A self-anchored suspension bridge is a suspension bridge

Suspension bridge

A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. Outside Tibet and Bhutan, where the first examples of this type of bridge were built in the 15th century, this type of bridge dates from the early 19th century...

 in which the main cables attach to the ends of the deck, rather than to the ground via large anchorages. The design is well-suited for construction atop elevated piers, or in areas of unstable soils where anchorages would be difficult to construct.

History

The self-anchored suspension bridge form originated in the mid-19th century, with a published description by Austrian engineer Josef Langer in 1859 and U.S. Patent No. 71,955 by American engineer Charles Bender in 1867. The form was applied to a handful of Rhine River crossings in Germany during the first half of the twentieth century.

Examples

The Three Sisters Bridges

Three Sisters (Pittsburgh)

A suspension bridge works by hanging a roadway from cables or chains under tension. Though a few unstiffened suspension bridges exist, a longitudinal stiffening truss or girder is usually added to prevent excessive movement of the deck. The cables pass over towers and are anchored at both ends...

 of Pittsburgh

Pittsburgh, Pennsylvania

Pittsburgh is the second-largest city in the US Commonwealth of Pennsylvania and the county seat of Allegheny County. Regionally, it anchors the largest urban area of Appalachia and the Ohio River Valley, and nationally, it is the 22nd-largest urban area in the United States...

 are the earliest examples (1924–28) of this bridge type in the US. Currently the largest self-anchored suspension bridges are the Konohana Bridge

Konohana Bridge

The is a self-anchored suspension bridge located in Osaka, Japan. Opened for traffic in 1990, it has a main span of 300 meters. Its unusual design has only a single main cable. At the time of its completion it was the largest self-anchored suspension bridge in the world. Its center span has...

 in Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

 and the Yeoungjong Grand Bridge in South Korea

South Korea

The Republic of Korea , , is a sovereign state in East Asia, located on the southern portion of the Korean Peninsula. It is neighbored by the People's Republic of China to the west, Japan to the east, North Korea to the north, and the East China Sea and Republic of China to the south...

. 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, with a 385 meter span (uniquely a half span as the bridge has only a single tower).

Construction method

Because the primary cables cannot be anchored until the bridge deck is completed, a self-anchored suspension bridge requires some falsework

Falsework

Falsework consists of temporary structures used in construction to support spanning or arched structures in order to hold the component in place until its construction is sufficiently advanced to support itself...

 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

Cantilever bridge

A cantilever bridge is a bridge built using cantilevers, structures that project horizontally into space, supported on only one end. For small footbridges, the cantilevers may be simple beams; however, large cantilever bridges designed to handle road or rail traffic use trusses built from...

, or it may be in the form of underdeck falsework, as is being employed in the Eastern span replacement of the San Francisco – Oakland Bay Bridge

Cable anchors

As in a traditional suspension bridge, the primary cable type may be multiple parallel independent cables as in the image at right of the Hutsonville Bridge

Hutsonville Bridge

-External links:* entry at Bridges.midwestplaces.org* record on this bridge** at Bridgemeister.com- Further reading:* Ratigan, W. . "Highways Over Broad Waters." Grand Rapids: Wm. B. Eerdmans Publishing. ASIN B0007IY0OC...

, or eyebar

Eyebar

In structural engineering and construction, an eyebar is a straight bar, usually of metal, with a hole at each end for fixing to other components...

s, or a more conventional composite cable.

External links

• Yeonglong Grand Bridge A two tower, three span self-anchored bridge