Bridge

This article is about the structure. For the card game, see Contract bridge. For other uses, see Bridge (disambiguation) and Bridges (disambiguation).

A bridge is a structure that crosses an obstacle such as a river, lake, railroad, road, ravine, or other barrier. The most important function of bridges is to transport cars, trains and pedestrians, but bridges can also accommodate pipelines, utility lines, buildings, wildlife, and canals.

Styles of bridges include arch, truss, beam, cantilever, suspension, and cable-stayed. Less common types of bridges are moveable bridges, double deck bridges, pontoon bridges, and military bridges. Bridges can also be categorized by their materials, which include wood, brick, stone, iron, steel, and concrete.

The history of bridge building reflects the evolution of humankind's construction technologies. The Romans and Sui dynasty Chinese were renowned for their bridges. The Renaissance in 1500s Europe brought a new emphasis on science and engineering leading to stronger bridges with longer spans. With the advent of the Industrial Revolution, iron became an important construction material for bridges. The abundance of inexpensive lumber in Canada and the United States caused timber bridges to be the most common type of bridge in those countries from the late 1700s to the late 1800s. Concrete – which was originally used within the Roman Empire – was improved with the invention of portland cement in the early 1800s, and replaced stone and masonry as the primary material for bridge foundations and abutments. Steel became a common building material for bridges in the late 1800s, leading to suspension bridges and cable-stayed bridges that spanned long distances.

The design of a new bridge must meet many requirements, including strength, traversing the obstacle, connecting to the transportation network, and providing safe transport for its users. Additional factors include cost, aesthetics, longevity, fire resistance, time available for construction, and experience of the builders. A bridge design must be strong enough to support many loads and tolerate many stresses, including the weight of the bridge itself, the traffic passing over the bridge, and all forces applied by the bridge's surroundings, including wind, rain, snow, earthquakes, mudslides, water currents, flooding, soil subsidence, frost heaving, temperature fluctuations, and collisions (such as a ship striking the support of a bridge over water). When designing a bridge, engineers use processes such as limit state design and finite element method.

History

Main article: History of bridges

Antiquity

The Pont du Gard aqueduct in France was built by the Roman Empire c. 40–60 AD, and is still standing.

The earliest forms of bridges were simple structures used to cross swamps and creeks, consisting of wooden boardwalks or logs. Pilings – which are critical elements of bridge construction – were used in Switzerland around 4,000 BC to support houses built over water.

Several corbel arch bridges were built c. 13th century BC by the Mycenaean Greece culture, including the Arkadiko Bridge, which is still in existence. In the 7th century BC, Sennacherib constructed stone aqueducts to carry water near the city of Ninevah. One of these aqueducts crossed a small valley at Jerwan with five corbelled arches, and was 280 meters (920 ft) long and 20 meters (66 ft) wide. In Babylonia in 626 BC, a bridge across the Euphrates was built with an estimated length of 120 to 200 meters (390 to 660 ft). In India, the Arthashastra treatise by Kautilya mentions the construction of dams and bridges. Ancient China has an extensive history of bridge construction, including cantilever bridges, rope bridges, and bridges built across floating boats.

The ancient Romans were prodigious bridge builders, renowned for their advanced engineering techniques and durable construction methods. Many Roman aqueducts – some still standing today – used a semicircular arch style. An example is the Alcántara Bridge, built over the river Tagus, in Spain. 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. Some Roman cements, particularly those containing volcanic ash, could be used in underwater applications. The enormous Trajan's Bridge (105 AD) featured open-spandrel segmental arches in wooden construction.

300 to 1500 AD

The Anji Bridge, which uses a shallow segmental arch, was built in China c. 600 AD.

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. 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.

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 major bridges inspired by religious influences. These included the Pont d'Avignon, bridges of the Durance river, the Old London Bridge, and the Ponte Vecchio in Florence.

Modern era

The superstructure of the West Montrose Covered Bridge is made of wood.

In 15th–16th century Europe, the Renaissance brought a new emphasis on science and engineering. 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. 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' Pont Neuf. A number of bridges, both for military and commercial purposes, were constructed in India by the Mughal administration in India. The Asante Empire in Africa built bridges over streams and rivers using tree trunks and beams.

In the late 1700s, the design of arch bridges was revolutionized in Europe by Jean-Rodolphe Perronet and John Rennie, who designed arches that were flatter than semi-circular Roman arches. These flatter arches enabled longer spans, fewer piers, and required less material. These designs were used for bridges such as Pont de la Concorde and New London Bridge.

With the advent of the Industrial Revolution, cast iron became an important construction material for bridges. Although cast iron was strong under compression, it was brittle, so it was supplanted by wrought iron – which was more ductile and better under tension. An early iron bridge was built in Shropshire, England crossing the river Severn.

The abundance of inexpensive lumber in Canada and the United States caused timber bridges to be the most common type of bridge in those countries 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.

The Sidi M'Cid Bridge in Algeria was the highest bridge in the world when it was built in 1912.

The mass production of steel in the late 1800's provided a new material for bridges, enabling lighter, stronger truss bridges and cantilever bridges, and producing cables strong enough to make suspension bridges and cable-stayed bridges feasible. Suspension bridges could span distances far longer than other bridge types – up to 2 kilometres (1.2 mi) – permitting transportation networks to cross deep waters that did not permit multiple piers or supports to be installed.

Concrete – which was originally used within the Roman Empire – was 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.

Straight, diagonal cables – known as "stays" – can be used to directly connect the bridge deck to bridge towers. Stays were used as supplemental supports in some suspension bridges in the 19th century – including the Brooklyn Bridge. Cable-stayed bridges – which used cable-stays as the exclusive means of support – became a popular bridge design following World War II.

Profession

See also: Regulation and licensure in engineering

The profession of civil engineering in general – and bridge building in particular – 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 Ecole de Paris, under the direction of Jacques Gabriel. In 1747 the first school dedicated to bridge building was founded, also in France: the École Nationale des Ponts et Chaussées led by engineers Daniel-Charles Trudaine and Jean-Rodolphe Perronet.

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). In many countries, bridge engineers must be licensed or meet minimal educational requirements. 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. International cooperation in the field of engineering is facilitated by the World Federation of Engineering Organizations.

Etymology

The Oxford English Dictionary traces the origin of the word bridge to the Old English word brycg, of Germanic origin. There is a possibility that the word can be traced farther back to Proto-Indo-European *bʰrēw-.

Types

Uses

The Magdeburg Water Bridge in Germany carries boats across a valley.

Bridges perform a wide variety of functions. Aqueducts were developed early in human history, and carried water to towns and cities. Until the 19th century, the most common use of bridges was to carry pedestrians, horses, and horse drawn carriages. Following the invention of railways, many rail bridges were built: in England, the number of bridges doubled during the railway-building boom in the mid 1800s. In the 20th century, the growth of motorway networks required the construction of vast numbers of bridges.

Canal bridges are used in a canal system to carry boats across a valley or ravine. Conservationists use wildlife overpasses to reduce habitat fragmentation and animal-vehicle collisions. 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.

