Concrete. Concrete and other similar compounds are frequently utilized in bridge building (approximately 70 percent of the bridges in the U.S. are concrete). Concrete is highly robust in compression, but it must be reinforced with steel bars if necessary. It is also useful as a medium for the construction of road surfaces because it can be poured into the shape of a mold or formwork and then cured by exposure to air quality moisture. The term "concrete" comes from the Latin word meaning "dried mud", reflecting its origin as loose soil mixed with water and placed in a mold to cure.
Glass has been used for centuries as a transparent material for windows and doors. It is strong, lightweight, and does not corrode. However it is not suitable for use in structures that receive heavy traffic due to its brittle nature.
Aluminum has been used extensively in aircraft manufacturing since it was introduced into military service in 1927. It is nearly twice as strong as steel but only one-seventh the weight. Unlike steel, which is usually cast in one piece, aluminum components are mostly manufactured by extruding a metal rod through a die to produce shapes with exactly the right cross-section for strength and rigidity. The most common source today is bauxite ore, which is refined into aluminum oxide (alumina) at high temperatures.
Steel and concrete are the most often used materials for contemporary bridge building. Wood, iron (a distinct sort of steel), plastic, and stone are among the other materials. Prior to the availability of steel and concrete, the majority of bridges were constructed of wood, rope, and/or stone. In some cases, when there is no suitable rock available, they are made from masonry.
The type of material used to build a bridge affects its cost and its durability. For example, a wooden bridge will last only as long as the quality of the wood and how it is treated. A metal bridge, on the other hand, can be very durable if it is built well. The choice of material also affects the weight that it can support without failing. For example, a heavy truck crossing a wooden bridge will cause it to fail. But on a metal bridge, because there is less weight per unit area, it can support more traffic.
A bridge builder has many choices when selecting a material for his or her project. They include: steel, concrete, wood, plastic, iron, stone, bamboo, and rammed earth. Each one has its advantages and disadvantages. For example, steel is strong but expensive; concrete is affordable but not as strong; while wood is relatively weak but can be used in large quantities for low-cost bridges.
Wood, stone, iron, and concrete have been the four basic materials utilized building bridges. Iron has had the largest impact on modern bridges. Steel is created from iron, and steel is used to make reinforced and prestressed concrete. Concrete is by far the most common bridge material, accounting for 95% of all bridges.
Wood was the earliest material used for bridges. The first wooden bridge known to exist today was built around 350 AD in China. It consisted of a single tree standing across a stream. This tree bridge was probably made out of pine trees because they are widely available and relatively easy to work with. In the Middle Ages, wood became more stable when it was joined together with crossbars and nails. With advances in metal working, more sophisticated bridges were built out of metal. By the 17th century, British bridge builders were using primarily imported French materials for their structures.
The first true iron bridge was built in 1550 over the River Swilgate in England. It was 100 feet long and used eight tons of iron plates welded together with copper cables as trusses. This bridge used technology that was also being developed for ships at this time so it is possible that it was built by the same person. Other countries followed suit and within a few decades almost every major city in Europe had several iron bridges.
Traditional bridge construction materials include stone, timber, and steel, as well as reinforced and pre-stressed concrete. Aluminum and its alloys, as well as various plastics, are utilized for specific elements. Composite materials are also used in some applications.
The choice of material depends on factors such as cost, durability, weight, ease of construction, and suitability to the intended use. Stone and brick are very durable but can be heavy. Wood is a common material for bridges because it is light and strong, and easy to work with. However, wood bridges can deteriorate over time due to water damage and insects. Steel is stronger than most other materials used for bridges and can be used in thinner sections, which reduces weight. But it can be expensive and hard to work with. Pre-stressed concrete is an engineered product where reinforcement is placed inside concrete before it sets up making the concrete stronger than normal concrete. This method allows for longer spans and fewer supports per span compared to other types of bridges.
Bridges are designed using structural analysis programs that calculate the requirements for strength, stiffness, and other characteristics for a given application. The designer may choose from among different types of structures (such as truss or cable-stayed) and sizes of components (such as single lane bridges).
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