Bridge_Project

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 * Script:**

Hi, my name is Sebastián D’Alessandor. I’m a Simón Bolívar univercity studente and today I will be talking about bridges and how they work. A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle. Designs of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed, the material used to make it and the funds available to build it.

There are many types of bridges and many tecnichs to construct them. The most used ones are: Briges are made With (Types of bridges):

Beam bridges are horizontal beams supported at each end by abutments, hence their structural name of //simply supported//. When there is more than one span the intermediate supports are known as piers. The earliest beam bridges were simple logs that sat across streams and similar simple structures. In modern times, beam bridges are large box steel girder bridges. Weight on top of the beam pushes straight down on the abutments at either end of the bridge. They are made up mostly of wood or metal. Beam bridges typically do not exceed 250 feet (76 m) long. The longer the bridge, the weaker.
 * Beam Bridges:**

Cantilever bridges are built using cantilevers—horizontal beams that are supported on only one end. Most cantilever bridges use a pair of continuous spans extending from opposite sides of the supporting piers, meeting at the center of the obstacle to be crossed. Cantilever bridges are constructed using much the same materials & techniques as beam bridges. The difference comes in the action of the forces through the bridge.
 * Cantilever Bridges:**

Arch bridges have abutments at each end. The earliest known arch bridges were built by the Greeks and include the Arkadiko Bridge. The weight of the bridge is thrust into the abutments at either side.
 * Arch Bridges:**

Suspension bridges are suspended from cables. The earliest suspension bridges were made of ropes or vines covered with pieces of bamboo. In modern bridges, the cables hang from towers that are attached to caissons or cofferdams. The caissons or cofferdams are implanted deep into the floor of a lake or river.
 * Suspension Bridges:**

Cable-stayed bridges, like suspension bridges, are held up by cables. However, in a cable-stayed bridge, less cable is required and the towers holding the cables are proportionately shorter.
 * Cable-stayed Bridges:**

Movable bridges are designed to move out of the way of boats or other kinds of traffic, which would otherwise be too tall to fit. Their design is generally the same used for beam bridges. These are generally electrically powered. Now that you heard about all this types of bridges, conventional types of bridges, Im going to introduce you to a diferent type, a modern variation of the Cable-satayed bridge. And to do it, Im also going to use a famous example of it so nobody has doubts. The Alamillo Bridge is a structure in Seville, Andalusia (Spain), which spans the Canal de Alfonso XIII, allowing access to La Cartuja, an island between the canal and the Guadalquivir River. The bridge was constructed as part of infrastructure improvements for Expo 92, which was held on a large site on the island. Today the island has a theme park called Magic Island and the bridge remains as an acces to it and to the La Cartuja Monastery. Construction of the bridge began in 1989 and was completed in 1992 from a design by Santiago Calatrava. The original intent was to build two symmetrical bridges on either side of the island, but the budget of the proyect didn’t conceived the pair, so only one was constructed on the more convinient side. The bridge is of the cantilever spar cable-stayed bridge type and consists of a single pylon, counterbalancing a 200 m span with thirteen lengths of cables. Built with steel and prestressed concrete, the bridge is of short to medium range and only for the use of pedestrians. This desing was introduced by Santiago Calatrava and has traveled around the world with him. Other bridges with similar desing are: · Puente de la Mujer Buenos Aries, Argentina, 2002 · Sundial Bridge at Turtle Bay Redding CA, USA, 2004 · Chords Bridge Jerusalem, Israel, opened 2008, won't be operative until April 7, 2011 · Samuel Beckett Bridge Dublin, Ireland, opened 10 December 2009 In two of his designs the force distribution does not depend solely upon the cantilever action of the spar; the angle of the spar away from the bridge and the weight distribution in the spar serve to reduce the overturning forces applied to the footing of the spar. In contrast, in his swinging Puente de la Mujer design the spar reaches toward the cable supported deck and is counterbalanced by a structural tail.
 * Movable Bridges:**
 * The Alamillo Bridge**