Cantilever Bridges: Types, Advantages, and Construction Techniques

Introduction of Cantilever Bridge

Cantilever Bridge is a special type of bridge which is constructed by using Cantilever members or the structures that project horizontally. In this article, you will get to know about cantilever bridges, type of cantilever bridge, and the Advantages and Disadvantages of cantilever bridges.

What Does Cantilever Means?

The cantilever is a type of support or a long projecting beam or girder which is generally fixed at only one end and free at another end.

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.

A cantilever is a beam supported only at one end, with load carried over the overhang. This is in contrast to a simply-supported beam, which is supported at both ends. Cantilevers provide a clear space underneath the beam without any supporting columns or bracing.

Cantilever Bridge

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.

Cantilever bridges should be able to resist tensile stresses in the upper support of the cantilever bridge and the compression stresses in the lower support. 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.

In the first stage of the construction of the cantilever Bridge, the arms are connected to the shore. 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.

Type of Cantilever Bridges

The cantilever bridges are mainly classified into two types.

1. Balance Cantilever Bridges
2. Continuous Cantilever Bridges

1. Balanced Cantilever Bridges

The Balanced Cantilever Bridge is one of the best Bridge without the need for falsework. Balanced cantilever bridges are constructed where the longer span is required.

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.

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

1. In the construction of the Cantilever bridges, the falsework is not required.
2. Cantilever bridges can higher withstand the effects of Thermal Expansion.
3. Cantilever bridges are suitable for the longest span.
4. Cantilever bridges have multiple cantilever spans and can be immediately started from all the columns.
5. 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.
6. The cantilever bridges are suitable for deep Rocky valleys and flood-prone areas where falsework is not possible.
7. In the construction of cantilever bridges, support is required on only one side of its cantilever.

Disadvantages of Cantilever Bridges

1. Cantilever Bridges experience a high amount of tension during the construction, which is known as a Negative moment.
2. Cantilever bridges have to take care of its stability by balancing between compressive as well as tensile forces acting on it.
3. Cantilever bridges are heavy, so it required larger and stronger support.
4. Cantilever bridges are not suitable for Earthquake-prone areas.
5. Construction of cantilever bridges is not suitable for excessive climate conditions.
6. Construction and the Maintenance of the Cantilever bridges are complex.

Cantilever Bridge Facts

1. 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.
2. 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.
3. Quebec Bridge is the longest span cantilever Bridge in all over the world which is 549 by length. It is the longest cantilever structure.

Frequently Asked Questions (FAQ) About Cantilever Bridges

What is a Cantilever Bridge?

A cantilever bridge is a type of bridge that is constructed using cantilever structures that project horizontally and are supported only at one end.

What does “cantilever” mean?

A cantilever is a support or a long projecting beam or girder that is fixed at only one end and free at the other end.

How does cantilever support work?

Cantilever support is a rigid structural element that extends horizontally and is supported only at one end. It is typically fixed to a vertical flat surface such as a wall.

What are the main types of cantilever bridges?

There are two main types of cantilever bridges:

1. Balanced Cantilever Bridges
2. Continuous Cantilever Bridges

What are the advantages of cantilever bridges?

1. No need for falsework during construction.
2. Can withstand thermal expansion.
3. Suitable for long spans.
4. Can be constructed without disrupting traffic.
5. Flexible in design and geometry.
6. Ideal for deep rocky valleys and flood-prone areas.

What are the disadvantages of cantilever bridges?

1. High tension during construction (negative moment).
2. Requires balance between compressive and tensile forces.
3. Heavy, requiring larger and stronger support.
4. Not suitable for earthquake-prone areas.
5. Complex construction and maintenance.
6. Not suitable for extreme climate conditions.

What is a Balanced Cantilever Bridge?

A balanced cantilever bridge is constructed without the need for falsework and is suitable for longer spans. It combines the benefits of both simply supported and continuous structures.

What is a Continuous Cantilever Bridge?

A continuous cantilever bridge is built using two gantries from opposite ends of the abutments, meeting in the center. It functions as a continuous beam with consistent bending moment and shear strength.

What materials are used in constructing cantilever bridges?

Materials commonly used include iron, structural steel, and prestressed concrete. Lightweight concrete is sometimes used to reduce the overall weight.

What is the longest cantilever bridge in the world?

The Quebec Bridge is the longest cantilever bridge in the world, with a span of 549 meters.

What was the first cantilever bridge ever built?

The first cantilever bridge, constructed by engineer Heinrich Gerber in 1867, was 38 meters long.

What is the most famous cantilever bridge?

The Forth Bridge is one of the most famous cantilever bridges, holding the world record for the longest span for 29 years.

Why are cantilever bridges used for spanning waterways?

Cantilever bridges are ideal for spanning waterways without dividing them with river piers, as they can support the load from one side and provide a clear passage underneath.