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{{Original research|date=August 2022}}
{{Infobox bridge type
|type_name=Cantilever bridge
|image=Pierre Pflimlin UC AdjAndCrop.jpg
|image_title=The [[Pierre Pflimlin Bridge]] is a balanced cantilever made of concrete, shown here under construction.
|sibling_names=None
|descendent_names=[[Swing bridge]]
|ancestor_names=[[Beam bridge]], [[truss bridge]]
|carries=[[Pedestrian]]s, [[automobile]]s, [[truck]]s, [[light rail]], [[heavy rail]]
|span_range=Medium|material=[[Iron]], [[structural steel]], [[prestressed concrete]]
|movable=No
|design=Medium
|falsework=Very little to none
}}
A '''cantilever bridge''' is a [[bridge]] built using structures that project horizontally into space, supported on only one end (called [[cantilever]]s). For small [[footbridges]], the cantilevers may be simple [[beam (structure)|beams]]; however, large cantilever bridges designed to handle road or rail traffic use [[truss]]es built from [[structural steel]], or [[box girder]]s built from [[prestressed concrete]].
The
== Origins ==
[[File:Tibetan log bridge.JPG|thumb|left|The original style of cantilever bridge]]
[[Civil engineer|Engineer]]s in the 19th century understood that a bridge continuous across multiple supports would distribute the loads among them. This would result in lower stresses in the girder or truss and meant that longer spans could be built.<ref name="dubois">{{cite book | last = DuBois | first = Augustus Jay | title = The Mechanics of Engineering| url = https://books.google.com/books?id=b-YeAAAAMAAJ| access-date = 2008-08-10 | year = 1902 | publisher = John Wiley & Sons | ___location = New York}}</ref>{{rp|57, 190}} Several 19th-century engineers patented continuous bridges with [[hinge]] points mid-span.<ref name="bender">{{cite journal | first = C. | last = Bender | year = 1890 | title = Discussion on ''Cantilever Bridges'' by C.F. Findlay| journal = Transactions of the Canadian Society of Civil Engineers| volume = 3| url = https://books.google.com/books?id=3RIOAAAAYAAJ| access-date = 2008-08-10 | publisher = Canadian Society of Civil Engineers. }}</ref>{{rp|75,79}} The use of a hinge in the multi-span system presented the advantages of a [[statically determinate]] system<ref name="delony">{{cite web|url=http://www.icomos.org/studies/bridges.htm |title=Context for World Heritage Bridges |last=DeLony |first=Eric |author-link=Eric Delony |year=1996 |access-date=2008-08-10 |work=World Heritage Sites |publisher=International Council on Monuments and Sites |url-status=dead |archive-url=https://web.archive.org/web/20050221084235/http://www.icomos.org/studies/bridges.htm |archive-date=2005-02-21 }}</ref> and of a bridge that could handle differential settlement of the foundations.<ref name="dubois"/>{{rp|190}} Engineers could more easily calculate the forces and stresses with a hinge in the girder.
[[Heinrich Gerber (civil engineer)|Heinrich Gerber]] was one of the engineers to obtain a patent for a hinged girder (1866) and is recognized as the first to build one.<ref name="bender"/>{{rp|79}} Located in Germany, the [[Hassfurt Bridge]] over the [[Main (river)|Main]] river in Germany with a central span of 124 feet (38 metres) was completed in 1867 and is recognized as the first modern cantilever bridge.<ref name="delony"/>{{rp|par. 2}}
[[File:Cantilever bridge human model.jpg|thumb|right|250px|The structural principles of the suspended span cantilever bridge]]
The [[High Bridge of Kentucky]] by [[C. Shaler Smith]] (1877), the [[Niagara Cantilever Bridge]] by [[Charles Conrad Schneider]] (1883) and the [[Poughkeepsie Bridge]] by John Francis O'Rourke and Pomeroy P. Dickinson (1889) were all important early uses of the cantilever design.<ref name="delony"/>{{rp|par. 3,5}} The Kentucky River Bridge spanned a gorge 275 feet (84 metres) deep and took full advantage of the fact that falsework, or temporary support, is not needed for the main span of a cantilever bridge.<ref name="delony"/>{{rp|par. 3}}
The [[Forth Bridge]] is a notable example of an early cantilever bridge. This bridge held the record for longest span in the world for twenty-nine years until it was surpassed by the [[Quebec Bridge]]. The engineers responsible for the bridge, [[Benjamin Baker (engineer)|Sir Benjamin Baker]] and [[Sir_John_Fowler,_1st_Baronet|Sir John Fowler]], demonstrated the structural principles of the suspended span cantilever by sitting in chairs and supporting their colleague, [[Kaichi Watanabe]], in between them, using just their arms and wooden poles. The suspended span, where Watanabe sits, is in the center. The wooden poles resist the compression of the lower [[Chord (truss construction)|chord]], while the outstretched arms support the tension of the upper chord. The placement of the brick counterweights demonstrates the action of the outer foundations.<ref name="delony"/>{{rp|par. 6}}
{{clear}}
== Function ==
{{Quotation|Cantilever Bridge.—A structure at least one portion of which acts as an anchorage for sustaining another portion which extends beyond the supporting pier.|[[John Alexander Low Waddell]]|Bridge Engineering<ref name="waddell">{{cite book
| last = Waddell
| first = J. A. L.