Some bridges accommodate uses other than transportation. Many historical bridges supported buildings, such as shrines, factories, shops, restaurants, and houses. Notable examples were the Old London Bridge and Ponte Vecchio. 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. An example is Will Rogers Archway over the Oklahoma Turnpike. The Nový Most bridge in Bratislava features a restaurant set atop its single tower.

Basic types

The Forth Bridge (foreground) uses two kinds of strcutures: trusses (left) and cantilevers (right).

The basic bridge structures are arch, truss, cantilever, suspension, cable-stayed, and beam. The choice of bridge structure to use in a particular situation is based on many factors, including aesthetics, environment, cost, and purpose.

Many bridges are composed of multiple structures, for example, some Roman aqueducts contain dozens of adjacent arches. Long causeways over large lakes may be composed of hundreds of individual beam structures. Some bridges combine two kinds of structures, for example, it is common for large suspension bridges, such as the Verrazzano-Narrows Bridge, to have beam or truss elements in the approaches; and some large cantilever bridges, such as the Forth Bridge, use a truss segment in the middle to connect cantilevers on either side.

Arch bridge

Arch bridge

Deck arch

Tied arch

Arch bridges consist of a curved arch, under compression, which supports the deck either above or below the arch. The shape of the arch can be a semicircle, elliptical, a pointed arch, or a segment of a circle. When the arch is semicircular, as used in Roman bridges, the force of the arch is directed vertically downward to the foundation. When the arch is elliptical or a circular segment, the force is directed diagonally, and abutments are often required. 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.

Truss bridge

Truss bridge

Through truss

Deck truss

A truss bridge is composed of multiple, connected triangular elements. The set of triangles form a rigid whole, which rests on the foundation at both ends, applying a vertical force downward. The deck can be carried on top of the truss ("deck truss") or at the bottom of the truss ("through truss"). 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. The individual bars can be made of iron or wood, but most modern truss bridges are made of steel. The horizontal bars along the top are usually in compression, and the horizontal bars along the bottom are usually in tension. Other bars in the truss may be in tension or compression, depending on the particular layout of the triangles. 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. Trusses tend to be relatively stiff, and are commonly used for rail bridges which are required to carry very heavy loads.

Cantilever bridge

Cantilever bridge

Two cantilevers extending from anchorages

Balanced cantilever bridge

Cantilever bridges consist of one or more trusses, each supported at only one end. Modern cantilever bridges are generally built from steel. In Asia, cantilever bridges made of large rocks or timber were used to span small obstacles. In the 1880s, some early cantilever bridges were built from wrought iron. A basic cantilever bridge has two cantilevers, anchored at each end of the span, extending toward the center, and meeting in the center. Some cantilever bridges have a suspended span (beam or truss) in the center, connecting the two cantilevers where they meet. A balanced cantilever bridge consists of two connected cantilevers extending outward in opposite directions from a single central support. The term "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.

Suspension bridge

Suspension bridge

With anchorages

Self-anchored

Modern suspension bridges usually consist of two or more large cables passing over one or more towers. The deck is suspended from the cables by large wire ropes called hangers. The earliest suspension bridges were made of ropes or vines. In the early 1800s, the first modern suspension bridges – such as the Jacob's Creek Bridge – were chain bridges that used iron bars rather than bundled wires for the main cable. When steel wire became widely available, hundreds of wires were strung between the towers and bundled to form large cables. Each cable can weigh hundreds of tons. When the bridge crosses a river, stringing hundreds of wires across the large span is a complex process. Steel wire cables enabled suspension bridges to achieve spans 2 km long. The cable of the bridge is in tension, and the towers are in compression. 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. Shorter towers require a smaller sag in the cable, which increases the tension in the cable, and thus requires stronger towers and anchorages.

Cable-stayed bridge

Cable-stayed bridge

Harp pattern, two towers

Fan pattern, single tower

Cable-stayed bridges are similar to suspension bridges, but the cables that support the deck connect directly to the towers. Cable-stayed bridges offer some advantages over suspension bridges: anchorages are not needed, and constructing the deck can be readily accomplished by cantilevering outward from the towers. The cables may be arranged in a fan pattern or a harp pattern. Modern cable-stayed bridges became popular after WW II, when the design was used for many new bridges in Germany. When evaluating the choice of suspension vs. cable-stayed structure for a given application, the suspension option generally uses more cable for a given span size, but provides a longer span (for comparable materials), and requires shorter towers (for a given span size).

Beam bridge

Beam bridge

Beam bridges – including girder bridges – are simple structures consisting of one or more parallel, horizontal beams that span an obstacle. They are the most common type of bridges for both railways and roadways. Beam bridges are ideal for shorter spans (less than about 50 meters (160 ft)), but for longer spans, other structures, such as trusses, may be more efficient. In many applications, beam bridges can be built rapidly and economically, because the individual beams can be produced offsite and transported to the bridge site. Modern beam bridges are generally made of steel or reinforced concrete, although wood may be suitable for small beam bridges intended for light use. Several different cross-sections may be utilized for beams, including I-beam (common for steel) or flat slabs (sometimes used with concrete). Beams can traverse longer spans when they are designed as hollow box girders; bridges made of box girders are termed box girder bridges. The vertical thickness of beam bridges is generally shallower than comparable deck truss bridges, permitting shorter and lower approach roads to cross an obstacle of a given height. Several beam bridges can be chained together, with supports at each juncture, to form elevated highways or causeways.

Other types

See also: List of bridge types

Movable bridge

Main article: Moveable bridges

Tower Bridge in London is a moveable bridge of the bascule type.

Moveable bridges are designed so that all or part of the bridge deck can be moved, usually to permit tall traffic – that would normally be obstructed by the bridge – to pass by. Early moveable 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 – a bascule bridge – made raising and lowering easier and safer. 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. Lift bridges are raised vertically between two towers by cables passing over pulleys at the top of the towers. Notable moveable bridges include El Ferdan Railway Bridge in Egypt, Erasmusbrug bascule in Rotterdam, and Limehouse Basin footbridge in London. In the modern era, designers sometimes create unusual moveable bridges with the intention of establishing signature bridges for a town or locality. Examples include Puente de la Mujer swing bridge in Buenos Aires, Gateshead Millennium – a rare example of a tilt bridge – over the River Tyne, and Hörn Bridge in Germany.

Double-deck bridge

See also: List of multi-level bridges

The Padma Bridge in Bangladesh carries rail traffic on the lower deck and vehicular traffic on the upper deck.

Double-deck bridges (also known as double-decked, or double-decker) carry two decks on top of each other. This technique may be used to increase the amount of traffic a bridge can carry, or to build in a location where space is limited. Double-deck bridges permit two different kinds of traffic to be safely carried, by separating, for example, motor vehicles from pedestrians or railways.

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. 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. Because of their ability to carry large amounts of motor vehicles, double-deck bridges are often found in large cities, such as Tsing Ma Bridge in Hong Kong, San Francisco–Oakland Bay Bridge in California, and Shimotsui-Seto Bridge in Japan.

