A bascule bridge (also referred to as a drawbridge or a lifting bridge) is a
moveable bridge
A moveable bridge, or movable bridge, is a bridge that moves to allow passage for boats or barges. In American English, the term is synonymous with , and the latter is the common term, but drawbridge can be limited to the narrower, historical d ...
with a counterweight that continuously balances a
span
Span may refer to:
Science, technology and engineering
* Span (unit), the width of a human hand
* Span (engineering), a section between two intermediate supports
* Wingspan, the distance between the wingtips of a bird or aircraft
* Sorbitan ester ...
, 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, and weight balances.
The traditional scale consists of two plates or bowls suspended at equal distances from a ...
, which employs the same principle. Bascule bridges are the most common type of movable span because they open quickly and require relatively little
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of hea ...
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 that, by applying an opposite force, provides balance and stability of a mechanical system. The purpose of a counterweight is to make lifting the load faster and more efficient, which saves energy and causes less wea ...
s to the span may be located above or below the bridge deck.
The fixed-
trunnion
A trunnion (from Old French "''trognon''", trunk) is a cylindrical protrusion used as a mounting or pivoting point. First associated with cannons, they are an important military development.
Alternatively, a trunnion is a shaft that positions a ...
(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.
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
William Donald Scherzer (January 27, 1858 – July 20, 1893) was an American engineer and inventor who invented the rolling lift bridge.
Early life
Scherzer's parents were William and Wilhelmina Scherzer, who immigrated from Germany in 1847 ...
.
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.
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 which provide vertical and lateral support for the span, as well as acting as retaining walls ...
.Henry Ford Bridge
The Henry Ford Bridge, also known as the Badger Avenue Bridge, is a bridge located in Los Angeles County, Southern California. It carries the Pacific Harbor Line railroad across the Cerritos Channel to Terminal Island from San Pedro, to serve t ...
)
File:MovableBridge roll.gif, Animation of a rolling lift bridge (such as the Pegasus Bridge
Pegasus Bridge, originally called the Bénouville Bridge after the neighbouring village, is a road crossing over the Caen Canal, between Caen and Ouistreham in Normandy. The original bridge, built in 1934, is now a war memorial and is the cent ...
)
See also
*
Double-beam drawbridge
A double-beam drawbridge, seesaw or folding bridge is a movable bridge . It opens by rotation about a horizontal axis parallel to the water. Historically, the double-beam drawbridge has emerged from the drawbridge. Unlike a drawbridge, a double ...
*
Drawbridge
*
Johnson Street Bridge
Four known bridges have spanned the narrows between the Inner Harbour and Upper Harbour of Victoria, British Columbia, connecting Johnson Street on the east shore with Esquimalt Road on the west shore. The current bridge is Canada's largest sin ...
*
List of bascule bridges
A list of bascule bridges by country:
Australia
* Birkenhead Bridge carries traffic across the Port River at Port Adelaide
* Tom 'Diver' Derrick Bridge - Port Adelaide, South Australia, single leaf road bascule
* Mary MacKillop Bridge - Po ...
*
Moveable bridges
A moveable bridge, or movable bridge, is a bridge that moves to allow passage for boats or barges. In American English, the term is synonymous with , and the latter is the common term, but drawbridge can be limited to the narrower, historical ...
for a list of other movable bridge types
*
Straussbrug
References
External links
*
{{DEFAULTSORT:Bascule Bridge
Bridges by structural type