A cable-stayed bridge has one or more towers (or pylons), from which cables support the bridge deck. A distinctive feature are the cables or stays, which run directly from the tower to the deck, normally forming a fan-like pattern or a series of parallel lines. This is in contrast to the modern suspension bridge, where the cables supporting the deck are suspended vertically from the main cable, anchored at both ends of the bridge and running between the towers. The cable-stayed bridge is optimal for spans longer than cantilever bridges and shorter than suspension bridges. This is the range within which cantilever bridges would rapidly grow heavier, and suspension bridge cabling would be more costly.
Cable-stayed bridges were being designed and constructed by the late 16th century, and the form found wide use in the late 19th century. Early examples, including the Brooklyn Bridge, often combined features from both the cable-stayed and suspension designs. Cable-stayed designs fell from favor in the early 20th century as larger gaps were bridged using pure suspension designs, and shorter ones using various systems built of reinforced concrete. It returned to prominence in the later 20th century when the combination of new materials, larger construction machinery, and the need to replace older bridges all lowered the relative price of these designs.
History
Cable-stayed bridges date back to 1595, where designs were found in Machinae Novae, a book by Croatian-Venetian inventor Fausto Veranzio. Many early suspension bridges were cable-stayed construction, including the 1817 footbridge Dryburgh Abbey Bridge, James Dredge's patented Victoria Bridge, Bath (1836), and the later Albert Bridge (1872) and Brooklyn Bridge (1883). Their designers found that the combination of technologies created a stiffer bridge. John A. Roebling took particular advantage of this to limit deformations due to railway loads in the Niagara Falls Suspension Bridge.
The earliest known surviving example of a true cable-stayed bridge in the United States is E.E. Runyon's largely intact steel or iron Bluff Dale Suspension bridge with wooden stringers and decking in Bluff Dale, Texas (1890), or his weeks earlier but ruined Barton Creek Bridge between Huckabay, Texas and Gordon, Texas (1889 or 1890). In the twentieth century, early examples of cable-stayed bridges included A. Gisclard's unusual Cassagnes bridge (1899), in which the horizontal part of the cable forces is balanced by a separate horizontal tie cable, preventing significant compression in the deck, and G. Leinekugel le Coq's bridge at Lézardrieux in Brittany (1924). Eduardo Torroja designed a cable-stayed aqueduct at Tempul in 1926. Albert Caquot's 1952 concrete-decked cable-stayed bridge over the Donzère-Mondragon canal at Pierrelatte is one of the first of the modern type, but had little influence on later development. The steel-decked Strömsund Bridge designed by Franz Dischinger (1955) is, therefore, more often cited as the first modern cable-stayed bridge.
Other key pioneers included Fabrizio de Miranda, 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
Cable-stayed bridges may appear to be similar to suspension bridges, but they are quite different in principle and construction. In suspension bridges, large main cables (normally two) hang between the towers and are anchored at each end to the ground. This can be difficult to implement when ground conditions are poor. The main cables, which are free to move on bearings in the towers, bear the load of the bridge deck. Before the deck is installed, the cables are under tension from their own weight. Along the main cables smaller cables or rods connect to the bridge deck, which is lifted in sections. As this is done, the tension in the cables increases, as it does with the live load of traffic crossing the bridge. The tension on the main cables is transferred to the ground at the anchorages and by downwards compression on the towers.