Bascule bridge
This animation shows the movement of a double leaf bascule.
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| Ancestor | Drawbridge, Plate girder bridge, cantilever bridge |
|---|---|
| Related | Lift bridge, swing bridge |
| Descendant | None |
| Carries | Pedestrian, automobile, truck, light rail, heavy rail |
| Span range | Short |
| Material | Steel |
| Movable | Yes |
| Design effort | Medium |
| Falsework required | Site and prefabrication specific |
A bascule bridge (commonly referred to as a drawbridge) is a moveable bridge with a counterweight that continuously balances a span, or "leaf", throughout its upward swing to provide clearance for boat traffic. It may be single or double leafed.
The name comes from the French term for balance scale, which employs the same principle. Bascule bridges are the most common type of movable span because they open quickly and require relatively little energy to operate, while providing the possibility for unlimited vertical clearance for marine traffic.
Contents
History
Bascule bridges have been in use since ancient times. However, it was not until the adoption of steam power in the 1850s that very long, heavy spans could be moved quickly enough for practical application.
Types
There are three types of bascule bridge designs,[1] and counterweights required to balance a bascule's span may be located either above or below the bridge deck.
The fixed-trunnion (sometimes a "Chicago" bascule) rotates around a large axle that raises the span(s). The Chicago bascule name derives from the location where it is widely used, and is a refinement by Joseph Strauss of the fixed-trunnion.[2]
The rolling lift trunnion (sometimes a "Scherzer" rolling lift), raises the span by rolling on a track resembling a rocking chair base. The "Scherzer" rolling lift is a patented refinement by the American engineer William Donald Scherzer.
The rarer Rall type combines rolling lift with longitudinal motion on trunnions when opening.[3] It was patented (1901) by Theodor Rall.[2][3][4] One of the few surviving examples is the Broadway Bridge (1913), in Portland, Oregon.[3][5]
Gallery
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Mystic River Bascule Bridge, Mystic, Connecticut
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Rolling lift Pegasus Bridge over the Caen Canal, Normandy, France
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Railway Rolling lift bridge in Oldenburg, Germany
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Single-leaf through truss with overhead counterweight, Seattle, Washington
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The Ashtabula lift bridge, a Strauss bascule built in Ohio in 1925
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The Patagones-Viedma Railway Bridge, Argentina. The longest rollling bridge in the world and the only with hydraulic counterweight.
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A double-leaf bascule bridge fully open
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The Strauss design Johnson Street Bridge across Victoria Harbour, British Columbia, built in 1924
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Bascule bridge in Montceau-les-Mines, France
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Wabash Avenue Bridge in Chicago, Illinois, honored for its elegance by the American Institute of Steel Construction in 1930
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Pamban Bridge in Rameswaram, India, over the Palk Strait
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White Cart Bridge, Renfrew, Scotland
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Cherry Street Strauss Trunnion Bascule Bridge at Toronto Harbour Shipping Channel, Toronto
See also
- List of bascule bridges
- Moveable bridge for a list of other movable bridge types.
References
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Wikimedia Commons has media related to Bascule bridges. |
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