A
cantilever bridge is a
bridgeA bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...
built using
cantileverA cantilever is a beam anchored at only one end. The beam carries the load to the support where it is resisted by moment and shear stress. Cantilever construction allows for overhanging structures without external bracing. Cantilevers can also be constructed with trusses or slabs.This is in...
s, structures that project horizontally into space, supported on only one end. For small footbridges, the cantilevers may be simple
beamsA beam is a horizontal structural element that is capable of withstanding load primarily by resisting bending. The bending force induced into the material of the beam as a result of the external loads, own weight, span and external reactions to these loads is called a bending moment.- Overview...
; however, large cantilever bridges designed to handle road or rail traffic use
trussIn architecture and structural engineering, a truss is a structure comprising one or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes. External forces and reactions to those forces are considered to act only at the nodes and result in...
es built from
structural steelStructural steel is steel construction material, a profile, formed with a specific shape or cross section and certain standards of chemical composition and mechanical properties...
, or
box girderA box or tubular girder is a girder that forms an enclosed tube with multiple walls, rather than an or H-beam. Originally constructed of riveted wrought iron, they are now found in rolled or welded steel, aluminium extrusions or pre-stressed concrete....
s built from
prestressed concretePrestressed concrete is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete...
. The steel truss cantilever bridge was a major engineering breakthrough when first put into practice, as it can span distances of over 1500 feet (457.2 m), and can be more easily constructed at difficult crossings by virtue of using little or no
falseworkFalsework consists of temporary structures used in construction to support spanning or arched structures in order to hold the component in place until its construction is sufficiently advanced to support itself...
.
A
cantilever bridge is a
bridgeA bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...
built using
cantileverA cantilever is a beam anchored at only one end. The beam carries the load to the support where it is resisted by moment and shear stress. Cantilever construction allows for overhanging structures without external bracing. Cantilevers can also be constructed with trusses or slabs.This is in...
s, structures that project horizontally into space, supported on only one end. For small footbridges, the cantilevers may be simple
beamsA beam is a horizontal structural element that is capable of withstanding load primarily by resisting bending. The bending force induced into the material of the beam as a result of the external loads, own weight, span and external reactions to these loads is called a bending moment.- Overview...
; however, large cantilever bridges designed to handle road or rail traffic use
trussIn architecture and structural engineering, a truss is a structure comprising one or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes. External forces and reactions to those forces are considered to act only at the nodes and result in...
es built from
structural steelStructural steel is steel construction material, a profile, formed with a specific shape or cross section and certain standards of chemical composition and mechanical properties...
, or
box girderA box or tubular girder is a girder that forms an enclosed tube with multiple walls, rather than an or H-beam. Originally constructed of riveted wrought iron, they are now found in rolled or welded steel, aluminium extrusions or pre-stressed concrete....
s built from
prestressed concretePrestressed concrete is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete...
. The steel truss cantilever bridge was a major engineering breakthrough when first put into practice, as it can span distances of over 1500 feet (457.2 m), and can be more easily constructed at difficult crossings by virtue of using little or no
falseworkFalsework consists of temporary structures used in construction to support spanning or arched structures in order to hold the component in place until its construction is sufficiently advanced to support itself...
.
Origins
Engineers in the nineteenth century understood that a bridge which was 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. Several nineteenth century engineers patented continuous bridges with
hingeA hinge is a type of bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation. Hinges may be made of flexible material or of moving components...
points mid-span. The use of a hinge in the multi-span system presented the advantages of a statically determinate system and of a bridge that could handle differential settlement of the foundations. Engineers could more easily calculate the forces and stresses with a hinge in the girder.
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. The Hassfurt Bridge over the Main river in Germany with a central span of 124 feet (38 meters) was completed in 1867 and is recognized as the first modern cantilever bridge.
The High Bridge of Kentucky by C. Shaler Smith (1877), the
Niagara Cantilever BridgeThe Niagara Cantilever Bridge or Michigan Central Railway Cantilever Bridge was a cantilever bridge across the Niagara Gorge. An international railway-only bridge between Canada and the United States, it connected Niagara Falls, New York, and Niagara Falls, Ontario, located just south of the...
by
Charles Conrad SchneiderCharles Conrad Schneider , often referred to as C. C. Schneider, was an American civil engineer and bridge designer.-Biography:Schneider was born in Apolda in the Grand Duchy of Saxe-Weimar-Eisenach. He graduated from the Royal Technical School at Chemnitz, Germany, in 1864, and came to the United...
