![]() | This article possibly contains original research .(August 2022) |
![]() The Pierre Pflimlin Bridge is a balanced cantilever made of concrete, shown here under construction. | |
Ancestor | Beam bridge, truss bridge |
---|---|
Related | None |
Descendant | Swing bridge |
Carries | Pedestrians, automobiles, trucks, light rail, heavy rail |
Span range | Medium |
Material | Iron, structural steel, prestressed concrete |
Movable | No |
Design effort | Medium |
Falsework required | Very little to none |
A cantilever bridge is a bridge built using structures that project horizontally into space, supported on only one end (called cantilevers). For small footbridges, the cantilevers may be simple beams; however, large cantilever bridges designed to handle road or rail traffic use trusses built from structural steel, or box girders built from prestressed concrete.
The steel truss cantilever bridge was a major engineering breakthrough when first put into practice, as it can span distances of over 1,500 feet (460 m), and can be more easily constructed at difficult crossings by virtue of using little or no falsework.
Engineers in the 19th century understood that a bridge that 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. [1] : 57, 190 Several 19th-century engineers patented continuous bridges with hinge points mid-span. [2] : 75, 79 The use of a hinge in the multi-span system presented the advantages of a statically determinate system [3] and of a bridge that could handle differential settlement of the foundations. [1] : 190 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. [2] : 79 The Hassfurt Bridge over the 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. [3] : par. 2
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. [3] : par. 3, 5 The Kentucky River Bridge spanned a gorge that was 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. [3] : 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, Sir Benjamin Baker and 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, while the outstretched arms support the tension of the upper chord. The placement of the brick counterweights demonstrates the action of the outer foundations. [3] : par. 6
Cantilever Bridge.—A structure at least one portion of which acts as an anchorage for sustaining another portion which extends beyond the supporting pier.
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.
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[ citation needed ] 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 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 construction.
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.
World's longest cantilever bridges (by longest span): [5]
No | Bridge | Location | Country | Date | Length |
---|---|---|---|---|---|
1 | Quebec Bridge | Quebec | Canada | 1919 | 1,800 ft (549 m) |
2 | Forth Bridge | Firth of Forth | Scotland | 1890 | 1,710 ft (521 m) × 2 |
3 | Minato Bridge | Osaka | Japan | 1973 | 1,673 ft (510 m) |
4 | Commodore Barry Bridge | Chester, Pennsylvania | United States | 1974 | 1,644 ft (501 m) |
5 | Crescent City Connection (dual spans) | New Orleans, Louisiana | United States | 1958 & 1988 | 1,575 ft (480 m) |
6 | Howrah Bridge | Kolkata, West Bengal | India | 1943 | 1,500 ft (457 m) |
7 | Gramercy Bridge | Gramercy, Louisiana | United States | 1995 | 1,460 ft (445 m) |
8 | Tokyo Gate Bridge | Tokyo | Japan | 2012 | 1,443 ft (440 m) |
9 | J. C. Van Horne Bridge | Campbellton, New Brunswick & Pointe-à-la-Croix, Quebec | Canada | 1961 | 1,247 ft (380 m) |
10 | Horace Wilkinson Bridge | Baton Rouge, Louisiana | United States | 1968 | 1,235 ft (376 m) |
11 | Tappan Zee Bridge | South Nyack, New York & Tarrytown, New York | United States | 1955 | 1,212 ft (369 m) |
12 | Lewis and Clark Bridge | Longview, Washington & Rainier, Oregon | United States | 1930 | 1,200 ft (366 m) |
A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. The first modern examples of this type of bridge were built in the early 1800s. Simple suspension bridges, which lack vertical suspenders, have a long history in many mountainous parts of the world.
A cable-stayed bridge has one or more towers, from which cables support the bridge deck. A distinctive feature are the cables or stays, which run directly from the tower to the deck, normally forming a fan-like pattern or a series of parallel lines. This is in contrast to the modern suspension bridge, where the cables supporting the deck are suspended vertically from the main cable, anchored at both ends of the bridge and running between the towers. The cable-stayed bridge is optimal for spans longer than cantilever bridges and shorter than suspension bridges. This is the range within which cantilever bridges would rapidly grow heavier, and suspension bridge cabling would be more costly.
An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side. A viaduct may be made from a series of arches, although other more economical structures are typically used today.
