Cable-stayed bridge

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A cable-stayed bridge is a bridge that consists of one or more pillars, with cables supporting the roadbed. There are two major classes of cable-stayed bridges, differentiated by how the cables are connected to the pillars. In a parallel attachment design, the cables are made nearly parallel by attaching cables to various points on the pillar so that the height of attachment of each on the pillar is similar to the distance from the pillar along the roadway to its lower attachment. In a radial attachment design, the cables all connect to or pass over the top of the pillar.

The cable-stay design occupies a sweet spot of length between cantilever bridges and suspension bridges. Within this sweet spot a suspension bridge would require lots more cable, while a full cantilever bridge would require considerably more material.

1 Comparison with suspension bridge
2 Variations
3 A related bridge type
4 Notable cable-stayed bridges
5 External links

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Comparison with suspension bridge

A multiple-pillar 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 pillars, 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 on the main cable, and used to support the load of the roadbed, 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.

In the cable-stayed bridge, the pillars form the primary load-bearing structure. A cantilever approach is often used for support of the roadbed near the pillars, but areas further from them are supported by cables running directly to the pillars. This has the disadvantage, compared to the suspension bridge, that the cables pull to the sides as opposed to directly up, requiring the roadbed to be stronger to resist these loads; but has the advantage of not requiring firm anchorages to resist a horizontal pull as in the suspension bridge. All static horizontal forces are balanced so that the supporting pillar does not tend to tilt or slide, needing only to resist such forces from the "live" loads.

A further advantage of the cable-stayed bridge is that any number of pylons may be used. While it is possible to build a suspension bridge with one central tower, they are usually built with a pair of towers. Note that the apparent four-tower western segment of the San Francisco-Oakland Bay Bridge is in fact a pair of two-tower suspension bridges with a massive central anchorage.

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Variations

Image:SundiaBridgeCA3.jpg A side-spar cable-stayed bridge uses a central pillar supported on only one side. The example shown in that article is not significantly different in structure from a conventional cable-stayed bridge, although this concept could allow the construction of a curved bridge. Far more radical in its structure, the Redding, California Sundial Bridge is a pedestrian bridge that uses a single cantilever spar on one side of the span, with cables on one side only to support the bridge deck. Unlike the other cable stayed types shown this bridge exerts considerable tipping force upon its foundation and the spar must resist the bending pull of the cables as these are not balanced by opposing cables. The spar of this particular bridge forms the gnomon of a large garden sundial.

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A related bridge type

Image:ProposedSFOBBEasternSpan.jpg A self-anchored suspension bridge is similar 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 pylon and horizontally along the deck structure. It is also related to the suspension bridge in having arcuate main cables with suspender cables, although angled rather than vertical. Unlike either a cable stayed bridge or a suspension bridge, this type must be supported by falsework during construction and so is more expensive to construct.

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Notable cable-stayed bridges

Arthur Ravenel, Jr. Bridge - the longest cable-stayed bridge in North America, spanning the Cooper River in Charleston, South Carolina.
Dee River Crossing (Pont Sur Y Fflint) - near Shotton, north Wales (largest asymmetric cable-stayed crossing in UK)
Hangzhou Bay Bridge - spanning Hangzhou Bay, off the east coast of China, between Jiaxing and Cixi. When completed, it will be the longest cable-stayed bridge in the world.
Kap Shui Mun Bridge - connecting Ma Wan and Lantau Island in Hong Kong, the world's longest cable-stayed bridge carrying both road and railway traffic, with a main span of 430 metres and an overall length of 1323 metres
Millau Viaduct - spanning the Tarn river in France, currently the world's tallest bridge with piers at 341 m (1,118 ft) and roadway at 270 m (886 ft)
Rio-Antirio bridge - spanning the Gulf of Corinth near Patra, Greece, the bridge with the longest cable-stayed section, a road bridge with four cable-stay pillars.
Sunshine Skyway Bridge - the world's longest cable-stayed concrete bridge. Spans Tampa Bay with a length of 29,040 feet (approximately 8.85 km)
Surgut Bridge in Siberia is the longest one-tower cable-stayed bridge in the world.
Sundial Bridge - An award winning single spar pedestrian bridge spanning the Sacramento River in Redding, California
Tatara Bridge - part of a series of bridges connecting Honshu and Shikoku in Japan, currently has the largest span of any cable-stayed bridge 890 m (2,290 ft)

Image:ImageTingKauBridgeEarlyMorn.jpg

Ting Kau Bridge (connects Hong Kong International Airport to Hong Kong) 1177 m; the world's first major 4-span (3 towers) cable-stayed bridge.
Zakim Bunker Hill Bridge - spanning Charles River in Boston, Massachusetts – the widest cable stayed bridge.
The detailed design of the Stonecutters Bridge in Hong Kong, a world record 1018 metres main span cable-stayed bridge has started.

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