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.

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

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.

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]

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]

Gallery

• 
  Tower Bridge in London
• 
  Palace Bridge in Saint Petersburg, Russia
• 
  Mystic River Bascule Bridge, Mystic, Connecticut
• 
  Rolling lift Pegasus Bridge over the Caen Canal, Normandy, France
• 
  Railway Rolling lift bridge in Oldenburg, Germany
• 
  Single-leaf through truss with overhead counterweight, Seattle, Washington
• 
  The Ashtabula lift bridge, a Strauss bascule built in Ohio in 1925
• 
  The Patagones-Viedma Railway Bridge, Argentina. The longest rolling bridge in the world and the only with hydraulic counterweight.
• 
  The Birkenhead Bridge in Port Adelaide, Australia, fully opened
• 
  The Strauss design Johnson Street Bridge across Victoria Harbour, British Columbia, built in 1924
• 
  Bascule bridge in Montceau-les-Mines, France
• 
  Wabash Avenue Bridge in Chicago, Illinois, honored for its elegance by the American Institute of Steel Construction in 1930
• 
  Pamban Bridge in Rameswaram, India, over the Palk Strait
• 
  White Cart Bridge, Renfrew, Scotland
• 
  Cherry Street Bridge at Keating Channel in Toronto, Ontario, Canada
• 
  Cherry Street Strauss Trunnion Bascule Bridge at Toronto Harbour Shipping Channel, Toronto
• 
  The old Johnson Street Bridge in Victoria, British Columbia, Canada
• 
  Yeongdodaegyo in Busan, South Korea

See also

• Drawbridge
• List of bascule bridges
• Moveable bridges for a list of other movable bridge types

References

Wikimedia Commons has media related to Bascule bridges.