4. Factors Affecting Lifting Capacity

Generally, for any crane, what are the list of factors which affects the lifting capacity of the crane. So, what is the operating radius? As you know, operating radius is nothing but your distance from the centre rotation, centre of axis of rotation of the crane to the hook point that is here. That horizontal distance is called as the operating radius. So, that is going to vary with your boom length. Greater the boom length, operating radius will be more. It depends upon the boom angle also. So, if you are going to have a luffing boom so, your boom angle is going to determine your operating radius.

The operating radius of a crane is the horizontal distance from the center of the crane's rotation to the hook. This distance changes depending on the length of the boom; a longer boom results in a longer operating radius. Additionally, the angle of the boom also influences this radius. For example, in a luffing boom crane, as the angle adjusts, it affects both the reach and the vertical lift capabilities of the crane, highlighting the importance of boom configuration in determining how far and how high a crane can safely lift.

Think of the crane as a basketball player who can shoot hoops. The closer they stand to the hoop (shorter operating radius), the easier it is to make a basket (lift a load). However, as they move further away (increase the operating radius), it becomes harder to make the shot. Similarly, the longer the boom, like the player moving back, the more challenging it is to effectively lift loads due to less stability.

As I told you earlier, at greater operating radius and we have even seen the load radius diagram for the mobile cranes as well as for the tower cranes. So, we have seen that greater operating radius, your stability of the crane is less at greater operating radius. As the load lane moves away from the centre of the crane, the stability gets reduced. So, the lifting capacity gets reduced.

When the operating radius increases, the stability of the crane decreases. This is because the further the load is from the center of the crane's rotation, the more it can tilt or topple. Consequently, this reduced stability means the crane cannot lift as heavy loads safely without risking tips over. Understanding this relationship between operating radius and crane stability is crucial for safe lifting practices.

Imagine a seesaw. If one side has a person sitting very close to the center, it balances easily. But if the person moves to the very end, the seesaw can become unbalanced and tip. In the same way, when a load is too far from the crane's center of gravity, it risks tipping over, which limits how much weight it can lift.

The condition of the supporting surface, your surface should be level. You have to level the surface. The soil bearing capacity should be good. Otherwise, your lifting capacity will get reduced. It will affect the safety of your crane. I have even shown you a picture the crane toppled over because of the poor or weak soil.

The surface under the crane must be stable and level to ensure the crane operates safely. If the surface is uneven or made of weak soil, it can cause the crane to tip, reducing its ability to lift as intended. This is so significant that even a slight tilt (as little as 3 degrees) can reduce the lifting capacity by as much as 50%. Therefore, ensuring proper ground conditions is vital for lifting safety.

Think of building a house on sand versus on solid concrete. The house on sand might sink or fall over if the wind blows hard. Similarly, if a crane is set up on weak soil, it may not stand firm when lifting heavy loads, posing a safety risk.

So, the amount of counterweights what you are going to use that is also going to decide the lifting capacity of the crane because that is only going to resist your overturning movement and apart from this, you should also consider the structural frame capacity. Every crane has its own structural limitations. Beyond that it is not possible to load the crane because other than the tipping failure, there is also structural failure.

Counterweights are crucial as they provide balance to the crane, resisting the forces trying to tip it over when lifting loads. The more counterweight used, the higher the crane's lifting capacity, but only up to the point that the crane's structural integrity remains intact. Each crane has a specified limit beyond which it risks structural failure, such as the boom breaking or collapsing under excessive weight.

Picture a seesaw again. If one person is much heavier than the other, the lighter person may be lifted off the ground. Adding more weight to the lighter side can balance the seesaw, but there's a limit to how much weight can be added without breaking the seesaw. Similarly, cranes must balance their load with appropriate counterweights to operate safely without risking structural damage.

The rated load as I told you, the crane rating, the load rating is done based on ideal conditions assuming that the machine is level; the surface is level; the air is calm; the wind speed is not high; there are no dynamic effects.

Crane load ratings are not just arbitrary numbers; they are determined under ideal conditions where everything is perfectly stable—no wind, level surfaces, and optimal crane orientation. If conditions vary—such as windy weather or uneven ground—these ratings must be adjusted downward, indicating that the crane can safely lift less than its maximum rated load under these compromised conditions.

It's like trying to drive a car on a smooth road versus a bumpy, gravel road. On the smooth road, you can drive at high speed safely, but on a rough road, you must slow down significantly to avoid accidents. Similarly, cranes must operate within their load ratings based on the actual working conditions they face.

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