- Bascule bridge
This animation shows the movement of a double leaf bascule.
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 (sometimes referred to as a drawbridge) is a moveable bridge with a counterweight that continuously balances the span, or "leaf," throughout the entire upward swing in providing clearance for boat traffic.
Bascule is a French term for seesaw and balance, and bascule bridges operate along the same principle. They are the most common type of movable bridge in existence because they open quickly and require relatively little energy to operate.
Although the bascule bridge has been in use since ancient times, it was not until the 1850s that engineers developed the ability to move very long, heavy spans quickly enough for practical application. The Blagoveshchensky Bridge across the Neva River in Saint Petersburg was the first large bascule bridge, opened in 1850. Since then, all bridges across the Neva and other major rivers in the city (21 in total) were bascule to facilitate navigation, which prevented the city's inhabitants from travelling across the river at night (this remained so until 2003 when the first cable-stayed bridge across the Neva was opened).
Counterweights may be located above the bridge or below the deck of the bridge. There are two common designs of bascule bridge. One is the fixed-trunnion bascule design, which is where the bridge rotates around a large axle called a trunnion to raise. This bridge type is sometimes called the 'Chicago bascule' as this type was developed and perfected there and is used for many of that city's river crossings. Joseph Strauss was a key person who worked on improving the trunnion bascule bridge. Another form of bascule bridge is the Scherzer rolling lift bridge, also known as a Rolling Bascule Bridge. The city of Joliet, Illinois has a number of this structure type. The Scherzer rolling lift bridge essentially rolls or rocks like a simple rocking chair on a track to raise.
- Scherzer rolling lift bascule bridge
- Rall bascule bridge, patented by Theodore Rall in 1901.
- Strauss bascule bridge, patented by Joseph Strauss.
- Chicago or fixed-trunnion bascule bridge.
Tower Bridge across the Thames in London, UK is a famous bascule bridge. Originally, Tower Bridge was a hydraulically operated bridge, using steam power from coal-burning boilers to pump river water into six hydraulic accumulators so that power was readily available when required. The water for the boilers was provided by a well. The hydraulic accumulators powered the bascule engines, which raised and lowered the bascules. Today, the bascule mechanism is driven by oil and electricity rather than by water and steam.
A double-leaf bascule bridge (Burnside Bridge, Portland, Oregon)
Rolling lift Pegasus Bridge
Single-leaf through truss with overhead counterweight, Seattle, Washington
Bascule bridge in Montceau-les-Mines, France
A view from a Bridge command center on the Fremont Bridge in Seattle, Washington, where the Bridge Operator is controlling the bridge.
Wabash Avenue Bridge in Chicago (Photo from the National Park Service)
- Joseph Strauss
- List of bascule bridges
- Moveable bridge for a list of other movable bridge types.
- Pegasus Bridge for an example of a rolling bascule bridge, employing a rack and pinion rather than hinge pins.
- ^ Koglin, Terry L. (2003), "4. Bascule Bridges", Movable bridge engineering, John Wiley and Sons, ISBN 9780471419600, http://books.google.co.uk/books?id=_cyqkMJ7QDgC&printsec=frontcover&cad=0#PPA33,M1, retrieved May 25, 2009.
- ^ "Tower Bridge Exhibition". http://www.towerbridge.org.uk/TBE/EN/BridgeHistory/. Retrieved May 25, 2009.
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