Safety is the number one concern for crane operators. While hand signals have been established as a reliable, low-tech and universal way to improve safety during operation, it is also critical to understand the ground conditions and provide the necessary foundation support prior to the lift for maximum crane safety. Sophie Barnes reports in Grounds to Proceed for Heavy Lift and Project Forwarding International.
DICA, a USA-based leading provider of outrigger pads, crane pads, and cribbing products, has developed 10 Tips for a Successful Crane Setup. In recent years, U.S. regulatory bodies have begun placing greater emphasis on understanding ground conditions and the use of foundational support such as crane pads and outrigger pads.
To that end, DICA’s first recommended step is for mobile crane operators to know their responsibilities to prepare for a successful crane set up. “In the U.S., the Occupational Safety and Health Administration (OSHA) states that cranes must be assembledon ground that is firm, drained and graded sufficiently, and that supporting materials, such as blocking, cribbing, pads or mats be used to provide adequate support and levelness,” says Kris Koberg, CEO of DICA. The American Society of Mechanical Engineers (ASME) also states that outrigger blocking or cribbing must have sufficient strength to prevent crushing, bending or shear failure. “And it needs to be of such thickness, width and length as to completely support the float, transmit the load to the supporting surface, and prevent shifting, toppling or excessive settlement under the load,” says Koberg.
“When selecting crane pads for specific jobs, lift planners and operators should know the maximum outrigger reaction force that could be generated while on-site. This information can be obtainedfrom the crane manufacturer’s software, or by using lift planning software such as 3D Lift Plan,” says Koberg. The outrigger load is not the load being picked, or the crane capacity. The outrigger load is specific to the amount of force applied to any one of the outriggers during set-up, operations and tear down of the equipment. To ensure safety, DICA believes the rated capacity of the pads should always exceed the maximum outrigger reaction force of the equipment.
According to Koberg, the next step in a successful crane set up is knowing the Allowable Ground Bearing Pressure (AGBP). The controlling entity is responsible for providing the ground conditions as noted by OSHA in the above paragraph and establishing the allowable bearing pressure criteria. The allowable pressure is a critical data point in determining the size of the pad you will need.
Once the allowable ground bearing pressure and maximum outrigger reaction force is known, you’re in the best position to select the right size outrigger pad or crane pads. Simply divide the maximum outrigger load by the allowable ground bearing pressure to determine the pad area you need. Example: Maximum outrigger load = 100,000 lbs. Allowable ground bearing pressure = 3,500 psf. (100,000 lbs / 3,500 psf = 29 ft2 of area).
Once you know the minimum area needed, you will want to confirm your pads can support the load and effectively distribute it based on your ground conditions. A qualified engineer or outrigger pad manufacturercan generate or provide this information. “Undersized pads can put you in an unstable condition, and oversized pads are inefficient in terms of purchase, labor, and transportation costs. Pads that are not able to appropriately support or distribute the load can be dangerous,” says Koberg.
Lastly, Koberg advises: “Use common sense and monitor every lift. If something doesn’t look right it’s probably not right, stop the lift and set the load down. Excessive pad deflection, or pads being driven into the ground may indicate outrigger forces are greater than what the pad and ground can support.”