Bridges+-+Notes+1


 * ...ABOUT BRIDGES... **


 * ....Bridges... **

A bridge is a structure of engineering built to span different obstacles that I could we found in the ways, like body of water, road or valley; the object is join spaces, get a shorter time of travels in difficult terrain. Designs of bridge is different depending on the function, the nature of the terrain where is constructed, the material, and more.

Bridges marked a breakthrough in engineering, but beyond that, are important for mobility between cities. Through the use of bridges trade between cities that were separated by geographic barriers could be creating more dynamic, since the trips were shorter, so there was greater ease of exchange and communication that could mean significant improvements in physical image of the city and its functioning. More benefits of a bridge: • Improve mobility of people using public and private transportation in the area. • Reduced travel time by increasing the average speed. • Reduction of pollutant emissions in the area, and fuel economy. • Modernize urban image. • Generation of jobs. • Take the right of way - Population growth and expansion of cities.
 * ... What social or/and political benefits can bridges provide to places?... **

The main types of bridges are arches, beam bridges, cable-stayed bridges, cantilever bridges and suspension bridges. You will have noticed that this list does not include truss bridges because these they are parts of bridges
 * ...Types of Bridges... **

**1. Arch - **An arch bridge is a semicircular structure with abutments on each end. The design of the arch, the semicircle, naturally diverts the weight from the bridge deck to the abutments. Arch bridges are always under compression. The force of compression is pushed outward along the curve of the arch toward the abutments.An arch bridge doesn't need additional supports or cables. In fact, an arch made of stone doesn't even need mortar **Advantages:** Inexpensive, because are made of materials available in all countries, reducing export costs. These materials are usually brick and stones. **Disadvantage:** Uses a lot of material, even on short spans.
 * Types of Arch Bridges: **<span style="font-family: Verdana,Geneva,sans-serif;">the types of arch bridges are in the form of cosmetic design.

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<span style="font-family: Verdana,Geneva,sans-serif;">**2. The Suspension Bridge -** A suspension bridge is one where cables (or ropes or chains) are strung across the river (or whatever the obstacle happens to be) and the deck is suspended from these cables. Modern suspension bridges have two tall towers through which the cables are strung. Thus, the towers are supporting the majority of the roadway's weight. The supporting cables, running between the two anchorages, are the lucky recipients of the tension forces. The cables are literally stretched from the weight of the bridge and its traffic as they run from anchorage to anchorage. The anchorages are also under tension, but since they, like the towers, are held firmly to the earth, the tension they experience is dissipated. <span style="font-family: Verdana,Geneva,sans-serif;">**Types of Suspension Bridges:** Suspension bridges come in two different designs: the suspension bridge, recognized by the elongated 'M' shape, and the less-common cable-stayed design, which has more of an 'A' shape. The cable-stayed bridge does not require two towers and four anchorages as does the suspension bridge. Instead, the cables are run from the roadway up to a single tower where they are secured.
 * <span style="font-family: Verdana,Geneva,sans-serif;">Advantage: **<span style="font-family: Verdana,Geneva,sans-serif;">Can cover very long spans
 * <span style="font-family: Verdana,Geneva,sans-serif;">Disadvantage: **<span style="font-family: Verdana,Geneva,sans-serif;">A very flexible bridge, so not used for railways.



<span style="font-family: Verdana,Geneva,sans-serif;">**3. The Beam Bridge. -** A beam bridge is basically a rigid horizontal structure that is resting on two piers, one at each end. The weight of the bridge and any traffic on it is directly supported by the piers. The weight is traveling directly downward. <span style="font-family: Verdana,Geneva,sans-serif;">The force of compression manifests itself on the top side of the beam bridge's deck (or roadway). This causes the upper portion of the deck to shorten. <span style="font-family: Verdana,Geneva,sans-serif;">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. <span style="font-family: Verdana,Geneva,sans-serif;">**Materials and function:**Many beam bridges that you find on highway overpasses use concrete or steel beams to handle the load. The size of the beam, and in particular the height of the beam, controls the distance that the beam can span. By increasing the height of the beam, the beam has more material to dissipate the tension. To create very tall beams, bridge designers add supporting lattice work, or a truss, to the bridge's beam. This support truss adds rigidity to the existing beam, greatly increasing its ability to dissipate the compression and tension. Once the beam begins to compress, the force is dissipated through the truss. <span style="font-family: Verdana,Geneva,sans-serif;">**Types of Beam Bridges:** Beam bridges come in dozens of different styles. The design, location and composition of the truss is what determines the type. Designers were coming up with many different truss designs and compositions: Wooden bridges were being replaced by all-iron or wood-and-iron combinations. The different truss patterns also made great strides during this period.

