Crane “upsets” occur once in every 10,000 hours of use, according to estimates by the CDC. These accidents occur most often with mobile cranes, which are more prone to tipping, particularly when handling a heavy load. To prevent such “upsets,” OHSA has put forth regulations for crane assembly and use. In addition to being assembled on firm, drained, and graded ground, OHSA specifies cranes be used with supporting materials such as blocks and outrigger crane pads.
When selecting an outrigger pad, three factors must be taken into consideration: the ground conditions upon which the crane will rest, the size of the outrigger foot, and the outrigger load of the equipment.
How ground conditions affect an outrigger crane pad
For obvious reasons, the ground conditions play a major part in the stability of your crane. Outrigger pads for cranes should always be set on ground that is level and compact. To prevent sinking, the ground should be thoroughly drained before assembly.
A geotechnical engineer can help determine the strength of the ground and soil upon which our crane will rest. He can also help determine any subterranean hazards that may pose a risk to your operation and impact a crane pad placement. If your ground surface is inadequate to support a crane, you can take steps to improve it by leveling or compacting the surface, removing un-compacted top layers, or even bringing in denser ground materials such as rock or other inorganic materials.
Use the size of the outrigger foot to determine the size of your crane pad
A rule of thumb is to use a outrigger crane pad that is at least three times as large as the outrigger foot. The best sizing methods take into account the ground conditions as laid out above.
Factor in the outrigger load
Outrigger pads are intended to distribute the weight of the load over a wide enough area that the ground can safely support the equipment. Any outrigger crane pads used should be designed to meet or exceed the bearing required. The optimum crane pad is one which is sturdy enough to bear the outrigger weight but light enough to provide cushion and make transport easy.
There are a variety of different materials to choose from. For instance, made from an engineered thermoplastic material, Safety Tech outrigger crane pads are four times lighter than aluminum and seven times lighter than steel. Despite their light weight material, Safety Tech outrigger crane pads have a crush rating up to 750 psi. They can sustain a load rating up to 300,000 pounds.
Alternatively, FiberMax crane pads can provide support for cranes with a lifting capacity up to 600 tons. They offer the same level of strength as steel at only 70% of the weight. A FiberMax crane pad has a crush rating of 1,000 psi and 375,000 pound capacity.
Inspecting outrigger crane pads
Before setting an outrigger crane pad, ensure it’s free of debris and smooth. Each outrigger float must be smooth to obtain solid contact with the crane pad. Make sure there are no signs of warping, cracking or other possible hindrances to the float or pads integrity. If you notice any signs that a crane pad may be compromised, do not use it. Contact the manufacturer immediately to discuss the issue and possible replacement.
How to properly place the outrigger float
As with crane pads, outrigger floats must be free of debris and show no signs of impairment before use. Place the outrigger float in the center of the crane mat. Certain crane pads will provide targets to help determine proper float placement. if the outrigger float isn’t squarely placed, it may disrupt uniform ground pressures and the integrity of your operation.
Monitoring the outrigger crane pad during operation
Once you’ve selected and outfitted the appropriate crane pads for your crane, don’t set it and forget it. It’s important to monitor each crane pad for issues such as ground displacement. If you see excessive deflection during operation, the ground isn’t sturdy enough to bear your load capacity. Deflection can damage outrigger pads by hindering proper load distribution over time.
To reduce deflection, you can employ additional, more rigid supporting materials. Be sure to read the outrigger crane pad manufacturer’s instructions on proper stacking when using additional supporting materials.