For millennia, humans have created bridges to get from one point to another. Depending on the distances between those points, the materials available and the type of land, different styles of bridges are used. Here is a list of six types of bridges that can be found around the world.
Suspension bridges date back to early 1800s in England and Europe. These bridges are made up of a series of cables held up by suspension towers and an "anchorage" at either end. Because most of the weight is shifted through cables to the secure anchorages, suspension bridges can be built to cover distances of several thousand feet. Some of the world's most famous bridges are suspensions, including the Golden Gate Bridge in San Francisco and the Brooklyn Bridge in New York.
Arch bridges are among the oldest bridges in the world. In fact, the modest Arkadiko Bridge in Greece is said to have been built by the Mycenaean people circa 1300BC. The physics of an arch bridge are similar to an arched doorway, in which pressure is pushed away from the top centre and down through the supporters on each end. This style of bridge remains popular, with builders finding materials that can handle compression even more effectively today than with earlier bridges.
The truss bridge was one of the most popular types of bridges in America during the second half of the 19th century and the early 20th century. This was because these are ideal bridges for the use of wrought iron, a material that became widely accessible after the Industrial Revolution. As the name suggests, the design of the truss bridge includes a series of trusses, which, when placed together, form a framework of pressure-distribution along each side and on top of the bridge.
The beam bridge is perhaps the most basic type of bridge. In its simplest form, the beam bridge is merely a plank supported by structures on either end. These support structures need to push inward so that they adequately absorb the tension of the beam. Depending on the length of the bridge, pillars may need to be placed in between each end for added support. The 24-mile-long Lake Pontchartrain Causeway in Louisiana consists of several thousand support pillars.
A drawbridge is a type of movable bridge that has been in use for centuries. The idea behind the drawbridge is that it can be lifted when need be to let boats pass. The design was originally used for castles, which were surrounded by moats with drawbridges that could be raised to exclude unwelcome visitors. Today, drawbridges are more commonly seen over rivers with a lot of boat traffic. This style of bridge allows for any size ship to pass through without danger of striking the bridge. While drawbridges used to be manoeuvred by a series of pulleys, many today are mechanically operated by electronics.
Cable-stayed bridges are often confused with suspension bridges because of the similarities in appearance. The physics of the two bridges are quite different, however. The cables in a cable-stayed bridge are never suspended, but in fact pull tightly to the bridge deck from the tops of the pillars, causing the pillars to burden the entire load of the bridge. Although cable-stayed bridges are not usually the most economical style of bridge to erect, they are efficient, and many have received much adoration simply because of their beauty. For example, in 1988, the Presidential Design Award from the National Endowment for the Arts was granted to the Sunshine Skyway bridge in Tampa, Florida.
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