Bascule bridge

A bascule bridge (sometimes 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.

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


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.


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.

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

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]

MovableBridge roll
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]


Tower Bridge (8151690991)

Tower Bridge in London

Palace Bridge SPB (img2)

Palace Bridge in Saint Petersburg, Russia

Mystic River Bascule Bridge 4

Mystic River Bascule Bridge, Mystic, Connecticut, US

Pegasus bridge new

Rolling lift Pegasus Bridge over the Caen Canal, Normandy, France

Rollklappbrücke in Oldenburg

Railway Rolling lift bridge in Oldenburg, Germany


Single-leaf through truss with overhead counterweight, Seattle, Washington, US

Ashtabula Lift Bridge

The Ashtabula lift bridge, a Strauss bascule built in Ohio in 1925

Rio Negro

The Patagones-Viedma Railway Bridge, Argentina. The longest rolling bridge in the world and the only with hydraulic counterweight.

Birkenhead Bridge open 2010

The Birkenhead Bridge in Port Adelaide, Australia, fully opened

JohnsonStreetBridge March 2009

The Strauss design Johnson Street Bridge across Victoria Harbour, British Columbia, built in 1924

Pont-levant Montceau-les-Mines

Bascule bridge in Montceau-les-Mines, France

Wabash Avenue Bridge Undated NPS

Wabash Avenue Bridge in Chicago, Illinois, US

Pamban Rail Bridge

Pamban Bridge in Rameswaram, India, over the Palk Strait

Cherry Bascule

Cherry Street Strauss Trunnion Bascule Bridge at Toronto Harbour Shipping Channel, Toronto


Yeongdodaegyo in Busan, South Korea


Curling Bridge, Paddington Basin, London

See also


  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. ^ 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 April 21, 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 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.

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