This section covers the following four primary factors to consider in order
to safely lift a load:
- Size, weight, and center of gravity of the load
- Number of sling legs and angle with the horizontal
- Rated capacity of a sling
- History of care and usage of the sling.
The load’s center of gravity should be known. The
center of gravity is the point at which the load’s entire weight may be considered as
concentrated. In order to make a level lift, the crane hook must be directly above the
center of gravity. Slight variations are usually permissible, but extreme variations could
result in dangerous load tilting causing unequal stresses in the different sling legs.
This imbalance must be compensated for at once.
The angle between the sling legs and the horizontal should be maximized. The rated
capacity of the sling decreases as the angle formed by the sling leg and the horizontal
line decreases. In other words, the smaller the angle between the sling leg and the
horizontal, the greater the stress on the sling leg. This greater stress means the sling
cannot support as much load. However, heavier loads can be safely moved if the weight of
the load is distributed among more sling legs. |
