Bridges

= BRIDGES. =

A bridge is an structure built that provides access between lands that are separated by obstacles such as water, valleys or roads. There are too many types of bridges, such as: cable-net bridges, covered bridges, girder bridges, hyperbolic paraboloid bridges, movable bridges, pontoon bridges, rigid fram bridges and trestle bridges. But, the main and the most basic bridges are:

 - **Beam bridges:** is the simplest type of bridges. It is made of two or more supports which hold up a beam.



 - **Arch bridges:** in this type of bridges, weight is carried outward along two paths, curving toward the ground.



 - **Suspension bridges:** consists in a hung by cables which hang from towers.



 - **Cantilever bridges:** in this type, two beams support another beam, which is where the trafficway is.





The bridges are constructed with different types of materials. The most used ones are:


 * - Stones:** materials used in the greatest old bridges. This material gives long life to the bridge.

- **Iron**


 * - Reinforced and pre-stressed concrete:** this material is used in almost all construction works. Concrete bridges turn out to be beautiful.

- **Steel:** has the highest and most favorable strength qualities.

 The principal problem in bridges, is that can twist or bend under sever weather conditions. The technology used in order to prevent this, bridges must be rigid enough to resist those movements. Also, each structural member of the bridge must be strong enough to resist the load which is placed.

 The advantages of bridges are very clear. Bridges ease communication between two places in a shorter time. This improvement helps the supplies of food, easier travel and better communication in an intellectual, political and religious way. Also, bridges require a lot of money for its construction and even more for its maintenance, which is an economical disadvantage.

 Some of the best bridges found in the world are:


 * Bridge over the Colorado river - United States.**




 * Mostar bridge - Bosnia Herzegovina.**




 * Half Penny Bridge - Ireland, Dublin.**

**Rio Antirio Bridge - Greece.**


 * Love Bridge - Taiwan.**