing Ma Bridge]] and [[Kap Shui Mun Bridge]] in [[Hong Kong]] have six lanes on their upper decks, and on their lower decks there are two lanes and a pair of tracks for [[MTR]] metro trains. Some double-decked bridges only use one level for street traffic; the [[Washington Avenue Bridge (Minneapolis)|Washington Avenue Bridge]] in [[Minneapolis, Minnesota|Minneapolis]] reserves its lower level for automobile and light rail traffic and its upper level for pedestrian and bicycle traffic (predominantly students at the [[University of Minnesota]]). Likewise, in [[Toronto]], the [[Prince Edward Viaduct]] has five lanes of motor traffic, bicycle lanes, and sidewalks on its upper deck; and a pair of tracks for the [[Bloor–Danforth line|Bloor–Danforth]] [[Toronto subway and RT|subway line]] on its lower deck. The western span of the [[San Francisco–Oakland Bay Bridge]] also has two levels.

[[Robert Stephenson]]'s [[High Level Bridge]] across the [[River Tyne]] in [[Newcastle upon Tyne]], completed in 1849, is an early example of a double-decked bridge. The upper level carries a railway, and the lower level is used for road traffic. Other examples include [[Britannia Bridge]] over the [[Menai Strait]] and [[Craigavon Bridge]] in [[Derry]], [[Northern Ireland]]. The [[Oresund Bridge]] between [[Copenhagen]] and [[Malmö]] consists of a four-lane highway on the upper level and a pair of railway tracks at the lower level. [[Tower Bridge]] in London is different example of a double-decked bridge, with the central section consisting of a low level [[Bascule bridge|bascule span]] and a high level [[footbridge]].

===Viaducts===

{{main article|Viaduct}}

A viaduct is made up of multiple bridges connected into one longer structure. The longest and some of the highest bridges are viaducts, such as the [[Lake Pontchartrain Causeway]] and [[Millau Viaduct]].

===Three-way bridges===

[[File:Tridge Undercarriage.jpg|thumb|right|The three-way [[The Tridge (Midland, Michigan)|Tridge]]]]

{{main article|Three-way bridge}}

A three-way bridge has three separate spans which meet near the center of the bridge. The bridge appears as a "T" or "Y" when viewed from above. Three-way bridges are extremely rare. [[The Tridge (Midland, Michigan)|The Tridge]], [[Margaret Bridge]], and [[Y-Bridge (Zanesville, Ohio)|Zanesville Y-Bridge]] are examples.

===Bridge types by use===

[[File:Željeznički most, Mursko Središće (Croatia).1.jpg|thumb|right|The railway bridge over [[Mura (Drava)|Mura River]] in [[Mursko Središće]], [[Croatia]]]]

A bridge can be categorized by what it is designed to carry, such as trains, pedestrian or road traffic, a pipeline or waterway for water transport or barge traffic. An [[aqueduct (bridge)|aqueduct]] is a bridge that carries water, resembling a viaduct, which is a bridge that connects points of equal height. A road-rail bridge carries both road and rail traffic. A bridge can carry overhead power lines as does the [[Storstrøm Bridge]].{{citation needed|date=May 2015}}

Some bridges accommodate other purposes, such as the tower of [[Nový Most]] Bridge in [[Bratislava]], which features a restaurant, or a [[bridge-restaurant]] which is a bridge built to serve as a restaurant. Other suspension bridge towers carry transmission antennas.{{citation needed|date=May 2015}}

Bridges are subject to unplanned uses as well. The areas underneath some bridges have become makeshift shelters and homes to homeless people, and the undersides of bridges all around the world are spots of prevalent graffiti. Some bridges attract people attempting [[suicide]], and become known as [[suicide bridge]]s.{{citation needed|date=May 2015}}

===Bridge types by material===

[[File:Ironbridge 6.jpg|thumb|[[The Iron Bridge]] completed in 1781 was the first cast iron bridge.]]

