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{{Short description|Structure built to span physical obstacles}}
{{Short description|Structure built to span physical obstacles}}
{{about|the structure|the card game|Contract bridge|other uses|Bridge (disambiguation)|and|Bridges (disambiguation)}}
{{about|the structure|the card game|Contract bridge|other uses|Bridge (disambiguation)|and|Bridges (disambiguation)}}
{{good article}}
{{Use dmy dates|date=August 2024}}
{{Use dmy dates|date=August 2024}}
[[File:Temporary wooden footbridge leading to the city of Luang Prabang.jpg|thumb|upright=1.35|A temporary wooden footbridge leading to [[Luang Prabang]] in Laos]]
{{Use American English|date=August 2025}}
A '''bridge''' is a structure built to [[Span (engineering)|span]] a physical obstacle (such as a [[body of water]], [[valley]], road, or railway) without blocking the path underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually something that is otherwise difficult or impossible to cross. There are many different designs of bridges, each serving a particular purpose and applicable to different situations. Designs of bridges vary depending on factors such as 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.
{{Bridge sidebar}}
A '''bridge''' is a [[Structure#Load-bearing|structure]] designed to span an obstacle, such as a river or valley, allowing vehicles, pedestrians, and other loads to pass across. Most bridges consist of a flat [[Deck (bridge)|deck]], supported by structures such as beams, arches, or cables. These structures rest on a [[Foundation (engineering)|foundation]] that is carefully designed to prevent the bridge from settling into the subsoil. Bridges can be constructed in a wide variety of forms, depending on their purpose and location. Notable types include [[viaduct]]s, which cross wide valleys; [[trestle bridge|trestle]]s to carry heavy trains; and [[pontoon bridge]]s which float on water.


The earliest bridges were likely made with fallen trees and [[stepping stones]]. The [[Neolithic]] people built [[boardwalk]] bridges across marshland. The [[Arkadiko Bridge]], dating from the 13th century BC, in the [[Peloponnese]] is one of the oldest [[arch bridge]]s in existence and use.
The [[Roman Empire|Romans]] and [[History of China#Ancient China|ancient Chinese]] built major [[arch bridge]]s of stone and timber. During the [[Renaissance]], advances in science and engineering led to wider bridge spans and more elegant designs. [[Concrete]] was perfected in the early 1800s, and proved to be superior to stone in many regards. With the [[Industrial Revolution]] came mass-produced steel, which enabled the creation of [[suspension bridge|suspension]] and [[cable-stayed bridge]]s that could span wide obstacles. Over time, the maximum achievable [[span (engineering)|span]] of bridges has steadily increased, reaching [[List of longest suspension bridge spans|{{convert|2|km|mile|sp=us}} in 2022]].


==Etymology==
The design of a bridge must satisfy many requirements, such as connecting to a transportation network, providing adequate [[Clearance (civil engineering)#Vertical clearance|clearances]], and safely transporting its users. A bridge must be strong enough to support the weight of the bridge itself, as well as the traffic passing over the bridge. It must also tolerate violent, unpredictable stresses imposed by the environment, such as winds, floods, and earthquakes. To meet all these goals, bridge engineers use analytical methods such as [[limit state design]] and [[finite element method]].
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><ref name=":0">{{Cite dictionary |year=2001 |title=bridge |encyclopedia=The Concise Oxford Dictionary |publisher=Oxford University Press |url=https://archive.org/details/conciseoxforddic0000unse_t1j9/ |access-date=27 December 2022 |editor-last=Pearsall |editor-first=Judy |edition=10th |page=173 |isbn=0-19-860438-6}}{{Via|Internet Archive}}{{Registration required}}</ref>{{Rp|location=bridge<sup>1</sup>}}


The Oxford English Dictionary also notes that there is some suggestion that the word can be traced directly back to Proto-Indo-European ''*bʰrēw-.'' However, they also note that "this poses semantic problems."<ref>{{Cite web |title=Bridge: Etymology |url=https://www.oed.com/dictionary/bridge_n1?tab=etymology#13632036}}</ref>
Many bridges are admired for their beauty, and some spectacular bridges serve as iconic landmarks that provide a sense of pride and identity for the local community. In art and literature, bridges are frequently used as metaphors to represent connection or transition.  Bridges can create beneficial impacts to a community, including shorter transport times and increased [[gross domestic product]]; and also negative effects such as increased pollution and contributions to [[global warming]].
{{TOClimit|3}}


The origin of the word for the [[Contract bridge|card game of the same name]] is unknown,<ref name=":0" />{{Rp|location=bridge<sup>2</sup>}} but may be from folk etymology.<ref>{{Cite web |title=Login {{!}} Merriam-Webster Unabridged |url=https://unabridged.merriam-webster.com/subscriber/login?redirect_to=%2Funabridged%2Fbridge |access-date=2024-12-31 |website=unabridged.merriam-webster.com}}</ref>
==History==
{{main|History of bridges}}
 
===Antiquity===
[[File:Pont_du_Gard_BLS.jpg|thumb|right|alt=A stone arch bridge passing over a river valley |upright=1.6|The [[Pont du Gard]] aqueduct in France was built by the [[Roman Empire]] {{circa|40–60 AD}}.{{sfn|Brown|2005|pp=22-23}} ]]
 
The earliest forms of bridges were simple structures for crossing wetlands and creeks, consisting of wooden [[boardwalk]]s or [[Trunk (botany)|logs]].<ref name=early>{{Multiref
|{{harvnb|Bennett|2000|pp=1–3}}.
|{{harvnb|Bennett|1999|pp=9–11}}.
|{{harvnb|Brown|2005|pp=12–13}}.
|{{harvnb|Brunning|2001}}.
}}</ref>{{efn|Examples of early bridges include the [[Sweet Track]] and the [[Post Track]] in England, approximately 6,000 years old.{{sfn|Brunning|2001}} }} [[Pilings]]{{snd}}which are critical elements of bridge construction{{snd}}were used in Switzerland around 4,000 BC to support [[stilt house]]s built over water.{{sfn|Bennett|2000|p=2}} Several [[corbel arch]] bridges were built {{circa}} 13th century BC by the [[Mycenaean Greece]] culture, including the [[Arkadiko Bridge]], which is still in existence.{{sfn|Cruickshank|2010|p=47}} In the 7th century BC, [[Neo-Assyrian Empire|Assyrian]] king [[Sennacherib]] constructed stone aqueducts to carry water near the city of [[Ninevah]]; one of the aqueducts crossed a small valley at [[Jerwan]] with five corbelled arches, and was {{convert|280|m|ft|sp=us}} long and {{convert|20|m|ft|sp=us}} wide.{{sfn|Brown|2005|p=18}} In [[Babylonia]] in 626 BC, a bridge across the [[Euphrates]] was built with an estimated length of {{convert|120|to|200|m|ft|sp=us}}.{{sfn|Brown|2005|pp=18-19}} In India, the ''[[Arthashastra]]'' treatise by [[Kautilya]] mentions the construction of bridges and dams.{{sfn|Dikshitar |1993|p=332}} Ancient China has an extensive history of bridge construction, including [[cantilever bridge]]s, rope bridges, and bridges built across floating boats.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|p=298}}.
|{{harvnb|Bennett|1999|pp=11–12}}.
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref>
 
The [[Roman Engineering|ancient Romans]] built many durable bridges using advanced engineering techniques.<ref name=roman>{{Multiref
|{{harvnb|Bennett|1999|pp=14–17}}.
|{{harvnb|Bennett|2000|pp=3–5}}.
|{{harvnb|Brown|2005|pp=20–25}}.
|{{harvnb|Cruickshank|2010|pp=58, 63–65, 68–73}}.
}}</ref> Many Roman [[aqueduct (bridge)|aqueducts]]{{snd}}some still standing today{{snd}} used a semicircular arch style.<ref name=roman/> An example is the [[Alcántara Bridge]], built over the river [[Tagus]], in Spain.<ref>{{Multiref
|{{harvnb|Brown|2005|p=25}}.
|{{harvnb|Cruickshank|2010|pp=71–73}}.
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref> The Romans used [[cement]] as a construction material, which could be mixed with small rocks to form [[concrete]], or mixed with sand to form [[Mortar (masonry)|mortar]] to join bricks or stones.{{sfn|Delatte|2001}} Some Roman cements, particularly those containing [[Pozzolana|volcanic ash]], were waterproof.<ref>{{Multiref
|{{harvnb|Brown|2005|pp=20–25, 26}}.
|{{harvnb|Bennett|2000|pp=3–5}}.
|{{harvnb|Delatte|2001}}.
}}</ref>{{efn|The volcanic ash, called ''[[pozzolana]]'', was used to create a variety of concrete called [[Roman concrete]].{{sfn|Delatte|2001}}}} The enormous timber and stone [[Trajan's Bridge]] ({{circa}} 105 AD) crossed the [[Danube river]] and was over {{convert|900|meter|ft|sp=us}} long.<ref>{{Multiref
|{{harvnb|Brown|2005|p=23}}. Caption.
|{{harvnb|Bennett|1999|p=101}}.
|{{harvnb|Watson|1937|pp=84, 150}}.
|{{harvnb|Bjelić|2022}}.
}}</ref>
 
===300 to 1400===
[[File:Anji Bridge, Zhao County, 2020-09-06 05.jpg|thumb|left|alt=A graceful stone bridge spanning a river, with trees in the background|The [[Anji Bridge]], which uses a shallow [[segmental arch]], was built in China {{circa}} 600 AD.{{sfn|Brown|2005|p=26}}]]
<!-- [[File:Ponte Vecchio from Ponte alle Grazie.jpg|thumb|alt=A bridge with buildings atop it, passing over a river|upright=1.2|During the [[Middle Ages]], bridge builders began employing flatter [[segmental arch]]es{{snd}}such as those seen in the [[Ponte Vecchio]] above{{snd}}which allowed for longer spans compared to the previously used [[semicircular arch]]es.{{sfn|Bennett|2000|pp=6-7}}]]-->
 
The oldest surviving stone bridge in China is the [[Anji 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.<ref name=anji>{{Multiref
|{{harvnb|Cruickshank|2010|pp=11–12}}.
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref><!--
{{efn|The Anji bridge is also called the Zhaozhou Bridge or Great Stone Bridge.<ref name=anji/>}}
--> [[Inca rope bridge|Rope bridges]], a simple type of [[suspension bridge]], were used by the [[Inca Empire|Inca]] civilization in the [[Andes]] mountains of South America prior to European colonization in the 16th century.<ref>{{Multiref
|{{harvnb|Brown|2005|p=17}}.
|{{harvnb|Squier|1877 |pp=505–506, 540, 544–548, 558 }}.
}}</ref>
 
In [[Middle Ages|Medieval Europe]], bridge design capabilities declined after the [[fall of Rome]], but revived in the [[High Middle Ages]] in France, England, and Italy with the construction of bridges such as the [[Pont d'Avignon]], bridges of the [[Durance#Middle Ages|Durance]] river, the [[Old London Bridge]], and the [[Ponte Vecchio]] in Florence.<ref>{{Multiref
|{{harvnb|Bennett|2000|pp=5–7}}.
|{{harvnb|Brown|2005|pp=28–32}}.
|{{harvnb|Cruickshank|2010|pp=84, 86, 88–91, 96}}.
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref>
{{clear}}
 
===1400 to 1800===
[[File:West Montrose Covered Bridge (Oct. 2018).jpg|thumb|right|alt=A wooden bridge, covered with a roof, passing over a river|The [[superstructure]] of the [[West Montrose Covered Bridge]] is made of wood.{{sfn| "West Montrose Covered Bridge". ''Canada's Historic Places'' }}]]
In 15th and 16th century Europe, the [[Renaissance]] brought a new emphasis on science and engineering.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|pp=32–33}}.
|{{harvnb|Brown|2005|pp=36–38}}.
}}</ref> Figures such as [[Galileo Galilei]], [[Fausto Veranzio]], and [[Andrea Palladio]] (author of ''[[I quattro libri dell'architettura]]'') wrote treatises that applied a rigorous, analytic approach to architecture and building.{{sfn|Cruickshank|2010|pp=32-33}} Their innovations included [[truss bridge]]s and stone segmental arches, resulting in bridges such as Florence's [[Ponte Santa Trinita]], [[Rialto Bridge]] in Venice, and Paris's [[Pont Neuf]].<ref>{{Multiref
|{{harvnb|Bennett|2000|pp=7–10}}.
|{{harvnb|Brown|2005|pp=36–45}}.
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref> Military and commercial bridges were constructed in India by the [[Mughal Empire|Mughal]] administration.{{sfn| Nath|1982|pp=183-185}} The [[Asante Empire]] in Africa built bridges over [[streams]] and [[rivers]] using tree trunks and beams.<ref>{{Multiref
|{{harvnb|Wilks|1989|p=38}}.
|{{harvnb|Edgerton|2010 |p=78}}.
}}</ref> In the late 1700s, the design of arch bridges was revolutionized in Europe by [[Jean-Rodolphe Perronet]] and [[John Rennie the Elder|John Rennie]]. They designed arches that were flatter than semi-circular Roman arches. This yielded faster construction times, better water flow under the bridge, and more slender piers. These designs were used for bridges such as [[Pont de la Concorde (Paris)|Pont de la Concorde]] and [[New London Bridge]].<ref name=rennie>{{Multiref
|{{harvnb|Bennett|2000|pp=11–12}}.
|{{harvnb|Brown|2005|pp=44–45}}.
}}</ref>
 
With the advent of the [[Industrial Revolution]], [[cast iron]] became an important construction material for bridges.{{sfn|Brown|2005|pp=45-51}} Although cast iron was strong under [[compression (physics)|compression]], it was brittle, so it was supplanted by [[wrought iron]]{{snd}}which was more ductile and better under [[Tension (physics)|tension]].<ref>{{Multiref
|{{harvnb|Brown|2005|pp=47–51}}.
|{{harvnb|Bennett|2000|pp=16–18}}.
}}</ref> An [[the Iron Bridge|early iron bridge]] was built in Shropshire, England crossing the [[river Severn]].{{sfn|Cruickshank|2010|pp=50-51}} Several long suspension bridges were built in the early 1800s using iron [[eyebar]]s (steel wire, vastly superior, would become available later in the century).<ref>{{Multiref
|{{harvnb| Brown |2005|pp=58–59}}.
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref> The abundance of inexpensive [[lumber]] in North America caused [[timber bridge|timber]] to be the most common material used for bridges there from the late 1700s to the late 1800s. Many of these timber bridges were [[covered bridges]]. Rail bridges used timber to obtain long spans that utilized strong truss designs, and also tall [[trestle bridge]]s that spanned deep ravines.<ref name=timber>{{Multiref
|{{harvnb|Bennett|2000|pp=12–16}}.
|{{harvnb|Brown|2005|pp=82–84}}.
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref>
 
===1800 to present===
[[File:1 Pont de Sidi M'Cid.JPG|thumb|left|alt=A suspension bridge crossing a deep rocky [[ravine]] |The [[Sidi M'Cid Bridge]] in Algeria was the [[highest bridge]] in the world when it was built in 1912.{{sfn|Sakowski|2014|pp=1259-1261}} ]]
<!--
[[File:Brooklyn Bridge Manhattan.jpg|thumb|alt=A large suspension bridge, with large towers made of stone| The mass production of steel enabled the construction of large suspension bridges. The [[Brooklyn Bridge]], built in the 1870s, was the first suspension bridge to use steel for its cables.{{sfn|Bennett|2000|p=22}}]] -->
The mass production of [[steel]] in the late 1800s provided a new material for bridges, enabling lighter, stronger truss bridges and cantilever bridges; and steel wires replaced iron bars as the preferred material for suspension bridge cables.<ref>{{Multiref
|{{harvnb|Bennett|2000|pp=16–21}}.
|{{harvnb|Brown|2005|pp=88–104}}.
}}</ref><!--
{{efn|Long before the steel era, people made suspension bridges from vines or ropes. Iron was used in a few early suspension bridges in the form of iron rods or chains (rather than steel wires or cables).{{sfn|Bennett|2000|pp=1, 22}}}}
--><!-- The flexible and dynamic nature of suspension bridges requires special design considerations to safely carry rail traffic.<ref name=SuspRail>{{Multiref
|{{harvnb|Cruickshank|2010|pp= 229–232 }}.
|{{harvnb|Brown|2005|pp=106, 123, 147}}.
}}</ref> --> Concrete{{snd}}which was originally used within the Roman Empire{{snd}}was improved with the invention of [[Portland cement]] in the early 1800s, and replaced stone and masonry as the primary material for bridge [[Foundation (engineering)|foundation]]s. When iron or steel is embedded in the concrete, as in [[reinforced concrete]] or [[prestressed concrete]], it is a strong, inexpensive material that can be used for horizontal elements of [[beam bridge]]s and [[box girder]] bridges.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|pp=312–318, 320–327}}.
|{{harvnb|Brown|2005|pp=126–144}}.
}}</ref>
 
Throughout the 20th century, new bridges by designers such as [[Othmar Ammann]] repeatedly broke records for span distances, enabling transportation networks to cross increasingly wider rivers and valleys.<ref>{{Multiref
|{{harvnb|Bennett|2000|pp=22–24}}.
|{{harvnb|Brown|2005|pp=102, 106–108, 110, 113–114, 116–119, 123, 152}}.
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref> [[Cable-stayed bridges]]{{snd}}which use cable-stays as the exclusive means of support{{snd}}became a popular bridge design following [[World War II]].<ref>{{Multiref
|{{harvnb|Bennett|2000|pp=27–29}}.
|{{harvnb|Brown|2005|pp=146–154}}.
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref>{{efn|Straight, inclined cables{{snd}}known as ''[[Stay (mechanics)|stays]]''{{snd}}are used to directly connect the [[Deck (bridge)|bridge deck]] to bridge towers.{{sfn|Bennett|1999|p=61}} An early cable-stayed bridge was the 1955 [[Strömsund Bridge]] in Norway.{{sfn|Bennett|2000|p=29}} Stays were used as supplemental supports in some suspension bridges in the 19th century{{snd}}including the [[Brooklyn Bridge]].{{sfn|Bennett|1999|p=157}} }} The late 20th century saw several major innovations in bridge design. [[Extradosed bridge]]s were introduced and found widespread use, predominantly in Japan.{{sfn|Schlaich|2019|pp=1, 3, 6-7}} In China, [[Concrete filled steel tube#Bridges|concrete-filled steel tube]]s were adopted as a new approach to building [[arch bridge]]s.{{sfn| Zheng|Wang|2018}} [[Fiber-reinforced polymer]]s{{snd}}which do not suffer from the rust problems that plague steel{{snd}}were used in bridges for many applications, such as beams, deck slabs, prestressing cables, wraps on the exterior of concrete elements, and internal reinforcing within concrete.{{sfn|Svecova|2014|pp=371-375, 382, 384-386, 389-392}}{{efn|[[Fiber-reinforced polymer]]s include [[carbon fiber]], [[fiberglass]], and [[aramid]]s.}} In the 21st century a bridge span exceeded {{convert|2|km|mi|sp=us}} for the first time, with the construction of the [[1915 Çanakkale Bridge]].{{sfn|Gülkan|2023}}{{efn|The maximum theoretical span lengths, using materials available in 2014, are: Beam/girder: {{convert|550|m|ft|sp=us}}. Arch: {{convert|4200|m|ft|sp=us}}. Cable-stayed: {{convert|5500|m|ft|sp=us}}. Suspension: {{convert|8000|m|ft|sp=us}}. As calculated by bridge engineer [[Man-Chung Tang]].{{sfn|Tang|2014|pp=11-15}}}}
{{clear}}
<!--
===Etymology===
The ''[[Oxford English Dictionary]]'' traces the origin of the word ''bridge'' to the [[Old English]] word ''brycg'', of Germanic origin.{{sfn|"Bridge". ''The Concise Oxford Dictionary''}} There is a possibility that the word can be traced farther back to [[Proto-Indo-European]] ''*bʰrēw-.''{{sfn|"Bridge". ''Oxford English Dictionary''}}
-->
 
==Uses==
 
<!--
[[File:WildlifeCrossingA1IsraelSept202022 01.jpg|thumb|alt=A bridge, topped with soil and vegetation, passing over a highway|This [[Wildlife crossing|wildlife crossing bridge]] is in Israel.{{sfn| "Why Do Foxes". ''Israel21C''}} ]]
-->
The purpose of any bridge is to traverse an obstacle. A bridge can provide support and transport for [[railway]]s, cars, pedestrians, pipelines, cables, or any combination of these.{{sfn|Tang|2014|p=1}} [[aqueduct (bridge)|Aqueducts]] were developed early in human history, and carried water to towns and cities.{{sfn|Brown|2005|pp=8, 18, 20-23}} Canal systems sometimes include [[navigable aqueduct]]s (also called ''canal bridges'') to carry boats across a valley or ravine.{{sfn|Brown|2005|p=53}}
 
===Transportation===
[[File:Magdeburg Kanalbrücke aerial view 13.jpg|thumb|right
|alt=A bridge carrying canal with water, passing over a valley|The [[Magdeburg Water Bridge]] in Germany carries boats across a valley.{{sfn|Denison|2012|p=72}} ]]
 
Until the early 19th century, most bridges were designed to carry pedestrians, horses, and horse-drawn carriages.{{sfn|Brown|2005|p=64}} Following the invention of railways, many [[rail bridge]]s were built; in Britain the number of bridges doubled during the railway-building boom in the mid-1800s.{{sfn|Brown|2005|p=64}} Railway bridges have unique requirements because of the heavy loads they carry{{snd}}a single [[locomotive]] can weigh {{convert|197|tonnes|short ton}}.{{sfn|Sorgenfrei|2014|p=144.}}<!-- source says 435,000 lbs --> Railway bridges are designed to minimize [[Deflection (engineering)|deflection]] (bending under load), to maximize [[Structural robustness|robustness]] (localize the damage caused by accidents), and to tolerate [[Impact (mechanics)|heavy impacts]] (sudden shocks from, for example, rail wheels striking an imperfection in the track).{{sfn|Sorgenfrei|2014|p=144}} These requirements lead railways to avoid curved bridges, suspension bridges, and cable-stayed bridges; instead, straight beam or truss bridges are commonly used.{{sfn|Sorgenfrei|2014|p=146}} The explosive growth of motorway networks in the 20th century required bridges to span ever longer distances to reach islands and cross valleys.{{sfn|Bennett|2000||p=17}}
===Grade separation===
{{further|Grade separation}}
An important application of bridges is improving safety and traffic flow  at [[Junction (traffic)|traffic junctions]] where roads or railways cross at ground level.  Such intersections require vehicles to stop, and lead to slower traffic, wasted fuel, and higher incidence of collisions.  One technique to mitigate these issues is to build a bridge, enabling one of the roads to [[overpass|pass over]] the other:  this process is known as [[grade separation]].<ref>{{multiref
|{{harvnb|Ogden|Cooper|2019 }}.
|{{harvnb|Chase|2020}}.
}}</ref>  Grade separation can be implemented at [[grade crossing|railway-road intersections]]{{sfn|Ogden|Cooper|2019}} or [[intersection (road)|road-road intersections]].{{sfn|Chase|2020}}
 
===Pedestrians===
Some bridges, known as [[footbridge]]s, are devoted to pedestrian traffic.{{sfn| "Footbridge". ''Merriam-Webster''}}  They range from simple [[boardwalk]]s enabling passage over marshy land to elevated [[skyway|skybridges]]{{snd}}such as the [[Minneapolis Skyway System]]{{snd}}which shield pedestrians from harsh winter weather.<ref>{{Multiref
|{{harvnb|Robertson|1988|pp=481–482}}.
|{{harvnb|Cai|Liu|2012}}.
|{{harvnb|"LRFD Guide Specifications for the Design of Pedestrian Bridges". ''AASHTO''}}.
}}</ref> When [[Pedestrian separation structure|used to cross roads]] in busy urban areas, footbridges are generally safer than crosswalks, but have been criticized by urbanists and disability advocates for inconveniencing pedestrians, hindering accessibility, diminishing the quality of city life, and perpetuating [[car dependency]].<ref>{{Multiref
|{{harvnb|Robertson|1988|pp=457–459, 464–477, 483–484}}.
|{{harvnb|Soliz | Pérez-López|2022}}.
}}</ref>
 
===Military===
 
[[File:PontBailey.jpg|thumb|left
|alt= A metal bridge in a forest.
| Invented for wartime use, [[Bailey bridge]]s found civilian use after WW II.{{sfn|Odrobiňák |2022}}]]
<!--
| image2 = Slovakia Town Presov 270.jpg
| alt2= A military vehicle carrying a bridge on its back, extending the bridge over a creek
| caption2 =A portable [[AM 50]] bridge is being deployed over a river in Slovakia.{{sfn| "Bridge Layer AM-50". ''Ministry of Defence and Armed Services of the Czech Republic'' }}
}}
-->
[[Military bridge]]s are an important type of equipment in the field of [[military engineering]]. They perform a variety of wartime roles, such as quickly traversing obstacles in the midst of battle, or facilitating resupply behind front lines.{{sfn|Tytler|1985|p=198}}{{efn|During wartime, although bridges are sometimes built, they are also destroyed by bombing or by [[combat engineers#Countermobility|combat engineers]].<ref>{{Multiref
|{{harvnb| Bennett | 1999| pp= 102, 104, 108, 181}}.
|{{harvnb| Brown | 2005| pp= 33, 105, 114–115}}.
|{{harvnb| Cruickshank |2010| pp= 20, 40–41, 43, 91, 327}}.
}}</ref>
}}
<!--
{{efn|An example of a portable military bridge is the [[Bailey bridge]].{{sfn|"Army Manual TM 5-277. Panel Bridge, Bailey Type, M2" }}}}
-->Military bridges can be categorized as ''wet'' bridges that rest on pontoon floats, and ''dry'' bridges that rest on piers, river banks, or anchorages.{{sfn|Tytler|1985|p=198}} A crude mechanism to cross a small ravine is to place a [[fascine]] (a large bundle of pipes or logs) into the ravine to enable vehicles to drive across.{{sfn|Tytler|1985|p=200}}
 
Some military bridges, referred to as [[armoured vehicle-launched bridge]]s, are carried on purpose-built vehicles.{{sfn|Tytler|1985|p=200}} These vehicles typically have the same cross-country performance as a tank, and can carry a bridge to an obstacle and deploy ("launch") the bridge.<ref>{{Multiref
|{{harvnb|Tytler|1985|pp=200–203}}.
|{{harvnb| "Close Support Bridging". ''British Army'' }}.
}}</ref> The UK [[Chieftain (tank)|Chieftain]] vehicle could launch a {{convert|23|m|ft|sp=us|adj=on}} bridge{{snd}}capable of supporting {{convert|54|tonne|short ton|adj=on}} loads{{snd}} in 3 minutes.{{sfn|Tytler|1985|pp=198, 200. The bridge could support a [[Chieftain Mark 5]] tank}} Military bridges have found use in civilian applications. The [[Bailey bridge]] was originally invented in 1940 for use in WW II, but continues to be used in peacetime. Bailey bridges are used as small, permanent bridges, as well as temporary bridges used while a permanent bridge is being replaced or repaired.{{sfn|Odrobiňák |2022}}
{{clear}}
 
===Other===
Some bridges accommodate uses other than transportation. [[Pipeline bridge]]s carry oil pipes or water pipes across valleys or rivers.{{sfn| Dusseau|2002}} Many historical bridges supported buildings, such as shrines, factories, shops, restaurants, and houses. Notable examples were the Old London Bridge and [[Ponte Vecchio]].{{sfn|Cruickshank|2010|pp= 144- 175}} In the modern era, [[bridge-restaurant]]s can be found at some highway [[rest area]]s; these support a restaurant or shops directly above the highway and are accessible to drivers moving in both directions.{{sfn|Greco|2016|pp=89-100}}
An example is [[Will Rogers Archway]] over the [[Oklahoma Turnpike]].{{sfn| "Will Rogers Archway". ''Travel Oklahoma''}} The [[Nový Most]] bridge in [[Bratislava]] features a restaurant set atop its single tower.{{sfn|"Bratislava UFO Classed One of the Craziest Places". ''Travel to Slovakia''}} Conservationists use [[Wildlife crossing|wildlife bridges]] to reduce [[habitat fragmentation]] and animal-vehicle collisions.<ref>{{Multiref
|{{harvnb|Greenfield|2021}}.
|{{harvnb| "Why Do Foxes". ''Israel21C''}}.
}}</ref> The first wildlife crossings were built in the 1950s, and these types of bridges are now used worldwide to protect both large and small wildlife.{{sfn|Newer|2012}}
 
==Structure and form==
{{see also|List of bridge types}}
 
Bridges are primarily classified by their basic structural design:  arch, truss, cantilever, suspension, cable-stayed, or beam.<ref>{{Multiref
|{{harvnb|Shirley-Smith|Billington}}.
|{{harvnb|Barker|2007|pp=2–21, 87–96}}.
}}</ref>{{efn|In some contexts, beams and girders are treated as distinct types of structures. Suspension and cable-stayed are sometimes grouped together as ''cable-supported bridges''.{{sfn|Shi|2014}}}} Several other terms can used to designate various aspects of a bridge's form or design, including [[viaduct]], [[trestle bridge|trestle]], and [[causeway]].
 
===Basic structures===
<!-- [[File:ScotRail Class 170 Forth Bridge.jpg|thumb| alt=A huge steel bridge passing over a wide body of water|The [[Forth Bridge]] (foreground) uses two kinds of structures: [[truss bridge|trusses]] (left) and [[cantilever bridge|cantilevers]] (right).{{sfn|Cruickshank|2010|pp=292-298}}]]-->
 
The choice of bridge structure to use in a particular situation is based on many factors, including aesthetics, environment, cost, and purpose.{{sfn|Barker|2007|pp=96-108}} Some bridge spans combine two types of basic structures; for instance, the [[Brooklyn Bridge]] is primarily a suspension structure, but also uses cable-stays.<ref>{{Multiref
|{{harvnb|Tang|2014|p=4}}. Two types of structures.
|{{harvnb|Bennett|1999|p=157}}. Brooklyn bridge example.
}}</ref> Some multi-span bridges{{snd}}called ''hybrid'' bridges{{snd}}use different basic structures for different spans.{{sfn|Denison|2012|p=35}}<!--
{{efn|The three bridges that cross the [[ Firth of Forth]] are all hybrids. They use beam or truss structures on the outer spans, but use another structure for the wide central span(s): [[Forth Bridge]] (cantilever central spans), [[Forth Road Bridge]] (suspension central span), and [[Queensferry Crossing]] (cable-stayed central spans).}}
-->
 
====Arch bridge====
{{multiple image
| header = [[Arch bridge]]
<!-- | width = 160 -->
| caption_align=center
| image1 = Arch bridge.svg
| alt1= an arched bridge spanning a river, deck resting on top of the arch.
| caption1 = Deck arch <!-- {{sfn|Denison|2012|p=42}}{{sfn|Shirley-Smith|Billington}}{{sfn|Brown|2005|pp=202-203}} -->
| image2 = Arch tied bridge.svg
| alt2= an arched bridge spanning a river, deck suspended below the arch by vertical lines.
| caption2 = [[Tied-arch bridge|Tied arch]] <!-- {{sfn|Denison|2012|p=42}}{{sfn|Shirley-Smith|Billington}}{{sfn|Brown|2005|pp=202-203}} -->
}}
[[Arch bridge]]s consist of a curved arch, under compression, which supports the [[bridge deck|deck]] either above or below the arch.{{sfn|Bennett|1999|pp=70-75}} The shape of the arch can be a [[semicircle]], [[Ellipse|elliptical]], a [[pointed arch]], or a [[Circular arc|segment of a circle]].<ref>{{Multiref
|{{harvnb|Bennett|1999|p=72}}.
|{{harvnb|Bennett|2000|p=11}}.
|{{harvnb|Brown|2005|p=46}}.
}}</ref> Arches exert a diagonal force at both ends, requiring strong supports or [[abutment]]s to prevent the arch from spreading or collapsing.<ref name=abutDiag/> Deck arch bridges hold the deck above the arch; [[tied-arch bridge]]s suspend the deck below the arch; and [[Through arch bridge|through-arch bridges]] position the deck through the middle of the arch.{{sfn|Bennett|1999|pp=75-76}}
 
====Truss bridge====
{{multiple image
| header = [[Truss bridge]]
<!-- | width = 160 -->
| caption_align=center
| image1 = Truss bridge.svg
| alt1= a bridge spanning a river, consisting of several triangles, and the bridge deck is the lower edge of the set of triangles.
| caption1 = Through truss <!-- {{sfn|Denison|2012|pp=45, 165}}{{sfn|Shirley-Smith|Billington}}{{sfn|Brown|2005|pp=202-203}} -->
| image2 = Inverted truss bridge.svg
| alt2= a bridge spanning a river, consisting of several triangles, and the bridge deck is the upper edge of the set of triangles.
| caption2 = Deck truss<!-- {{sfn|Denison|2012|pp=45, 165}}{{sfn|Shirley-Smith|Billington}}{{sfn|Brown|2005|pp=202-203}} -->
}}
A [[truss bridge]] is composed of multiple, connected triangular elements.{{sfn|Bennett|1999|pp=77-79}}<!--
{{efn|A truss can be considered as a deep beam, out of which numerous triangular holes have been cut to reduce the weight.{{sfn|Bennett|1999|pp=77-79}}}}
--> The set of triangles form a rigid whole, which rests on the foundation at both ends, applying a vertical force downward.{{sfn|Bennett|1999|pp=77-79}} The deck can be carried on top of the truss ("deck truss") or at the bottom of the truss ("through truss").<ref>{{Multiref
|{{harvnb|Kulicki|2014|p=284}}.
|{{harvnb|Wright|2022|pp=7–9, 19–20}}.
}}</ref> Through trusses are useful when more clearance under the bridge is required; deck trusses permit oversized loads and do not interfere with overhead objects, such as electrical lines.{{sfn|Wright|2022|pp=4, 7-9, 19-20}} The individual bars can be made of iron or wood, but most modern truss bridges are made of steel.{{sfn|Bennett|2000|pp=14–17, 21}} The horizontal bars along the top are usually in [[Compression (physics)|compression]], and the horizontal bars along the bottom are usually in [[Tension (physics)|tension]].{{sfn|Bennett|1999|pp=77-79}} Bars connecting the top and bottom may be in tension or compression, depending on the layout of the triangles.{{sfn|Bennett|1999|p=77}} Trusses typically have a span-to-depth ratio (the width of a structure divided by its height) ranging from 10 to 16, compared to beam bridges which typically have a ratio ranging from 20 to 30.{{sfn|Collings|2000|p=413}} Trusses tend to be relatively stiff, and are commonly used for rail bridges which are required to carry very heavy loads.{{sfn|Collings|2000|p=413}}
 
====Cantilever bridge====
{{multiple image
| header = [[Cantilever bridge]]
<!-- | width = 160 -->
| caption_align=center
| image2 = Cantilever bridge.svg
| alt2 = a bridge spanning a river, where the bridge is in two disjoint parts: the left part is supported entirely from the leftmost edge where it rests on the ground; and the right part is supported entirely from the rightmost edge where it rests on the ground.
| caption2 = Two cantilevers extending from anchorages <!-- {{sfn|Denison|2012|p=53, 55}}{{sfn|Shirley-Smith|Billington}}{{sfn|Brown|2005|pp=202-203}} -->
| image1 = Cantilever bridge, balanced.svg
| alt1= a bridge spanning a river, where there is a solid pier in the middle of the river, and the entire bridge is resting on that pier (and not resting on the banks of the river).
| caption1 = Balanced cantilever on a single pier <!-- {{sfn|Denison|2012|p=53, 55}}{{sfn|Shirley-Smith|Billington}}{{sfn|Brown|2005|pp=202-203}} -->
}}
[[Cantilever bridge]]s consist of beams or trusses that are rigidly attached to a support (pier or anchorage) and extend horizontally from the support without additional supports.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|pp=292–294, 361}}.
|{{harvnb|Brown|2005|p=202}}.
}}</ref> In ancient Asia, cantilever bridges made of large rocks or timber were used to span small obstacles.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|p=298}}.
|{{harvnb|Brown|2005|p=15}}.
|{{harvnb|Bennett|1999|p=12}}.}}</ref> In the 1880s, some early cantilever bridges were built from wrought iron, but steel began to be used starting in the late 1800s.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|pp=292–294}}.
|{{harvnb|Brown|2005|p=78}}.}}</ref> A balanced cantilever bridge consists of two connected cantilevers extending outward in opposite directions from a single central support.<ref name=balcant>{{Multiref
|{{harvnb|Cruickshank|2010|pp=36, 294}}.
|{{harvnb|Bennett|1999|pp=42, 53, 78, 94, 97, 145, 223}}.
}}</ref> Other cantilever bridges have two cantilevers, anchored at each end of the span, extending toward the center, and meeting in the center.{{sfn|Bennett|1999|p=12}} <!--
Some cantilever bridges have a suspended span (beam or truss) in the center, connecting the two cantilevers where they meet.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|p=296, 361}}.
|{{harvnb|Brown|2005|p=202}}.
|{{harvnb|Adams|1909|p=169}}.
}}</ref>
--> ''Cantilever construction'' is a method of building a bridge [[superstructure]], which can be utilized for arch and cable-stayed bridges, as well as cantilever bridges. In this technique, construction begins at a support (such as a pier, abutment, or tower) and extends outwards across the obstacle, with no support from below.<ref>{{Multiref
|{{harvnb|Collings|2000|p=433}}.
|{{harvnb|Cruickshank|2010|pp=262–266}}.
|{{harvnb|Bennett|1999|pp=74, 96, 113, 145}}.
|{{harvnb|Brown|2005|pp=89, 105, 141, 149}}.
}}</ref>
 
====Suspension bridge====
{{multiple image
| header = [[Suspension bridge]]
<!-- | width = 160 -->
| caption_align=center
| image1 = Suspension bridge.svg
| alt1= a bridge spanning a river, with two tall towers in the river, and a curved cable passing from one river bank to the other, passing over the tops of the towers. The bridge deck (road) is suspended from the curved cable by vertical lines.
| caption1 = With anchorages <!-- {{sfn|Denison|2012|pp=57, 59}}{{sfn|Shirley-Smith|Billington}}{{sfn|Brown|2005|pp=202-203}} -->
| image2 =Bridge_suspension_self_anchored.svg
| alt2 = a bridge spanning a river, with a single tall towers in the middle of the river, and a curved cable passing from one river bank to the other, passing over the top of the tower. The bridge deck (road) is suspended from the curved cable by vertical lines.
| caption2 = [[Self-anchored suspension bridge|Self-anchored]]<!-- {{sfn|Gimsing|1997|p=193}} -->
}}
[[Suspension bridge]]s have large, curved cables attached to the tops of tall towers,{{efn|name=OneTower}} and suspend the bridge deck from the cables.{{sfn|Brown|2005|p=203}}{{efn|The deck is suspended from the cables by large [[wire rope]]s called ''hangers'', also called ''suspenders''.{{sfn|Bennett|1999|p=84}}}} In the early 1800s, the first modern suspension bridges{{snd}}such as the [[Jacob's Creek Bridge (Pennsylvania)|Jacob's Creek Bridge]]{{snd}}were [[chain bridge]]s that used iron bars rather than bundled wires for the cables.{{sfn|Brown|2005|p=58}} After steel wire became widely available, longer cables could be built by stringing hundreds of wires between the towers and bundling them,{{sfn|Bennett|1999|pp=84, 88-90}} enabling suspension bridges to achieve spans {{convert|2|km|mile|sp=us}} long. When the bridge crosses a river, stringing the wires across the large span is a complex process.<ref>{{Multiref
|{{harvnb|Gimsing |1997|pp=37–38}}.
|{{harvnb|Bennett|1999|pp=84, 88–90}}.
}}</ref> The cable of a suspension bridge assumes the shape of a [[catenary]] when initially suspended between the bridge towers; however, once the uniform load of the bridge deck is applied, the cable adopts a [[parabola|parabolic]] shape.{{sfn|Cruickshank|2010|pp=232-233}} Shorter towers require a smaller sag in the cable, which increases the tension in the cable, and thus requires stronger towers and anchorages.{{sfn|Bennett|1999|pp=88-89}}
 
