My+magazine

 Bridges_notes



====A structure carrying a road, path, railway, etc. across a river, road, or other obstacle. ==== ====Designs of bridges vary depending on the function of the bridge and the ==== ==== nature of the terrain where the bridge is to be constructed. ====

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__**Types of Bridges **__=====

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Suspension Bridges: ===== A typical suspension bridge is a continuous girder with one or more towers, witch is the main structure, erected above piers in the middle of the span. At both ends of the bridge large anchors or counter weights are placed to hold the ends of the cables. The main cables are stretched from one anchor over the tops of the tower(s) and attached to the opposite anchor. The cables pass over a special structure known as a saddle. From the main cables, smaller cables (suspenders) known as hanger cables are hung down and attached to the girder, and they hold on the railway. The anchor, towers and cable do the main work in bridges because they support the whole structure.



Beam Bridges: 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.

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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, practically 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. =====