Outrigger pads and ground protection: sizing the pad from the reaction, not the guess.

1. Start with the reaction

A crane with a load out on the boom does not put a quarter of its weight on each outrigger. The moment shifts most of it onto the one or two legs under the load, and at full chart that single pad can carry more than the whole machine weighs. Jekko and Maeda publish the maximum pad reaction for each model; Broderson publishes it for each carry deck. Those are the numbers to design from.

The Outrigger Reaction Simulator provides preliminary estimates for supported machines. Use the manufacturer reaction limits for the exact unit and configuration, and have the site reviewer confirm the design basis. The tool does not establish ground capacity or approve a lift.Outrigger Reaction Simulator

2. What the ground will take

Allowable bearing pressure is the other required input. It depends on the actual ground, its condition, and the site investigation; a material name alone does not establish it.

3. The pad-area formula

Required area = design reaction divided by allowable pressure, with compatible units. The design reaction and any dynamic allowance must come from the applicable documentation and lift plan; the allowable pressure must come from the site assessment. This area calculation is only an initial check. It does not prove pad stiffness, ground stability, or the capacity of a slab.

Then check the result against reality: does the pad actually spread the load across its whole footprint? A thin plastic pad under a heavy reaction bends, the corners lift, and the effective area shrinks to a circle around the float. Pad thickness controls stiffness, not area. Match the pad rating to the reaction, not just the footprint to the math.

4. Pads, mats, and cribbing

• Engineered composite pads: use the manufacturer load rating and application limits, then check the selected size and stiffness for the reaction.
• Steel plates: very stiff, spread load well, heavy. Good over cribbing or on a slab where the concern is local crushing.
• Timber and crane mats: use a designed arrangement suited to the ground and loading; grain direction, contact, and the complete support stack matter.
• Track mats: for the travel path over turf, pavers, and finished floors. Not outrigger support.
• Cribbing: use an approved design and the applicable equipment instructions, with full bearing and stable support. Do not choose stack height from a generic rule of thumb.

CLE rents outrigger pads and ground-protection mats. Tell us the surface and proposed machine when you book so the required support can be confirmed and quoted.

5. Stacked pads and eccentric loads

Every interface in a stack is a separate pressure check: float to pad, pad to plate, plate to mat, mat to ground. The force is the same at every layer plus the weight of what is above; the area changes with each material's stiffness and overlap. An outrigger float set off-center on a pad does not load the whole pad, and a pad bridging a crack, a joint, or a curb edge loads only the part that is touching. Center the float, keep full contact, and keep pads off edges.

6. When the pad is not the answer

On a suspended slab, a parking deck, or a roof, the structure carries the whole reaction no matter how large the pad. Lowering the pressure protects the surface from local crushing; it does nothing for the beam under it. Those floors need the engineer of record to review the reaction, the pad location relative to beams and columns, and any shoring. Our floor loading guide and the suspended-slab guide cover what the reviewer will ask for.

Manufacturer references for the figures above: TD_JF235_Imperial_Rev1.2.pdf; Rev1.2, 26.06.2025, p3 footnote. These are specification ratings, not allowable loads for a planned lift. Confirm the exact configuration and load chart with CLE.