Cantilever Bridges | Advantages & Disadvantages of Cantilever Bridge | Top Longest Cantilever Bridges
What is a Cantilever Bridge? Who Invented the Cantilever Bridge?| | Advantages & Disadvantages of Cantilever Bridge | Top Longest Cantilever Bridges | Lifespan of a Cantilever Bridge
What is a Cantilever Bridge?
A cantilever bridge is a bridge constructed using cantilevers, which project horizontally into space, supported on only one end. It is built with two cantilevers that meet in the middle bridge span – a structure that allows pedestrians or vehicles to cross an obstacle such as a river or canal or railway. The bridge uses projecting beams (called cantilevers) to support the central part.
A cantilever bridge is a type of bridge that uses two or more projecting cantilever beams, extending from opposite sides of a platform to support a central span over a valley.
A cantilever bridge is a type of construction that uses two rigid beams to support the deck, or roadway, from each side. The beams are anchored on either end and project outward.
Cantilever bridges typically have an arch shape because of how their supports meet at the center. They can also be seen as part trusses with a truss being made up of many smaller pieces while a cantilever bridge only has two main members.
Cantilever bridges were first designed in 1867 by Heinrich Gerber and became popular for railroad crossings during the Industrial Revolution when railroads needed large structures but did not have enough money to build them out of stone like other bridges built before. These types of trains required large spans.
A cantilever bridge is a type of truss bridge that uses only one beam on each side of the deck to support it. This design allows for long spans and narrow decks, which are often cheaper than other types of bridges.
For small footbridges, the cantilevers can be simple beam structures; but, large cantilever bridges are designed to handle road or rail traffic use huge trusses built from structural steel or box girders built from prestressed concrete.
The steel truss cantilever bridge became a major engineering breakthrough when first put into practice. It can span distances of over 460 Meters and can be more easily constructed at difficult crossings using little or no falsework.
Who Invented the Cantilever Bridge?
Heinrich Gerber built the first cantilever bridge in 1867. He built two bridges: one across the Regnitz river in Bamberg and the Main Bridge across the Main River in Haßfurt.
Heinrich Gerber was one of the engineers that obtained a patent for a hinged girder in 1866 and is credited with being the first to construct one. The Hassfurt Bridge in Germany, with a central span of 124 feet (38 metres), was constructed in 1867 and is regarded as the first modern cantilever bridge.
The steel truss cantilever bridge was a great engineering advance when it was initially used, as it can span distances of over 1,500 feet (460 m) and can be built more quickly at challenging crossings due to the use of little or no falsework.
Soon after, several other cantilever bridges were built, including the Kentucky High Bridge, the Niagara Cantilever Bridge, and the Poughkeepsie Bridge.
History of Cantilever Bridges
The first cantilever bridge was constructed in 1867 by Engineer Heinrich Gerber. Engineer Heinrich had earlier invented the hinge girder and with his new invention, Engineer Heinrich was able to lengthen the cantilevers and construct a bridge that was long enough to cross the Main River in Germany
As of 2018, the Quebec Bridge in Canada is the longest cantilever bridge span of of 1800 feet (549 Metres). Forth Bridge inScotland, the is another famous cantilever bridge span of 1710 feet. It is made of steel and uses balanced cantilevers on river piers and on land to make a combined span of 3,300 feet .
Cantilevers must be firmly anchored on one side in order to support the the necessary load on the free standing side and prevent shear stress. The best example of a small cantilever is a diving board. as one side is firmly attached to the ground so that the other side can hold a person’s weight suspended over the water.
Cantilevers must resist compression in the lower and tension in the upper supports. Sometimes, a gap or waterway is too wide to be spanned by one cantilever on each side. In this case, a beam bridge or truss bridge is often placed between the arms of the two cantilevers, connecting them into one bridge. This type of bridge is known as a suspended span bridge.
Building Cantilever Bridges
Bridges are designed, first, to carry their own permanent load weight( dead load) and secondly to carry the live loads(traffic) and, finally, to resist natural forces such as earthquakes, or wind.
The first step in constructing a cantilever bridge is to build and connect the arms to the shore. River piers for balanced cantilevers should not be built until the cantilevers that touch the land are completed. If a truss bridge or beams bridges are necessary, they cannot be added until the cantilevers are ready. The beam bridges are most often built off-site and later when ready lowered with a crane into their position.
Advantages of Cantilever Bridge
What are the advantages of using a cantilever bridge?
People prefer cantilever bridges over other types of bridges for a variety of reasons, including:
- Cantilever bridges are easier to build. Most bridges require a lot of space to be built, which might cause roads to be closed or boats to be unable to go along rivers. A cantilever bridge provides plenty of room for traffic to continue moving.