| author-link = John Alexander Low Waddell
| title = Bridge Engineering - Volume 2
| url = https://archive.org/details/bridgeengineeri01waddgoog
| access-date = 2008-08-19
| year = 1916
| publisher = John Wiley & Sons, Inc.
| ___location = New York
| pages = [https://archive.org/details/bridgeengineeri01waddgoog/page/n865 1917]
}}</ref>
}}
A simple cantilever span is formed by two cantilever arms extending from opposite sides of an obstacle to be crossed, meeting at the center. In a common variant, the '''suspended span''', the cantilever arms do not meet in the center; instead, they support a central [[truss bridge]] which rests on the ends of the cantilever arms. The suspended span may be built off-site and lifted into place, or constructed in place using special travelling supports.
{{clear}}
[[File:CooperRiverBridge.svg|500px|thumb|center|A diagram of the parts of the [[John P. Grace Memorial Bridge]] ]]
{{clear}}
A common way to construct steel truss and prestressed concrete cantilever spans is to counterbalance each cantilever arm with another cantilever arm projecting the opposite direction, forming a '''balanced cantilever'''; when they attach to a solid foundation, the counterbalancing arms are called '''anchor arms'''. Thus, in a bridge built on two foundation piers, there are four cantilever arms: two which span the obstacle, and two anchor arms that extend away from the obstacle. Because of the need for more strength at the balanced cantilever's supports, the bridge superstructure often{{cn|date=March 2022}} takes the form of towers above the foundation piers. The [[Commodore Barry Bridge]] is an example of this type of cantilever bridge.
Steel truss cantilevers support loads by [[tension (mechanics)|tension]] of the upper members and [[compression (physical)|compression]] of the lower ones. Commonly, the structure distributes the tension via the anchor arms to the outermost supports, while the compression is carried to the foundations beneath the central towers. Many truss cantilever bridges use pinned joints and are therefore [[statically determinate]] with no members carrying mixed loads.
Prestressed concrete balanced cantilever bridges are often built using [[Segmental bridge|segmental construction]].
== Construction methods==
Some steel arch bridges (such as the [[Navajo Bridge]]) are built using pure cantilever spans from each side, with neither falsework below nor temporary supporting towers and cables above. These are then joined with a pin, usually after forcing the union point apart, and when jacks are removed and the bridge decking is added the bridge becomes a [[truss arch bridge]]. Such unsupported construction is only possible where appropriate rock is available to support the tension in the upper chord of the span during construction, usually limiting this method to the spanning of narrow canyons.
[[File:SFOBB-OldEastSpanDismantleCropped.png|500px|thumb|center|The old eastern span of the [[San Francisco–Oakland Bay Bridge]], pictured in August 2014, is deconstructed in an order nearly reverse that of its construction. Similar temporary supports were used under each anchor arm during the bridge's construction.]]