<span style="font-family: Verdana,Geneva,sans-serif;">**Advantage:** Wide distances can be spanned by resting beams on piers

<span style="font-family: Verdana,Geneva,sans-serif;">**Disadvantage:** Can be expensive, even for fairly short spans, because of the need to use steel



<span style="font-family: Verdana,Geneva,sans-serif;">**4. The Cable-stayed bridge. -** is a bridge that consists of one or more columns (normally referred to as towers or pylons), with cables supporting the bridge deck. <span style="font-family: Verdana,Geneva,sans-serif;">A typical cable-stayed bridge is a continuous girder with one or two towers erected above piers in the middle of the span. From these piers, cables are attached diagonally to the girder to provide additional support. Cable-stayed bridges have a low center of gravity which makes them strong against earthquakes, but at the same time makes them vulnerable to uneven sinking of the ground. <span style="font-family: Verdana,Geneva,sans-serif;">Cables are extremely well suited for axial tension, however are weak against compression and bending forces. As a result, long span cable stayed bridges, though strong under normal traffic loads, are vulnerable to the forces of winds. Special measures are taken to assure that the bridge does not vibrate or sway under heavy winds. <span style="font-family: Verdana,Geneva,sans-serif;">**Advantage:** One of the main reasons for building a cable stay bridge is that it is more stable in the wind than a suspension bridge but also it is less expensive to construct. <span style="font-family: Verdana,Geneva,sans-serif;">**Disadvantage:** Cables are extremely well suited for axial tension, however are weak against compression and bending forces. <span style="font-family: Verdana,Geneva,sans-serif;">Different between the suspension bridge and The Cable-stayed bridge. || **<span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Suspension bridge ** || **<span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Cable-stayed bridge ** ||
 * <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Two towers || <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Two towers ||
 * <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Suspended structure || <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Suspended structure ||
 * <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Two main cables ||  ||
 * <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Many hanger cables || <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Many inclined cables ||
 * <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Two terminal piers || <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Two terminal piers ||
 * <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Four anchorages ||  ||

<span style="font-family: Verdana,Geneva,sans-serif;">**5. The cantilever bridge. -** A cantilever bridge is a bridge built using cantilevers, structures that project horizontally into space, supported on only one end. For small footbridges, the cantilevers may be simple beams; however, large cantilever bridges designed to handle road or rail traffic use trusses built from structural steel, or box girders built from prestressed concrete. The steel truss cantilever bridge was a major engineering breakthrough when first put into practice, as it can span distances of over 1,500 feet (460 m), and can be more easily constructed at difficult crossings by virtue of using little or no falsework. <span style="font-family: Verdana,Geneva,sans-serif;">**Advantage:** Can be more easily constructed at difficult crossings by virtue of using little or no falsework. <span style="font-family: Verdana,Geneva,sans-serif;">**Disadvantage:** A cantilever bridge is limited in its length. they require more material to make plus they are heavier

<span style="font-family: Verdana,Geneva,sans-serif;">**6. The Truss bridge. -** A truss bridge is a bridge composed of connected elements (typically straight) which may be stressed from tension, compression, or sometimes both in response to dynamic loads. Truss bridges are one of the oldest types of modern bridges. <span style="font-family: Verdana,Geneva,sans-serif;">A truss bridge design consists of vertical, lower horizontal and diagonal members. The vertical members of a truss bridge face tensile stress while the lower horizontal ones are under the stress resulting from bending, tension and shear stress. The diagonal members that run outwards, are under compression while the inner diagonals face tensile stress. <span style="font-family: Verdana,Geneva,sans-serif;">**Advantage:** Truss bridges are strong, since they are made of triangles, which are ridged. Another advantage about truss bridges is that they can be built in a convenient area, then placed over where it has to bridge, although this is not always possible. That makes the truss bridge a perfect replacement to span over railways and roads. <span style="font-family: Verdana,Geneva,sans-serif;">**Disadvantage:** trusses are not economical from a material standpoint for long spans.

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 * ...Glossary of bridges... **

<span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: normal;">**Cables:** (Cables): Extremely strong wires, formed from thousands of single steel threads bound together.<span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">Cable-stayed bridge: is a bridge that consists of one or more columns (normally referred to as //towers// or //pylons//), with cables supporting the bridge deck. <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: normal;">**Deck:** (Cubierta) - The roadway surface of a bridge. Is usually horizontal, and often suspended from cables or resting on an arch. <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: normal;">Girders: **(Vigas)**<span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">is a support beam used in construction. Girders often have an I-shape cross section for strength, but may also have a box shape, Z shape or other forms. Girder is the term used to denote the main horizontal support of a structure which supports smaller beams. A girder is commonly used many times in the building of bridges, and planes. <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: normal;">**Piers:** (Muelles) - A pier is a raised structure, including bridge and building supports and walkways, over water, typically supported by widely spread piles or pillars. <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: normal;">Span: **(extensión)****<span style="font-family: 'Verdana','sans-serif';"> - **a section between two intermediate supports <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: normal;">Ties: **(Lazos)****<span style="font-family: 'Verdana','sans-serif';"> - ** A part of a framework that is carrying tensile forces, or keeping two elements of a structure together. <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: normal;">**<span style="font-family: 'Verdana','sans-serif';">Truss: **<span style="font-family: 'Verdana','sans-serif'; font-size: 10pt;">In architecture and structural engineering, a truss is a structure comprising one or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes.
 * Abutments: **<span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: normal;">(Pilares) -<span style="font-family: 'Verdana','sans-serif';">**<span style="font-family: 'Verdana','sans-serif'; font-weight: normal;">The side support at either end of an arch bridge, necessary to withstand the horizontal forces generated by the arch's shape. **
 * <span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: normal;">Cantilever: **<span style="font-family: 'Verdana','sans-serif'; font-size: 10pt; line-height: normal;"><span style="font-family: 'Verdana','sans-serif';">(Voladizo) - is a beam supported on only one end. The beam carries the load to the support where it is resisted by moment and shear stress. Cantilever construction allows for overhanging structures without external bracing. Cantilevers can also be constructed with trusses or slabs.