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A bridge is a structure built to
span Span may refer to: Science, technology and engineering * Span (unit), the width of a human hand * Span (engineering), a section between two intermediate supports * Wingspan, the distance between the wingtips of a bird or aircraft * Sorbitan ester ...
a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way 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 Terrain or relief (also topographical relief) involves the vertical and horizontal dimensions of land surface. The term bathymetry is used to describe underwater relief, while hypsometry studies terrain relative to sea level. The Latin wo ...
where the bridge is constructed and anchored, and the material used to make it, and the funds available to build it. The earliest bridges were likely made with fallen trees and
stepping stones Stepping stones or stepstones are sets of stones arranged to form an improvised causeway that allows a pedestrian to cross a natural watercourse such as a river; or a water feature in a garden where water is allowed to flow between stone steps. U ...
. The
Neolithic The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several p ...
people built
boardwalk A boardwalk (alternatively board walk, boarded path, or promenade) is an elevated footpath, walkway, or causeway built with wooden planks that enables pedestrians to cross wet, fragile, or marshy land. They are also in effect a low type of brid ...
bridges across marshland. The Arkadiko Bridge (dating from the 13th century BC, in the Peloponnese) is one of the oldest
arch bridge An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side. A viaduct ...
s still in existence and use.


Etymology

The ''
Oxford English Dictionary The ''Oxford English Dictionary'' (''OED'') is the first and foundational historical dictionary of the English language, published by Oxford University Press (OUP). It traces the historical development of the English language, providing a co ...
'' traces the origin of the word ''bridge'' to an
Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlers in the mid-5th c ...
word ''brycg'', of the same meaning. The word can be traced directly back to Proto-Indo-European ''*bʰrēw-.'' The word for the card game of the same name has a different origin.


