Types of Bridges

Bridge is not merely a piece of construction, it's a concept, I think sometimes. It represents the idea of crossing over large spans of land or water, thus 'bridging' the gaps spanning long distances. A bridge connects two far-off points thus reducing the distance between them and bringing them within reach. What does it take to construct this 'idea'? It takes ingenuity! Here, we take you through all the different types of bridges, and tell you about the civil engineering and aesthetics they involve.

Arch Bridge: It is arch-shaped and has supports at both its ends. The weight of an arch-shaped bridge is borne by the supports at its ends. The Mycenaean Arkadiko Bridge in Greece of 1300 BC is the oldest existing arch-shaped bridge. Etruscans and ancient Greeks were aware of the concept of arches since a very long time. But the Romans were foremost in discovering the use of arches in the construction of bridges. Arch bridges have now evolved into compression arch suspended-deck bridges that enable the use of light and tensile materials in their construction. Moon arch, pointed arch, deck arch and two or three storied arches are some of the designs in this type of bridges. Quick Fact: The Chaotianmen Bridge in Chongqing, Southwest China is the largest arch bridge in the world. It is 1741 meters in length.

Beam Bridge: A beam bridge was derived from the log bridge. It is built from shallow steel beams, box girders and concrete. Highway overpasses, flyovers or walkways are often beam bridges. A horizontal beam supported at its ends is roughly how the structure of a beam bridge is. The construction of a beam bridge is the simplest of all types of bridges. The design of a beam bridge should be such that it does not bend under load. For this, the top surface of this bridge is compressed and the bottom surface is under tension, thus helping the beam remain in a straight line. Quick Fact: The longer a beam bridge, the weaker it is! Typically, beam bridges are not more than 76 meters long.

Cable-stayed Bridge: Structured similar to suspension bridges, the difference lies in the way they support load. In cable-stayed bridges, the cables are attached to the towers, which bear the load. Two variants of cable-stayed bridges are harp and fan. In the harp design, cables are attached to multiple points of the tower in a parallel manner. In the fan variant, all the cables connect to the tower or pass over it. Cable-stayed bridges are much stiffer than suspension bridges. The cables serve as a good support for the bridge deck. Also any number of towers can be used and it requires less cable than a suspension bridge does. Quick Fact: Skybridge, Canada is the longest transit-only cable-supported bridge in the world.

Cantilever bridge: Cantilevers are structures that project along the X-axis in space. They are supported on one end only. Bridges intended to carry lesser traffic may use simple beams while those meant to handle larger traffic make use of trusses or box girders. In a typical cantilever bridge, cantilever arms extending from opposite ends meet at the center, while in a suspended span design, they do not meet. The Forth Bridge in Scotland is a railway bridge using the cantilever design and is one of the oldest known cantilever bridges. San Francisco-Oakland Bay Bridge that is 1400 feet long is another known example of a cantilever bridge. Quick Fact: The 1800 feet Quebec Bridge of Canada holds the record of being the world's longest cantilever bridge.

Drawbridge: The term is used to refer to a bridge-like structure which is movable. Typically, a drawbridge opens up to extend over the distance it is meant to span. A castlebridge, for example, opens like a door, serving as a doorway to the castle. It could be in the form of a plank that is pivoted to the center that rotates along a designated circumference. This type of construction is often used above tidal waters, where the water levels rise and fall. A vertical lift bridge is a drawbridge that moves vertically in a plane parallel to its deck. Bascule bridges are drawbridges that swing up and down to facilitate boat traffic. Quick Fact: Tower Bridge across Thames in London is a well-known bascule bridge.

Suspension Bridge: Simply put, a bridge suspended from cables is a suspension bridge. Suspension cables are anchored at each end of the bridge. The load that the bridge bears converts into the tension in the cables and is transferred to the towers. Cables stretch beyond the pillars up to the dock-level supports further to the anchors in the ground. Vertical cables suspended down, bear the weight of the deck. One advantage of this bridge design is that it can span long distances and resist earthquakes. It requires less construction material, which reduces its cost of construction. The Tsing Ma Bridge of China and the Humber Bridge of England are some of the famous suspension bridges. Quick Fact: The Golden Gate Bridge of USA, declared as one of the Modern Wonders of the World is a suspension bridge.

Truss Bridge: A truss bridge is built by connecting straight elements with the help of pin joints. Triangular units connected at joints form the skeleton of a truss bridge. Owing to the abundance of wood in the United States, truss bridges of the olden times used timber for compression and iron rods for bearing tension. Truss bridges came to be commonly constructed from the 1870s to the 1930s. Truss is the oldest form of modern bridge design. Deck truss railroad bridge that extends over the Erie Canal is one of the many famous truss bridges. For more on this bridge type, go through Truss bridge design and types. Quick Fact: Quebec Bridge, the longest cantilever bridge span, has a riveted steel truss structure.

Man's desire to reach the 'unreachable' and venture new places led him to construct bridges that spanned huge distances and helped him overcome obstacles. A log of wood floating on water might have inspired man to build bridges for the very first time! Thanks to the developments in engineering and architecture, distances could be bridged and seemingly unreachable destinations came within man's reach.