Bridges_Notes

= BRIDGE = 

A bridge is a structure designed to save natural obstacles such asrivers, valleys, lakes or stretches of water, and artificial barriers such as railways or roads, in order to unite travelers roads, animals and goods



= =

Tipe of Bridges
1. **Beam bridge****:** This is the earliest and simplest kind of bridge: a fallen tree lying over a stream. Is basically a horizontal structure that is resting on two piers, one at each side. Its weight and any traffic on it is directly supported by the piers. The weight is traveling directly downward. The compression force manifests itself on the top side of the beam bridge's deck (or roadway). This causes the upper portion of the deck to shorten. The result of the compression on the upper portion of the deck causes tension in the lower portion of the deck. This tension causes the lower portion of the beam to lengthen.



2. **Arch bridge****:** It is a semicircular structure with abutments on each end. The design of the arch naturally diverts the weight from the bridge deck to the abutments, and they're always under compression. The force of compression is pushed along the curve of the arch toward the abutments, practicly there's no tension because the natural curve of the arch and its ability to dissipate the force greatly reduces the tension on the underside of the arch. The greater the degree of curvature (the larger the semicircle of the arch), however, the greater the effects of tension on the underside.



3. **Suspension bridge****:** Its one where cables (or ropes, or chains) are strung across the obstacle and the deck is suspended from these cables. Modern suspension bridges have two towers through which the cables are strung. Thus, the towers are supporting the majority of the roadway's weight. The compression pushes down on the suspension bridge's deck, but because it is a suspended roadway, the cables transfer the compression to the towers, which dissipate the compression directly into the earth where they are entrenched.

The supporting cables, running between the anchorages are the recipients of the tension. The cables are literally stretched from the weight of the bridge and its traffic as they run from anchorage to anchorage. The anchorages are under tension too, but since they, like the towers, are held firmly to the earth, the tension they experience is dissipated.



Why were the bridges built?
Human beings have used new technology to solve problems and ease their physical burdens, and bridges are technological tools that aim to solve the problem of crossing an obstacle in such a way as to shortening the effort and time needed to do so.



Did they provide benefits? To whom? why?
Some of the benefits of bridges are obvious: supplies of food and traded goods can get across an obstacle or through difficult terrain in a shorter time. In economic terms, the cost of travel and the financial benefits of increased social cohesion and sharing resources rise. Today bridges allow easy travel across major rivers and estuaries, over the new obstacles of motorways and railway lines, and between neighbouring islands. International trade and travel depend on shipping and air routes, but efficient distribution networks depend on bridges.

What are they made of?

 * Wooden bridges, are quick to build and cost, but they are very resistant and durable, they are very sensitive to the weather

 =<span style="background-color: #008080; color: #ffff00; display: block; font-family: 'Comic Sans MS',cursive; text-align: center;">Vasco da Gama Bridge =
 * <span style="color: #008000; font-family: 'Comic Sans MS',cursive; font-size: 17.6px;">Stone bridges, are extremely resistant, compact and durable, butnow construction is very expensive. Care necessary for their maintenance are scarce, as well resist climate agents.
 * <span style="color: #008000; font-family: 'Comic Sans MS',cursive; font-size: 17.6px;">Metal bridges: they are very versatile designs allow for large areas,are built quickly, but are expensive to build and are also subject to corrosion, both from the weather as the gases and smoke from factories and cities, which is an expensive maintenance.
 * <span style="color: #008000; font-family: 'Comic Sans MS',cursive; font-size: 17.6px;">Reinforced concrete bridges, are mounting rapidly, and in manycases supporting prefabricated elements, are resistant to breakinglonger spans the bridges of stone, although lower than those of iron, and maintenance costs are very low, since are very resistant to theaction of atmospheric agents