Bascule bridge
{{Short description|Moveable bridge with a counterweight which keeps the span(s) balanced during the upswing}}
{{BridgeTypePix|
|type_name= Bascule bridge
|image=MovableBridge_draw.gif
|image_title=This animation shows the movement of a double-leaf bascule.
|sibling_names= Lift bridge, swing bridge
|descendent_names= None
|ancestor_names= Drawbridge, Plate girder bridge, cantilever bridge
|carries= Pedestrian, bicycle, automobile, truck, light rail, heavy rail
|span_range= Short
|material= Steel
|movable= Yes
|design= Medium
|falsework= Site and prefabrication specific
|}}
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.
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
{{Redirect|Strauss bascule|the company started by its inventor|Joseph Strauss (engineer)#Early career and the bascule bridge}}
File:Vienna Convention road sign Aa-5-V1.svg
There are three types of bascule bridge{{cite book | last=Koglin | first=Terry L. | title=Movable bridge engineering | url=https://books.google.com/books?id=_cyqkMJ7QDgC | access-date=May 25, 2009 | year=2003 | publisher=John Wiley and Sons | isbn=978-0-471-41960-0 | chapter=4. Bascule Bridges | chapter-url=https://books.google.com/books?id=_cyqkMJ7QDgC }} 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.{{cite web|title=Landmark Designation Report: Historic Chicago Bridges|orig-year=September 2006|date=September 2007|publisher=Commission on Chicago Landmarks| url=https://www.cityofchicago.org/dam/city/depts/zlup/Historic_Preservation/Publications/Historic_Chicago_Railroad_Bridges.pdf |pages=12, 15 (pdf pages 14, 17)|access-date=April 21, 2013}} 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 {{vanchor|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 American engineer William Donald Scherzer.{{cite patent |country=US |number=511713 |status=grant |title=Lift-Bridge |pubdate= |gdate=26 December 1893 |fdate=29 May 1893 |pridate= |inventor=Scherzer, William |invent1= |invent2= |assign1= |assign2= |class= |url=}}
The rarer Rall type combines rolling lift with longitudinal motion on trunnions when opening. It was patented (1901) by Theodor Rall.{{cite book | last=Wood Wortman | first=Sharon |author2=Wortman, Ed | title=The Portland Bridge Book | publisher=Urban Adventure Press | year=2006 | pages=32, 35 | isbn=0-9787365-1-6 | edition=3rd }}{{cite web|title=Patent number 669348: T. Rall movable bridge|year=1901|publisher=United States Patent and Trademark Office (referenced online by Google Patents)|url=https://patents.google.com/patent/US669348|access-date=April 21, 2013}} One of the few surviving examples is the Broadway Bridge (1913), in Portland, Oregon.{{cite web|author=Historic American Engineering Record|author-link=Historic American Engineering Record|title=Broadway Bridge, Spanning Willamette River at Broadway {{Sic|Street|nolink=y}}, Portland, Multnomah County, OR|publisher=Library of Congress|url=https://www.loc.gov/pictures/item/or0292/|access-date=April 21, 2013}}
File:Amaliabrug_(Waddinxveen)_-_opening_2.jpg|The counterweight is often hidden below the road surface in the bridge abutment.{{Cite web|last=Van Zantvliet|first=P. S.|date=June 2015|title=Analysis of the force distribution on operating mechanisms in a bascule bridge|url=http://homepage.tudelft.nl/p3r3s/MSc_projects/reportVanZandvliet.pdf|url-status=live|archive-url=https://web.archive.org/web/20210921234322/http://homepage.tudelft.nl/p3r3s/MSc_projects/reportVanZandvliet.pdf |archive-date=2021-09-21 }}
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
See also
- Double-beam drawbridge
- Drawbridge
- Johnson Street Bridge
- List of bascule bridges
- Moveable bridges for a list of other movable bridge types
- Straussbrug {{In lang|nl}}
References
{{Reflist}}
External links
- {{Commons category inline|Bascule bridges}}
{{Bridge footer}}
{{Authority control}}
{{DEFAULTSORT:Bascule Bridge}}