====Cable-stayed bridge====
{{multiple image
<!-- | width = 160 -->
| caption_align=center
| header = [[Cable-stayed bridge]]
| image1 = Cable-stayed bridge.svg
| alt1= a bridge spanning a river, with two tall towers in the river, The bridge deck (road) is suspended from the two towers by numerous straight, diagonal lines.
| caption1 = Harp pattern, two towers <!-- {{sfn|Denison|2012|p=61, 63}}{{sfn|Shirley-Smith|Billington}}{{sfn|Brown|2005|pp=202-203}} -->
| image2 = Bridge cable stay fan.svg
| alt2= a bridge spanning a river, with a single tall towers in the middle of the river, The bridge deck (road) is suspended from the tower by numerous straight, diagonal lines.
| caption2 = Fan pattern, single tower <!-- {{sfn|Denison|2012|p=61, 63}}{{sfn|Shirley-Smith|Billington}} -->
}}
[[Cable-stayed bridge]]s are similar to suspension bridges, but the cables that support the deck connect directly to the towers.{{sfn|Bennett|1999|pp=92–94, 228}}{{efn|name=OneTower|Most suspension bridges and cable-stayed bridges have two or more towers, but some have only one tower. A single-tower cable-stayed bridge is the [[Flehe Bridge]] in Germany,{{sfn|Troyano |2003 |pp= 623, 656, 664 }} and a single-tower suspension bridge is the east span of the [[San Francisco-Oakland Bay Bridge]].{{sfn|Brown|2005|pp=194-195}} }} The inclined cables may be arranged in a fan pattern or a harp pattern.<ref>{{Multiref
|{{harvnb|Vejrum|2014|pp=407–410}}.
|{{harvnb|Cruickshank|2010|p=347}}.
|{{harvnb|Gimsing|1997|pp= 194, 211, 351–352}}.
}}</ref>{{efn|In a harp pattern all the cables are parallel; in a fan pattern the cables all radiate from near the top of the tower. The [[Severins Bridge]] was the first cable-stayed bridge that arranged its cables in a fan pattern, rather than a harp pattern.{{sfn|Bennett|2000|p=29}} Other cable-stay patterns include star and radial.{{sfn|Tang|2014|p=13}}}} Modern cable-stayed bridges became popular after WW II, when the design was used for many new bridges in Germany.{{sfn|Bennett|2000|pp=27-29}} When traversing a wide obstacle, designers have a choice of suspension or cable-stayed structures. Suspension bridges can achieve a longer span, but cable-stayed bridges use less cable for a given span size, do not require anchorages, and the deck can be readily built by cantilevering outward from the towers.<ref>{{Multiref
|{{harvnb|Bennett|2000|pp=27–28}}.
|{{harvnb|Cruickshank|2010|pp=343–347}}.
}}</ref>


==History==
====Beam bridge====
[[File:Seasonal bridge north of Jispa, H.P., India. 2010.jpg|thumb|Seasonal bridge north of [[Jispa]] in Himachal Pradesh, India]]
{{multiple image
[[File:West Montrose Covered Bridge (Oct. 2018).jpg|thumb|The covered bridge in [[West Montrose, Ontario]], Canada]]
| header = [[Beam bridge]] <!-- {{sfn|Denison|2012|pp=37, 39}}{{sfn|Shirley-Smith|Billington}} -->
[[File:2007 - South Eighth Street Viaduct.jpg|thumb|The [[Albertus L. Meyers Bridge]] in [[Allentown, Pennsylvania]], U.S., "one of the earliest surviving examples of monumental, reinforced concrete construction", according to the [[American Society of Civil Engineers]]<ref>{{Cite web|title=South Eighth Street Viaduct, Spanning Little Lehigh Creek at Eighth Street (State Route 2055), Allentown, Lehigh County, PA (HAER No. PA-459)|url=https://www.loc.gov/pictures/item/pa3578/|access-date=11 January 2021 |website=Historic American Engineering Record}}</ref>]]
<!-- | width = 160 -->
[[File:Mohammed VI bridge.jpg|thumb|[[Mohammed VI Bridge]] in Morocco]]
| caption_align=center
[[File:King Mindaugas Bridge, Vilnius.jpg|thumb|[[Mindaugas Bridge]] in Lithuania]]
| image1 =Beam bridge.svg
| alt1= A flat, straight bridge spanning a river. There are no towers or piers: the entire bridge is a flat, wide, rectangular shape.
| caption1 =
}}
[[Beam bridges]] are simple structures consisting of one or more parallel, horizontal [[Beam (structure)|beam]]s or [[girder]]s that span an obstacle.<ref name=beam>{{multiref
|{{harvnb|Bennett|1999|p=78}}.
|{{harvnb|Bennett|2000|pp=24–26}}.
|{{harvnb|Barker|2007|pp=20–21}}.
|{{harvnb|Cruickshank|2010|pp=360, 362}}.
}}</ref> A [[box girder bridge]] is a variant that is generally shallower than an [[I-beam]] equivalent, permitting shorter and lower approach roads to cross an obstacle of a given height.{{sfn|Bennett|2000|p=24}} Beam bridges are commonly used for both railways and roadways.<ref name=beam/> Beam bridges are often used for spans shorter than about {{convert|50|m|ft|sp=us}}; for longer spans other structures, such as trusses, are generally more efficient.<ref>{{Multiref
|{{harvnb|Barker|2007|pp=20–21}}.
|{{harvnb|Bennett|1999 |p =78}}.
}}</ref> The majority of beam bridges have a flat, horizontal bottom; but some have a bottom that arches upward, called ''haunching''. Haunching looks more graceful than a flat bottom, and can provide greater clearance below the bridge, but it tends to be more costly because flat bottom beams are easier to build.<ref>{{Multiref
|{{harvnb|Zhao| 2017|pp =79, 214–215}}.
|{{harvnb|Troitsky|1994| p =104}}.
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref>


The simplest and earliest types of bridge were [[stepping stones]].
===Other forms===


[[Neolithic]] people also built a form of [[boardwalk]] across [[marshes]]; examples of such bridges include the [[Sweet Track]] and the [[Post Track]] in England, approximately 6000 years old.<ref name="Current_Archaeology_somerset-levels">{{cite journal |last=Brunning |first=Richard |date=February 2001 |title=The Somerset Levels |journal=[[Current Archaeology]] |volume=XV (4) |issue=172 (Special issue on Wetlands) |pages=139–143}}</ref> Ancient people would also have used [[log bridge]]s<ref>{{cite book |last=National Parks Conference |first=Department of the Interior |url=https://archive.org/details/proceedingsnati01confgoog/page/n391/mode/2up |title=Proceedings of the National parks conference held at Berkeley, California March 11, 12, and 13, 1915 |publisher=[[United States Government Publishing Office|Government Printing Office]] |year=1915 |location=Washington, DC |page=[https://archive.org/details/proceedingsnati01confgoog/page/n443 60] |quote=(A log bridge) is a bridge composed of log beams, the logs being in natural condition or [[hewn]], which are thrown across two [[abutments]], and over which traffic may pass. |ref=NPC |access-date=14 March 2010 |via=Internet Archive}}</ref> consisting of logs that fell naturally or were intentionally felled or placed across streams. Some of the first [[human-made]] bridges with significant span were probably intentionally felled trees.<ref>{{cite book |last1=Bennett |first1=David |url=https://books.google.com/books?id=8PGk81gtCywC |title=The manual of bridge engineering |publisher=Thomas Telford |year=2000 |isbn=978-0-7277-2774-9 |editor1-last=Ryall |editor1-first=M.J. |location=London |page=1 |chapter=The history and aesthetic development of bridges |format= |access-date=14 March 2010 |editor2-last=Parke |editor2-first=G.A.R. |editor3-last=Harding |editor3-first=J.E. |chapter-url=https://books.google.com/books?id=8PGk81gtCywC&pg=PA1 |via=Google books}}</ref> Among the oldest [[timber bridge]]s is the [[Holzbrücke Rapperswil-Hurden]] bridge that crossed upper [[Lake Zürich]] in Switzerland; prehistoric timber pilings discovered to the west of the [[Seedamm]] causeway date back to 1523 BC. The first wooden footbridge there led across Lake Zürich; it was reconstructed several times through the late 2nd century AD, when the [[Roman Empire]] built a {{convert|6|m|ft|adj=mid|-wide}} wooden bridge to carry transport across the lake. Between 1358 and 1360, [[Rudolf IV, Duke of Austria]], built a 'new' wooden bridge across the lake that was used until 1878; it was approximately {{convert|1450|m|ft}} long and {{convert|4|m|ft}} wide. On 6 April 2001, a reconstruction of the original wooden footbridge was opened; it is also the longest wooden bridge in Switzerland.
====Movable bridge====
[[File:Tower Bridge (8151690991).jpg|thumb|alt=A tall drawbridge, open, over a river| [[Tower Bridge]] in London is a [[movable bridge]].{{sfn|Birnstiel|2000|pp=688-690}} ]]


The [[Arkadiko Bridge]] is one of four Mycenaean [[corbel arch]] bridges part of a former network of roads, designed to accommodate [[chariot]]s, between the fort of Tiryns and town of Epidauros in the [[Peloponnese]], in southern [[Greece]]. Dating to the Greek [[Bronze Age]] (13th century BC), it is one of the oldest [[arch bridge]]s still in existence and use. Several intact, arched stone bridges from the [[Hellenistic age|Hellenistic era]] can be found in the Peloponnese.<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=978-0-07-161477-1}}</ref>
[[Movable bridge]]s are designed so that all or part of the bridge deck can be moved, usually to permit tall traffic{{snd}}that would normally be obstructed by the bridge{{snd}}to pass by.<ref>{{Multiref
|{{harvnb|Brown|2005|pp=80–81}}.
|{{harvnb|Birnstiel|2000|pp=663–664}}.
}}</ref> Early movable bridges include [[drawbridge]]s that pivoted at one end, and required a large amount of work to raise. Adding counterweights on the pivot side of the drawbridge creates a [[bascule bridge]], and makes moving the bridge easier and safer.<ref>{{Multiref
|{{harvnb|Brown|2005|pp=80–81}}.
|{{harvnb|Birnstiel|2000|pp=668–678, 684}}.}}</ref> [[Swing bridge]]s pivot horizontally around an anchor point on the bank of a canal, or sometimes from a pier in the middle of the water.<ref>{{Multiref
|{{harvnb|Brown|2005|p=80}}.
|{{harvnb|Birnstiel|2000|pp=665–668, 682–683}}.
}}</ref> [[Lift bridge]]s are raised vertically between two towers by cables passing over pulleys at the top of the towers.<ref>{{Multiref
|{{harvnb|Brown|2005|p=80}}.
|{{harvnb|Birnstiel|2000|pp=676–679}}.
}}</ref> Notable movable bridges include [[El Ferdan Railway Bridge]] in Egypt, [[Erasmusbrug]] bascule in Rotterdam, and [[Limehouse Basin#Swing bridge|Limehouse Basin footbridge]] in London.{{sfn|Brown|2005|pp=164-165, 184-185}} In the modern era, designers sometimes create unusual movable bridges with the intention of establishing signature bridges for a town or locality.{{sfn|Brown|2005|pp=164-165, 184-185}} Examples include [[Puente de la Mujer]] swing bridge in Buenos Aires, [[Gateshead Millennium Bridge|Gateshead Millennium]]{{snd}}a rare example of a [[tilt bridge]]{{snd}}over the [[River Tyne]], and [[Hörn Bridge]] in Germany.{{sfn|Brown|2005|p=164}}{{efn|These bridges were designed by [[Santiago Calatrava]] (Spain), [[WilkinsonEyre]] (England), and [[Schlaich Bergermann]] (Germany).{{sfn|Brown|2005|p=164}} }}


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 |archive-url=https://web.archive.org/web/20050221084235/http://www.icomos.org/studies/bridges.htm |archive-date=21 February 2005 }}</ref> The Romans built arch bridges and [[aqueduct (bridge)|aqueducts]] that could stand in conditions that would damage or destroy earlier designs, some of which still stand today.<ref name=historyworld>{{cite web |title=History of Bridges |url=http://www.historyworld.net/wrldhis/PlainTextHistories.asp?historyid=ab97 |publisher=Historyworld.net |access-date=4 January 2012 |url-status=live |archive-url=https://web.archive.org/web/20120106101748/http://historyworld.net/wrldhis/PlainTextHistories.asp?historyid=ab97 |archive-date=6 January 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 |access-date=4 January 2012 |archive-url=https://web.archive.org/web/20050210043706/http://www.pubs.asce.org/WWWdisplay.cgi?0103045 |archive-date=10 February 2005 }}</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).
====Long multi-span bridge====


In India, the ''[[Arthashastra]]'' treatise by [[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>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>
[[File:ViaducdeMillau.jpg|thumb|left|alt=A large bridge, consisting of multiple tall sections, passing over a wide valley |The [[Millau Viaduct]] crosses the [[Tarn (river)|Tarn river]] valley in France.{{sfn|Brown|2005|pp=192-193}}]]


Although large bridges of wooden construction existed in China at the time of the [[Warring States period]], 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 [[Spandrel|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.<ref>{{Cite journal |last=Bjelić |first=Igor |date=2022 |title=Use of Building Materials During the Construction of Trajan's Bridge on the Danube |journal=Arheologija i Prirodne Nauke |volume=18 |pages=45–58 |doi=10.18485/arhe_apn.2022.18.4 |issn=1452-7448|url=http://rai.ai.ac.rs/handle/123456789/709 }}</ref>
There are a variety of terms that describe long, multi-span bridges{{snd}}including viaduct, trestle, continuous, and causeway. The usage of the terms can overlap, but each has a specific focus.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|p=349}}.
|{{harvnb|Honan|2018}}.
}}</ref> [[Viaduct]]s (carrying vehicles) and [[aqueduct (bridge)|aqueduct]]s (carrying water) are bridges crossing a valley, supported by multiple arches or piers.<ref>{{Multiref
|{{harvnb|"Aqueduct". ''The Concise Oxford Dictionary''}}.
|{{harvnb|"Viaduct". ''The Concise Oxford Dictionary''}}.
}}</ref> Romans built many aqueducts, some of which are still standing today.{{sfn|Cruickshank|2010|pp=58, 60–63, 70}} Notable viaducts include [[Penponds Viaduct]] in England,{{sfn|Brown|2005|p=69}} [[Garabit Viaduct]] in France,{{sfn|Brown|2005|pp=92-93}} [[Tunkhannock Viaduct]] in Pennsylvania,{{sfn|Brown|2005|pp=130-131}} and [[Millau Viaduct]] in France.{{sfn|Brown|2005|pp=192-193}}


[[Inca rope bridge|Rope bridges]], a simple type of [[suspension bridge]], were used by the [[Inca Empire|Inca]] civilization in the [[Andes]] mountains of South America, just prior to European colonization in the 16th century.
A [[trestle bridge]]{{snd}}commonly used in the 19th century for railway bridges{{snd}} consists of multiple short spans supported by closely spaced structural elements.{{sfn|Cruickshank|2010|pp=46-47}} A trestle is similar to a viaduct, but viaducts typically have taller piers and longer spans.{{sfn|Honan|2018}} A [[continuous truss bridge]] is a long, single truss that rests upon multiple [[Pier (bridge structure)|supports]]. A continuous truss bridge may use less material than a series of simple trusses because a continuous truss distributes live loads across all the spans (in contrast to a series of simple trusses, where each truss must be capable of supporting the entire live load). Visually, a continuous truss looks similar to a cantilever bridge, but a continuous truss experiences [[Hogging and sagging|hogging]] stresses at the supports and [[Hogging and sagging|sagging]] stresses between the supports.<ref name=contTruss>{{Multiref
|{{harvnb|Denison|2012|p=153}}.
|{{harvnb|Adams|1909|p=168}}.
}}</ref>{{efn|Similarly, a ''continuous beam'' consists of a single, rigid beam that crosses two or more spans.{{sfn|Shirley-Smith|Billington}}}} A [[causeway]] is a low, raised road, usually crossing a lake or other body of water.<ref name=causeway>{{Multiref
| {{harvnb|"Causeway". ''Merriam-Webster''}}.
| {{harvnb|"Causeway". ''Oxford English Dictionary''}}.
| {{harvnb|Cruickshank|2010|p=349}}.
}}</ref> The {{convert|38.4|km|mile|sp=us}} [[Lake Pontchartrain Causeway]] in Louisiana is a bridge, but other causeways are built on earthen embankments.<ref name=causeway/>


The [[Ashanti Empire|Ashanti]] built bridges over [[streams]] and [[rivers]].<ref>{{cite book | url= https://books.google.com/books?id=NSs4AAAAIAAJ | title= Asante in the Nineteenth Century: The Structure and Evolution of a Political Order| page=38 |author=Ivor Wilks |author-link=Ivor Wilks| publisher= CUP Archive |via = Books.google.com |access-date= 29 December 2020|isbn= 978-0-521-37994-6|date= 1989}}</ref><ref name="Edgerton page 38">{{cite book |url=https://books.google.com/books?id=Tkm5UZJz8z0C&q=Bridges+constructed+by+pounding|last=Edgerton |first=Robert B. |year=2010 |title=The Fall of the Asante Empire: The Hundred-Year War For Africa's Gold Coast |page=62|publisher=Simon and Schuster |isbn=978-1-4516-0373-6 }}</ref> They were constructed by pounding four large forked tree trunks into the stream bed, placing beams along these forked pillars, then positioning cross-beams that were finally covered with four to six inches of dirt.<ref name="Edgerton page 38"/>
====Extradosed====


During the 18th century, there were many innovations in the design of timber bridges by [[Hans Ulrich Grubenmann]], [[Johannes Grubenmann]], as well as others. The first book on bridge engineering was written by [[Hubert Gautier]] in 1716.
[[File:Shinmeisai Bridge and Akatonbo Bridge.jpg|alt=A concrete bridge over a river|thumb|The Shin Meisei bridge (foreground) in Japan is an example of an [[extradosed bridge]].{{sfn|Hu|2016|p=40}}]]
An [[extradosed bridge]] combines features of a box girder bridge and a cable-stayed bridge.<ref>{{Multiref
|{{harvnb|Vejrum|2014|pp=410–412}}.
|{{harvnb|Schlaich|2019|p=3}}.
|{{harvnb|Hu|2016|pp=i, 1, 7–13}}.
}}</ref> Visually, extradosed bridges can be distinguished from cable-stayed bridges because the tower height (above the deck) is relatively low: between 7% and 13% of the span width.{{sfn|Schlaich|2019|pp=3-4}}<!--
{{efn|Another definition of an extradosed bridge is one where the ''stiffness ratio'' (load carried by stay cables divided by total vertical load) is less than 30%.{{sfn|Hu|2016|p=12}}}}
--> Extradosed bridges are appropriate for spans ranging from {{convert|100|meters|sp=us}} to {{convert|250|meters|sp=us}}.{{sfn|Schlaich|2019|pp=3-4}} Unlike suspension bridges or cable-stayed bridges, the towers of an extradosed bridge often rest on the deck (rather than on a footing) and are solidly connected to the deck.{{sfn|Schlaich|2019|p=5}} Because of the relatively flat angle of the cables, the cables of an extradosed bridge compress the deck horizontally, performing a function comparable to prestressing wires that are used within concrete girders.{{sfn|Schlaich|2019|pp=3–7, 58}} Extradosed bridges may be appropriate in applications where the deck must have a shallow depth to maximize clearance under the bridge; or where towers must be relatively short to abide by aviation safety constraints.{{sfn|Schlaich|2019|p=6}}


A major breakthrough in bridge technology came with the erection of [[the Iron Bridge]] in Shropshire, England in 1779. It used [[cast iron]] for the first time as arches to cross the [[river Severn]].<ref>{{cite web |url= http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=80 |title= Iron Bridge |author= <!--"ECPK"--> |website= Engineering Timelines |access-date= 18 November 2016 |url-status=live |archive-url= https://web.archive.org/web/20160304204815/http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=80 |archive-date= 4 March 2016 |df= mdy-all }}</ref> With the [[Industrial Revolution]] in the 19th century, [[truss]] systems of [[wrought iron]] were developed for larger bridges, but iron does 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]].<ref>{{Cite web|date=20 June 2020|title=Gustave Eiffel-15 Iconic Projects|url=https://www.re-thinkingthefuture.com/know-your-architects/a1078-gustave-eiffel-15-iconic-projects/|access-date=2021-06-12|website=Rethinking the Future|language=en-US}}</ref>
====Pontoon bridge====


In Canada and the United States, numerous timber [[covered bridges]] were built in the late 1700s to the late 1800s, reminiscent of earlier designs in Germany and Switzerland. Some covered bridges were also built in Asia.<ref>{{cite web|url=http://user.hs-nb.de/biw/caston/haer/haer.html|title=Historic Wooden Bridges/"Covered Bridges"|date=11 July 2011|publisher=HSNB.DE|access-date=15 October 2018|archive-url=https://web.archive.org/web/20160304091121/http://user.hs-nb.de/biw/caston/haer/haer.html|archive-date=4 March 2016}}</ref> In later years, some were partly made of stone or metal but the trusses were usually still made of wood; in the United States, there were three styles of trusses, the Queen Post, the Burr Arch and the Town Lattice.<ref>{{cite web|url=https://pabook.libraries.psu.edu/literary-cultural-heritage-map-pa/feature-articles/hidden-masterpieces-covered-bridges-pa |title=Hidden Masterpieces: Covered Bridges in PA |date=Spring 2010 |publisher=Pennsylvania Book Center|access-date=15 October 2018}}</ref> Hundreds of these structures still stand in North America. They were brought to the attention of the general public in the 1990s by the novel, movie and play ''[[The Bridges of Madison County]]''.<ref>{{cite web|url=https://www.canadiangeographic.ca/article/throwback-thursday-covered-bridges |title=Throwback Thursday: Covered bridges |date=28 May 2015 |publisher=[[Canadian Geographic]]|access-date=15 October 2018}}</ref><ref>{{cite magazine|url=https://www.architecturaldigest.com/gallery/historic-covered-bridges-slideshow/all |title=Visit America's Most Idyllic Covered Bridges |date=December 2016|magazine=[[Architectural Digest]] |access-date=15 October 2018}}</ref>
[[File:Nordhordalandsbrua towards north.jpg|thumb|alt=A concrete bridge over a large body of water|Floating concrete pontoons support the weight of the [[Nordhordland Bridge]] as it crosses a deep [[fjord]] in Norway.{{sfn|Watanabe|2003|pp=129-130}}
]]
A [[pontoon bridge]], also known as a floating bridge, uses [[float (nautical)|floats]] or shallow-[[draft (hull)|draft]] boats to support a continuous deck for pedestrian or vehicle travel over water.<ref>{{Multiref
|{{harvnb|Watanabe|2003|p=128}}.
|{{harvnb|Brown|2005|p=203}}.
|{{harvnb|Bennett|1999|p=229}}.
}}</ref> Pontoon bridges are typically used where waters are too deep to build piers, or as a mechanism to implement a movable [[swing bridge]] in a canal.{{sfn|Birnstiel|2000|pp=668, 679}}
<!--
Pontoon bridges were used in ancient China.<ref>{{Multiref
|{{harvnb|Bennett|1999|p=12}}.
|{{harvnb|Brown|2005|pp=8, 19}}.
|{{harvnb|Bennett|2000|p=2}}.
}}</ref> c
-->
During the [[Second Persian invasion of Greece]], Persian ruler [[Xerxes I|Xerxes]] built a [[Xerxes' pontoon bridges|large pontoon bridge]] across the [[Hellespont]], consisting of two parallel rows of 360 boats.<ref>{{Multiref
|{{harvnb|Brown|2005|pp=8, 19, 80}}.
|{{harvnb|Bennett|2000|p=3}}.
}}</ref>


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=22 February 2008 |publisher=WeldingHistory.org |access-date=29 April 2008 |archive-url=https://web.archive.org/web/20080803060938/http://www.weldinghistory.org/whistoryfolder/welding/wh_1900-1950.html |archive-date=3 August 2008 }}</ref>
Several pontoon bridges are in use in the modern world. Washington state in the US has several, including [[Hood Canal Bridge]].{{sfn|Watanabe|2003|pp=128-129}} In Norway, [[Nordhordland Bridge]] crosses a deep [[fjord]] by resting on floating concrete pontoons.{{sfn|Watanabe|2003|pp=129-130}} Many armies have pontoon bridges that can be rapidly deployed, including the [[PMP Floating Bridge]], designed by the USSR.{{sfn|"Handbook on Soviet Ground Forces". ''Department of the Army''|pp=6.78-6.80}}


==Types of bridge==
==Design==
[[File:Penrith Walk Bridge.jpg|thumb|124x124px|Victoria Bridge, Penrith NSW Australia]]
{{main|Bridge design}}
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 types===
===Design process===
Bridges may be classified by how the actions 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 these to some degree, but only a few will predominate. The separation of forces and moments may be quite clear. In a [[Suspension bridge|suspension]] or [[cable-stayed bridge]], 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.
<!--
{{Clear}}
[[File:Sandhill Road overpass.jpg|thumb|alt=A freeway with several cars driving on it, with two concrete bridges passing overhead| Many overpass bridges in the United States [[Interstate Highway System]] are concrete [[box girder bridge]]s, such as these bridges over [[Interstate 280 (California)|Interstate 280]] in California.]]
{| class="wikitable"
-->
|-
The process for designing a new bridge typically goes through several stages, progressively refining the design.{{sfn|Tang|2014|p=2}} An early step in the design process{{snd}}sometimes called ''conceptual design''{{snd}}is to consider the multiple requirements that a bridge must satisfy.{{sfn|Tang|2014|p=2}} Requirements that are directly related to function include lifespan, safety, climate, soil condition, traffic volume, the size and nature of the obstacle to be traversed, and clearance required for passage underneath.<ref name=reqmnt>{{Multiref
| style="text-align:center;"|[[File:BeamBridge-diagram.svg|200px]]'''Beam bridge'''
|{{harvnb|Tang|2014|pp=3–4}}.
|[[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 | access-date=14 May 2008 | url-status=live | archive-url=https://web.archive.org/web/20080518121256/http://www.design-technology.org/beambridges.htm | archive-date=18 May 2008 | df=mdy-all }}</ref> They are typically made of steel, concrete or wood. [[Girder bridge]]s and [[plate girder bridge]]s, usually made from steel, are types of beam bridges. [[Box girder bridge]]s, made from steel, concrete, or both, are also beam bridges. Beam bridge spans rarely exceed {{convert|250|ft|m}} long, as the flexural stresses increase proportionally to the square of the length (and deflection increases proportionally 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] {{webarchive|url=https://archive.today/20130122060213/http://www.engineersedge.com/beam_bending/beam_bending1.htm |date=22 January 2013 }}. ''Engineers Edge''. Retrieved on 23 April 2013.</ref> However, the main span of the [[Rio–Niteroi Bridge]], a box girder bridge, is {{convert|300|m|ft}}.<ref>{{cite book |author1=de Vasconcelos, Augusto Carlos |title=Handbook of International Bridge Engineering |author2=Marchesini, Gilson L. |author3=Timerman, Júlio |date=2014 |publisher=CRC Press |isbn=978-1-4398-1029-3 |editor1=Chen, Wai-Fah |location=Boca Raton, Florida |pages=184–186 |chapter=4.4 Steel Box Bridges |editor2=Duan, Lian |chapter-url=https://books.google.com/books?id=fYcAAQAAQBAJ&pg=PA184 |accessdate=26 July 2015}}</ref>
|{{harvnb|Barker|2007|pp=96–101}}.
|{{harvnb|Hu|2016|pp=98, 106–108, 112}}.
|{{harvnb|Cruickshank|2010|p=38}}.
}}</ref> Other constraints may include construction cost, maintenance cost, aesthetics, time available for construction, owner preference, and experience of the builders.<ref name=reqmnt/> Some bridge designs consider factors such as impact to environment and wildlife; and the bridge's economic, social, and historic relationship to the local community.{{sfn|Hu|2016|pp=98, 106–108}} After the requirements of a bridge are established, a bridge designer uses [[structural analysis]] methods to identify candidate designs.{{sfn|Barker|2007|pp=45-51}} Several designs may meet the requirements. The [[value engineering]] methodology can be used to select a final design from multiple alternatives.{{sfn|Hu|2016|pp=66, 69–72, 106–109, 112}} This methodology evaluates candidate designs based on weighted scores assigned to several different criteria, such as: cost, service life, durability, availability of resources, ease of construction, construction time, and maintenance cost.{{sfn|Hu|2016|pp=66, 69–72, 106–109, 112}}


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 magazine|date=28 May 1956|title=A big prefabricated bridge|magazine=[[Life (magazine)|Life]]|volume=40|issue=22|pages=53–60}}</ref> Beam bridges are the simplest and oldest type of bridge in use today,<ref>{{cite web|url=http://www.asceville.org/cw_bridges_explore.html|title=Civil What?!: Explore Bridges|website=ASCEville |access-date=2 February 2017|url-status=live|archive-url=https://web.archive.org/web/20170203161112/http://www.asceville.org/cw_bridges_explore.html|archive-date=3 February 2017}}</ref> and are a popular type.<ref>{{Cite journal|title=Forensic Examination of a Noncomposite Adjacent Precast Prestressed Concrete Box Beam Bridge|journal=Journal of Bridge Engineering|volume=15|issue=4|doi=10.1061/(ASCE)BE.1943-5592.0000110|year=2010|pages=408–418 | last1 = Naito | first1 = Clay | last2 = Sause | first2 = Richard | last3 = Hodgson | first3 = Ian | last4 = Pessiki | first4 = Stephen | last5 = Macioce | first5 = Thomas|issn=1084-0702 }}</ref>
An important requirement considered during the design process is the [[service life]], which is a specific number of years that the bridge is expected to remain in operation with routine maintenance (and without requiring major repairs).<ref>{{Multiref
|-
|{{harvnb|Hopper|Langlois|2022|pp=1–5, 19–20}}.
| style="text-align:center;"|[[File:TrussBridge-diagram.svg|200px]]'''Truss bridge'''
|{{harvnb|Kulicki|2014|p=113}}.
| 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.<ref>[https://books.google.com/books?id=A3oSAAAAYAAJ Science and Industry] {{Webarchive|url=https://web.archive.org/web/20170215092202/https://books.google.com/books?id=A3oSAAAAYAAJ |date=2017-02-15 }}, Members of a Truss Bridge by Benj. F. La Rue, Home Study Magazine, Published by the Colliery Engineer Company, Vol 3, No. 2, March 1898, pages 67–68.</ref> 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.
|{{harvnb|Mangus|2014|p=632}}.
|-
}}</ref>{{efn|Routine maintenance includes replacing bridge elements that are designed to be replaced, such as the wearable surface of the deck, or certain cables.{{sfn|Hopper|Langlois|2022|p=5}} }} For example, wood bridge [[Superstructure#Bridges|superstructures]] typically have a service life of 10 to 50 years.{{sfn|Fridley|Duan|2014|pp=348-350}}{{efn|Bridges made from [[glued laminated timber]], if properly designed, can have service lives longer than 50 years.{{sfn|Fridley|Duan|2014|p=350}}}} Concrete highway bridges can have service lives of 75 to 150 years.{{sfn|Hopper|Langlois|2022|p=5}} A bridge design methodology incorporates the service life into the design process.{{sfn|Hopper|Langlois|2022|pp=5-20}}
| style="text-align:center;"|[[File:CantileverBridge-diagram.svg|200px]]'''Cantilever bridge'''
|[[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 and 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.
===Specifications and standards===
One of the requirements a new bridge must satisfy is compliance with the local bridge design specifications and codes which{{snd}}in some countries{{snd}}may be legally binding requirements.<ref>{{Multiref
|{{harvnb|Tang|2014|p=3}}.
|{{harvnb|Barker|2007|p=101}}.
}}</ref> In many countries, these specifications are developed and published by [[standards organizations]] that define acceptable bridge-building practices and designs. In Europe, the organization is the [[European Committee for Standardization]], and the standards it publishes are the [[Eurocodes]].{{sfn|"Eurocodes: Building the Future". ''European Commission'' }} In the United States, the [[American Association of State Highway and Transportation Officials]] (AASHTO) publishes the AASHTO LRFD Bridge Design Specifications.{{sfn|"AASHTO LRFD Bridge Design Specifications"}}{{efn|A list of some bridge-related specifications in the US is found in ''[[#CITEREFTroitsky1994|Planning and Design of Bridges]]''.{{sfn|Troitsky|1994|pp=177-179}}}} Canada's bridge standard is the Canadian Highway Bridge Design Code, developed by the non-profit [[CSA Group]].{{sfn| "CSA S6:19, Canadian Highway Bridge Design Code". ''CSA Group'' }} Agencies that regulate [[aviation safety|aviation]] or [[waterway]]s may also impose standards that dictate some aspects of a bridge design, such as requirements for [[Aviation obstruction lighting|aviation warning lights]] at the top of bridge towers, or [[Navigational aid|navigational warning lights]] on bridge supports located in [[navigable waterway]]s.<ref>{{Multiref
|{{harvnb| "Obstruction Marking and Lighting". ''FAA''}}. Aviation.
|{{harvnb| "Bridge Lighting". ''US National Archives'' }}. Navigable waterways.
}}</ref>


The longest cantilever bridge is the single-spanned {{conv|549|m}} [[Quebec Bridge]] of 1919 in Quebec, Canada. It took this title from the [[Forth Bridge]] of 1890, spanning between [[North Queensferry|North]] and [[South Queensferry]], [[Edinburgh]], Scotland with a double-span of {{conv|521|m}} each.
===Aesthetics===
|-
[[File:RhB ABe 4-4 III Kreisviadukt Brusio.jpg|thumb|left|alt=A train moving atop a stone bridge in an attractive valley|upright=1.3|The [[Brusio spiral viaduct]]{{snd}}a part of the [[Bernina railway]] in Switzerland{{snd}}is designated as a [[World Heritage Site]].{{sfn| "Rhaetian Railway in the Albula". ''UNESCO World Heritage Convention'' }}
| style="text-align:center;"|[[File:ArchBridge-diagram.svg|200px]]'''Arch bridge'''
]]
|[[Arch bridge]]s 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=https://books.google.com/books?id=E7ywmb24EQMC&q=%22world+famous+arch+bridges+in+slovenia%22&pg=PA121 |title=World Famous Arch Bridges in Slovenia |language=en, fr |author=Gorazd Humar |date=September 2001 |publisher=Presses des Ponts |book-title=Arch'01: troisième Conférence internationale sur les ponts en arc Paris |editor=Charles Abdunur |pages=121–124 |location=Paris |isbn=2-85978-347-4 |url-status=live |archive-url=https://web.archive.org/web/20160730012023/https://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 |archive-date=30 July 2016}}</ref>
A bridge's appearance is one of the factors considered during its design.{{sfn|Tang|2014|pp=22-24}} Attractive bridges can have a positive impact on a community, and some bridges can even be considered as works of art.<ref>{{Multiref
|{{harvnb|Goettemoeller|2014|pp=49–55, 75}}.
|{{harvnb|Barker|2007|pp=51–66}}.
|{{harvnb|Cruickshank|2010|p=312}}.
}}</ref> Bridge designers that are known for emphasizing the visual appeal of their bridges include [[Thomas Telford]], [[Gustave Eiffel]], [[John Roebling]], [[Robert Maillart]], and [[Santiago Calatrava]].<ref>{{Multiref
|{{harvnb|Goettemoeller|2014|pp=52–53}}. Telford, Eiffel, Roebling.
|{{harvnb|Brown|2005|pp= 164, 174-17}}. Calatrava.
|{{harvnb|Shirley-Smith|Billington}}. Maillart.
}}</ref> Qualities that influence the perceived attractiveness of a bridge include proportion, color, texture, order, refinement, environmental integration, and functionality.{{sfn|Leonhardt|2014|pp=43-46}}


The world's largest arch bridge is the [[Chaotianmen Bridge]] over the [[Yangtze River]] with a length of {{convert|1741|m|ft|0|abbr=on}} and a span of {{convert|552|m|ft|0|abbr=on}}. The bridge was opened 29 April 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 | access-date=18 February 2013 | title=Longest bridge, steel arch bridge | archive-url=https://web.archive.org/web/20131019124452/http://www.guinnessworldrecords.com/records-1/longest-bridge-steel-arch-bridge/ | archive-date=19 October 2013 | df=mdy-all }}</ref>
The art historian [[Dan Cruickshank]] notes that bridges are regarded as manifestations of human imagination and ambition, and that many bridges transcend their original utilitarian role and become a work of art.{{sfn|Cruickshank|2010|pp=8-9}} He writes "[a] great bridge has an emotional impact, it has a sublime quality and a heroic beauty that moves even those who are not accustomed to having their senses inflamed by the visual arts."{{sfn|Cruickshank|2010|pp=8-9}}
|-
{{clear}}
| style="text-align:center;"|[[File:TiedarchBridge-diagram.svg|200px]]'''Tied&nbsp;arch bridge'''
|[[Tied-arch bridge]]s 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.<ref>{{cite web |url=http://www.bath.ac.uk/ace/uploads/StudentProjects/Bridgeconference2009/Papers/MASKELL.pdf |title=A Critical Analysis of North Shore Footbridge, Stockton-on-Tees, UK |first=Daniel |last=Maskell |work=Proceedings of Bridge Engineering 2 Conference 2009 |publisher=bath.ac.uk |year=2009 |access-date=11 December 2009 |quote=Under vertical  dead  loads  and  uniform  imposed  loads  the arches  support  the  loads  under  pure  axial compression with  the  deck  edge  cables  acting  as  horizontal  ties.}}</ref> They are also called bowstring arches.
|-
| style="text-align:center;"|[[File:SuspensionBridge-diagram.svg|200px]]'''Suspension bridge'''
|[[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 bed of the lake, river or sea. 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{{full citation needed|date=November 2019}}</ref>


The longest suspension bridge in the world is the {{convert|4608|m|0|abbr=on}} [[1915 Çanakkale Bridge]] in Turkey.
===Material===
|-
| style="text-align:center;"|[[File:CableStayedBridge-diagram.svg|200px]]'''Cable-stayed bridge'''
|[[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 | url-status=live | archive-url=https://web.archive.org/web/20080518142005/http://www.newton.dep.anl.gov/askasci/eng99/eng99373.htm | archive-date=18 May 2008 | df=mdy-all }}</ref> The first known cable-stayed bridge was designed in 1784 by C. T. (or C. J.) Löscher.<ref>{{cite book|url = https://books.google.com/books?id=AhSgrMcT4sgC&q=loescher+cable-stayed&pg=PA5 |title = Cable Stayed Bridges|page = 7|url-status = live|first =René|date = 1999 |last=Walther | publisher=Thomas Telford |archive-url=https://web.archive.org/web/20161115132533/https://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 |archive-date=15 November 2016 |isbn = 978-0-7277-2773-2}}</ref><ref>{{cite web|url = http://www.contech.co.nz/uploaded/Marcel%20Poser%20-%20Cable%20Stayed%20Structures%20and%20Stay%20Cable%20Technology.pdf |title = Cable Stayed Structures and Stay Cable Technology|last = Poser|first =Marcel |archive-url=https://web.archive.org/web/20130209123954/http://www.contech.co.nz/uploaded/Marcel%20Poser%20-%20Cable%20Stayed%20Structures%20and%20Stay%20Cable%20Technology.pdf |archive-date=9 February 2013 }}</ref>


