Self-anchored suspension bridge

:"This article is concerned with a particular type of suspension bridge, the self-anchored type.:For an index to the several types see suspension bridge types.

A self-anchored suspension bridge is a suspension bridge in which the main cables do not attach to the ground via large anchorages; instead, the main cables attach to the ends of the road deck, which experiences compression forces equal to the horizontal component of the tension force in the cables. The vertical component of the tension force is balanced by the own weight of the road deck. The result of this design is that the bridge does not exert any horizontal pulling forces on the ground; the bridge foundations need only support the bridge's weight. Therefore, the self-anchored suspension bridge design is well-suited for construction atop elevated piers, or in areas of unstable soils where anchorages would be difficult to construct.

Examples

The Three Sisters Bridges of Pittsburgh are the earliest examples (1924-28) of this bridge type in the US. Currently the largest self-anchored suspension bridges are the Konohana Bridge in Japan and the Yeoungjong Grand arcitecture Bridge in South Korea. Both of these bridges have a central span of 300 meters. The eastern span replacement of the San Francisco – Oakland Bay Bridge (currently under construction) will be larger when completed.

Construction method

Because the primary cables cannot be anchored until the bridge deck is completed, a self-anchored suspension bridge requires some falsework during construction. This falsework may take the form of compression struts (pictured here [http://pghbridges.com/pittsburghW/0584-4477/7th1927clpgh1.jpg] and in the above diagram) which hold up the main cables (or the parts of them which have already been constructed), allowing the ends of the span to be constructed first in the fashion of a cantilever bridge, or it may be in the form of underdeck falsework.

Cable anchors

As in a traditional suspension bridge, the primary cable type may be multiple parallel independent cables as in the image at left of the Hutsonville Bridge, or eyebars, or a more conventional composite cable.

ee also

*Eastern span replacement of the San Francisco–Oakland Bay Bridge - a single tower, asymmetrical bridge under construction

Reference Links

* [http://pghbridges.com/pittsburghW/0584-4477/seventh_st_br.htm Seventh Street Bridge] from pghbridges.com
* [http://en.structurae.de/structures/stype/index.cfm?ID=4089 List of self-anchored suspension bridges at Structurae.de]

External links

* [http://www.yeongjongbridge.com/english/young/habugon/shang-01.asp Yeonglong Grand Bridge] A two tower, three span self-anchored bridge