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Worst Case Crane Outrigger Loading Guidance Using ALIMATS
The table is extracted from the PFF Code of Practice For Precast Flooring Installation and provides example data, which should be used for guidance only.
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.
More information on the topic of outrigger loads / calculation and appropriate safety factors will appear in our Ground Assessment section shortly.
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.
Details of companies who offer a range of engineering considerations / crane foundation design services will follow here shortly.