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A cable-stayed bridge is a Bridge that consists of one or more Column s (normally referred to as '''towers''' or '''pylons'''), with Cable s supporting the bridge deck. There are two major classes of cable-stayed bridges, differentiated by how the cables are connected to the tower(s). In a '''harp''' design, the cables are made nearly parallel by attaching cables to various points on the tower so that the height of attachment of each on the tower is similar to the distance from the tower along the roadway to its lower attachment. In a '''fan''' design, the cables all connect to or pass over the top of the tower. The cable-stay design is the optimum bridge for a span length between that of Cantilever Bridges and Suspension Bridges . Within this range of span lengths a suspension bridge would require a great deal more cable, while a full cantilever bridge would require considerably more material and be substantially heavier. HISTORY OF DEVELOPMENT Cable-stayed bridges can be dated back to the 1784 design of a timber bridge by German carpenter C.T. Loescher. Many early suspension bridges were of hybrid suspension and cable-stayed construction, including the 1817 footbridge at Dryburgh Abbey , and the later Albert Bridge ( 1872 ) and Brooklyn Bridge ( 1883 ). Their designers found that the combination of technologies created a stiffer bridge, and John A. Roebling took particular advantage of this to limit deformations due to railway loads in the Niagara Falls Suspension Bridge . The earliest known example of a true cable-stayed bridge in the United States is E.E. Runyon's extant steel (or perhaps iron) bridge with wooden stringers and decking in Bluff Dale, Texas ( by Franz Dischinger ( 1955 ) is therefore more often cited as the first modern cable-stayed bridge. Other key pioneers included Riccardo Morandi and Fritz Leonhardt . Early bridges from this period used very few stay cables, as in the Theodor Heuss Bridge ( 1958 ). However, this involves substantial erection costs, and more modern structures tend to use many more cables to ensure greater economy. COMPARISON WITH SUSPENSION BRIDGE ]] A multiple-tower cable-stayed bridge may appear similar to a Suspension Bridge , but in fact is very different in principle and in the method of construction. In the suspension bridge, a large cable is made up by "spinning" small diameter wires between two towers, and at each end to anchorages into the ground or to a massive structure. These cables form the primary load-bearing structure for the bridge deck. Before the deck is installed, the cables are under Tension from only their own weight. Smaller cables or rods are then suspended from the main cable, and used to support the load of the bridge deck, which is lifted in sections and attached to the suspender cables. As this is done the tension in the cables increases, as it does with the Live Load of vehicles or persons crossing the bridge. The tension on the cables must be transferred to the earth by the anchorages, which are sometimes difficult to construct due to poor soil conditions. |
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