Long, multi-span bridge

See also: Viaduct, Causeway, and Continuous truss bridge

The Millau Viaduct crosses the Tarn river valley in France.

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

A trestle bridge – commonly used in the 19th century for railway bridges – consists of multiple short spans supported by closely spaced structural elements. A trestle is similar to a viaduct, but viaducts typically have taller piers and longer spans. 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 distinct 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. A causeway is a raised road, usually built over a lake or other body of water. Some causeways are bridges, such as the 38.4 km Lake Pontchartrain Causeway in Louisiana; but many – such as the King Fahd Causeway in Saudi Arabia – are partially or entirely built on solid dirt or rock embankments.

Pontoon bridge

Main article: Pontoon bridge

Floating concrete pontoons support the weight of the Nordhordland Bridge as it crosses a deep fjord in Norway.

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. Pontoon bridges are typically used where waters are too deep to build piers, or as a mechanism to implement a moveable swing bridge in a canal. Pontoon bridges were used in ancient China. Duing 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.

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

Portable military bridge

See also: Military bridge

This portable AM 50 bridge is being laid over a river in Slovakia.

Portable 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.

Military bridges can be categorized as "wet" bridges that rest on pontoon floats, and "dry" bridges that rest on piers, river banks, or anchorages. 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.

Some military bridges, referred to as armoured vehicle-launched bridges (AVLB), are carried on purpose-built vehicles. 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. The UK Chieftain AVLB could launch a 23-meter (75 ft) bridge – capable of supporting 60 ton loads – in 3 minutes.

Extradosed

Main article: Extradosed bridge

The Shin Meisei bridge (foreground) in Japan is an example of an extradosed bridge.

An extradosed bridge combines features of a box girder bridge and a cable-stayed bridge. 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. Extradosed bridges are appropriate for spans ranging from 100 meters (330 ft) to 250 meters (820 ft). Unlike suspension bridges or cable-stayed bridges, the towers of a extradosed bridge rest on the deck, rather than on a pier; and in some implementations, are solidly connected to the deck. 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. 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.

Requirements

Many overpass bridges in the United States Interstate Highway System are concrete box girder bridges, such as these bridges over Interstate 280 in California.

When designing a bridge to traverse a specific obstacle, the designer must identify a design that meets several requirements. The requirements may be categorized as engineering requirements and non-engineering requirements. Engineering requirements include safety, strength, lifespan, climate, traffic, the size and nature of the obstacle to be traversed, and clearance required for passage underneath.

Non-engineering requirements include construction cost, maintenance cost, aesthetics, time available for construction, owner preference, and experience of the builders. Other factors that may be weighed include impact to environment and wildlife; and the bridge's economic, social, and historic relationship to the local community.

Service life

The designer bases the design of a bridge on a service life, which is a specific number of years that the bridge is expected to remain in operation with routine maintenance, and without major repairs. The bridge design methodology incorporates the service life into the design process. Wood bridges may have a service life of ten to 50 years. In the United States, highway bridges typically have service lives of 75 to 150 years.

Aesthetics

The Brusio spiral viaduct is part of the Bernina railway in Switzerland, designated as a World Heritage Site.

Many bridges are utilitarian in appearance, but in some cases, the appearance of the bridge can have great importance. 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.

The art historian Dan Cruickshank notes that bridges are regarded as manifestations of human imagination and ambition, and that many bridges bridge transcend their original utilitarian role to and become a work of art. 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."

Material

The Iron Bridge in Shropshire, England, completed in 1781, is the first major bridge made of entirely of cast iron.

This concrete bridge support is being prepared for a concrete pour. The green reinforcing bars will be embedded inside the concrete after the concrete cures.

The small circular holes in this box girder will hold prestressing cables, which run the length of the girder and keep the concrete in compression.

Bridges are built from a wide variety of materials, including wood, brick, rope, stone, iron, steel, and concrete. A bridge made from two or more distinct materials (such as steel and concrete) is known as a composite bridge.

Wood is an inexpensive material that is rarely used for modern motor vehicle roads. Wood is used in bridges primarily in a beam structure or truss structure, and is also used to build huge trestle bridges for railways. When wood is used, it is often in the form of glued laminated timber.

Masonry includes stone and brick, and is suitable only for elements of a bridge that are under compression, since masonry will crack if under tension. Therefore, masonry is limited to structures such as arches or foundations. In the twentieth century, large masonry bridges  – although superseded by concrete in the West – continued to be built in China.

Iron, including cast iron and wrought iron, was used extensively from the late 1700s to late 1800s, primarily for arch and truss structures. Iron is relatively brittle, and has been superseded by the much stronger steel for all but ornamental uses.

Steel is one of the most common materials used in modern bridges. 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. Steel is especially useful for bridges, because it is strong in both compression and tension. Steel is widely used for truss bridges and beam bridges, and steel wires are an essential component of virtually all suspension bridges and cable-stayed bridges. Concrete bridges make extensive use of steel, because all concrete used in bridges contains steel reinforcing bars or steel prestressed cables. 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.

Concrete is a strong and inexpensive material, but is brittle and can crack when in tension. Concrete is useful for bridge elements that are in compression, such as foundations and arches. Many roadway bridges are built entirely of concrete using a beam structure, often of the box girder variety. Virtually all concrete used in bridges contains steel reinforcing bars, which greatly increase the strength. Reinforcing bars are set inside the concrete form, and the concrete is poured into the form, and cures with the bars inside. If concrete is used in elements that experience tension – such as the lower region of a horizontal beam or slab – prestressed cables must be embedded within the concrete and tightened. The prestressed cables can be pre-tensioned (stretched before – and while – the concrete cures); or post-tensioned (placed within tubes in the concrete, and tightened after the concrete cures). The prestressed cables compress the concrete. When the 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. Concrete beams can be precast offsite and transported to the bridge site, or cast in place.

Specifications and standards

Many countries have standards organizations which publish documents 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. In the United States, the American Association of State Highway and Transportation Officials (AASHTO) publishes the AASHTO LRFD Bridge Design Specifications. Canada's bridge standard is the Canadian Highway Bridge Design Code, developed by the non-profit CSA Group.

Design

Main article: Bridge design

After the requirements of a bridge are established, the bridge designer uses structural analysis methods and techniques to identify candidate designs. Several designs may meet the requirements. After considering all factors, the bridge designer – in consultation with the owner – will select a particular design. The value engineering methodology can be used to select a final design from multiple alternatives. 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.

Load

See also: Structural load

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.

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

Many of the load sources vary over time, such as vehicle traffic, wind, and earthquakes. The bridge designer must anticipate the maximum values that those loads may reach during the course of the bridge's lifespan. For sporadic events like floods, earthquakes, collisions, and hurricanes, bridge designers must select a maximum severity that the design must accommodate. The designer first selects a return period, which may range from 100 to 2,500 years. 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.

Stress and strain

See also: Stress (mechanics)

Software applications are used in the bridge design process, such as this app that evaluates stress and strain.

Bridge engineers use stress–strain curves to assist with the design process.

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).

The 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 includes forces that compacts 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.