(1883) and the
Poughkeepsie BridgeThe Poughkeepsie Bridge is a steel cantilever bridge spanning the Hudson River between Poughkeepsie, New York on the east bank and Highland, New York on the west bank...
by John Francis O'Rourke and Pomeroy P. Dickinson (1889) were all important early uses of the cantilever design. The Kentucky River Bridge spanned a gorge that was 275 feet (84 meters) deep and took full advantage of the fact that falsework, or temporary support, is not needed for the main span of a cantilever bridge.
The most famous early cantilever bridge is the Forth Rail Bridge. This bridge held the record for longest span in the world for seventeen years only to be surpassed by the
Quebec Bridgeright|thumb|Lifting the centre span in place was considered to be a major engineering achievement. Photo caption from [[Popular Mechanics]] Magazine, December 1917...
, still the current record holder. Benjamin Baker illustrated the structural principles of the suspended span cantilever in the photo on the left. The suspended span, where
Kaichi WatanabeKaichi Watanabe was a Japanese engineer who studied and worked in Scotland, United Kingdom during the 1880s. He was one of the first Japanese engineers who came to study in the UK...
sits, is seen in the center. The need to resist compression of the lower chord is seen in the use of wooden poles while the tension of the upper chord is shown by the outstretched arms. The action of the outer foundations as anchors for the cantilever is visible in the placement of the counterweights.
Function
A simple cantilever span is formed by two cantilever arms extending from opposite sides of the 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 bridgeA truss bridge is a bridge composed of connected elements which may be stressed from tension, compression, or sometimes both in response to dynamic loads. Truss bridges are one of the oldest types of modern bridges...
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 traveling supports.
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 which extend away from the obstacle. Because of the need for more strength at the balanced cantilever's supports, the bridge superstructure often takes the form of towers above the foundation piers. The
Commodore Barry BridgeThe Commodore Barry Bridge is a cantilever bridge that spans the Delaware River from Chester, Pennsylvania to Bridgeport, in Logan Township, New Jersey, USA...
is an example of this type of cantilever bridge.
Steel truss cantilevers support loads by
tensionIn physics, tension is the magnitude of the pulling force exerted by a string, cable, chain, or similar object on another object. It is the opposite of compression. As tension is the magnitude of a force, it is measured in newtons and is always measured parallel to the string on which it applies...
of the upper members and 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 constructionAs its name implies, a segmental bridge is a bridge built in short sections , i.e., one piece at a time, as opposed to traditional methods that build a bridge in very large sections...
.
Construction methods
Some steel arch bridges (such as the
Navajo BridgeNavajo Bridge crosses the Colorado River's Marble Canyon near Lee's Ferry in the US state of Arizona. Apart from the Glen Canyon Bridge a few miles upstream at Page, Arizona, it is the only roadway crossing of the river and the Grand Canyon for nearly...
) 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 bridgeA truss arch bridge combines the elements of the truss bridge and the arch bridge. The actual resolution of forces will depend upon the design. If no horizontal thrusting forces are generated this becomes an arch-shaped truss, essentially a bent beam — see moon bridge for an example...
. 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.
List by length
World's longest cantilever bridges (by longest span):
- Quebec Bridge
right|thumb|Lifting the centre span in place was considered to be a major engineering achievement. Photo caption from [[Popular Mechanics]] Magazine, December 1917...
(QuebecQuebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....
, CanadaCanada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
) 1800 feet (549 m)
- Forth Bridge
The Forth Bridge is a cantilever railway bridge over the Firth of Forth in the east of Scotland, to the east of the Forth Road Bridge, and 14 kilometres west of central Edinburgh. It was opened on 4 March 1890, and spans a total length of...
(Firth of ForthThe Firth of Forth is the estuary or firth of Scotland's River Forth, where it flows into the North Sea, between Fife to the north, and West Lothian, the City of Edinburgh and East Lothian to the south...
, ScotlandScotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
) 2 x 1710 feet (521 m)
- Minato Bridge
The Minato Bridge is a double-deck cantilever truss bridge in Osaka, Japan. It opened in 1974. It is the third-longest cantilever truss span in the world, behind the Quebec Bridge and the Forth Rail Bridge....
(Osaka, Japan) 1673 feet (510 m)
- Commodore Barry Bridge
The Commodore Barry Bridge is a cantilever bridge that spans the Delaware River from Chester, Pennsylvania to Bridgeport, in Logan Township, New Jersey, USA...
