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Ready Reckoner Conversion Tool




The IPAF “Spread the load Ready Reckoner” is a simple interactive tool designed to offer guidance to operators and those involved in determining the size of spreader plates to be used when setting up a boom-type MEWP where the weight will be fully supported on the outriggers, also known as jacklegs. After the gross vehicle weight of the MEWP has been entered, the ready reckoner will display the minimum area of the spreader plate and identify minimum sizes of spreader plates required for differing ground types and strengths. Before using the device, an assessment of the ground strength should be conducted.

The correct assessment of ground strength can vary from a visual inspection of the ground surface to a full geotechnical survey. In the case of MEWPs, a visual inspection is often adequate, as outrigger loads are relatively low compared with machines such as mobile cranes. However, it is essential that the assessment is made by persons with adequate knowledge and experience to know when further expert advice and assessment is required.

Outrigger Foundations

The area of the foot attached to the outrigger of a MEWP is relatively small and consequently generates high pressures on the ground. Most soils, unmade ground and some paved and tarmac covered areas are not capable of supporting these pressures and some form of foundation or spreader pad is often required to reduce the pressure to an acceptable level. It is therefore strongly recommended that suitable spreader plates should always be used under the outrigger feet irrespective of the apparent ground conditions.

In addition, poorer ground conditions may require the advance preparation of additional foundations, such as timber mats, proprietary mats, steel grillages or concrete pads, before the MEWP outriggers are deployed. If timbers are used, these must be in good condition, dry and of adequate thickness (not scaffold boards).

Spreader plates should be of suitable strength and appropriate material to: a) prevent distortion when a load is imposed upon them and b) spread the load evenly across the whole area of the spreader plate. 

It is recommended that spreader plates up to 600mm square or diameter should be at least 25mm thick. Spreader plates up to 900mm square or diameter should be a minimum of 50mm thick. Professional advice should be sought on the appropriate material for spreaders above 900mm.

For further information on ground conditions, please refer to IPAF's technical guidance on the assessment of ground conditions.

Simple explanation of the relationship between weight, force and pressure

Detailed advice on assessment of ground conditions, calculation of bearing pressure and selection of spreader plates is given in the Construction Industry Research and Information Association (CIRIA) publication Crane Stability on Site, C703, 2003.
Additional general guidance is given in the British Standards publication
BS 8460:2005 Safe use of MEWPs — Code of practice.

Ready Reckoner

The IPAF “Ready Reckoner” is for guidance purposes only. Those responsible for assessing the ground and identifying the correct size of spreader plate to be used with any MEWP must do so in accordance with the manufacturers’ instructions and best practice guidance.

In accessing the IPAF “Ready Reckoner”, the user acknowledges the above statement and agrees not to hold IPAF responsible for any damage, loss or injury that may result from incorrect assessment of ground conditions or incorrect selection and use of spreader plates.


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