History

The simplest and earliest types of bridges were
stepping stones Stepping stones or stepstones are sets of stones arranged to form an improvised causeway that allows a pedestrian to cross a natural watercourse such as a river; or a water feature in a garden where water is allowed to flow between stone steps. U ...
.
Neolithic The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several p ...
people also built a form of
boardwalk A boardwalk (alternatively board walk, boarded path, or promenade) is an elevated footpath, walkway, or causeway built with wooden planks that enables pedestrians to cross wet, fragile, or marshy land. They are also in effect a low type of brid ...
across
marshes A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found at ...
; examples of such bridges include the
Sweet Track The Sweet Track is an ancient trackway, or causeway, in the Somerset Levels, England, named after its finder, Ray Sweet. It was built in 3807 BC (determined using dendrochronology) and is the second-oldest timber trackway discovered in ...
and the
Post Track The Post Track is an ancient causeway in the valley of the River Brue on the Somerset Levels, England. It dates from around 3838 BCE, making it some 30 years older than the Sweet Track in the same area. Various sections have been scheduled as a ...
in England, approximately 6000 years old. Undoubtedly, ancient people would also have used
log bridge A log bridge is a timber bridge that uses logs that fall naturally or are intentionally felled or placed across streams. The first man-made bridges with significant span were probably intentionally felled trees. The use of emplaced logs is now ...
s; that is a
timber bridge A timber bridge or wooden bridge is a bridge that uses timber or wood as its principal structural material. One of the first forms of bridge, those of timber have been used since ancient times. History The most ancient form of timber bridge is ...
that fall naturally or are intentionally felled or placed across streams. Some of the first
man-made Artificiality (the state of being artificial or manmade) is the state of being the product of intentional human manufacture, rather than occurring naturally through processes not involving or requiring human activity. Connotations Artificiality ...
bridges with significant span were probably intentionally felled trees. Among the oldest
timber bridge A timber bridge or wooden bridge is a bridge that uses timber or wood as its principal structural material. One of the first forms of bridge, those of timber have been used since ancient times. History The most ancient form of timber bridge is ...
s is the
Holzbrücke Rapperswil-Hurden Holzbrücke Rapperswil-Hurden is a wooden pedestrian bridge between the city of Rapperswil and the village of Hurden crossing the upper Lake Zürich (''Obersee'') in Switzerland. The prehistoric timber piles discovered to the west of the Seedam ...
crossing upper
Lake Zürich __NOTOC__ Lake Zurich ( Swiss German/ Alemannic: ''Zürisee''; German: ''Zürichsee''; rm, Lai da Turitg) is a lake in Switzerland, extending southeast of the city of Zürich. Depending on the context, Lake Zurich or ''Zürichsee'' can be used ...
in Switzerland; the prehistoric timber piles discovered to the west of the
Seedamm The Rapperswil Seedamm is the partially artificial causeway and bridge at the most narrow area of Lake Zurich, between Hurden (SZ) and Rapperswil (SG). The Seedamm carries a road and a railway across the lake, with the railway being used by the ...
date back to 1523 BC. The first wooden footbridge led across Lake Zürich, followed by several reconstructions at least until the late 2nd century AD, when the
Roman Empire The Roman Empire ( la, Imperium Romanum ; grc-gre, Βασιλεία τῶν Ῥωμαίων, Basileía tôn Rhōmaíōn) was the post- Republican period of ancient Rome. As a polity, it included large territorial holdings around the Mediter ...
built a wooden bridge. Between 1358 and 1360,
Rudolf IV, Duke of Austria Rudolf IV (1 November 1339 – 27 July 1365), also called Rudolf the Founder (german: der Stifter), was a scion of the House of Habsburg who ruled as duke of Austria (self-proclaimed archduke), Styria and Carinthia from 1358, as well as count ...
, built a 'new' wooden bridge across the lake that has been used to 1878 – measuring approximately in length and wide. On April 6, 2001, the reconstructed wooden footbridge was opened, being the longest wooden bridge in Switzerland. The Arkadiko Bridge is one of four Mycenaean corbel arch bridges part of a former network of roads, designed to accommodate chariots, between the fort of Tiryns and town of Epidauros in the Peloponnese, in southern Greece. Dating to the Greek
Bronze Age The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second prin ...
(13th century BC), it is one of the oldest
arch bridge An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side. A viaduct ...
s still in existence and use. Several intact arched stone bridges from the
Hellenistic era In Classical antiquity, the Hellenistic period covers the time in Mediterranean history after Classical Greece, between the death of Alexander the Great in 323 BC and the emergence of the Roman Empire, as signified by the Battle of Actium in 3 ...
can be found in the Peloponnese. The greatest bridge builders of antiquity were the
ancient Romans In modern historiography, ancient Rome refers to Roman civilisation from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD. It encompasses the Roman Kingdom (753–509 ...
. The Romans built arch bridges and
aqueducts Aqueduct may refer to: Structures *Aqueduct (bridge), a bridge to convey water over an obstacle, such as a ravine or valley *Navigable aqueduct, or water bridge, a structure to carry navigable waterway canals over other rivers, valleys, railw ...
that could stand in conditions that would damage or destroy earlier designs. Some stand today. An example is the
Alcántara Bridge The Alcántara Bridge (also known as Trajan's Bridge at Alcantara) is a Roman bridge at Alcántara, in Extremadura, Spain. Alcántara is from the Arabic word ''al-Qantarah'' (القنطرة) meaning "the arch". The stone arch bridge was bui ...
, built over the river
Tagus The Tagus ( ; es, Tajo ; pt, Tejo ; see below) is the longest river in the Iberian Peninsula. The river rises in the Montes Universales near Teruel, in mid-eastern Spain, flows , generally west with two main south-westward sections, to e ...
, in
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...
. The Romans also used
cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mi ...
, which reduced the variation of strength found in natural stone. One type of cement, called
pozzolana Pozzolana or pozzuolana ( , ), also known as pozzolanic ash ( la, pulvis puteolanus), is a natural siliceous or siliceous- aluminous material which reacts with calcium hydroxide in the presence of water at room temperature (cf. pozzolanic reacti ...
, consisted of water,
lime Lime commonly refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany ...
, sand, and
volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic ...
. Brick and mortar bridges were built after the Roman era, as the technology for cement was lost (then later rediscovered). In India, the '' Arthashastra'' treatise by
Kautilya Chanakya (Sanskrit: चाणक्य; IAST: ', ; 375–283 BCE) was an ancient Indian polymath who was active as a teacher, author, strategist, philosopher, economist, jurist, and royal advisor. He is traditionally identified as Kauṭilya o ...