Traffic

An important component of the live load carried by a bridge is the vehicle and rail traffic the bridge is expected to carry. In addition to the weight of the vehicle, other forces must be considered, including braking, acceleration, centrifugal forces, and resonant frequencies. For roadways, the loads imposed by truck traffic far exceeds the loads imposed by passenger cars, and so the bridge design process focuses on trucks.

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 standards such as Eurocode or AASHTO bridge specifications. In addition to algorithmic models contained in specifications, designers may determine traffic loads by utilizing data from real-world measurements on existing bridges that experience traffic comparable to that the proposed bridge will experience: technologies such as weigh-in-motion (WIM) can produce accurate data without the guesswork inherent in an algorithmic model.

Vibration and resonance

The Tacoma Narrows Bridge collapsed shortly after opening in 1940 due to failure of the design to properly account for wind forces.

Many loads imposed on a bridge – such as wind and vehicular traffic – can cause a bridge to experience irregular or periodic forces, which may cause bridge components to vibrate or oscillate. Many bridge components may have inherent resonant frequencies to which they are particularly susceptible, and vibrations near those frequencies can cause very large stresses.

Winds can produce a variety of forces on a bridge, including flutter and vortexes. Considering wind forces during the design process is especially important for long, slender bridges (typically suspension or cable-stayed bridges). Vibration and resonance concerns are especially important in longer bridges, but still must be accounted for in smaller bridges. 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).

The bridge design process must identify potential vibrations and oscillations, and address them with techniques to minimize vibration, such as adding components to dampen movement or stiffen the structure. One technique to combat oscillations is tuned mass dampers, which have been installed in bridges such as Pont de Normandie, which in 1995 was the first bridge to utilize them. The Akashi Kaikyo Bridge has twenty tuned mass dampers, weighing ten tons each, inside its steel towers.

Neglecting to account for vibrations and oscillations can lead to bridge failure. 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. The Tacoma Narrows Bridge collapsed in the 1940 in winds of 42 mph (68 km/h), even though the bridge was designed to withstand winds up to 128 mph (206 km/h). Investigations revealed that the designer failed to account for wind effects such as flutter and resonant vibrations. The Golden Gate Bridge was damaged in 1951 due to wind forces, and as a result was reinforced with additional stiffening elements.

Methodologies and tools

See also: Structural analysis and Structural engineering

Engineers use finite element method software tools to evaluate a bridge design.

The process used to design bridges uses structural analysis methods and techniques. These methods divide the bridge into smaller components, and analyze the components individually, subject to certain constraints. A proposed bridge design is then modeled with formulas or computer applications. The models incorporate the loads and stresses the bridge will experience, as well as the bridge's structure and material. The models calculate the stresses in the bridge and provide data to the designer indicating whether the design meets the required design goals.

Bridge design models include both mathematical models and numerical models. 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. The finite element method is the most common numerical model used to perform detailed analysis of stresses and loads of a bridge design. 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.

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, flexure, shear, torsion, buckling, settlement, bearing, and sliding. The criteria, and their allowable values, are termed limit states. The set of limit states selected for a design are based on the bridge's structure and purpose.

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). These methodologies add a margin of safety to the bridge design by incorporating safety factors into the design process. 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. 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, snow or ice on the bridge; winds; settling into the soil; and collisions (such as vehicles on the deck striking a bridge tower; or a ship striking a bridge foundation).

Protection

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.

To achieve a longer lifespan, a bridge should 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.

Deterioration can be slowed – thus prolonging the life of the bridge – by various measures, primarily aimed at excluding water and oxygen from the bridge elements. Techniques to prevent water-based damage include drainage systems, waterproofing membranes (such as polymer films), and eliminating expansion joints.

Concrete bridge elements can be protected with waterproof seals and coatings. Reinforcing steel within concrete can be protected by using high-quality concrete and increasing the thickness of the concrete surrounding the steel. Steel elements of a bridge can be protected by paints or by galvanizing with zinc. 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).

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.

Suspension 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.

Construction

See also: Bridge design

Elements

Some elements of a fictional bridge. 1 Approach, 2 Arch, 3 Truss, 4 Abutment, 5 Bearing, 6 Deck, 7 Pier Cap, 8 Pier, 9 Piling, 10 Footing, 11 Caisson, 12 Subsoil.

The structural elements of a bridge are generally divided into the superstructure and the substructure. The superstructure consists of most of the visible parts of a bridge, including the deck, wearing surface (e.g. the asphalt on top surface of the deck), trusses, arches, towers, cables, beams, and girders. The substructure consists of the lower portions of the bridge which support the superstructure, including the footings, abutments, piers, pilings, anchorages, and bearings.

Substructure

Abutments are an important element in 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.

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

Abutments are usually located at the ends of a bridge deck, where it reaches the subsoil. They direct the weight into the subsoil, either vertically or diagonally. Abutments may also act as retaining walls, keeping the subsoil under the approach road from eroding. After footings for the piers have been created, the piers and pier caps are built to complete the substructure. Suspension bridges usually require anchorages, which are large reinforced concrete blocks solidly anchored into the earth – 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.

Superstructure

Gantries are one technique used to gradually assemble a bridge deck.

The deck of this arch bridge is being horizontally pushed onto the substructure with jacks.

This temporary falsework will be removed after an arch is built over it.

After the substructure is complete, the superstructure is built, resting on the substructure. Beam bridge superstructures may be fabricated off-site (common for steel beams) or cast-in-place (for many concrete beams). The beams may be laid across the piers by a crane or gantry. If the span crosses a deep ravine, a technique known as launching may be used: the full span (beams and deck) are assembled on the approach road, then pushed horizontally across the obstacle.

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. Some steel arch bridges are constructed without falsework: both sides are built in a cantilever fashion from the abutments, and when they reach the middle, they are jacked slightly apart for the final section to be inserted.

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.

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 and moving outward. 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. The deck proceeds outwards in both directions at the same rate, to ensure the forces applied to the tower are balanced. 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.

Suspension bridge superstructure construction usually begins with the towers. 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. The cables are securely fastened to the anchorages at both ends. 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.

Building supports in water

This concrete bridge pier is being built within a cofferdam (the rusted, vertical steel walls).

To build a bridge pier in water, caissons may be used to hold workers and machinery during excavation.

When bridge supports (piers or towers) are built in a river, lake, or ocean, caissons are often 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. Air pressure inside a sealed caisson must be kept high to prevent water from seeping in. Workers, if they do not properly decompress when exiting the caisson, can get decompression sickness. 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).

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. Another approach for constructing foundations in water was employed for the Akashi Kaikyo suspension bridge: the two foundations for its towers are 70 meters (230 ft) tall and 80 meters (260 ft) in diameter. The foundations were partially built on land, then towed by tugboats to the bridge site.They were sunk to the bottom in water 60 meters (200 ft) deep, and each was filled with 355,000 cubic meters of concrete. The foundations rest directly on the ocean bottom, without pilings or footings.

Bearings

Main article: Bridge bearing

Two types of bridge bearings are used in this application: a hinge bearing above a pair of roller bearings.

