Bridges_page


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__BRIDGES-PART I__
A **bridge**is a structure built to span a gorge, valley, road, railroad track, river, body of water, or any other physical obstacle. Designs of bridges vary depending on the function of the bridge and the nature of the terrain where the bridge is to be constructed. the information
 * What are they?
 * Different types of bridges

The first bridges were spans made of wooden logs or planks and eventually stones, using a simple support and crossbeam arrangement. Most of these early bridges were very poorly built and could rarely support heavy weights. It was this inadequacy which led to the development of better bridges.
 * ==Characteristics==
 * ==Materials used==
 * Iron and steel, wood, concrete, stones, etc.

> > Advantages: > To connect two cities, or two places > To transfer people > It allows to cross without no problems rivers, etc. > > Disadvantages: The costs are high The repair of the bridges is expensive They requiere long time to construct them, etc.
 * Technology involved in their contructionGiven the present technological possibilities, the laying of a bridge, except for the very small ones, one will be due to divide in parts; this division will be as much greater whichever greater is the light of the bridge, although in it other factors take part that can correct this basic exposition. The bridge will be due to construct by addition of successive parts, so that in each stage of construction a partial structure is created that is due to resist to itself and must allow the construction of the following phase; or, an auxiliary structure can be used that resists the different parts, until the structure is finished, resists to itself, and then the auxiliary structure can be retired
 * ==Advantages and disadvantages==