== List by length ==
World's longest cantilever bridges (by longest span):<ref name="NSBA-longbridge">{{Cite book |url=http://www.aisc.org/Content/ContentGroups/Documents/NSBA5/20_NSBA_LongestSpans.PDF |title=National Steel Bridge Alliance: World's Longest Bridge Spans |last=Durkee |first=Jackson |publisher=American Institute of Steel Construction, Inc |date=1999-05-24 |access-date=2007-11-03 |url-status=dead |archive-url=https://web.archive.org/web/20020601114245/http://www.aisc.org/Content/ContentGroups/Documents/NSBA5/20_NSBA_LongestSpans.PDF |archive-date=2002-06-01 }}</ref>
{|class="wikitable sortable"
! No !! Bridge !! Location !! Country !! Date !! Length
|-
| 1 || [[Quebec Bridge]] || [[Quebec]] || [[Canada]] || 1919 || {{cvt|1800|ft|m|0}}
|-
| 2 || [[Forth Bridge]] || [[Firth of Forth]] || [[Scotland]] || 1890 || {{cvt|1710|ft|m|0}} × 2
|-
|-
| 4 || [[Commodore Barry Bridge]] || [[Chester, Pennsylvania]] || [[United States]] || 1974 || {{cvt|1644|ft|m|0}}
| 5 || [[Crescent City Connection]] (dual spans) || [[New Orleans, Louisiana]] || United States || 1958 & 1988 || {{cvt|1575|ft|m|0}}
|-
| 6 || [[Howrah Bridge]] || [[Kolkata]], [[West Bengal]] || [[India]] || 1943 || {{cvt|1500|ft|m|0}}
|-
| 7 || [[Gramercy Bridge]] || [[Gramercy, Louisiana]] || United States || 1995 || {{cvt|1460|ft|m|0}}
|-
| 8 || [[Tokyo Gate Bridge]] || [[Tokyo]] || Japan || 2012 || {{cvt|1443|ft|m|0}}
|-
| 9 || [[J. C. Van Horne Bridge]] || [[Campbellton, New Brunswick]] & [[Pointe-à-la-Croix, Quebec]] || Canada || 1961 || {{cvt|1247|ft|m|0}}
|-
| 10 || [[Horace Wilkinson Bridge]] || [[Baton Rouge, Louisiana]] || United States || 1968 || {{cvt|1235|ft|m|0}}
|-
| 11 || [[Tappan Zee Bridge (1955–2017)|Tappan Zee Bridge]] || [[South Nyack, New York]] & [[Tarrytown, New York]] || United States || 1955 || {{cvt|1212|ft|m|0}}
|-
| 12 || [[Lewis and Clark Bridge (Columbia River)|Lewis and Clark Bridge]] || [[Longview, Washington]] & [[Rainier, Oregon]] || United States || 1930 || {{cvt|1200|ft|m|0}}
|}
== Examples ==
<gallery mode="packed">
File:Quebec bridge pont de quebec.jpg|The [[Quebec Bridge]] is of the general structure described above.
File:VejleFjordBridge.jpg|The [[Vejle Fjord Bridge]] is a concrete bridge built using the balanced cantilever method.
File:SFOakBrEastPartVEast.jpg|Former eastern span of the [[San Francisco–Oakland Bay Bridge]]
File:Howrah Bridge, Kolkata.jpg|[[Howrah Bridge]], [[Kolkata]]
File:ForthBridgeEdinburgh.jpg|The [[Forth Bridge]] with its three double cantilevers.
File:North Span Bluewater Bridge (Port Huron Mich).jpg|Original 1938 span of the [[Blue Water Bridge]]
File:Pulaski Skyway full view.jpg|[[Pulaski Skyway]]
File:Vrengenbrua.jpg|[[:no:Vrengen bru|Vrengen Bridge]], a concrete bridge.
</gallery>
== References ==
{{reflist}}
== External links ==
{{commons category|Cantilever bridges}}
*[http://demonstrations.wolfram.com/CantileverBridge/ "Cantilever Bridge"] by Sándor Kabai, [[The Wolfram Demonstrations Project]], 2007.
*''Biggest of Finished Girders Go Traveling: six giants of 70 tons gave engineers a hard nut to crack'', [[Popular Science]] monthly, February 1919, page 79, [https://books.google.com/books?id=7igDAAAAMBAJ&pg=PA79 Scanned] by [[Google Books]]
*{{Cite NSRW|short=x|wstitle=Bridge, Cantilever}}
== Related Articles ==
* [[Southwest Line]]
{{Bridge footer}}
{{Authority control}}
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