mentions the construction of dams and bridges. A
Mauryan The Maurya Empire, or the Mauryan Empire, was a geographically extensive Iron Age historical power in the Indian subcontinent based in Magadha, having been founded by Chandragupta Maurya in 322 BCE, and existing in loose-knit fashion until 1 ...
bridge near
Girnar Girnar is an ancient hill in Junagadh, Gujarat, India. Geology Mount Girnar is a major igneous plutonic complex which intruded into the basalts towards the close of the Deccan Trap period. The rock types identified in this complex are ga ...
was surveyed by James Princep. The bridge was swept away during a flood, and later repaired by Puspagupta, the chief architect of emperor
Chandragupta I Chandragupta I (Gupta script: ''Cha-ndra-gu-pta'', r. c. 319–335 or 319–350 CE) was a king of the Gupta Empire, who ruled in northern and central India. His title ''Maharajadhiraja'' ("great king of kings") suggests that he was the firs ...
.Dutt, Romesh Chunder (2000). ''A History of Civilisation in Ancient India: Vol II'', Routledge, p. 46, . The use of stronger bridges using plaited bamboo and iron chain was visible in India by about the 4th century. A number of bridges, both for military and commercial purposes, were constructed by the Mughal administration in India. Although large Chinese bridges of wooden construction existed at the time of the
Warring States period The Warring States period () was an era in ancient Chinese history characterized by warfare, as well as bureaucratic and military reforms and consolidation. It followed the Spring and Autumn period and concluded with the Qin wars of conquest ...
, the oldest surviving stone bridge in China is the
Zhaozhou Bridge The Anji Bridge () is the world's oldest open-spandrel segmental arch bridge of stone construction.This title strictly applies only to the ''sum of attributes given'' (O’Connor, Colin: ''Roman Bridges'', Cambridge University Press 1993, , p.171) ...
, 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 A spandrel is a roughly triangular space, usually found in pairs, between the top of an arch and a rectangular frame; between the tops of two adjacent arches or one of the four spaces between a circle within a square. They are frequently fill ...
stone segmental arch bridge. European segmental arch bridges date back to at least the
Alconétar Bridge The Alconétar Bridge (Spanish: ''Puente de Alconétar''), also known as Puente de Mantible, was a Roman segmental arch bridge in the Extremadura region, Spain. The ancient structure, which featured flattened arches with a span-to-rise ratio of ...
(approximately 2nd century AD), while the enormous Roman era Trajan's Bridge (105 AD) featured open-spandrel segmental arches in wooden construction. Rope bridges, a simple type of suspension bridge, were used by the
Inca The Inca Empire (also known as the Incan Empire and the Inka Empire), called ''Tawantinsuyu'' by its subjects, (Quechua for the "Realm of the Four Parts",  "four parts together" ) was the largest empire in pre-Columbian America. The admin ...
civilization in the
Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
mountains of South America, just prior to European colonization in the 16th century. The Ashanti built bridges over streams and rivers. 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. During the 18th century, there were many innovations in the design of timber bridges by
Hans Ulrich Grubenmann Several members of the Swiss family Grubenmann were famous as carpenters and civil engineers in the 18th century. The sons were innovators in bridge construction. (1668 – 27 June 1736) lived all his life in Gstalden, Appenzell Ausserrhoden whe ...
, Johannes Grubenmann, and others. The first book on bridge engineering was written by Hubert Gautier in 1716. A major breakthrough in bridge technology came with the erection of
the Iron Bridge The Iron Bridge is a cast iron arch bridge that crosses the River Severn in Shropshire, England. Opened in 1781, it was the first major bridge in the world to be made of cast iron. Its success inspired the widespread use of cast iron as a st ...
in Shropshire, England in 1779. It used
cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impur ...
for the first time as arches to cross the
river Severn , name_etymology = , image = SevernFromCastleCB.JPG , image_size = 288 , image_caption = The river seen from Shrewsbury Castle , map = RiverSevernMap.jpg , map_size = 288 , map_c ...
. With the
Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going f ...
in the 19th century,
truss A truss is an assembly of ''members'' such as beams, connected by ''nodes'', that creates a rigid structure. In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assembl ...
systems of
wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which give it a wood-like "grain" ...
were developed for larger bridges, but iron does not have the
tensile strength Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials t ...
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 Alexandre Gustave Eiffel (born Bonickhausen dit Eiffel; ; ; 15 December 1832 – 27 December 1923) was a French civil engineer. A graduate of École Centrale des Arts et Manufactures, he made his name with various bridges for the French railway ...
. In Canada and the United States, numerous timber
covered bridges A covered bridge is a timber-truss bridge with a roof, decking, and siding, which in most covered bridges create an almost complete enclosure. The purpose of the covering is to protect the wooden structural members from the weather. Uncovered woo ...
were built in the late 1700s to the late 1800s, reminiscent of earlier designs in
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
and Switzerland. Some covered bridges were also built in Asia. 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. 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 ''The Bridges of Madison County'' (also published as ''Love in Black and White'') is a 1992 best-selling romance novel by American writer Robert James Waller that tells the story of a married Italian-American woman (WWII war bride) living on a ...
''. In 1927
welding Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as bra ...
pioneer Stefan Bryła designed the first welded
road bridge A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...
in the world, the
Maurzyce Bridge The Maurzyce Bridge ( Polish: ''Most w Maurzycach'') is a bridge over the Słudwia River (tributary of Bzura) in Central Poland. It is known as the first entirely welded road bridge and the second welded bridge of any category in the world. The b ...
which was later built across the river Słudwia at Maurzyce near
Łowicz Łowicz is a town in central Poland with 27,896 inhabitants (2020). It is situated in the Łódź Voivodeship (since 1999); previously, it was in Skierniewice Voivodeship (1975–1998). Together with a nearby station of Bednary, Łowicz is a ma ...
, Poland in 1929. In 1995, the
American Welding Society The American Welding Society (AWS) was founded in 1919 as a non-profit organization to advance the science, technology and application of welding and allied joining and cutting processes, including brazing, soldering and thermal spraying. Headq ...
presented the Historic Welded Structure Award for the bridge to Poland.


