Bridges_notes

=The Bridge =

** Benefits of bridges **

 * ====Supplies of food and traded goods can get across an obstacle or through difficult terrain in a shorter time. ====
 * ==== Other longer-term payoffs from easier travel, which is crucially dependent on good bridges, come as a result of increased opportunities to share ideas, intellectual, political and religious. ====
 *  International trade and travel depend on shipping and air routes, but efficient distribution networks depend on bridges.International trade and travel depend on shipping and air routes, but efficient distribution networks depend on bridges.

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This is the earliest and simplest kind of bridge. We still come across these when walking in
==== the hills, and there is no way of dating the first time some hominid straightened or stabilized such a 'beam' and thereby became the world's first bridge engineer. ==== ====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. The compression force manifests itself on the top side of the beam bridge's deck (or roadway). This causes the upper portion of the deck to shorten. 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. ====

Truss Strength
====A single beam spanning any distance experiences compression and tension. The very top of the beam experiences the most compression, and the very bottom of the beam experiences the most tension. The middle of the beam experiences very little compression or tension ==== ====A truss has the ability to dissipate a load through the truss work. The design of a truss, which is usually a variant of a triangle, creates both a very rigid structure and one that transfers the load from a single point to a considerably wider area, that's the reason reason why a truss is more rigid than a single beam ====

The Arch Bridge
====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. ====

Suspension bridge
==== In a suspension bridge cables, ropes, or chains are strung across the obstacle and the deck is suspended from these cables. Modern suspension bridges have two towers through which the cables are strung. The compression pushes down on the suspension bridge's deck, but because it is a suspended roadway, the cables transfer the compression to the towers, which dissipate the compression directly into the earth where they are entrenched. The supporting cables, running between the anchorages are the recipients of the tension. The cables are literally stretched from the weight of the bridge and its traffic as they run from anchorage to anchorage. The anchorages are under tension too, but since they, like the towers, are held firmly to the earth, the tension they experience is dissipated. ====

Suitable materials
====<span style="font-family: Verdana,Geneva,sans-serif;">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. 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. ====