[[File:Hiroshige39 okazaki.jpg|thumb|[[Okazaki-shuku|Okazaki]] Bridge, Japan, painted by [[Utagawa Hiroshige|Hiroshige]] 1833/1834]]

The materials used to build the structure are also used to categorize bridges. Until the end of the 18th Century, bridges were made out of timber, stone and masonry. Modern bridges are currently built in concrete, steel, fiber reinforced polymers (FRP), stainless steel or combinations of those materials. [[living root bridges|Living bridges]] have been constructed of live plants such as tree roots in India and vines in Japan.{{citation needed|date=May 2015}}

{| class="wikitable"

|-

! Bridge Type !! Materials Used

|-

| Cantilever || For small footbridges, the cantilevers may be simple beams; however, large cantilever bridges designed to handle road or rail traffic use trusses built from [[structural steel]], or box girders built from [[prestressed concrete]].<ref>{{cite web|title=Cantilever|url=http://www.bridgesofdublin.ie/bridge-building/types/cantilever|website=Bridges of Dublin}}</ref>

|-

| Suspension || The cables are usually made of [[steel cable]]s galvanised with [[zinc]],{{fact|reason=Galvanising is rare on highly stressed structural wires as it can cause cracking.|date=September 2016}} along with most of the bridge, but some bridges are still made with steel [[reinforced concrete]].<ref>{{cite web|title=Suspension Bridges|url=http://www.madehow.com/Volume-5/Suspension-Bridge.html|website=Made How}}</ref>

|-

| Arch || [[Stone]], [[brick]] and other such materials that are strong in compression and somewhat so in shear.

|-

| Beam || Beam bridges can use pre-stressed concrete, an inexpensive building material, which is then embedded with [[rebar]]. The resulting bridge can resist both compression and tension forces.<ref>{{cite web|title=Beam Bridges|url=https://www.pbs.org/wgbh/nova/lostempires/china/meetbeam.html|website=PBS}}</ref>

|-

| Truss ||The triangular pieces of Truss bridges are manufactured from straight and steel bars, according to the truss bridge designs.<ref>{{cite web|last1=K|first1=Aggeliki|last2=Stonecypher|first2=Lamar|title=Truss Bridge Designs|url=http://www.brighthubengineering.com/structural-engineering/63635-truss-bridge-designs/|website=Bright Hub Engineering}}</ref>

|}

==Aesthetics==

[[File:Stari_Most22.jpg|thumb|[[Stari Most]], World Heritage Site of [[Mostar]], [[Bosnia and Herzegovina]]]]

Most bridges are utilitarian in appearance, but in some cases, the appearance of the bridge can have great importance. Often, this is the case with a large bridge that serves as an entrance to a city, or crosses over a main harbor entrance. These are sometimes known as ''signature bridges''. Designers of bridges in parks and along parkways often place more importance to aesthetics, as well. Examples include the stone-faced bridges along the [[Taconic State Parkway]] in New York.

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.

==Bridge maintenance==

Bridge maintenance consisting of a combination of structural health monitoring and testing. This is regulated in country-specific engineer standards and includes e.g. an ongoing monitoring every three to six months, a simple test or inspection every two to three years and a major inspection every six to ten years. In Europe, the cost of maintenance is higher than spending on new bridges. The lifetime of welded steel bridges can be significantly extended by [[High Frequency Impact Treatment|aftertreatment of the weld transitions]] . This results in a potential high benefit, using existing bridges far beyond the planned lifetime.

[[File:Example HiFIT-treated assembly.jpg|thumb|Highway bridge with steel hollow box sections, performed for lifetime extension by welding aftertreatment]]

==Bridge failures==

<!-- [[bridge failure]] and [[bridge failures]] redirect here; be sure to update them if changing the section title -->

{{see also|List of bridge failures}}

The failure of bridges is of special concern for [[structural engineers]] in trying to learn lessons vital to bridge design, construction and maintenance. The failure of bridges first assumed national interest during the [[Victorian era]] when many new designs were being built, often using new materials.