The longest cable-stayed bridge since 2012 is the {{convert|1104|m|0|abbr=on}} [[Russky Bridge]] in [[Vladivostok]], Russia.<ref>{{cite news|work=The Guardian|date=2 July 2012|author=Elder, Miriam|location=London|title=Russian city of Vladivostok unveils record-breaking suspension bridge|url=https://www.theguardian.com/world/2012/jul/02/russian-vladivostok-record-suspension-bridge|access-date=3 February 2016|url-status=live|archive-url=https://web.archive.org/web/20160120162508/http://www.theguardian.com/world/2012/jul/02/russian-vladivostok-record-suspension-bridge|archive-date=20 January 2016}}</ref>
<!--
|}
[[File:Reinforcing Steel for Stem Wall at South Abutment (September 12, 2016) (29075882214).jpg|thumb|alt=A construction site with a halfway built concrete structure|This concrete bridge support is being prepared for a concrete pour. After the concrete [[Concrete#Curing|cures]], the green [[reinforcing bar]]s will be permanently embedded inside.<ref name=rebar/>]]
-->
<!--
{{multiple image
| header = [[Prestressed_concrete]]
| caption_align=center
| image1 = Acero postesado.jpg
| alt1= A concrete beam with several steel cables emerging from holes in the side of the beam
| caption1 = These [[Prestressed_concrete#Post-tensioned_concrete|post-tensioned]] cables are tightened with [[Jack_(device)#Hydraulic_jack|hydraulic jacks]] to ensure the concrete stays in [[compression (physics)|compression]].
--> <!--
[[File:DallasHighFiveSegmentalBridge.jpg|thumb | alt= A large concrete section of a bridge is suspended above the ground by a large crane| The small circular holes in this section of [[box girder]] will hold [[Prestressed concrete|prestressing cables]], which run the length of the girder.<ref name=prestress/> ]]
-->
A bridge designer can select from a wide variety of materials, including wood, brick, rope, stone, iron, steel, and concrete.<ref>{{Multiref
|{{harvnb|Collings|2000|pp=407–408}}.
|{{harvnb|Brown|2005|p=6}}.
}}</ref>{{efn|The number of bridges in the US in 2018, based on their primary material, are: 60% concrete, 30% steel, and 3% wood (the remainder are masonry, aluminum iron, etc).{{sfn|Nowak|Iatsko|2018}}}} A bridge made from two or more distinct materials (such as steel and concrete) is known as a composite bridge.{{sfn|Collings|2000|pp=407–408}} Some of the largest arch bridges are composite, because they are made from concrete and steel.{{sfn| Zheng|Wang|2018}}


Some Engineers sub-divide 'beam' bridges into slab, beam-and-slab and box girder on the basis of their cross-section.<ref name=":1" /> A slab can be solid or [[hollow-core slab|voided]] (though this is no longer favored for inspectability reasons) while beam-and-slab consists of concrete or steel girders connected by a concrete slab.<ref name=":2" /> A [[Box girder bridge|box-girder]] cross-section consists of a single-cell or multi-cellular box. In recent years, [[integral bridge]] construction has also become popular.
Wood is an inexpensive, [[renewable resource]] with a high [[strength-to-weight ratio]], but it is rarely used for modern roadway bridges because it is prone to degradation from the environment, and is much weaker than steel or concrete.{{sfn|Zhao|2017|pp=84-85}}  Wood is primarily used in beam or truss bridges, and is also used to build large [[trestle bridge]]s for railways.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|pp=39–47}}.
|{{harvnb|Zhao|2017|pp=84–85}}.
}}</ref> When wood is used, it is often in the form of [[glued laminated timber]].{{sfn|Zhao|2017|pp=84-85}} [[Masonry]] includes stone and brick, and is suitable only for elements of a bridge that are under [[compression (physics)|compression]] (as opposed to [[tension (physics)|tension]]), therefore, masonry is limited to structures such as arches or foundations.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|pp=47–50}}.
|{{harvnb|Bennett|1999|pp=14–16}}.
}}</ref> In the twentieth century, large masonry bridges {{snd}}although superseded by concrete in the West{{snd}}continued to be built in China.{{sfn|Ou|Chen|2005}}
[[File:Ironbridge 6.jpg|thumb|alt= An ornate bridge made of iron, passing over a small, lush valley|[[The Iron Bridge]] in [[Shropshire]], England, completed in 1781, is the first major bridge made entirely of [[cast iron]].{{sfn|Cruickshank|2010|pp=50-51}}]]


===Fixed or movable bridges===
Iron{{snd}}including [[cast iron]] and [[wrought iron]]{{snd}}was used extensively from the late 1700s to late 1800s, primarily for arch and truss structures. Iron is relatively brittle, and has been replaced by steel for all but ornamental uses.<ref>{{Multiref
{{Redirect|Fixed link|other uses|Intercontinental and transoceanic fixed links|and|Link (disambiguation)}}
|{{harvnb|Cruickshank|2010|pp=50–52}}.
[[File:AVLB 01.jpg|thumb|Alvis Unipower TBT (tank bridge transporter) of the British army]]
|{{harvnb|Bennett|1999|pp=31–33}}.
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, 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.<ref>{{Cite book|last=Hovey|first=Otis Ellis|title=Movable bridges|publisher=John Wiley & Sons, Inc.|year=1927|location=New York|pages=1–2|hdl=2027/mdp.39015068174518}}</ref>
|{{harvnb|Bennett|2000|pp=17–18}}.
|{{harvnb|Brown|2005|p=92}}.
}}</ref> Steel is one of the most common materials used in modern bridges because it is strong in both compression and tension.{{sfn|Bennett|2000|pp=16-21}} Steel was made in small quantities in antiquity, but became widely available in the late 1800s following invention of new [[smelting]] processes by [[Henry Bessemer]] and [[William Siemens]]. Truss bridges and beam bridges are often made of steel, and steel wires are an essential component of virtually all suspension bridges and cable-stayed bridges.<ref>{{Multiref
|{{harvnb|Bennett|1999|pp=36–42}}.
|{{harvnb|Bennett|2000|pp=18–20}}.
|{{harvnb|Brown|2005|pp=92–104}}.
}}</ref> Concrete bridges make extensive use of steel, because all concrete used in bridges contains steel [[reinforcing bars]] or steel [[prestressed]] cables.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|pp=321–327}}.
|{{harvnb|Brown|2005|pp=140–141}}.
|{{harvnb|Bennett|1999|pp=68–69}}.
}}</ref> Steel bridges are more expensive than comparable concrete bridges, but they are much lighter (for the same strength), faster to build, and offer more flexibility during construction and repair.<ref>{{Multiref
|{{harvnb|Bennett|1999|p=70}}.
|{{harvnb|Ellobody|2014|pp=1–2}}.
}}</ref>


The tank bridge transporter (TBT) has the same cross-country performance as a tank even when fully loaded. It can deploy, drop off and load bridges independently, but it cannot recover them.<ref>{{cite web |url=http://army.mod.uk/royalengineers/equipment/702.aspx |title=Close Support Bridging (CSB) - British Army Website |publisher=Army.mod.uk |accessdate=2012-08-07 |archive-url=https://web.archive.org/web/20111126032356/http://army.mod.uk/royalengineers/equipment/702.aspx |archive-date=2011-11-26 |url-status=live }}</ref>
Concrete is commonly used in modern bridges, and many [[roadway]] bridges are built primarily with a [[reinforced concrete]] beam structure, often of the [[box girder]] variety.{{sfn|Bennett|2000|pp=25-27}}{{efn|
[[High-performance concrete]] is becoming more commonly used in bridges (compared to conventional concrete) because it suffers less damage from heavy traffic and lasts longer.{{sfn|Blank|2014|pp=74, 76-77, 81}} Conventional concrete has strength about 25 to 50 MPa, whereas high-performance concrete has strength about 50 to 100 MPa.{{sfn|Blank|2014|pp=74, 76-77, 81}}
}} The shape of concrete elements is determined by the [[formwork]] ([[Molding (process)|mold]]) into which the concrete is poured (cast): the concrete will adopt the shape of the formwork as it [[Concrete#Curing|cures]].<ref>{{Multiref
|{{harvnb|Bennett|2000|p=25}}.
|{{harvnb|Blank|2014|p=82}}.
}}</ref> Beams can be [[Precast concrete|precast offsite]] and transported to the bridge site, or [[Cast-in-place concrete|cast in place]].{{sfn|Bennett|1999|p=53}} Bridges use concrete that contains embedded steel reinforcing bars{{snd}}placed within the concrete when it is initially poured{{snd}}which greatly increase the strength.<ref name=rebar>{{Multiref
|{{harvnb|Bennett|1999|pp=68–69}},
|{{harvnb|Brown|2005|pp=126–134}}.
|{{harvnb|Cruickshank|2010|pp=322–327}}.
}}</ref> Concrete is a strong and inexpensive material, but is brittle and can crack when in tension.{{sfn|Bennett|1999|pp=68-69}} <!-- thus concrete is suitable for bridge elements that are in compression, such as foundations and arches.{{cn}} --> If concrete is used in elements that may experience tension, prestressed cables are usually embedded within the concrete and tightened, which compresses the concrete.<ref name=prestress>{{Multiref
|{{harvnb|Bennett|1999|pp=68–69}}.
|{{harvnb|Cruickshank|2010|pp=322–327}}.
|{{harvnb|Hewson|2000|pp=241–255}}.
|{{harvnb|Zhao|2017|pp=290–294}}.
|{{harvnb|Blank|2014|pp=77–78}}.
}}</ref> When a horizontal beam is placed into the bridge and carries a load, the undesirable tension (produced by the tendency of the beam to sag) is counteracted by the compression from the prestressed cables.<ref name="Cruickshank 2010 322–327"/> The prestressed cables can be pre-tensioned (stretched before{{snd}}and while{{snd}}the concrete cures); or post-tensioned (placed within tubes in the concrete, and tightened after the concrete cures).<ref name="Cruickshank 2010 322–327">{{Multiref
|{{harvnb|Cruickshank|2010|pp=322–327}}.
|{{harvnb|Hewson|2000|pp=241–255}}.
|{{harvnb|Blank|2014|pp=77–78}}.
}}</ref>


===Double-decked bridges{{Anchor|Double-decked}}===
===<span class="anchor" id="Double-decked bridges"></span>Double-deck bridge===
{{See also|List of multi-level bridges}}
{{See also|List of multi-level bridges}}
[[File:George Washington Bridge from New Jersey-edit.jpg|thumb|The double-decked [[George Washington Bridge]], connecting New York City and [[Bergen County, New Jersey]], is the world's busiest bridge, carrying 106 million vehicles annually.<ref name="panynj.gov">{{cite web |url=http://www.panynj.gov/bridges-tunnels/george-washington-bridge.html |access-date=14 February 2023|title=Port Authority of New York and New Jersey – George Washington Bridge |publisher=The Port Authority of New York and New Jersey |url-status=live |archive-url=https://web.archive.org/web/20130920192211/http://www.panynj.gov/bridges-tunnels/george-washington-bridge.html |archive-date=20 September 2013}}</ref>]]
<!--
[[File:The padma bridge 02.jpg|thumb|alt=A long, straight, flat bridge over a large body of water|The [[Padma Bridge]] in Bangladesh carries rail traffic on the lower deck and vehicular traffic on the upper deck.{{sfn|"Main Bridge Details". ''Padma Multipurpose Bridge Project''}} ]]
-->
Designers may choose to use a double-deck design (also known as double-decked or double-decker), that carries two decks on top of each other. This technique can be used to increase the amount of traffic a bridge can carry; or when the location constrains the size of the bridge.{{sfn|Kumar|2025}} Double-deck bridges also permit two different kinds of traffic to be safely carried. For example, motor vehicles can be separated from pedestrians or railways.{{sfn|Kumar|2025}} An early double-deck bridge was [[Niagara Falls Suspension Bridge]], which carried rail on the upper deck, and carriages and pedestrians on the lower deck.{{sfn|Brown|2005|p= 87}} [[George Washington Bridge]] in New York carries 14 motor vehicle lanes (eight above, six below), and is the world's busiest bridge, carrying over 100 million vehicles annually.{{sfn|"2024 Monthly Traffic and Percent of E‐ZPass Usage". ''Port Authority of New York and New Jersey''}} Because of their ability to carry large amounts of motor vehicles, double-deck bridges are often found near large cities, such as [[Tsing Ma Bridge]] in Hong Kong,{{sfn|Brown|2005|pp=178-179}} [[Øresund Bridge]] connecting Copenhagen and Malmö,{{sfn|Brown|2005|p=181}} and [[Great Seto Bridge#Constituent bridges|Shimotsui-Seto Bridge]] near Kurashiki.{{sfn|Brown|2005|pp=170-171}}
 
===Load analysis===
[[File:East span San Francisco Oakland Bay bridge.jpg|thumb|left
|alt= A very large suspension bridge passing over a large body of water|upright=1.3|The [[San Francisco–Oakland Bay Bridge]] is designed to withstand severe earthquakes. The [[Eastern span replacement of the San Francisco–Oakland Bay Bridge|eastern span]], shown above, is a [[self-anchored suspension bridge]] which can survive a once-in-1,500-year earthquake.{{sfn| "SAS Maintenance Travelers". ''California Department of Transportation'' }}
]]
A bridge design must accommodate all loads and forces that the bridge might reasonably experience. The totality of the forces that the bridge must tolerate is the [[structural load]], which is often divided into three components: dead load, live load, and environmental load. The [[Structural load#Dead load|dead load]] is the weight of the bridge itself.<ref name=load/>{{efn|The dead load also includes any permanent fixtures on the bridge, such as light poles, traffic signage, and guardrails;{{sfn|Barker|2007|p=161}}}} The [[Structural load#Live load|live load]] is all forces and vibrations caused by traffic passing over the bridge, including weight, braking, and acceleration.<ref name=load/><!--
{{efn|
An important component of the live load carried by a bridge is the vehicle and rail traffic the bridge carries.<ref name=traffic>{{multiref
|{{harvnb|Barker|2007|pp=164–188}}.
|{{harvnb|Ellobody|2014|pp=24, 116–154}}.
}}</ref> <!--
In addition to the weight of the vehicle, other forces must be considered, including braking, acceleration, centrifugal forces, and resonant vibrations.<ref name=braking>{{harvnb|Barker|2007|pp=161–165}}.
</ref>
For roadways, the loads imposed by truck traffic far exceed the loads imposed by passenger cars, and so the bridge design process focuses on trucks.{{sfn|Barker|2007|pp=164-165}}
The loads created by trains and vehicles can be determined by modelling, or by relying on data and algorithms contained in engineering specifications published by organizations such as [[Eurocode]] or [[AASHTO]].{{sfn|Ellobody|2014|pp=4-7, 24}} Alternatively, [[weigh-in-motion]] technology can measure loads on existing bridges with comparable traffic patterns, providing real-world data which can be used to evaluate a proposed bridge design.{{sfn|O'Brien|2015|pp=41-43}}
--> The [[Structural load#Environmental load|environmental load]] encompasses all forces applied by the bridge's surroundings, including weather, earthquakes, mudslides, water currents, flooding, soil subsidence, frost heaving, temperature fluctuations, and collisions (such as a ship striking the pier of a bridge).<!--  
[[Subsidence|soil subsidence]], [[frost heaving]], [[Thermal expansion|temperature fluctuations]], and [[Bridge strike|collisions]] (such as a [[Ship collision|ship striking]] the pier of a bridge).
--><ref name=load>{{Multiref
|{{harvnb|Cruickshank|2010|p=34}}.
|{{harvnb|Ryall|2000|pp=43–44}}.
|{{harvnb|Huff|2022|pp=23–26}}.
|{{harvnb|Barker|2007|pp=161–165}}.
|{{harvnb|Zhao|2017|pp=100–109}}.
}}</ref><!--
{{efn|In addition to classifying loads as dead/live/environmental, an alternative is: dead (or permanent) load (bridge structure) and live (or transient) load (traffic and environment).<ref>{{Multiref
|{{harvnb|Barker|2007|p=161}}.
|{{harvnb|Cruickshank|2010|p=34}}.
}}</ref>
}} -->
Many load sources vary over time, such as vehicle traffic, wind, and earthquakes. A bridge designer must anticipate the maximum values that those loads are likely to reach during the bridge's lifespan.{{sfn|Barker|2007|p=161}} For sporadic events like floods, earthquakes, collisions, and hurricanes, bridge designers select a maximum severity that the design must accommodate.{{sfn|Barker|2007|pp=197, 201}} The severity is based on the [[return period]], which is average time between events of a given magnitude. Return periods range from 10 to 2,500 years, depending on type of event and the country in which the bridge is located.<ref name=returnPeriod>{{Multiref
|{{harvnb|Barker|2007|pp=197, 201}}.
|{{harvnb|Kulicki|2014|p=122}}.
|{{harvnb|Chen|Duan|2014|pp=52, 99, 301, 334, 420, 435, 502, 539, 542, 645, 836, 918}}.
}}</ref>{{efn|
Authors discussing international bridge design policies provide return period examples of 10, 50, 350, 475, 500, 1000, 2000, and 2500 years.<ref name=returnPeriod/>
}} Longer return periods are used for bridges that are a critical part of the transportation infrastructure. For example, if the bridge is a key lifeline in case of emergencies, the designer may utilize relatively long return period, such as 2,000 years; in this example, the design must endure the strongest storm that is expected to happen once every 2,000 years.{{sfn|Barker|2007|pp=161, 197, 201}}
 
====Stress and strain====
{{Further|Stress (mechanics)}}
<!--
[[File:Software app that performs stress analysis on structures.jpg|thumb|alt=A computer screen running an app that is displaying engineering information| [[Computer-aided design|Software applications]] are used in the bridge design process, such as this app that evaluates [[Stress (mechanics)|stress]] and [[Strain (mechanics)|strain]].{{sfn|Krimotat|2014|p=256}}
]]
-->
<!--
[[File:Stress strain ductile.svg|thumb|alt=A two-dimensional graph showing a curved line|Bridge engineers use [[stress–strain curve]]s to assist with the design process.<ref name=stressstrain/>]]
-->
The load forces acting on a bridge cause the components of the bridge to become [[Stress (mechanics)|stressed]]. Stress is a measure of the internal force experienced within a material. Strain is a measure of how much a bridge component bends, stretches, or twists in response to stress. Some strain (bending or twisting) may be acceptable in a bridge component if the material is [[Elasticity (physics)|elastic]]. For example, steel can tolerate some stretching or bending without failing. Other materials, such as concrete, are [[Elasticity (physics)|inelastic]], and their change in shape when stressed is negligible (until the stress becomes excessive and the concrete fails).<ref name=stressstrain>{{Multiref
|{{harvnb|Ellobody|2014|pp=47–54}}.
|{{harvnb|Beer|2017|pp=7–13, 28–34, 55–77, 100–104, 119–122, 237–247}}.
}}</ref>


Double-decked (or double-decker) bridges have two levels, such as the [[George Washington Bridge]], connecting New York City to [[Bergen County]], [[New Jersey]], US, as the world's busiest bridge, carrying 102 million vehicles annually;<ref name="panynj.gov"/><ref name=abcgwb>{{cite web|url=https://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|name-list-style=amp|work=ABC News|date=20 November 2012|access-date=13 September 2013|url-status=live|archive-url=https://web.archive.org/web/20130928002159/https://abcnews.go.com/US/george-washington-bridge-painters-dangerous-job-top-worlds/story?id=17771877|archive-date=28 September 2013}}</ref> [[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]] 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.
A bridge designer must calculate the maximum stress that each bridge component will experience, then select an appropriate design and size for the components to ensure they will safely tolerate the loads on the bridge. Stresses are categorized based on the nature of the force that causes the stress, namely: compression, tension, shear, and torsion. Compression forces compact a component by pushing inward (for example, as felt by a bridge foundation when a heavy tower is resting on it). Tension is a stretching force experienced by a component when pulled (for example by the cables of a suspension bridge). [[Shear force|Shear]] is a sliding force experienced by a component when two offset external forces are applied in opposite directions (for example, during an earthquake when the upper part of a structure is pulled north, and the lower part is pulled south). [[Torsion (mechanics)|Torsion]] is a twisting force.<ref name=stress>{{multiref
|{{harvnb|Brown|2005|pp=14–15}}.
|{{harvnb|Bennett|1999|pp=67–70}}.
}} <!-- |{{harvnb|Shanmugam|2000|pp=95–123}}. -->
</ref>


[[Robert Stephenson]]'s [[High Level Bridge, River Tyne|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 [[Øresund Bridge|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]].
<!--
[[File:Puente atirantado CivilFEM.png|thumb|alt=A computer app displaying a bridge with engineering data|Engineers use [[finite element method]] software tools to evaluate a bridge design.<ref>{{Multiref
|{{harvnb|Shanmugam|2000|pp=188, 293}}.
|{{harvnb|Jones|Howells|2000|pp=640–641}}.
}}</ref>
]]
-->
The bridge design process employs [[structural analysis]] methods that divide the bridge into smaller components, and analyze the components individually, subject to certain constraints.{{sfn|Barker|2007|pp=283-288}} A proposed bridge design is then [[mathematical model|modeled]] with formulas or computer applications.<ref name=computr>{{Multiref
|{{harvnb|Krimotat|2014|pp=253–257}}.
|{{harvnb|Barker|2007|pp=283–288}}.
}}</ref> The models incorporate the loads the bridge will experience, calculate the stresses in the bridge, and provide data to the designer indicating whether the design meets the required design goals.<ref name=computr/><!--
{{efn|Bridge design models include both [[mathematical model]]s and [[numerical model]]s.{{sfn|Barker|2007|pp=283-288}} The mathematical models that assess bridge loads and stresses are complex formulas that typically include differential equations. Solving these formulas directly is virtually impossible, so numerical models are used to provide approximate, but accurate, results.{{sfn|Barker|2007|pp=283-288}}
}}
--> The [[finite element method]] is a numerical model commonly used to perform detailed analysis of stresses and loads of a bridge design.<ref>{{Multiref
|{{harvnb|Yamaguchi|2014|pp=225–226, 236}}.
|{{harvnb|Ellobody|2014|pp=1–7}}.
|{{harvnb|Reddy|2004|pp=1–23}}.
}}</ref><!--
{{efn|An alternative to the finite element method is the simpler, but less powerful, [[finite strip method]].{{sfn|Barker|2007|p=303}} The finite element method models a proposed bridge by dividing it into numerous small, interconnected pieces, and applying a computer algorithm to the pieces. The algorithm simulates the stresses on the bridge that are caused by the loads, and can iterate over time to simulate dynamic movements.{{sfn|Reddy|2004|pp=1-23}}
}}
--> To ensure that a proposed bridge design is sufficiently strong to endure foreseeable stresses, many bridge designers use methodologies such as [[limit state design]] (used in Europe and China) or [[Load and Resistance Factor Design]] (LRFD) (used in US).<ref>{{Multiref
|{{harvnb|Barker|2007|pp=113–118}}.
|{{harvnb|Zhao|2017|pp=125–131, 341–349}}.
|{{harvnb|Du|Au|2005}}.
}}</ref> <!--
These methodologies add a margin of safety to the bridge design by incorporating [[safety factor]]s into the design process.{{sfn|Barker|2007|pp=114-120, 134-137, 142, 157-158}}
The safety factors are applied two ways: (a) increasing the assumed loads and stresses the bridge will experience; and (b) decreasing the assumed strength of the bridge's structure.{{sfn|Barker|2007|pp=117-118}}
{{efn|The strength of a bridge component is referred to as ''resistance'' in the context of LRFD.{{sfn|Barker|2007|pp=113-114}} The magnitude of the safety factors are based on several considerations, including the bridge's own dead weight, vehicle traffic, earthquakes, water or ice flows (from rivers or ocean currents) impacting the bridge foundations, rain or snow on the bridge, wind, settling into the soil, and collisions.{{sfn|Barker|2007|pp=113-114, 161-162, 463}} Collisions include vehicles on the deck striking a bridge structure; or a ship striking a bridge foundation.{{sfn|Barker|2007|p=463}}}}


===Viaducts===
A bridge designer evaluates the output of the models to determine if the design meets the design goals. Many criteria are evaluated when determining if a bridge design is sufficient, including deflection, cracking, fatigue, [[Bending|flexure]], shear, torsion, buckling, settlement, bearing, and sliding.{{sfn|Barker|2007|pp=114, 124-127}} The criteria, and their allowable values, are termed [[limit state]]s. The set of limit states selected for a design are based on the bridge's structure and purpose.<ref>{{Multiref
{{main|Viaduct}}
|{{harvnb|Barker|2007|pp=114, 124–127}}.
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]].
|{{harvnb|Zhao|2017|pp=127–131 }}.
}}</ref>
-->


===Multi-way bridge===
==== Vibration ====
{{main|Multi-way bridge}}
<!--
[[File:Tridge Undercarriage.jpg|thumb|The [[The Tridge (Midland, Michigan)|Tridge]], a [[multi-way bridge]] in [[Midland, Michigan]], U.S.]]
[[File:Tacoma Narrows Bridge destruction.ogv|alt=Video shows a large suspension bridge moving and twisting wildly, pushed by the wind, eventually collapsing.|thumb|The [[Tacoma Narrows Bridge (1940)#Collapse|Tacoma Narrows Bridge]] collapsed shortly after opening in 1940 due to failure of the design to properly account for wind forces.<ref name=narrows/>]]
A multi-way bridge has three or more separate spans which meet near the center of the bridge. Multi-way bridges with only three spans appear as a "T" or "Y" when viewed from above. Multi-way bridges are extremely rare. [[The Tridge (Midland, Michigan)|The Tridge]], [[Margaret Bridge]], and [[Y-Bridge (Zanesville, Ohio)|Zanesville Y-Bridge]] are examples.
-->


{{anchor|road bridge}}
<!--
[[File:Vortex-street-animation.gif|thumb|alt=An animated video showing wind blowing left to right, creating circular vortexes as it passes by a fixed object|Bridge designers must account for forces caused by wind, such as the [[vortex shedding]] shown here.<ref name=flutter_vortex/>]]
-->


===Bridge types by use===
Many loads imposed on a bridge{{snd}}such as wind, earthquakes, and vehicular traffic{{snd}}can cause a bridge to experience irregular or periodic forces, which may cause bridge components to vibrate or [[oscillate]].<ref>{{Multiref
A bridge can be categorized by what it is designed to carry, such as trains, pedestrian or road traffic ('''road bridge'''), a pipeline ('''Pipe bridge''') 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. Overway is a term for a bridge that separates incompatible intersecting traffic, especially road and rail.<ref>{{cite news |url=http://nla.gov.au/nla.news-article170491612 |title=The Mile-End Crossing |newspaper=[[The Observer (Adelaide)|The Observer]] |volume=LXXXI |issue=6,004 |location=South Australia |date=23 February 1924 |access-date=26 March 2018 |page=16 |via=National Library of Australia}}</ref>
|{{harvnb|Ryall|2000|pp=62–68}}.
|{{harvnb|Barker|2007|pp=178–179, 195}}.
|{{harvnb|O'Brien|2015|pp=40, 57–58}}.
}}</ref> Some bridge components have inherent [[resonant frequencies]] to which they are particularly susceptible, and vibrations near those frequencies can cause very large stresses.<ref>{{Multiref
|{{harvnb|Ellobody|2014|pp=24, 130, 142–144}}.
|{{harvnb|Cruickshank|2010|pp=252–253}}.
|{{harvnb|O'Brien|2015|pp=40, 57–58}}.
}}</ref>
[[File:FEMA - 2816 - Photograph by FEMA News Photo taken on 01-17-1994 in California.jpg|thumb|alt=A collapsed concrete bridge, with a broken support pier.
|The [[1994 Northridge earthquake]] damaged several bridges.<ref>{{Multiref
|{{harvnb|Yashinsky|2014|p=54}}.
|{{harvnb|"Northridge Earthquake Image 2816". ''National Archives''}}.
}}</ref> ]]
Winds can produce a variety of vibrational forces on a bridge, including [[Aeroelasticity#Flutter|flutter]], [[galloping (wind)|galloping]], and [[vortex shedding]].<ref name=flutter_vortex>{{Multiref
|{{harvnb|Cai|2014|pp=541–547}}.
|{{harvnb|Ryall|2000|pp=63–66}}.
|{{harvnb|Jones|Howells|2000|pp=641–644}}.
|{{harvnb|Scott|2001|pp=89–93}}.
}}</ref> Considering wind forces during the design process is especially important for long, slender bridges (typically suspension or cable-stayed bridges).<ref>{{Multiref
|{{harvnb|Cai|2014|pp=535–536}}.
|{{harvnb|Ryall|2000|p=63}}.
|{{harvnb|Jones|Howells|2000|pp=641–644}}.
|{{harvnb|O'Brien|2015|pp=40, 57–58}}.
}}</ref>
<!--
The Eurocode guideline for bridge design specifies that vibration stress due to moving vehicles should be accounted for by including an additional 10% to 70% of the vehicles' static load; the exact value depends on the span length, the number of traffic lanes, and the type of stress (bending moment or shear force).{{sfn|Dawe |2003 |p=149}}
-->
If resonance issues are identified in the design process, they must be mitigated. Common techniques to address vibration include increasing the rigidity of the bridge deck by adding trusses and adding dampers to cables and towers.<ref>{{Multiref
|{{harvnb| O'Brien|2015 |pp=41–46, 57}}.
|{{harvnb|Cruickshank|2010|pp=243–244}}.
|{{harvnb|Brown|2005|pp=170, 184, 203}}.
|{{harvnb| "Resisting the Twisting". ''Golden Gate Bridge Highway and Transportation District'' }}.
}}</ref><!--
{{efn|
One mechanism used to combat oscillations is a [[tuned mass damper]], which was first used in the [[Pont de Normandie]] in 1995.<ref>{{Multiref
|{{harvnb|Brown|2005|pp=170, 184, 203}}.
|{{harvnb|Cai|2014|pp=552-553}}.
|{{harvnb|Farquhar |2000|p=589 }}.
}}</ref> The [[Akashi Kaikyo Bridge]] has twenty tuned mass dampers, weighing {{convert|9|tonne|lbs|spell=in|round=10}} each, inside its steel towers.{{sfn|Sangree|Shafer|2003}}
}}
--> Neglecting to account for vibrations and oscillations can lead to bridge failure.<!--
{{efn|
An early example of a bridge failure related to resonant vibration was the [[Angers Bridge]] collapsed in 1850, killing over 200 people, partly due to soldiers [[marching]] on the bridge in a manner that increased resonant oscillations.{{sfn|Cruickshank|2010|pp=243-244}} In spite of advances in engineering technologies, modern bridges continue to experience severe swaying issues when large numbers of pedestrians are walking on the bridge, even when they are not marching in a synchronized manner.<ref name=millen/>
}}
--> The [[Tacoma Narrows Bridge (1940)#Collapse|Tacoma Narrows Bridge]] collapsed in the 1940 in winds of {{convert|68|km/h|mph|abbr=on|sp=us}}, even though the bridge was designed to withstand winds up to {{convert|206|km/h|mph|abbr=on|sp=us}}. Investigations revealed that the designer failed to account for wind effects such as flutter and resonant vibrations.<ref name=narrows>{{Multiref
|{{harvnb|Barker|2007|pp=12–14}}.
|{{harvnb|Cruickshank|2010|pp=252–253}}.
|{{harvnb|"Tacoma Narrows Bridge History". ''Washington Department of Transportation''}}.
}}</ref> <!-- 
The [[Golden Gate Bridge]] was damaged in 1951 due to wind forces, and as a result was reinforced with additional stiffening elements.{{sfn| "Resisting the Twisting". ''Golden Gate Bridge Highway and Transportation District'' }}
-->


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.<ref>{{cite journal |last1=Roberts |first1=Gethin |last2=Brown |first2=Christopher |last3=Tang |first3=Xu |last4=Ogundipe |first4=Oluporo |date=February 2015 |title=Using satellites to monitor Severn Bridge structure, UK |journal=Proceedings of the Institution of Civil Engineers - Bridge Engineering |volume=168 |issue=4 |pages=330–339 |doi=10.1680/bren.14.00008 |url=http://bura.brunel.ac.uk/handle/2438/12192 }}</ref>
Bridges can suffer severe damage when subjected to [[earthquake]] ground motions.<ref>{{Multiref
|{{harvnb|Yashinsky|2014|pp=53–55, 61, 77, 83, 94}}.
|{{harvnb|Bennett|1999|p=173}}.
}}</ref> During a seismic event, several phenomena can occur, such as long-period velocity pulses, shear cracks, large ground motions, vertical accelerations, and [[soil liquefaction]].{{sfn|Yashinsky|2014|pp=53-56}} To mitigate risks, [[earthquake engineer]]s study seismic data to classify and quantify the motions experienced by bridges.{{sfn|Yashinsky|2014|pp=53-54}} These studies are used by governments to create and revise design standards that specify the types of seismic movements that new [[Earthquake-resistant structures|bridges must withstand]].{{sfn|Yashinsky|2014|p=53}}<!--
{{
efn|Government agencies that have published earthquake engineering standards for bridges include: [[Chinese Ministry of Transport]], [[Japan Road Association]], [[Eurocode 8: Design of structures for earthquake resistance| European Committee for Standardization]], [[American Association of State Highway and Transportation Officials]], and [[California Department of Transportation]].{{sfn|Yashinsky|2014|p=53}}
}}
-->


Conservationists use [[Wildlife crossing|wildlife overpasses]] to reduce [[habitat fragmentation]] and animal-vehicle collisions.<ref>{{Cite web|last=Greenfield|first=Patrick|date=23 January 2021|title=How creating wildlife crossings can help reindeer, bears – and even crabs|url=http://www.theguardian.com/environment/2021/jan/23/how-wildlife-crossings-are-helping-reindeer-bears-and-even-crabs-aoe|url-status=live|archive-url=https://web.archive.org/web/20210123083528/https://www.theguardian.com/environment/2021/jan/23/how-wildlife-crossings-are-helping-reindeer-bears-and-even-crabs-aoe |archive-date=23 January 2021 |access-date=2021-01-26|website=The Guardian|language=en}}</ref> The first [[Wildlife crossing|animal bridges]] sprung up in France in the 1950s, and these types of bridges are now used worldwide to protect both large and small wildlife.<ref>{{cite news|title=Animals Need Infrastructure Too|author=Sarah Holder|date=31 July 2018|newspaper=Bloomberg.com|access-date=21 February 2019|url=https://www.citylab.com/life/2018/07/wildlife-crossings-bridges-tunnels-animals-roads-highways-roadkill/566210/}}</ref><ref>{{cite web|title=Bridges for Animals to Safely Cross Freeways Are Popping Up Around the World|date=9 February 2017|access-date=21 February 2019|website=My Modern Met|author=Jessica Stewart|url=https://mymodernmet.com/wildlife-crossings/}}</ref><ref>{{cite web|title=World's Coolest Animal Bridges|author=Rachel Newer|date=23 July 2012|website=Smithsonian.com|access-date=21 February 2019|url=https://www.smithsonianmag.com/smart-news/worlds-coolest-animal-bridges-5774855/}}</ref>
==Construction==
{{Further|Bridge design}}


Bridges are subject to unplanned uses as well. The areas underneath some bridges have become makeshift shelters and homes to homeless people, and the undertimbers of bridges all around the world are spots of prevalent graffiti. Some bridges attract people attempting suicide, and become known as [[suicide bridge]]s.<ref>{{Cite journal|last=Glasgow|first=Garrett|date=1 March 2011|title=Do local landmark bridges increase the suicide rate? An alternative test of the likely effect of means restriction at suicide-jumping sites|url=http://www.sciencedirect.com/science/article/pii/S0277953611000384|journal=Social Science & Medicine|language=en|volume=72|issue=6|pages=884–889|doi=10.1016/j.socscimed.2011.01.001|pmid=21320739|issn=0277-9536|url-access=subscription}}</ref><ref>{{cite web | last=Marsh | first=Julia | title=Port Authority not liable for NYC bridge jumpers: judge | date=30 December 2018 | url=https://nypost.com/2018/12/30/george-washington-bridge-jumpers-only-have-themselves-to-blame-judge/ | work=[[New York Post]] | access-date=3 January 2019}}</ref>
The structural elements of a bridge are generally divided into the [[Substructure (engineering)|substructure]] and the [[superstructure#Bridges|superstructure]].{{sfn|Zhao|2017|pp=4-7}} The substructure consists of the lower portions of the bridge, including the [[foundation (engineering)|footing]]s,{{efn|The term ''[[foundation (engineering)|foundation]]'' is sometimes used to represent footings, but in other contexts ''foundation'' may mean all or most of the substructure.{{sfn|Elnashai|2000|pp=530-531}}}} [[abutment]]s, piers, pilings, anchorages, and bearings.{{sfn|Zhao|2017|pp=6, 7}} The superstructure rests upon the substructure, and consists of the [[Deck (bridge)|deck]], trusses, arches, towers, cables, beams, and girders.<ref>{{Multiref
|{{harvnb|Zhao|2017|pp=4–5}}.
|{{harvnb|"Tacoma Narrows Bridge History". ''Washington Department of Transportation''}}.
}}</ref>


===Bridge types by material===
===Construction process===
[[File:Ironbridge 6.jpg|thumb|[[The Iron Bridge]] in Shropshire, England, completed in 1781, the first cast iron bridge]]
[[File:Schematic diagram showing some structural elements of a bridge.svg|thumb|alt=A schematic diagram identifying the various parts of a Hypothetical bridge|right|upright=1.2|Some elements of a fictional bridge. 1 Approach, 2 Arch, 3 Truss, 4 Abutment, 5 Bearing, 6 Deck and beams, 7 Pier Cap, 8 Pier, 9 Piling, 10 Footing, 11 Caisson, 12 Subsoil.<ref>{{Multiref
[[File:Kraemerbruecke und Aegidienkirche Erfurt 2017.jpg|thumb|[[Krämerbrücke]] in [[Erfurt]], Germany, a bridge with [[half timbered]] buildings]]
|{{harvnb|Zhao|2017|pp=2–6}}.
[[File:Stone bridge, Othoni island.jpg|thumb|A small stone bridge in [[Othonoi]], Greece]]
|{{harvnb|"Tacoma Narrows Bridge History". ''Washington Department of Transportation''}}.
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 bridge|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 ''[[Ficus elastica]]'' tree roots in India<ref>{{Cite news|url=https://livingrootbridges.com/methods-of-creating-living-root-bridges/|title=How are Living Root Bridges Made?|date=5 May 2017|work=The Living Root Bridge Project|access-date=8 September 2017|url-status=live|archive-url=https://web.archive.org/web/20170905002548/https://livingrootbridges.com/methods-of-creating-living-root-bridges/|archive-date=5 September 2017}}</ref> and [[wisteria]] vines in Japan.<ref>{{cite web|url=http://www.atlasobscura.com/places/vine-bridges-japan|title=The Vine Bridges of Iya Valley|website=Atlas Obscura|access-date=8 September 2017|url-status=live|archive-url=https://web.archive.org/web/20170908110829/http://www.atlasobscura.com/places/vine-bridges-japan|archive-date=8 September 2017}}</ref>
}}</ref>]]
Construction of a bridge is typically managed by [[construction engineer]]s, who are responsible for planning and supervising the construction process. Important aspects of this role include budgeting, scheduling, periodically conducting formal [[design review]]s, and communicating with the bridge designers to interpret and update the [[Engineering drawing|design plans]].<ref>{{Multiref
|{{harvnb|Durkee|2014|pp=24–25}}.
|{{harvnb|Blank|2014|pp=67–71}}.
}}</ref>{{efn|An example schedule for design reviews is to hold them at 33%, 65%, 95%, and 100% of bridge completion.{{sfn|Blank|2014|p=70}}}} When an existing bridge is being replaced or refurbished, the impact on traffic flow can have a detrimental effect on residents and services. [[Accelerated bridge construction]] processes{{snd}}that focus on using pre-fabricated components and a rapid timetable{{snd}}may be used to mitigate the impacts.{{sfn|Tang|2014a|pp=175-179}}


{| class="wikitable"
The forces experienced by a bridge during construction can be larger or have a different nature than the forces it will experience after completion. The bridge design process typically focuses on the strength of the fully completed bridge, but it should also consider the unusual stresses that individual elements will experience during construction. Special techniques may be required during construction to avoid excessive stresses, such as temporary supports under the bridge, temporary bracing or reinforcement, or permanently strengthening specific elements.<ref>{{Multiref
|-
|{{harvnb|Durkee|2014|pp=3–4}}.
! Bridge type !! Materials used
|{{harvnb|Kulicki|2014a|pp=307–308 }}.
|-
|{{harvnb|Gimsing|1997|p=375}}.
| 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|url-status=live|archive-url=https://web.archive.org/web/20141029131006/http://www.bridgesofdublin.ie/bridge-building/types/cantilever|archive-date=29 October 2014}}</ref>
}}</ref> For instance, when a cable-stayed bridge with concrete towers is complete, the towers will experience desirable compression forces from the heavy load of the cables; but during construction, without that load, the towers may experience undesirable tension forces caused by lateral winds.{{sfn|Gimsing|1997|p=375}}
|-
| Suspension || The cables are usually made of [[steel cable]]s galvanised with [[zinc]],{{citation needed|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|url-status=live|archive-url=https://web.archive.org/web/20150102202158/http://www.madehow.com/Volume-5/Suspension-Bridge.html|archive-date=2 January 2015}}</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 |work = Nova Online|url=https://www.pbs.org/wgbh/nova/lostempires/china/meetbeam.html|publisher=PBS|url-status=live|archive-url= https://web.archive.org/web/20150106053043/http://www.pbs.org/wgbh/nova/lostempires/china/meetbeam.html|archive-date= 6 January 2015}}</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|url-status=live|archive-url=https://web.archive.org/web/20150219192803/http://www.brighthubengineering.com/structural-engineering/63635-truss-bridge-designs/|archive-date=19 February 2015|date=10 February 2010}}</ref>
|}


== Analysis and design ==
===Substructure ===
[[File:Burbank Ave I-5 overpass under construction in Burbank, California.JPG|thumb|A highway [[overpass]] over construction on [[Interstate 5 in California|Interstate 5]] in [[Burbank, California]], in 2021]]
[[File:Bridge abutment diagram side-by-side.svg|alt=Two schematic diagrams showing how force is transmitted in a flat bridge compared to an arched bridge|thumb|left|upright=1.2|Abutments are an important element of a substructure. Beam bridges (left) direct force vertically into the abutments; some arch bridges (right) direct forces diagonally. 1 Deck, 2 Abutments, 3 Subsoil, 4 Load on bridge, 5 Force from abutment into subsoil.<ref name=abutDiag/>]]
Unlike buildings whose design is led by architects, bridges are usually designed by engineers. This follows from the importance of the engineering requirements; namely spanning the obstacle and having the durability to survive, with minimal maintenance, in an aggressive outdoor environment.<ref name=":2" /> Bridges are first analysed; the bending moment and shear force distributions are calculated due to the applied loads. For this, the [[finite element method]] is the most popular. The analysis can be one-, two-, or three-dimensional. For the majority of bridges, a two-dimensional plate model (often with stiffening beams) is sufficient or an upstand finite element model.<ref>{{Cite journal|last1=O'Brien|first1=E.J|last2=Keogh|first2=D.L|date=December 1998|title=Upstand finite element analysis of slab bridges|journal=Computers & Structures|volume=69|issue=6|pages=671–683|doi=10.1016/S0045-7949(98)00148-5|hdl=10197/4054|hdl-access=free}}</ref> On completion of the analysis, the bridge is designed to resist the applied bending moments and shear forces, section sizes are selected with sufficient capacity to resist the stresses. Many bridges are made of [[prestressed concrete]] which has good durability properties, either by pre-tensioning of beams prior to installation or post-tensioning on site.


