The cantilever beam is a beam that is fixed at one end and set to be free at the other end and distributes the load back to the support where it is forced against a moment and shear stress, and cantilever beam allows the creation of a bay window, some bridges, and balconies.
The cantilever beam carries a specific weight on its open end as a result of the support on its enclosed end and the weight would generate on beam structure in addition to breaking down as a result of the shear stress.
Without external support pillars, cantilever construction allows for overhanging structures, and also with trusses or slabs cantilever beam can be constructed. The support must be fixed which means it can support forces and moments in all directions in order to ensure the structure is static.
A balcony is a good example of a cantilever beam and it is supported on one end only and the rest of the beam extends over open space and there is nothing supporting it.
Cantilever deflects more because they are only supported from one end so there is less support for the load to be transferred. In a few different ways, cantilever beam deflection can be calculated such as from simplified cantilever beam equations or cantilever beam software and calculators.
To the support, a load applied to the beam and is resisted by the shear stress and a moment at the point of attachment. The beam experiences a shear stress parallel to the z-axis (vertical) and a moment with axial loading and this moment consists of a force and an instantaneous axis of rotation.
Uses of Cantilever Beam:
Without any supporting columns or bracing, cantilevers provide a clear space underneath the beam and with the introduction of steel and reinforced concrete, cantilevers became a popular structural form.
The cantilever beam is used in;
- In Buildings.
- Cantilever bridges.
- Overhanging projections and elements.
- Balconies such as at Frank Lloyd Wright’s Falling Water.
- Machinery and plants such as cranes.
- Overhanging roofs like shelters, and stadium roofs.
- Shelving and Furniture.
In building constructions, there are various applications of the cantilevered beam such as cantilevers carrying a gallery, roof, runway for an overhead traveling crane, or part of a building above and also used in various structures such as sun shed, shelves, large halls, exhibition buildings, and armories.
For large spans in certain sites, the cantilever construction is employed especially for heavy loading in bridge building and the Forth Bridge Scotland composed of three cantilevers with two connecting suspended spans as showing in fig;
In 1866 the first cantilever bridge in modern history was built by Heinrich Gerber taking influence from ancient Chinese bridges.
Advantages of Cantilever Beam:
There are the following advantages of this beam such as;
- In constructions, these beams are simple.
- On the opposite side, it does not require support.
- This beam generates a negative bending moment which counteracts the positive bending moment of back spans.
- Because of the beam added to the cantilever arms, the span can be greater than that of a simple beam.
- Thermal expansion and ground movement are fairly simple to sustain because the beam is resting simply on the arms.
- Due to their depth, cantilever beams are very rigid.
Disadvantages of Cantilever Beam:
There are the following disadvantages of this beam such as;
- These beams have large deflections.
- This beam generally results in larger moments.
- You need to check for the uplift of the far support and either need to have fixed support or have a back span.
- The moment at the fixed end is higher when the beam is loaded at one end and it can break free from the support if more load is applied.