Bascule bridge
Template:Short description Template:BridgeTypePix
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.
HistoryEdit
Bascule bridges have been in use since ancient times, but until the adoption of steam power in the 1850s, very long, heavy spans could not be moved quickly enough for practical application.
TypesEdit
There are three types of bascule bridge<ref>Template:Cite book</ref> and the counterweights to the span may be located 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.<ref name="chicago landmarks">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The Jackknife Bascule Bridge in Fort William, Ontario (now Thunder Bay, Ontario) was the first double-decked bascule bridge in the world, accommodating rail on the bottom and road/foot traffic on top. It was designed by Joseph Strauss for the Canadian Pacific Railway.
The Template:Vanchor 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 American engineer William Donald Scherzer.<ref>Template:Cite patent</ref>
The rarer Rall type combines rolling lift with longitudinal motion on trunnions when opening.<ref name="wood-wortman"/> It was patented (1901) by Theodor Rall.<ref name="chicago landmarks"/><ref name="wood-wortman">Template:Cite book</ref><ref name="Rall patent">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> One of the few surviving examples is the Broadway Bridge (1913), in Portland, Oregon.<ref name="wood-wortman"/><ref name="haer-broadwaybridge">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
- Amaliabrug (Waddinxveen) - opening 2.jpg
CitationClass=web }}</ref>
- Ford Bridge Schematic open-close.gif
Animation of a double-leaf Strauss fixed-trunnion bridge (based on engineering drawings from the Henry Ford Bridge)
- MovableBridge roll.gif
Animation of a rolling lift bridge (such as the Pegasus Bridge)
- Bascule bridge.jpg
A rolling-lift bascule bridge in the down position
See alsoEdit
- Double-beam drawbridge
- Drawbridge
- Johnson Street Bridge
- List of bascule bridges
- Moveable bridges for a list of other movable bridge types
- Straussbrug Template:In lang