In most countries, bridges, like other structures, are designed according to [[Limit state design|Load and Resistance Factor Design]] (LRFD) principles. In simple terms, this means that the load is factored up by a factor greater than unity, while the resistance or capacity of the structure is factored down, by a factor less than unity. The effect of the factored load (stress, bending moment) should be less than the factored resistance to that effect. Both of these factors allow for uncertainty and are greater when the uncertainty is greater.
Construction of all bridge types begins by creating the substructure. The first elements built are usually the footings and abutments, which are typically large blocks of reinforced concrete, entirely or partially buried underground. The footings and abutments support the entire weight of the bridge, and transfer the weight to the [[subsoil]].<ref name=foundation>{{Multiref
|{{harvnb|Zhao|2017|pp=6, 7}}.
|{{harvnb|Islam|Malek|2014|pp=181–182}}.
|{{harvnb|Ma|2014|pp=239–240}}.
}}</ref> Based on their height-to-width ratio, footings are categorized as: [[shallow foundations|shallow]] (height is less than width) or [[deep foundations|deep]] (height is greater than width).<ref name=deep>{{Multiref
|{{harvnb|Islam|Malek|2014|pp=181–182}}.
|{{harvnb|Ma|2014|pp=239–240}}.
}}</ref> If the subsoil cannot support the load placed on the footings, [[piling]]s must first be driven below the footings: pilings are long structures{{snd}}made of wood, steel, or concrete{{snd}}placed vertically below footings.<ref name=piles>{{Multiref
|{{harvnb|Gerwick|2014|pp=138–147}}.
|{{harvnb|Ma|2014|pp=239–244, 247, 272}}.
|{{harvnb|Denison|2012|pp=233–234, 246, 248}}.
|{{harvnb|Cruickshank|2010|p=206}}.
}}</ref> Some pilings reach down and rest on [[bedrock]]; others rely on friction to prevent the footing from sinking lower.<ref name=piles/>


==Aesthetics==
Abutments are usually located at the ends of a bridge deck, where it reaches the subsoil.{{sfn|Zhao|2017|pp=6, 23, 356-362}} They direct the weight into the subsoil, either vertically or diagonally.<ref name=abutDiag>{{Multiref
[[File:The Ben van Berkel cable stayed bridge across the Amsterdam-Rhine canal Utrecht - panoramio.jpg|thumb|The Prins Clausbrug across the [[Amsterdam–Rhine Canal]] in [[Utrecht]], Netherlands]]
|{{harvnb|Bennett|1999|pp=72, 228}}.
[[File:Stari_Most22.jpg|thumb|The [[World Heritage Site]] of [[Stari Most]] (Old Bridge) gives its name to the city of [[Mostar]] in Bosnia and Herzegovina]]
|{{harvnb|Brown|2005|p=15}}.
[[File:Bridge to Pier 6, Gatwick North Terminal - geograph.org.uk - 74055.jpg|thumb|The bridge at [[Gatwick Airport]] in London, under which planes pass]]
|{{harvnb|Cruickshank|2010|pp=35, 64, 162, 207, 364–365}}.
Most bridges are utilitarian in appearance, but in some cases, the appearance of the bridge can have great importance.<ref>{{Cite book|title=Bruc̈ken: Asthetik und Gestaltung |trans-title=Bridges: aesthetics and design |last=Leonhardt |first=Fritz |date=1984 |publisher=MIT Press |isbn=0-262-12105-0 |location=Cambridge, MA |oclc=10821288}}</ref> 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 on aesthetics, as well. Examples include the stone-faced bridges along the [[Taconic State Parkway]] in New York.
}}</ref> Abutments may also act as retaining walls, keeping the subsoil under the approach road from eroding.{{sfn|Zhao|2017|pp=6, 23, 356-362}} After footings for the [[Pier (bridge structure)|piers]] have been created, the piers and pier caps are built to complete the substructure.<ref>{{Multiref
|{{harvnb|Rookhuyzen|2018 }}.
|{{harvnb|Zhao|2017|pp= 395–403}}.
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref>{{efn|A pier cap is a block of concrete at the top of a pier, upon which rests the deck.{{sfn|Zhao|2017|pp=33, 67, 397}} }} Suspension bridges usually require anchorages, which are large reinforced concrete blocks solidly anchored into the earth{{snd}}they must be exceptionally heavy and tied into the subsoil because they must withstand the lateral pull of the large cables that hold the entire deck and live load.<ref name=anchor>{{Multiref
|{{harvnb|Cruickshank|2010|pp= 227, 249–250, 343, 360}}.
|{{harvnb| Brown|2005|pp= 107–108, 110, 113, 202}}.
|{{harvnb|Bennett|1999 |pp= 84, 118, 228}}.
}}</ref>{{efn|[[Self-anchored suspension bridge]]s do not require anchorages.{{sfn|Brown|2005|p=107}}}}


Bridges are typically more aesthetically pleasing if they are simple in shape, the deck is thinner in proportion to its span, the lines of the structure are continuous, and the shapes of the structural elements reflect the forces acting on them.<ref>{{Cite web|url=https://roads-waterways.transport.nsw.gov.au/business-industry/partners-suppliers/documents/centre-for-urban-design/bridge-aesthetics-guidelines.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://roads-waterways.transport.nsw.gov.au/business-industry/partners-suppliers/documents/centre-for-urban-design/bridge-aesthetics-guidelines.pdf |archive-date=2022-10-09 |title=Bridge Aesthetics. Design guideline to improve the appearance of bridges in NSW|date=February 2009}}</ref> 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 and Empress, with their attendants.
====Constructing supports in water====


==Bridge maintenance==
[[File:Abernethy Bridge Project June 2023 (52956248522), enclosed column.jpg|thumb
[[File:Example HiFIT-treated assembly.jpg|thumb|A highway bridge treated with [[high-frequency impact treatment]]]]
| alt= A large concrete structure in the middle of a river, kept dry by a steel wall surrounding it
The estimated life of bridges varies between 25 and 80 years depending on location and material.<ref>{{Cite journal|last1=Estes|first1=Allen C.|last2=Frangopol|first2=Dan M.|date=1 December 2001|title=Bridge Lifetime System Reliability under Multiple Limit States|url=http://ascelibrary.org/doi/10.1061/%28ASCE%291084-0702%282001%296%3A6%28523%29|journal=Journal of Bridge Engineering|language=en|volume=6|issue=6|pages=523–528|doi=10.1061/(ASCE)1084-0702(2001)6:6(523)|issn=1084-0702|url-access=subscription}}</ref><ref name=":12">{{Cite book|last1=Ford|first1= K.|last2= Arman|first2= M.|last3 = Labi|first3= S.|last4= Sinha|first4= K.C.|last5= Thompson|first5 = P.D.|last6= Shirole|first6 = A.M.|last7= Li|first7 = Z.|date = 2012|id= NCHRP Report 713 |title = Estimating life expectancies of highway assets|publisher = Transportation Research Board, National Academy of Sciences|location = Washington, DC}}</ref>
| This concrete bridge pier is being built within a steel [[cofferdam]].{{sfn|"I-205 Abernethy Bridge". ''Oregon Department of Transportation''}} ]]


Bridges may age hundred years with proper maintenance and rehabilitation. Bridge maintenance consisting of a combination of structural health monitoring and testing. This is regulated in country-specific engineer standards and includes 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 considerable<ref name=":1">{{Cite journal|last1=Žnidarič|first1=Aleš|last2=Pakrashi|first2=Vikram|last3=O'Brien|first3=Eugene|last4=O'Connor|first4=Alan|s2cid=110344262|date=December 2011|title=A review of road structure data in six European countries|journal=Proceedings of the Institution of Civil Engineers - Urban Design and Planning|volume=164|issue=4|pages=225–232|doi=10.1680/udap.900054|issn=1755-0793|hdl=10197/4877|hdl-access=free}}</ref> and is higher in some countries 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.
<!--
| image2 = Caisson Schematic diagram.svg
| alt2 = A schematic diagram showing the cross section of a structure used to excavate bridge foundations under water
| caption2 = To build a bridge pier in water, [[Caisson (engineering)|caissons]] may be used to hold workers and machinery during excavation.{{sfn|Bennett|1999|pp=111-112}}
}}
-->
When bridge supports (such as piers or towers) are built in a river, lake, or ocean, special technologies must be utilized.{{sfn|Gerwick|2014|pp=137-138}} [[Caisson (engineering)|Caissons]] can be used to provide a workspace while constructing the submerged portion of the supports. A caisson is a large, watertight, hollow structure, open on the bottom. It is usually sunk to the bottom of the water and workers can work inside, preparing the ground for the footings. When excavation is complete, a caisson is typically filled with concrete to create all or part of the footing.<ref name=caisson>{{multiref
|{{harvnb|Gerwick|2014|pp=161–162}}.
|{{harvnb|Cruickshank|2010|pp= 283–285}}.
|{{harvnb|Brown|2005|pp=77–78, 92–93}}.
|{{harvnb|Bennett|1999|pp=111–112}}.
}}</ref> Air pressure inside a sealed caisson must be kept high to prevent water from seeping in.{{sfn|Cruickshank|2010|p=53}} Workers, if they do not properly [[Decompression (diving)|decompress]] when exiting the caisson, can get [[decompression sickness]].<ref name=bends/> Early bridge builders did not understand decompression, and deaths were common: thirteen workers died from decompression sickness when building the [[Eads Bridge]] (completed in 1874).<ref name=bends>{{multiref
|{{harvnb|Brown|2005|p=89}}.
|{{harvnb|Bennett|1999|pp=111–112 }}.
}}</ref>


== Bridge traffic loading ==
Another approach for constructing foundations in water is a [[Caisson (engineering)#Box|box caisson]], which is a large steel or concrete box, open on top, which is towed by [[tugboat]]s to the bridge site, then sunk to the bottom and filled with concrete.<ref name=boxCaisson>{{Multiref
While the response of a bridge to the applied loading is well understood, the applied traffic loading itself is still the subject of research.<ref name="engineer. 2015">{{Cite book |title=Bridge deck analysis|last1=OBrien|first1=Eugene J. |last2=Keogh |first2=Damien L. |last3=O'Connor |first3=Alan |date=2015 |publisher=CRC Press |isbn=978-1-4822-2723-9 |oclc=897489682}}</ref> This is a statistical problem as loading is highly variable, particularly for road bridges. Load Effects in bridges (stresses, bending moments) are designed for using the principles of [[Limit state design|Load and Resistance Factor Design]]. Before factoring to allow for uncertainty, the load effect is generally considered to be the maximum characteristic value in a specified [[return period]]. Notably, in Europe, it is the maximum value expected in 1000 years.
|{{harvnb|Sangree|Shafer|2003}}.
|{{harvnb|Kashima|Sakamoto|1998|pp=71–72}}.
|{{harvnb|Gerwick|2014|pp=162–163}}.
}}</ref> The [[Akashi Kaikyo Bridge|Akashi Kaikyo suspension bridge]] used box caissons for its two foundations{{snd}}each {{convert|70|m|ft|sp=us}} tall and {{convert|80|m|ft|sp=us}} in diameter. The caissons were sunk to the bottom in water {{convert|60|m|ft|sp=us}} deep, and each was filled with 355,000 cubic meters of concrete. The foundations rest directly on the ocean bottom, without pilings or footings.<ref name=boxCaisson/> An alternative to a caisson is a [[cofferdam]], which is a temporary dam surrounding the support location, open on top, where workers may work while constructing the footings.<ref name=coffer>{{Multiref
|{{harvnb|Gerwick|2014|pp=148–155}}.
|{{harvnb|Bennett|1999|p=228}}.
|{{harvnb|Shi|2014|pp=88–95}}.
}}</ref>


Bridge standards generally include a load model, deemed to represent the characteristic maximum load to be expected in the return period. In the past, these load models were agreed by standard drafting committees of experts but today, this situation is changing. It is now possible to measure the components of bridge traffic load, to weigh trucks, using [[Weigh in motion|weigh-in-motion]] (WIM) technologies. With extensive WIM databases, it is possible to calculate the maximum expected load effect in the specified return period. This is an active area of research, addressing issues of opposing direction lanes,<ref>{{Cite journal |last1=Enright |first1=Bernard |last2=O'Brien |first2=Eugene J. |date=December 2013 |title=Monte Carlo simulation of extreme traffic loading on short and medium span bridges |journal=Structure and Infrastructure Engineering |volume=9 |issue=12 |pages=1267–1282 |doi=10.1080/15732479.2012.688753 |bibcode=2013SIEng...9.1267E |issn=1573-2479 |hdl=10197/4868 |s2cid=10042252 |hdl-access=free}}</ref><ref>{{Cite journal |last1=Caprani |first1=Colin C. |last2=OBrien |first2=Eugene J. |date=March 2010 |title=The use of predictive likelihood to estimate the distribution of extreme bridge traffic load effect |journal=Structural Safety |volume=32 |issue=2 |pages=138–144 |doi=10.1016/j.strusafe.2009.09.001 |hdl=10197/2329 |s2cid=44049002 |hdl-access=free}}</ref> side-by-side (same direction) lanes,<ref>{{Cite journal |last1=OBrien |first1=Eugene J. |last2=Enright |first2=Bernard |date=July 2011 |title=Modeling same-direction two-lane traffic for bridge loading |journal=Structural Safety |volume=33 |issue=4–5 |pages=296–304 |doi=10.1016/j.strusafe.2011.04.004 |hdl=10197/3062 |s2cid=53475878 |url=https://arrow.dit.ie/engschcivart/41 |hdl-access=free}}</ref><ref>{{Cite journal |last1=OBrien |first1=Eugene J. |last2=Leahy |first2=Cathal |last3=Enright |first3=Bernard |last4=Caprani |first4=Colin C. |date=30 September 2016 |title=Validation of scenario modelling for bridge loading |journal=The Baltic Journal of Road and Bridge Engineering |volume=11 |issue=3 |pages=233–241 |doi=10.3846/bjrbe.2016.27 |issn=1822-427X |hdl=10197/9252 |url=https://bjrbe-journals.rtu.lv/article/view/bjrbe.2016.27|doi-access=free|hdl-access=free }}</ref> traffic growth,<ref>{{Cite journal |last1=OBrien |first1=E.J. |last2=Bordallo-Ruiz |first2=A. |last3=Enright |first3=B. |date=September 2014 |title=Lifetime maximum load effects on short-span bridges subject to growing traffic volumes |journal=Structural Safety |volume=50 |pages=113–122 |doi=10.1016/j.strusafe.2014.05.005 |hdl=10197/7069 |s2cid=59945573 |hdl-access=free}}</ref> permit/non-permit vehicles<ref>{{Cite journal |last1=Enright |first1=Bernard |last2=OBrien |first2=Eugene J. |last3=Leahy |first3=Cathal |date=December 2016 |title=Identifying and modelling permit trucks for bridge loading |journal=Proceedings of the Institution of Civil Engineers - Bridge Engineering |volume=169 |issue=4 |pages=235–244 |doi=10.1680/bren.14.00031 |issn=1478-4637 |hdl=10197/9246 |hdl-access=free}}</ref> and long-span bridges (see below). Rather than repeat this complex process every time a bridge is to be designed, standards authorities specify simplified notional load models, notably HL-93,<ref>{{Cite web |url=https://engineeringcivil.org/articles/bridge/hl-93-aashto-vehicular-live-loading-truck-tandem-design-lane-load/ |title=HL-93 AASHTO Vehicular Live Loading {{!}} Truck {{!}} Tandem {{!}} Design Lane Load|date=17 August 2016|website=EngineeringCivil.org|access-date=2019-03-15}}</ref><ref>{{Cite journal |last1=Leahy |first1=Cathal |last2=OBrien |first2=Eugene J. |last3=Enright |first3=Bernard |last4=Hajializadeh |first4=Donya |date=October 2015 |title=Review of HL-93 Bridge Traffic Load Model Using an Extensive WIM Database |journal=Journal of Bridge Engineering |volume=20 |issue=10 |doi=10.1061/(ASCE)BE.1943-5592.0000729 |issn=1084-0702 |hdl=10197/7068 |s2cid=53503763 |hdl-access=free}}</ref> intended to give the same load effects as the characteristic maximum values. The [[Eurocode]] is an example of a standard for bridge traffic loading that was developed in this way.<ref>{{Cite journal |last1=O'Connor |first1=Alan |last2=Jacob |first2=Bernard |last3=O'Brien |first3=Eugène |last4=Prat |first4=Michel |date=June 2001 |title=Report of Current Studies Performed on Normal Load Model of EC1: Part 2. Traffic Loads on Bridges |journal=Revue Française de Génie Civil |volume=5 |issue=4 |pages=411–433 |doi=10.1080/12795119.2001.9692315 |s2cid=111112374 |issn=1279-5119 |hdl=10197/4024 |hdl-access=free}}</ref>
====Bearings====
{{main|Bridge bearing}}
[[File:Bajai hid 06.jpg|thumb|upright=0.9|alt=Two cylinders of steel, supporting a large steel bridge, and resting on a concrete support|<!-- The superstructure of this bridge can accommodate slight movements without damage, --> [[bridge bearing|Bearings]] can prevent damage to the superstructure by permitting small movements.{{sfn|Zhao|2017|pp=424–434}}]]
[[Bridge bearing|Bearing]]s are often placed between the superstructure and the substructure at the points of contact. Bearings are mechanical devices that enable small movements{{snd}}which may result from
[[thermal expansion|thermal expansion and contraction]], [[Creep (deformation)|material creep]], or minor [[seismic event]]s. Without bearings, the bridge structure may be damaged when such movements occur. Bearings can be selected to permit small rotational or slipping movements in a specific direction, without permitting movements in other directions. Types of bearings used on bridges include hinge bearings, roller bearings, rocker bearings, sliding bearings, spring bearings, and [[Elastomeric bridge bearing|elastomeric bearings]].<ref name=bearing>{{Multiref
|{{harvnb|Dornsife|2014|pp=1–9}}.
|{{harvnb|Zhao|2017|pp=424–434}}.
}}</ref>


=== Traffic loading on long span bridges ===
===Superstructure ===
[[File:Forth from above.jpg|thumb|Traffic on [[Forth Road Bridge]] in Scotland prior to its opening to general traffic; traffic has now been moved to the [[Queensferry Crossing]] (on left)]]
Most bridge standards are only applicable for short and medium spans<ref>{{Cite journal|last1=A.S|first1=Nowak|last2=M|first2=Lutomirska|last3=F.I|first3=Sheikh Ibrahim|date=2010|title=The development of live load for long span bridges|journal=Bridge Structures|volume=6|issue=1, 2|pages=73–79|doi=10.3233/BRS-2010-006|issn=1573-2487}}</ref> - for example, the Eurocode is only applicable for loaded lengths up to 200 m. Longer spans are dealt with on a case-by-case basis. It is generally accepted that the intensity of load reduces as span increases because the probability of many trucks being closely spaced and extremely heavy reduces as the number of trucks involved increases. It is also generally assumed that short spans are governed by a small number of trucks traveling at high speed, with an allowance for dynamics. Longer spans on the other hand, are governed by congested traffic and no allowance for dynamics is needed.


Calculating the loading due to congested traffic remains a challenge as there is a paucity of data on inter-vehicle gaps, both within-lane and inter-lane, in congested conditions. [[Weigh in motion|Weigh-in-Motion]] (WIM) systems provide data on inter-vehicle gaps but only operate well in free flowing traffic conditions. Some authors have used cameras to measure gaps and vehicle lengths in jammed situations and have inferred weights from lengths using WIM data.<ref>{{Cite journal|last1=Micu|first1=Elena Alexandra|last2=Obrien|first2=Eugene John|last3=Malekjafarian|first3=Abdollah|last4=Quilligan|first4=Michael|date=21 December 2018|title=Estimation of Extreme Load Effects on Long-Span Bridges Using Traffic Image Data|journal=The Baltic Journal of Road and Bridge Engineering|volume=13|issue=4|pages=429–446|doi=10.7250/bjrbe.2018-13.427|issn=1822-4288|doi-access=free|hdl=10344/7494|hdl-access=free}}</ref> Others have used [[microsimulation]] to generate typical clusters of vehicles on the bridge.<ref>{{Cite journal|last1=OBrien|first1=E. J.|last2=Hayrapetova|first2=A.|last3=Walsh|first3=C.|date=March 2012|title=The use of micro-simulation for congested traffic load modeling of medium- and long-span bridges|journal=Structure and Infrastructure Engineering|volume=8|issue=3|pages=269–276|doi=10.1080/15732471003640477|bibcode=2012SIEng...8..269O |issn=1573-2479|hdl=10197/3061|s2cid=54812838 |hdl-access=free}}</ref><ref>{{Cite journal|last1=Caprani|first1=Colin C.|last2=OBrien|first2=Eugene J.|last3=Lipari|first3=Alessandro|date=May 2016|title=Long-span bridge traffic loading based on multi-lane traffic micro-simulation|journal=Engineering Structures|volume=115|pages=207–219|doi=10.1016/j.engstruct.2016.01.045|bibcode=2016EngSt.115..207C }}</ref><ref>{{Cite journal|last1=OBrien|first1=Eugene J.|last2=Lipari|first2=Alessandro|last3=Caprani|first3=Colin C.|date=July 2015|title=Micro-simulation of single-lane traffic to identify critical loading conditions for long-span bridges|journal=Engineering Structures|volume=94|pages=137–148|doi=10.1016/j.engstruct.2015.02.019|bibcode=2015EngSt..94..137O |hdl=10197/6998|s2cid=56030686 |hdl-access=free}}</ref>
<!--
[[File:Gewoelbebruecke A73.jpg|thumb|alt=A huge wooden arch structure, over which an arch bridge is being built|This temporary [[falsework]] will be removed after an arch is built over it.<ref name=falsework/>]]
-->
After the substructure is complete, the superstructure is built, resting on the substructure. [[Beam bridge]] superstructures may be built in place, or fabricated off-site ([[precast]]) and transported to the bridge site.<ref>{{Multiref
|{{harvnb| Bennett| 2000 | pp=25–26 }}.
|{{harvnb|Hewson| 2000| p=283}}.
|{{harvnb| Barker | 2007| pp=94, 100, 103–106 }}.  
}}</ref> Precast beams may be placed atop the supports by a crane or [[Gantry crane|gantry]].<ref>{{Multiref
|{{harvnb|Hewson|2000|pp=286–288}}.
|{{harvnb|Brown|2005|p=141}}.
}}</ref> If the span crosses a deep ravine, a technique known as [[incremental launching|launching]] may be used: the beams and deck are assembled on the approach road, then pushed horizontally across the obstacle.<ref name=launch/>{{efn|[[Incremental launching]] may be employed for several types of bridges: beam bridges, deck arch bridges, and cable-stay bridges with short spans. In all cases, the substructure is completed first, then the deck is pushed horizontally across the top of the substructure.<ref name=launch/>}}
[[File:Golden Horn Metro Bridge Mars 2013.jpg|thumb|left|alt=A bridge being constructed, with two large cranes on top|[[Gantry crane|Gantries]] are one technique used to gradually assemble a bridge deck.<ref>{{Multiref
|{{harvnb|Bennett|1999|pp=79–80, 97, 226}}.
|{{harvnb|Shi|2014|p=102}}.
}}</ref>
]]


== Bridge vibration ==
[[Arch bridge]] superstructure construction methods depend on the material. Concrete or stone arches use a temporary wood structure known as [[falsework]] or [[centering]] to support the arch while it is built.<ref name=falsework>{{Multiref
Bridges vibrate under load and this contributes, to a greater or lesser extent, to the stresses.<ref name=":2">{{Cite book |title=Bridge deck analysis |last1=O'Brien |first1=Eugene J. |last2=Keogh |first2=Damien L. |last3=O'Connor |first3=Alan J. |isbn=978-1-4822-2724-6 |edition=Second |location=Boca Raton |oclc=892094185|date=6 October 2014 |publisher=CRC Press }}</ref> Vibration and dynamics are generally more significant for slender structures such as pedestrian bridges and long-span road or rail bridges. One of the most famous examples is the [[Tacoma Narrows Bridge]] that collapsed shortly after being constructed due to excessive vibration. More recently, the [[Millennium Bridge, London|Millennium Bridge]] in London vibrated excessively under pedestrian loading and was closed and retrofitted with a system of dampers. For smaller bridges, dynamics is not catastrophic but can contribute an added amplification to the stresses due to static effects. For example, the Eurocode for bridge loading specifies amplifications of between 10% and 70%, depending on the span, the number of traffic lanes and the type of stress (bending moment or shear force).<ref>{{Cite book |title=Research perspectives: traffic loading on highway bridges |first=Peter |last=Dawe |date=2003 |publisher=Thomas Telford |isbn=0-7277-3241-2 |location=London |oclc=53389159}}</ref>
|{{harvnb|Zhao|2017|p=16}}.
|{{harvnb|Cruickshank| 2010|pp = 64, 97, 334, 362 }}.
|{{harvnb|Brown | 2005|pp=21, 44, 54, 101, 140, 202}}.
|{{harvnb|Bennett|1999|pp=16, 70, 228}}.
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref> Some steel arch bridges are constructed with falsework, but others use cantilevering to build both halves out from the abutments.<ref>{{Multiref
|{{harvnb|Durkee| 2014|pp=10–12}}.
|{{harvnb|Brown | 2005|pp=101, 140}}.
|{{harvnb|Shirley-Smith|Billington}}
}}</ref>


=== Vehicle–bridge dynamic interaction ===
[[Cantilever bridge]] superstructures are usually built incrementally by proceeding outward from anchorages or piers. Most cantilever superstructures can be built without temporary support piers, as the bridge can support itself as it extends outward. A similar process is used for steel or concrete cantilevers: prefabricated sections may be positioned at ground (or water) level and hoisted into place with a gantry, or may be transported horizontally along the previously completed portion of the cantilever. Concrete cantilevers require steel prestressing cables to be passed through tubes within each section and tightened, which will put the concrete into compression.<ref>{{Multiref
There have been many studies of the dynamic interaction between vehicles and bridges during vehicle crossing events. Fryba<ref>{{Cite book |title=Dynamics of railway bridges |last=Fryba |first=L. |date=2009 |publisher=Thomas Telford |isbn=978-0-7277-3956-8 |oclc=608572498}}</ref> did pioneering work on the interaction of a moving load and an Euler–Bernoulli beam. With increased computing power, vehicle-bridge interaction (VBI) models have become ever more sophisticated.<ref>{{Cite journal|last1=Li|first1=Yingyan|last2=OBrien|first2=Eugene|last3=González|first3=Arturo|date=May 2006|title=The development of a dynamic amplification estimator for bridges with good road profiles|journal=Journal of Sound and Vibration|volume=293|issue=1–2|pages=125–137|doi=10.1016/j.jsv.2005.09.015|bibcode=2006JSV...293..125L|hdl=10197/2529|s2cid=53678242 |hdl-access=free}}</ref><ref>{{Cite journal|last1=Cantero|first1=D.|last2=González|first2=A.|last3=OBrien|first3=E. J.|date=June 2009|title=Maximum dynamic stress on bridges traversed by moving loads|journal=Proceedings of the Institution of Civil Engineers - Bridge Engineering|volume=162|issue=2|pages=75–85|doi=10.1680/bren.2009.162.2.75|issn=1478-4637|hdl=10197/2553|s2cid=53057484 |hdl-access=free}}</ref><ref>{{Cite journal|last1=Cantero|first1=D|last2=O'Brien|first2=E J|last3=González|first3=A|date=June 2010|title=Modelling the vehicle in vehicle—infrastructure dynamic interaction studies|journal=Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-Body Dynamics|volume=224|issue=2|pages=243–248|doi=10.1243/14644193JMBD228|issn=1464-4193|hdl=10197/2551|s2cid=59583241|hdl-access=free}}</ref><ref>{{Cite journal|last1=González|first1=A.|last2=Cantero|first2=D.|last3=OBrien|first3=E.J.|date=December 2011|title=Dynamic increment for shear force due to heavy vehicles crossing a highway bridge|journal=Computers & Structures|volume=89|issue=23–24|pages=2261–2272|doi=10.1016/j.compstruc.2011.08.009|hdl=10197/3426|s2cid=53367765 |hdl-access=free}}</ref> The concern is that one of the many natural frequencies associated with the vehicle will resonate with the bridge's first natural frequency.<ref>{{Cite journal|last1=González|first1=Arturo|last2=OBrien|first2=Eugene J.|last3=Cantero|first3=Daniel|last4=Li|first4=Yingyan|last5=Dowling|first5=Jason|last6=Žnidarič|first6=Ales|date=May 2010|title=Critical speed for the dynamics of truck events on bridges with a smooth road surface|journal=Journal of Sound and Vibration|volume=329|issue=11|pages=2127–2146|doi=10.1016/j.jsv.2010.01.002|bibcode=2010JSV...329.2127G|hdl=10197/2138|s2cid=56078933 |hdl-access=free}}</ref> The vehicle-related frequencies include body bounce and axle hop but there are also pseudo-frequencies associated with the vehicle's speed of crossing<ref>{{Cite journal|last1=Brady Sean P.|last2=O'Brien Eugene J.|last3=Žnidarič Aleš|date=1 March 2006|title=Effect of Vehicle Velocity on the Dynamic Amplification of a Vehicle Crossing a Simply Supported Bridge|journal=Journal of Bridge Engineering|volume=11|issue=2|pages=241–249|doi=10.1061/(ASCE)1084-0702(2006)11:2(241)|hdl=10197/2327|s2cid=53417698 |hdl-access=free}}</ref> and there are many frequencies associated with the surface profile.<ref name="engineer. 2015"/> Given the wide variety of heavy vehicles on road bridges, a statistical approach has been suggested, with VBI analyses carried out for many statically extreme loading events.<ref>{{Cite journal|last1=OBrien|first1=Eugene J.|last2=Cantero|first2=Daniel|last3=Enright|first3=Bernard|last4=González|first4=Arturo|date=December 2010|title=Characteristic Dynamic Increment for extreme traffic loading events on short and medium span highway bridges|journal=Engineering Structures|volume=32|issue=12|pages=3827–3835|doi=10.1016/j.engstruct.2010.08.018|bibcode=2010EngSt..32.3827O |url=https://arrow.dit.ie/engschcivart/40|hdl=10197/4045|s2cid=52250745 |hdl-access=free}}</ref>
|{{harvnb|Theryo|2014|pp=97–101 }}.
|{{harvnb|Kulicki|2014a|pp= 283–287, 293–301 }}.
|{{harvnb|Cruickshank|2010|pp=292–297}}.
|{{harvnb|Brown | 2005|pp=78–79}}.
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref> [[Truss bridge]]s are built using a variety of methods, including piece-by-piece, cantilevering, or falsework.{{sfn|Kulicki|2014a|pp=307-308 }}


==Bridge failures==
[[Cable-stayed bridge]] superstructures begin with the construction of one or more towers which rest directly on footings that are part of the substructure. The deck is constructed in pieces beginning at the towers{{efn|name=OneTower}} and moving outward. The pieces can be put into place by hoisting, supporting from below, [[incremental launching|launching]], or cantilevering from the portion of the deck that has been assembled.<ref name=CabStyConstr>{{Multiref
<!-- [[bridge failure]] and [[bridge failures]] redirect here; be sure to update them if changing the section title -->
|{{harvnb|Shi|2014|pp=85–87}}.
{{see also|List of bridge failures}}
|{{harvnb|Gimsing|1997|pp=437–443}}.
[[Image:HomochittoRiver1974.jpg|thumb|[[Mississippi Highway 33]] bridge over the [[Homochitto River#River modification|Homochitto River]] failed due to flood-induced [[erosion]].]]
}}</ref> As each piece of the deck is added, it is connected to towers with steel cables, and the cables are tightened to take the load of the deck.<ref name=CabStyConstr/> <!--
The failure of bridges is of special concern for [[structural engineers]] in trying to learn lessons vital to bridge design, construction and maintenance.
If the deck is made of concrete, steel prestressing cables are inserted through tubes inside each deck section, and tightened to put the concrete into compression.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|pp=340–355}}.
|{{harvnb|Shirley-Smith|Billington}}.
|{{harvnb|Gimsing |1997|pp=438-444}}.
}}</ref>
-->


The failure of bridges first assumed national interest in Britain during the [[Victorian era]] when many new designs were being built, often using new materials, with some of them failing catastrophically.
[[Suspension bridge]] superstructure construction usually begins with the towers.{{sfn|Gimsing |1997|pp=434-436}}{{efn|name=OneTower}} The towers may be steel or concrete, and rest directly on footings. The large cables are created by hauling a large pulley back and forth across the span, stringing multiple wires between the anchorages in each pass, in a process termed ''spinning''. After the wires are spun, they are bundled together to form the cables.{{efn|Spinning the wires took 209 days for the [[George Washington Bridge]].{{sfn|Bennett|1999|p=118}}}} The cables are securely fastened to the anchorages at both ends.{{efn|Some suspension bridges, called [[self-anchored suspension bridges]], do not use anchorages.{{sfn|Gimsing |1997|pp=192-193}}}} Vertical wires called ''hangers'' are suspended from the cables, then small sections of the deck are attached to the hangers, and the sections are attached to each other.<ref>{{Multiref
|{{harvnb|Gimsing |1997|pp=434–436}}.
|{{harvnb|Bennett|1999|pp=84, 89–90, 118}}.
|{{harvnb|Shirley-Smith|Billington}}.
|{{harvnb|Brown|2005|pp=8, 87, 91, 106, 109, 202}}.
}}</ref>


In the United States, the [[National Bridge Inventory]] tracks the structural evaluations of all bridges, including designations such as "structurally deficient" and "functionally obsolete".
====Towers====
[[File:Tacoma Narrows bridge cable saddle.jpg|thumb|alt=A thick steel cable passing over the top of a suspension bridge tower.|A [[suspension bridge]] cable transfers its load to the tower by resting on a curved saddle.]]
<!--
[[File:Bridge cable saddle vs anchor.svg |upright=1.3|alt=A diagram showing a curved line passing over a curved object on top of a tower; and another diagram showing two lines that each of which end inside a tower.|thumb| A cable transfers its load to a tower by either (a) passing over a curved saddle (left image); or (b) the end of the cable is anchored into the tower (right image). Key: 1 Cable, 2 Saddle, 3 Anchor, 4 Tower.{{sfn| Gimsing|1997| pp= 395-406}}{{efn|When cables are anchored to a tower (as in the right diagram) the anchors are placed in pairs at the same height, so the horizontal forces of the two cables cancel each other out. For clarity, this diagram shows anchors from pairs at different heights.}}]]
-->
<!--
|image2 = Verazanno Narrows bridge cable anchorage.jpg
|width2=200
|alt2= Many parallel steel wires, attached at one end to a large concrete block.
|caption2=A large concrete anchorage (right) holds the end of a suspension bridge cable, visible here as multiple wire strands (left).-->
<!--
[[ File:CableStayedBridge Multi-Strand Anchor.jpg|thumb|alt= A steel cylinder with several thick wires passing through it. | Anchors like this are used at both ends of a cable in a cable-stayed bridge, to attach the cable to the tower and to the deck.{{efn|If the cable passes over a saddle in the tower, then anchors are only used where the cable attaches to the deck.}}
]]
-->
Towers, made of either concrete or steel, are an important component of the superstructure of cable-stayed bridges and suspension bridges.{{efn|In the context of bridges, the term ''pylon'' is interchangeable with the word ''tower''.{{sfn|Gimsing |1997|p=345}}}} Concrete is generally suitable for towers up to about {{convert|250|meters}} tall, whereas steel towers can be taller.<ref>{{Multiref
|{{harvnb|Gimsing |1997|p=345}}.
|{{harvnb|Shi|2014|p=85}}.
}}</ref>{{efn|Most towers are rigidly attached to the footings below them, but some relatively short towers have bearings at their base which permit pivoting.{{sfn|Gimsing |1997|p=347}}}} Towers support the bridge cables, which{{snd}}in turn{{snd}} hold the weight of the bridge deck and the vehicular traffic. Most of the load imposed on a tower is applied vertically downward on the tower, rather than sideways.{{sfn|Gimsing |1997|pp=345-347}} Towers experience a compression stress, in contrast to cables, which experience a tension stress.{{sfn|Bennett|1999|p=84}} There are two mechanisms used to attach a cable to a tower: saddles or anchors. Saddles are curved structures which allow a cable to pass through (or over the top of) a tower. An anchor holds the end of a cable. Saddles are often used in suspension bridges, and anchors are often used in cable-stayed bridges.<ref>{{Multiref
|{{harvnb|Gimsing |1997|pp=377–383, 395–406, 427–429}}.
|{{harvnb|Shi|2014|p=88}}.
}}</ref>


