Bascule Bridge
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Bascule Bridge
Bascule bridge
This animation shows the movement of a double-leaf bascule.
This animation shows the movement of a double-leaf bascule.
AncestorDrawbridge, Plate girder bridge, cantilever bridge
RelatedLift bridge, swing bridge
DescendantNone
CarriesPedestrian, bicycle, automobile, truck, light rail, heavy rail
Span rangeShort
MaterialSteel
MovableYes
Design effortMedium
Falsework requiredSite and prefabrication specific

A bascule bridge (sometimes referred to as a drawbridge or a lifting bridge) 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.

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

Animation of a double-leaf Strauss fixed-trunnion bridge (based on engineering drawings from the Henry Ford Bridge)

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]

Animation of a rolling lift bridge (such as the Pegasus Bridge)

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 refinement patented in 1893 by the American engineer William Donald Scherzer.[3]

The rarer Rall type combines rolling lift with longitudinal motion on trunnions when opening.[4] It was patented (1901) by Theodor Rall.[2][4][5] One of the few surviving examples is the Broadway Bridge (1913), in Portland, Oregon.[4][6]

Examples

See also

References

  1. ^ Koglin, Terry L. (2003). "4. Bascule Bridges". Movable bridge engineering. John Wiley and Sons. ISBN 978-0-471-41960-0. Retrieved 2009.
  2. ^ a b "Landmark Designation Report: Historic Chicago Bridges" (PDF). Commission on Chicago Landmarks. September 2007 [September 2006]. pp. 12, 15 (pdf pages 14, 17). Retrieved 2013.
  3. ^ US grant 511713, Scherzer, William, "Lift-Bridge", issued 26 December 1893 
  4. ^ a b c Wood Wortman, Sharon; Wortman, Ed (2006). The Portland Bridge Book (3rd Edition). Urban Adventure Press. pp. 32, 35. ISBN 0-9787365-1-6.
  5. ^ "Patent number 669348: T. Rall movable bridge". United States Patent and Trademark Office (referenced online by Google Patents). 1901. Retrieved 2013.
  6. ^ Historic American Engineering Record. "Broadway Bridge, Spanning Willamette River at Broadway Street [sic], Portland, Multnomah County, OR". Library of Congress. Retrieved 2013.

  This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.

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