A member is used as an structural member for establishing industrial infrastructures to support loads. Different types of structural members are used in engineering purposes depending upon the required strength of the member. A horizontal structural member is called a beam. It is a slender member made of certain material which is designed to have sufficient strength for supporting of load and sustain longer duration without failure. Different types of beam are used in engineering and technology.
Structural members used in engineering purposes are called differently depending upon their usage. These structural members are –
- Beams – The horizontally placed structural members are called beams. The load is applied either perpendicular or inclined at an angle to the longitudinal axis of the member. Thus, the member is subjected to shear force and bending moment across its transverse cross section.
- Column – The vertically placed structural members are called column. The load is applied either coaxially or eccentric to the longitudinal axis of the member. Thus, the member is subjected to longitudinal stress (normally compressive stress) and buckling force.
- Strut – The structural members which are placed at an angle to the horizontal or vertical, are called struts. The load is applied either in vertical or horizontal direction. Thus, the member is subjected to complex nature of longitudinal stress and shear stress.
When a beam is loaded, sometime it fails and bends downward due to the action of load. This is called bending failure of the beam. The extent of bending depends on following factors –
- Types of beam – It depends upon the fixing of ends of beam.
- Total length of beam.
- Elasticity of beam material.
- Type of loading.
A beam is subjected to bending moment. Hence, stress developed in a beam is mainly bending stress.
Types of Beam
In general, the beams are of following types –
- Cantilever beam.
- Prop Cantilever.
- Simply supported beam.
- Overhanging beam.
- Rigidly fixed or built-in beam.
- Continuous beam.
Consider about the type of beams shown in figure.
A beam which is fixed at one end and free at the other end is known as a cantilever or a cantilever beam.
A cantilever is shown in figure ( A ).
A beam which is fixed at one end and simply supported at other end is known as prop cantilever beam.
A propped cantilever beam is shown in figure ( B ). Support at the free end is called a prop.
A beam whose both ends are supported or resting freely on the walls or columns is known as a simply supported beam.
A Simply supported beam is shown in figure ( C ).
A beam whose one end is either fixed or simply supported on walls and a portion of other end is extending beyond a support in the form of a cantilever is known as an overhanging beam.
An overhanging beam is shown in figure ( D ). It may be overhanging at one end or at both ends. So, it is of two types.
- Overhanging cantilever beam – It has one end fixed and other end overhang over a support.
- Overhanging simply supported beam – It has both ends overhang over supports.
A beam whose both ends are rigidly fixed or built up in walls is known as rigidly fixed beam or a built-in beam.
A rigidly fixed beam is shown in figure ( E ).
A beam which is supported on more than two supports is known as a continuous beam.
A continuous beam is shown in figure ( F ). It may be noted that a continuous beam may be an overhanging beam or not.
A beam may be loaded with the following types of loads –
- Vertical point load.
- Inclined point load.
- Uniformly distributed load.
- Uniformly varying load.
- Loading of couple.
- Point loading on bracket.
Consider about the type of loading of beams shown in figure.
When a load is acting at a point on a beam and perpendicular to the axis of beam is known as a point load.
A point load is shown in figure ( A ). In actual practice, it is not possible to apply a load at a point, because a load has some contact area. But this area is very small in comparison to the length of the beam and so it is neglected.
When the line of action of a load is not vertical but it makes an angle with the axis of beam, then it is called an inclined point load.
An inclined point load is shown in figure ( B ). Inclined point loads are resolved in vertical and horizontal components.
- The vertical component which is perpendicular to the beam axis will cause shear force and bending moments.
- The axial component which is parallel to the beam axis will cause axial stress i.e. pull or push in the beam.
To relieve from axial stresses in this type of loading, one end of the beam is either hinged or supported on rollers.
A load which is spread over a length of the beam in a manner that, each unit length of beam is loaded at the same rate, then it is known as a uniformly distributed load.
A uniformly distributed load is shown in figure ( C ). For calculations, the total uniformly distributed load is assumed to concentrated at the centre of gravity of the load. In short form it is called ( UDL ) .
A load which is spread over a length of beam in a manner that, it varies uniformly on each unit length, then it is known as a uniformly varying load.
For calculations, the total uniformly varying load is assumed to concentrated at the centre of gravity of the load. In short form it is called ( UVL ) .
Sometimes a beam is loaded with a couple.
A beam loaded with a couple is shown in figure ( E ). A couple does not affect the other vertical loads on beam. Magnitude of the couple is only considered during calculating end reactions at supports of beam.
Due to certain reasons, sometimes a load is not directly mounted on the beam, but it is mounted on a ( L ) shaped bracket fixed on beam. This is called loading on a bracket.
A load mounted on a bracket is shown in figure ( F ). If the length of the bracket is ( l ) and magnitude of vertical load is ( W ) , then it may be considered as a combination of two types of load –
- A couple of magnitude ( W \ l )
- A point load of magnitude ( W ) .
Both loads are assumed to act at the point of attachment of the bracket with beam.