Mechanical Engineering: Beam Load Calculations Explained

In the field of construction, beam load calculations can become truly critical and require special attention as well as accurate implementation of the results. A simple yet effective way of calculating beam loads is discussed here through derived formulas and expressions.

Just a look around will relate to us the simple, yet interesting fact that each and every object, living or non-living, is constantly applying a certain load over a certain base and also simultaneously is being subjected to an equal and opposite magnitude of force by the supported base.

A car parked over a place exerts a force or offers a load on the ground that may be equal to its weight; however the ground also presents an equal but opposite force to the car so that it stays in place intact. Since the car is held at one constant position, this implies that the two forces must be equal and acting in opposite directions.

Basically the following two forces normally act over any object that fundamentally constitute a load:

• Weight of the object, acting toward the ground
• Reaction of the ground or the base, acting upwards over the object

Before we move into the details of beam load calculations, it would be important to first know about types of loads that may act over a beam supported at its ends.

A load may be classified into the following important types:

• Point load, confined sharply over a single point,
• Equally or uniformly distributed load and,
• Uniformly varying load.

Let’s understand them one by one.

Point Load: A load or weight subjected over a point area is called a point load. However, mathematically a point load doesn’t look feasible, simply because any load will need to have a certain area of impact and cannot possibly balance over a point, but if the impact area is too small compared to the length of the beam, may be taken as defined.

Equally Distributed Load: As the name implies a load that’s equally aligned across the whole beam is termed an equally distributed load.

Uniformly Varying Load: Loads distributed over a beam which produces a uniformly increasing load gradient across the entire beam end to end is called a uniformly varying load.

A beam possibly may be subjected to one of the above loads or in combinations.

Beam Reactions

The following simple illustration will walk us through formulas relating to beam load calculations or, more accurately, beam reactions:

Referring to the diagram alongside, let’s consider a beam being supported at its ends (left and right), denoted by the letters A and B respectively.

Let there be point loads acting on the beam over positions marked as W1, W2, and W3.

Also let,

R_A = Reaction at the end A of the beam.

R_B = Reaction at the end B of the beam.

Now, there are primarily a couple of forces (turning effect) that’s acting over the beam ends A and B viz. clockwise and anti-clockwise moment of force.