Bridges+notes

Bridges Notes


 * ===== What are bridges? A bridge is a structure built to help to cross a valley, road, body of water, or any other obstacle, for the purpose of providing passage over the obstacle. Designs of bridges vary depending on the function of the terrain where the bridge is going to be constructed. =====

> 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.
 * === 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.
 * 1) 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.
 * 1) 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.

Think of the bridges you remember: Bridges are usually made of concrete, steel, cement, iron, wood, stone and/or metal. Bridges connect one place to another. A bridge's economic efficiency will be site and traffic dependent, the ratio of savings by having a bridge (instead of, for example, a ferry, or a longer road route) compared to its cost. The lifetime cost is composed of materials, labor, machinery, engineering, cost of money, insurance, maintenance, refurbishment, and ultimately, demolition and associated disposal, recycling, and replacement, less the value of scrap and reuse of components. Bridges employing only compression are relatively inefficient structurally, but may be highly cost efficient where suitable materials are available near the site and the cost of labor is low. For medium spans, trusses or box beams are usually most economical, while in some cases, the appearance of the bridge may be more important than its cost efficiency. The longest spans usually require suspension bridges.
 * What are they made of?
 * What are they connecting?
 * How is the span between their piers or towers?

2. What social and/or political benefits can bridges provide to places?
A bridge is designed for trains, pedestrian or road traffic, a pipeline or waterway for water transport or barge traffic. An aqueduct is a bridge that carries water, resembling a viaduct, which is a bridge that connects points of equal height. A road-rail bridge carries both road and rail traffic. Bridges can improve communication, popularity and the quality of life in the places they are built. The first bridges were made by nature itself — as simple as a log fallen across a stream or stones in the river. The first bridges made by humans were probably spans of cut wooden logs or planks and eventually stones, using a simple support and crossbeam arrangement. Some early Americans used trees or bamboo poles to cross small caverns or wells to get from one place to another. A common form of lashing sticks, logs, and deciduous branches together involved the use of long reeds or other harvested fibers woven together to form a connective rope capable of binding and holding together the materials used in early bridges. Bridges provide benefits to people living on either side of the bridge. 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.
 * Why were the bridges built?
 * Did they provide benefits? To whom? Why?