Bearings are often placed between the superstructure and the substructure at the points of contact. Bearings are mechanical devices that enable small movements – which may result from thermal expansion and contraction, material creep, or minor seismic events. Without bearings, the bridge may be damaged when 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.

Towers and cables

See also: Wire rope

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.

The cables of the Verrazano-Narrows Bridge are passing over the saddles at the top of the tower. The individual strands are wrapped with bands.

This suspension bridge cable, shown in cross-section, consists of 37 strands, and each strand consists of multiple wires.

Towers are an important component of the superstructure of cable-stayed bridges and suspension bridges. Towers are made of either concrete or steel. Steel towers are much lighter than concrete towers (of the same height). Concrete is generally suitable only for towers up to about 250 meters (820 ft) tall, whereas steel towers can be much taller.

Towers hold the bridge cables, which – in turn – 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. 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.

Cables are made of one or more strands, and each strand consists of multiple wires. Each wire is a thin, flexible piece of solid steel, of higher tensile strength than normal steel, and with a diameter of 3mm to 7mm. Cables for large suspension bridges can reach over 1 meter (3 ft 3 in) in diameter and weigh over 20,000 tonnes. Cables are typically constructed at the bridge site by unspooling wires or strands from large reels.

After the towers of a suspension bridge are built, the next step is to build a temporary catwalk to support the wires while they are drawn across the span and over the tops of the towers. There are two approaches to pulling the wires across the span: the air spinning (AS) method where the individual wires are carried across by pulleys; or the prefabricated parallel-wire strand (PPWS) method where entire strands are individually pulled across.

The AS method was used for all suspension bridges until the PPWS method was invented in the 1960s. The AS method is slower because it requires the spinning pulley to cross the span thousands of times, pulling a pair of wires each time. After 300 to 500 wires are pulled, aluminum bands are used to bundle them into strands.. The PPWS method permits strands to be built away from the bridge site, but the process of pulling the heavy strands across the full span of the bridge is more difficult. The PPWS method was used for the Akashi Kaikyo Bridge, where each strand weighed 94 tonnes and was 4 kilometres (2.5 mi) long.

The wires within a strand may be parallel, or they may wrap around each other in a twisted (spiral) pattern. Air spinning always produces strands that contain parallel wires. The PPWS method can produce strands with parallel or twisted wires.

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 an hydraulic device that moves along the cable and compresses the wires together. Then a wire is usually wrapped around the cable in a helical manner, to provide protection against water intrustion. 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.

Operations

Maintenance, inspection, and monitoring

This pier of a bridge in Germany is degrading, and the internal steel reinforcing bars are exposed and rusting.

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 – collectively referred to as bridge management – include technical activities such as maintenance, inspection, monitoring, and testing.

In addition to technical tasks, management encompasses planning, budgeting, and prioritization of maintenance activities. Bridge designers use Life-Cycle Cost Analysis (LCCA) methodologies to estimate the maintenance costs of a bridge throughout its lifetime. Annual maintenance costs increase as the bridge ages and degrades.

An important part of maintenance is inspecting for damage or degradation, and taking steps to mitigate any issues detected. Degradation can come from a variety of sources: expansion/contraction from freeze/thaw cycles, rain and snow, oxidation of steel, saltwater spray, carbonatation of concrete, vehicular traffic, corrosion, mechanical abrasion, poor bridge design, and improper repair procedures.

A variety of inspection techniques can be utilized to measure degradation of bridge elements. Destructive testing removes material samples from the bridge – such as cores drilled from concrete, or a small piece of steel wire cut from a cable – to a laboratory. In the laboratory, the samples are analyzed using microscopes, sonic devices, or X-ray diffraction.

Non-destructive testing that can be performed on a bridge in situ include hammer strike tests, ultrasonic pulse velocity tests, seismic tomography, and ground penetrating radar. Magnetometers can be used to detect the location of reinforcing steel within concrete. Various electrical tests, such as permeability and resistance, can give insight into the condition of surface concrete. X-rays can be passed through concrete to obtain data about concrete density and condition. Videography using slender probes can be used where access is available.

During bridge construction, permanent sensors may be placed within bridge elements at critical locations, and may be measured at any time to obtain data about stresses and chemical degradation in hard-to-reach locations. Many long-span bridges are now routinely monitored with a range of sensors, including strain transducers, Sodar, accelerometers, tiltmeters, and GPS.

Scaffolding is erected under the Sitterviadukt rail bridge in Switzerland while maintenance on the deck truss is performed.

To evaluate the condition of large steel cables, as used in suspension bridges or cable-stayed bridges, electrical coils are moved along the cable, measuring the induction of the cable, which can reveal corrosion issues.

A variety of 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. 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.

Failures

See also: List of bridge failures

The Nanfang'ao Bridge in Taiwan collapsed because of excessive corrosion that went undetected.

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. 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. In the United States, 25% of all bridges failed during the 1870s. Over time, bridge failures led to improvements in bridge design, construction, and maintenance practices. In the modern era, the majority of bridge failures in the United States are due to water-related causes, such as damage from floods, or scouring (due to water currents) undermining bridge supports.

In culture

See also: Bridges in art

The Pulitzer Prize winning novel The Bridge of San Luis Rey revolves around a bridge failure that killed five people.

Bridges occur extensively in art, legend, and literature, often employed in a metaphorical manner. In Norse mythology, the home of the gods – Asgard – is connected to the earth by Bifröst, a rainbow bridge. Many bridges in Europe are named "Devil's Bridge", and sometimes have folkloric stories that explain why the bridge is associated with the devil. There are many stories, mostly apocryphal, relating bridges to Christian saints. Stories and poems often employ a bridge as a metaphor of the human lifespan, or human experiences. Bridges are often the setting for pageants, celebrations, and processions.

Bridges are often venerated as symbols of humankind's heroism and accomplishments. The inspirational nature of bridges has led them to be featured in the works of poets, painters and writers. Bridges feature prominently in paintings – often in the background – as in the Mona Lisa. 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.

Signature bridges

Many bridges – known as signature bridges – are strongly identified with a particular community. In some cases they are deliberately built with an especially magnificent design, to serve as a landmark or icon. The art historian Dan Cruickshank writes: "I am ... enthralled by [the] ability [of bridges] to transform a place a community and amazed by the way a bold bridge 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." 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.

Numismatics

The 500 euro banknote displays a cable-stayed bridge.

Bridges have been featured on coins since antiquity. In the modern era, brides are prominently displayed on euro banknotes. 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. Bridges were 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. The initial designs by Kalina were discovered to be of specific bridges, including the Rialto and the Pont de Neuilly, and were subsequently changed to be more generic. Each banknote depicts a bridge design representative of a certain architectural era.

References

Sources

Books

• Abdunur, Charles (2000). "Inspection, Monitoring, and Assessment". In Ryall, Michael (ed.). The Manual of Bridge Engineering. Thomas Telford. pp. 883–942. ISBN 0727727745. Retrieved 1 September 2025.

• Adams, Charles Kendall (1909). "Bridges". Universal Cyclopædia and Atlas. D. Appleton and Company. p. 168. Retrieved 1 September 2022.

