Swing bridge

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Template:BridgeTypePix Image:MovableBridge swing.gif A swing bridge is a bridge that has as its primary structural support a vertical locating pin and support ring at or near to its center, about which it can then pivot horizontally as shown in the animated illustration below.

In its closed position, a swing bridge carrying a road over a river or canal, for example, allows road traffic to cross. When a water vessel needs to pass the bridge, road traffic is stopped (usually by traffic signals and barriers), and then motors rotate the bridge approximately 90 degrees horizontally about its pivot point.

1 Advantages
2 Disadvantages
3 examples
4 See also

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Advantages

As this type requires no counterweights the complete weight is significantly reduced as compared to other moveable bridges.
Where sufficient channel is available to have individual traffic directions on each side the likelihood of vessel-to-vessel collisions is reduced.
The central support is often mounted upon a berm along the axis of the watercourse, intended to protect the bridge from watercraft collisions when it is opened. This artificial island forms an excellent construction area for building the movable span as the construction will not impede channel traffic.

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Disadvantages

The central pier forms a hazard to navigation.
Where a wide channel is not available a large portion of the bridge may be over an area that would be easily spanned by other means.
A wide channel will be reduced by the center pivot and foundation.
When open, the bridge will have to maintain its own weight as a balanced double cantilever, while when closed and in use for traffic the live loads will be distributed as in a pair of conventional truss bridges, which may require additional stiffness in some members whose loading will be alternately in compression or tension.
If struck from the water near the edge of the span, it may rotate enough to cause safety problems (cf. Big Bayou Conot train disaster).

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examples

Image:PyrmontBridgeSydney1 gobeirne.jpg

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Argentina

Puente de la Mujer, a uniquely beautiful and dramatic asymmetrical cable-stayed span.

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Australia

old Pyrmont Bridge, Sydney.

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Canada

Little Current Swing Bridge, crossing the North Channel in Little Current, Ontario.
- Google maps image
A swing bridge crosses the Canso Canal in Nova Scotia.
The Derwent Way Bridge crosses the Annacis Channel of the Fraser River between Queensbourogh in New Westminster, British Columbia and Annacis Island in Delta, British Columbia.
The Fraser River Swing Bridge is a rail bridge that crosses the Fraser River between New Westminster and Surrey in British Columbia.

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Egypt

The longest swing bridge span is 340 metres, by the El Ferdan Railway Bridge across the Suez Canal.

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Great Britain

Connaught Crossing in London Docklands, built as a low-rising swing bridge to allow marine traffic in the Royal Docks to pass at a place when the proximity of London City Airport meant a higher fixed bridge was not practicable.

Manchester Ship Canal at Latchford, Stockton Heath and Lower Walton in Warrington, and also slightly further west at Moore. Near the eastern end of the canal in Salford, the Barton swing bridge is adjacent to the Barton Swing Aqueduct - a 234-foot, 800-tonne trough holding some 800 tonnes of water (retained by gates at either end) swings so that it is at right angles to the Bridgewater Canal to allow ships to pass up the Ship Canal.

Swing Bridge, River Tyne at Newcastle Upon Tyne. The Tyne swing bridge has an 85.7 metre cantilevered span with a central axis of rotation able to move through 90° to allow vessels to pass on either side of it.