(Chester, PennsylvaniaChester is a city in Delaware County, Pennsylvania, United States, with a population of 33,972 at the 2010 census. Chester is situated on the Delaware River, between the cities of Philadelphia and Wilmington, Delaware.- History :...
, USA) 1644 feet (501 m)
- Crescent City Connection
The Crescent City Connection, abbreviated as CCC, refers to twin cantilever bridges that carry U.S. Route 90 Business over the Mississippi River in New Orleans, Louisiana, United States. They are tied as the fifth-longest cantilever bridges in the world...
(dual spans) (New Orleans, LouisianaNew Orleans is a major United States port and the largest city and metropolitan area in the state of Louisiana. The New Orleans metropolitan area has a population of 1,235,650 as of 2009, the 46th largest in the USA. The New Orleans – Metairie – Bogalusa combined statistical area has a population...
, USA) 1575 feet (480 m)
- Howrah Bridge
The Howrah Bridge is a cantilever bridge that spans the Hooghly River in West Bengal, India. Commissioned in 1943, the bridge was originally named the New Howrah Bridge, because it links the city of Howrah to its twin city, Kolkata . On 14 June 1965 it was renamed Rabindra Setu, after Rabindranath...
(KolkataKolkata , formerly known as Calcutta, is the capital of the Indian state of West Bengal. Located on the east bank of the Hooghly River, it was the commercial capital of East India...
, West BengalWest Bengal is a state in the eastern region of India and is the nation's fourth-most populous. It is also the seventh-most populous sub-national entity in the world, with over 91 million inhabitants. A major agricultural producer, West Bengal is the sixth-largest contributor to India's GDP...
, IndiaIndia , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
) 1500 feet (457 m)
- Veterans Memorial Bridge (Gramercy, Louisiana
Gramercy is a town in St. James Parish, Louisiana, United States. The population was 3,066 at the 2000 census.-History:Gramercy was originally an Indian and French settlement and trading post. In 1739, much of the area which is now known as Gramercy was sold to Joseph Delille Dupart, Commissioner...
, USA) 1460 feet (445 m)
- San Francisco – Oakland Bay Bridge (East Bay Span) (San Francisco, California
San Francisco , officially the City and County of San Francisco, is the financial, cultural, and transportation center of the San Francisco Bay Area, a region of 7.15 million people which includes San Jose and Oakland...
, USA) 1400 feet (427 m)
- Horace Wilkinson Bridge
The Horace Wilkinson Bridge is a cantilever bridge carrying Interstate 10 in Louisiana across the Mississippi River from Port Allen in West Baton Rouge Parish to Baton Rouge in East Baton Rouge Parish...
(Baton Rouge, LouisianaBaton Rouge is the capital of the U.S. state of Louisiana. It is located in East Baton Rouge Parish and is the second-largest city in the state.Baton Rouge is a major industrial, petrochemical, medical, and research center of the American South...
, USA) 1235 feet (376 m)
- Tappan Zee Bridge
The Governor Malcolm Wilson Tappan Zee Bridge, usually referred to as Tappan Zee Bridge, is a cantilever bridge in New York over the Hudson River at one of its widest points; the Tappan Zee is named for an American Indian tribe from the area called "Tappan"; and zee being the Dutch word for "sea"....
(South Nyack, New YorkSouth Nyack is a village in the town of Orangetown in Rockland County, New York, located north of Grand View-on-Hudson; northeast of Orangeburg; east of Blauvelt State Park; south of the village of Nyack and west of the Hudson River...
& Tarrytown, New YorkTarrytown is a village in the town of Greenburgh in Westchester County, New York, United States. It is located on the eastern bank of the Hudson River, about north of midtown Manhattan in New York City, and is served by a stop on the Metro-North Hudson Line...
, USA) 1212 feet (369 m)
External links
- "Cantilever Bridge" by Sándor Kabai, The Wolfram Demonstrations Project, 2007.
- Bridges – Their Structure and Function, Brantacan
- Biggest of Finished Girders Go Traveling: six giants of 70 tons gave engineers a hard nut to crack, Popular Science
Popular Science is an American monthly magazine founded in 1872 carrying articles for the general reader on science and technology subjects. Popular Science has won over 58 awards, including the ASME awards for its journalistic excellence in both 2003 and 2004...
monthly, February 1919, page 79, Scanned by Google Books: http://books.google.com/books?id=7igDAAAAMBAJ&pg=PA79