Important Terms For Your Safety

Specific to outrigger pads, crane pads, and foundational support.

Allowable Ground Bearing Pressure:The maximum permissible pressure, typically expressed in pounds per square foot (psf) or Pascals (Pa), that may be imposed on the supporting surface.This value may be equal to the Soil Bearing Capacity divided by a suitable safety factor or it may be a lesser value as limited by other considerations, such as the strength of the subsurface pipes. See Ground Bearing Pressure; see Soil Bearing Capacity.

Average Ground Bearing Pressure (AGBP): Force/Area = AGBP.

Blocking: Material used to support equipment or a component and distribute loads to the ground. It is typically used to support lattice boom sections during assembly/disassembly and under outrigger and stabilizer floats. Also called dunnage, cribbing, pads, and mats.

Crane Mat: An assembly of structural members arranged to distribute the loads from a crane’s tires, outriggers, or crawler tracks over a large area in order to reduce the ground bearing pressure.

Crane Pad: An area of compacted or otherwise specially prepared soil, concrete, mats, steel plate or other materials designed to support a mobile crane

Cribbing: Blocking materials that are used to increase the bearing area and height. See blocking.

Crush Rating: The allowable amount of pressure that an outrigger pad, crane outrigger pad, cribbing or crane pad is rated to carry, based on the strength of the material.

Deflection: The bending of supporting materials as downforce is applied.

Displacement: The difference between the unloaded horizontal positions of the outrigger pad, compared with the fully loaded horizontal position of the outrigger pad.

Downforce: The force that is generated in a downward direction from the outriggers through the outrigger float and onto the outrigger pads.

Dunnage: Materials used to increase foundational support under outrigger enabled equipment. Generally smaller parts that are assembled in a specific arrangement to decrease weight while providing adequate rigidity and area for foundational support. See cribbing.

Effective Bearing Area: The area under a crane mat that is effective in distributing the applied load to the underlying surface.

Flex Modulus (Bending Stiffness): The ratio of stress to strain that determines the tendency of a material to bend.

Float: The rigid structural component that attaches to the outer end of a mobile crane’s outrigger to provide some load spreading of the outrigger load to the supporting surface. The floats are provided by the crane manufacturer. Also commonly called outrigger float, outrigger pad, outrigger pan, foot, or pad.

Ground Bearing Pressure (GBP): The pressure, typically expressed in pounds per square foot (psf) or Pascals (Pa), that a crane imposed on the supporting surface.  See Allowable Ground Bearing Pressure.

Ground Bearing Capacity (GBC): The strength of the ground, or its ability to support a pressure.

Ground Conditions: The ability of the ground to support the equipment (including slope, compaction, and firmness) (29 CFR 1926.1402)

Ground Load Rating (GLR): The amount of weight that can be applied to the outrigger pad or crane pad based on the ability of the ground to support it. The GLR assumes that the pad/mat is able to effectively spread the load emitted from the outrigger contact area over the entire area of the mat/pad.

Maximum Outrigger Reaction Force: The maximum amount of weight that the equipment can exert through its outriggers.

Outrigger Pad/Float/Foot: The device supplied by the equipment manufacturer that distributes the total load from the outrigger to the underlying blocking and ground surface. Typical shapes are round, square, rectangular or octagonal. See Float.

Outrigger Pad: A wood, metal, or synthetic structural element that is placed on the supporting surface and on which bears the crane’s float that is used to distribute the outrigger load over a larger area.

Yield: The point at which material begins to deform, bend or break. Once yield occurs, materials will not return to their original shape and material properties are permanently altered.

Supporting Materials:  OSHA 1926.1402(a)(2) “Supporting materials” means blocking, mats, cribbing, marsh buggies (in marshes/wetlands), or similar supporting materials or devices.

Outrigger Pads