==Bridge health monitoring==
====Cables====
There are several methods used to monitor the condition of large structures, like bridges. Many long-span bridges are now routinely monitored with a range of sensors, including strain transducers, [[accelerometer]]s,<ref>{{cite web|url=http://www.mnme.com/pdf/smartbridge.pdf|title=The new Minnesota smart bridge|work=mnme.com|access-date=30 January 2012|archive-url=https://web.archive.org/web/20120823002008/http://www.mnme.com/pdf/smartbridge.pdf|archive-date=23 August 2012}}</ref> tiltmeters, and GPS. Accelerometers have the advantage that they are inertial, i.e., they do not require a reference point to measure from. This is often a problem for distance or deflection measurement, especially if the bridge is over water.<ref>{{citation | last1=Bagher Shemirani | first1=Alireza |title = Experimental and numerical studies of concrete bridge decks using ultra high-performance concrete and reinforced concrete | journal=Computers and Concrete |date = 2022 | volume=29 | issue=6 | doi=10.12989/cac.2022.29.6.407 }}</ref>  [[Crowdsourcing]] bridge conditions by accessing data passively captured by cell phones, which routinely include accelerometers and GPS sensors, has been suggested as an alternative to including sensors during bridge construction and an augment for professional examinations.<ref>{{Cite magazine |last=Riordon |first=James R. |date=3 December 2022 |title=Cell phones track bridge integrity |magazine=[[Science News]] |type=Paper |volume=202 |issue=10 |page=8}}</ref>
[[File:Verrazano-Narrows Bridge- The Beginning (15694087186).jpg|thumb|left
| alt= Two men are standing high in the air on a walkway, and a wheel is above them, suspended by wires.
| A spinning wheels pulls two wires at a time to gradually build-up a suspension bridge cable.{{sfn|Talese|2014|pp=65-77}}
]]
<!--
{{multiple image
| caption_align=center
| image1 = Suspension bridge cable cross section strands wires.svg
| alt1= A circular cross section, showing 37 smaller circles inside a large circle; and a small dot inside one of the small circles.
| caption1 = This cross-section of a cable shows 37 strands, where each strand consists of multiple small wires.<ref>{{Multiref
|{{harvnb| Gimsing|1997| pp=87-94}}. Wires within a strand.
|{{harvnb| Gimsing|1997| pp= 95-100}}. Strands within a cable.
}}</ref>
-->


An 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|access-date=25 January 2012|url-status=live|archive-url=https://web.archive.org/web/20120610192737/http://www.polytec.com/us/solutions/vibration-measurement/basic-principles-of-vibrometry/|archive-date=10 June 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. However, vibrometers are relatively expensive and have the disadvantage that a reference point is needed to measure from.
Steel cables are an element of both cable-stayed bridges and suspension bridges. Cables are made of one or more strands, and each strand consists of multiple wires. A wire is a thin, flexible piece of solid steel, of higher tensile strength than normal steel, and with a diameter of 3mm to 7mm.{{sfn|Gimsing |1997|pp=87-88}}{{efn|The number of wires in a strand is typically 37 to 127 (for prefabricated strand construction) and 200 to 500 (for air-spinning construction).{{sfn|Jones|Howells|2000|pp=602-604}}}}
Cables are typically constructed at the bridge site by unspooling wires or strands from large [[reel]]s.<ref>{{Multiref
|{{harvnb|Gimsing|1997|pp=431–433}}.
|{{harvnb|Jones| Howells |2000|pp=652–653}}.
}}</ref><!--  
{{efn|Some cables consist of a single strand. In that situation, if the strand is delivered to the bridge site on a reel, there is no need to construct the cable at the bridge site.}}
--> Large suspension bridges may use cables that are over {{convert|1|meter|sp=us}} in diameter and weigh over {{convert|20000|tonne|lb|round=10}}.<ref>{{Multiref
|{{harvnb|Gimsing |1997|p=56}}. Diameter over 1m.
|{{harvnb|Sangree |Shafer|2003}}. 290 strands per cable.
|{{harvnb|Jones| Howells |2000|pp=599–603}}. 94 tonnes per strand.
}}</ref>


Snapshots in time of the external condition of a bridge can be recorded using [[Lidar]] to aid bridge inspection.<ref name="omer">{{cite journal | last1 = Omer | display-authors = et. al. | year = 2018 | title = Performance evaluation of bridges using virtual reality | url = https://www.researchgate.net/publication/325194259 | journal = Proceedings of the 6th European Conference on Computational Mechanics (ECCM 6) & 7th European Conference on Computational Fluid Dynamics (ECFD 7), Glasgow, Scotland}}</ref> This can provide measurement of the bridge geometry (to facilitate the building of a computer model) but the accuracy is generally insufficient to measure bridge deflections under load.
Before building the cables of a suspension bridge, temporary [[Footbridge#Catwalk|catwalk]]s must be constructed to support the wires while they are drawn across the span and over the tops of the towers.<ref>{{Multiref
|{{harvnb|Jones| Howells |2000|pp=650–651}}.
|{{harvnb|Gimsing|1997|pp=419–424}}.
}}</ref> There are two approaches to pulling the wires across the span: the air spinning method (in which individual wires are carried across by pulleys); and the prefabricated strand method (in which entire strands are pulled across).<ref>{{Multiref
|{{harvnb|Jones| Howells|2000|pp= 602–605}}.
|{{harvnb|Gimsing |1997|pp=97–99}}.
}}</ref>{{efn|The prefabricated method is sometimes called the ''prefabricated parallel-wire strands'' (PPWS) method.{{sfn|Gimsing|1997|pp=37-38}}}}


While larger modern bridges are routinely monitored electronically, smaller bridges are generally inspected visually by trained inspectors. There is considerable research interest in the challenge of smaller bridges as they are often remote and do not have electrical power on site. Possible solutions are the installation of sensors on a specialist inspection vehicle and the use of its measurements as it drives over the bridge to infer information about the bridge condition.<ref>{{Cite journal|last1=Yang|first1=Y.-B.|last2=Lin|first2=C.W.|last3=Yau|first3=J.D.|date=May 2004|title=Extracting bridge frequencies from the dynamic response of a passing vehicle|journal=Journal of Sound and Vibration|volume=272 |issue=3–5|pages=471–493|doi=10.1016/S0022-460X(03)00378-X|bibcode=2004JSV...272..471Y}}</ref><ref>{{Cite journal|last1=Yang|first1=Y. B.|last2= Yang|first2=Judy P.|date=February 2018|title=State-of-the-Art Review on Modal Identification and Damage Detection of Bridges by Moving Test Vehicles|journal=International Journal of Structural Stability and Dynamics|volume=18|issue= 2|page=1850025|doi=10.1142/S0219455418500256|issn=0219-4554}}</ref><ref>{{Cite journal|last1=Malekjafarian|first1=Abdollah |last2=McGetrick|first2=Patrick J.|last3=OBrien|first3=Eugene J.|date=2015|title=A Review of Indirect Bridge Monitoring Using Passing Vehicles|journal=Shock and Vibration|volume=2015|pages=1–16|doi=10.1155/2015/286139|issn=1070-9622|doi-access=free|hdl=10197/7054|hdl-access=free}}</ref> These vehicles can be equipped with accelerometers, gyrometers, Laser Doppler Vibrometers<ref>{{Cite journal|last1=OBrien |first1=E. J.|last2=Keenahan|first2=J.|date=May 2015|title=Drive-by damage detection in bridges using the apparent profile |journal=Structural Control and Health Monitoring|volume=22|issue=5|pages=813–825|doi=10.1002/stc.1721|hdl=10197/7053|s2cid=55735216 |hdl-access=free}}</ref><ref>{{Cite journal|last1=Malekjafarian|first1=Abdollah|last2=Martinez|first2=Daniel|last3=OBrien|first3=Eugene J.|date=2018|title=The Feasibility of Using Laser Doppler Vibrometer Measurements from a Passing Vehicle for Bridge Damage Detection|journal=Shock and Vibration|volume=2018|pages=1–10|doi=10.1155/2018/9385171|issn=1070-9622|doi-access=free|hdl=10197/9539|hdl-access=free}}</ref> and some even have the capability to apply a resonant force to the road surface to dynamically excite the bridge at its resonant frequency.
The air spinning method was used for all suspension bridges until the prefabricated strand method was invented in the 1960s.{{sfn|Gimsing|1997|pp=37-38}}
<!--
The air spinning method is slower because it requires the spinning pulley to cross the span thousands of times, pulling a pair of wires each time.<ref name=AS_PPWS>{{Multiref
|{{harvnb|Jones| Howells|2000|pp= 601-603}}.
|{{harvnb|Gimsing |1997|pp= 37-38, 88, 98}}.
|{{harvnb|Bennett|1999|pp=84-85}}.
}}</ref>
-->  
After 300 to 500 wires are pulled, aluminum bands are used to bundle them into strands.{{sfn|Gimsing|1997|pp=424-425}}{{efn|For large suspension bridges, the length of wire or strand on a reel may not reach across the full span, so when a reel reaches its end, the wires (or strands) must be spliced to the wires (or strands) of a new reel.{{sfn|Gimsing|1997|pp=422-423}}}} The wires within a strand may be parallel, or they may wrap around each other in a twisted (spiral) pattern.{{sfn|Jones| Howells|2000|pp= 599-602}} Air spinning always produces strands that contain parallel wires. The prefabricated strand method can utilize strands with parallel or twisted wires.{{sfn|Jones| Howells|2000|pp= 599-602}}{{efn|The prefabricated strand method was used for the Akashi Kaikyo Bridge, where each strand weighed {{convert|94|tonne|lb|round=10}} and was {{convert|4|km|sp=us}} long.{{sfn|Jones| Howells|2000|pp= 599-603}} }}
<!--
After all the wires have been drawn across the full span and are connected to the towers, they are compacted into a tight bundle by a hydraulic device that moves along the cable and compresses the wires together.<ref>{{Multiref
|{{harvnb|Gimsing |1997|pp=99, 429-430}}.
|{{harvnb|Jones| Howells|2000|p=604}}
}}</ref> Then a wire is usually wrapped around the cable in a helical manner, to provide protection against water intrusion.{{sfn|Gimsing |1997|pp= 430-431}} The deck is suspended from the cable with vertical strands called hangers. Each hanger is attached to the main cable by a bracket called a ''cable band''.{{sfn|Gimsing |1997|pp=392-394}}
-->


==Visual index==
====Deck====
{{Further|List of bridge types|List of longest bridges in the world}}
{{main|Deck (bridge)}}
[[File:Ilmtalbruecke-April2009b.jpg|thumb|right
|alt=A large concrete arch bridge being constructed|The deck of this arch bridge is being [[incremental launching|horizontally pushed]] onto the substructure with [[Jack (device)|jacks]]
<ref name=launch>{{Multiref
|{{harvnb|Hewson|2000|pp=302–306}}.
|{{harvnb|Collings|2000|pp=432–433}}.
|{{harvnb|Brown|2005|p=193}}
|{{harvnb|Shirley-Smith|Billington}}.
}}</ref>
]]
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|alt=The underside of a green bridge, consisting of many parallel pieces of steel
|caption=The [[:de:Agnes-Bernauer-Brücke (Straubing)|Agnes Bernauer Bridge]] in Germany has an [[orthotropic deck]], visible as numerous small, parallel steel ribs on its underside.
}}
-->
The [[Deck (bridge)|deck]] of a bridge is the horizontal, continuous surface that extends across the full span of a bridge, and upon which vehicles or pedestrians travel. Decks generally rest on beams or box girders. When a deck is rigidly attached to its supporting beams or girders they function together as a single structure.<ref name=deckgirder>{{Multiref
|{{harvnb|Chavel|2022|p=1}}.
|{{harvnb|Vejrum|2014|p=413}}.
|{{harvnb|Mangus|2014|pp=592, 594, 596}}.
|{{harvnb|Shi|2014|pp=85–87}}. Uses term ''girder'' to refer to deck/girder structure.
}}</ref><!--
{{efn|The beams or girders (that the deck rests upon) may be steel or concrete. The deck and its supporting beams or girders are sometimes considered as a single structure, which may be referred to as either the ''deck'' or the ''girder''. The top surface of a concrete box girder bridge may act as a deck, in which case, the deck is not a separate element of the bridge.<ref name=deckgirder/>}}
--> Two common types of decks are concrete decks and [[orthotropic steel deck]]s.<ref>{{Multiref
|{{harvnb|Mangus|2014|p=590}}.
|{{harvnb|Shen|2014|p=573}}.
}}</ref>{{efn|Some bridges use both types of deck: concrete in some parts of the bridge, and orthotropic steel in other parts.{{sfn|Mangus|2014|p=604}} Other materials (in addition to concrete and steel plates) used to build decks include wood planks and open steel [[grating]]s.{{sfn|Chavel|2022|pp=20, 31–32}}}} Concrete decks are flat [[Concrete slab|slabs]] of reinforced concrete. The slabs may [[Precast concrete|precast]] off-site, or [[Cast-in-place concrete|cast-in-place]] by pouring concrete into [[formwork|forms]] on the bridge superstructure.<ref>{{Multiref
|{{harvnb|Chavel|2022|pp=5–6, 11–13}}.
|{{harvnb|Shen|2014|pp=573–575}}.
}}</ref>{{efn|An advantage of pre-cast slabs is that{{snd}}after bridge construction{{snd}}they do not shrink or [[Creep (deformation)|creep]] as much as cast-in-place slabs.{{sfn|Vejrum|2014|p=413}}}} Orthotropic steel decks consist of a flat steel plate, coated with a [[wearing surface]].<ref>{{Multiref
|{{harvnb|Mangus|2014|pp=590, 602}}.
|{{harvnb|Chavel|2022|pp=26–28}}.
}}</ref> Numerous small steel [[wiktionary:rib|ribs]] are welded to the underside of the top plate, running in the direction of the bridge roadway.{{efn|''Orthotropic'' means (a) the ribs are perpendicular to the crosswise floor beams (''ortho''gonal); and (b) the ribs are more closely spaced than the crosswise floor beams (aniso''tropic'').{{sfn|Dahlberg|2022|p=2 }}
}} Below the ribs are steel floor beams, placed crosswise to the ribs.{{sfn|Mangus|2014|pp=590, 592}}{{efn|Floor beams are small beams that cross the width of the bridge, and rest on larger beams that run lengthwise and span the full distance between bridge supports.{{sfn|Mangus|2014|pp=590, 592}}}} Orthotropic steel decks are more expensive than concrete steel decks, but weigh less. They are useful in applications where weight is critical, a thin deck is required, or the environment is subject to earthquakes or extreme cold weather.{{sfn|Mangus|2014|pp=590, 604}}


Many decks have a wearing surface on top, which is a layer of material designed to be periodically replaced after it is worn away by vehicular traffic. Wearing surfaces are typically made of [[Construction aggregate|aggregate]] (small rocks) mixed with a [[Binder (material)|binder]] such asphalt, polyurethane, epoxy resins, or polyester.<!--
[[asphalt concrete|asphalt]], [[polyurethane]], [[epoxy resins]], or [[polyester]].
--><ref>{{Multiref
|{{harvnb|Mangus|2014|pp=625–628}}.
|{{harvnb|Chavel|2022|pp=27, 29–30}}.
}}</ref>{{efn|[[Wearing surface]]s are essential for steel decks, but a concrete deck often acts as its own wearing surface. Concrete decks must be designed to accommodate the weight of a future addition of a wearing surface, which will be applied when the concrete wears down due to vehicular traffic.{{sfn|Shen|2014|pp=279-280}}}} Railway bridge decks are categorized as open decks (the [[Railroad tie|ties]] rest directly on beams or girders, with air gaps between) and [[Track ballast|ballast]] decks (the ties rest on ballast rocks, and the ballast rests on a deck slab).{{sfn|Sorgenfrei|2014|pp=147-148}}
Constructing the deck (and its supporting beams or girders) can be difficult when the bridge is over water or a deep valley. A variety of techniques are available, and the choice depends on factors such as the topography of the site, the deck material (concrete or steel), traffic or obstacles under the bridge, and whether sections can be built off-site and transported to the bridge. Methods of deck construction include building atop [[Falsework#In bridge construction|temporary supports]], [[Jack (device)|jacking up]] from the ground, [[incremental launching]] (building the entire deck on the approach road and pushing it horizontally), lifting from below with a [[Hoist (device)|hoist]] mounted on the bridge, [[Cantilever#In bridges, towers, and buildings|cantilevering]] (incrementally extending the deck, starting from towers or abutments), and lifting with a [[Crane vessel|floating crane]].<ref name=constrMethod>{{Multiref
| {{harvnb|Bakhoum|2014|pp=568–578}}.
| {{harvnb|Shi|2014|pp=86–87}}.
| {{harvnb|Hewson|2000|pp=283–310}}.
}}</ref>
===Protection===
<!--
[[File:Peeling paint.jpg|alt=A thick, old wire cable, with paint that is partially worn off|thumb|Paint can be used to reduce deterioration of steel components. Steel bridges need to be repainted periodically, as seen in this wire hanger from the [[Golden Gate Bridge]], which is painted [[International orange#Golden Gate Bridge|international orange]].{{sfn|"Painting The Golden Gate Bridge". ''Golden Gate Bridge, Highway and Transportation District''}} ]]
-->
To achieve the designed service life, a bridge must be protected from deterioration by incorporating certain features into the design. Bridges can deteriorate due to a variety of causes, including rust, corrosion, chemical actions, and mechanical abrasion. Deterioration is sometimes visible as rust on steel components, or cracks and [[spall#Spalling in refractory concrete|spalling]] in concrete.{{sfn|Mulheron|2000|pp=805-807}} Deterioration can be slowed with various measures, primarily aimed at excluding water and oxygen from the bridge elements.{{sfn|Mulheron|2000|pp=807-809}} Techniques to prevent water-based damage include drainage systems, waterproofing membranes (such as polymer films), and eliminating [[expansion joints]].{{sfn|Mulheron|2000|pp=810-816}}{{efn|Expansion joints relieve stress due to thermal expansion and contraction, but permit water to seep into vulnerable bridge elements, which can lead to corrosion and degradation. [[Integral bridge]] concepts are an alternative to expansion joints.{{sfn|Mulheron|2000|pp=815-816}} }} Concrete bridge elements can be protected with waterproof seals and coatings.{{sfn|Mulheron|2000|pp=816-822}}{{efn|Concrete can deteriorate by the process of [[carbonatation]], or by penetration of [[chloride ion]]s, typically from salt. The salt may come from ocean water, or from [[road salt]] applied during winter de-icing procedures.{{sfn|Mulheron|2000|pp=806-808, 817-819, 821, 824 }}}} Reinforcing steel within concrete can be protected by using high-quality concrete and increasing the thickness of the concrete surrounding the steel.{{sfn|Mulheron|2000|pp=822-830}} Steel elements of a bridge can be protected by paints or by [[galvanizing]] with zinc.<ref>{{Multiref
|{{harvnb|Mulheron|2000|pp=808, 822–826, 830–837}}.
|{{harvnb|Zhao|2017|pp=252–268, 284–286}}.
}}</ref> Paint can be avoided entirely for steel members by using certain steel alloys, such as [[stainless steel]] or [[weathering steel]] (a steel alloy that eliminates the need for paint, by forming a protective outer layer of rust).<ref>{{Multiref
|{{harvnb|Mulheron|2000|pp=837–842}}.
|{{harvnb|Zhao|2017|pp=279–284}}.
}}</ref>
[[Bridge scour]] is a potentially serious problem when bridge footings are located in water. Currents in the water can cause the sand and rocks around and below the footings to wash-away over time. This effect can be mitigated by placing a cofferdam around the footings, or surrounding the footings with [[rip-rap|large, carefully placed rocks]].<ref>{{Multiref
|{{harvnb|Mulheron|2000|pp=842–844}}.
|{{harvnb|Kashima|Sakamoto|1998|p=72}}.
}}</ref>{{efn|As an example of measures taken to combat scour: the underwater foundations of the [[Akashi Kaikyo Bridge]] are surrounded with [[rip rap]] {{convert|8|m|ft|sp=us}} thick.{{sfn|Kashima|Sakamoto|1998|pp=72}}}} Suspension bridges and cable-stayed bridges have large cables containing hundreds of steel wires. Several techniques are used to minimize corrosion inside the cables, such as wrapping the cables with galvanized wire, injecting the cables with grout or epoxy, using interlocking S-profile wires, and circulating dry air through the interior of the cable.<ref>{{Multiref
|{{harvnb|Jones|Howells|2000|pp=557–559, 604–605}}.
|{{harvnb|Gimsing|1997|pp=102–108}}.
}}</ref> Bridges with supports in navigable waterways are designed to withstand [[ship strike]]s up to a specific, predefined magnitude. In addition to waterway markings and pilot warning systems, bridge supports in water may be surrounded by physical protections such as [[fender (boating)|fenders]], [[Dolphin (structure)|pilings]], or small artificial islands.{{sfn|Knott|Prucz|2014|pp =107-109}}
==Operation and financing==
===Management===
{{further|Bridge management system}}
After a bridge is completed and becomes operational, management processes are employed to ensure that it remains open to traffic, avoids safety incidents, and achieves its intended lifespan. These processes{{snd}}collectively referred to as ''bridge management''{{snd}} include technical activities such as maintenance, inspection, [[Structural health monitoring|monitoring]], and testing.{{sfn|Vassie|2000|p=849}} In addition to technical tasks, management encompasses planning, budgeting, and prioritization of maintenance activities.{{sfn|Vassie|2000|p=849}} Bridge managers use methodologies such as [[bridge management system]]s and [[life-cycle cost analysis]] to manage a bridge and estimate the maintenance costs of a bridge throughout its lifetime.<ref>{{Multiref
|{{harvnb|Hu|2016|pp=66–69}}.
|{{harvnb|Fu|Devaraj |2014|pp=233–234}}.
}}</ref> Annual maintenance costs increase as the bridge ages and degrades.{{sfn|Hu|2016|p=67}}
===Maintenance===
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|caption=A crew of workers are using a maintenance traveler (the mobile cage structure) to inspect the [[Clifton Suspension Bridge]].
}}
Maintenance activities seek to prolong the life of the bridge, reduce lifecycle costs, and ensure the safety of the community.{{sfn|Alampalli|2014|pp=269-272}} Maintenance tasks can be categorized as corrective tasks and preventive tasks.{{sfn|Alampalli|2014|pp=276, 282}} Corrective tasks are implemented in response to unexpected issues that arise, such as repairing structural elements (piers, beams, girders, towers, or cables) and replacing bearings.{{sfn|Alampalli|2014|pp=288-292}}
Preventive tasks include washing, painting, lubricating bearings, sealing the deck, filling cracks, removing snow, filling potholes, and repairing minor issues with structures and electrical fixtures.{{sfn|Alampalli|2014|pp=282-288}} Some preventive tasks are performed on a periodic schedule. An example schedule for periodic bridge maintenance tasks is:
washing entire structure (1–2 years);
sealing deck surface (4–6 years);
lubricating bearings (4 years);
painting steel bridge components (12–15 years);
replacing the deck's wearing surface (12 years);
sealing sidewalks (5 years);
filling cracks (4 years);
and cleaning drains (2 years).<ref>{{harvnb|Alampalli|2014|pp=285–286}}. Maintenance periods shown are from the [[New York City Department of Transportation]].</ref>
{{clear}}
===Inspection and monitoring===
[[File:SOB Sitterviadukt über die Sitter, St. Gallen SG - Herisau AR 20190720-jag9889.jpg|thumb|right
|alt=A tall bridge covered in temporary scaffolding|[[Scaffolding]] is erected under the ''[[:de:Sitterviadukt (Südostbahn)|Sitterviadukt]]'' rail bridge in Switzerland while maintenance on the deck truss is performed.{{sfn|Quirchmair|2022}}]]
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|caption= Concrete can degrade and [[spall]], as seen in this bridge pier, exposing internal steel [[rebar|reinforcing bars]].
}}
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An important part of maintenance is inspecting a bridge for damage or degradation, and taking steps to mitigate any issues detected. Degradation can come from environmental sources such as  expansion/contraction from freeze/thaw cycles, rain, oxidation of steel, and sea spray.  Human activities may also cause damage, such as  vehicular traffic, mechanical abrasion, poor bridge design, and improper repair procedures.<ref>{{Multiref
|{{harvnb|Abdunur|2000|pp=883–895}}.
|{{harvnb|Mulheron|2000|pp=804–808, 834–836}}.
}}</ref> Some countries mandate periodic inspection schedules, for example, routine inspections every 24 months, or inspecting underwater foundations for scouring every 60 months.{{sfn|Copelan|2014|p=338}}
Relying solely on visual inspection to assess degradation of a bridge can be unreliable, so inspectors use a variety of [[nondestructive testing]] techniques.{{sfn|Washer|2014|pp=301-305}} These techniques include [[Schmidt hammer|hammer strike]] tests, [[Ultrasonic testing|ultrasonic pulse velocity]] tests, [[seismic tomography]], and [[ground penetrating radar]].<ref>{{Multiref
|{{harvnb|Abdunur|2000|pp=898–907}}.
|{{harvnb|Washer|2014|pp=305–306, 317–318}}.
|{{harvnb|Alampalli|2014|p=295 }}.
}}</ref> <!-- [[Magnetometer]]s can be used to detect the location of reinforcing steel within concrete.{{sfn|Abdunur|2000|pp=898-906 }} --> Various electrical tests, such as those assessing [[permeability (electromagnetism)|permeability]] and [[electrical resistance|resistance]], can give insight into the condition of surface concrete.{{sfn|Abdunur|2000|pp=904-905 }} X-rays can be passed through concrete to obtain data about concrete density and condition.{{sfn|Abdunur|2000|pp=907-909 }} Videography using slender probes can be used where access is available.{{sfn|Abdunur|2000|pp=910-912 }} Measurements of the state of a bridge may be made automatically and periodically using [[structural health monitoring]] (SHM) technologies.{{sfn|Frangopol |2014|pp= 247-248 }} Some testing{{snd}}termed [[destructive testing]]{{snd}}requires removing samples from the bridge and taking them to a laboratory for analysis with microscopes, sonic devices, or X-ray diffraction.{{sfn|Abdunur|2000|pp=896-898, 955}} Destructive testing is performed on samples such as [[Core sample|cores drilled]] from concrete, or a small piece of steel wire cut from a cable.{{sfn|Abdunur|2000|pp=896-898, 955}}<!--
{{efn|1=The process of cutting-out a small piece of wire from a large cable of a heavily trafficked suspension bridge is seen in [https://www.youtube.com/watch?v=XMbiq5aleOc&t=74 this video].}}
SHM places permanent sensors at critical locations in the bridge, which may be sampled at any time to obtain data about stresses and chemical degradation.{{sfn|Abdunur|2000|p=906}} The sensors may be placed in the bridge during construction, or while it is in operation{{snd}}for example, to monitor the quality of a repair.<ref>{{Multiref
|{{harvnb|Abdunur|2000|p=906}}.
|{{harvnb|Frangopol |2014|pp= 248-249 }}.
}}</ref> Many long-span bridges are routinely monitored with a range of sensors, including [[Strain gauge|strain transducers]], [[sodar]], [[accelerometer]]s, [[tiltmeter]]s, and [[GPS]].{{sfn|Xu|2011|pp=41-42, 45-46, 62-64, 68-69, 110-111, 216-217, 252}}
To evaluate the condition of large steel cables, electrical coils are moved along the cable, measuring the induction of the cable, which can reveal corrosion issues.{{sfn|Abdunur|2000|pp=912-914}} Detailed measurements of the external surface of a bridge can be recorded using [[lidar]] technology. Comparing measurements taken at multiple points in time can reveal long-term changes.{{sfn|Omer|2018 }}
A variety of [[Structural testing|structural tests]] may be performed to evaluate a bridge's condition. One test involves placing loads in selected locations on the bridge, and measuring the resulting deflections: sensitive instruments measure how much the bridge elements bend or twist, and the results can reveal if the element is not performing within expected limits. Another test involves jacking the bridge deck off its supports slightly, and measuring the force required. Cables can be evaluated by vibrating them and measuring their dynamic response.{{sfn|Abdunur|2000|pp=915-934}}
-->{{clear}}
===Financing===
Funding for bridge construction and operation comes from a variety of sources, including  [[fuel tax]]es, annual [[Vehicle registration plate|vehicle registration fee]]s, [[Toll (fee)|tolls]], [[Congestion pricing|congestion fees]], and usage fees based on satellite tracking.{{sfn|Queiroz|2016|pp=7-9}}  Some bridges{{snd}}particularly in [[developing countries]]{{snd}}are financed by international sources such as the [[World Bank]] or China's [[Belt and Road Initiative]].<ref>{{Multiref
|{{harvnb|"A Small Bridge". ''World Bank''}}.
|{{harvnb|Marlow|2025}}.
}}</ref>  [[toll bridge|Toll systems]] are generally an inefficient mechanism for collecting funding, particularly when [[toll booth]]s are used, because they are expensive to build and manage.  Toll booths can  slow down traffic and interfere with the construction of entry or exit points.{{sfn|Queiroz|2016|pp=7-8}}
The cost of building a bridge is typically borne by government agencies, but since 1990 an increasing number of bridges are built and paid for by private companies using a [[public–private partnership]] (PPP) agreement.  In a PPP project, the government grants the right to build the bridge to a company, and the company recoups its expenses by collecting tolls for fixed period of time.<ref>{{Multiref
|{{harvnb|Engel|2020|pp=3–7}}.
|{{harvnb|Queiroz|2016|pp=4–5, 21}}.
}}</ref>{{efn|Some PPP agreements specify that the agreement terminates at the end of the fixed period, or when the private company recoups its expenses, whichever comes first.{{sfn|Engel|2020|pp=28-29}} See also the [[build–operate–transfer]] financing method.}}  At the end of the period, the bridge is transferred to government ownership, and the government may choose to continue to charge tolls or not. Notable bridges constructed with a PPP model include the [[Queen Elizabeth II Bridge]] (built in 1991, toll collection period 20 years) and the [[Second Severn Crossing]] (built in 1996, toll collection period 30 years).{{sfn|Engel|2020|pp=28-29}}
===Failures===
{{see also|List of bridge failures}}{{Anchor|Bridge failures}}
[[File:Nanfangao Bridge Collapse 20191003d.jpg|thumb|left
|alt=A broken bridge, which has fallen into the water over which it used to pass
|The [[Nanfang'ao Bridge]] in Taiwan collapsed because of excessive corrosion that went undetected.{{sfn| "TTSB Details Reasons for Nanfang'ao Bridge Collapse". ''Focus Taiwan''}} ]]
<!--
| image1 = Francis_Scott_Key_Bridge_and_Cargo_Ship_Dali_NTSB_view_(cropped).jpg
| caption1 = This [[Francis Scott Key Bridge collapse|bridge in Balimore]] collapsed after a powerless [[containership]] collided with it.{{sfn| "Contact of Containership Dali". ''National Transportation Safety Board'' }}
[[File:FEMA - 16965 - Photograph by John Fleck taken on 10-04-2005 in Mississippi.jpg|thumb|left|alt= A concrete bridge, passing over a lake, that is broken, and many pieces have fallen into the water.|This [[St. Louis Bay Bridge|bridge in the US]] failed during [[Hurricane Katrina]].{{sfn|Capka|2005}}]]
-->
Bridge failures are of special importance to [[structural engineers]], because the [[failure analysis|analyses of the failures]] provide [[lessons learned]] that serve to improve design and construction processes.<ref>{{Multiref
|{{harvnb|Petroski |1994|pp=169–171}}.
|{{harvnb| "Bridge Failure". ''United Nations'' }}.
|{{harvnb|Barker|2007|pp=21–39}}.
}}</ref> Bridge failures have a variety of causes, which can be categorized as natural factors (flood, scour, earthquake, landslide, and wind) and human factors
(improper design and construction method, collision, overloading, fire, corrosion, and lack of inspection and
maintenance).{{sfn|Choudhury|Hasnat|2015|pp=26-28}} Over time, bridge failures have led to significant improvements in bridge design, construction, and maintenance practices.<ref>{{Multiref
|{{harvnb|Barker|2007|pp=23–25}}.
|{{harvnb|Petroski |1994|pp=158–171}}.
}}</ref> Before the advent of bridge engineering procedures based on rigorous, scientific principles, bridges frequently failed. Failures were most common in the mid-1800s, when the rapidly expanding railway networks were building hundreds of new bridges every year around the globe.{{sfn|Barker|2007|p=22}} In the United States, 40 bridges per year failed in the 1870s, amounting to 25% of all bridges built in that decade.<ref>{{Multiref
|{{harvnb|Barker|2007|p=22}}.
|{{harvnb|Bennett|1999|p=31}}.
}}</ref>
In the modern era, in spite of advances in bridge engineering methodologies, bridge failures continue to occur regularly.<ref>{{Multiref
|{{harvnb|Choudhury|Hasnat|2015|pp=26, 33}}.
|{{harvnb|Cheng|Duan|2014|pp=445–451}}.
}}</ref> In Australia, the [[King Street Bridge (Melbourne)|King Street Bridge]] collapsed in 1962, a year after opening, due to improper welding techniques.{{sfn|Choudhury|Hasnat|2015|pp=30-31}} In Palau, the [[Koror–Babeldaob Bridge]] collapsed in 1996, three months after a repair operation made major changes to the bridge.{{sfn|Burgoyne |Scantlebury |2008}} In 1998, the [[Turag-Bhakurta Bridge]] in Bangladesh collapsed due to river waters scouring away the soil around the bridge supports.{{sfn|Choudhury|Hasnat|2015|p=32}} The [[Millennium Bridge, London|Millennium Bridge]] in London opened in 2000, but closed two days later due to excessive swaying.<!--
{{efn|The Millennium Bridge received the nickname "Wobbly Bridge" as a result of the swaying.{{sfn|Warren|2025}}}}
--> It did not open until two years later{{snd}}after dampers were installed.<ref name=millen>{{Multiref
|{{harvnb|Dallard|2001}}.
|{{harvnb|Warren|2025}}.
}}</ref> About half of all bridge failures in the early 21st century in the US were due to water-related causes, such as flood damage or scouring (water currents undermining the bridge supports).<ref>{{Multiref
| {{harvnb|Cook|2014}}.
| {{harvnb|Nowak|Iatsko|2018}}.
| {{harvnb|Wardhana |Hadipriono|2003}}.
}}</ref>
{{clear}}
==Society and culture==
===Signature bridges===
[[File:炫彩津门35大沽桥.jpg|thumb|right
|alt=A large bridge crossing a river, in nighttime, with skyscrapers in the background|The [[Dagu Bridge]] in China was designed to be a signature bridge.{{sfn|Tang|2014|pp=19-20}}]]
<!-- [[File:Bristol Balloon Fiesta - panoramio (1).jpg|thumb|alt=A large bridge, and about thirty large, colorful balloons in the sky above the bridge|left| upright=1.2|The [[Clifton Suspension Bridge]] is a landmark associated with the city of [[Bristol]] in England.{{sfn|Cruickshank|2010|p=233}}]] -->
Many bridges{{snd}}known as ''signature bridges''{{snd}}are strongly identified with a particular community.<ref>{{Multiref
|{{harvnb|Brown|2005|pp=130, 164–165, 168, 186 }}.
|{{harvnb|Cruickshank|2010|pp=23, 233 }}.
}}</ref>{{efn|Most signature bridges are roadway bridges or pedestrian bridges; railways rarely construct signature bridges.{{sfn|Sorgenfrei|2014|p=144}}
}} Large suspension bridges, in particular, are often regarded as iconic landmarks that symbolize the cities in which they are located. Notable examples include the [[Brooklyn Bridge]] in New York; the [[Golden Gate Bridge]] in San Francisco; the [[Clifton Suspension Bridge]] in Bristol; and the [[Széchenyi Chain Bridge]] in Budapest.{{sfn|Cruickshank|2010|p=233}}{{efn|Some large cable-stayed bridges also have iconic designs.{{sfn|Vejrum|2014|pp=405-407}}}} Some visually impressive bridges, such as the [[Dagu Bridge]] in China, are designed with the express goal of creating a landmark for the host city.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|pp=8–9}}.
|{{harvnb|Hu|2016|pp=103–112}}.
|{{harvnb|Tang|2014|pp=19–20, 23}}. Dagu bridge.
}}</ref> The art historian Dan Cruickshank notes that some bridges have the ability to "transform a place a community and ... can make its mark on the landscape and in men's minds, capture the imagination, engender pride and sense of identity and define a time and place."{{sfn|Cruickshank|2010|pp=8-9}}
=== Economic and environmental impact===
Bridges can have a significant impacts{{snd}}both positive and negative{{snd}} on a community's environment, society, and economy.  During the bridge design process, these effects may be modeled with [[sustainability]] methodologies such as [[Life-cycle assessment|life cycle sustainability assessment]] or [[Building information modeling in green building|building information modeling]], and the results can be used to adjust the bridge's design to improve its effect on the environment, society, and economy.<ref name=sustain>{{Multiref
|{{harvnb| Ahmad|2025}}.
|{{harvnb| Zhou |2021}}.
}}</ref>
Positive effects of a new bridge can include shorter transport times, employment opportunities, improvements to social equity, improved productivity, and increases to the [[gross domestic product]] (GDP).<ref name=sustain/> Construction of a new bridge can increase wages in the surrounding region, but can also increase income inequity between genders (men see larger wage gains than women) and between education levels (higher-educated persons see more gains that lower-educated persons).<ref>{{Multiref
|{{harvnb|Bütikofer|2024}}.
|{{harvnb|De Borger|2025}}.
}}</ref> In locales where flooding is common, bridges can increase overall income by providing reliable crossings across rivers.{{sfn|Brooks|2021}} In underdeveloped regions with mountainous topography, construction of bridges that cross deep valleys can bring major benefits to the communities they connect. Without bridges, such areas often have a core region that is more prosperous, surrounded by less developed peripheral regions. Building bridges over deep valleys can reduce developmental disparities between areas, as well as generate economic development, and improve accessibility to goods and services.{{sfn|Cai|Deng|2024}}
[[Global warming]] can be exacerbated by the creation of a new bridge, because the [[Cement#CO2 emissions|production of concrete]] significantly contributes to the  [[greenhouse effect]].{{sfn| Zhou |2021}}{{efn| Bridges often utilize large amounts of concrete, which is a major source of [[carbon dioxide#Atmosphere|carbon dioxide]], a gas that contributes to the  [[greenhouse effect]].{{sfn| Zhou |2021}}}} Although bridges can boost the economy of the surrounding region, they also increase environmental [[pollution]] proportionally.{{sfn| Zhou |2021}} [[Corruption]] is endemic in the construction industry (including bridge building) and the associated  [[bribery|bribes]] and inefficiencies produce negative societal and economic consequences.<ref name=corrupt>{{Multiref
|{{harvnb|Sohail|Cavill|2008}}.
|{{harvnb|Zhou |2021}}.
}}</ref>  Bridges that carry highways can result in increased vehicular collisions, which have economic costs (medical care and lost productivity) averaging over {{Euro|14,000}} each.<ref>{{harvnb|Zhou |2021}}.  Value as of 2021.</ref>
===Art and culture===
{{Further|Bridges in art}}
{{Easy CSS image crop
|image = Heimdall an der Himmelsbrücke by E. Doepler.jpg
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|alt==A man blowing a trumpet, with a rainbow in the background
|caption=In [[Norse mythology]], the [[Bifröst]] rainbow bridge connects Earth with [[Asgard]].{{sfn|Watson|1937|p=1}}
}}
<!--
[[File:BridgeOfSanLuisRey.JPG|thumb|alt= The cover of a book, which has an illustration of a Catholic priest standing before a mountain and a bridge | upright=0.7|The [[Pulitzer Prize]] winning novel ''[[The Bridge of San Luis Rey]] ''revolves around a bridge failure that killed five people.{{sfn|Cruickshank|2010|pp=17-19}}]]-->
<!--
{{Quote box
|qalign = center
| align = right
| quote = <poem>
Reaching for the world, as our lives do,
As all lives do, reaching that we may give
The best of what we are and hold as true:
Always it is by bridges that we live.</poem>
| source = [[Philip Larkin]] "Bridge for the Living" (1981)<ref>{{Multiref
|{{harvnb| Cruickshank| 2010| pp= 13–14}}.
|{{harvnb|French|1993}}.
}}</ref>
}}
-->
Bridges occur extensively in art, legend, and literature, often employed as metaphors or symbols of human accomplishment, lifespan, or experience.<ref>{{Multiref
|{{harvnb|Cruickshank|2010|pp=8–20}}.
|{{harvnb|Watson|1937|pp=vii–viii, 65–66, 71–74, 231–233}}.
}}</ref> In [[Norse mythology]], the home of the gods{{snd}}[[Asgard]]{{snd}}is connected to the earth by [[Bifröst]], a rainbow bridge.{{sfn|Watson|1937|p=1}} Many bridges in Europe are named ''[[Devil's Bridge]]'', and in some cases have folkloric stories that explain why the bridge is associated with the devil.{{sfn|Watson|1937|pp=33, 35-39}} Christian legend holds that [[St. Bénézet]] lifted a huge boulder to begin construction of the [[Pont Saint-Bénézet]] bridge, and went on to found the apocryphal [[Bridge-Building Brotherhood]].{{sfn|Watson|1937|pp=43-48}} Bridges feature prominently in paintings{{snd}}often in the background{{snd}}as in the ''[[Mona Lisa]]''.{{sfn|Cruickshank|2010|pp=14-16}}
In the modern era, bridges continue to feature prominently in culture. Bridges are often the setting for pageants, celebrations, and processions.{{sfn|Watson|1937|pp=103-106}} Authors have used bridges as the centerpiece of novels, such as ''[[The Bridge on the Drina]]'' by [[Ivo Andrić]] and [[Thornton Wilder]]'s ''[[The Bridge of San Luis Rey]]''.{{sfn|Cruickshank|2010|pp=17-19}} British poet [[Philip Larkin]], inspired by the construction of the [[Humber Bridge]] near his home, wrote "Bridge for the Living" in 1981.<ref>{{Multiref
|{{harvnb| Cruickshank| 2010| pp= 13–14}}.
|{{harvnb|French|1993}}.
}}</ref> Neighboring nations have chosen to designate some shared bridges as ''friendship bridges'' or ''peace bridges''.<ref>{{Multiref
|{{harvnb|Brown|2005|p=6}}.
|{{harvnb|Watson|1937|p=147}}.
}}</ref>{{efn|See this [[Friendship Bridge (disambiguation)|list of bridges with "friendship" in the name]], and this [[Peace Bridge (disambiguation)|list of bridges with "peace" in the name]].}} In 1996, the European Commission held a competition to select art for the [[euro banknotes]]. [[Robert Kalina]], an Austrian designer, won with a set of illustrations of bridges, chosen because they symbolize links between states in the union and paths to the future.<ref name=euro>{{Multiref
|{{harvnb|"Money Talks". ''BBC News''}}.
|{{harvnb|Schmid|2001}}.
|{{harvnb| "Design Elements". ''European Central Bank'' }}.
}}</ref>
===Profession and regulation===
{{Further|Regulation and licensure in engineering}}
<!--
[[File:The Institution of Civil Engineers porch 2025-10-03.jpg|thumb|left|The [[Institution of Civil Engineers]], located in London, is the world's oldest professional civil engineering association.{{sfn|Watson|1988|pp=viii, 14-16, 53}}]]
-->
The profession of [[civil engineering]]{{snd}}which includes the discipline of bridge building{{snd}} began to be formalized in the 1700s when a school of engineering was created in France within the [[Corps des Ponts et Chaussées]] at the [[École de Paris (engineering)|École de Paris]], under the direction of [[Jacques Gabriel]].{{sfn|Bennett|1999|p=24}} In 1747 the first school dedicated to bridge building was founded: the [[École Nationale des Ponts et Chaussées]]<!--
{{efn|Originally named '' Bureau des dessinateurs du Roi'', it was given its current name in 1775.}}
--> led by French engineers [[Daniel-Charles Trudaine]] and [[Jean-Rodolphe Perronet]].{{sfn|Bennett|1999|p=24}} The first professional organization focused on civil engineering was the [[Institution of Civil Engineers]] founded in 1818 in the UK, initially led by [[Thomas Telford]].{{sfn|Watson|1988|pp=viii, 14–16, 53}}
In the modern era, bridge engineering is regulated by national organizations, such as the [[National Council of Examiners for Engineering and Surveying]] (US), the [[Canadian Council of Professional Engineers]] (Canada), and the [[Engineering Council]] (UK).{{sfn|"The History of the National Council". ''NCEES''|pp=1, 161, 366}} In many countries, bridge engineers must be licensed or meet minimal educational requirements.{{sfn|"Engineering: Issues Challenges and Opportunities". ''UNESCO''|pp=27-28, 135-136, 358-365 }} Some countries require engineers to pass qualification examinations, for example, in the US engineers must pass the [[Fundamentals of Engineering exam]] followed by the [[Principles and Practice of Engineering exam]].{{sfn|"Occupational Outlook Handbook". ''Department of Labor''|p=148}} In Poland, bridge engineers are required to obtain certification by accumulating several years of experience under a senior engineer, and passing an exam administered by the [[:pl:Polska Izba Inżynierów Budownictwa|Polish Chamber of Civil Engineers]].{{sfn|Biliszczuk|2014|p=632}} International cooperation in the field of engineering is facilitated by the [[World Federation of Engineering Organizations]].{{sfn|"The History of the National Council". ''NCEES'' |pp=70–71, 88, 123–125, 366, 377}}
===Suicide===
[[Suicide]]s are sometimes carried out by [[Suicide bridge|jumping off bridges]]. This method can account for 20% to 70% of suicides in urban areas with access to tall bridges.{{efn|In general, less than 10% of suicides are from jumping.{{sfn|Merli |Costanza |2024}}}} In some regions, suicide by jumping disproportionately affects young adults, who tend to have lower [[inhibitory control]]. Specific bridges can gain notoriety and attract persons experiencing a [[suicidal crisis]], which creates a [[feedback loop]]. High-risk bridges often have [[Suicide barrier|suicide prevention barriers]] installed,{{efn|Arguments against installing suicide prevention measures include cost, aesthetics, and questions of effectiveness.{{sfn|Merli |Costanza |2024}}}} which dramatically decrease the suicide rate on the bridge.{{efn|Many bridges have installed barriers to prevent suicide.  The heights range from {{convert|2|meters|ft|sp=us}} to {{convert|5|meters|ft|sp=us}}, and are generally successful at reducing suicide rates.{{sfn|Merli |Costanza |2024}}}} Installing barriers on a high-risk bridge generally reduces the jumping suicide rate in a region, although in some instances, other bridges become substitutes.{{sfn|Merli |Costanza |2024}}
<!-- ===Numismatics===
[[File:EUR 500 reverse (2002 issue).jpg|alt=A colorful 500 euro bank note illustrated with a bridge and a map of Europe|thumb|The 500 [[euro]] banknote displays a cable-stayed bridge.<ref name=euro/>]]
Bridges have been featured on coins since antiquity.{{sfn|Markowitz |2016}} In 1996, the European Commission held a competition to select art for the [[euro banknotes]]. [[Robert Kalina]], an Austrian designer, won with a set of illustrations of bridges, chosen because they symbolize links between states in the union and with the future. The designs were supposed to be devoid of any identifiable characteristics, so as to not show favoritism to specific countries. But the initial designs by Kalina were discovered to be of specific bridges, including the [[Rialto]] and the [[Pont de Neuilly]], and so were changed to be more generic. Each banknote denomination depicts a bridge design representative of a certain architectural era.<ref name=euro>{{Multiref
|{{harvnb|"Money Talks". ''BBC News''}}.
|{{harvnb|Schmid|2001}}.
|{{harvnb| "Design Elements". ''European Central Bank'' }}.
}}</ref>{{efn|
The eras utilized for bridge images on Euro banknotes are:
Classical (€5),
Romanesque (€10),
Gothic (€20),
Renaissance (€50),
Baroque and Rococo (€100),
19th century iron and glass (€200), and 20th century (€500).<ref name=euro/>}}-->
{{clear}}
<!--
==See also==
==See also==
{{Portal|Transport|Engineering}}
 
