Bridges_notes



A bridge is a structure built to help to cross a, 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. Beam Bridge: 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. 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. 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. 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. They are connecting usually places, either side of an obstacle, such as a river, chasm, or estuary. 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)
 * What are bridges? **
 * Type of Bridges: **
 * 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.
 * Suspension bridge: ** Its one where cables (or 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. Thus, the towers are supporting the majority of the roadway's weight. 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.
 * What are they made of? **
 * What are they connecting? **
 * How is the span between their piers or towers? **