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 where cantilever bridges would rapidly grow heavier if the span were lengthened, while suspension bridge cabling would not be more economical if the span were shortened.
Cable-stayed bridges have been known since the 16th century and used widely since the 19th. Early examples often combined features from both the cable-stayed and suspension designs, including the Brooklyn Bridge. The design fell from favor through the 20th century as larger gaps were bridged using pure suspension designs, and shorter ones using various systems built of reinforced concrete. It once again rose 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.
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.
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.
Difference between types of bridges
Cable-stayed bridge, fan design
In the cable-stayed bridge, the towers are the primary load-bearing structures that transmit the bridge loads to the ground. A cantilever approach is often used to support the bridge deck near the towers, but lengths further from them are supported by cables running directly to the towers. This has the disadvantage, compared to the suspension bridge, that the cables pull to the sides as opposed to directly up, requiring the bridge deck to be stronger to resist the resulting horizontal compression loads; but has the advantage of not requiring firm anchorages to resist the horizontal pull of the main cables of the suspension bridge. By design all static horizontal forces of the cable-stayed bridge are balanced so that the supporting towers do not tend to tilt or slide, needing only to resist horizontal forces from the live loads.
Key advantages of the cable-stayed form are as follows:
much greater stiffness than the suspension bridge, so that deformations of the deck under live loads are reduced
can be constructed by cantilevering out from the tower – the cables act both as temporary and permanent supports to the bridge deck
for a symmetrical bridge (i.e. spans on either side of the tower are the same), the horizontal forces balance and large ground anchorages are not required
There are four major classes of rigging on cable-stayed bridges: mono, harp, fan, and star.
The mono design uses a single cable from its towers and is one of the lesser-used examples of the class.
In the harp or parallel design, the cables are nearly parallel so that the height of their attachment to the tower is proportional to the distance from the tower to their mounting on the deck.
In the fan design, the cables all connect to or pass over the top of the towers. The fan design is structurally superior with a minimum moment applied to the towers, but, for practical reasons, the modified fan (also called the semi-fan) is preferred, especially where many cables are necessary. In the modified fan arrangement, the cables terminate near to the top of the tower but are spaced from each other sufficiently to allow better termination, improved environmental protection, and good access to individual cables for maintenance.
In the star design, another relatively rare design, the cables are spaced apart on the tower, like the harp design, but connect to one point or a number of closely spaced points on the deck.
Difference between types of bridges
There are also four arrangements for support columns: single, double, portal and A-shaped.
The single arrangement uses a single column for cable support, normally projecting through the center of the deck, but in some cases located on one side or the other.
The double arrangement places pairs of columns on both sides of the deck.
The portal is similar to the double arrangement but has a third member connecting the tops of the two columns to form a door-like shape or portal. This offers additional strength, especially against traverse loads.
The A-shaped design is similar in concept to the portal but achieves the same goal by angling the two columns towards each other to meet at the top, eliminating the need for the third member. The inverted Y design combines the A-shaped on the bottom with the single on top.
Depending on the design, the columns may be vertical or angled or curved relative to the bridge deck.
Cable-stayed bridges with more than three spans involve significantly more challenging designs than do 2-span or 3-span structures.
In a 2-span or 3-span cable-stayed bridge, the loads from the main spans are normally anchored back near the end abutments by stays in the end spans. For more spans, this is not the case and the bridge structure is less stiff overall. This can create difficulties in both the design of the deck and the pylons.
Examples of multiple-span structures in which this is the case include Ting Kau Bridge, where additional 'cross-bracing' stays are used to stabilise the pylons; Millau Viaduct and Mezcala Bridge, where twin-legged towers are used; and General Rafael Urdaneta Bridge, where very stiff multi-legged frame towers were adopted. A similar situation with a suspension bridge is found at both the Great Seto Bridge and San Francisco–Oakland Bay Bridge where additional anchorage piers are required after every set of three suspension spans – this solution can also be adapted for cable-stayed bridges.
The Twinkle-Kisogawa is an extradosed design, with long gaps between the cable supported sections.
A cradle system carries the strands within the stays from the bridge deck to bridge deck, as a continuous element, eliminating anchorages in the pylons. Each epoxy-coated steel strand is carried inside the cradle in a one-inch (2.54 cm) steel tube. Each strand acts independently, allowing for removal, inspection, and replacement of individual strands. The first two such bridges are the Penobscot Narrows Bridge, completed in 2006, and the Veterans' Glass City Skyway, completed in 2007.
