Introduction of Cantilever Bridge
What Does Cantilever Means?
What Is Cantilever Support?
Cantilever support is a rigid structural element which is extended towards the horizontal direction and supported only at one end. In general cases, the cantilever supports extend from a vertical flat surface such as a wall or other element which is firmly attached.
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The Cantilever bridge is widely used all over the world for the construction of Major Bridges. The cantilever bridges come into existence because there is a need for construction of bridges without support. It is not possible to construct continuous Bridges with several supports.
There are some special conditions where the number of supports cannot be given, in that case, Cantilever Bridges are suitable.
With the help of proper construction material and perfect design of the bridge, a Steel Truss cantilever Bridge can span up to the length of 1500 feet. This type of bridges is generally used for pedestrians, vehicles and trains.
Cantilever bridges are best suitable for the construction of the bridges where spanning on a waterway is required without dividing it with the river piers.
It is very necessary that cantilever bridges should firmly be attached at one side so that it can carry the total superimposed load, which is coming from the free-standing side to avoid shear stress.
In some cases the length between two supports where Bridge has to be constructed it is very long which cannot be spanned by one cantilever on each side.
In such a situation, the special Beam Bridge or truss Bridge is placed between the arms of two cantilever which connects them into one Bridge. The type of bridge is known as Suspended Span Bridge.
The material which is used for the construction of the cantilever Bridge is Iron, Structural Steel and Prestressed concrete.
Cantilever structure has a maximum bending moment at the support and zero bending moment it at the free end So that the section at the Support should be Maximum to withstand the bending moment.
A Balance cantilever Bridges is another technique of spanning long distances between two points. In this case, engineer constructs the year in the middle side of the river or span.
The thin-walled circular Steel tubes are used as the piers for the construction of cantilever bridges. For the construction of long-span cantilever bridges, it is necessary that both strength and weight criteria should be satisfied.
To reduce the total weight of the long-span cantilever bridges, lightweight concrete is also sometimes used in the construction of the Cantilever Bridges.
The cantilever bridges also serve the purpose to provide the passage of pedestrians, Railways and vehicles through it from one end to another end.
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Type of Cantilever Bridges
The cantilever bridges are mainly classified into two types.
- Balance Cantilever Bridges
- Continuous Cantilever Bridges
1. Balanced Cantilever Bridges
Balance cantilever bridges are suitable were simply supported, or continuous frame type structures are not suitable. To construct continuous or simply supported bridges for the longer span required solid Foundation at greater than which is more expensive for the construction.
Balanced Cantilever Bridges are the combination of both simply supported structure and continuous structure.
The construction of the cantilever structure with only one cantilever the length should be made small otherwise there may be chances of uplift at another end.
Cantilever balance Bridge has advantages of both simply supported as well as the continuous structures. Cantilever balance Bridge required one line of bearings over the piers, which is similar to the continuous bridges.
This method of Balanced Cantilever Bridges is more helpful as compared to other construction where the temporary showing can disrupt the traffic.
Also, Read: What Is Bridge Pier | Type of Bridge Pier
2. Continuous Cantilever Bridges
The continuous cantilever bridges are the special types of bridges which are constructed by using two gantries from the opposite end of the abutments, which will be made in the centre to complete the structure.
To compensate for the absence of balanced cantilever, the Abutments should be made heavy. Continuous Cantilever bridges work as continuous beam feet span between two support with maintaining its Bending moment and Shear Strength throughout the beam.
Advantages of Cantilever Bridges
- In the construction of the Cantilever bridges, the falsework is not required.
- Cantilever bridges can higher withstand the effects of Thermal Expansion.
- Cantilever bridges are suitable for the longest span.
- Cantilever bridges have multiple cantilever spans and can be immediately started from all the columns.
- Due to lack of supporting piers in the Cantilever Bridges, it gives extra flexibility to the style and geometry of the highway supported by this Bridge.
- The cantilever bridges are suitable for deep Rocky valleys and flood-prone areas where falsework is not possible.
- In the construction of cantilever bridges, support is required on only one side of its cantilever.
Disadvantages of Cantilever Bridges
- Cantilever Bridges experience a high amount of tension during the construction, which is known as a Negative moment.
- Cantilever bridges have to take care of its stability by balancing between compressive as well as tensile forces acting on it.
- Cantilever bridges are heavy, so it required larger and stronger support.
- Cantilever bridges are not suitable for Earthquake-prone areas.
- Construction of cantilever bridges is not suitable for excessive climate conditions.
- Construction and the Maintenance of the Cantilever bridges are complex.
Cantilever Bridge Facts
- The first cantilever bridge in the world was 38 metres long, which is also known as modern cantilever This Bridge was constructed by the engineer Heinrich Gerber in the year 1867.
- The most famous cantilever bridge in the world is the Forth Bridge. This Bridge held the world record of the longest pen in all over the world for the 29 years.
- Quebec Bridge is the longest span cantilever Bridge in all over the world which is 549 by length. It is the longest cantilever structure.