Cantilever
beams are elements that are supported at one end and carry a load at the other
end or are distributed along the unsupported part. To ensure that the structure
is static, the support must be fixed, which means that it can withstand forces
and moments in all directions.

The
upper half of the cantilever beam thickness is subjected to tensile stress,
tendency to elongate the fibers, the lower half to compressive stress, tendency
to crush them. Beams may be raised outside their supports by a distance equal
to a quarter of the span between supports.

Cantilevers deflect more than most other types of beams
because they only rest at one end. This means that there is less support for
the load to be transferred.

A great
example of a cantilever beam is a balcony. A balcony is only supported at one
end, the rest of the beam runs over open space; there is nothing to support it
on the other side.

This
structural beam is widely used in the construction of bridges, towers and
buildings and can add a unique charm to the structure.

*This article, explains some important structural steps and basic
concepts of a cantilever beam in construction.*

**How
to calculate Cantilever beam deflection?**

Cantilever beam deflection
can be calculated in different ways, for example with simplified cantilever
beam equations or calculators and cantilever software.

**Structural Behaviour of Cantilever Beam**

As shown in Fig-2 below, a
cantilever beam bends downwards when subjected to vertical loads. A cantilever
beam can be subjected to

· Point
load,

· Uniform
load

· Varying
load

Fig--2: Cantilever Beam Bending Downwards Due to a Load 'F' at Free End |

Regardless of the type of
load, it bends downward creating an upward convexity. This flexion creates
tension in the upper fiber and compression in the lower fibres. Therefore, the
main reinforcement is provided to the upper fiber of the concrete beam, because
there is a high tensile stress as shown in Fig 4.

**Cantilever Beam - Shear Force (SF) and
Bending Moment (BM) Diagram**

The shear force of any part
of a cantilever beam is the sum of the loads between the section and the free
end. The moment of bending in a given section of a cantilever beam is the sum
of each moment according to the section of all loads acting between the section
and the free end.

**Consider,**

Cantilever beam **AB** of length **'l'** subjected to a point load 'W' at the end **B**.

A section **X-X **at a distance **'x' **from the free end **B**
is placed.

The shear force at section **X-X** is **Rx**, which is equal to **W **and
the bending moment of section **X-X** is
**Mx**, which is equal to **W.x.**

Fig-3: Bending and Shear Force Diagram of Cantilever Beam with Point Load at Free End |

The shear force at fixed support A is determined by
holding the part at A,

Which gives the shear force **Ra=W;** and

Moment **Ma = W.l. **

Based on which the shear force and bending moment
diagram are developed.

The cantilever beam has a maximum
bending moment at the fixed end and decreases to zero at the free end. The
diagram of bending and shear forces is determined for all possible load
combinations in order to design a cantilever beam for a structure. The load
applied to the beam is a combination of dead load and live loads in accordance
with design standards.

**Cantilever Beam Design**

A cantilever beam is subjected to moment and shear
stresses under the action of structural loads. The purpose of any design
process is to safely transfer these stresses to support.

Figure-4: Structural Behavior of Cantilever Beam |

The cantilever beam has a bending moment that varies from zero at
the free end to the maximum value at the fixed end support (Fig- 3). Therefore,
when designing the cantilever beams, the main reinforcement is provided to the
upper beam of the concrete beam to safely resist the tensile stress.

The maximum spacing of a cantilever
beam generally depends on the following factors:

·
Depth of cantilever

·
Load size, type and
location

·
Quality and type of
materials used

Generally,
for small cantilever beams, the span is limited to 2 to 3 m. But the depth can
be increased to increase the span or by using a steel or pre-pressed structural
unit. This structure can last a long time because it can be safely shifted to
the ground in the face of the moments created by the cantilever. Detailed
analysis and design of the structure will help to explore the feasibility of
cantilever beams at long intervals.

The
cantilever beam must be properly fixed or supported against the wall to
minimize the inverse effect.

**Uses of Cantilever
Beam in Construction**

*Cantilever beam elements are used in
the following applications:*

· Construction of cantilever beams and balconies

·
Temporary cantilever
support structures

·
Freestanding radio
towers without guy-wires

·
Pergolas
construction

·
Construction of
lintel in buildings

Fig-5: Applications of Cantilever Beam in Buildings and Bridge Girders |

·
In building
construction, there are various applications such as the cantilever beam, i.e.
gallery, roof, upward crane runway, or part of a building above and the sun
shed, shelves, large halls, exhibition buildings and weapons.

**ADVANTAGES OF CANTILEVER BEAM:**

*This
beam has the following advantages;*

· In
construction, these beams are simple.

· On
the opposite side, it does not need support.

· This
beam creates a negative bending moment, which counteracts the positive bending
moment of the rear spans.

· As
the beam is inserted into the cantilever arms, the gap will be larger than a
simple beam.

· Thermal
expansion and ground movement are much simpler to maintain because the beam
simply rests on the hands.

· Due
to their depth, the cantilever beams are very stiff.

**DISADVANTAGES OF CANTILEVER BEAMS**

·
The cantilever beams
are subjected to large deviations.

·
The cantilever beams
are subjected to large moments.

·
Strong fixed support
or backspan is essential to keep the structure stable

**FAQs**

**What is a cantilever beam?**

Cantilever
beams are elements that are supported at one end and carry a load at the other
end or are distributed along the unsupported part. To ensure that the structure
is static, the support must be fixed, which means that it can withstand forces
and moments in all directions.

**What is the maximum span of cantilever beams?**

Generally,
for small cantilever beams, the span is limited to 2 to 3 m. But the depth can
be increased to increase the span or by using a steel or pre-pressed structural
unit. This structure can last a long time because it can be safely shifted to
the ground in the face of the moments created by the cantilever. Detailed
analysis and design of the structure will help to explore the feasibility of
cantilever beams at long intervals.

**How
to calculate Cantilever beam deflection?**

Cantilever beam deflection
can be calculated in different ways, for example with a simplified cantilever
beam equations or calculators and cantilever software.

**How does a cantilever beam behave under loads?**

a cantilever beam bends
downwards when subjected to vertical loads. A cantilever beam can be subjected
to

· Point
load,

· Uniform
load

· Varying
load

Regardless of the type of
load, it bends downward, creating a pile upwards. This curve creates tension in
the upper fibres and contraction in the lower fibres. Therefore, during the
design of the cantilever beams, the main reinforcement is provided to the top
fibre of the concrete beams to safely withstand the tensile stress.

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