Types of bridges

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


Structure types

Bridges may be classified by how the actions of
tension Tension may refer to: Science * Psychological stress * Tension (physics), a force related to the stretching of an object (the opposite of compression) * Tension (geology), a stress which stretches rocks in two opposite directions * Voltage or el ...
,
compression Compression may refer to: Physical science *Compression (physics), size reduction due to forces *Compression member, a structural element such as a column *Compressibility, susceptibility to compression * Gas compression *Compression ratio, of a ...
,
bending In applied mechanics, bending (also known as flexure) characterizes the behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element. The structural element is assumed to ...
,
torsion Torsion may refer to: Science * Torsion (mechanics), the twisting of an object due to an applied torque * Torsion of spacetime, the field used in Einstein–Cartan theory and ** Alternatives to general relativity * Torsion angle, in chemistry Bi ...
and
shear Shear may refer to: Textile production *Animal shearing, the collection of wool from various species **Sheep shearing *The removal of nap during wool cloth production Science and technology Engineering *Shear strength (soil), the shear strength ...
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 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. Some Engineers sub-divide 'beam' bridges into slab, beam-and-slab and box girder on the basis of their cross-section. A slab can be solid or 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. A box-girder cross-section consists of a single-cell or multi-cellular box. In recent years, integral bridge construction has also become popular.


Fixed or movable bridges

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 A Bailey bridge is a type of portable, pre-fabricated, truss bridge. It was developed in 1940–1941 by the British for military use during the Second World War and saw extensive use by British, Canadian and American military engineering units. ...
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 A moveable bridge, or movable bridge, is a bridge that moves to allow passage for boats or barges. In American English, the term is synonymous with , and the latter is the common term, but drawbridge can be limited to the narrower, historical d ...
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. 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.


