Example crane outrigger loadings/minimum ground bearing pressure required lifting a component up to 4.00 tonnes using ALIMATS

Crane Capacity Typical Gross Weight of Crane Gross Weight of Crane +4.0 Tonne Lift = Maximum Potential Outrigger Load/Pad Revised ALIMAT Outrigger Pad Size Revised Outrigger Pad Area Minimum Ground Bearing Pressure Required Applying 100% of Gross Crane Weight Minimum Ground Bearing Pressure Required Applying 75% of Gross Crane Weight
25 Tonne 26.5 Tonnes 30.5 Tonnes 1740 x 1740mm 3.00 m² 10.2 Tonnes / m² 7.6 Tonnes / m²
30 Tonne 27.7 Tonnes 31.7 Tonnes 1740 x 1740mm 3.00 m² 10.6 Tonnes / m² 7.9 Tonnes / m²
35 Tonne 35.7 Tonnes 39.7 Tonnes 1740 x 1740mm 3.00 m² 13.2 Tonnes / m² 9.9 Tonnes / m²
40 Tonne 39.5 Tonnes 43.5 Tonnes 1740 x 1740mm 3.00 m² 14.5 Tonnes / m² 10.9 Tonnes / m²
50 Tonne 45.4 Tonnes 49.4 Tonnes 1740 x 1740mm 3.00 m² 16.5 Tonnes / m² 12.4 Tonnes / m²
55 Tonne 43.0 Tonnes 47.0 Tonnes 1740 x 1740mm 3.00 m² 15.7 Tonnes / m² 11.8 Tonnes / m²
60 Tonne 52.5 Tonnes 56.5 Tonnes 1740 x 1740mm 3.00 m² 18.8 Tonnes / m² 14.1 Tonnes / m²
70 Tonne 55.8 Tonnes 59.8 Tonnes 1740 x 1740mm 3.00 m² 19.9 Tonnes / m² 15.0 Tonnes / m²
80 Tonne 59.7 Tonnes 63.7 Tonnes 1740 x 1740mm 3.00 m² 21.2 Tonnes / m² 15.9 Tonnes / m²
90 Tonne 61.0 Tonnes 65.0 Tonnes 1740 x 1740mm 3.00 m² 21.7 Tonnes / m² 16.3 Tonnes / m²
95 Tonne 70.0 Tonnes 74.0 Tonnes 1740 x 1740mm 3.00 m² 24.7 Tonnes / m² 18.5 Tonnes / m²
100 Tonne 75.9 Tonnes 79.9 Tonnes 1740 x 1740mm 3.00 m² 26.6 Tonnes / m² 20.0 Tonnes / m²
120 Tonne 77.6 Tonnes 81.6 Tonnes 1740 x 1740mm 3.00 m² 27.2 Tonnes / m² 20.4 Tonnes / m²

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The outrigger loads noted above are based on the combined gross weight of the crane, plus the weight of the product being lifted.

The tables indicate the whole of this load acting in the worst case scenario, over a single crane outrigger support pad. We advise 100% of the gross crane weight be used in your calculations. Some sources of crane planning training, advocate 75% of the gross crane weight to be used in outrigger loading calculations. In acknowledgement of this, we have included a 75% loading column to indicate the effect on minimum ground bearing pressures, for the benefit of our clients who choose this option. In all cases engineering advice should be sought regarding the bearing capacity of the hardstand area. The Appointed Person should request the gross weight of the specific crane being used from the crane hire company and take care to ensure any additional counterweights / ancillary equipment being used for the lift is added to the “as travels” gross crane weights used in the tables above.

It is possible to obtain Actual Predicted type outrigger loads for crane operations from your crane hire company. These loads will be significantly lower than the above “worst case” scenarios noted above and are produced from crane specific software produced by the crane manufacturer. When using this type of loading it is important to ensure an appropriate factor of safety is included in consideration of ground bearing capacity / mat size.
We advocate the services of an experienced specialist engineer to both assess the hardstand bearing capacity and work with the Crane Appointed Person to ensure adequate safety factors have been incorporated. It should also be noted that factors of safety applied by engineers to ground calculations and AP’s onto outrigger loadings separately should be treated with caution. We encourage communication between AP’s and engineers to discuss the possibility of overly cautious factors of safety being incorporated into crane planning overall. Such overly cautious factors of safety can result in the specification / a “requirement” for impractically large mats.

Note: AP’s should refer to CIRIA publication C703 – Crane Stability On Site for guidance on factors of safety.

Always seek the advise of an experienced specialist engineer in consideration of your crane hardstand capacity and subsequent load spread requirements.