What is the meaning of load?

In mechanical terminology, the term load indicates that external force/weight, either constant or variable, acts on a mechanical member/structure. The weight of an object of a specific material is also an external load, and the external force that works on a structure comes under the categories of loading. The external load generates its effects as stress and strain in the structure.

What is the importance of loading?

Whenever a specific structure/beam is loaded with different types of mechanical loading, then the response of the structure/beam is very important to analyze for purposes like safety, efficiency, durability, etc. Every material under different types of loading behaves differently because some of the materials are more strong in one type of loading but weak in another. So, the analysis of loading is of utmost importance before any construction or development.

Types of loading

There are many different ways in which load can be applied to a mechanical member made of a specific material. Generally, the basic detail about typical loading types is given in the following steps.

Static loading

The term static loading is defined as a stationary force or moment that acts on a structure/member without changing its magnitude with respect to time. The size of this loading is constant in magnitude as well as in position and direction. The static loading analysis helps to obtain the maximum allowable loads that act on a member/object. Example- The weight of a constant machine/structure, constant external force, etc.

Dynamic loading

The term "dynamic loading" refers to live loading that is defined as a variable load/force or moment that acts on a structure/member that changes its magnitude with respect to time. The size of this loading varies in magnitude as well as in position and direction. The dynamic loading analysis helps obtain the stresses that act at the different points of a member due to changing conditions with respect to time. Examples are earthquakes, the effect of boom blast, the flow of wind, etc.

Impact loading

The term "impact loading" refers to shock loading that is defined as the load which is applied to a mechanical member/structure quickly for a very short time or the application of load on the member takes place with an initial velocity. The analysis of impact loading is important because the effect of impact loading on a mechanical member/structure is different from the constant load. Examples are hammer strike on a mechanical object, punching press operation, etc.

Cyclic loading

The term "cyclic loading" refers to repeated loading, defined as the load/force that repeatedly acts on a mechanical member/structure. In other words, it is that loading which acts when a specific magnitude (constant) of external load works on a mechanical member repeatedly over time. The effect of cyclic loading is more prone towards material deformation/failure. The variation of stress in a bar due to cyclic loading is given below:

Tensile loading

When a specific force/load works on a mechanical object/bar in such a way that due to this force, there is an expansion in the object that takes place along the force axis, and due to this, there would be tensile stress generated in the object. So, the applied force is referred to as tensile force/load. A schematic diagram of tensile loading on a mechanical bar construction is given below:

Compressive loading

When a force/load acts on a mechanical member in such a way that the load/force tries to compress the member so that stress is generated in the member, is referred to as compressive stress, and the force is referred to as compressive stress force/load. The compressive force acts towards the member. A schematic diagram of compressive loading on a mechanical component is given below:

Torsional loading

When a specific couple of forces acts on the surface of an object that tries to rotate the object about its longitudinal axis is referred to as torsional loading. Due to this torsional loading, there would be stress generated in the object referred to as torsional stress. The term torsional loading refers to the rotational equivalent of the linear force that acts on the object. A schematic diagram of torsional loading on a mechanical bar is given below:

Transverse loading

When an external load acts on a beam perpendicular to the direction of the longitudinal axis of the beam is referred to as transverse load. There would be stress generated in the beam due to the transverse loading that is known as transverse or bending stress. A schematic diagram of a transverse loading on a cantilever beam is given below:

The expression of bending stress in the beam can be represented as,

${\sigma }_b=F·x$

Here, ${\sigma }_b$ represents bending stress, $F$ represents transverse load.

Shear loading

It is a type of loading condition in which a constant linear external force acts parallel to an object's surface. The applied external force is referred to as shear load. Due to this shear load, there would be shear stress generated in the object. The expression of shear stress can be represented as,

$\tau =\frac{F}{A_s}$

Here, $\tau$ represents shear stress, $F$ represents shear force, and $A_s$ represents surface the area of the object where the shear force acts.

Concentrated loading

Whenever a specific load acts on a structural member over a very small length, this type of loading is referred to as concentrated loading. Some examples of concentrated loading are point load, moment, etc. The weight of a specific object of uniform density acts at the midpoint of the object as a point load. A schematic diagram of concentrated loading on a beam is given below:

Uniformly Distributed loading (UDL)

It is also a type of loading in which a specific magnitude of the load is distributed uniformly over a particular distance of a beam member in the transverse direction. This type of loading can be seen in our day-to-day life like railway bridges, highways, roof weight over house beam, etc. A schematic diagram of distributed loading over a beam is given below:

Uniformly varying loading (UVL)

The term uniformly varying loading indicates the uniform variation of an external load/linear force over a cross-section of the mechanical beam. Due to the uniform variation of linear force over a beam surface, there would be a uniform variation of stress generated in the beam. The variation of stress between maximum and minimum stress depends on the value of load variation over the beam.

Eccentric loading

When the line of action of an external linear constant force would not pass over the axis of a beam/structure, it can be considered an eccentric load. The equivalent/resultant effect due to this eccentric loading generates two types of forces: an axial force that acts along the longitudinal axis of the beam, and another is the bending moment. This type of loading may be of tensile or compressive type. So, it is essential to know the effect of eccentric loading on a beam/structure.

Common Mistakes

• Students sometimes get confused about the difference between the torque and the moment. However, torque is a type of loading which tries to rotate the object about its longitudinal axis, whereas moment is a loading type that tries to move towards the longitudinal axis of the object means trying to bend.
• Sometimes, students also get confused about the consequences of eccentric loading on a mechanical object. However, for an eccentric load that works at a specific distance parallel to the longitudinal axis of the object, the resultant consequence of this load is an axial load, and another is a bending moment.
• The student also gets confused about the difference between the terms axial load and tensile/compressive load. However, axial load acts along the axis of a mechanical object, whereas tensile/compressive load may act along the longitudinal axis or can act perpendicular to the object's axis.

Context and Applications

Types of loading is very significant in several professional exams and courses for undergraduate, diploma level, graduate, postgraduate. For example:

• Bachelor of Technology in Mechanical Engineering
• Bachelor of Technology in Civil Engineering
• Master of Technology in Mechanical and Civil engineering
• Doctor of Philosophy in Mechanical Engineering
• Diploma in Mechanical Engineering
• Diploma in Civil Engineering

Related concepts

• Stress distribution
• Shear force diagram
• Bending moment diagram
• Axial force diagram
• Effects of different types of load
• Torque distribution diagram
• Torsional stress
• Torsional distribution diagram
• Equivalent resultant effects of different loading

Practice problems

Q 1. A horizontal structural member that is subjected to transverse load perpendicular to its axis is referred to as

a. Beam

b. Column

c. Strut

d. Truss

Correct option: (a)

Q 2. Whenever an external force acts on a horizontal member perpendicular to the cross-section of the member, then the external force is referred to as,

a. Shear force

b. Normal force

c. Torsion

d. None of these

Correct option: (b)

Q 3. Whenever an external force acts on a horizontal member parallel to the cross-section of the member, then the external force Q 2. Whenever an external force acts on a horizontal member perpendicular to the cross-section of the member, then the external force is referred to as,

a. Normal force

b. Axial force

c. Shear force

d. Moment

Correct option: (c)

Q 4. A type of load that acts on a circular member which tries to rotate the member about its axis is,

a. Shear load

b. Axial load

c. Bending moment

d. Toque

Correct option: (d)

Q 5. Which of the following option is correct regarding a beam which extends beyond its external supports?

a. Simply supported beam

b. Over span beam

c. Overhang beam

d. None of these

Correct option: (c)