Double-decked bridges

Double-decked (or double-decker) bridges have two levels, such as the
George Washington Bridge The George Washington Bridge is a double-decked suspension bridge spanning the Hudson River, connecting Fort Lee, New Jersey, with Manhattan in New York City. The bridge is named after George Washington, the first president of the United S ...
, connecting
New York City New York, often called New York City or NYC, is the most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the most densely populated major city in the Un ...
to Bergen County,
New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...
, US, as the world's busiest bridge, carrying 102 million vehicles annually;
truss A truss is an assembly of ''members'' such as beams, connected by ''nodes'', that creates a rigid structure. In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assembl ...
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 Tsing Ma Bridge is a bridge in Hong Kong. It is the world's 16th-longest span suspension bridge, and was the second longest at time of completion. The bridge was named after the two islands it connects, namely Tsing Yi and Ma Wan. It has tw ...
and
Kap Shui Mun Bridge The Kap Shui Mun Bridge (KSMB) in Hong Kong, part of Lantau Link of Route 8, is one of the longest cable-stayed bridges in the world that transports both road and railway traffic, with the upper deck used for motor vehicles and the lower deck u ...
in
Hong Kong Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China (abbr. Hong Kong SAR or HKSAR), is a city and special administrative region of China on the eastern Pearl River Delta i ...
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 in
Minneapolis Minneapolis () is the largest city in Minnesota, United States, and the county seat of Hennepin County. The city is abundant in water, with thirteen lakes, wetlands, the Mississippi River, creeks and waterfalls. Minneapolis has its origins ...
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 The University of Minnesota, formally the University of Minnesota, Twin Cities, (UMN Twin Cities, the U of M, or Minnesota) is a public land-grant research university in the Twin Cities of Minneapolis and Saint Paul, Minnesota, United States. ...
). Likewise, in
Toronto Toronto ( ; or ) is the capital city of the Canadian province of Ontario. With a recorded population of 2,794,356 in 2021, it is the most populous city in Canada and the fourth most populous city in North America. The city is the anch ...
, the
Prince Edward Viaduct The Prince Edward Viaduct System, commonly referred to as the Bloor Viaduct, is the name of a truss arch bridge system in Toronto, Ontario, Canada, connecting Bloor Street East, on the west side of the system, with Danforth Avenue on the east. The ...
has five lanes of motor traffic, bicycle lanes, and sidewalks on its upper deck; and a pair of tracks for the Bloor–Danforth subway line on its lower deck. The western span of the
San Francisco–Oakland Bay Bridge The San Francisco–Oakland Bay Bridge, known locally as the Bay Bridge, is a complex of bridges spanning San Francisco Bay in California. As part of Interstate 80 and the direct road between San Francisco and Oakland, it carries about 260,000 ...
also has two levels.
Robert Stephenson Robert Stephenson FRS HFRSE FRSA DCL (16 October 1803 – 12 October 1859) was an English civil engineer and designer of locomotives. The only son of George Stephenson, the "Father of Railways", he built on the achievements of his father ...
's High Level Bridge across the River Tyne in
Newcastle upon Tyne Newcastle upon Tyne ( RP: , ), or simply Newcastle, is a city and metropolitan borough in Tyne and Wear, England. The city is located on the River Tyne's northern bank and forms the largest part of the Tyneside built-up area. Newcastle is ...
, 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 Britannia Bridge ( cy, Pont Britannia) is a bridge across the Menai Strait between the island of Anglesey and the mainland of Wales. It was originally designed and built by the noted railway engineer Robert Stephenson as a tubular bridge of w ...
over the Menai Strait and
Craigavon Bridge The Craigavon Bridge is one of three bridges in Derry, Northern Ireland. It crosses the River Foyle further south than the Foyle Bridge and Peace Bridge. It is one of only a few double-decker road bridges in Europe. It was named after Lord Craiga ...
in Derry,
Northern Ireland Northern Ireland ( ga, Tuaisceart Éireann ; sco, label= Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is variously described as a country, province or region. Nort ...
. The Oresund Bridge between
Copenhagen Copenhagen ( or .; da, København ) is the capital and most populous city of Denmark, with a proper population of around 815.000 in the last quarter of 2022; and some 1.370,000 in the urban area; and the wider Copenhagen metropolitan ar ...
and
Malmö Malmö (, ; da, Malmø ) is the largest city in the Swedish county (län) of Scania (Skåne). It is the third-largest city in Sweden, after Stockholm and Gothenburg, and the sixth-largest city in the Nordic region, with a municipal pop ...
consists of a four-lane highway on the upper level and a pair of railway tracks at the lower level.
Tower Bridge Tower Bridge is a Grade I listed combined bascule and suspension bridge in London, built between 1886 and 1894, designed by Horace Jones and engineered by John Wolfe Barry with the help of Henry Marc Brunel. It crosses the River Thames clos ...
in London is different example of a double-decked bridge, with the central section consisting of a low-level bascule span and a high-level
footbridge A footbridge (also a pedestrian bridge, pedestrian overpass, or pedestrian overcrossing) is a bridge designed solely for pedestrians.''Oxford English Dictionary'' While the primary meaning for a bridge is a structure which links "two points at a ...
.


Viaducts

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 The Lake Pontchartrain Causeway (french: Chaussée du lac Pontchartrain), also known simply as The Causeway, is a fixed link composed of two parallel bridges crossing Lake Pontchartrain in southeastern Louisiana, United States. The longer of th ...
and
Millau Viaduct The Millau Viaduct (french: Viaduc de Millau, ) is a multispan cable-stayed bridge completed in 2004 across the gorge valley of the Tarn near (west of) Millau in the Aveyron department in the Occitanie Region, in Southern France. The design t ...
.


Multi-way bridge

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,
Margaret Bridge Margaret Bridge or Margit híd (sometimes ''Margit Bridge'') is a three-way bridge in Budapest, Hungary, connecting Buda and Pest across the Danube and linking Margaret Island to the banks. It is the second-northernmost and second-oldest publi ...
, and Zanesville Y-Bridge are examples.


