11.3 Sloping ground—pick-and-carry cranes
Many crane roll overs occur when pick-and-carry cranes travel with a load along a side slope. This may also occur to telescopic handlers and other mobile plant when travelling with a suspended load. Working on a slope has the effect of either increasing or decreasing the working radius of the crane, which may in turn affect the stability of the crane, and cause the crane to overturn either forwards, backwards or sideways.
Where the centre of gravity of the mobile crane is high above the ground, a minimal ground slope can be a major factor in causing the crane to overturn. This particularly applies when:
- the boom has a high luff angle;
- the boom is telescoped out; or
- the centre of gravity of the suspended load is high.
A side slope of only two or three degrees can have a drastic effect on the stability of the crane. Soft ground, pneumatic tyres and suspension movement will also tend to increase the side angle of the crane and make the risk of overturning greater.
Most manufacturers of pick-and-carry mobile cranes specify the cranes are to be operated on firm level ground. AS 1418.5 Cranes, hoists and winches - Mobile cranes (non-Queensland Government link) does not require that mobile cranes be tested on gradients unless the crane is rated to operate on a gradient exceeding 1% (0.57 degrees).
In practice, it can be very difficult to ensure the supporting surface for a pick-and-carry crane does not exceed a side gradient of 1%. This is particularly the case at a workplace where construction work is being performed where the ground condition and slope may be constantly changing. A pothole in the ground will have the same effect as a gradient if the crane’s wheel enters the hole.
Where possible, avoid working or travelling on sloping ground. If working or travelling on a slope is unavoidable, consider carrying the load on the uphill side of the crane, regardless of the direction of travel. Travel on a slope should be up or down the slope, not across the slope. Reference should be made to side de-ration charts19 prior to carrying out this work.
19. See appendix 1 for definitions.
Last updated June 9, 2006