- Most parts of cantilever bridges do not require falsework, which is a temporary structure that supports the bridge while it is being built. This makes cantilever bridges excellent for situations where falsework would be risky, such as deep valleys and rivers prone to flooding.
- Cantilever bridges are also well-suited to bearing big weights. Cantilever bridges are extremely robust for a reason. Because cantilever decks are denser than other types of bridges, they are stiffer. This would be extremely useful if a bridge required to support a huge train.
- Although cantilever bridges require more maintenance than other types of bridges, this need can be avoided by adding strengthening elements to keep the weight of the bridge supported by its base.
- These bridges are usually cheaper than other types of bridge to build. They are also simpler to construct, which makes them easier to build.
- Most of the time, cantilever bridges last longer than other bridges. Concrete is a popular material for making these bridges stronger and more durable. Even materials like steel lasts longer in these bridges when they are well-maintainence
Disadvantages of Cantilever Bridge
- The main disadvantage of a cantilever bridge is that, although they are stronger than traditional beam bridges, construction and maintenance of cantilever bridges are complicated.
- A cantilever bridge does not hold up so well in earthquakes. Cantilever bridges should not be used in earthquake-prone locations.
- Cantilever bridges require a lot of maintenance because they have a lot of moving parts that can cause problems over time. They are subject to wear and tear, and they need to be checked regularly for damages and cracks.
- Cantilever bridges have an increased risk of accidents in comparison with other types of bridges because there is extra space underneath where people can fall off if the bridge collapses or falls apart during an earthquake, for example.
- During the construction of a Cantilever Bridge, there is a lot of stress, which is known as a Negative moment.
- Cantilever bridges must maintain their stability by balancing compressive and tensile forces acting on them
Cantilever Bridge FAQs
How are cantilever bridges built?
Construction of a cantilever bridge begins by laying the foundation on both sides of the bridge at the same time. The steel supporting beams are then put in place and welded together in the middle, which creates a solid foundation.
A pier is built to support each end of the bridge, and then construction continues with placing additional beams and an upper deck is supported by those beams.
Workers bolt everything down as they go to ensure it stays firm. Finally, cables and steel or concrete flooring are added.
What is the average lifespan of a cantilever bridge?
This depends on the maintenance that goes into the bridge over its lifetime. A well-maintained bridge that is properly painted has a considerable lifespan of approximately 100 years for small bridges and 50 years for major ones.
This also depends on traffic loads and environmental factors, so some may last longer than others, but this is the rough average.
There are many different factors that may have an effect on the lifespan of a cantilever bridge, such as traffic loads, environmental factors, and maintenance.
What are the disadvantages of using a cantilever bridge?
Advantages like no falsework and few parts to cross are small drawbacks for this unique construction method.
However, a cantilever bridge is not as strong as other bridges with beams spanning over long distances. That is why many cantilever bridges require additional mass to hold them up at a certain point on the span.
Can a cantilever bridge fall?
A cantilever bridge can very easily fall. There are several factors that affect the longevity of a cantilever bridge, including the materials used, the quality of construction, and how regularly it is maintained and painted.
How are cantilever bridges financed?
The most common way to finance a cantilever bridge project is through public debt. An owner/user pays back the cost of the bridge over time through user fees and tolls. Wider spans also tend to be paid for with a combination of equity, property taxes and user fees.
What is the difference between a cantilever bridge and a suspension bridge?
A suspension bridge requires two main supporting rods extending from the bridge’s pylon to hold up the deck, as well as cables or chains that run along the length of the deck to reduce or eliminate movement during breezes. Cantilever bridges require only one supporting beam and do not usually have cables.
What are some other important facts about cantilever bridges?
Cantilever bridges can be built in many different shapes; however, the most common shapes are arch or curved-arch and curved-strand. These types of trusses are most commonly seen in major cities and can also be found in small towns as well as rural counties.
What type of repairs are needed for a cantilever bridge?
Repairing a cantilever bridge is dependent on the type of damage incurred. If a deck is damaged, it can be replaced. If the beams are damaged, they can be repaired with steel plates that are welded on. If the cables or rods are damaged, they must be replaced altogether with new ones.
What type of vehicles do cantilever bridges support?
A cantilever bridge is built to accommodate very large vehicles such as trucks and buses, or trains but not planes. These types of bridges typically have a high clearance underneath them which allows for large trucks to pass without striking the sides.
The pressure caused by heavy vehicles can also damage the cantilever bridge, so they are built with stronger materials to withstand these impacts.
What is the difference between a cantilever bridge and a truss bridge?
Truss bridges are made up of the same base components as cantilever bridges, i.e., beams and cables. However, truss bridges can be seen as smaller pieces leading up to the main components of a cantilever bridge—the deck and supporting beams. The truss bridge is built in sections, each of which is supported by the main components.
