Bascule bridge

Bascule bridge

Bascule bridge
This animation shows the movement of a double leaf bascule.
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 (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.


  • History 1
  • Types 2
  • Gallery 3
  • See also 4
  • References 5


Tower Bridge, London.

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 rolling lift bridge (such as the Pegasus 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]

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]


See also


  1. ^ Koglin, Terry L. (2003). "4. Bascule Bridges". Movable bridge engineering. John Wiley and Sons.  
  2. ^ a b "Landmark Designation Report: Historic Chicago Bridges" (PDF).  
  3. ^ a b c Wood Wortman, Sharon; Wortman, Ed (2006). The Portland Bridge Book (3rd Edition). Urban Adventure Press. pp. 32, 35.  
  4. ^ "Patent number 669348: T. Rall movable bridge".  
  5. ^