Bridges_notes

BRIDGE

Def: "A structure spanning and providing passage over a gap or barrier, such as a river or road"

Bridges represent a very important progress for civilizations because they can provide easier ways for transportation and communication, what generates a spread of the natural boundaries of towns, making possible their development in all areas.

There are different kind of bridges and they are built with different materials

Beam bridges: the beam type is the simplest type of bridge. The beam bridge could be anything as simple as a plank of wood to a complex structure. It is made of two or more supports which hold up a beam.

Arch bridges: in the arch type of bridge, weight is carried outward along two paths, curving toward the ground.

Suspension/Cable-stayed bridges: the deck (trafficway) of a suspension bridge is hung by cables which hang from towers. The cables transfer the weight to the towers, which transfer the weight to the ground. Cable-stayed bridges have towers, but cables from the towers go directly to the road deck, instead of spanning from tower to tower.

Cantilever: in the cantilever type of bridge, two beams support another beam, which is where the deck or trafficway is. The two beams must be anchored, and this must be done well.

The most common materials used in bridge construction are: stone, concrete, steel, wood and composite products made of fiber-reinforced polymers.

Stone bridges: natural stone is one of the of the oldest bridge construction materials. It is strog and able to resist erosion caused by wind and water. Materials such as granite and limestone are naturally attractive and will last for centuries with little or no maintenance. At the same time, stone is heavy and has high installation costs. It is often used to build bridge piers and footers, which allow the upper portions of the bridge to be built from more affordable and lighter materials,

Concrete bridges: concrete is popular for all types of bridge construction because of its affordability and strength. Concrete requires little maintenance, although it tends to hold up poorly against saltwater and erosion. Though it can be easily shaped and formed, concrete is often thought of as unattractive because of its dull, gray finish. When used on longers sapans concrete can be reinforced with steel bars or subject to a treatment known as "pre-stressing" to help increase its strength.

Steel bridges: steel is one of the strongest bridge materials available, and can be used to span distances that are not possible with other products. It is 10 to 100 times stronger than concrete and weighs less. Steel bridges are susceptible to rust and corrosion, and tend to require a lot of maintenance. Many steel bridges are painted to improve their appeareance. Aluminum is sometimes used in place of steel because of its anti-corrosive properties.

Wood bridges: wood is not as reliable as other bridge construction materials, and should only be used in relatively simple structures. It is one of the most affordable bridge-building materials, and easy to work with using basic tools and equipment. Wood bridges are primarily chosen for their natural beauty, and are used for pedestrian acces or light vehicle traffic. Because wood can swell and rot when exposed to moisture, wood bridges will last longer when protected from rain by a chemical treatment.

Composite products made of fiber-reinforced polymers (FRP): are one of the most newest materials to be used for bridge construction. They weight 70 percent or 80 percent less than steel, yet are just as strong and durable. While even the strongest steel or reinforced concrete bridge will require substantial maintenance over the years, FRP require virtually no upkeep. It will also not corrode in saltwater, making it the superior choice for construction in the water. This product has only been used to construct bridges since 1975, so its long-term properties are still under evaluation.

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