Bridge types by use

A bridge can be categorized by what it is designed to carry, such as trains, pedestrian or road traffic (road bridge), a pipeline or waterway for water transport or barge traffic. An 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. A bridge can carry overhead power lines as does the
Storstrøm Bridge The Storstrøm Bridge ( da, Storstrømsbroen, ) is a road and railway arch bridge that crosses Storstrømmen between the islands of Falster and Masnedø in Denmark. Together with Masnedsund Bridge it connects Falster and Zealand (''Sjælland''). ...
. Some bridges accommodate other purposes, such as the tower of
Nový Most Most SNP ("Bridge of the Slovak National Uprising"), commonly referred to as Most Slovenského národného povstania or the UFO Bridge, and named Nový most ("New Bridge") from 1993 to 2012, is a road bridge over the Danube in Bratislava, the c ...
Bridge in Bratislava, which features a restaurant, or a
bridge-restaurant A bridge restaurant or restaurant bridge is a restaurant, usually indoors, built like a bridge over a road, mostly over freeways or motorways. It usually provides access from both sides of the road without the need of crossing the road by tunnel or ...
which is a bridge built to serve as a restaurant. Other suspension bridge towers carry transmission antennas. Conservationists use wildlife overpasses to reduce habitat fragmentation and animal-vehicle collisions. The first 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. 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 A suicide bridge is a bridge used frequently by people to end their lives, most typically by jumping off and into the water or ground below. A fall from the height of a tall bridge into water may be fatal, although some people have survived jump ...
s.


Bridge types by material

The materials used to build the structure are also used to categorize bridges. Until the end of the 18th century, bridges were made out of timber, stone and masonry. Modern bridges are currently built in concrete, steel, fiber reinforced polymers (FRP), stainless steel or combinations of those materials. Living bridges have been constructed of live plants such as ''
Ficus elastica ''Ficus elastica'', the rubber fig, rubber bush, rubber tree, rubber plant, or Indian rubber bush, Indian rubber tree, is a species of flowering plant in the family Moraceae, native to eastern parts of South and Southeast Asia. It has become nat ...
'' tree roots in India and
wisteria ''Wisteria'' is a genus of flowering plants in the legume family, Fabaceae (Leguminosae), that includes ten species of woody twining vines that are native to China, Japan, Korea, Vietnam, Southern Canada, the Eastern United States, and north ...
vines in Japan.


Analysis and design

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. Bridges are first analysed; the bending moment and shear force distributions are calculated due to the applied loads. For this, the
finite element method The finite element method (FEM) is a popular method for numerically solving differential equations arising in engineering and mathematical modeling. Typical problem areas of interest include the traditional fields of structural analysis, heat ...
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. 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 Prestressed concrete is a form of concrete used in construction. It is substantially "prestressed" ( compressed) during production, in a manner that strengthens it against tensile forces which will exist when in service. Post-tensioned concreted i ...
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 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.


Aesthetics

Most bridges are utilitarian in appearance, but in some cases, the appearance of the bridge can have great importance. Often, this is the case with a large bridge that serves as an entrance to a city, or crosses over a main harbor entrance. These are sometimes known as signature bridges. Designers of bridges in parks and along parkways often place more importance on aesthetics, as well. Examples include the stone-faced bridges along the
Taconic State Parkway The Taconic State Parkway (often called the Taconic or the TSP and known administratively as New York State Route 987G or NY 987G) is a parkway between Kensico Dam and Chatham, the longest in the U.S. state of New York. It follows ...
in New York. Generally bridges are 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. 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 A moon bridge (月桥), also known as “''sori-bashi"'' (反り橋) in Japanese, or as a drum bridge (“taiko-bashi” 太鼓橋),Liu, Yan (2020-09-01). "A full moon in another land: The Moon Bridge in the Japanese garden of the Huntington Libra ...
, 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 The Forbidden City () is a palace complex in Dongcheng District, Beijing, China, at the center of the Imperial City of Beijing. It is surrounded by numerous opulent imperial gardens and temples including the Zhongshan Park, the sacrifi ...
in
Beijing } Beijing ( ; ; ), alternatively romanized as Peking ( ), is the capital of the People's Republic of China. It is the center of power and development of the country. Beijing is the world's most populous national capital city, with over 21 ...
, China. The central bridge was reserved exclusively for the use of the Emperor and Empress, with their attendants.


Bridge maintenance

The estimated life of bridges varies between 25 and 80 years depending on location and material. However, 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 and is higher in some countries than spending on new bridges. The lifetime of welded steel bridges can be significantly extended by aftertreatment of the weld transitions. This results in a potential high benefit, using existing bridges far beyond the planned lifetime.


