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A bridge is a structure designed to span an obstacle, such as a river or railway, 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. 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 19th century, and arch bridges are now built primarily of concrete or steel. The longest spans use suspension or cable-stayed designs, both of which rely on high-strength steel cables to support the deck. 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. To meet all these goals, bridge engineers typically use limit state design processes and the finite element method.

Ancient China has an extensive history of bridge construction, including cantilever bridges, rope bridges, and bridges built across floating boats. This bridge is also historically significant as it is the world's oldest open-spandrel stone segmental arch bridge. 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. Notable bridges of that era include the High Level Bridge (1849), Royal Border Bridge (1850), Britannia Bridge (1850), Royal Albert Bridge (1859), and Clifton Suspension Bridge (1864).

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.

Examples include the Puente de la Mujer swing bridge in Buenos Aires, the Gateshead Millennium – a rare example of a tilt bridge – over the River Tyne, and the Hörn Bridge in Germany.

An extradosed bridge combines features of a box girder bridge and a cable-stayed bridge.

A bridge made from two or more distinct materials (for example, steel and concrete) is known as a composite bridge.

Because of their ability to carry large amounts of motor vehicles, double-deck bridges are often found near large cities carrying cars on both decks, for example, the DuSable Bridge in Chicago, Tsing Ma Bridge in Hong Kong, the Øresund Bridge connecting Copenhagen and Malmö, and the Shimotsui-Seto Bridge near Kurashiki.

Many loads imposed on a bridge – wind, earthquakes, and vehicular traffic – can cause a bridge to experience irregular or periodic forces, which may cause bridge components to vibrate or oscillate.

The deck of a bridge is the flat, horizontal surface that extends across the full span of a bridge.

Bridge managers use bridge management systems and life-cycle cost analysis methodologies to manage a bridge and estimate the maintenance costs of a bridge throughout its lifetime.

Over time, bridge failures have led to significant improvements in bridge design, construction, and maintenance practices.

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.

Quick Facts

• Notable bridges of that era include the High Level Bridge (1849), Royal Border Bridge (1850), Britannia Bridge (1850), Royal Albert Bridge (1859), and Clifton Suspension Bridge (1864).
• 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.
• Simple bridge structures include beam bridges made from logs, and suspension bridges made of ropes or vines.
• 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.
• Bridge managers use bridge management systems and life-cycle cost analysis methodologies to manage a bridge and estimate the maintenance costs of a bridge throughout its lifetime.

Source material: Wikipedia - "Bridge". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.