• Barker, Richard M. (2007). Design of Highway Bridges: An LRFD Approach. Wiley. ISBN 9781119646310. Retrieved 1 September 2025.

• Beer, Ferdinand (2017). Mechanics of Materials. McGraw Hill. ISBN 9789339217624. Retrieved 17 September 2025.

• Bennett, David (1999). The Creation of Bridges: From Vision to Reality - the Ultimate Challenge of Architecture, Design and Distance. Aurum. ISBN 1550415522. Retrieved 1 September 2025.

• Bennett, David (2000). "The History and Aesthetic Development of Bridges". In Ryall, Michael (ed.). The Manual of Bridge Engineering. Thomas Telford. pp. 1–42. ISBN 0727727745. Retrieved 1 September 2025.

• Birnstiel, Charles (2000). "Moveable Bridges". In Ryall, Michael (ed.). The Manual of Bridge Engineering. Thomas Telford. pp. 663–698. ISBN 0727727745. Retrieved 1 September 2025.

• Brown, David (2005). Bridges: Three Thousand Years of Defying Nature. Mitchell Beazley. ISBN 1845330803. Retrieved 1 September 2025.

• Chen, Wai-Fah; Duan, Lian (1999). Bridge Engineering Handbook. CRC Press. ISBN 0849374340. Retrieved 1 September 2025.

• Chen, Wai-Fah, ed. (2013). Handbook of International Bridge Engineering. Taylor & Francis. ISBN 9781439810293. Retrieved 1 September 2025.

• Collings, David (2000). "Composite Construction". In Ryall, Michael (ed.). The Manual of Bridge Engineering. Thomas Telford. pp. 407–448. ISBN 0727727745. Retrieved 1 September 2025.

• Cruickshank, Dan (2010). Bridges: Heroic Designs that Changed the World. Harper Collins. ISBN 9780007881086. Retrieved 1 September 2025.

• Dawe, Peter (2003). Research Perspectives: Traffic Loading on Highway Bridges. Thomas Telford. ISBN 0727732412. Retrieved 15 September 2025.

• Denison, Edward (2012). How to Read Bridges: A Crash Course In Engineering and Architecture. Rizzoli. ISBN 9781408171769. Retrieved 1 September 2025.

• Dikshitar, V.R.R. (1993) [1932]. The Mauryan Polity. Motilal Banarsidass. ISBN 8120810236. Retrieved 20 September 2025. Reprinted in 1993.

• Edgerton, Robert B. (2010). The Fall of the Asante Empire: The Hundred-Year War For Africa's Gold Coast. Simon and Schuster. ISBN 9781451603736.

• Ellobody, Ehab (2014). Finite Element Analysis and Design of Steel and Steel–Concrete Composite Bridges. Butterworth-Heinemann. ISBN 9780124172470. Retrieved 1 September 2025.

• Elnashai, Amr (2000). "Seismic Response and Design". In Ryall, Michael (ed.). The Manual of Bridge Engineering. Thomas Telford. pp. 519–548. ISBN 0727727745. Retrieved 1 September 2025.

• Farquhar, Daniel (2000). "Cable-Stay Bridges". In Ryall, Michael (ed.). The Manual of Bridge Engineering. Thomas Telford. pp. 549–594. ISBN 0727727745. Retrieved 1 September 2025.

• Gimsing, Niels J. (1997). Cable Supported Bridges: Concept and Design (Second ed.). Wiley. ISBN 9781119951872. Retrieved 1 September 2025.

• Greco, Laura (2016). Architetture Autostradali in Italia (in Italian). Gangemi Editore. ISBN 9788849292121. Retrieved 1 September 2025.

• Hewson, Nigel (2000). "Design of Prestressed Concrete Beams". In Ryall, Michael (ed.). The Manual of Bridge Engineering. Thomas Telford. pp. 241–314. ISBN 0727727745. Retrieved 1 September 2025.

• Holstine, Craig (2005). Spanning Washington: Historic Highway Bridges of the Evergreen State. Washington State University Press. ISBN 9780874222814. Retrieved 15 September 2025.

• Huff, T. (2022). LRFD Bridge Design: Fundamentals and Applications. CRC Press. ISBN 9781000543377. Retrieved 10 September 2025.

• Jones, Vardiman; Howells, John (2000). "Suspension Bridges". In Ryall, Michael (ed.). The Manual of Bridge Engineering. Thomas Telford. pp. 595–662. ISBN 0727727745. Retrieved 1 September 2025.

• Mulheron, Mike (2000). "Protection". In Ryall, Michael (ed.). The Manual of Bridge Engineering. Thomas Telford. pp. 805–848. ISBN 0727727745. Retrieved 1 September 2025.

• Nath, Ram (1982). History of Mughal Architecture. Vol. 3. Abhinav Publications. ISBN 8170172977. Retrieved 17 September 2025.

• O'Brien, Eugene (2015). Bridge Deck Analysis (Second ed.). CRC. ISBN 9781482227239. Retrieved 12 September 2025.

• Petroski, Henry (1994). To Engineer Is Human: The Role of Failure in Successful Design. Barnes & Noble. ISBN 1566195020. Retrieved 20 September 2025.

• Reddy, J. N. (2004). An Introduction to the Finite Element Method (Third ed.). McGraw Hill. ISBN 9780070607415. Retrieved 10 September 2025.

• Ryall, Michael (2000). "Loads and Load Distribution". In Ryall, Michael (ed.). The Manual of Bridge Engineering. Thomas Telford. pp. 43–94. ISBN 0727727745. Retrieved 1 September 2025.

• Scott, Richard (2001). In the Wake of Tacoma: Suspension Bridges and the Quest for Aerodynamic Stability. ASCE Press. ISBN 0784405425. Retrieved 1 September 2025.

• Shanmugam, N. E. (2000). "Structural Analysis". In Ryall, Michael (ed.). The Manual of Bridge Engineering. Thomas Telford. pp. 95–224. ISBN 0727727745. Retrieved 1 September 2025.

• Schlaich, Mike (2019). "General". In Schlaich, Mike (ed.). Extradosed Bridges (PDF). International Association for Bridge and Structural Engineering. pp. 3–8. ISBN 9783857481680. Retrieved 16 October 2025.

• Squier, Ephraim George (1877). Peru; Incidents of Travel and Exploration in the Land of the Incas. Harper & Brothers. LCCN 03002357. Retrieved 13 September 2025.

• Troitsky, M.S. (1994). Planning and Design of Bridges. Wiley. ISBN 0471028533. Retrieved 1 September 2025.

• Troyano, L.F. (2003). Bridge Engineering: A Global Perspective. Thomas Telford. ISBN 9780727732156. Retrieved 25 October 2025.

• Tytler, I.F.B. (1985). Vehicles and Bridging. Battlefield Weapons Systems and Technology. Brasey's Defense Publishers. ISBN 0080283225. Retrieved 13 September 2025.

• Vassie, Perry (2000). "Bridge Management". In Ryall, Michael (ed.). The Manual of Bridge Engineering. Thomas Telford. pp. 849–882. ISBN 0727727745. Retrieved 1 September 2025.

