Ancestor | Suspension bridge |
---|---|
Related | None |
Descendant | None |
Carries | Pedestrians, automobiles, trucks, light rail |
Span range | Medium |
Material | Steel rope, steel eye-bar, concrete spar, post-tension-ed concrete deck |
Movable | No |
Design effort | high |
Falsework required | Usually |
A self-anchored suspension bridge is a suspension bridge type in which the main cables attach to the ends of the deck, rather than directly to the ground or via large anchorages. [1] The design is well-suited for construction atop elevated piers, or in areas of unstable soils where anchorages would be difficult to construct.
The load path of the self-anchored suspension (SAS) bridge converts vertical loads into tension forces in the main cables which are countered by compressive forces in the towers and deck. The system balances forces internally without external anchorage requirements, making it suitable for sites where large horizontal forces are difficult to anchor. This is similar to the method used in a tied-arch bridge where arch member compression is balanced by tension in the deck.
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. [2]
The nature of the self-anchored suspension bridge necessitates the temporary construction of falsework, in the form of compression struts or an underdeck, before work begins on the permanent structure. This requirement is inherent in the structure's definition.
In the absence of suspension via cableage, the deck of a suspension bridge is incapable of self-support. On a suspension bridge of the more usual earth-anchored type, both of the primary (i.e., horizontal) cable's anchorages exist prior to construction in the form of solid terrain. In the self-anchored suspension bridge, however, the cable must be anchored to the bridge deck, which has yet to be built and will not bear its own weight; ergo, falsework must be employed until the final method of suspension is possible.
The cables apply strong axial forces onto the bridge girders, which may require strengthening. Therefore, self-anchored suspension bridge spans tend to be smaller than earth-anchored ones. [4]
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 (no longer extant), or eyebars, or a more conventional composite cable.
A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. The first modern examples of this type of bridge were built in the early 1800s. Simple suspension bridges, which lack vertical suspenders, have a long history in many mountainous parts of the world.
A cable-stayed bridge has one or more towers, 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 within which cantilever bridges would rapidly grow heavier, and suspension bridge cabling would be more costly.
The San Francisco–Oakland Bay Bridge, commonly referred to as the Bay Bridge, is a complex of bridges spanning San Francisco Bay in California. As part of Interstate 80 and the direct road between San Francisco and Oakland, it carries about 260,000 vehicles a day on its two decks. It includes one of the longest bridge spans in the United States.
A cantilever bridge is a bridge built using 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 structural steel, or box girders built from prestressed concrete.
The 25 de Abril Bridge is a suspension bridge connecting the city of Lisbon, capital of Portugal, to the municipality of Almada on the left (south) bank of the Tagus River. It has a main span length of 1,013 metres (3,323 ft), making it the 48th longest suspension bridge in the world.
A simple suspension bridge is a primitive type of bridge in which the deck of the bridge lies on two parallel load-bearing cables that are anchored at either end. They have no towers or piers. The cables follow a shallow downward catenary arc which moves in response to dynamic loads on the bridge deck.
The Carquinez Bridge is a pair of parallel bridges spanning the Carquinez Strait at the northeastern end of San Francisco Bay. They form the part of Interstate 80 between Crockett and Vallejo, California, United States.
The eastern span replacement of the San Francisco–Oakland Bay Bridge was a construction project to replace a seismically unsound portion of the Bay Bridge with a new self-anchored suspension bridge (SAS) and a pair of viaducts. The bridge is in the U.S. state of California and crosses the San Francisco Bay between Yerba Buena Island and Oakland. The span replacement took place between 2002 and 2013, and is the most expensive public works project in California history, with a final price tag of $6.5 billion, a 2,500% increase from the original estimate of $250 million, which was an initial estimate for a seismic retrofit of the span, not the full span replacement ultimately completed. Originally scheduled to open in 2007, several problems delayed the opening until September 2, 2013. With a width of 258.33 ft (78.74 m), comprising 10 general-purpose lanes, it is the world's widest bridge according to Guinness World Records.
Falsework consists of temporary structures used in construction to support a permanent structure until its construction is sufficiently advanced to support itself. For arches, this is specifically called centering. Falsework includes temporary support structures for formwork used to mold concrete in the construction of buildings, bridges, and elevated roadways.
The Kurushima Kaikyō Bridge, which connects the island of Ōshima to the main part of Shikoku, was the world's longest suspension bridge structure when completed, in 1999. The bridge is part of the Shimanami Kaidō, an expressway that spans a series of islands and connects Hiroshima Prefecture in Honshū to Ehime Prefecture in Shikoku. The bridge and the expressway were both conceived by the Honshū-Shikoku Bridge Project.
A suspension bridge supports its structural load with cables, ropes, or chains anchored at each end. Cables on the earliest suspension bridges were anchored in the ground; some modern suspension bridges anchor the cables to the ends of the bridge itself. Earliest suspension bridges had no towers or piers but the majority of larger modern suspension bridges have them. All of the 14 longest bridges in the world are suspension bridges.
The Roberto Clemente Bridge, also known as the Sixth Street Bridge, spans the Allegheny River in downtown Pittsburgh, Pennsylvania, United States.
Hampden Bridge is a heritage-listed single-span suspension bridge that carries Moss Vale Road (B73) across the Kangaroo River, in Kangaroo Valley, in the City of Shoalhaven local government area of New South Wales, Australia. The bridge was designed by Ernest de Burgh and built by Loveridge and Hudson. The property is owned by Transport for NSW. It was added to the New South Wales State Heritage Register on 2 August 2019.
The Waldo–Hancock Bridge was the first long-span suspension bridge erected in Maine, as well as the first permanent bridge across the Penobscot River downstream from Bangor. The name comes from connecting Waldo and Hancock counties. The bridge was built in 1931 and retired in 2006, when the new Penobscot Narrows Bridge was opened just a few yards away. Demolition of the structure was completed by 2013.
An extradosed bridge employs a structure that combines the main elements of both a prestressed box girder bridge and a cable-stayed bridge. The name comes from the word extrados, the exterior or upper curve of an arch, and refers to how the "stay cables" on an extradosed bridge are not considered as such in the design, but are instead treated as external prestressing tendons deviating upward from the deck. In this concept, they remain part of the main bridge superstructure.
The Konohana Bridge is a self-anchored suspension bridge located in Osaka, Japan. Opened for traffic in 1990, it has a main span of 300 metres (980 ft). The bridge's 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 centre span has been tied by the Yeongjong Grand Bridge in Korea which has slightly larger side spans. As of late 2012, the single tower eastern span replacement of the San Francisco – Oakland Bay Bridge has a longer span of 385 metres (1,263 ft).
A tied-arch bridge is an arch bridge in which the outward-directed horizontal forces of the arch(es) are borne as tension by a chord tying the arch ends rather than by the ground or the bridge foundations. This strengthened chord may be the deck structure itself or consist of separate, independent tie-rods.
The Térénez bridge is a cable-stayed bridge, located between Landévennec and Rosnoën, Finistère, France.
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