Related bridge types
Self-anchored suspension bridge
A self-anchored suspension bridge has some similarity in principle to the cable-stayed type in that tension forces that prevent the deck from dropping are converted into compression forces vertically in the tower and horizontally along the deck structure. It is also related to the suspension bridge in having arcuate main cables with suspender cables, although the self-anchored type lacks the heavy cable anchorages of the ordinary suspension bridge. Unlike either a cable-stayed bridge or a suspension bridge, the self-anchored suspension bridge must be supported by falsework during construction and so it is more expensive to construct.
Twin bridges constructed in 2005–2006 that cross over roads connecting to the Autostrada A1motorway in Reggio Emilia, Italy. In 2009, the European Convention for Constructional Steelwork gave the two bridges a European Steel Design Award, stating that the structures' original visual effects at different angles give the bridges "the aspect of huge musical instruments."
Erasmus Bridge crosses the Nieuwe Maas in Rotterdam, Netherlands. The southern span of the bridge has an 89 metres (292 ft) bascule bridge for ships that cannot pass under the bridge. The bascule bridge is the largest and heaviest in West Europe and has the largest panel of its type in the world.
Kosciuszko Bridge (New York City): This connects the boroughs of Brooklyn and Queens in New York City, replacing a truss bridge of the same name that could no longer handle the modern volume of traffic. The first six-lane cable-stayed span (temporarily bi-directional) opened to traffic in April 2017. The old bridge was demolished in summer 2017, and a second, nearly identical span will be built in its place; when finished, each span will carry traffic in a single direction. Both new bridges include decorative lighting.
Dongting Lake Railway Bridge is a 1,290 metres (4,230 ft) long four-span (three towers) bridge that is one of the very few large cable-stayed bridges for dedicated mainline railway use.
Millau Viaduct, the bridge with the tallest piers in the world: 341 metres (1,119 ft) tall and roadway 266 metres (873 ft) high, spanning the river Tarn in France. With a total length of 2,460 metres (8,070 ft) and seven towers, it also has the longest cable-stayed suspended deck in the world.
Most SNP (Bridge of the Slovak National Uprising) – the world's longest cable-stayed bridge to have one pylon and one cable-stayed plane (Bratislava, Slovakia, 1967–1972).
Most SNP (Nový most), the world's longest cable-stayed bridge in category with one pylon and with one cable-stayed plane, spanning the Danube in Bratislava, Slovakia. The main span is 303 metres (994 ft), total length 430.8 metres (1,413 ft). The only member of World Federation of Great Towers that is primarily used as a bridge. It houses a flying-saucer restaurant at the top of pylon 85 metres (279 ft) tall.
Queensferry Crossing (formerly the Forth Replacement Crossing) is a road bridge in Scotland. It is built alongside the existing, suspension, Forth Road Bridge across the Firth of Forth and upon completion in 2017 became the longest triple-tower cable-stayed bridge in the world at 2700m. 
Rande Bridge in Spain near Vigo is the highway cable-stayed bridge with the longest and slenderest span in the world at the time of construction (1973–1977). Three long spans of 148 metres (486 ft) + 400 metres (1,300 ft) + 148 metres (486 ft). Pylons in concrete, girder in steel.
Rio-Antirio bridge crosses the Gulf of Corinth near Patras, Greece. At a total length of 2,880 metres (9,450 ft) and four towers, it has the second longest cable-stayed suspended deck (2,258 metres (7,408 ft) long) in the world, with only the deck of the Millau Viaduct in southern France being longer at 2,460 metres (8,070 ft). However, as the latter is also supported by bearings at the pylons apart from cable stays, the Rio–Antirrio bridge deck might be considered the longest cable-stayed fully suspended deck in the world.
Second Severn Crossing between England and Wales is 3.186 miles (5.127 km) long, consisting of a single central navigation span over the "Shoots" channel and approach viaducts on either side. The Second Severn Crossing Bridge uses Freyssinet cable stays.
Varina-Enon Bridge, Carries I-295 across the James River between Henrico and Chesterfield Counties in Virginia. Varina-Enon Bridge features the world's first use of precast concrete delta frames for construction of its 630 feet (190 m) cable-stayed main span. It is an instrumental part of the Peregrine Falcon program overseen by the Virginia Department of Transportation.
Vasco da Gama Bridge in Lisbon, Portugal is the longest bridge in Europe, with a total length of 17.2 kilometres (10.7 mi), including 0.829 kilometres (0.515 mi) for the main bridge, 11.5 kilometres (7.1 mi) in viaducts and 4.8 kilometres (3.0 mi) in extension roads.
Zárate–Brazo Largo Bridges over the Paraná Guazú and Paraná de las Palmas Rivers in Argentina (1972–1976) are the first two road and railway long-span cable-stayed steel bridges in the world. Spans: 110 metres (360 ft) + 330 metres (1,080 ft) + 110 metres (360 ft).