Bridge traffic loading

While the response of a bridge to the applied loading is well understood, the applied traffic loading itself is still the subject of research. 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 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 A return period, also known as a recurrence interval or repeat interval, is an average time or an estimated average time between events such as earthquakes, floods, landslides, or river discharge flows to occur. It is a statistical measurement typ ...
. Notably, in Europe, it is the maximum value expected in 1000 years. 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 (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, side-by-side (same direction) lanes, traffic growth, permit/non-permit vehicles 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, 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.


Traffic loading on long span bridges

Most bridge standards are only applicable for short and medium spans - 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 (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. Others have used microsimulation to generate typical clusters of vehicles on the bridge.


Bridge vibration

Bridges vibrate under load and this contributes, to a greater or lesser extent, to the stresses. 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 The Tacoma Narrows Bridge is a pair of twin suspension bridges that span the Tacoma Narrows strait of Puget Sound in Pierce County, Washington. The bridges connect the city of Tacoma with the Kitsap Peninsula and carry State Route 16 (know ...
that collapsed shortly after being constructed due to excessive vibration. More recently, the
Millennium Bridge Several bridges are known as the Millennium Bridge: * in the United Kingdom **Gateshead Millennium Bridge ** Lune Millennium Bridge, Lancaster ** Millennium Bridge, Glasgow ** Millennium Bridge, London ** Millennium Bridge (Salford Quays) ** Teesqua ...
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).


Vehicle-bridge dynamic interaction

There have been many studies of the dynamic interaction between vehicles and bridges during vehicle crossing events. Fryba 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. The concern is that one of the many natural frequencies associated with the vehicle will resonate with the bridge first natural frequency. The vehicle-related frequencies include body bounce and axle hop but there are also pseudo-frequencies associated with the vehicle's speed of crossing and there are many frequencies associated with the surface profile. 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.


Bridge failures

The failure of bridges is of special concern for
structural engineers Structural engineers analyze, design, plan, and research structural components and structural systems to achieve design goals and ensure the safety and comfort of users or occupants. Their work takes account mainly of safety, technical, economic ...
in trying to learn lessons vital to bridge design, construction and maintenance. The failure of bridges first assumed national interest in Britain during the
Victorian era In the history of the United Kingdom and the British Empire, the Victorian era was the period of Queen Victoria's reign, from 20 June 1837 until her death on 22 January 1901. The era followed the Georgian period and preceded the Edwardia ...
when many new designs were being built, often using new materials, with some of them failing catastrophically. In the United States, the
National Bridge Inventory The National Bridge Inventory (NBI) is a database, compiled by the Federal Highway Administration, with information on all bridges and tunnels in the United States that have roads passing above or below them. That is similar to the grade-crossing ...
tracks the structural evaluations of all bridges, including designations such as "structurally deficient" and "functionally obsolete".


Bridge health monitoring

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. Many types of sensors are used, including strain transducers,
accelerometer An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is acc ...
s, 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. An option for structural-integrity monitoring is "non-contact monitoring", which uses the Doppler effect (Doppler shift). A
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fi ...
beam from a
Laser Doppler Vibrometer A laser Doppler vibrometer (LDV) is a scientific instrument that is used to make non-contact vibration measurements of a surface. The laser beam from the LDV is directed at the surface of interest, and the vibration amplitude and frequency are extr ...
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. 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. Snapshots in time of the external condition of a bridge can be recorded using Lidar to aid bridge inspection. 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. 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. These vehicles can be equipped with accelerometers, gyrometers, Laser Doppler Vibrometers and some even have the capability to apply a resonant force to the road surface in order to dynamically excite the bridge at its resonant frequency.