In the United States, the [[National Bridge Inventory]] tracks the structural evaluations of all bridges, including designations such as "structurally deficient" and "functionally obsolete".

==Bridge monitoring==

There are several methods used to monitor the stress on large structures like bridges. The most common method is the use of an [[accelerometer]], which is integrated into the bridge while it is being built. This technology is used for long-term surveillance of the bridge.<ref>{{cite web|url=http://www.mnme.com/pdf/smartbridge.pdf|title=The new Minnesota smart bridge|work=mnme.com |accessdate=January 30, 2012}}</ref>

Another option for structural-integrity monitoring is "non-contact monitoring", which uses the [[Doppler effect]] (Doppler shift). A [[laser]] beam from a [[Laser Doppler Vibrometer]] is directed at the point of interest, and the vibration amplitude and frequency are extracted from the Doppler shift of the laser beam frequency due to the motion of the surface.<ref>{{cite web|url=http://www.polytec.com/us/solutions/vibration-measurement/basic-principles-of-vibrometry/|title=Basic Principles of Vibrometry|work=polytec.com |accessdate=January 25, 2012}}</ref> The advantage of this method is that the setup time for the equipment is faster and, unlike an accelerometer, this makes measurements possible on multiple structures in as short a time as possible. Additionally, this method can measure specific points on a bridge that might be difficult to access.

==Visual index==

{{Further information|List of bridge types|List of longest bridges in the world}}

==See also==

{{Portal|Bridges}}

{{div col|2}}

* [[Architectural engineering]]

* [[Bridge chapel]]

* [[Bridge tower]]

* [[Bridge to nowhere]]

* [[Bridges Act]]

* [[BS 5400]], a British Standard for steel, concrete and composite bridges

* [[BT Centre for Major Programme Management]]

* [[Coal trestle]]

* [[Cost overrun]] in bridge construction

* [[Cross-sea traffic ways]]

* [[Culvert]]

* [[Deck (bridge)|Deck]]

* [[Footbridge]]

* [[Landscape architecture]]

* [[Megaproject]]

* [[Overpass]]

* [[Rigid-frame bridge]]

* [[Transporter bridge]]

* [[Tensegrity]]

* [[Trestle bridge]]

* [[Tunnel]]

{{div col end}}

==References==

{{reflist|35em}}

==Further reading==

* Brown, David J. ''Bridges: Three Thousand Years of Defying Nature''. Richmond Hill, Ont: Firefly Books, 2005. ISBN 1-55407-099-6.

* Sandak, Cass R. ''Bridges''. An Easy-read modern wonders book. New York: F. Watts, 1983. ISBN 0-531-04624-9.

* Whitney, Charles S. ''Bridges of the World: Their Design and Construction''. Mineola, NY: Dover Publications, 2003. ISBN 0-486-42995-4 (Unabridged republication of ''Bridges : a study in their art, science, and evolution''. 1929.)

==External links==

{{Sister project links|voy=no|Bridge}}

* [http://bridges.lib.lehigh.edu/ Digital Bridge: Bridges of the Nineteenth Century], a collection of digitized books at Lehigh University

* [http://en.structurae.de/ Structurae] – International Database and Gallery of Engineerings Structures with over 10000 Bridges.

* [http://www.fhwa.dot.gov/bridge/ U.S. Federal Highway Administration Bridge Technology]

* [http://tbl.tec.fukuoka-u.ac.jp/index-en.shtml The Museum of Japanese Timber Bridges] [[Fukuoka University]]

* [http://www.bridge-info.org "bridge-info.org": site for bridges]

* [http://www.cnngo.com/explorations/none/24-worlds-most-amazing-bridges-062644] (CNN) 24 of the World's Most Amazing Bridges -retrieved April 30, 2011

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[[Category:Structural engineering]]

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