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Cable-stayed bridge

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Cable-stayed bridge
Megyeri Bridge in Budapest, opened 2008
Megyeri Bridge in Budapest, opened 2008
AncestorSuspension bridge
RelatedNone
DescendantSide-spar cable-stayed bridge, Self-anchored suspension bridge, cantilever spar cable-stayed bridge
CarriesPedestrians, bicycles, automobiles, trucks, light rail
Span rangeMedium
MaterialSteel rope, post-tensioned concrete box girders, steel or concrete pylons
MovableNo
Design effortmedium
Falsework requiredNormally none

A cable-stayed bridge is a bridge that consists of one or more columns (normally referred to as towers or pylons), with cables supporting the bridge deck.

There are two major classes of cable-stayed bridges: In a harp design, the cables are made nearly parallel by attaching them to various points on the tower(s) so that the height of attachment of each cable 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(s).

Compared to other bridge types, the cable-stayed is optimal for spans longer than typically seen in cantilever bridges, and shorter than those typically requiring a suspension bridge. This is the range in which cantilever spans would rapidly grow heavier if they were lengthened, and in which suspension cabling does not get more economical, were the span to be shortened.

History of development

Cable-stayed bridge by the Renaissance polymath Fausto Veranzio, from 1595/1616

Cable-stayed bridges can be dated back to 1595, where designs were found in a book by the Venetian inventor Fausto Veranzio, called Machinae Novae. Many early suspension bridges were cable-stayed construction, including the 1817 footbridge Dryburgh 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, 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 surviving example of a true cable-stayed bridge in the United States is E.E. Runyon's largely intact steel or iron 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).[1][2] 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.[3] 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.[3] 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.

Abdoun Bridge, Amman, Jordan

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 hangs between two towers, and is fastened at each end to anchorages in 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 owing to poor soil conditions.

  • Difference between types of bridges
  • Suspension bridge
    Suspension bridge
  • Cable-stayed bridge, fan design
    Cable-stayed bridge, fan design
  • Cable-stayed bridge, harp design
    Cable-stayed bridge, harp design
Ada Bridge at dusk in Belgrade (Serbia)

In the cable-stayed bridge, the towers form the primary load-bearing structure. A cantilever approach is often used for support of the bridge deck near the towers, but areas further from them are supported by cables running directly to the towers. This has the disadvantage, compared to the suspension bridge, of the cables pulling 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 a horizontal pull of the cables, as in the suspension bridge. All static horizontal forces are balanced so that the supporting tower does not tend to tilt or slide, needing only to resist such 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

Variations

Side-spar cable-stayed bridge

Puente de la Unidad, joining San Pedro Garza García and Monterrey, a Cantilever spar cable-stayed bridge
Anzac Bridge, Sydney
Proposed eastern span replacement of the San Francisco – Oakland Bay Bridge in the USA - a self-anchored suspension span

A side-spar cable-stayed bridge uses a central tower supported on only one side. This design could allow the construction of a curved bridge.

Cantilever-spar cable-stayed 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 overturning force upon its foundation and the spar must resist the bending caused by the cables, as the cable forces are not balanced by opposing cables. The spar of this particular bridge forms the gnomon of a large garden sundial. Related bridges by the architect Santiago Calatrava include the Puente del Alamillo (1992), Puente de la Mujer (2001), and Chords Bridge (2008).

Multiple-span cable-stayed bridge

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 both in 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.[4]

Extradosed bridge

The extradosed bridge is a cable-stayed bridge but with a more substantial bridge deck that, being stiffer and stronger, allows the cables to be omitted close to the tower and for the towers to be lower in proportion to the span.

Cable-stayed cradle-system bridge

A cradle system carries the strands within the stays from 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.[5]

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.

Notable cable-stayed bridges

See also: List of largest cable-stayed bridges and Category:Cable-stayed bridges

Bandra–Worli Sea Link in Mumbai, India
Octavio Frias de Oliveira bridge, in São Paulo, Brazil. It is the only bridge in the world that has two curved tracks supported by a single concrete mast.
Rama VIII Bridge, Thailand, a single tower asymmetrical type

References

  1. ^ "Bluff Dale Suspension Bridge". Historic American Engineering Record. Library of Congress.
  2. ^ "Barton Creek Bridge". Historic American Engineering Record. Library of Congress.
  3. ^ a b Troyano, Leonardo (2003). Bridge Engineering: A Global Perspective. Thomas Telford. pp. 650–652. ISBN 0-7277-3215-3.
  4. ^ Virlogeux, Michel (2001-02-01). "Bridges with multiple cable-stayed spans". Structural Engineering International. 11 (1): 61–82. doi:10.2749/101686601780324250. Retrieved 2008-03-08.
  5. ^ "Bridging To The Future Of Engineering" (Press release). American Society of Civil Engineers. 2007-03-12. Retrieved 2008-03-08.
  6. ^ "Longest Single-Pylon Cable Bridge In The World". Science.discovery.com. 30 March 2010. Retrieved 3 May 2012.

Further reading

  • De Miranda F., et al., (1979), "Basic problems in long span cable stayed bridges", Rep. n. 25, Dipartimento di Strutture - Università di Calabria - Arcavacata (CS) Italy, (242 pagg.) September 1979.
  • Gregory, Frank Hutson (1987). The Bangkok Cable Stayed Bridge. 3 F Engineering Consultants, Bangkok. ISBN 974-410-097-4. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  • Walther, Rene (1999). Cable Stayed Bridges (2nd ed.). Thomas Telford. ISBN 0-7277-2773-7. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
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