A truss is an assembly of members such as beams, connected by nodes, that creates a rigid structure.
A truss bridge is a bridge whose load-bearing superstructure is composed of a truss, a structure of connected elements, usually forming triangular units. The connected elements, typically straight, may be stressed from tension, compression, or sometimes both in response to dynamic loads. There are several types of truss bridges, including some with simple designs that were among the first bridges designed in the 19th and early 20th centuries. A truss bridge is economical to construct primarily because it uses materials efficiently.
Beam bridges are the simplest structural forms for bridge spans supported by an abutment or pier at each end. No moments are transferred throughout the support, hence their structural type is known as simply supported.
The Howrah Bridge is a balanced steel bridge over the Hooghly River in West Bengal, India. Commissioned in 1943, the bridge was originally named the New Howrah Bridge, because it replaced a pontoon bridge at the same location linking the twin cities of Howrah and Kolkata, which are located at the opposite banks of each other. On 14 June 1965, it was renamed Rabindra Setu after the Bengali poet Rabindranath Tagore, who was the first Indian and Asian Nobel laureate. It is still popularly known as the Howrah Bridge.
Bangabandhu Bridge, also known as the Jamuna Multi-purpose Bridge is a bridge opened in Bangladesh in June 1998. It connects Bhuapur on the Jamuna River's east bank to Sirajganj on its west bank. It was the 11th longest bridge in the world when constructed in 1998 and at present is the 6th longest bridge in South Asia. The Jamuna River, which it spans, is one of the three major rivers of Bangladesh, and is fifth largest in the world in discharge volume.
The 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 Whirlpool Bridge, and opened to traffic in 1883, it was replaced by the Michigan Central Railway Steel Arch Bridge in 1925.
The Roberto Clemente Bridge, also known as the Sixth Street Bridge, spans the Allegheny River in downtown Pittsburgh, Pennsylvania, United States.
A girder is a beam used in construction. It is the main horizontal support of a structure which supports smaller beams. Girders often have an I-beam cross section composed of two load-bearing flanges separated by a stabilizing web, but may also have a box shape, Z shape, or other forms. Girders are commonly used to build bridges.
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. The bridge is made of concrete that is either cast-in-place or precast concrete.
A tied-arch bridge is an arch bridge in which the outward-directed horizontal forces of the arch(es) are borne as tension by a chord tying the arch ends rather than by the ground or the bridge foundations. This strengthened chord may be the deck structure itself or consist of separate, independent tie-rods.
This is an alphabetical list of articles pertaining specifically to structural engineering. For a broad overview of engineering, please see List of engineering topics. For biographies please see List of engineers.
A Howe truss is a truss bridge consisting of chords, verticals, and diagonals whose vertical members are in tension and whose diagonal members are in compression. The Howe truss was invented by William Howe in 1840, and was widely used as a bridge in the mid to late 1800s.
A deck is the surface of a bridge. A structural element of its superstructure, it may be constructed of concrete, steel, open grating, or wood. Sometimes the deck is covered by a railroad bed and track, asphalt concrete, or other form of pavement for ease of vehicle crossing. A concrete deck may be an integral part of the bridge structure or it may be supported with I-beams or steel girders.
The Godavari Arch Bridge is a bowstring-girder bridge that spans the Godavari River in Rajahmundry, India. It is the latest of the three bridges that span the Godavari river at Rajahmundry. The Havelock Bridge being the earliest, was built in 1897, and having served its full utility, was decommissioned in 1997. The second bridge known as the Godavari Bridge is a truss bridge and is India's third longest road-cum-rail bridge crossing a water body.
The Sharavati Bridge is a railway bridge, south of Honnavar, in the state of Karnataka, India, completed in 1994. It carries the Konkan Railway over the Sharavati river.
Sadliers Crossing Railway Bridge is a heritage-listed railway bridge at over Bremer River between Tallon Street, Sadliers Crossing and Dixon Street, Wulkuraka, Queensland, Australia on the Main Line (this section is now the Ipswich and Rosewood railway line. It was added to the Queensland Heritage Register on 13 November 2008.
A launching gantry is a special-purpose mobile gantry crane used in bridge construction, specifically segmental bridges that use precast box girder bridge segments or precast girders in highway and high-speed rail bridge construction projects. The launching gantry is used to lift and support bridge segments or girders as they are placed while being supported by the bridge piers instead of the ground.