Heavy Equipment

All About Cranes

Because cranes are used to hoist and move loads from one location to another, it is necessary to know the lifting capacity and working range of a crane selected to perform a given service. Manufacturers and suppliers furnish this information in literature describing their products.

When a crane lifts a load attached to the hoist line that passes over a sheave located at the boom point of the machine, there is a tendency to tip the machine over. This introduces what is defined as the tipping condition. A machine is considered to be at the point of tipping when a balance is reached between the overturning moment of the load and the stabilizing moment of the machine when the crane is on a firm, level supporting surface.

During a test to determine the tipping load for a crane, the outriggers, if used, should be lowered to relieve the wheels or crawler tracks of all weights on the supporting surface or ground. The radius of the load is the distance horizontally from the crane's rotation axis to the vertical hoist line's tackle or center with the load applied.

The tipping load is the load that produces a tipping condition at a specified radius. The load includes the weight of the item being lifted plus the weights of the hooks, hook blocks, slings, and any other items used in hoisting the load but excludes the weight of the hoist rope.

Cranes used for lifting are classified by a symbol consisting of two numbers based on the rated loads of the crane in the direction of least stability, with the outriggers set if the crane is so equipped.

1. The first number of the group is the crane rating radius, expressed in feet for the maximum rated load, when the crane is equipped with the base boom length.

2. The second number of the group is the rated load (expressed in pounds divided by 100 and rounded off to the nearest whole number) when the load is applied at a 40 foot radius with the use of a 50 foot boom length.

It's important to know and respect the tipping load of the crane as serious accidents and injuries have occurred on construction sites all over the world when workers push the limits with disastrous results. Heavy equipment safety has come to the forefront in recent years as the incidence of accidents has increased. Over half of the accidents involve heavy construction equipment such as cranes.