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simple suspension foot bridge

A simple suspension bridge also rope bridge, swing bridge (in New Zealand), suspended bridge, hanging bridge and catenary bridge) is a primitive type of bridge in which the deck of the bridge lies on two parallel load-bearing cables that are anchored at either end. They have no towers or piers. The cables follow a shallow downward catenary arc which moves in response to dynamic loads on the bridge deck. The arc of the deck and its large movement under load make them unsuitable for vehicular, or railroad, traffic. Simple suspension bridges are restricted in their use to foot traffic. For safety, they are built with stout handrail cables, supported on short piers at each end, and running parallel to the load-bearing cables. Sometime these may be the primary load-bearing element, with the deck suspended below. Simple suspension bridges are considered the most efficient, and sustainable design, in rural regions, especially for river crossings that lie in non-floodplain topography such as gorges. In some contexts the term "simple suspension bridge" refers not to this type of bridge but rather to a suspended deck bridge that is "simple" in that its deck is not stiffened. Although simple suspension bridges and "simple" suspended deck bridges are similar in many respects, they differ in their physics. On a simple suspension bridge, the main cables (or chains) follow a hyperbolic curve, the catenary. This is because the main cables are free hanging. In contrast, on a suspended deck bridge (whether "simple" or not) the main cables follow a parabolic curve. This is because the main cables are tied at uniform intervals to the bridge deck below (see suspension bridge curve). The differences between these two curves were a question of importance in the 17th century, worked on by Isaac Newton. The solution was found in 1691, by Gottfried Leibniz, Christiaan Huygens, and Johann Bernoulli who derived the equation in response to a challenge by Jakob Bernoulli. Their solutions were published in the Acta Eruditorum for June 1691.