Bridges Types (1) : Suspension Bridge

A suspension bridge is a type of bridge where the main load-bearing elements are hung from suspension cables. While modern suspension bridges with level decks date from the early 19th century, earlier types are reported from the 3rd century BC. Simple suspension bridges, for use by pedestrians and livestock, are still constructed.

Suspended well from two high locations over a river or canyon, simple suspension bridges follow a shallow downward arc and are not suited for modern roads and railroads. The suspension cables must be anchored at each end of the bridge, since any load applied to the bridge is transformed into a tension in these main cables. The main cables continue beyond the pillars to deck-level supports, and further continue to connections with anchors in the ground.

The roadway is supported by vertical suspender cables or rods, called hangers. In some circumstances the towers may sit on a bluff or canyon edge where the road may proceed directly to the main span, otherwise the bridge will usually have two smaller spans, running between either pair of pillars and the highway, which may be supported by suspender cables or may use a truss bridge to make this connection. In the latter case there will be very little arc in the outboard main cables.

Suspension bridges have the longest spans of any type of bridge. Cable-stayed bridges, the next longest design, are practical for spans up to around one kilometer.

Advantages over other bridge types
  • A suspension bridge can be made out of simple materials such as wood and common wire rope.Longer main spans are achievable than with any other type of bridge

  • Less material may be required than other bridge types, even at spans those can achieve, leading to a reduced construction cost

  • Except for installation of the initial temporary cables, little access from below is required during construction, for example allowing a waterway to remain open while the bridge is built above

  • May be better able to withstand seismic movements than heavier and more rigid bridges
Disadvantages compared with other bridge types

  • Considerable stiffness or aerodynamic profiling may be required to prevent the bridge deck vibrating under high winds

  • The relatively low deck stiffness compared to other types makes it more difficult to carry heavy rail traffic where high concentrated live loads occur

  • Some access below may be required during construction, to lift the initial cables or to lift deck units. This access can often be avoided in cable-stayed bridge construction

Source : wikipedia

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