Bridge

A bridge is a structure that crosses a river, lake, railroad, road, ravine, or other obstacle. Bridges perform a wide variety of functions, and can carry cars, trains, pedestrians, 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.

Bridges have been created by humans throughout history. The greatest bridge builders of antiquity were the ancient Romans, who built numerous semicircular-arch 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. Concretewhich was originally used within the Roman Empirewas 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, customer preference, 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.

After a bridge is built, maintenance must be performed to ensure that the bridge remains open to traffic, avoids safety incidents, and achieves its intended lifespan. An important part of maintenance is inspecting for damage or degradation, and taking steps to mitigate any issues. Degradation can come from a variety of sources: expansion/contraction from freeze/thaw cycles, rain and snow, oxidation of steel, saltwater spray, carbonation of concrete, vehicular traffic, corrosion, mechanical abrasion, poor bridge design, and improper repair procedures. Provided by Wikipedia