Visual index


See also

*
Air draft Air draft (or air draught) is the distance from the surface of the water to the highest point on a vessel. This is similar to the " deep draft" of a vessel which is measured from the surface of the water to the deepest part of the hull below th ...
*
Architectural engineering Architectural engineers apply and theoretical knowledge to the engineering design of buildings and building systems. The goal is to engineer high performance buildings that are sustainable, economically viable and ensure the safety health. Archi ...
* Bridge chapel *
Bridge tower A bridge tower (german: Brückenturm) was a type of fortified tower built on a bridge. They were typically built in the period up to early modern times as part of a city or town wall or castle. There is usually a tower at both ends of the brid ...
*
Bridge to nowhere A bridge to nowhere is a bridge where one or both ends are broken, incomplete, or unconnected to any roads. If it is an overpass or an interchange, the term overpass to nowhere or interchange to nowhere may be used respectively. There are fi ...
* Bridges Act *
BS 5400 BS 5400 was a British Standard code of practice for the design and construction of steel, concrete and composite bridges. It was applicable to highway, railway and pedestrian bridges. It has now been replaced by the European standard, BS EN 1991-2_ ...
* Causeway * Coal trestle *
Covered bridges A covered bridge is a timber-truss bridge with a roof, decking, and siding, which in most covered bridges create an almost complete enclosure. The purpose of the covering is to protect the wooden structural members from the weather. Uncovered woo ...
*
Cross-sea traffic ways Cross-sea traffic ways are vehicle or railroad traffic ways across the sea. Such traffic ways could include bridges or tunnels. Sea bridges Existing sea bridges * Anping Bridge (China) * Donghai Bridge (China) *Haicang Bridge (China) *Hangzhou Ba ...
* Culvert * Deck * Devil's Bridge *
Footbridge A footbridge (also a pedestrian bridge, pedestrian overpass, or pedestrian overcrossing) is a bridge designed solely for pedestrians.''Oxford English Dictionary'' While the primary meaning for a bridge is a structure which links "two points at a ...
*
Jet bridge A jet bridge (also termed jetway, jetwalk, airgate, gangway, aerobridge/airbridge, skybridge, finger, airtube, expedited suspended passenger entry system (E-SPES), or its official industry name passenger boarding bridge (PBB)) is an enclosed, ...
* Landscape architecture *
Megaproject A megaproject is an extremely large-scale investment project. According to the ''Oxford Handbook of Megaproject Management'', "Megaprojects are large-scale, complex ventures that typically cost $1 billion or more, take many years to develop and ...
*
Military bridge The following is a partial list of ''Military bridges'' * AM 50 * Armoured vehicle-launched bridge * Bailey bridge * Callender-Hamilton bridge *DSB Dry Support Bridge * Mabey Logistic Support Bridge * MGB Medium Girder Bridge * Pontoon bridge S ...
s * Orphan bridge * Outline of bridges * Overpass *
Pontoon bridge A pontoon bridge (or ponton bridge), also known as a floating bridge, uses floats or shallow-draft boats to support a continuous deck for pedestrian and vehicle travel. The buoyancy of the supports limits the maximum load that they can carry. ...
*
Rigid-frame bridge A Rigid-frame bridge is a bridge in which the superstructure and substructure are rigidly connected to act as a continuous unit. Typically, the structure is cast monolithically, making the structure continuous from deck to foundation. The conn ...
*
Structure gauge A structure gauge, also called the minimum clearance outline, is a diagram or physical structure that sets limits to the extent that bridges, tunnels and other infrastructure can encroach on rail vehicles. It specifies the height and width of pl ...
*
Transporter bridge A transporter bridge, also known as a ferry bridge or aerial transfer bridge, is a type of movable bridge that carries a segment of roadway across a river. The gondola is slung from a tall span by wires or a metal frame. The design has been us ...
*
Tensegrity Tensegrity, tensional integrity or floating compression is a structural principle based on a system of isolated components under compression inside a network of continuous tension, and arranged in such a way that the compressed members (usua ...
*
Trestle bridge A trestle bridge is a bridge composed of a number of short spans supported by closely spaced frames. A trestle (sometimes tressel) is a rigid frame used as a support, historically a tripod used to support a stool or a pair of isosceles triangl ...
*
Tunnel A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...


References


Further reading

* Bagher Shemirani, Alireza. ''Experimental and numerical studies of concrete bridge decks using ultra high-performance concrete and reinforced concrete''. Computers and Concrete, 29(6), p. 407-418, 2022. * Brown, David J. ''Bridges: Three Thousand Years of Defying Nature''. Richmond Hill, Ont: Firefly Books, 2005. . * Sandak, Cass R. ''Bridges''. An Easy-read modern wonders book. New York: F. Watts, 1983. . * Whitney, Charles S. ''Bridges of the World: Their Design and Construction''. Mineola, NY: Dover Publications, 2003. (Unabridged republication of ''Bridges : a study in their art, science, and evolution''. 1929.)


External links


Digital Bridge: Bridges of the Nineteenth Century
a collection of digitized books at Lehigh University
Structurae
– International Database and Gallery of Engineerings Structures with over 10000 Bridges.
U.S. Federal Highway Administration Bridge Technology

The Museum of Japanese Timber Bridges
Fukuoka University Fukuoka University is a private research university located in Fukuoka, Japan. The university has nine faculties with a total of around 20,000 students, 800 of whom are foreign. Its two campuses are in Nanakuma and Kitakyushu. Fukuoka Universit ...

"bridge-info.org": site for bridges
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