Different types of bridges
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Written on 30-04-2010 by Loretta
A bridge is one way to lead traffic through obstacles. This obstacle could be a natural one (like a river or a valley), but can also be an artifical one (canal, railway).
The Roman and Chinese were one of the first to build bridges. It was often necessary to build bridges, because these nations had large empires with a great road system. These bridges were often build out of wood, natural stone or lianes, but sometimes also other constructions were used. In the middle ages, traffic increased, so more solid bridges had to be build. Most of the times these were made of stone, and very often they were beautified with little arches. Because this system of bows was relatively new, the arches were merely higher than 60 metres.
In the 18th century, constructions were calculated to build better and firmer bridges. In the 19th century, there was a large demand for more robust bridges. The intensity of traffic increased, trains and cars got heavier, and longer distances had to be crossed. Therefore, more iron and steal being used for the construction of bridges. With this material spans could be made. An other solid material that was used for this end was reinforced concrete. Through combining these materials, bridges of good quality could be made.
These developments went on and on, and the material got lighter and lighter. Besides that, it became possible to produce certain parts of a bridge in a factory beforehand, after which they could be fitted in with large cranes. This way, it became more easy to bridge large valleys.
Types of bridges
There are many ways to build a bridge. Bridges could be categorized into different types. Below is a short summary:
- Drawbridge. To one end of this bridge, a heavy weight is attached, exactly enough to keep the bridge down. When the bridge needs to be raised, little force is needed. Nowadays this bridge is not very often used anymore.
- Swing bridge. This bridge is able to turn, so an opening emerges. These types of bridges are applied with rivers along which boats sail.
- Vertical lift bridge. This bridge can be lifted, for example when a boat passes. The bridge is attached to a few poles.
- Leaf bridge. This bridge can be compared with the drawbridge. A weight is attached to the back side of the actuator.
For a busy canal on which many boats sail, these types of bridges aren’t that practical. Traffic will encounter inconvenience, and traffic jams will occur because the bridge has to be opened every time. That’s why on these places stable bridges are build. A short summary:
- Arch bridge. This bridge has arches, making it more robust.
- Hanging bridge. This bridge has pillars with towers. Hanging from these towers are steel cables, from which every few metres are more steal cables. Therefore, optimal strength is reached.
- Slab bridge. This bridge only consist of a concrete plate. Only of use for small distances.
- Beam bridge. This is a type of slab bridge, only this bridge is accomplished with steel to, making the bridge more solid.
Contruction of a bridge
Before a bridge can be build, questions needs to be answered. Such as the place of the bridge, and the purpose. These are important questions for considering which type of bridge has to be build. Besides that, a bridge has to meet five important criteria:
- It has to be strong. The pillars have to be able to support the bridge, and the traffic that is crossing it
- It has to be stable
- It has to be able to vibrate
- It has to be resistant to very hot and very low temperatures, for some parts will shrink with cold, and enlarge with heath
- Besides, a bridge has to be sage. Fences along the sides of the bridge are important.
Long ago, ships often encountered inconvenience with the construction of bridges, because often they were build from out the water. Nowadays, bridges are build through an extension method. From both sides the bridge is being built. Finally, only one piece, the middle piece, has to be fit in. Mostly this is done from out the water, with a special crane.
Famous and special bridges
Many bridges are build all over the world. Below some national (Dutch) and international bridges are listed, each with a special feature
|Golden Gate Bridge, San Fransisco||Yearly, about 150.000 litres of red paint is needed to paint this bridge.|
|Ponte Vecchio, Florence (Italië)||Shops are established on this bridge.|
|Brooklyn Bridge, New York||When standing on this bridge, one can see the skyline of New York in front of him.|
|Erasmusbrug, Rotterdam||This bridge is also known as ‘the Swan’, for the white part to which the shoring is attached looks like the neck of a swan|
|Martinus Nijhoffbrug, Zaltbommel||Bridge that is build through the extension method|
|Sint-Servaasbrug, Maastricht||The oldest bridge of The Netherlands.|
|Zeelandbrug, over de Oosterschelde||Has a length of 5 kilometres, making it the longest bridge of The Netherlands|
|Spoorbrug, Gouda||A drawbridge, a type that is not encountered very often|