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 A scale or balance is a device used to measure weight or mass. These are also known as mass scales, weight scales, mass balances, massometers, and weight balances. The traditional scale consists of two plates or bowls suspended at equal dis ...

, which employs the same principle. Bascule bridges are the most common type of movable span because they open quickly and require relatively little

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

to operate, while providing the possibility for unlimited vertical clearance for marine traffic.

History

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.

Types

There are three types of bascule bridge and the

counterweight A counterweight is a weight (object), weight that, by applying an opposite force, provides balance and stability of a machine, mechanical system. The purpose of a counterweight is to make lifting the load faster and more efficient, which saves e ...

s to the span may be located above or below the bridge deck. The fixed-

trunnion A trunnion () is a cylinder, cylindrical Boss (engineering), protrusion used as a mounting or pivoting point. First associated with cannons, they are an important military development. In mechanical engineering (see the Trunnion#Trunnion bearin ...

(sometimes a "Chicago" bascule) rotates around a large

axle An axle or axletree is a central shaft for a rotation, rotating wheel and axle, wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In ...

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. The

Jackknife Bascule Bridge The Jackknife (or Jack-knife) Bascule Bridge is a bascule bridge that spans the Kaministiquia River at Thunder Bay, Ontario, Canada, to link the city to Mission Island, one of two islands in the Kaministiquia River delta. The bridge was built by ...

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 Canadian Pacific Railway () , also known simply as CPR or Canadian Pacific and formerly as CP Rail (1968–1996), is a Canadian Class I railway incorporated in 1881. The railway is owned by Canadian Pacific Kansas City, Canadian Pacific Ka ...

. The 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. The rarer Rall type combines rolling lift with longitudinal motion on trunnions when opening. It was patented (1901) by Theodor Rall. One of the few surviving examples is the Broadway Bridge (1913), in Portland, Oregon. File:Amaliabrug_(Waddinxveen)_-_opening_2.jpg, The counterweight is often hidden below the road surface in the bridge

abutment An abutment is the substructure at the ends of a bridge span or dam supporting its superstructure. Single-span bridges have abutments at each end that provide vertical and lateral support for the span, as well as acting as retaining walls ...

. File:Ford Bridge Schematic open-close.gif, Animation of a double-leaf Strauss fixed-trunnion bridge (based on engineering drawings from the Henry Ford Bridge) File:MovableBridge roll.gif, Animation of a rolling lift bridge (such as the Pegasus Bridge) File:Bascule bridge.jpg, A rolling-lift bascule bridge in the down position

References

External links

* {{DEFAULTSORT:Bascule Bridge Bridges by structural type

History

Types

See also

References

External links