• Watson, Wilbur J. (1937). Bridges in History and Legend. J. H. Jansen. LCCN 37017069. Retrieved 1 September 2025.

• Wilks, Ivor (1989). Asante in the Nineteenth Century: The Structure and Evolution of a Political Order. CUP Archive. ISBN 9780521379946. Retrieved 29 December 2020 – via Books.google.com.

• Wright, William J. (2022). "Selecting the Right Bridge Type" (PDF). Steel Bridge Design Handbook. National Steel Bridge Alliance. Retrieved 18 September 2025.

• Xu, You Lin; et al. (2011). Structural Health Monitoring of Long-Span Suspension Bridges. Taylor & Francis. ISBN 9780415597937.

• Zhao, Jim; et al. (2017). Bridge Engineering: Design, Rehabilitation, and Maintenance of Modern Highway Bridges (Fourth ed.). McGraw Hill. ISBN 9781259643101. Retrieved 16 September 2025.

Journals and websites

• Bjelić, Igor (2022). "Use of Building Materials During the Construction of Trajan's Bridge on the Danube" (PDF). Arheologija I Prirodne Nauke. 18. Institute of Archaeology, Belgrade: 45–58. doi:10.18485/arhe_apn.2022.18.4. ISSN 1452-7448. Retrieved 3 October 2025.

• Brunning, Richard (2001). "The Somerset Levels". Current Archaeology. XV (4) (172). Current Publishing: 139–143. ISSN 0011-3212.

• Cook, Wesley (2014). Bridge Failure Rates, Consequences, and Predictive Trends (PhD thesis). Utah State University. Retrieved 2 October 2025.

• Delatte, Norbert (July 2001). "Lessons from Roman Cement and Concrete". Journal of Professional Issues in Engineering Education and Practice. 127 (3). American Society of Civil Engineers: 109–115. doi:10.1061/(ASCE)1052-3928(2001)127:3(109). ISSN 1052-3928. Retrieved 3 October 2025.

• Du, Jin Sheng; Au, Francis T.K. (July 2005). "Deterministic and Reliability Analysis of Prestressed Concrete Bridge Girders: Comparison of the Chinese, Hong Kong and AASHTO LRFD Codes". Structural Safety. 27 (3). Elsevier: 230–245. doi:10.1016/j.strusafe.2004.10.004. ISSN 0167-4730. Retrieved 9 October 2025.

• Greenfield, Patrick (23 January 2021). "How Creating Wildlife Crossings Can Help Reindeer, Bears – and Even Crabs". The Guardian. ISSN 1756-3224. Archived from the original on 23 January 2021. Retrieved 26 January 2021.

• Honan, David (2018). "Railroad Bridges, Viaducts, and Trestles". Trains Magazine. ISSN 0041-0934. Retrieved 11 September 2020.

• Hopper, Travis; Langlois, Anne-Marie; et al. (November 2022). "Service Life Design Reference Guide" (PDF). Federal Highway Administration. Retrieved 2 October 2025.

• Hu, Jiong; et al. (March 2016). "Synthesis on Cost-Effectiveness of Extradosed Bridges" (PDF). Texas A&M Transportation Institute. Technical Report. Retrieved 17 September 2025.

• Kashima, Satoshi; Sakamoto, Mitsushige (1998). "Construction of Akashi Kaikyo Bridge Foundation". IABSE Symposium (Kobe): Long-Span and High-Rise Structures. 79. IABSE: 69–74. doi:10.5169/seals-59833. Retrieved 2 October 2025. PDF version

• Kumar, Saket; et al. (2025). "Dynamic Response of Double Deck Cable-Stayed Bridge Subjected to Train Load on Lower Deck". Journal of Vibration Engineering & Technologies. 13 (20) 20. Springer Nature. Bibcode:2025JVET...13...20K. doi:10.1007/s42417-024-01562-2. ISSN 2523-3939. Retrieved 12 September 2025.

• Markowitz, Mike (29 December 2016). "Bridges on Ancient Coins". CoinWeek. Retrieved 2 October 2025.

• Newer, Rachel (23 July 2012). "World's Coolest Animal Bridges". Smithsonian.com. ISSN 1930-5508. Retrieved 21 February 2019.

• Omer, Muhammad; et al. (2018). "Performance Evaluation of Bridges Using Virtual Reality". Proceedings of the 6th European Conference on Computational Mechanics (ECCM 6) & 7th European Conference on Computational Fluid Dynamics (ECFD 7), Glasgow, Scotland. International Center for Numerical Methods in Engineering.

• Ou, Z.; Chen, B. (2005). "Stone Arch Bridges in Fujian, China" (PDF). Retrieved 10 September 2025.

• Quirchmair, Martin (2022). "Track Maintenance: Sittertobel Renovation Improves Track Forces". Railway Gazette International. ISSN 0373-5346. Retrieved 21 September 2025.

• Rookhuyzen, David (2018). "Transportation Defined: Pier Caps". Arizona Department of Transportation. Retrieved 20 September 2025.

• Sangree, Rachel; Shafer, Ben; et al. (2003). "The Structural Art of the Akashi Kaikyo Bridge" (PDF). Perceptions on the Evolution of Structures. Retrieved 2 October 2025.

• Schmid, John (3 August 2001). "Etching the Notes of a New European Identity". International Herald Tribune. ISSN 0294-8052. Retrieved 23 September 2025.

• Shirley-Smith, Hubert. "Bridge". Britannica. Retrieved 19 September 2025.

• Wardhana, Kumalasari; Hadipriono, Fabian (2003). "Analysis of Recent Bridge Failures in the United States". Journal of Performance of Constructed Facilities. 17 (3). American Society of Civil Engineers: 144. doi:10.1061/(ASCE)0887-3828(2003)17:3(144). ISSN 1943-5509. Retrieved 2 October 2025.

• Watanabe, Eiichi (2003). "Floating Bridges: Past and Present". Structural Engineering International. 13 (2). Taylor & Francis: 128–132. doi:10.2749/101686603777964810. ISSN 1016-8664. Retrieved 13 September 2025.

Unknown author

• "2024 Monthly Traffic and Percent of E-ZPass Usage" (PDF). Port Authority of New York and New Jersey. Retrieved 12 September 2025. This data states 50,241,454 eastbound vehicles in 2024.

• "AASHTO Store". American Association of State Highway and Transportation Officials. Retrieved 17 September 2025.

• "Aqueduct". The Concise Oxford Dictionary. Oxford University Press. 2001. p. 66. ISBN 0198604386. Retrieved 27 December 2022.

• Army Manual TM 5-277. Panel Bridge, Bailey Type, M2. 1948. Retrieved 13 September 2025.

• "Bratislava UFO Classed One of the Craziest Places". Travel to Slovakia. Ministry of Tourism and Sports of the Slovak Republic. Retrieved 17 September 2025.

• "Bridge". Oxford English Dictionary. Oxford University Press. Retrieved 11 September 2025.

