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A Bridge is a structure spanning and providing passage over a gap or barrier, such as a river or roadway (thefreedictionary, "no date"). They are used to cross over natural obstacles or artificial ones. Some of them serve highways, canals, railways, and pedestrian walkways. They are works of art as well as engineering. The idea beyond bridges started long time ago, when the primitive man tried to cross small rivers or shallow streams and then developed to the way it is. Bridges are not only meant to join separated pieces of land, but also to make people closer to each other, to make a world without strangers and living together in one place without any boundaries. They increase the communication between cultures. So, they are considered as social and cultural constructions beside their rule in transportation. Bridges are very important elements of any city's infrastructure. Some countries build remarkable bridges just to make them landmarks. Many of the ancient bridges are restored today as a memory of the past rather than their practical utility ( Knapp, 2008). Bridges have so many different types in terms of structure, design and construction purposes. However, there are four main types of bridges: the pile bridges, the arch bridges, the truss bridges and the cable-supported bridges.
People in the past used to travel long distances in order to get over a lake or a river. Then, the primitive man might build many crossing over shallow streams and small rivers not only by falling trees but also by pilling rocks for piers. So, the wood is considered as the first material the human used for building bridges. The early man also used cable of ropes stretched across a river which were used only for people to get over places. The early types of bridges were less than reliable because moving heavy loads on them were often impossible. Then, they found out that they can use supports to get over larger lakes and rivers. This kind of bridges which contains a beam and some columns is called "a Pile Bridge" which is considered as the first model of bridges. It first started in the ancient ages. The Babylon built many bridges of this type in the period 100-300 B.C. The construction of such bridges is very common today since it is the simplest and the cheapest type to construct. After that, the Chinese used sophisticated rope of bridges to cross over places which were practical for light loads and were spanned for 1800ft. Such types are used nowadays in different parts of the world as pedestrian bridges. Then, the Romans came up with a different type of a bridge called "an Arch Bridge" in 100 B.C. These bridges were made of stone, wood or concrete. They are good to cross over rivers since they do not require columns. The Romans were considered as the best bridge builders in that time. They introduced some developments which were not existed before such as the using of the natural cement. Then, another type of bridges came up called" a Truss Bridge". These truss bridges were composed of connected elements oriented in triangles and were made of wood or stone. It can support large amount of weight and span great distances. This era is called the beginning of the modern bridges. It started in the middle ages 11th-16th. There were some famous bridges built in the United Kingdom in Old London particularly. In the 1779, the world's first iron bridge-Coalbrookdale bridge- was built across the river Severn in the county of Shropshire in England (cortright, 1988). This new technology of using iron in bridges helped a lot in reducing the time of assembling the parts. The main benefit of using iron in bridges was carrying thousands of tons. Then, the idea of cable-supported bridges was first used in 1867 by John A. Roebling in the Brooklyn bridge across East River in New York in addition to the traditional suspension system (steel 13 pg). It was the first of its kind. In the last centuries, engineers started developing those types and designing bridges using more than one method.
A girder bridge or "a beam bridge" is the simplest type of bridges and the most basic one. They are called girder bridges because they are built of girders placed on the foundation piers. They are the cheapest to construct and the faster to build. A beam bridge consists of three separate parts: a deck, a pile, and a pile base. When the load of traffic is subjected on the bridge, the deck will carry the load and transfer it to the girders, piles, and in turn to the pile base and then to the ground. The primitive man built such kind of bridges and used them to cross shallow streams or small rivers. They were mainly made of wood. However, the use of it increased a lot and they are now made of a horizontal beam "a deck" and columns "piers". The number of those columns depends on the length of the bridge. The longer the bridge the more columns needed. Girder bridges have always been popular for bridges of spans up to 20m, both for railways and highways. The reason for this popularity was primarily because of the simplicity in their design and manufacture, as well as the ease and speed of their construction at site. They first used concrete in the design of girder bridges for economical issues. Then, steel was being used as a material in the construction of bridges in the support of beams, a rigid horizontal structural element, to support the deck ( Ghosh,2006). They are commonly used for elevated structures of light rail transport and also they are very commonly used for highway flyovers. Another benefit of girder bridges is they have very good resistance to winds and natural disasters. Moreover, the failure percentage of this type of bridges is very low comparing to the other types. They are part of any city's infrastructure. They are used to reduce the congestion as well as connect a city to others. There are four types of girder bridges: rolled steel girder, a plate girder, a concrete girder, and a box girder bridge. A rolled steel girder bridge is usually used for spans between 10-30 meters. The height of columns used for this type is usually 3 meters. It is made of I-beams or H-beams, used for straight decks. The second type is a plate girder bridge. These girders are usually used for spans between 10-100 meters and height of more than 3 meters. It can take more strength than the first type. The third type of girder bridges is a concrete girder bridge. It is made of concrete in an I-beam. They used precast or prestressed concrete for this type. It is best for spans between 10-50 meters. Finally, a box girder bridge is made of rectangular box shape girders instead of the H-beams and I-beams shapes. These box girders are used for curved bridge deck which is subjected to twisting. They are more expensive than the other types (Stern et al.,1996). The most famous girder bridge is the Rio-Neteroi in Brazil. It is considered as the sixth longest bridge in the world. The length of this bridge is 13,290 meters, 8.837 over water.