{{Div col|colwidth=15em}}
* [[International Association for Bridge and Structural Engineering]]
* [[Air draft]]
* [[European Engineer]]
* [[Architectural engineering]]
* [[World Federation of Engineering Organizations]]
* [[Bridge chapel]]
* [[Regulation and licensure in engineering]]
* [[Bridge tower]]
* [[National Council of Examiners for Engineering and Surveying]] USA
* [[Bridge to nowhere]]
* [[Canadian Council of Professional Engineers]]
* [[Bridges Act]]
* [[Chartered Engineer (UK)]]  
* [[BS 5400]]
* [[Engineering Council]] UK
* [[Causeway]]
* [[Civil engineer]]
* [[Coal trestle]]
* [[American Society of Civil Engineers]]
* [[Covered bridges]]
* [[Institution of Civil Engineers]] UK?
* [[Cross-sea traffic ways]]
* [[ Canadian Society for Civil Engineering]]
* [[Culvert]]
-->
* [[Deck (bridge)|Deck]]
* [[Devil's Bridge]]
* [[Footbridge]]
* [[Jet bridge]]
* [[Landscape architecture]]
* [[Megaproject]]
* [[Military bridge]]s
* [[Orphan bridge]]
* [[Outline of bridges]]
* [[Overpass]]
* [[Pier (bridge structure)]]
* [[Pontoon bridge]]
* [[Rigid-frame bridge]]
* [[Steel bridge]]
* [[Structure gauge]]
* [[Transporter bridge]]
* [[Tensegrity]]
* [[Trestle bridge]]
* [[Tunnel]]
{{Div col end}}
{{clear}}


==References==
==References==
===Footnotes===
{{notelist}}
===Citations===
{{reflist}}
{{reflist}}


==Further reading==
===Sources===
* {{Cite journal |last=Shemirani |first=Alireza Bagher |date=25 June 2022 |title=Experimental and numerical studies of concrete bridge decks using ultra high-performance concrete and reinforced concrete |journal=Computers and Concrete |volume=29 |issue=6 |pages=407–418 |doi=10.12989/CAC.2022.29.6.407}}
 
* {{Cite book |last=Brown |first=David J. |title=Bridges: three thousand years of defying nature |date=2005 |publisher=Firefly Books |isbn=978-1-55407-099-2 |location=Buffalo, NY}}
====Books====
* {{Cite book |last=Sandak |first=Cass R. |title=Bridges |date=31 December 1983 |publisher=Franklin Watts |isbn=978-0-531-04624-1 |language=English}}
{{refbegin}}
* 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.)
 
<!-- {{sfn|Abdunur|2000|p=?}} -->
* {{cite book
| last=Abdunur
| first=Charles
| chapter = Inspection, Monitoring, and Assessment
| title=The Manual of Bridge Engineering
| editor-last=Ryall
| editor-first= Michael
| isbn= 0727727745
| chapter-url=https://archive.org/details/manualofbridgeen0000unse/page/883
| access-date=1 September 2025
| year=2000
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
| pages= 883–942
}}
 
<!-- {{sfn|Adams |1909|p=?}} -->
* {{cite book
| last=Adams
| first=Charles Kendall
| author-link = Charles Kendall Adams
|title=Universal Cyclopædia and Atlas
|date=1909
|oclc=707041389
|publisher=D. Appleton and Company
|pages=161–174
|url=https://books.google.com/books?id=TttTAAAAYAAJ
|access-date=September 1, 2022
|language=en
|chapter=Bridges
}}
 
<!-- {{sfn|Alampalli|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 5. Construction and Maintenance
| edition = Second
| first= Sreenivas
| last= Alampalli
| chapter = Bridge Maintenance
| pages = 269–298
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852330
| url= https://books.google.com/books?id=BCeOAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Bakhoum|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 5. Construction and Maintenance
| edition = Second
| first= Mourad
| last= Bakhoum
| chapter = Bridge Construction Methods
| pages = 567–627
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852330
| url= https://books.google.com/books?id=BCeOAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Barker|2007|p=?}} -->
* {{Cite book
| title=Design of Highway Bridges: An LRFD Approach
| last =Barker
| first= Richard M.
| isbn=9781119646310
| url=https://archive.org/details/designofhighwayb0000bark_s2n4
| access-date=1 September 2025
| year=2007
| publisher=Wiley
}}
 
<!-- {{sfn|Beer|2017|p=?}} -->
* {{Cite book
| title=Mechanics of Materials
| last=Beer
| first=Ferdinand
| author-link = Ferdinand P. Beer
| isbn= 9789339217624
| url=https://archive.org/details/mechanicsofmater0000beer_a6t7
| access-date=17 September 2025
| year=2017
| publisher=[[McGraw Hill]]
}}
 
<!-- {{sfn|Bennett|1999|p=?}} -->
* {{Cite book
| title=The Creation of Bridges: From Vision to Reality - the Ultimate Challenge of Architecture, Design and Distance
| last=Bennett
| first=David
| isbn= 1550415522
| url=https://archive.org/details/creationofbridge0000davi
| access-date=1 September 2025
| year=1999
| publisher=[[Aurum Press]]
}}


==External links==
<!-- {{sfn|Bennett|2000|p=?}} -->
{{Sister project links|voy=no|Bridge}}
* {{cite book
* [http://bridges.lib.lehigh.edu/ Digital Bridge: Bridges of the Nineteenth Century] {{Webarchive|url=https://web.archive.org/web/20050826183135/http://bridges.lib.lehigh.edu/ |date=26 August 2005 }}, a collection of digitized books at Lehigh University
|last=Bennett
* [http://en.structurae.de/ Structurae] – International Database and Gallery of Engineerings Structures with over 10000 Bridges.
| first=David
* [https://www.fhwa.dot.gov/bridge/ U.S. Federal Highway Administration Bridge Technology]
| chapter = The History and Aesthetic Development of Bridges
* [http://tbl.tec.fukuoka-u.ac.jp/index-en.shtml The Museum of Japanese Timber Bridges] {{Webarchive|url=https://web.archive.org/web/20110623165007/http://tbl.tec.fukuoka-u.ac.jp/index-en.shtml |date=23 June 2011 }} [[Fukuoka University]]
| title=The Manual of Bridge Engineering
* [http://www.bridge-info.org "bridge-info.org": site for bridges]
| editor-last=Ryall
| editor-first= Michael
| isbn= 0727727745
| chapter-url=https://archive.org/details/manualofbridgeen0000unse/page/1
| access-date=1 September 2025
| year=2000
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
| pages= 1–42
}}
 
<!-- {{sfn|Biliszczuk|2014|p=?}} -->
* {{cite book
| title=Handbook of International Bridge Engineering
| last=Biliszczuk
| first=Jan
| display-authors=etal
| chapter = Bridge Engineering in Poland
| pages = 593–634
| editor-last1 =Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2= Lian
| isbn=9781439810293
| url=https://archive.org/details/handbookofintern0000unse_j3m6
| access-date= 1 September 2025
| year=2014
| publisher=Taylor & Francis
}}
 
<!-- {{sfn|Birnstiel|2000|p=?}} -->
* {{cite book
| last=Birnstiel
| first=Charles
| chapter = Moveable Bridges
| title=The Manual of Bridge Engineering
| editor-last=Ryall
| editor-first= Michael
| isbn= 0727727745
| chapter-url=https://archive.org/details/manualofbridgeen0000unse/page/663
| access-date=1 September 2025
| year=2000
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
| pages= 663–698
}}
 
<!-- {{sfn|Blank|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 5. Construction and Maintenance
| edition = Second
| first= Simon
| last= Blank
| display-authors=etal
| chapter = Concrete Bridge Construction
| pages = 67–84
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852330
| url= https://books.google.com/books?id=BCeOAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Brown|2005 |p=?}} -->
* {{Cite book
| last=Brown
| first=David
| title=Bridges: Three Thousand Years of Defying Nature
| date=2005
| publisher=[[Mitchell Beazley]]
| isbn=1845330803
| url=https://archive.org/details/bridgesthreethou0000davi
| access-date=1 September 2025
}}
 
<!-- {{sfn|Cai|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 1. Fundamentals
| edition = Second
| first= Steve
| last= Cai
| display-authors=etal
| chapter = Wind Effects on Long-Span Bridges
| pages = 535–554
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852347
| url= https://books.google.com/books?id=WaONAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Chavel|2022|p=?}} -->
* {{cite book
| last=Chavel
| first=Brandon
| chapter =Bridge Deck Design
| title=Steel Bridge Design Handbook
| publisher= [[American Institute of Steel Construction]]
| isbn=
| chapter-url=https://www.aisc.org/globalassets/nsba/design-resources/steel-bridge-design-handbook/b917_sbdh_chapter17.pdf
| access-date=4 November 2025
| year=2022
}}
 
<!-- {{sfn|Chen|Lian|2014|p=?}} -->
* {{cite book
| title=Handbook of International Bridge Engineering
| editor-last1 =Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2= Lian
| isbn=9781439810293
| url=https://archive.org/details/handbookofintern0000unse_j3m6
| access-date= 1 September 2025
| year=2014
| publisher=Taylor & Francis
}}
 
<!-- {{sfn|Cheng|Duan|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 5. Construction and Maintenance
| edition = Second
| first1= Xiaohua
| last1= Cheng
| first2= Lian
| last2= Duan
| chapter = Rehabilitation and Strengthening of Highway Bridge Superstructures
| pages = 443–485
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852330
| url= https://books.google.com/books?id=BCeOAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Choudhury|Hasnat|2015}} -->
* {{cite book
| last1=Choudhury
| first1=Jamilur
| last2=Hasnat
| first2=Ariful
| title = IABSE-JSCE Joint Conference on Advances in Bridge Engineering-III
| chapter =Bridge Collapses Around the World: Causes and Mechanisms
| isbn= 9789843393135
| chapter-url = https://www.iabse-bd.org/session/k2.pdf
| access-date=4 November 2025
| year=2015
| publisher=[[International Association for Bridge and Structural Engineering]]
| pages= 26–34
}}
 
<!-- {{sfn|Collings|2000|p=?}} -->
* {{cite book
| last=Collings
| first=David
| chapter =Composite Construction
| title=The Manual of Bridge Engineering
| editor-last=Ryall
| editor-first= Michael
| isbn= 0727727745
| chapter-url=https://archive.org/details/manualofbridgeen0000unse/page/407
| access-date=1 September 2025
| year=2000
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
| pages= 407–448
}}
 
<!-- {{sfn|Copelan|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 5. Construction and Maintenance
| edition = Second
| first= Joyce
| last= Copelan
| chapter = Bridge Maintenance
| pages = 337–350
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852330
| url= https://books.google.com/books?id=BCeOAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Cruickshank|2010|p=?}} -->
* {{cite book
| title=Bridges: Heroic Designs that Changed the World
| last= Cruickshank
| first= Dan
| author-link=Dan Cruickshank
| isbn= 9780007881086
| url = https://archive.org/details/isbn_9780007881086
| access-date= 1 September 2025
| year=2010
| publisher=[[Harper Collins]]
}}
 
<!-- {{sfn|Dawe |2003 |p=?}}
* {{Cite book
|title=Research Perspectives: Traffic Loading on Highway Bridges
| url=https://archive.org/details/researchperspect0000dawe
|access-date=15 September 2025
|first=Peter
|last=Dawe
|date=2003
|publisher=[[Thomas Telford (publisher)|Thomas Telford]]
|isbn=0727732412
}}
-->
<!-- {{sfn|Denison|2012|p=?}} -->
* {{cite book
| title=How to Read Bridges: A Crash Course In Engineering and Architecture
| last=Denison
| first= Edward
| isbn= 9781408171769
| url=https://archive.org/details/howtoreadbridges0000deni
| access-date= 1 September 2025
| year=2012
| publisher=[[Rizzoli Libri|Rizzoli]]
}}
 
<!-- {{sfn|Dikshitar |1993|p=?}} -->
* {{cite book
| title=The Mauryan Polity
| last= Dikshitar
| first= V.R.R.
| isbn= 8120810236
|orig-year=1932
| year=1993
| publisher=[[Motilal Banarsidass]]
| url=https://archive.org/details/in.ernet.dli.2015.78927/page/n340/mode/1up?q=bridge
|access-date = 20 September 2025
}} Reprinted in 1993.
 
<!-- {{sfn|Dornsife|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 3. Substructure Design
| edition = Second
| first= Ralph
| last= Dornsife
| chapter = Bearings
| pages = 1–34
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852309
| url= https://books.google.com/books?id=Q6iNAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Durkee|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 5. Construction and Maintenance
| edition = Second
| first= Jackson
| last= Durkee
| chapter = Steel Bridge Construction
| pages = 1–50
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852330
| url= https://books.google.com/books?id=BCeOAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Edgerton|2010 |p=?}} -->
* {{cite book
|url=https://books.google.com/books?id=Tkm5UZJz8z0C&q=Bridges+constructed+by+pounding
|last=Edgerton
|first=Robert B.
|year=2010
|title=The Fall of the Asante Empire: The Hundred-Year War For Africa's Gold Coast
|publisher=[[Simon and Schuster]]
|isbn=9781451603736
}}
 
<!-- {{sfn|Ellobody|2014|p=?}} -->
* {{cite book
| title=Finite Element Analysis and Design of Steel and Steel–Concrete Composite Bridges
| last =Ellobody
| first= Ehab
| isbn= 9780124172470
| year=2014
| publisher=[[Butterworth-Heinemann]]
| url = https://archive.org/details/finiteelementana0000ello
| access-date= 1 September 2025
}}
 
<!-- {{sfn|Elnashai|2000|p=?}} -->
* {{cite book
| last=Elnashai
| first= Amr
| chapter = Seismic Response and Design
| title=The Manual of Bridge Engineering
| editor-last=Ryall
| editor-first= Michael
| isbn= 0727727745
| chapter-url=https://archive.org/details/manualofbridgeen0000unse/page/519
| access-date=1 September 2025
| year=2000
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
| pages= 519–548
}}
 
<!-- {{sfn|Farquhar |2000|p=?}}
* {{cite book
| last=Farquhar
| first= Daniel
| chapter = Cable-Stay Bridges
| title=The Manual of Bridge Engineering
| editor-last=Ryall
| editor-first= Michael
| isbn= 0727727745
| chapter-url=https://archive.org/details/manualofbridgeen0000unse/page/549
| access-date=1 September 2025
| year=2000
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
| pages= 549–594
}}
-->
<!-- {{sfn|Frangopol |2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 5. Construction and Maintenance
| edition = Second
| first= Dan
| last= Frangopol
| display-authors=etal
| chapter = Bridge Health Monitoring
| pages = 247–268
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852330
| url= https://books.google.com/books?id=BCeOAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Fridley|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 1. Fundamentals
| edition = Second
| first1= Kenneth
| last1= Fridley
| first2 = Lian
| last2= Duan
| chapter = Timber Design
| pages = 341–369
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852347
| url= https://books.google.com/books?id=WaONAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Fu|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 5. Construction and Maintenance
| edition = Second
| first1 = Gongkang
| last1 = Fu
| first2 = Dinesh
| last2 = Devaraj
| chapter = Bridge Management Using Pontis and Improved Concepts
| pages = 233–245
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852330
| url= https://books.google.com/books?id=BCeOAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Gerwick|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 5. Construction and Maintenance
| edition = Second
| first= Ben
| last= Gerwick
| chapter = Substructures of Major Overwater Bridges
| pages = 137–174
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852330
| url= https://books.google.com/books?id=BCeOAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Gimsing |2011|p=?}} -->
* {{cite book
| title=Cable Supported Bridges: Concept and Design
| last=Gimsing
| first=Niels J.
| isbn=9781119951872
| url=https://archive.org/details/cablesupportedbr0000gims
| access-date=1 September 2025
| year=1997
| edition= Second
| publisher=Wiley
}}
 
<!-- {{sfn|Goettemoeller|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 1. Fundamentals
| edition = Second
| first= Frederick
| last= Goettemoeller
| chapter = Bridge Aesthetics: Achieving Structural Art in Bridge Design
| pages = 49–76
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852347
| url= https://books.google.com/books?id=WaONAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Greco|2016|p=?}} -->
* {{cite book
| title=Architetture Autostradali in Italia
| last =Greco
| first= Laura
| isbn= 9788849292121
| year=2016
|language =Italian
| publisher=[[:it:Gangemi Editore]]
| url = https://books.google.com/books?id=_fZTCwAAQBAJ
| access-date= 1 September 2025
}}
 
<!-- {{sfn|Hewson|2000|p=?}} -->
* {{cite book
| last= Hewson
| first= Nigel
| chapter = Design of Prestressed Concrete Beams
| title=The Manual of Bridge Engineering
| editor-last=Ryall
| editor-first= Michael
| isbn= 0727727745
| chapter-url=https://archive.org/details/manualofbridgeen0000unse/page/241
| access-date=1 September 2025
| year=2000
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
|pages= 241–314
}}
 
<!-- {{sfn|Holstine|2005|p=??}}
* {{cite book
| title=Spanning Washington: Historic Highway Bridges of the Evergreen State
| last=Holstine
| first=Craig
| isbn=9780874222814
| url=https://books.google.com/books?id=NDJSAAAAMAAJ
| access-date=15 September 2025
| year=2005
| publisher=[[Washington State University Press]]
}}
-->
<!-- {{sfn|Huff|2022|p=??}} -->
* {{cite book
| title=LRFD Bridge Design: Fundamentals and Applications
| last=Huff
| first=T.
| isbn=9781000543377
| url=https://books.google.com/books?id=MCtaEAAAQBAJ
| access-date=10 September 2025
| year=2022
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Islam|Malek2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 3. Substructure Design
| edition = Second
| first1= Mohammed
| last1 = Islam
| first2= Amir
| last2= Malek
| chapter = Shallow Foundations
| pages = 181–238
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852309
| url= https://books.google.com/books?id=Q6iNAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Jones|Howells|2000|p=?}} -->
* {{cite book
| last1=Jones
| first1=Vardiman
| last2 = Howells
| first2= John
| chapter = Suspension Bridges
| title=The Manual of Bridge Engineering
| editor-last=Ryall
| editor-first= Michael
| isbn= 0727727745
| chapter-url=https://archive.org/details/manualofbridgeen0000unse/page/595
| access-date=1 September 2025
| year=2000
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
| pages= 595–662
}}
 
<!-- {{sfn|Knott |Prucz |2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 3. Substructure Design
| edition = Second
| first1= Michael
| last1= Knott
| first2= Zolan
| last2= Prucz
| chapter = Vesssel Collision Design of Bridges
| pages = 89–112
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852309
| url= https://books.google.com/books?id=Q6iNAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Krimotat|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 1. Fundamentals
| edition = Second
| first1= Alexander
| last1 = Krimotat
| chapter = Structural Modeling
| pages = 253–269
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852309
| url= https://books.google.com/books?id=WaONAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn| Kulicki|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 1 Fundamentals
| edition = Second
| first= John
| last= Kulicki
| chapter = Highway Bridge Design Specifications
| pages = 113–130
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852309
| url= https://books.google.com/books?id=WaONAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn| Kulicki|2014a|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 2. Superstructure Design
| edition = Second
| first= John
| last= Kulicki
| chapter = Highway Truss Bridges
| pages = 283–308
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852293
| url= https://books.google.com/books?id=JpClAgAAQBAJ
| access-date= 31 October 2025
| year=2014a
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Leonhardt|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 1. Fundamentals
| edition = Second
| first= Fritz
| last= Leonhardt
| chapter = Aesthetics: Basics
| pages = 29–48
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852347
| url= https://books.google.com/books?id=WaONAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Ma|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 3. Substructure Design
| edition = Second
| first= Youzhi
| last= Ma
| chapter =Deep Foundations
| pages = 238–278
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852309
| url= https://books.google.com/books?id=Q6iNAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Mangus |2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 2. Superstructure Design
| edition = Second
| first= Alfred
| last= Mangus
| chapter = Orthotropic Steel Decks
| pages = 589–646
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852293
| url= https://books.google.com/books?id=JpClAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Mulheron|2000|p=?}} -->
* {{cite book
| last=Mulheron
| first=Mike
| chapter = Protection
| title=The Manual of Bridge Engineering
| editor-last=Ryall
| editor-first= Michael
| isbn= 0727727745
| chapter-url=https://archive.org/details/manualofbridgeen0000unse/page/805
| access-date=1 September 2025
| year=2000
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
| pages= 805–848
}}
 
<!-- {{sfn| Nath|1982|p=?}} -->
* {{cite book
| last= Nath
| first=Ram
| author-link =Ram Nath
| title=History of Mughal Architecture
|volume=3
| year=1982
| isbn= 8170172977
| publisher= Abhinav Publications
| url= https://books.google.com/books?id=ha5fG13V3XcC
|access-date= 17 September 2025
}}
 
<!-- {{sfn| O'Brien|2014 |p=?}} -->
* {{cite book
| last= O'Brien
| first=Eugene
| title= Bridge Deck Analysis
| url=https://archive.org/details/bridgedeckanalys0000obri_m0m0
| access-date=12 September 2025
| year=2015
| edition=Second
| isbn= 9781482227239
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Ogden|Cooper|2019 }} -->
* {{cite book
| last1 =  Ogden
|first1=  Brent
| last2 =  Cooper
|first2=  Chelsey
| year =  2019
| title =  Highway-Rail Crossing Handbook
|edition=3rd
|isbn=9781998295067
| url =  https://highways.dot.gov/sites/fhwa.dot.gov/files/2022-06/fhwasa18040v2.pdf
|access-date=  7 December 2025
|publisher=  [[Federal Highway Administration]]
}}
 
<!-- {{sfn|Petroski |1994|p=?}} -->
* {{cite book
| last=Petroski
| first= Henry
| author-link=Henry Petroski
| title=To Engineer Is Human: The Role of Failure in Successful Design
| url=https://archive.org/details/toengineerishuma0000henr
| access-date=20 September 2025
| year=1994
| isbn=1566195020
| publisher=Barnes & Noble
}}
 
<!-- {{sfn|Reddy|2004|p=?}} -->
* {{cite book
| last=Reddy
| first=J. N.
| author-link = J. N. Reddy (engineer)
| title=An Introduction to the Finite Element Method
| url=https://archive.org/details/introductiontofi0000jnre
| access-date=10 September 2025
| edition=Third
| year=2004
| isbn=9780070607415
| publisher=[[McGraw Hill]]
}}
 
<!-- {{sfn|Ryall|2000|p=?}} -->
* {{cite book
| last=Ryall
| first=Michael
| chapter = Loads and Load Distribution
| title=The Manual of Bridge Engineering
| editor-last=Ryall
| editor-first= Michael
| isbn= 0727727745
| chapter-url=https://archive.org/details/manualofbridgeen0000unse/page/43
| access-date=1 September 2025
| year=2000
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
| pages= 43–94
}}
 
<!-- {{sfn|Sakowski|2014|p=?}} -->
* {{cite book
| title=Handbook of International Bridge Engineering
| last=Sakowski
| first=Eric
| chapter = Highest Bridges
| pages = 1251–1306
| editor-last1 =Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2= Lian
| isbn=9781439810293
| url=https://archive.org/details/handbookofintern0000unse_j3m6
| access-date= 1 September 2025
| year=2014
| publisher=[[Taylor & Francis]]
}}
 
<!-- {{sfn|Scott|2001|p=?}} -->
* {{cite book
| title=In the Wake of Tacoma: Suspension Bridges and the Quest for Aerodynamic Stability
| last=Scott
| first= Richard
| isbn= 0784405425
| url=https://archive.org/details/inwakeoftacomasu0000scot
| access-date=1 September 2025
| year=2001
| publisher=[[American Society of Civil Engineers#Publications|ASCE Press]]
}}
 
<!-- {{sfn|Schlaich|2019|p=?}} -->
* {{cite book
|url=https://concrete.ethz.ch/assets/sed17.pdf
|access-date=16 October 2025
|author-last=Schlaich
|author-first=Mike
|editor-last1=Schlaich
|editor-first1=Mike
|year=2019
|title=Extradosed Bridges
|chapter=General
| pages=3–8
|isbn=9783857481680
| publisher =[[International Association for Bridge and Structural Engineering]]
}}
 
<!-- {{sfn|Shanmugam|2000|p=?}}
* {{cite book
| last=Shanmugam
| first=N. E.
| chapter = Structural Analysis
| title=The Manual of Bridge Engineering
| editor-last=Ryall
| editor-first= Michael
| isbn= 0727727745
| chapter-url=https://archive.org/details/manualofbridgeen0000unse/page/95
| access-date=1 September 2025
| year=2000
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
| pages= 95–224
}}
-->
<!-- {{sfn|Shi|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 5. Construction and Maintenance
| edition = Second
| first= Junfeng
| last= Shi
| display-authors=etal
| chapter = Cable-Supported Bridge Construction
| pages = 85–112
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852330
| url= https://books.google.com/books?id=BCeOAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Shen|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 2. Superstructure Design
| edition = Second
| first= John
| last= Shen
| chapter = Concrete Decks
| pages = 573–588
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852293
| url= https://books.google.com/books?id=JpClAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Sorgenfrei|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 1. Fundamentals
| edition = Second
| first= Donald
| last= Sorgenfrei
| display-authors=etal
| chapter = Railroad Bridge Design Specifications
| pages = 143–158
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852347
| url= https://books.google.com/books?id=WaONAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Squier|1877 |p=?}} -->
* {{cite book
| last=Squier
| first=Ephraim George
| author-link=E. G. Squier
| title=Peru; Incidents of Travel and Exploration in the Land of the Incas
| oclc = 2396588
| url=https://archive.org/details/peruincidentsoft00squi
| access-date=13 September 2025
| year=1877
| publisher=[[Harper & Brothers]]
}}
 
<!-- {{sfn|Svecova|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 1. Fundamentals
| edition = Second
| first= Dagmar
| last= Svecova
| display-authors=etal
| chapter = Application of Fiber Reinforced Polymers in Bridges
| pages = 371–404
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852347
| url= https://books.google.com/books?id=WaONAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Talese|2014|p=?}} -->
*{{cite book
|last=Talese
|first=Gay
|author-link=Gay Talese
|title=The Bridge: The Building of the Verrazano–Narrows Bridge
|url=https://books.google.com/books?id=cK-pBAAAQBAJ
|isbn=9781620409114
|publisher=[[Harper & Row]]
|orig-year=1964
|year=2014
}}
 
<!-- {{sfn|Tang|2014a|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 5. Construction and Maintenance
| edition = Second
| first= Benjamin
| last= Tang
| chapter = Accelerated Bridge Development
| pages = 175–206
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852330
| url= https://books.google.com/books?id=BCeOAgAAQBAJ
| access-date= 31 October 2025
| year=2014a
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Tang|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 1. Fundamentals
| edition = Second
| first= Man-Chung
| last= Tang
| author-link = Man-Chung Tang
| chapter = Conceptual Design
| pages = 1–34
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852347
| url= https://books.google.com/books?id=WaONAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Theryo|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 2. Superstructure Design
| edition = Second
| first= Teddy
| last= Theryo
| chapter = Segmental Concrete Bridges
| pages = 91–170
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852293
| url= https://books.google.com/books?id=JpClAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Troitsky|1994|p=?}} -->
* {{cite book
| title=Planning and Design of Bridges
| author=Troitsky
| first= M.S.
| isbn= 0471028533
| url= https://archive.org/details/planningdesignof0000troi
| access-date=1 September 2025
| year=1994
| publisher=[[Wiley (publisher)|Wiley]]
}}
<!-- {{sfn|Troyano |2003 |pp= 623, 656, 664 }} -->
* {{cite book
| last=Troyano
| first=L.F.
| title=Bridge Engineering: A Global Perspective
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
| year=2003
| isbn=9780727732156
| url=https://books.google.com/books?id=0u5G8E3uPUAC
| access-date= 25 October 2025
}}
 
<!-- {{sfn|Tytler|1985 |p=?}} -->
* {{cite book
| last=Tytler
| first= I.F.B.
| display-authors=etal
| title=Vehicles and Bridging
| isbn = 0080283225
| url=https://archive.org/details/vehiclesbridging0000unse
| access-date=13 September 2025
| year=1985
| series = Battlefield Weapons Systems and Technology
| publisher=Brasey's Defense Publishers
}}
 
<!-- {{sfn|Vassie|2000|p=?}} -->
* {{cite book
| last=Vassie
| first=Perry
| chapter = Bridge Management
| title=The Manual of Bridge Engineering
| editor-last=Ryall
| editor-first= Michael
| isbn= 0727727745
| chapter-url=https://archive.org/details/manualofbridgeen0000unse/page/849
| access-date=1 September 2025
| year=2000
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
| pages= 849–882
}}
 
<!-- {{sfn| Vejrum|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 2. Superstructure Design
| edition = Second
| first= Tina
| last= Vejrum
| chapter = Cable-Stayed Bridges
| pages = 399–434
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852293
| url= https://books.google.com/books?id=JpClAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Washer|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 5. Construction and Maintenance
| edition = Second
| first= Glenn
| last= Washer
| chapter = Nondestructive Evaluation Methods for Bridge Elements
| pages = 301–336
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852330
| url= https://books.google.com/books?id=BCeOAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Watson|1937|p=?}} -->
* {{cite book
| title=Bridges in History and Legend
| last=Watson
| first= Wilbur J.
| oclc=1393531
| url=https://archive.org/details/bridgesinhistory0000wilb
| access-date=1 September 2025
| year=1937
| publisher=J. H. Jansen
}}
 
<!-- {{sfn|Watson|1988|p=?}} -->
* {{cite book
| title=The Civils: The Story of the Institution of Civil Engineers
| author=Watson
| first= Garth
| isbn=9780727703927
| url=https://archive.org/details/civilsstoryofins0000wats
| access-date= 31 October 2025
| year=1988
| publisher=[[Thomas Telford (publisher)|Thomas Telford]]
}}
 
<!-- {{sfn|Wilks|1989|p=?}} -->
* {{cite book
| url= https://books.google.com/books?id=NSs4AAAAIAAJ
| title= Asante in the Nineteenth Century: The Structure and Evolution of a Political Order
| first=Ivor
|last= Wilks
|author-link=Ivor Wilks
| publisher= [[CUP Archive]]
|via = Books.google.com
|access-date= 29 December 2020
|isbn= 9780521379946
|date= 1989
}}
 
<!-- {{sfn| Wright|2022|p=?? }} -->
* {{Cite book
|first=William J.
|last=Wright
| chapter-url=https://www.aisc.org/globalassets/nsba/design-resources/steel-bridge-design-handbook/b905_sbdh_chapter5.pdf
| url=https://www.aisc.org/nsba/design-and-estimation-resources/steel-bridge-design-handbook/
|access-date=18 September 2025
|chapter=Selecting the Right Bridge Type
|title= Steel Bridge Design Handbook
|year=2022
|publisher=[[American Institute of Steel Construction]]
}}
 
