1.-+Bridges-Notes




 * What is the meaning of the word bridge? **

 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.

__**Types of bridge**__

There are three different types of bridges, the beam bridge, the arch bridge and the suspension bridge. Each one of them have their own characteristics, for example, the beam bridge is the oldest type of bridge and it’s basically a rigid horizontal structure laying over two piers on each side of it, which are supporting all the weight. The arch bridge has a semicircular structure supported on each side by abutments which are always under compression, minimizing the tension in the arch. And finally, we have the suspension bridge, where the cables, ropes or chains are the most important part. All the cables end in an anchorage system which takes all the tension and transmit it to the columns.

Beam Bridge:

is a rigid, horizontal structure that rests on two end supports, and carries traffic loads by acting structurally as a beam. It is frequently used in pedestrian bridges and for highway overpasses and flyovers. As is its ancestor, this bridge is in structural terms the simplest of the many bridge types.

Cantilever Bridge: The part of the beam near to the pier support is so strong that it can support the slender parts in the middle of the span.

Arch Bridge: is shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side. A viaduct may be made from a series of arches, although other more economical structures are typically used today. The picture shows the Iron Bridge at Coalbrookdale, UK, it is the first bridge made of iron, we can see that is arch shaped.

Suspension Bridge : in this case the sections of the bridge are suspended by cables hanged on supports. The cables go vertically to a larger cable and then to the supports. There is no support in the center of the span, which allows ships to cross underneath the bridge.

Cable-stayed Bridge: consists of one or more columns (towers or pylons), with cables supporting the bridge deck, the cables go directly from the columns to the deck. It might be confused with the suspension bridge, but the difference is simple nad notable. Next, there is a graphic that helps understand the difference

__**What are they made of?**__  Wood, brick, stone, cast iron, wrought iron, mild steel, high-tensile steels, aluminium, steel-reinforced concrete, pre-stressed concrete, glass-reinforced plastic. These are some of the materials that are available for bridge building. <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;"> Bending, compression, impact, oscillation, pressure, tension, vibration; contraction, corrosion, erosion, friction, rain, river flow, sea-water, scouring, temperature changes, tidal flow, turbulence, waves, wind erosion, wind gusts, wind pressure. These are some of the stresses that bridge materials must withstand, in a variety of combinations.



<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;"> **__What are they connecting?__** <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">They are connecting usually places, either side of an obstacle, such as a river, chasm, or estuary.

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">**__How is the span between their piers or towers?__** <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;"> A span is the distance between the bridge supports, whether they are columns, towers or the wall of a canyon. The span depends on the type or bridge (Beam bridge, Arch bridge or Suspension bridge). A modern beam bridge is likely of up to 200 feet (60 meters), while a modern arch can safely span up to 800 or 1,000 feet (240 to 300 m). A suspension bridge, is capable of spanning up to 7,000 feet (2,100 m)

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">**__Why were the bridges built?__** <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;"> 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.

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">**__Did they provide benefits? To whom? Why?__** <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">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.