• "Bridge". The Concise Oxford Dictionary (10th ed.). Oxford University Press. 2001. p. 173. ISBN 0198604386. Retrieved 27 December 2022.

• "Bridge Aesthetics. Design Guideline to Improve the Appearance of Bridges in NSW" (PDF). Transport for NSW. February 2009. Archived from the original (PDF) on 9 October 2022.

• "Bridge Failure". United Nations Office for Disaster Risk Reduction. 2025. Retrieved 2 October 2025.

• "Bridge Layer AM-50". Ministry of Defence and Armed Services of the Czech Republic. Retrieved 17 September 2025.

• "Causeway". Merriam-Webster Dictionary. Merriam-Webster. 12 September 2025. Retrieved 16 September 2025.

• "Close Support Bridging". British Army. Archived from the original on 26 November 2011. Retrieved 7 August 2012.

• "Design Elements". European Central Bank. 15 November 2024.

• "CSA S6:19, Canadian Highway Bridge Design Code". CSA Group. Retrieved 17 September 2025.

• Engineering: Issues Challenges and Opportunities. United Nations Educational, Scientific and Cultural Organization. 2010. ISBN 9789231041563. Retrieved 26 October 2025.

• "Eurocodes: Building the Future". European Commission. Retrieved 17 September 2025.

• Handbook on Soviet Ground Forces. Field manual FM 30-40. U.S. Department of the Army. 1975. ISBN 9781119646310. Retrieved 1 September 2025.

• "I-205 Abernethy Bridge" (PDF). Oregon Department of Transportation. Retrieved 2 October 2025.

• "Main Bridge Details (Technical)". Padma Multipurpose Bridge Project. Retrieved 10 December 2020.

• "Money Talks: The New Euro Cash". BBC News. Retrieved 1 September 2025.

• Occupational Outlook Handbook. JIST Publishing, U. S. Department of Labor. 2008. ISBN 9781593575137. Retrieved 26 October 2025.

• "Painting The Golden Gate Bridge". Golden Gate Bridge. Golden Gate Bridge, Highway and Transportation District. Archived from the original on 22 August 2011. Retrieved 20 August 2007.

• "Resisting the Twisting". Golden Gate Bridge Highway and Transportation District. Retrieved 12 September 2025.

• "Rhaetian Railway in the Albula / Bernina Landscapes". UNESCO World Heritage Convention. Retrieved 14 September 2025.

• "SAS Maintenance Travelers". California Department of Transportation. Archived from the original on 25 June 2012. Retrieved 24 June 2012.

• "Tacoma Narrows Bridge History - Suspension Bridge Basics". Washington State Department of Transportation. Retrieved 18 September 2025.

• "The History of the National Council of Examiners for Engineering and Surveying" (PDF) (Third ed.). National Council of Examiners for Engineering and Surveying. 2004. Retrieved 25 October 2025.

• "Transportation & Communication: The King Fahd Causeway". The Embassy of The Kingdom of Saudi Arabia. Retrieved 15 September 2025.

• "TTSB Details Reasons for Nanfang'ao Bridge Collapse". Focus Taiwan. 25 November 2020. Retrieved 16 September 2025.

• "Viaduct". The Concise Oxford Dictionary. Oxford University Press. 2001. p. 1596. ISBN 0198604386. Retrieved 27 December 2022.

• "West Montrose Covered Bridge". Canada's Historic Places. Parks Canada. Retrieved 22 October 2023.

• "Why Do Foxes, Jackals and Hyenas Cross Israel's Highway 1?". ISRAEL21c. 28 March 2016. Retrieved 19 September 2025.

• "Will Rogers Archway". Travel Oklahoma. Oklahoma Department of Tourism and Recreation. Retrieved 17 September 2025.

Further reading

• DeLony, Eric (1993). Landmark American Bridges. American Society of Civil Engineers. ISBN 0872628574. Retrieved 1 September 2025.

• Journal of Bridge Engineering. American Society of Civil Engineers. ISSN 1084-0702.

• Kawada, Tadaki (2010). History of the Modern Suspension Bridge: Solving the Dilemma Between Economy and Stiffness. American Society of Civil Engineers. ISBN 9780784410189. Retrieved 1 September 2025.

• Kutz, Myer (2011). Handbook of Transportation Engineering, Volume II: Applications and Technologies, Second Edition. McGraw-Hill Professional. ISBN 9780071614771. Retrieved 17 September 2025.

• Mermigas, Konstantinos (2009). Behaviour and Design of Extradosed Bridges (Masters thesis). University of Toronto. hdl:1807/17203. Retrieved 16 September 2025. PDF file online

• Modjeski and Masters, Inc. (May 2019). "Manual for Refined Analysis in Bridge Design and Evaluation" (PDF). U.S. Deptartment of Transportation - Federal Highway Administration. Retrieved 1 September 2025.

• Mahmoud, Kahled, ed. (2011). Modern Techniques in Bridge Engineering. CRC Press. ISBN 9780415684156. Retrieved 1 September 2025.

• Pipinato, Alessio (2021). Innovative Bridge Design Handbook: Construction, Rehabilitation and Maintenance. Butterworth-Heinemann. ISBN 9780323860147. Retrieved 13 September 2025.

• Ross, David (2018). Bridges of the World. Amber Books. ISBN 9781782746263. Retrieved 1 September 2025. Photographs of many unique or important bridges.

• Whitney, Charles S. (2003) [1929]. Bridges of the World: Their Design and Construction. Dover Publications. ISBN 0486429954. Retrieved 1 September 2025.

• Xanthakos, Petros (1994). Theory and Design of Bridges. Wiley. ISBN 0471570974. Retrieved 1 September 2025.

External links

• Angelo, Gordon (February 2017). "Exploring The Design Process And Construction Of Akashi Kaikyo Bridge". Youtube. Retrieved 21 October 2025. Video of the construction of the Akashi Kaikyo Bridge, including the extraordinarily large foundations that were towed into place and sunk in deep water.

• "BridgeView, Episode 17: Stressing the permanent cables". Youtube. TriMet. November 2013. Retrieved 21 October 2025. Video describing tightening of cables on the Tilikum Crossing cable-stayed bridge.

• "DYWIDAG Stay Cable Systems - Kampen Bridge, Netherlands". Youtube. Dyckerhoff & Widmann. May 2012. Retrieved 21 October 2025. Video that illustrates a particular process for tightening cables on a cable-stayed bridge.

• Jones, Mark (November 2024). "Exclusive look at the Bay Bridge's suspension cables". Youtube. Retrieved 21 October 2025. Video that shows the process of removing a small piece of steel wire from the main cable of the San Francisco–Oakland Bay Bridge. The wire will be taken to a laboratory and tested for degradation.

• "Spinning the Cables". American Experience. PBS. May 2004. Retrieved 21 October 2025. Video that demonstrates the technique for air-spinning wires to build the main cables of the Golden Gate Bridge.

• "Viaduc de Millau - Longest Cable-stayed Bridge in the World". Youtube. Space and Science. December 2022. Retrieved 21 October 2025. Video that describes the construction of the Millau Viaduct, including the unusual launching process for pushing the deck onto the piers.