Beams In Engineering - Definition And Classifications

A beam is a structural element that is capable of withstanding load primarily by resisting bending. The bending force induced into the material of the beam as a result of the external loads, own weight, span (distance between two intermediate supports for a structure,) and external reactions to these loads is called a bending moment.

Beams are traditionally descriptions of building or civil engineering structural elements, but smaller structures such as truck or automobile frames, machine frames, and other mechanical or structural systems contain beam structures that are designed and analyzed in a similar fashion.


Beams generally carry vertical gravitational forces but can also be used to carry horizontal loads (i.e., loads due to an earthquake or wind). The loads carried by a beam are transferred to columns, walls, or girders, which then transfer the force to adjacent structural compression members. In light frame construction the joists rest on the beam.

 Types of beams

Beams are characterized by their profile (the shape of their cross-section), their length, and their material. In contemporary construction, beams are typically made of steel, reinforced concrete, wood, composites, or cased fluids (inflatable beams). One of the most common types of steel beam is the I-beam or wide-flange beam (also known as a "universal beam" or, for stouter sections, a "universal column"). This is commonly used in steel-frame buildings and bridges. Other common beam profiles are the C-channel, the hollow structural section beam, the pipe, and the angle.

Beams are also described by how they are supported. Supports restrict lateral and/or rotational movements so as to satisfy stability conditions as well as to limit the deformations to a certain allowance. A simple beam is supported by a pin support at one end and a roller support at the other end. A beam with a laterally and rotationally fixed support at one end with no support at the other end is called a cantilever beam. A beam simply supported at two points and having one end or both ends extended beyond the supports is called an overhanging beam.

So for more comprehensive classifications, beams can be classified into many types based on three main criteria. They are as follows:

1. Based on geometry:
   1. Straight beam – Beam with straight profile
   2. Curved beam – Beam with curved profile
   3. Tapered beam – Beam with tapered cross section
   4. Based on the shape of cross section:
      1. I-beam – Beam with ‘I’ cross section
      2. T-beam – Beam with ‘T’ cross section
      3. C-beam – Beam with ‘C’ cross section
      
      
2. Based on equilibrium conditions:
   1. Statically determinate beam – For a statically determinate beam, equilibrium conditions alone can be used to solve reactions.
   2. Statically indeterminate beam – For a statically indeterminate beam, equilibrium conditions are not enough to solve reactions. Additional deflections are needed to solve reactions.
   
   
3. Based on the type of support:
   1. Simply supported beam
   2. Cantilever beam
   3. Overhanging beam
   4. Continuous beam
   5. Fixed beam

Classification of beams based on the type of support is discussed in detail below:

1. Simply supported beam:

A simply supported beam is a type of beam that has pinned support at one end and roller support at the other end. Depending on the load applied, it undergoes shearing and bending. It is the one of the simplest structural elements in existence.
The following image illustrates a simply supported beam.

2. Cantilever beam:

A cantilever beam is fixed at one end and free at other end. It can be seen in the image below.

3. Overhanging beam:

A overhanging beam is a beam that has one or both end portions extending beyond its supports. It may have any number of supports. If viewed in a different perspective, it appears as if it is has the features of simply supported beam and cantilever beam.

4. Continuous beam:

A continuous beam has more than two supports distributed throughout its length. It can be understood well from the image below.

 

5. Fixed beam:

As the name suggests, fixed beam is a type of beam whose both ends are fixed.

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