In order to create a truss bridge, the main support beams must be connected at a precise angle. This allows for the beams to act as hinges without any major structural concern and would allow them to not only stand apart but also twist and bend according to what needs to be done.
What are the different materials used to build cantilever bridges?
The materials used to make a cantilever bridge include steel, concrete and cables. Steel beams are used as a base for the bridge and are attached to the deck by screws.
The cantilever beams which hang from the deck can be either made of steel or reinforced concrete, depending on the type of bridge being built and its location.
What are some Parts of cantilever bridges?
There are a lot of different design aspects that go into designing a cantilever bridge, but they all have some basic characteristics which contribute to their strength and durability.
1. Superstructure:
A superstructure, or the main vertical supports of a bridge, can be made of steel or reinforced concrete. Steel is more commonly used as these beams are often longer and require less maintenance than reinforced concrete.
2. Deck:
A cantilever bridge’s deck may be made out of steel or reinforced concrete, which is covered with asphalt to prevent it from becoming slippery. The deck also supports the cantilever beams when they rest on it.
3. Cantilever beams:
The main components of a cantilever bridge are the cantilever beams and rods. Cantilever beams are steel or reinforced concrete which rest on the deck, while rods are steel cables that run through the bridge from pylon to pylon.
4. Cross-beams:
Cross-beams, or struts, are structural elements that connect two cantilever beams together for support in different areas of the bridge and can also be used as a type of guardrail. They are usually made of steel with two support bars.
5. Pivots and pivots:
Pivots are vertical columns that raise and lower the bridge deck in order to allow access to the middle of the bridge. They can also be used as a guardrail for areas where traffic is heavier, i.e., near the sides of the bridge.
6. Supports:
Composed of steel, these supports are used to help support the deck. They also allow the deck to move slightly up and down in order to reduce wind loads and provide some protection for cables or rods from dust.
7. Cables:
Cables are run through the bridge from one end supporting beam to the other as well as across each of the main beams. They can be used to reduce or eliminate wind loading on the structure.
8. Stringers:
Stringers are horizontal timbers which help create the appearance of a more uniform base.
9. Deck plates:
An important element of a cantilever bridge is the deck plates. They are made out of reinforced concrete or steel and fit between the supports to create a solid surface for vehicles to pass over safely.
10. Pylons:
Pylons are permanent pillars on either side of a bridge, and hold up both the cantilevers and crossbeams on either end.
Note: A cantilever bridge is a type of bridge whose main support is found in a single point on the bridge, unlike truss bridges which have multiple support beams which are connected at specific angles.
The deck of a cantilever bridge rests directly on the ground below without any crossbeams—compared to truss bridges which have a base similar to that of a base-plate, or arch, to hold up the deck and beams
Top Longest Cantilever Bridges
Currently, the world longest cantilever bridges by their longest length span are Quebec Bridge in Quebec, (549 Metres )Canada and Forth Bridge (521 Metres) a cantilever railway bridge over the Firth of Forth in the east of Scotland, near of Edinburgh City Centre
| No | Bridge Name | Bridge Location | Length in meters (feet) | Year |
| 1 | Pont de Québec (longest from 1917 to present) |
Quebec City and Lévis, Canada | 549 (1,800) | 1917 |
| 2 | Forth Bridge (longest from 1890 to 1917) |
Lothian/Fife, Scotland, United Kingdom | 521 (1,710) x2 | 1890 |
| Minato Bridge | Osaka, Japan | 510 (1,673) | 1973 | |
| 4 | Commodore Barry Bridge | Chester, Pennsylvania, to Bridgeport, New Jersey, United States | 501 (1,644) | 1974 |
| 5 | Crescent City Connection | New Orleans, Louisiana, United States | 480 (1,575) | 1958 (eastbound) 1988 (westbound) |
| 6 | Howrah Bridge | Kolkata, West Bengal, India | 457 (1,500) | 1943 |
| 7 | Veterans Memorial Bridge | Gramercy, Louisiana, United States | 445 (1,460) | 1995 |
| 8 | Tokyo Gate Bridge | Tokyo, Japan | 440 (1,443) | 2012 |
| 9 | San Francisco–Oakland Bay Bridge (east Bay span) | San Francisco, California, United States | 427 (1,400) | 1936 (demolished 2016) |
| 10 | J. C. Van Horne Bridge | Campbellton, New Brunswick, to Pointe-à-la-Croix, Quebec, Canada | 380 (1,247) | 1961 |
| 11 | Astoria–Megler Bridge | Astoria, Oregon, to Point Ellice near Megler, Washington, United States | 376 (1,232) | 1966 |
| 12 | Horace Wilkinson Bridge | Baton Rouge, Louisiana, United States | 376 (1,235) | 1968 |