<!-- {{sfn|Xu|2011|p=?}}
* {{cite book
| title=Structural Health Monitoring of Long-Span Suspension Bridges
| last=Xu
| first= You Lin
|display-authors = etal
| isbn=9780415597937
| url=https://books.google.com/books?id=9F9pNdAk4WAC
| year=2011
| publisher=[[Taylor & Francis]]
}}
-->
<!-- {{sfn|Yamaguchi|2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 1. Fundamentals
| edition = Second
| first= Eiki
| last= Yamaguchi
| chapter = Finite Element Method
| pages = 225–251
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852309
| url= https://books.google.com/books?id=WaONAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Yashinsky |2014|p=?}} -->
* {{cite book
| title=Bridge Engineering Handbook. Vol 4. Seismic Design
| edition = Second
| first= Mark
| last= Yashinsky
| display-authors=etal
| chapter = Earthquake Damage to Bridges
| pages = 53–98
| editor-last1=Chen
| editor-first1= Wai-Fah
| editor-last2 = Duan
| editor-first2 = Lian
| isbn= 9781439852323
| url= https://books.google.com/books?id=EqSNAgAAQBAJ
| access-date= 31 October 2025
| year=2014
| publisher=[[CRC Press]]
}}
 
<!-- {{sfn|Zhao|2017|p=?}} -->
* {{cite book
| title=Bridge Engineering: Design, Rehabilitation, and Maintenance of Modern Highway Bridges
| last=Zhao
| first= Jim
|display-authors = etal
| edition=Fourth
| isbn=9781259643101
| url= https://books.google.com/books?id=Ii1zDgAAQBAJ
| access-date=16 September 2025
| year=2017
| publisher=McGraw Hill
}}
{{refend}}
 
====Journals and websites====
{{refbegin}}
 
<!-- {{sfn|Ahmad |2025}} -->
* {{Cite journal
|last=Ahmad
|first=DM
|date=2025
|title= A Risk-Informed BIM-LCSA Framework for Lifecycle Sustainability Optimization of Bridge Infrastructure
|journal= Buildings
|publisher=[[MDPI]]
|volume=15
|issue =16
|article-number= 2853
|doi= 10.3390/buildings15162853
|doi-access=free
|issn= 2075-5309
}}
 
<!-- {{sfn|Bjelić |2022 }} -->
* {{Cite journal
|last=Bjelić
|first=Igor
|date=2022
|title=Use of Building Materials During the Construction of Trajan's Bridge on the Danube
|journal=Arheologija I Prirodne Nauke
|publisher= Institute of Archaeology, Belgrade
|volume=18
|pages=45–58
|doi=10.18485/arhe_apn.2022.18.4
|issn=1452-7448
|url= https://doi.fil.bg.ac.rs/pdf/journals/arhe_apn/2022/arhe_apn-2022-18-4.pdf
|access-date=3 October 2025
}}
 
<!-- {{sfn|Brooks|2021}} -->
* {{cite magazine
| title= Building Bridges Can Boost Income for the Rural Poor
| url= https://insights.som.yale.edu/insights/building-bridges-can-boost-income-for-the-rural-poor
| access-date = 20 November 2025
| last = Brooks
|first= Wyatt
| display-authors=etal
| date = 5 August 2021
| magazine= [[Yale Insights]]
| publisher = [[Yale School of Management]]
}}
 
<!-- {{sfn|Brunning|2001}} -->
* {{cite journal
| last=Brunning
|first=Richard
|year=2001
|title=The Somerset Levels
|journal=[[Current Archaeology]]
|publisher=[[Current Publishing]]
|volume=XV (4)
|issue=172
|pages=139–143
|issn = 0011-3212
}}
 
<!-- {{sfn|Burgoyne |Scantlebury |2008}} -->
* {{cite journal
|last1=Burgoyne
|first1= C
|last2=Scantlebury
|first2= R
|year=2008
|title=Lessons Learned from the Bridge Collapse in Palau
|journal = [[University of Cambridge]]
|publisher = [[Institution of Civil Engineers#Publishing|Institution of Civil Engineers]]
|volume= 161
|issue= 6
|article-number=700038
|doi= 10.1680/cien.2008.161.6.28
|issn = 1751-7672
| url=https://cjb.emma.cam.ac.uk/cjbpubs/p62.pdf
|access-date= 14 November 2025
}}
 
<!-- {{sfn|Bütikofer |2024}} -->
* {{cite journal
| first = Aline
| last = Bütikofer
| display-authors = etal
| title = Building Bridges and Widening Gaps
| journal = [[The Review of Economics and Statistics]]
| publisher= [[MIT Press]]
| volume = 106
| issue = 3
| pages = 681–697
| year = 2024
| issn = 0034-6535
| doi = 10.1162/rest_a_01183
| url = https://direct.mit.edu/rest/article-pdf/106/3/681/2372679/rest_a_01183.pdf
}}
 
<!-- {{sfn|Cai|Deng|2024}} -->
* {{cite journal
|last1= Cai
|first1= J.
|last2= Deng
|first2= Z.
|year=2024
| title= The Spatial Impact of High Bridges on Travel Accessibility and Economic Integration in Guizhou, China
|journal= [[Humanities and Social Sciences Communications]]
|publisher= [[Nature Portfolio]]
|volume= 11
|issue=
|article-number= 1565
|issn = 2662-9992
|url= https://www.nature.com/articles/s41599-024-04106-x
| doi= 10.1057/s41599-024-04106-x
|access-date= 14 November 2025
}}
 
<!-- {{sfn|Cai|Liu|2012}} -->
* {{ cite journal
| last1= Cai
|first1= Ming
|last2= Liu
|first2= Yonghong
|url=https://link.springer.com/article/10.1007/s10666-011-9292-0
|  date =2012
|pages=301–313
| title = Integrated Benefit Evaluation of Pedestrian Bridge
| volume = 17
| journal = Environmental Modeling & Assessment
|issue= 3
|issn =1573-2967
|  doi = 10.1007/s10666-011-9292-0
|bibcode= 2012EMdAs..17..301L
}}
 
<!-- {{sfn|Capka|2005}}
* {{cite web
|url=https://www.transportation.gov/testimony/rebuilding-highway-and-transit-infrastructure-gulf-coast-following-hurricane-katrina-0
|access-date=21 September 2025
|last=Capka
|first=J. Richard
|author-link =J. Richard Capka
|year=2005
|title=Rebuilding Highway and Transit Infrastructure on the Gulf Coast Following Hurricane Katrina
|website=[[U.S. Department of Transportation]]
}}
-->
<!-- {{sfn|Chase|2020}} -->
* {{cite web
|url=  https://connect.ncdot.gov/projects/research/RNAProjDocs/2018-20%20Final%20Report.pdf#:~:text=Grade%2Dseparated%20intersections%20increase%20the%20capacity%20of%20two,is%20needed%20for%20bicycles%2C%20pedestrians%20and%20driveways
|access-date= 7 December 2025
|last= Chase
|first=  Thomas
|display-authors=etal
|year=2020
|title= Reasonable Alternatives for Grade-Separated Intersections
|publisher= [[North Carolina Department of Transportation]]
}}
 
<!-- {{sfn|Cook|2014}} -->
* {{cite thesis
|url=https://digitalcommons.usu.edu/etd/2163
|access-date=2 October 2025
|last=Cook
|first= Wesley
|year=2014
|publisher= [[Utah State University]]
| degree = PhD
|title=Bridge Failure Rates, Consequences, and Predictive Trends
}}
 
<!-- {{sfn|Dahlberg|2022|p= ?? }} -->
* {{cite web
|last = Dahlberg
| first=Justin
| display-authors=etal
| title=Guide for Orthotropic Steel Deck Level 1 Design
| access-date= 10 November 2025
| year= 2022
| url= https://www.fhwa.dot.gov/bridge/pubs/hif22056.pdf#:~:text=Orthotropic%20steel%20deck:%20A%20system%20where%20a,to%20the%20deck%20directly%20supporting%20live%20loads
| publisher = U. S. [[Federal Highway Administration]]
}}
 
<!-- {{sfn|Dallard|2001}} -->
* {{cite journal
|last=Dallard
|first= P.
|display-authors=etal
|title=London Millennium Bridge: Pedestrian-Induced Lateral Vibration
|journal= [[Journal of Bridge Engineering]]
|volume= 6
|issue=6
|pages= 412–417f
|date=2001
|url=http://ascelibrary.org/doi/pdf/10.1061/(ASCE)1084-0702(2001)6:6(412)
|doi= 10.1061/(ASCE)1084-0702(2001)6:6(412)
|access-date= 5 November 2025
|issn=1084-0702
}}
 
<!-- {{sfn|De Borger|2001}} -->
* {{cite journal
| title = Productivity and Wage Effects of An Exogenous Improvement in Transport Infrastructure: Accessibility and the Great Belt Bridge
| journal = [[Regional Science and Urban Economics]]
| publisher = [[Elsevier]]
| volume = 114
| article-number= 104133
| year = 2025
| issn = 0166-0462
| doi = 10.1016/j.regsciurbeco.2025.104133
| url = https://www.sciencedirect.com/science/article/pii/S016604622500050X
| first= Bruno
|last= De Borger
|display-authors=etal
}}
 
<!-- {{sfn|Delatte|2001}} -->
* {{cite journal
|journal=Journal of Professional Issues in Engineering Education and Practice
|publisher= [[American Society of Civil Engineers]]
|issn=1052-3928
|volume=127
|issue=3
|date= July 2001
|pages= 109–115
|last=Delatte
|first= Norbert
|url=https://engagedscholarship.csuohio.edu/cgi/viewcontent.cgi?article=1039&context=encee_facpub
|title=Lessons from Roman Cement and Concrete
|doi= 10.1061/(ASCE)1052-3928(2001)127:3(109)
|access-date=3 October 2025
}}
 
<!-- {{sfn|Du|Au|2005}} -->
* {{cite journal
|journal=Structural Safety
|publisher=[[Elsevier]]
|issn=0167-4730
|volume=27
|issue=3
|date= July 2005
|pages=230–245
|last1=Du
|first1= Jin Sheng
|last2= Au
|first2= Francis T.K.
|url=https://www.sciencedirect.com/science/article/abs/pii/S0167473004000505
|title=Deterministic and Reliability Analysis of Prestressed Concrete Bridge Girders: Comparison of the Chinese, Hong Kong and AASHTO LRFD Codes
|doi=10.1016/j.strusafe.2004.10.004
|access-date= 9 October 2025
}}
 
<!-- {{sfn| Dusseau| 2002}} -->
* {{cite book
| chapter = The Evolution of Pipeline Suspension Bridges in North America Since 1952
| title = Pipelines 2002 Beneath Our Feet: Challenges and Solutions (Proceedings)
| pages = 1–10
| date = 2002
| last= Dusseau
| first= Ralph
| publisher = [[American Society of Civil Engineers]]
| doi = 10.1061/40641(2002)60
| isbn = 978-0-7844-0641-0
| url = https://ascelibrary.org/doi/pdf/10.1061/40641%282002%2960
| access-date= 25 November 2025
}}
 
<!-- {{sfn|Engel|2020}} -->
* {{cite web
|last=  Engel
|first=  Eduardo
|display-authors=etal
|date= 2020
|title=When and How to Use Public-Private Partnerships in Infrastructure: Lessons from the International Experience
|publisher=[[National Bureau of Economic Research]]
|url= https://www.nber.org/system/files/working_papers/w26766/w26766.pdf
|access-date=3 December 2025 
|doi= 10.3386/w26766
}}
 
<!-- {{sfn|French|1993}} -->
* {{cite journal
|last= French
|first= Patricia Ross
|date= January 1993
|title=Living by Bridges: Philip Larkin's Resisting Subtext
|journal= [[South Atlantic Review]]
|issn= 0277-335X
|volume= 58
|issue=1
|pages= 85–100
|doi=10.2307/3201102
|jstor= 3201102
}}
 
<!-- {{sfn|Greenfield|2021}} -->
* {{Cite news
|last=Greenfield
|first=Patrick
|date=23 January 2021|title=How Creating Wildlife Crossings Can Help Reindeer, Bears – and Even Crabs|url=http://www.theguardian.com/environment/2021/jan/23/how-wildlife-crossings-are-helping-reindeer-bears-and-even-crabs-aoe
|url-status=live
|archive-url=https://web.archive.org/web/20210123083528/https://www.theguardian.com/environment/2021/jan/23/how-wildlife-crossings-are-helping-reindeer-bears-and-even-crabs-aoe
|archive-date=23 January 2021
|access-date=2021-01-26
|newspaper=[[The Guardian]]
|language=en
|issn = 1756-3224
}}
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|ref={{sfnRef|"Occupational Outlook Handbook". ''Department of Labor'' }}
|url=https://archive.org/details/occupationaloutl00usde_2
|title=Occupational Outlook Handbook
|publisher=[[JIST Publishing]], [[U. S. Department of Labor]]
|isbn=9781593575137
| access-date=26 October 2025
|year =2008
}}
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|title=Painting The Golden Gate Bridge
|website= Golden Gate Bridge
|publisher=[[Golden Gate Bridge, Highway and Transportation District]]
|access-date=August 20, 2007
|archive-date=August 22, 2011
|archive-url=https://web.archive.org/web/20110822071258/http://www.goldengatebridge.org/research/factsGGBIntOrngPaint.php
|url-status=dead
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<!-- {{sfn| "Resisting the Twisting". ''Golden Gate Bridge Highway and Transportation District'' }} -->
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|ref={{sfnRef| "Resisting the Twisting". ''Golden Gate Bridge Highway and Transportation District'' }}
|url=https://www.goldengate.org/exhibits/resisting-the-twisting/
|access-date=12 September 2025
|title=Resisting the Twisting
|publisher= [[Golden Gate Bridge, Highway and Transportation District]]
}}
 
<!-- {{sfn| "Rhaetian Railway in the Albula". ''UNESCO World Heritage Convention'' }} -->
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|ref={{sfnRef| "Rhaetian Railway in the Albula". ''UNESCO World Heritage Convention'' }}
|url=https://whc.unesco.org/en/list/1276
|title=Rhaetian Railway in the Albula / Bernina Landscapes
|publisher=[[UNESCO]]
|website=UNESCO World Heritage Convention
|access-date=14 September 2025
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|ref={{sfnRef| "SAS Maintenance Travelers". ''California Department of Transportation'' }}
| url=http://baybridgeinfo.org/sas-travelers-page
|access-date=June 24, 2012
|title=SAS Maintenance Travelers
|publisher=[[California Department of Transportation]]
|archive-url=https://web.archive.org/web/20120625142735/http://baybridgeinfo.org/sas-travelers-page
|url-status=dead
|archive-date=June 25, 2012
}}
 
<!-- {{sfn| "Tacoma Narrows Bridge History". ''Washington Department of Transportation'' }} -->
* {{Cite web
|ref={{sfnRef| "Tacoma Narrows Bridge History". ''Washington Department of Transportation'' }}
| url=https://www.wsdot.wa.gov/TNBHistory/suspension-bridges.htm
|access-date=18 September 2025
|title=Tacoma Narrows Bridge History - Suspension Bridge Basics
|publisher=[[Washington State Department of Transportation]]
}}
 
<!-- {{sfn| "The History of the National Council". ''NCEES'' }} -->
* {{Cite web
|ref={{sfnRef| "The History of the National Council". ''NCEES'' }}
| url= https://ncees.org/wp-content/uploads/2022/09/2020_history_web_version.pdf
|access-date=25 October 2025
|year=2004
|edition=Third
|title=The History of the National Council of Examiners for Engineering and Surveying
|publisher=[[National Council of Examiners for Engineering and Surveying]]
}}
 
<!-- {{sfn| "TTSB Details Reasons for Nanfang'ao Bridge Collapse". ''Focus Taiwan'' }} -->
* {{Cite news
|ref={{sfnRef| "TTSB Details Reasons for Nanfang'ao Bridge Collapse". ''Focus Taiwan'' }}
|date=25 November 2020|url=https://focustaiwan.tw/society/202011250017
|title=TTSB Details Reasons for Nanfang'ao Bridge Collapse
|website=[[Central News Agency (Taiwan)|Focus Taiwan]]
|access-date=16 September 2025
}}
 
<!-- {{sfn|"Viaduct". ''The Concise Oxford Dictionary''}} -->
* {{Cite book
|ref={{sfnRef|"Viaduct". ''The Concise Oxford Dictionary ''}}
|year=2001
|chapter=Viaduct
|title=The Concise Oxford Dictionary
|publisher=[[Oxford University Press]]
|chapter-url= https://archive.org/details/conciseoxforddic0000unse_t1j9/page/1596
|access-date=27 December 2022
|pages=1596
|isbn=0198604386
}}
 
<!-- {{sfn| "West Montrose Covered Bridge". ''Canada's Historic Places'' }} -->
*{{cite web
|ref={{sfnRef| "West Montrose Covered Bridge". ''Canada's Historic Places''}}
|title=West Montrose Covered Bridge
|url=https://www.historicplaces.ca/en/rep-reg/place-lieu.aspx?id=8291&pid=0
|website=Canada's Historic Places
|publisher= [[Parks Canada]]
|access-date=22 October 2023}}
 
<!-- {{sfn| "Why Do Foxes". ''Israel21C''}} -->
* {{Cite web
|ref={{sfnRef| "Why Do Foxes". ''Israel21C''}}
|url=https://israel21c.org/why-do-foxes-jackals-and-hyenas-cross-israels-highway-1/
|title=Why Do Foxes, Jackals and Hyenas Cross Israel's Highway 1?
|website= [[ISRAEL21c]]
|date=28 March 2016
|access-date=19 September 2025
}}
 
<!-- {{sfn| "Will Rogers Archway". ''Travel Oklahoma''}} -->
* {{Cite web
|ref={{sfnRef| "Will Rogers Archway". ''Travel Oklahoma''}}
|url=https://www.travelok.com/listings/view.profile/id.22615
|title=Will Rogers Archway
|website=Travel Oklahoma
|publisher= [[Oklahoma Department of Tourism and Recreation]]
|access-date=17 September 2025
}}
{{refend}}


{{Bridge footer}}
{{Bridge footer}}
{{Construction overview}}
{{Infrastructure}}
{{Infrastructure}}
{{Subject bar|auto=yes|wikt=yes|Engineering}}
{{Authority control}}
{{Authority control}}


[[Category:Bridges| ]]
[[Category:Bridges| ]]
[[Category:Transport buildings and structures]]
[[Category:Civil engineering]]
[[Category:Articles containing video clips]]
[[Category:Infrastructure]]
[[Category:Infrastructure]]
[[Category:Structural engineering]]
[[Category:Structural engineering]]
[[Category:Transport buildings and structures]]

Latest revision as of 13:38, 30 December 2025

Template:Short description Script error: No such module "about". Template:Good article Template:Use dmy dates Template:Use American English Template:Bridge sidebar

A bridge is a structure designed to span an obstacle, such as a river or valley, allowing vehicles, pedestrians, and other loads to pass across. Most bridges consist of a flat deck, supported by structures such as beams, arches, or cables. These structures rest on a foundation that is carefully designed to prevent the bridge from settling into the subsoil. Bridges can be constructed in a wide variety of forms, depending on their purpose and location. Notable types include viaducts, which cross wide valleys; trestles to carry heavy trains; and pontoon bridges which float on water.

The Romans and ancient Chinese built major arch bridges of stone and timber. During the Renaissance, advances in science and engineering led to wider bridge spans and more elegant designs. Concrete was perfected in the early 1800s, and proved to be superior to stone in many regards. With the Industrial Revolution came mass-produced steel, which enabled the creation of suspension and cable-stayed bridges that could span wide obstacles. Over time, the maximum achievable span of bridges has steadily increased, reaching Script error: No such module "convert". in 2022.

The design of a bridge must satisfy many requirements, such as connecting to a transportation network, providing adequate clearances, and safely transporting its users. A bridge must be strong enough to support the weight of the bridge itself, as well as the traffic passing over the bridge. It must also tolerate violent, unpredictable stresses imposed by the environment, such as winds, floods, and earthquakes. To meet all these goals, bridge engineers use analytical methods such as limit state design and finite element method.

Many bridges are admired for their beauty, and some spectacular bridges serve as iconic landmarks that provide a sense of pride and identity for the local community. In art and literature, bridges are frequently used as metaphors to represent connection or transition. Bridges can create beneficial impacts to a community, including shorter transport times and increased gross domestic product; and also negative effects such as increased pollution and contributions to global warming. Template:TOClimit

History

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Antiquity

A stone arch bridge passing over a river valley
The Pont du Gard aqueduct in France was built by the Roman Empire c. Template:TrimScript error: No such module "Check for unknown parameters"..Template:Sfn

The earliest forms of bridges were simple structures for crossing wetlands and creeks, consisting of wooden boardwalks or logs.[1]Template:Efn PilingsTemplate:Sndwhich are critical elements of bridge constructionTemplate:Sndwere used in Switzerland around 4,000 BC to support stilt houses built over water.Template:Sfn Several corbel arch bridges were built c.Script error: No such module "Check for unknown parameters". 13th century BC by the Mycenaean Greece culture, including the Arkadiko Bridge, which is still in existence.Template:Sfn In the 7th century BC, Assyrian king Sennacherib constructed stone aqueducts to carry water near the city of Ninevah; one of the aqueducts crossed a small valley at Jerwan with five corbelled arches, and was Script error: No such module "convert". long and Script error: No such module "convert". wide.Template:Sfn In Babylonia in 626 BC, a bridge across the Euphrates was built with an estimated length of Script error: No such module "convert"..Template:Sfn In India, the Arthashastra treatise by Kautilya mentions the construction of bridges and dams.Template:Sfn Ancient China has an extensive history of bridge construction, including cantilever bridges, rope bridges, and bridges built across floating boats.[2]

The ancient Romans built many durable bridges using advanced engineering techniques.[3] Many Roman aqueductsTemplate:Sndsome still standing todayTemplate:Snd used a semicircular arch style.[3] An example is the Alcántara Bridge, built over the river Tagus, in Spain.[4] The Romans used cement as a construction material, which could be mixed with small rocks to form concrete, or mixed with sand to form mortar to join bricks or stones.Template:Sfn Some Roman cements, particularly those containing volcanic ash, were waterproof.[5]Template:Efn The enormous timber and stone Trajan's Bridge (c.Script error: No such module "Check for unknown parameters". 105 AD) crossed the Danube river and was over Script error: No such module "convert". long.[6]

300 to 1400

A graceful stone bridge spanning a river, with trees in the background
The Anji Bridge, which uses a shallow segmental arch, was built in China c.Script error: No such module "Check for unknown parameters". 600 AD.Template:Sfn

The oldest surviving stone bridge in China is the Anji 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.[7] Rope bridges, a simple type of suspension bridge, were used by the Inca civilization in the Andes mountains of South America prior to European colonization in the 16th century.[8]

In Medieval Europe, bridge design capabilities declined after the fall of Rome, but revived in the High Middle Ages in France, England, and Italy with the construction of bridges such as the Pont d'Avignon, bridges of the Durance river, the Old London Bridge, and the Ponte Vecchio in Florence.[9]

1400 to 1800

A wooden bridge, covered with a roof, passing over a river
The superstructure of the West Montrose Covered Bridge is made of wood.Template:Sfn

In 15th and 16th century Europe, the Renaissance brought a new emphasis on science and engineering.[10] Figures such as Galileo Galilei, Fausto Veranzio, and Andrea Palladio (author of I quattro libri dell'architettura) wrote treatises that applied a rigorous, analytic approach to architecture and building.Template:Sfn Their innovations included truss bridges and stone segmental arches, resulting in bridges such as Florence's Ponte Santa Trinita, Rialto Bridge in Venice, and Paris's Pont Neuf.[11] Military and commercial bridges were constructed in India by the Mughal administration.Template:Sfn The Asante Empire in Africa built bridges over streams and rivers using tree trunks and beams.[12] In the late 1700s, the design of arch bridges was revolutionized in Europe by Jean-Rodolphe Perronet and John Rennie. They designed arches that were flatter than semi-circular Roman arches. This yielded faster construction times, better water flow under the bridge, and more slender piers. These designs were used for bridges such as Pont de la Concorde and New London Bridge.[13]

With the advent of the Industrial Revolution, cast iron became an important construction material for bridges.Template:Sfn Although cast iron was strong under compression, it was brittle, so it was supplanted by wrought ironTemplate:Sndwhich was more ductile and better under tension.[14] An early iron bridge was built in Shropshire, England crossing the river Severn.Template:Sfn Several long suspension bridges were built in the early 1800s using iron eyebars (steel wire, vastly superior, would become available later in the century).[15] The abundance of inexpensive lumber in North America caused timber to be the most common material used for bridges there from the late 1700s to the late 1800s. Many of these timber bridges were covered bridges. Rail bridges used timber to obtain long spans that utilized strong truss designs, and also tall trestle bridges that spanned deep ravines.[16]

1800 to present

A suspension bridge crossing a deep rocky ravine
The Sidi M'Cid Bridge in Algeria was the highest bridge in the world when it was built in 1912.Template:Sfn

The mass production of steel in the late 1800s provided a new material for bridges, enabling lighter, stronger truss bridges and cantilever bridges; and steel wires replaced iron bars as the preferred material for suspension bridge cables.[17] ConcreteTemplate:Sndwhich was originally used within the Roman EmpireTemplate:Sndwas improved with the invention of Portland cement in the early 1800s, and replaced stone and masonry as the primary material for bridge foundations. When iron or steel is embedded in the concrete, as in reinforced concrete or prestressed concrete, it is a strong, inexpensive material that can be used for horizontal elements of beam bridges and box girder bridges.[18]

Throughout the 20th century, new bridges by designers such as Othmar Ammann repeatedly broke records for span distances, enabling transportation networks to cross increasingly wider rivers and valleys.[19] Cable-stayed bridgesTemplate:Sndwhich use cable-stays as the exclusive means of supportTemplate:Sndbecame a popular bridge design following World War II.[20]Template:Efn The late 20th century saw several major innovations in bridge design. Extradosed bridges were introduced and found widespread use, predominantly in Japan.Template:Sfn In China, concrete-filled steel tubes were adopted as a new approach to building arch bridges.Template:Sfn Fiber-reinforced polymersTemplate:Sndwhich do not suffer from the rust problems that plague steelTemplate:Sndwere used in bridges for many applications, such as beams, deck slabs, prestressing cables, wraps on the exterior of concrete elements, and internal reinforcing within concrete.Template:SfnTemplate:Efn In the 21st century a bridge span exceeded Script error: No such module "convert". for the first time, with the construction of the 1915 Çanakkale Bridge.Template:SfnTemplate:Efn

Uses

The purpose of any bridge is to traverse an obstacle. A bridge can provide support and transport for railways, cars, pedestrians, pipelines, cables, or any combination of these.Template:Sfn Aqueducts were developed early in human history, and carried water to towns and cities.Template:Sfn Canal systems sometimes include navigable aqueducts (also called canal bridges) to carry boats across a valley or ravine.Template:Sfn

Transportation

A bridge carrying canal with water, passing over a valley
The Magdeburg Water Bridge in Germany carries boats across a valley.Template:Sfn

Until the early 19th century, most bridges were designed to carry pedestrians, horses, and horse-drawn carriages.Template:Sfn Following the invention of railways, many rail bridges were built; in Britain the number of bridges doubled during the railway-building boom in the mid-1800s.Template:Sfn Railway bridges have unique requirements because of the heavy loads they carryTemplate:Snda single locomotive can weigh Script error: No such module "convert"..Template:Sfn Railway bridges are designed to minimize deflection (bending under load), to maximize robustness (localize the damage caused by accidents), and to tolerate heavy impacts (sudden shocks from, for example, rail wheels striking an imperfection in the track).Template:Sfn These requirements lead railways to avoid curved bridges, suspension bridges, and cable-stayed bridges; instead, straight beam or truss bridges are commonly used.Template:Sfn The explosive growth of motorway networks in the 20th century required bridges to span ever longer distances to reach islands and cross valleys.Template:Sfn

Grade separation

Script error: No such module "labelled list hatnote". An important application of bridges is improving safety and traffic flow at traffic junctions where roads or railways cross at ground level. Such intersections require vehicles to stop, and lead to slower traffic, wasted fuel, and higher incidence of collisions. One technique to mitigate these issues is to build a bridge, enabling one of the roads to pass over the other: this process is known as grade separation.[21] Grade separation can be implemented at railway-road intersectionsTemplate:Sfn or road-road intersections.Template:Sfn

Pedestrians

Some bridges, known as footbridges, are devoted to pedestrian traffic.Template:Sfn They range from simple boardwalks enabling passage over marshy land to elevated skybridgesTemplate:Sndsuch as the Minneapolis Skyway SystemTemplate:Sndwhich shield pedestrians from harsh winter weather.[22] When used to cross roads in busy urban areas, footbridges are generally safer than crosswalks, but have been criticized by urbanists and disability advocates for inconveniencing pedestrians, hindering accessibility, diminishing the quality of city life, and perpetuating car dependency.[23]

Military

A metal bridge in a forest.
Invented for wartime use, Bailey bridges found civilian use after WW II.Template:Sfn

Military bridges are an important type of equipment in the field of military engineering. They perform a variety of wartime roles, such as quickly traversing obstacles in the midst of battle, or facilitating resupply behind front lines.Template:SfnTemplate:Efn Military bridges can be categorized as wet bridges that rest on pontoon floats, and dry bridges that rest on piers, river banks, or anchorages.Template:Sfn A crude mechanism to cross a small ravine is to place a fascine (a large bundle of pipes or logs) into the ravine to enable vehicles to drive across.Template:Sfn

Some military bridges, referred to as armoured vehicle-launched bridges, are carried on purpose-built vehicles.Template:Sfn These vehicles typically have the same cross-country performance as a tank, and can carry a bridge to an obstacle and deploy ("launch") the bridge.[24] The UK Chieftain vehicle could launch a Script error: No such module "convert". bridgeTemplate:Sndcapable of supporting Script error: No such module "convert". loadsTemplate:Snd in 3 minutes.Template:Sfn Military bridges have found use in civilian applications. The Bailey bridge was originally invented in 1940 for use in WW II, but continues to be used in peacetime. Bailey bridges are used as small, permanent bridges, as well as temporary bridges used while a permanent bridge is being replaced or repaired.Template:Sfn

Other

Some bridges accommodate uses other than transportation. Pipeline bridges carry oil pipes or water pipes across valleys or rivers.Template:Sfn Many historical bridges supported buildings, such as shrines, factories, shops, restaurants, and houses. Notable examples were the Old London Bridge and Ponte Vecchio.Template:Sfn In the modern era, bridge-restaurants can be found at some highway rest areas; these support a restaurant or shops directly above the highway and are accessible to drivers moving in both directions.Template:Sfn An example is Will Rogers Archway over the Oklahoma Turnpike.Template:Sfn The Nový Most bridge in Bratislava features a restaurant set atop its single tower.Template:Sfn Conservationists use wildlife bridges to reduce habitat fragmentation and animal-vehicle collisions.[25] The first wildlife crossings were built in the 1950s, and these types of bridges are now used worldwide to protect both large and small wildlife.Template:Sfn

Structure and form

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Bridges are primarily classified by their basic structural design: arch, truss, cantilever, suspension, cable-stayed, or beam.[26]Template:Efn Several other terms can used to designate various aspects of a bridge's form or design, including viaduct, trestle, and causeway.

Basic structures

The choice of bridge structure to use in a particular situation is based on many factors, including aesthetics, environment, cost, and purpose.Template:Sfn Some bridge spans combine two types of basic structures; for instance, the Brooklyn Bridge is primarily a suspension structure, but also uses cable-stays.[27] Some multi-span bridgesTemplate:Sndcalled hybrid bridgesTemplate:Snduse different basic structures for different spans.Template:Sfn

Arch bridge

Script error: No such module "Multiple image". Arch bridges consist of a curved arch, under compression, which supports the deck either above or below the arch.Template:Sfn The shape of the arch can be a semicircle, elliptical, a pointed arch, or a segment of a circle.[28] Arches exert a diagonal force at both ends, requiring strong supports or abutments to prevent the arch from spreading or collapsing.[29] Deck arch bridges hold the deck above the arch; tied-arch bridges suspend the deck below the arch; and through-arch bridges position the deck through the middle of the arch.Template:Sfn

Truss bridge

Script error: No such module "Multiple image". A truss bridge is composed of multiple, connected triangular elements.Template:Sfn The set of triangles form a rigid whole, which rests on the foundation at both ends, applying a vertical force downward.Template:Sfn The deck can be carried on top of the truss ("deck truss") or at the bottom of the truss ("through truss").[30] Through trusses are useful when more clearance under the bridge is required; deck trusses permit oversized loads and do not interfere with overhead objects, such as electrical lines.Template:Sfn The individual bars can be made of iron or wood, but most modern truss bridges are made of steel.Template:Sfn The horizontal bars along the top are usually in compression, and the horizontal bars along the bottom are usually in tension.Template:Sfn Bars connecting the top and bottom may be in tension or compression, depending on the layout of the triangles.Template:Sfn Trusses typically have a span-to-depth ratio (the width of a structure divided by its height) ranging from 10 to 16, compared to beam bridges which typically have a ratio ranging from 20 to 30.Template:Sfn Trusses tend to be relatively stiff, and are commonly used for rail bridges which are required to carry very heavy loads.Template:Sfn

Cantilever bridge

Script error: No such module "Multiple image". Cantilever bridges consist of beams or trusses that are rigidly attached to a support (pier or anchorage) and extend horizontally from the support without additional supports.[31] In ancient Asia, cantilever bridges made of large rocks or timber were used to span small obstacles.[32] In the 1880s, some early cantilever bridges were built from wrought iron, but steel began to be used starting in the late 1800s.[33] A balanced cantilever bridge consists of two connected cantilevers extending outward in opposite directions from a single central support.[34] Other cantilever bridges have two cantilevers, anchored at each end of the span, extending toward the center, and meeting in the center.Template:Sfn Cantilever construction is a method of building a bridge superstructure, which can be utilized for arch and cable-stayed bridges, as well as cantilever bridges. In this technique, construction begins at a support (such as a pier, abutment, or tower) and extends outwards across the obstacle, with no support from below.[35]

Suspension bridge

Script error: No such module "Multiple image". Suspension bridges have large, curved cables attached to the tops of tall towers,Template:Efn and suspend the bridge deck from the cables.Template:SfnTemplate:Efn In the early 1800s, the first modern suspension bridgesTemplate:Sndsuch as the Jacob's Creek BridgeTemplate:Sndwere chain bridges that used iron bars rather than bundled wires for the cables.Template:Sfn After steel wire became widely available, longer cables could be built by stringing hundreds of wires between the towers and bundling them,Template:Sfn enabling suspension bridges to achieve spans Script error: No such module "convert". long. When the bridge crosses a river, stringing the wires across the large span is a complex process.[36] The cable of a suspension bridge assumes the shape of a catenary when initially suspended between the bridge towers; however, once the uniform load of the bridge deck is applied, the cable adopts a parabolic shape.Template:Sfn Shorter towers require a smaller sag in the cable, which increases the tension in the cable, and thus requires stronger towers and anchorages.Template:Sfn

Cable-stayed bridge

Script error: No such module "Multiple image". Cable-stayed bridges are similar to suspension bridges, but the cables that support the deck connect directly to the towers.Template:SfnTemplate:Efn The inclined cables may be arranged in a fan pattern or a harp pattern.[37]Template:Efn Modern cable-stayed bridges became popular after WW II, when the design was used for many new bridges in Germany.Template:Sfn When traversing a wide obstacle, designers have a choice of suspension or cable-stayed structures. Suspension bridges can achieve a longer span, but cable-stayed bridges use less cable for a given span size, do not require anchorages, and the deck can be readily built by cantilevering outward from the towers.[38]

Beam bridge

Script error: No such module "Multiple image". Beam bridges are simple structures consisting of one or more parallel, horizontal beams or girders that span an obstacle.[39] A box girder bridge is a variant that is generally shallower than an I-beam equivalent, permitting shorter and lower approach roads to cross an obstacle of a given height.Template:Sfn Beam bridges are commonly used for both railways and roadways.[39] Beam bridges are often used for spans shorter than about Script error: No such module "convert".; for longer spans other structures, such as trusses, are generally more efficient.[40] The majority of beam bridges have a flat, horizontal bottom; but some have a bottom that arches upward, called haunching. Haunching looks more graceful than a flat bottom, and can provide greater clearance below the bridge, but it tends to be more costly because flat bottom beams are easier to build.[41]

Other forms

Movable bridge

A tall drawbridge, open, over a river
Tower Bridge in London is a movable bridge.Template:Sfn

Movable bridges are designed so that all or part of the bridge deck can be moved, usually to permit tall trafficTemplate:Sndthat would normally be obstructed by the bridgeTemplate:Sndto pass by.[42] Early movable bridges include drawbridges that pivoted at one end, and required a large amount of work to raise. Adding counterweights on the pivot side of the drawbridge creates a bascule bridge, and makes moving the bridge easier and safer.[43] Swing bridges pivot horizontally around an anchor point on the bank of a canal, or sometimes from a pier in the middle of the water.[44] Lift bridges are raised vertically between two towers by cables passing over pulleys at the top of the towers.[45] Notable movable bridges include El Ferdan Railway Bridge in Egypt, Erasmusbrug bascule in Rotterdam, and Limehouse Basin footbridge in London.Template:Sfn In the modern era, designers sometimes create unusual movable bridges with the intention of establishing signature bridges for a town or locality.Template:Sfn Examples include Puente de la Mujer swing bridge in Buenos Aires, Gateshead MillenniumTemplate:Snda rare example of a tilt bridgeTemplate:Sndover the River Tyne, and Hörn Bridge in Germany.Template:SfnTemplate:Efn

Long multi-span bridge

A large bridge, consisting of multiple tall sections, passing over a wide valley
The Millau Viaduct crosses the Tarn river valley in France.Template:Sfn

There are a variety of terms that describe long, multi-span bridgesTemplate:Sndincluding viaduct, trestle, continuous, and causeway. The usage of the terms can overlap, but each has a specific focus.[46] Viaducts (carrying vehicles) and aqueducts (carrying water) are bridges crossing a valley, supported by multiple arches or piers.[47] Romans built many aqueducts, some of which are still standing today.Template:Sfn Notable viaducts include Penponds Viaduct in England,Template:Sfn Garabit Viaduct in France,Template:Sfn Tunkhannock Viaduct in Pennsylvania,Template:Sfn and Millau Viaduct in France.Template:Sfn

A trestle bridgeTemplate:Sndcommonly used in the 19th century for railway bridgesTemplate:Snd consists of multiple short spans supported by closely spaced structural elements.Template:Sfn A trestle is similar to a viaduct, but viaducts typically have taller piers and longer spans.Template:Sfn A continuous truss bridge is a long, single truss that rests upon multiple supports. A continuous truss bridge may use less material than a series of simple trusses because a continuous truss distributes live loads across all the spans (in contrast to a series of simple trusses, where each truss must be capable of supporting the entire live load). Visually, a continuous truss looks similar to a cantilever bridge, but a continuous truss experiences hogging stresses at the supports and sagging stresses between the supports.[48]Template:Efn A causeway is a low, raised road, usually crossing a lake or other body of water.[49] The Script error: No such module "convert". Lake Pontchartrain Causeway in Louisiana is a bridge, but other causeways are built on earthen embankments.[49]

Extradosed

A concrete bridge over a river
The Shin Meisei bridge (foreground) in Japan is an example of an extradosed bridge.Template:Sfn

An extradosed bridge combines features of a box girder bridge and a cable-stayed bridge.[50] Visually, extradosed bridges can be distinguished from cable-stayed bridges because the tower height (above the deck) is relatively low: between 7% and 13% of the span width.Template:Sfn Extradosed bridges are appropriate for spans ranging from Script error: No such module "convert". to Script error: No such module "convert"..Template:Sfn Unlike suspension bridges or cable-stayed bridges, the towers of an extradosed bridge often rest on the deck (rather than on a footing) and are solidly connected to the deck.Template:Sfn Because of the relatively flat angle of the cables, the cables of an extradosed bridge compress the deck horizontally, performing a function comparable to prestressing wires that are used within concrete girders.Template:Sfn Extradosed bridges may be appropriate in applications where the deck must have a shallow depth to maximize clearance under the bridge; or where towers must be relatively short to abide by aviation safety constraints.Template:Sfn

