6. Modified Cranes for Heavy Lifting

So, you balance both the moments now; equate both the moments. One is the overturning moment. Other one is just stabilizing moment. So, what is contributing to the overturning moment? (L + H) × X = W × (P + f) – (B × u)

In this first chunk, we discuss how to balance the forces acting on the crane when lifting a load. There are two main forces to consider: the overturning moment, which can cause the crane to tip over, and the stabilizing moment that helps keep the crane steady. The equation represents the relationship between these forces, where 'L' represents the length from the pivot point, 'H' is height, 'X' is the distance from the load line to the pivot, 'W' is the self-weight of the crane, 'P' is the projection, 'f' is additional factors, and 'u' is the distance from the boom center to the pivot.

Imagine you’re trying to balance a seesaw. If too much weight is on one side, it tips over—this is similar to the crane’s overturning moment. To keep the seesaw balanced, you need an equal amount of force (stabilizing moment) on the other side, which prevents it from tipping.

So, this L will give you the working load, permissible working load. Apart from this, you have to deduct some margin for safety. How will you determine that margin for safety?

After determining the length 'L' from the previous calculations, which gives the permissible working load, it is essential to implement a margin for safety. This margin ensures that the crane operates within safe limits, avoiding any potential accidents due to unforeseen conditions or load increases. Various organizations, such as the Power Crane Shovel Association (PCSA), provide guidelines on how much additional load should be safely deducted based on different types of crane setups.

Think of it like carrying a backpack. If you can comfortably carry 20 kg, you might choose to only carry 15 kg to avoid straining your back. This 'buffer' is similar to the safety margin that protects cranes from overloading.

For example, if your crane is going to be crawler mounted, in that case, you should not go beyond 75% of the tipping load. If your crane is going to be truck mounted, tire mounted, you should not go beyond 85% of the tipping load.

Different types of cranes have varying safety limits based on their design and purpose. For example, crawler-mounted cranes should not exceed 75% of their tipping load whereas truck-mounted cranes are advised to stay below 85% of the tipping load. This is crucial because exceeding these limits can result in significant hazards, including tipping over.

It's like driving a car. If the speed limit is 60 km/h, you should not drive over that to avoid losing control. Similarly, cranes have their speed limits (load limits) to ensure they function safely without tipping.

As the radius increases as the operating radius increases, so, what is happening to the lifting capacity?

The operating radius of a crane is the distance between the center of the crane’s rotation and the load line. As this radius increases, the crane’s lifting capacity decreases. At maximum operating radius, the stability of the crane is compromised because the center of gravity shifts away from the foundation, which may lead to a reduced ability to safely lift loads.

Consider reaching out with your arm while holding a heavy object. The further you extend your arm (increase the radius), the harder it is to hold the object steady without dropping it (decreased capacity).

To enhance the stability of the crane particularly during the lifting operation, you have to use these outriggers.

Outriggers are extensions that stabilize the crane during operations. They spread out the base of the crane, increasing its stability by distributing the weight more evenly. This helps prevent tipping during lifting, especially for tire-mounted cranes. When using outriggers, the crane's tires are lifted off the ground, transferring the load to the outriggers.

It’s similar to a tripod stand for a camera. The wider the base, the steadier the camera is. If the tripod has just two legs on an uneven surface, it might tip over. In comparison, extending all three legs can stabilize it, just like outriggers stabilize the crane.

To prevent that tipping backward, particularly for heavy lifting cranes, we can go for modified cranes like this. Instead of conventional mounting like a crawler mounting or truck mounting, you can go for mounting called as ringer base.

For very heavy lifting tasks where tipping backward is a concern—especially when using heavy counterweights—modified cranes with a ringer base are utilized. This design provides a broader base, enhancing stability and preventing backward tipping. Modern technology allows even these mounted cranes to be mobile, aiding in site flexibility.

Imagine a heavy shelf loaded with books; if it’s too top-heavy, it might fall backward. Having a wide base, like a sturdy table, helps ensure it remains steady, just like a ringer base prevents crane tipping.

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