Bascule bridge

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Bascule bridge
MovableBridge draw.gif
This animation shows the movement of a double-leaf bascule.
Ancestor Drawbridge, Plate girder bridge, cantilever bridge
Related Lift bridge, swing bridge
CarriesPedestrian, bicycle, automobile, truck, light rail, heavy rail
Span rangeShort
Design effortMedium
Falsework requiredSite and prefabrication specific

A bascule bridge (also 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.


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.


Animation of a double-leaf Strauss fixed-trunnion bridge (based on engineering drawings from the Henry Ford Bridge) Ford Bridge Schematic open-close.gif
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) MovableBridge roll.gif
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]


See also

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Burnside Bridge bridge in Portland, Oregon, USA

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Moveable bridge bridge that moves to allow passage, usually of watercraft

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North Avenue Bridge

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Glimmer Glass Bridge bridge in United States of America

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Cortland Street Drawbridge

The Cortland Street Drawbridge over the Chicago River is the original Chicago-style fixed-trunnion bascule bridge, designed by John Ericson and Edward Wilmann. When it opened in 1902, on Chicago's north side, it was the first such bridge built in the United States. The bridge was a major advance in American movable bridge engineering, and was the prototype for over 50 additional bridges in Chicago alone. The bridge was designated as an ASCE Civil Engineering Landmark in 1981, and a Chicago Landmark in 1991.

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Grand Street Bridge (Connecticut) bridge in United States of America

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William Donald Scherzer American engineer

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A double-beam drawbridge, seesaw or folding bridge is a movable bridge. It opens by rotation about a horizontal axis parallel to the water. Historically, the double-beam drawbridge has emerged from the drawbridge. Unlike a drawbridge, a double-beam drawbridge has counterweights, so that opening requires much less energy.


  1. Koglin, Terry L. (2003). "4. Bascule Bridges". Movable bridge engineering. John Wiley and Sons. ISBN   978-0-471-41960-0 . Retrieved May 25, 2009.
  2. 1 2 "Landmark Designation Report: Historic Chicago Bridges" (PDF). Commission on Chicago Landmarks. September 2007 [September 2006]. pp. 12, 15 (pdf pages 14, 17). Retrieved April 21, 2013.
  3. USgrant 511713,Scherzer, William,"Lift-Bridge",issued 26 December 1893
  4. 1 2 3 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 April 21, 2013.
  6. Historic American Engineering Record. "Broadway Bridge, Spanning Willamette River at Broadway Street [sic], Portland, Multnomah County, OR". Library of Congress . Retrieved April 21, 2013.