What Is A Cantilever Bridges? Who Invented The Cantilever Bridge?
What Is A Cantilever Bridges?
A cantilever bridge is a type of bridge that is supported on only one end and projects horizontally into space. The structures used in building a cantilever bridge can range from simple beams for small footbridges to more complex structures such as trusses made of structural steel or box girders made of prestressed concrete for larger bridges that need to handle road or rail traffic.
The use of steel truss cantilever bridges was a significant engineering advancement, as they are capable of spanning distances of over 1500 feet and can be built in challenging locations with little or no need for false work.
In the 19th century, engineers understood that a continuous bridge with multiple supports would distribute loads and result in lower stresses in the girder or truss, allowing for the construction of longer spans.
Engineers patented continuous bridges with hinge points mid-span, which offered the benefits of a statically determinate system and the ability to handle differential settlement of the foundations. Heinrich Gerber was one of the engineers who obtained a patent for a hinged girder and built the first modern cantilever bridge, the Hassfurt Bridge over the Main river in Germany, in 1867.
Important early examples of cantilever bridges include the High Bridge of Kentucky, the Niagara Cantilever Bridge, and the Poughkeepsie Bridge. The Kentucky River Bridge was particularly impressive, spanning a gorge that was 275 feet deep without the need for falsework.
The Forth Bridge, which held the record for the longest span in the world for 29 years, is one of the most famous early cantilever bridges.
A photo of Benjamin Baker illustrates the structural principles of the suspended span cantilever, showing how the need to resist compression of the lower chord is achieved through 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 also visible through the placement of the counterweights.
Who Invented The Cantilever Bridge?
Heinrich Gerber invented the cantilever bridge in 1867, when he created two bridges – one over the Regnitz river in Bamberg and the Main Bridge over the Main river in Haßfurt. This invention is his legacy and therefore was also known as the Gerber Beam.
Subsequently, several more cantilever bridges were built, such as The High Bridge of Kentucky, The Niagara Cantilever Bridge, and The Poughkeepsie Bridge.
Despite advances in technology making it possible to use different materials for constructing them, these bridges still adhere to Gerber’s basic design concept almost 150 years later.
What Are The Best Cantilever Bridge Materials?
Cantilever bridges come in a variety of sizes and can be made out of different materials to suit the traffic load it needs to bear. Traditionally in Asia, cantilever bridges were made using wood, but this would not be suitable for heavier loads.
Instead metals like steel or iron are usually employed. An example is the Forth Bridge in Scotland which is comprised of 58,000 tonnes of steel and uses iron to weigh down the cantilevers so they can support the bridge’s weight.
Alternatively, concrete can also be used for reinforcement, as seen with the Alamillo Bridge which combines steel with concrete for its structural support.
What Are The Advantages Of A Cantilever Bridge?
Cantilever bridges are an excellent choice for many projects due to their minimal disruption during construction, lack of need for falsework, and ability to carry heavy loads.
Building a cantilever bridge requires less space since it does not require extensive falsework and can keep roads and rivers open while construction is taking place.
Furthermore, the rigid structure of the deck creates a strong framework that is capable of carrying heavy loads such as trains or ships.
Therefore, its versatility makes it ideal for building any type of bridge structure in various environments, from deep gorges to flood-prone areas where other types of bridges may not be feasible.
Disadvantages Of Cantilever Bridges
Cantilever bridges have several disadvantages such as the accumulation of stress during construction and the requirement for large and robust support piers. Additionally, their immense foundation structures make it difficult to build and maintain them.
Furthermore cantilever bridge depths can be risky or difficult in rocky valleys and wet places and these bridges cannot be used in earthquake-prone locations or areas with restricted rock stabilization.
As a result, this form of bridge is not ideal for places with harsh weather conditions.