The second type of bridges is the arch bridge. It is considered as the second oldest bridge type after the girder bridge. The Romans first came up with the idea of an arch bridge from the ancient time. They used stone because of its beauty beside its durability. Many ancient and well known examples of arch bridges are still in use today. The best example is the Emperor Trajan Bridge which was built in 104 A.D. this bridge was built about 1900 years ago though still looks new(cortright,1988). an arch bridge can be most the beautiful bridge type. Arch bridges are good choice of crossing rivers, valleys and any artificial obstacles since there are no columns in the middle of the arch bridge. It contains a curved structure either above the deck or below it and supports. There are three types of arch bridges: hinge-less arch, three-hinged arch and the tied arch. The first one cannot be built if the ground is not solid enough to hold the supports. This type was common long time ago. The second type is the three-hinged arch. It is called a three-hinged arch because there is an extra hinge in the middle of the arch in additional to the two hinges on the ground. The problem of this type it does not resist movement in the foundation, due to earthquakes. So this type is rarely used anymore. The third type which is commonly used nowadays is the tied arch. It does not require a solid or stable ground, so it allows construction anywhere regardless to the types of soil. It also resist any movement occur in the structure due to winds, earthquakes etc. the most famous arch bridge is the Sydney Harbour Bridge in Australia. It was constructed in 1932 by Sir Ralph Freeman. It is still considered as a remarkable landmark bridge in Australia.( Ghosh,2006 )
The truss bridge is composed of rigid frames of short straight pieces connected together to form a series of stable beams oriented in triangles. Those beams when they are comprised together can support large amount weight. They are considered as the oldest types of modern bridges. according to Ghosh(2006), the concept of modern truss system was first developed by Andrea Palladio, a 16th century Italian architect. They can span great distances without using columns. But if it is too long, so they put some columns arranged in equal distances to support the truss bridge. The design of the structure of a truss bridge is quiet simple and particularly cheap to construct. These beams are can support large amount of force in tension. According to cortright(1998), there are two types of truss bridges: king post truss and queen post truss. The king post truss bridge is the simplest truss styles to implement. It contains a deck and beams that have a shape of two angled supports leaning into a common vertical support. When the force is subjected to this kind of bridge from any angle, it will be distributed equally between the component supports. The second type of truss bridges is the queen post truss. It is similar to the first type in that the support beams are angled to the center of the structure. The only difference is there is a horizontal support beam, keystone, which connects two different support beams subjected to the center of the structure. the first true truss bridge is called" Town Lattice" which was built in the 1820. It was called a true truss because it was the first of its kinds free from arch action( Ghosh,2006). the most popular truss bridge is Queen Post Truss King Post Truss
A cable-supported bridge is a bridge that consists of one or more columns (normally referred to as towers or pylons), with cables supporting the bridge deck. There are two major classes of cable-stayed bridges, differentiated by how the cables are connected to the tower(s). Steel cables are extremely strong but very flexible. Cables are very economical as they allow a slender and lighter structure which is still able to span great distances. Though only a few cables are strong enough to support the entire bridge, their flexibility makes them weak to a force we rarely consider: the wind. For longer span cable-stayed bridges, careful studies must be made to guarantee the stability of the cables and the bridge in the wind. The lighter weight of the bridge, though a disadvantage in a heavy wind, is an advantage during an earthquake. However, should uneven settling of the foundations occur during an earthquake or over time, the cable-stayed bridge can suffer damage so care must be taken in planning the foundations. The modern yet simple appearance of the cable-stayed bridge makes it an attractive and distinct landmark. There are no distinct classifications for cable-stayed bridges. However, they can be distinguished by the number of spans, number of towers, girder type, number of cables, etc. The most famous cable-supported bridge is the Tsurumi Tsubasa Bridge in Yokohama. It has a center span of 510m making it the longest single plane cable stay bridge in the world.