What size outrigger pads do I need?

The following information provides guidance for the proper use of outrigger pads to set up cranes or other devices with outriggers or stabilizers. For more information refer to OSHA&#;s standard on cranes and derricks in construction ( Subpart CC).

You can find more information on our web, so please take a look.

General Calculations to Determine the Correct Outrigger Pad (Blocking) Size:

• Rule of 5: Take the maximum lifting capacity in tons of the unit such as 50 tons, divide that by 5 = 10 sq. ft. of cribbing or blocking
• Rule of 3: Take the square footage of the cranes fl oats and multiply by 3. Such as a 2×2 fl oat = 4 sq. ft. Take 4 sq. ft. x 3 = 12 sq. ft. of cribbing or blocking

Examples of Soil Types and Load Bearing Capacities:

SOIL TYPELOAD BEARING CAPACITYVirgin Ground22 psiAsphalt29 psiCompressed Crushed Stone36 psiClay/Silt Soil, Firm43 psiMixed Granular Soil51 psiFirm Compacted Gravel58 psiFirm Compacted Gravel (more compacted)72 psiFirm Compacted Gravel (more compacted)109 psiBrittle Weathered Rock145 psiConcrete psi

*check the load chart or consult the unit manufacturer for the maximum outrigger down pressure for a single outrigger.

Outrigger Pad/Float Size in Square Inches:

ROUND24 inch diameter452 square inches36 inch diameter square inches48 inch diameter square inchesSQUARE24 X square inches36 X square inches48 X square inches

Specific Calculations to Determine the Correct Outrigger Pad Size:

Maximum outrigger down pressure* ÷ outrigger pad/fl oat square inches = amount of pressure per square inch on the blocking material.

Example:

62,800* ÷ (sq. outrigger pad 36×36) = 48.5 lbs psi

Now consult the soil type chart above. With 48.5 lbs psi, the unit can be safely set up on &#;Mixed granular soil&#; or any soil with a higher load bearing pressure than 48.5 lbs psi.

This information was originally developed by Altec through the OSHA and Altec Alliance Program.

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Determining the right sized crane pad is not always an easy task. There are many factors that come into play, which is why the Crane Industry Council of Australia (CICA) released crane outrigger pad size calculator advice for the right size pads. Cranes and Lifting magazine recently reported on this topic.

CICA states that determining crane pad size is a four-step process:

• Calculate the force exerted on the ground by the crane.
• Determine what the allowable Ground Bearing Pressure is for the soil you are setting up on.
• Determine area by calculating force divided by pressure.
• Find the square root of the area to determine the crane pad dimensions.

DICA has created (see below) a crane pad and outrigger pad sizing graph as a quick and easy way to identify the outrigger pad or crane pad area needed to reduce the outrigger load to the target ground bearing pressure.

While it is simple to calculate the right crane pad area for your needs, determining the right material, construction, and thickness required to provide appropriate stability and distribute the load over the intended area is product and manufacturer specific. At DICA we are able to provide guidance for selecting either the outrigger pad or crane pad area, type, construction and thickness in addition to performance projections for each pad.

If you want to learn more, please visit our website Composite Outrigger Pads.