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Page history last edited by mariufernandez 15 years, 6 months ago
Summary about bridges. 
BRIDGES. Conecting people.
Every day when we are walking on the streets or just walking around, you can see many structures that help us to get over some obstacles that we find on the road. For example, if mountains go into pieces we use a retaining wall, if we need to pass across the mountain we use the tunnel, and if we need to pass or establish a connection between 2 parts, we use a bridge.

Bridges are structures made to connect places, cross obstacles or avoid problems with the terrain, river, lake, and any other trouble with the nature. To choose the type of bridge than you are going to use, we must take into consideration some aspects like the conditions of the place, the span that you have to cover and obviously, the form and design that you want to your bridge looks like. Following this, it could be a beam bridge, arch bridge, suspension bridge, cantilever bridge, truss bridge or cable-stayed bridge
The beam bridge is the most common and basic type of bridge, its span is around 10 m to 200 m, and the structure rest on two or more piers, depends on the length of it. The structure is based on I-beam girders or box girders of steel. This type of bridge is limited in the design that it can take, especially in the I- beam bridges because of the rigidity of the girder, if its design have any curves, it can’t take it.

Beam Bridge

In the same way works the arch bridge but this time it covers 40 m to 150 m. This bridge because of its structure, doesn’t need any piers at the center and it’s commonly used to cross valleys, rivers or another condition, that doesn’t need support at the center. At the beginning of this type of bridge, the materials used for it were stone but nowadays the materials for this structure are reinforced concrete most of the time. It also could be made of precast concrete and some steel; this is one of the oldest and the classic type of bridge.
Sidney Harbour Bridge
 Following with the different types of bridges, we have the truss bridge. This is a simple skeletal structure based on connected elements, that together act in tension and compression to support the load and span great distances of 40m to 500 m aprox. This type of bridge were developed starting with the beam bridge, and it is one of the less expensive and quick bridge to construct, it is usually made of steel, iron, reinforced concrete and prestressed concrete. Next, we have the cantilever bridge, this type of bridge usually uses pairs of cantilevers on the extremes with a short beam bridge between the cantilevers, and this is a variation of a simple beam bridge.



 Truss Bridge. Little Manatee River

 Cantilever bridge. Forth bridge Edinburgh
Approached a little more to modernity, we have the suspension and cable-stayed bridges. These structures may look similar but in fact they are a little different, the suspension bridge allows the longest spans until these days, about 70 m to 1000 m or more. This bridge is a continuous girder with one o two towers above piers in the middle of the span, where the main load are supported by suspension cables, very rigid. On the other hand, the cable stayed bridge is a continuous girder too, with one or two piers in the middle of the span but this time from these towers, to cables elongated down diagonally to both sides and support the girder. The cable stayed bridge in contrast with suspension bridge has less span length, 110 m to 480m, this design is a great option for a span length between a cantilever bridges and suspension bridges.

Suspension Bridge. Bristol, UK.



 Cable stayed Bridge. Rama VIII, Thailand.
Another important thing to take into account when we are studying bridges are the forces that act on it. When we see a bridge, we can’t imagine how many forces act on it. Making a bridge isn’t just put towers at the extreme and put a road above it. To make a bridge you need to think about the forces that will work, the lenght of the distance you need to cover or the sites you want to connect.
  Some forces that act on a bridge are tension, compression, torsion, resonance, but the basic forces are tension and compression. Tension is a force that works to expand or make longer the part it is acting on, and compression is a force that acts to compress or shorten the part. One more force that we have to take into consideration is the natural force because this influences the behavior of the other forces.


Nowadays bridges are very important structures for the world. Along the years the civilizations advanced because the use of them, these structures have promoted the exchange between cultures, the economy, and technology, discovering different materials and techniques for the construction of bridges and the resistance of them. And the most important thing, the communication between countries because without this we couldn’t have the amount  of knowledge and development that we have these days. 

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