A Primer on Mobile Crane Stability

Updated: May 2, 2019

Of all mobile crane-related accidents that happen out there, tipping accidents happen with the most regularity. Incidentally, they are also one of the most dangerous categories of crane accidents, often involving fatalities and property damage.

The common theme in these accidents?

A loss of crane stability!

A Primer on Mobile Crane Stability
Image source: Wikipedia

Mobile cranes are designed to operate on the principles of leverage and balance. They must lift heavy loads, through the use of leverage, while maintaining balance at both sides of the tipping axis.

For a crane, the leverage on its superstructure side always remains fixed. However, leverage on its boom side can vary depending on the weight of the load being lifted.

If the leverage on the boom side exceeds the value of the leverage on the superstructure side, any established balance will be lost, and resultantly, the mobile crane will lose its stability.

This can be better understood by looking at the following balance beam model.

Consider, you have a beam, balanced on a fulcrum with two equal loads on its either ends. Both the loads have same weight and are at the same distance from the fulcrum.

The leverage on the Load 1 side is:

Weight of Load 1 x Perpendicular distance of Load 1 from the center of the fulcrum

The leverage on the Load 2 side is:

Weight of Load 2 x Perpendicular distance of Load 2 from the center of the fulcrum

Counterbalance of the beam is dependent on both sides having an equal leverage.

If, at this point, the weight of Load 2 is increased, the leverage on the Load 2 side will increase as a result. To keep the beam then balanced, you must either:

· Increase the weight of Load 1 by same factor as of Load 2; or

· Increase the distance between Load 1 and the fulcrum by moving the fulcrum closer to Load 2

In the case of mobile crane, the tipping axis is the fulcrum, the superstructure side is the Load 1 side, and the boom side is the Load 2 side.

Since the tipping axis and the superstructure side of a mobile crane are fixed, any instability that may result, can only be caused if there is excess weight on its boom side—the crane’s weight loading side.

That’s why, during operations, it is recommended not to exceed the load ratings specified for a mobile crane by the crane’s manufacturer.  

By keeping the load guidelines in check, mobile crane stability can be kept intact, and tipping accidents can be avoided. Additionally, you can install a crane capacity indicator on your mobile crane to ensure the crane is operated within a safe load range.

At Crane Warning Systems Atlanta, we sell RaycoWylie crane capacity indicators at affordable prices. View our complete product range here.

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