Bridge
A bridge is a structure designed to span an obstacle, such as a river or valley, allowing vehicles, pedestrians, and other loads to pass across. Most bridges consist of a flat deck, supported by beams, arches, or cables. These structures rest on a foundation that is carefully designed to transfer the weight of the bridge to the subsoil without settling.
Bridges can be constructed in a wide variety of forms, determined by the location, intended purpose, and available construction technologies. Simple bridge structures include beam bridges made from logs, and suspension bridges made of ropes or vines. The Romans and ancient Chinese built major arch bridges of timber, stone, and brick. During the Renaissance, advances in science and engineering led to wider bridge spans and more elegant designs. Concrete was perfected in the early nineteenth century, and arch bridges are now built primarily of concrete or steel.
With the Industrial Revolution came mass-produced steel, which enabled the creation of more complex formsincluding truss and cantilever bridgesthat permitted bridges to cross wide rivers or deep valleys. The longest spans use suspension or cable-stayed designs, both of which rely on high-strength steel cables to support the deck. Over time, the maximum achievable span of bridges has steadily increased, reaching in 2022. Other bridge forms include multi-span viaducts, which can cross wide valleys; trestles, a common design for carrying heavy trains; and movable bridges including drawbridges and swing bridges.
The design of a bridge must satisfy many requirements, namely connecting to a transportation network, providing adequate clearances, and safely transporting its users. A bridge must be strong enough to support its own weight as well as the weight of the traffic passing over it. It must also tolerate violent, unpredictable stresses imposed by the environment, including winds, floods, and earthquakes. To meet all these goals, bridge engineers typically use limit state design processes and the finite element method.
Many bridges are admired for their beauty, and some spectacular bridges serve as iconic landmarks that provide a sense of pride and identity for the local community. In art and literature, bridges are frequently used as metaphors to represent connection or transition. Bridges can create beneficial impacts on a community, including shorter transport times and increased gross domestic product; and also negative effects such as increased pollution and contributions to global warming.
History
Antiquity
The earliest forms of bridges were simple structures for crossing wetlands and creeks, consisting of wooden boardwalks or logs. Pilingswhich are critical elements of bridge constructionwere used in Switzerland around 4,000 BC to support stilt houses built over water. Several corbel arch bridges were built 13th century BC by the Mycenaean Greece culture, including the Arkadiko Bridge, which is still in existence. In the 7th century BC, Assyrian king Sennacherib constructed stone aqueducts to carry water near the city of Nineveh; one of the aqueducts crossed a small valley at Jerwan with five corbelled arches, and was long and wide. In Babylonia in 626 BC, a bridge across the Euphrates was built with an estimated length of. In India, the Arthashastra treatise by Kautilya mentions the construction of bridges and dams. Ancient China has an extensive history of bridge construction, including cantilever bridges, rope bridges, and bridges built across floating boats.The ancient Romans built many durable bridges using advanced engineering techniques. Many Roman aqueductssome still standing today used a semicircular arch style. Examples include the Alcántara Bridge in Spain and the Pont du Gard in France. 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, were waterproof. The enormous timber and stone Trajan's Bridge crossed the Danube river and was over long.
300 to 1400
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 bridges like the Pont d'Avignon, bridges of the Durance river, and the Old London Bridge. Surviving examples include the Ponte Vecchio in Florence, the Old Exe Bridge, and the Monnow Bridge in Wales.
1400 to 1750
In 15th- and 16th-century Europe, the Renaissance brought a new emphasis on science and engineering. Figures such as Galileo Galilei, Fausto Veranzio, and Andrea Palladio wrote treatises that applied a rigorous, analytic approach to architecture and building. Their innovations included truss bridges and stone segmental arches, resulting in Florence's Ponte Santa Trinita, Rialto Bridge in Venice, and Paris's Pont Neuf. Military and commercial bridges were constructed in India by the Mughal administration. The Asante Empire in Africa built bridges over streams and rivers using tree trunks and beams.1750 to 1900
In the late eighteenth century, the design of arch bridges was revolutionized in Europe by Jean-Rodolphe Perronet and John Rennie. They designed arches that were flatter than semicircular Roman arches, which yielded faster construction times, better water flow under the bridge, and slimmer piers. These designs were used for Pont de la Concorde and New London Bridge.With the advent of the Industrial Revolution, iron became an important construction material for bridges. Both cast iron and wrought iron were used for building bridges. The Iron Bridge in Englandmade of cast iron and completed in 1781was the first major bridge made entirely of metal. Several long suspension bridges were built in the early nineteenth century using iron eyebars.
The age of railways began in the 1820s, and led to major innovations in bridge design. Britain is representative of how railways influenced bridge-building in industrialized nations: led by designers Isambard Kingdom Brunel, Robert Stephenson, and Joseph Locke, British railway bridges steadily grew in size as the decades passed. Notable bridges of that era include the High Level Bridge, Royal Border Bridge, Britannia Bridge, Royal Albert Bridge, and Clifton Suspension Bridge. The number of railway bridges in Britain increased from 30,000 to 60,000 during the Railway Mania era. Railway bridges primarily used masonry and stone arch designs, because those could withstand the tremendous loads imposed by trains, but iron beam designs were also used. The abundance of inexpensive lumber in North America led that continent to favor timber as a bridge material: using truss designs and trestle designs.
The mass production of steel in the late nineteenth century provided a new material for bridges, enabling lighter, stronger truss bridges and cantilever bridges; and steel wires replaced iron bars as the preferred material for suspension bridge cables. Concretewhich was originally used within the Roman Empirewas improved with the invention of Portland cement in the early nineteenth century, 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.