Suspension bridge
The Akashi Kaikyō Bridge in Japan, world's longest mainspan.
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| Ancestor | Simple suspension bridge |
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| Related | Underspanned suspension bridge; see also cable-stayed bridge |
| Descendant | Self-anchored suspension bridge |
| Carries | Pedestrians, bicycles, livestock, automobiles, trucks, light rail |
| Span range | Medium to long |
| Material | Steel rope, multiple steel wire strand cables or forged or cast chain links |
| Movable | No |
| Design effort | medium |
| Falsework required | No |
A suspension bridge is a type of bridge in which the deck (the load-bearing portion) is hung below suspension cables on vertical suspenders. The first modern examples of this type of bridge were built in the early 19th century.Simple suspension bridges, which lack vertical suspenders, have a long history in many mountainous parts of the world.
This type of bridge has cables suspended between towers, plus vertical suspender cables that carry the weight of the deck below, upon which traffic crosses. This arrangement allows the deck to be level or to arc upward for additional clearance. Like other suspension bridge types, this type often is constructed without falsework.
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.
The earliest suspension bridges were ropes slung across a chasm, with a deck possibly at the same level or hung below the ropes such that the rope had a catenary shape.
The Tibetan saint and bridge-builder Thangtong Gyalpo originated the use of iron chains in his version of simple suspension bridges. In 1433, Gyalpo built eight bridges in eastern Bhutan. The last surviving chain-linked bridge of Gyalpo's was the Thangtong Gyalpo Bridge in Duksum en route to Trashi Yangtse, which was finally washed away in 2004. Gyalpo's iron chain bridges did not include a suspended deck bridge which is the standard on all modern suspension bridges today. Instead, both the railing and the walking layer of Gyalpo's bridges used wires. The stress points that carried the screed were reinforced by the iron chains. Before the use of iron chains it is thought that Gyalpo used ropes from twisted willows or yak skins. He may have also used tightly bound cloth.
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