Pontoon bridge

A concrete bridge over a large body of water
Floating concrete pontoons support the weight of the Nordhordland Bridge as it crosses a deep fjord in Norway.Template:Sfn

A pontoon bridge, also known as a floating bridge, uses floats or shallow-draft boats to support a continuous deck for pedestrian or vehicle travel over water.[51] Pontoon bridges are typically used where waters are too deep to build piers, or as a mechanism to implement a movable swing bridge in a canal.Template:Sfn During the Second Persian invasion of Greece, Persian ruler Xerxes built a large pontoon bridge across the Hellespont, consisting of two parallel rows of 360 boats.[52]

Several pontoon bridges are in use in the modern world. Washington state in the US has several, including Hood Canal Bridge.Template:Sfn In Norway, Nordhordland Bridge crosses a deep fjord by resting on floating concrete pontoons.Template:Sfn Many armies have pontoon bridges that can be rapidly deployed, including the PMP Floating Bridge, designed by the USSR.Template:Sfn

Design

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Design process

The process for designing a new bridge typically goes through several stages, progressively refining the design.Template:Sfn An early step in the design processTemplate:Sndsometimes called conceptual designTemplate:Sndis to consider the multiple requirements that a bridge must satisfy.Template:Sfn Requirements that are directly related to function include lifespan, safety, climate, soil condition, traffic volume, the size and nature of the obstacle to be traversed, and clearance required for passage underneath.[53] Other constraints may include construction cost, maintenance cost, aesthetics, time available for construction, owner preference, and experience of the builders.[53] Some bridge designs consider factors such as impact to environment and wildlife; and the bridge's economic, social, and historic relationship to the local community.Template:Sfn After the requirements of a bridge are established, a bridge designer uses structural analysis methods to identify candidate designs.Template:Sfn Several designs may meet the requirements. The value engineering methodology can be used to select a final design from multiple alternatives.Template:Sfn This methodology evaluates candidate designs based on weighted scores assigned to several different criteria, such as: cost, service life, durability, availability of resources, ease of construction, construction time, and maintenance cost.Template:Sfn

An important requirement considered during the design process is the service life, which is a specific number of years that the bridge is expected to remain in operation with routine maintenance (and without requiring major repairs).[54]Template:Efn For example, wood bridge superstructures typically have a service life of 10 to 50 years.Template:SfnTemplate:Efn Concrete highway bridges can have service lives of 75 to 150 years.Template:Sfn A bridge design methodology incorporates the service life into the design process.Template:Sfn

Specifications and standards

One of the requirements a new bridge must satisfy is compliance with the local bridge design specifications and codes whichTemplate:Sndin some countriesTemplate:Sndmay be legally binding requirements.[55] In many countries, these specifications are developed and published by standards organizations that define acceptable bridge-building practices and designs. In Europe, the organization is the European Committee for Standardization, and the standards it publishes are the Eurocodes.Template:Sfn In the United States, the American Association of State Highway and Transportation Officials (AASHTO) publishes the AASHTO LRFD Bridge Design Specifications.Template:SfnTemplate:Efn Canada's bridge standard is the Canadian Highway Bridge Design Code, developed by the non-profit CSA Group.Template:Sfn Agencies that regulate aviation or waterways may also impose standards that dictate some aspects of a bridge design, such as requirements for aviation warning lights at the top of bridge towers, or navigational warning lights on bridge supports located in navigable waterways.[56]

Aesthetics

A train moving atop a stone bridge in an attractive valley
The Brusio spiral viaductTemplate:Snda part of the Bernina railway in SwitzerlandTemplate:Sndis designated as a World Heritage Site.Template:Sfn

A bridge's appearance is one of the factors considered during its design.Template:Sfn Attractive bridges can have a positive impact on a community, and some bridges can even be considered as works of art.[57] Bridge designers that are known for emphasizing the visual appeal of their bridges include Thomas Telford, Gustave Eiffel, John Roebling, Robert Maillart, and Santiago Calatrava.[58] Qualities that influence the perceived attractiveness of a bridge include proportion, color, texture, order, refinement, environmental integration, and functionality.Template:Sfn

The art historian Dan Cruickshank notes that bridges are regarded as manifestations of human imagination and ambition, and that many bridges transcend their original utilitarian role and become a work of art.Template:Sfn He writes "[a] great bridge has an emotional impact, it has a sublime quality and a heroic beauty that moves even those who are not accustomed to having their senses inflamed by the visual arts."Template:Sfn

Material

A bridge designer can select from a wide variety of materials, including wood, brick, rope, stone, iron, steel, and concrete.[59]Template:Efn A bridge made from two or more distinct materials (such as steel and concrete) is known as a composite bridge.Template:Sfn Some of the largest arch bridges are composite, because they are made from concrete and steel.Template:Sfn

Wood is an inexpensive, renewable resource with a high strength-to-weight ratio, but it is rarely used for modern roadway bridges because it is prone to degradation from the environment, and is much weaker than steel or concrete.Template:Sfn Wood is primarily used in beam or truss bridges, and is also used to build large trestle bridges for railways.[60] When wood is used, it is often in the form of glued laminated timber.Template:Sfn Masonry includes stone and brick, and is suitable only for elements of a bridge that are under compression (as opposed to tension), therefore, masonry is limited to structures such as arches or foundations.[61] In the twentieth century, large masonry bridges Template:Sndalthough superseded by concrete in the WestTemplate:Sndcontinued to be built in China.Template:Sfn

An ornate bridge made of iron, passing over a small, lush valley
The Iron Bridge in Shropshire, England, completed in 1781, is the first major bridge made entirely of cast iron.Template:Sfn

IronTemplate:Sndincluding cast iron and wrought ironTemplate:Sndwas used extensively from the late 1700s to late 1800s, primarily for arch and truss structures. Iron is relatively brittle, and has been replaced by steel for all but ornamental uses.[62] Steel is one of the most common materials used in modern bridges because it is strong in both compression and tension.Template:Sfn Steel was made in small quantities in antiquity, but became widely available in the late 1800s following invention of new smelting processes by Henry Bessemer and William Siemens. Truss bridges and beam bridges are often made of steel, and steel wires are an essential component of virtually all suspension bridges and cable-stayed bridges.[63] Concrete bridges make extensive use of steel, because all concrete used in bridges contains steel reinforcing bars or steel prestressed cables.[64] Steel bridges are more expensive than comparable concrete bridges, but they are much lighter (for the same strength), faster to build, and offer more flexibility during construction and repair.[65]

Concrete is commonly used in modern bridges, and many roadway bridges are built primarily with a reinforced concrete beam structure, often of the box girder variety.Template:SfnTemplate:Efn The shape of concrete elements is determined by the formwork (mold) into which the concrete is poured (cast): the concrete will adopt the shape of the formwork as it cures.[66] Beams can be precast offsite and transported to the bridge site, or cast in place.Template:Sfn Bridges use concrete that contains embedded steel reinforcing barsTemplate:Sndplaced within the concrete when it is initially pouredTemplate:Sndwhich greatly increase the strength.[67] Concrete is a strong and inexpensive material, but is brittle and can crack when in tension.Template:Sfn If concrete is used in elements that may experience tension, prestressed cables are usually embedded within the concrete and tightened, which compresses the concrete.[68] When a horizontal beam is placed into the bridge and carries a load, the undesirable tension (produced by the tendency of the beam to sag) is counteracted by the compression from the prestressed cables.[69] The prestressed cables can be pre-tensioned (stretched beforeTemplate:Sndand whileTemplate:Sndthe concrete cures); or post-tensioned (placed within tubes in the concrete, and tightened after the concrete cures).[69]

Double-deck bridge

Script error: No such module "Labelled list hatnote". Designers may choose to use a double-deck design (also known as double-decked or double-decker), that carries two decks on top of each other. This technique can be used to increase the amount of traffic a bridge can carry; or when the location constrains the size of the bridge.Template:Sfn Double-deck bridges also permit two different kinds of traffic to be safely carried. For example, motor vehicles can be separated from pedestrians or railways.Template:Sfn An early double-deck bridge was Niagara Falls Suspension Bridge, which carried rail on the upper deck, and carriages and pedestrians on the lower deck.Template:Sfn George Washington Bridge in New York carries 14 motor vehicle lanes (eight above, six below), and is the world's busiest bridge, carrying over 100 million vehicles annually.Template:Sfn Because of their ability to carry large amounts of motor vehicles, double-deck bridges are often found near large cities, such as Tsing Ma Bridge in Hong Kong,Template:Sfn Øresund Bridge connecting Copenhagen and Malmö,Template:Sfn and Shimotsui-Seto Bridge near Kurashiki.Template:Sfn

Load analysis

A very large suspension bridge passing over a large body of water
The San Francisco–Oakland Bay Bridge is designed to withstand severe earthquakes. The eastern span, shown above, is a self-anchored suspension bridge which can survive a once-in-1,500-year earthquake.Template:Sfn

A bridge design must accommodate all loads and forces that the bridge might reasonably experience. The totality of the forces that the bridge must tolerate is the structural load, which is often divided into three components: dead load, live load, and environmental load. The dead load is the weight of the bridge itself.[70]Template:Efn The live load is all forces and vibrations caused by traffic passing over the bridge, including weight, braking, and acceleration.[70] The environmental load encompasses all forces applied by the bridge's surroundings, including weather, earthquakes, mudslides, water currents, flooding, soil subsidence, frost heaving, temperature fluctuations, and collisions (such as a ship striking the pier of a bridge).[70]

Many load sources vary over time, such as vehicle traffic, wind, and earthquakes. A bridge designer must anticipate the maximum values that those loads are likely to reach during the bridge's lifespan.Template:Sfn For sporadic events like floods, earthquakes, collisions, and hurricanes, bridge designers select a maximum severity that the design must accommodate.Template:Sfn The severity is based on the return period, which is average time between events of a given magnitude. Return periods range from 10 to 2,500 years, depending on type of event and the country in which the bridge is located.[71]Template:Efn Longer return periods are used for bridges that are a critical part of the transportation infrastructure. For example, if the bridge is a key lifeline in case of emergencies, the designer may utilize relatively long return period, such as 2,000 years; in this example, the design must endure the strongest storm that is expected to happen once every 2,000 years.Template:Sfn

Stress and strain

Script error: No such module "labelled list hatnote". The load forces acting on a bridge cause the components of the bridge to become stressed. Stress is a measure of the internal force experienced within a material. Strain is a measure of how much a bridge component bends, stretches, or twists in response to stress. Some strain (bending or twisting) may be acceptable in a bridge component if the material is elastic. For example, steel can tolerate some stretching or bending without failing. Other materials, such as concrete, are inelastic, and their change in shape when stressed is negligible (until the stress becomes excessive and the concrete fails).[72]

A bridge designer must calculate the maximum stress that each bridge component will experience, then select an appropriate design and size for the components to ensure they will safely tolerate the loads on the bridge. Stresses are categorized based on the nature of the force that causes the stress, namely: compression, tension, shear, and torsion. Compression forces compact a component by pushing inward (for example, as felt by a bridge foundation when a heavy tower is resting on it). Tension is a stretching force experienced by a component when pulled (for example by the cables of a suspension bridge). Shear is a sliding force experienced by a component when two offset external forces are applied in opposite directions (for example, during an earthquake when the upper part of a structure is pulled north, and the lower part is pulled south). Torsion is a twisting force.[73]

The bridge design process employs structural analysis methods that divide the bridge into smaller components, and analyze the components individually, subject to certain constraints.Template:Sfn A proposed bridge design is then modeled with formulas or computer applications.[74] The models incorporate the loads the bridge will experience, calculate the stresses in the bridge, and provide data to the designer indicating whether the design meets the required design goals.[74] The finite element method is a numerical model commonly used to perform detailed analysis of stresses and loads of a bridge design.[75] To ensure that a proposed bridge design is sufficiently strong to endure foreseeable stresses, many bridge designers use methodologies such as limit state design (used in Europe and China) or Load and Resistance Factor Design (LRFD) (used in US).[76]

Vibration

Many loads imposed on a bridgeTemplate:Sndsuch as wind, earthquakes, and vehicular trafficTemplate:Sndcan cause a bridge to experience irregular or periodic forces, which may cause bridge components to vibrate or oscillate.[77] Some bridge components have inherent resonant frequencies to which they are particularly susceptible, and vibrations near those frequencies can cause very large stresses.[78]

A collapsed concrete bridge, with a broken support pier.
The 1994 Northridge earthquake damaged several bridges.[79]

Winds can produce a variety of vibrational forces on a bridge, including flutter, galloping, and vortex shedding.[80] Considering wind forces during the design process is especially important for long, slender bridges (typically suspension or cable-stayed bridges).[81] If resonance issues are identified in the design process, they must be mitigated. Common techniques to address vibration include increasing the rigidity of the bridge deck by adding trusses and adding dampers to cables and towers.[82] Neglecting to account for vibrations and oscillations can lead to bridge failure. The Tacoma Narrows Bridge collapsed in the 1940 in winds of Script error: No such module "convert"., even though the bridge was designed to withstand winds up to Script error: No such module "convert".. Investigations revealed that the designer failed to account for wind effects such as flutter and resonant vibrations.[83]

Bridges can suffer severe damage when subjected to earthquake ground motions.[84] During a seismic event, several phenomena can occur, such as long-period velocity pulses, shear cracks, large ground motions, vertical accelerations, and soil liquefaction.Template:Sfn To mitigate risks, earthquake engineers study seismic data to classify and quantify the motions experienced by bridges.Template:Sfn These studies are used by governments to create and revise design standards that specify the types of seismic movements that new bridges must withstand.Template:Sfn

Construction

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The structural elements of a bridge are generally divided into the substructure and the superstructure.Template:Sfn The substructure consists of the lower portions of the bridge, including the footings,Template:Efn abutments, piers, pilings, anchorages, and bearings.Template:Sfn The superstructure rests upon the substructure, and consists of the deck, trusses, arches, towers, cables, beams, and girders.[85]

Construction process

A schematic diagram identifying the various parts of a Hypothetical bridge
Some elements of a fictional bridge. 1 Approach, 2 Arch, 3 Truss, 4 Abutment, 5 Bearing, 6 Deck and beams, 7 Pier Cap, 8 Pier, 9 Piling, 10 Footing, 11 Caisson, 12 Subsoil.[86]

Construction of a bridge is typically managed by construction engineers, who are responsible for planning and supervising the construction process. Important aspects of this role include budgeting, scheduling, periodically conducting formal design reviews, and communicating with the bridge designers to interpret and update the design plans.[87]Template:Efn When an existing bridge is being replaced or refurbished, the impact on traffic flow can have a detrimental effect on residents and services. Accelerated bridge construction processesTemplate:Sndthat focus on using pre-fabricated components and a rapid timetableTemplate:Sndmay be used to mitigate the impacts.Template:Sfn

The forces experienced by a bridge during construction can be larger or have a different nature than the forces it will experience after completion. The bridge design process typically focuses on the strength of the fully completed bridge, but it should also consider the unusual stresses that individual elements will experience during construction. Special techniques may be required during construction to avoid excessive stresses, such as temporary supports under the bridge, temporary bracing or reinforcement, or permanently strengthening specific elements.[88] For instance, when a cable-stayed bridge with concrete towers is complete, the towers will experience desirable compression forces from the heavy load of the cables; but during construction, without that load, the towers may experience undesirable tension forces caused by lateral winds.Template:Sfn

Substructure

Two schematic diagrams showing how force is transmitted in a flat bridge compared to an arched bridge
Abutments are an important element of a substructure. Beam bridges (left) direct force vertically into the abutments; some arch bridges (right) direct forces diagonally. 1 Deck, 2 Abutments, 3 Subsoil, 4 Load on bridge, 5 Force from abutment into subsoil.[29]

Construction of all bridge types begins by creating the substructure. The first elements built are usually the footings and abutments, which are typically large blocks of reinforced concrete, entirely or partially buried underground. The footings and abutments support the entire weight of the bridge, and transfer the weight to the subsoil.[89] Based on their height-to-width ratio, footings are categorized as: shallow (height is less than width) or deep (height is greater than width).[90] If the subsoil cannot support the load placed on the footings, pilings must first be driven below the footings: pilings are long structuresTemplate:Sndmade of wood, steel, or concreteTemplate:Sndplaced vertically below footings.[91] Some pilings reach down and rest on bedrock; others rely on friction to prevent the footing from sinking lower.[91]

Abutments are usually located at the ends of a bridge deck, where it reaches the subsoil.Template:Sfn They direct the weight into the subsoil, either vertically or diagonally.[29] Abutments may also act as retaining walls, keeping the subsoil under the approach road from eroding.Template:Sfn After footings for the piers have been created, the piers and pier caps are built to complete the substructure.[92]Template:Efn Suspension bridges usually require anchorages, which are large reinforced concrete blocks solidly anchored into the earthTemplate:Sndthey must be exceptionally heavy and tied into the subsoil because they must withstand the lateral pull of the large cables that hold the entire deck and live load.[93]Template:Efn

Constructing supports in water

A large concrete structure in the middle of a river, kept dry by a steel wall surrounding it
This concrete bridge pier is being built within a steel cofferdam.Template:Sfn

When bridge supports (such as piers or towers) are built in a river, lake, or ocean, special technologies must be utilized.Template:Sfn Caissons can be used to provide a workspace while constructing the submerged portion of the supports. A caisson is a large, watertight, hollow structure, open on the bottom. It is usually sunk to the bottom of the water and workers can work inside, preparing the ground for the footings. When excavation is complete, a caisson is typically filled with concrete to create all or part of the footing.[94] Air pressure inside a sealed caisson must be kept high to prevent water from seeping in.Template:Sfn Workers, if they do not properly decompress when exiting the caisson, can get decompression sickness.[95] Early bridge builders did not understand decompression, and deaths were common: thirteen workers died from decompression sickness when building the Eads Bridge (completed in 1874).[95]

Another approach for constructing foundations in water is a box caisson, which is a large steel or concrete box, open on top, which is towed by tugboats to the bridge site, then sunk to the bottom and filled with concrete.[96] The Akashi Kaikyo suspension bridge used box caissons for its two foundationsTemplate:Sndeach Script error: No such module "convert". tall and Script error: No such module "convert". in diameter. The caissons were sunk to the bottom in water Script error: No such module "convert". deep, and each was filled with 355,000 cubic meters of concrete. The foundations rest directly on the ocean bottom, without pilings or footings.[96] An alternative to a caisson is a cofferdam, which is a temporary dam surrounding the support location, open on top, where workers may work while constructing the footings.[97]

Bearings

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Two cylinders of steel, supporting a large steel bridge, and resting on a concrete support
Bearings can prevent damage to the superstructure by permitting small movements.Template:Sfn

Bearings are often placed between the superstructure and the substructure at the points of contact. Bearings are mechanical devices that enable small movementsTemplate:Sndwhich may result from thermal expansion and contraction, material creep, or minor seismic events. Without bearings, the bridge structure may be damaged when such movements occur. Bearings can be selected to permit small rotational or slipping movements in a specific direction, without permitting movements in other directions. Types of bearings used on bridges include hinge bearings, roller bearings, rocker bearings, sliding bearings, spring bearings, and elastomeric bearings.[98]

Superstructure

After the substructure is complete, the superstructure is built, resting on the substructure. Beam bridge superstructures may be built in place, or fabricated off-site (precast) and transported to the bridge site.[99] Precast beams may be placed atop the supports by a crane or gantry.[100] If the span crosses a deep ravine, a technique known as launching may be used: the beams and deck are assembled on the approach road, then pushed horizontally across the obstacle.[101]Template:Efn

A bridge being constructed, with two large cranes on top
Gantries are one technique used to gradually assemble a bridge deck.[102]

Arch bridge superstructure construction methods depend on the material. Concrete or stone arches use a temporary wood structure known as falsework or centering to support the arch while it is built.[103] Some steel arch bridges are constructed with falsework, but others use cantilevering to build both halves out from the abutments.[104]

Cantilever bridge superstructures are usually built incrementally by proceeding outward from anchorages or piers. Most cantilever superstructures can be built without temporary support piers, as the bridge can support itself as it extends outward. A similar process is used for steel or concrete cantilevers: prefabricated sections may be positioned at ground (or water) level and hoisted into place with a gantry, or may be transported horizontally along the previously completed portion of the cantilever. Concrete cantilevers require steel prestressing cables to be passed through tubes within each section and tightened, which will put the concrete into compression.[105] Truss bridges are built using a variety of methods, including piece-by-piece, cantilevering, or falsework.Template:Sfn

Cable-stayed bridge superstructures begin with the construction of one or more towers which rest directly on footings that are part of the substructure. The deck is constructed in pieces beginning at the towersTemplate:Efn and moving outward. The pieces can be put into place by hoisting, supporting from below, launching, or cantilevering from the portion of the deck that has been assembled.[106] As each piece of the deck is added, it is connected to towers with steel cables, and the cables are tightened to take the load of the deck.[106]

Suspension bridge superstructure construction usually begins with the towers.Template:SfnTemplate:Efn The towers may be steel or concrete, and rest directly on footings. The large cables are created by hauling a large pulley back and forth across the span, stringing multiple wires between the anchorages in each pass, in a process termed spinning. After the wires are spun, they are bundled together to form the cables.Template:Efn The cables are securely fastened to the anchorages at both ends.Template:Efn Vertical wires called hangers are suspended from the cables, then small sections of the deck are attached to the hangers, and the sections are attached to each other.[107]

Towers

A thick steel cable passing over the top of a suspension bridge tower.
A suspension bridge cable transfers its load to the tower by resting on a curved saddle.

Towers, made of either concrete or steel, are an important component of the superstructure of cable-stayed bridges and suspension bridges.Template:Efn Concrete is generally suitable for towers up to about Script error: No such module "convert". tall, whereas steel towers can be taller.[108]Template:Efn Towers support the bridge cables, whichTemplate:Sndin turnTemplate:Snd hold the weight of the bridge deck and the vehicular traffic. Most of the load imposed on a tower is applied vertically downward on the tower, rather than sideways.Template:Sfn Towers experience a compression stress, in contrast to cables, which experience a tension stress.Template:Sfn There are two mechanisms used to attach a cable to a tower: saddles or anchors. Saddles are curved structures which allow a cable to pass through (or over the top of) a tower. An anchor holds the end of a cable. Saddles are often used in suspension bridges, and anchors are often used in cable-stayed bridges.[109]

Cables

Two men are standing high in the air on a walkway, and a wheel is above them, suspended by wires.
A spinning wheels pulls two wires at a time to gradually build-up a suspension bridge cable.Template:Sfn

Steel cables are an element of both cable-stayed bridges and suspension bridges. Cables are made of one or more strands, and each strand consists of multiple wires. A wire is a thin, flexible piece of solid steel, of higher tensile strength than normal steel, and with a diameter of 3mm to 7mm.Template:SfnTemplate:Efn Cables are typically constructed at the bridge site by unspooling wires or strands from large reels.[110] Large suspension bridges may use cables that are over Script error: No such module "convert". in diameter and weigh over Script error: No such module "convert"..[111]

Before building the cables of a suspension bridge, temporary catwalks must be constructed to support the wires while they are drawn across the span and over the tops of the towers.[112] There are two approaches to pulling the wires across the span: the air spinning method (in which individual wires are carried across by pulleys); and the prefabricated strand method (in which entire strands are pulled across).[113]Template:Efn

The air spinning method was used for all suspension bridges until the prefabricated strand method was invented in the 1960s.Template:Sfn After 300 to 500 wires are pulled, aluminum bands are used to bundle them into strands.Template:SfnTemplate:Efn The wires within a strand may be parallel, or they may wrap around each other in a twisted (spiral) pattern.Template:Sfn Air spinning always produces strands that contain parallel wires. The prefabricated strand method can utilize strands with parallel or twisted wires.Template:SfnTemplate:Efn

Deck

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A large concrete arch bridge being constructed
The deck of this arch bridge is being horizontally pushed onto the substructure with jacks [101]

The deck of a bridge is the horizontal, continuous surface that extends across the full span of a bridge, and upon which vehicles or pedestrians travel. Decks generally rest on beams or box girders. When a deck is rigidly attached to its supporting beams or girders they function together as a single structure.[114] Two common types of decks are concrete decks and orthotropic steel decks.[115]Template:Efn Concrete decks are flat slabs of reinforced concrete. The slabs may precast off-site, or cast-in-place by pouring concrete into forms on the bridge superstructure.[116]Template:Efn Orthotropic steel decks consist of a flat steel plate, coated with a wearing surface.[117] Numerous small steel ribs are welded to the underside of the top plate, running in the direction of the bridge roadway.Template:Efn Below the ribs are steel floor beams, placed crosswise to the ribs.Template:SfnTemplate:Efn Orthotropic steel decks are more expensive than concrete steel decks, but weigh less. They are useful in applications where weight is critical, a thin deck is required, or the environment is subject to earthquakes or extreme cold weather.Template:Sfn

Many decks have a wearing surface on top, which is a layer of material designed to be periodically replaced after it is worn away by vehicular traffic. Wearing surfaces are typically made of aggregate (small rocks) mixed with a binder such asphalt, polyurethane, epoxy resins, or polyester.[118]Template:Efn Railway bridge decks are categorized as open decks (the ties rest directly on beams or girders, with air gaps between) and ballast decks (the ties rest on ballast rocks, and the ballast rests on a deck slab).Template:Sfn

Constructing the deck (and its supporting beams or girders) can be difficult when the bridge is over water or a deep valley. A variety of techniques are available, and the choice depends on factors such as the topography of the site, the deck material (concrete or steel), traffic or obstacles under the bridge, and whether sections can be built off-site and transported to the bridge. Methods of deck construction include building atop temporary supports, jacking up from the ground, incremental launching (building the entire deck on the approach road and pushing it horizontally), lifting from below with a hoist mounted on the bridge, cantilevering (incrementally extending the deck, starting from towers or abutments), and lifting with a floating crane.[119]

Protection

To achieve the designed service life, a bridge must be protected from deterioration by incorporating certain features into the design. Bridges can deteriorate due to a variety of causes, including rust, corrosion, chemical actions, and mechanical abrasion. Deterioration is sometimes visible as rust on steel components, or cracks and spalling in concrete.Template:Sfn Deterioration can be slowed with various measures, primarily aimed at excluding water and oxygen from the bridge elements.Template:Sfn Techniques to prevent water-based damage include drainage systems, waterproofing membranes (such as polymer films), and eliminating expansion joints.Template:SfnTemplate:Efn Concrete bridge elements can be protected with waterproof seals and coatings.Template:SfnTemplate:Efn Reinforcing steel within concrete can be protected by using high-quality concrete and increasing the thickness of the concrete surrounding the steel.Template:Sfn Steel elements of a bridge can be protected by paints or by galvanizing with zinc.[120] Paint can be avoided entirely for steel members by using certain steel alloys, such as stainless steel or weathering steel (a steel alloy that eliminates the need for paint, by forming a protective outer layer of rust).[121]

Bridge scour is a potentially serious problem when bridge footings are located in water. Currents in the water can cause the sand and rocks around and below the footings to wash-away over time. This effect can be mitigated by placing a cofferdam around the footings, or surrounding the footings with large, carefully placed rocks.[122]Template:Efn Suspension bridges and cable-stayed bridges have large cables containing hundreds of steel wires. Several techniques are used to minimize corrosion inside the cables, such as wrapping the cables with galvanized wire, injecting the cables with grout or epoxy, using interlocking S-profile wires, and circulating dry air through the interior of the cable.[123] Bridges with supports in navigable waterways are designed to withstand ship strikes up to a specific, predefined magnitude. In addition to waterway markings and pilot warning systems, bridge supports in water may be surrounded by physical protections such as fenders, pilings, or small artificial islands.Template:Sfn

Operation and financing

Management

Script error: No such module "labelled list hatnote". After a bridge is completed and becomes operational, management processes are employed to ensure that it remains open to traffic, avoids safety incidents, and achieves its intended lifespan. These processesTemplate:Sndcollectively referred to as bridge managementTemplate:Snd include technical activities such as maintenance, inspection, monitoring, and testing.Template:Sfn In addition to technical tasks, management encompasses planning, budgeting, and prioritization of maintenance activities.Template:Sfn Bridge managers use methodologies such as bridge management systems and life-cycle cost analysis to manage a bridge and estimate the maintenance costs of a bridge throughout its lifetime.[124] Annual maintenance costs increase as the bridge ages and degrades.Template:Sfn

Maintenance

Template:Easy CSS image crop

Maintenance activities seek to prolong the life of the bridge, reduce lifecycle costs, and ensure the safety of the community.Template:Sfn Maintenance tasks can be categorized as corrective tasks and preventive tasks.Template:Sfn Corrective tasks are implemented in response to unexpected issues that arise, such as repairing structural elements (piers, beams, girders, towers, or cables) and replacing bearings.Template:Sfn

Preventive tasks include washing, painting, lubricating bearings, sealing the deck, filling cracks, removing snow, filling potholes, and repairing minor issues with structures and electrical fixtures.Template:Sfn Some preventive tasks are performed on a periodic schedule. An example schedule for periodic bridge maintenance tasks is: washing entire structure (1–2 years); sealing deck surface (4–6 years); lubricating bearings (4 years); painting steel bridge components (12–15 years); replacing the deck's wearing surface (12 years); sealing sidewalks (5 years); filling cracks (4 years); and cleaning drains (2 years).[125]

Inspection and monitoring

A tall bridge covered in temporary scaffolding
Scaffolding is erected under the Sitterviadukt rail bridge in Switzerland while maintenance on the deck truss is performed.Template:Sfn

An important part of maintenance is inspecting a bridge for damage or degradation, and taking steps to mitigate any issues detected. Degradation can come from environmental sources such as expansion/contraction from freeze/thaw cycles, rain, oxidation of steel, and sea spray. Human activities may also cause damage, such as vehicular traffic, mechanical abrasion, poor bridge design, and improper repair procedures.[126] Some countries mandate periodic inspection schedules, for example, routine inspections every 24 months, or inspecting underwater foundations for scouring every 60 months.Template:Sfn

Relying solely on visual inspection to assess degradation of a bridge can be unreliable, so inspectors use a variety of nondestructive testing techniques.Template:Sfn These techniques include hammer strike tests, ultrasonic pulse velocity tests, seismic tomography, and ground penetrating radar.[127] Various electrical tests, such as those assessing permeability and resistance, can give insight into the condition of surface concrete.Template:Sfn X-rays can be passed through concrete to obtain data about concrete density and condition.Template:Sfn Videography using slender probes can be used where access is available.Template:Sfn Measurements of the state of a bridge may be made automatically and periodically using structural health monitoring (SHM) technologies.Template:Sfn Some testingTemplate:Sndtermed destructive testingTemplate:Sndrequires removing samples from the bridge and taking them to a laboratory for analysis with microscopes, sonic devices, or X-ray diffraction.Template:Sfn Destructive testing is performed on samples such as cores drilled from concrete, or a small piece of steel wire cut from a cable.Template:Sfn

Financing

Funding for bridge construction and operation comes from a variety of sources, including fuel taxes, annual vehicle registration fees, tolls, congestion fees, and usage fees based on satellite tracking.Template:Sfn Some bridgesTemplate:Sndparticularly in developing countriesTemplate:Sndare financed by international sources such as the World Bank or China's Belt and Road Initiative.[128] Toll systems are generally an inefficient mechanism for collecting funding, particularly when toll booths are used, because they are expensive to build and manage. Toll booths can slow down traffic and interfere with the construction of entry or exit points.Template:Sfn

The cost of building a bridge is typically borne by government agencies, but since 1990 an increasing number of bridges are built and paid for by private companies using a public–private partnership (PPP) agreement. In a PPP project, the government grants the right to build the bridge to a company, and the company recoups its expenses by collecting tolls for fixed period of time.[129]Template:Efn At the end of the period, the bridge is transferred to government ownership, and the government may choose to continue to charge tolls or not. Notable bridges constructed with a PPP model include the Queen Elizabeth II Bridge (built in 1991, toll collection period 20 years) and the Second Severn Crossing (built in 1996, toll collection period 30 years).Template:Sfn

Failures

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A broken bridge, which has fallen into the water over which it used to pass
The Nanfang'ao Bridge in Taiwan collapsed because of excessive corrosion that went undetected.Template:Sfn

Bridge failures are of special importance to structural engineers, because the analyses of the failures provide lessons learned that serve to improve design and construction processes.[130] Bridge failures have a variety of causes, which can be categorized as natural factors (flood, scour, earthquake, landslide, and wind) and human factors (improper design and construction method, collision, overloading, fire, corrosion, and lack of inspection and maintenance).Template:Sfn Over time, bridge failures have led to significant improvements in bridge design, construction, and maintenance practices.[131] Before the advent of bridge engineering procedures based on rigorous, scientific principles, bridges frequently failed. Failures were most common in the mid-1800s, when the rapidly expanding railway networks were building hundreds of new bridges every year around the globe.Template:Sfn In the United States, 40 bridges per year failed in the 1870s, amounting to 25% of all bridges built in that decade.[132]

In the modern era, in spite of advances in bridge engineering methodologies, bridge failures continue to occur regularly.[133] In Australia, the King Street Bridge collapsed in 1962, a year after opening, due to improper welding techniques.Template:Sfn In Palau, the Koror–Babeldaob Bridge collapsed in 1996, three months after a repair operation made major changes to the bridge.Template:Sfn In 1998, the Turag-Bhakurta Bridge in Bangladesh collapsed due to river waters scouring away the soil around the bridge supports.Template:Sfn The Millennium Bridge in London opened in 2000, but closed two days later due to excessive swaying. It did not open until two years laterTemplate:Sndafter dampers were installed.[134] About half of all bridge failures in the early 21st century in the US were due to water-related causes, such as flood damage or scouring (water currents undermining the bridge supports).[135]

Society and culture

Signature bridges

A large bridge crossing a river, in nighttime, with skyscrapers in the background
The Dagu Bridge in China was designed to be a signature bridge.Template:Sfn

Many bridgesTemplate:Sndknown as signature bridgesTemplate:Sndare strongly identified with a particular community.[136]Template:Efn Large suspension bridges, in particular, are often regarded as iconic landmarks that symbolize the cities in which they are located. Notable examples include the Brooklyn Bridge in New York; the Golden Gate Bridge in San Francisco; the Clifton Suspension Bridge in Bristol; and the Széchenyi Chain Bridge in Budapest.Template:SfnTemplate:Efn Some visually impressive bridges, such as the Dagu Bridge in China, are designed with the express goal of creating a landmark for the host city.[137] The art historian Dan Cruickshank notes that some bridges have the ability to "transform a place a community and ... can make its mark on the landscape and in men's minds, capture the imagination, engender pride and sense of identity and define a time and place."Template:Sfn

Economic and environmental impact

Bridges can have a significant impactsTemplate:Sndboth positive and negativeTemplate:Snd on a community's environment, society, and economy. During the bridge design process, these effects may be modeled with sustainability methodologies such as life cycle sustainability assessment or building information modeling, and the results can be used to adjust the bridge's design to improve its effect on the environment, society, and economy.[138]

Positive effects of a new bridge can include shorter transport times, employment opportunities, improvements to social equity, improved productivity, and increases to the gross domestic product (GDP).[138] Construction of a new bridge can increase wages in the surrounding region, but can also increase income inequity between genders (men see larger wage gains than women) and between education levels (higher-educated persons see more gains that lower-educated persons).[139] In locales where flooding is common, bridges can increase overall income by providing reliable crossings across rivers.Template:Sfn In underdeveloped regions with mountainous topography, construction of bridges that cross deep valleys can bring major benefits to the communities they connect. Without bridges, such areas often have a core region that is more prosperous, surrounded by less developed peripheral regions. Building bridges over deep valleys can reduce developmental disparities between areas, as well as generate economic development, and improve accessibility to goods and services.Template:Sfn

Global warming can be exacerbated by the creation of a new bridge, because the production of concrete significantly contributes to the greenhouse effect.Template:SfnTemplate:Efn Although bridges can boost the economy of the surrounding region, they also increase environmental pollution proportionally.Template:Sfn Corruption is endemic in the construction industry (including bridge building) and the associated bribes and inefficiencies produce negative societal and economic consequences.[140] Bridges that carry highways can result in increased vehicular collisions, which have economic costs (medical care and lost productivity) averaging over Template:Euro each.[141]

Art and culture

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Template:Easy CSS image crop Bridges occur extensively in art, legend, and literature, often employed as metaphors or symbols of human accomplishment, lifespan, or experience.[142] In Norse mythology, the home of the godsTemplate:SndAsgardTemplate:Sndis connected to the earth by Bifröst, a rainbow bridge.Template:Sfn Many bridges in Europe are named Devil's Bridge, and in some cases have folkloric stories that explain why the bridge is associated with the devil.Template:Sfn Christian legend holds that St. Bénézet lifted a huge boulder to begin construction of the Pont Saint-Bénézet bridge, and went on to found the apocryphal Bridge-Building Brotherhood.Template:Sfn Bridges feature prominently in paintingsTemplate:Sndoften in the backgroundTemplate:Sndas in the Mona Lisa.Template:Sfn

In the modern era, bridges continue to feature prominently in culture. Bridges are often the setting for pageants, celebrations, and processions.Template:Sfn Authors have used bridges as the centerpiece of novels, such as The Bridge on the Drina by Ivo Andrić and Thornton Wilder's The Bridge of San Luis Rey.Template:Sfn British poet Philip Larkin, inspired by the construction of the Humber Bridge near his home, wrote "Bridge for the Living" in 1981.[143] Neighboring nations have chosen to designate some shared bridges as friendship bridges or peace bridges.[144]Template:Efn In 1996, the European Commission held a competition to select art for the euro banknotes. Robert Kalina, an Austrian designer, won with a set of illustrations of bridges, chosen because they symbolize links between states in the union and paths to the future.[145]

Profession and regulation

Script error: No such module "labelled list hatnote". The profession of civil engineeringTemplate:Sndwhich includes the discipline of bridge buildingTemplate:Snd began to be formalized in the 1700s when a school of engineering was created in France within the Corps des Ponts et Chaussées at the École de Paris, under the direction of Jacques Gabriel.Template:Sfn In 1747 the first school dedicated to bridge building was founded: the École Nationale des Ponts et Chaussées led by French engineers Daniel-Charles Trudaine and Jean-Rodolphe Perronet.Template:Sfn The first professional organization focused on civil engineering was the Institution of Civil Engineers founded in 1818 in the UK, initially led by Thomas Telford.Template:Sfn

In the modern era, bridge engineering is regulated by national organizations, such as the National Council of Examiners for Engineering and Surveying (US), the Canadian Council of Professional Engineers (Canada), and the Engineering Council (UK).Template:Sfn In many countries, bridge engineers must be licensed or meet minimal educational requirements.Template:Sfn Some countries require engineers to pass qualification examinations, for example, in the US engineers must pass the Fundamentals of Engineering exam followed by the Principles and Practice of Engineering exam.Template:Sfn In Poland, bridge engineers are required to obtain certification by accumulating several years of experience under a senior engineer, and passing an exam administered by the Polish Chamber of Civil Engineers.Template:Sfn International cooperation in the field of engineering is facilitated by the World Federation of Engineering Organizations.Template:Sfn

Suicide

Suicides are sometimes carried out by jumping off bridges. This method can account for 20% to 70% of suicides in urban areas with access to tall bridges.Template:Efn In some regions, suicide by jumping disproportionately affects young adults, who tend to have lower inhibitory control. Specific bridges can gain notoriety and attract persons experiencing a suicidal crisis, which creates a feedback loop. High-risk bridges often have suicide prevention barriers installed,Template:Efn which dramatically decrease the suicide rate on the bridge.Template:Efn Installing barriers on a high-risk bridge generally reduces the jumping suicide rate in a region, although in some instances, other bridges become substitutes.Template:Sfn

References

Footnotes

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Citations

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Sources

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