Girder bridges, also known as beam bridges, are the most common and simplest type of bridge. They basically consist of a horizontal beam supported at each end by a pier or other similar structure. Longer girder bridges must be supported along their span by additional structures. Girder bridges are typically used over short to medium distances. The need for numerous additional supporting structures below the bridge makes them unsuitable for spanning greater distances.
I-beam girders are among the most commonly used girders in bridge construction. I-beam girders are made from rolled steel, and bridges constructed using I-beams are often called rolled steel girder bridges. I-beam girder bridges are economical, simple to design and relatively straightforward to build, making them a good option in most cases. However, according to AboutCivil.com, “if the bridge contains any curves, the beams become subject to twisting forces, also known as torque." I-beams, therefore, are best used to construct bridges that do not have any significant curves.
Box girders are often used in the construction of roadway flyovers and elevated bridges for light rail transport. Box girders are more expensive than I-beams and not as easy to build. However, they do have some important advantages. For example, box girders are better suited to handling twisting forces, notes the Minneapolis Riverfront District Bridges website. As such, they are ideal for the construction of curved bridges. Box girders are also more effective than I-beams over longer spans.
Plate girders became popular in the late 1800s when they were used in the construction of railroad bridges, according to the website The Constructor. Flat steel sections were initially riveted or bolted together to obtain the desired overall span. In the 1950s, welding became the preferred method of joining the large steel sections. This was a more economical and efficient construction method, and also allowed the construction of more aesthetically pleasing bridges.
A concrete girder bridge is made of pre-stressed concrete in an I-beam shape. The concrete is also reinforced with steel rods. This combination is particularly effective in bridge construction. “The concrete withstands the forces of compression well and the steel rods embedded within resist the forces of tension,” notes Nova Online. Concrete is also one of the cheapest construction materials.