What Is Cantilever Bridge?
Cantilever bridges are widely seen in major cities and movies. Though you have seen them but might not know the name it is called, yes, they are the long cantilever bridges that can carry heavy loads. These types of bridges are built with cantilevers; hence they are named Cantilever bridges. Before getting into details, let us know what a cantilever is? A cantilever is a structure with one of its ends fixed and free at other ends. The other end projects horizontally into space, and it is this end that helps support the bridge.
A cantilever bridge works in such a way that the bottom part of each cantilever is fixed or anchored into the ground, while the upper end of the cantilever supports the bridge itself.
The Cantilever bridge is a widely constructed bridge all over the world. These bridges are widely adopted mainly because They do not need any support. Usually, cantilever bridges are built when providing many supports is not possible.
Types Of Cantilever Bridge
The cantilever bridges are mainly divided into two types:
- Balanced Cantilever Bridges
- Continuous Cantilever Bridges
1. Balanced Cantilever Bridges
The balanced cantilever bridge does not require any falsework. Usually, this type of bridge is opted for constructing a long-span bridge. If the bridge construction requirement is not suitable for simply supported or continuous frame type structures, then balanced cantilever bridges can be used. We know that constructing a long-span continuous or simply supported bridge requires a solid foundation, which would be more expensive to construct.
Generally, balanced cantilever bridges are the combination of both simply supported structure and continuous structure. The cantilever structure, which is constructed with only one cantilever length, must be small; otherwise, there may be chances of uplift at another end. A balanced cantilever bridge has the advantage of both continuous and simply supported structures. Like continuous bridges, the balanced cantilever bridge needs one line of bearings over the piers.
2. Continuous Cantilever Bridges
The continuous cantilever bridge is a truss bridge that extends across three or more supports without hinges or joints. Cantilever bridges are highly simplified, but they will explain the basic concepts of a conventional beam.The abutments should be made heavy to compensate for the absence of a balanced cantilever. These types of Cantilever bridges work as continuous beam feet span between two support by maintaining their bending moment and Shear Strength throughout the beam.
Advantages Cantilever Bridges
- Generally, the requirement of falsework is not much, other than the requirement for the pier.
- The suspended bridges sections are assembled that can only be elevated and attached between two cantilever spans.
- Only one side of each cantilever requires support.
- The floor of the bridge is simply formed into sections to preserve uniformity and ensure high quality.
- It is less time-consuming, As multiple cantilever spans construction can be started simultaneously from all its columns.
- Navigation or passage under the bridge is not disturbed during the construction process.
- There is no need for synthetic support if the area has a strong rock structure and anchor arms are connected to the surrounding rock.
- The span of cantilever bridges is usually longer than conventional beams since the cantilever is attached at the ends of the bridge.
- Cantilever bridges can withstand the effects of thermal expansion and floor speed than other types of bridges.
- In cantilever bridges, the lack of supporting piers provides extra flexibility to the styles and geometry of the highway supported by this bridge.
- These bridges are most suitable for flood-prone areas and deep rocky valleys, where falsework might be dangerous or difficult.
Disadvantages Of Cantilever Bridges
- A cantilever bridge requires a heavier structure to take care of its own stability by creating stability between compressive and tensile forces.
- During the construction of Cantilever bridges, they experience a high level of tension which is known as negative moments.
- Cantilever bridges cannot be constructed in extreme climate conditions due to the lack of multiple seasons.
- Cantilever bridges require advanced analysis to prevent future fatigue failure of elements and welds.
- Disability of the RC floor as part of a composite section.
- It is challenging to construct and maintain these bridges, as they are large scale structures.
- Requires bigger and stronger support columns to withstand the bridge load.
- Generally, Long span bridges have truss bridges between the two cantilevers to reduce their weight.
- Cantilever beams are not suitable for earthquake-prone areas or areas with low-rock stability.