TIGHT HEADROOM, HEAVY WEIGHT AND UNCERTAIN CENTER OF GRAVITY
DRIVE THE DESIGN OF AN UNUSUAL PIECE OF RIGGING HARDWARE
Our customer needed to dismantle and remove an old rolling mill from a defunct steel mill in the eastern US. The mill components each weighed approximately 200 tons and were housed within a mill building that had a fairly low clearance below the roof trusses. The customer needed a crane-based solution and had ruled out the use of alternative lift methods such as hydraulic gantries or strand jacks. Based on the weight and radius requirements, W. O. Grubb Crane Rental determined that the best solution would be to use a pair of 550-ton class all-terrain hydraulic cranes. Because of the number of voids in the floor under one of the cranes, we elected to place steel barge ramps on the floor under the crane’s outriggers to safely span the floor openings.
The first piece to be lifted, called an edger, presented the greatest challenge of all of the pieces that needed to be lifted. In addition to weighing 200 tons, it was the top piece and had the tightest vertical clearance. One crane was able to swing with the load and keep its boom tip between two roof trusses and was outfitted with a slings in a bridle configuration. However, the other crane had to swing under one of the roof trusses and needed to maintain a much tighter headroom. Traditional rigging methods were no longer feasible - a specialized fabrication was required.
A lift beam was designed to pin directly to the hook of the crane and to grip the top flange of the edger. Another feature of the lift beam was that it had to be adjustable to accommodate some uncertainty with respect to the center of gravity of the edger. To address this need, the crane hook was attached to a sliding bearing that was integral with the lift beam. The sliding mechanism was actuated by means of hydraulic cylinders that were mounted to the lift beam.
During the lifting sequence, the adjustibility in the lift beam proved important. After several adjustments, the edger lifted off the supports in a level orientation and was swung over the drive aisle and lowered on to the heavy haul trailer. The combination of a solid team effort and the use of the right rigging hardware set the stage for the successful removal of the remaining components.