When an offset CoG is coupled with multiple lift points, skill and experience are key.
The Challenge
Safely lift a load with offset centre of gravity and multiple lift points.
The Solution
Loads with an offset centre of gravity (CoG) can prove challenging for any lifting contractor, but when an offset CoG is coupled with multiple lift points, skill and experience are key.
Metcalf Crane Services was engaged to install multiple precast units. Not only did each of the units vary in weight (ranging from 55t-80t), but all units had varying CoG’s and lift points.
In the images below, the load came in at just under 60t with only six lift points. The industry preference is to cast either four or eight lifters into precast, as six lift points are extremely challenging to equalise. In this situation, the unit was already cast and developing a viable rigging solution was the only option.
To design the rigging for this lift, our in-house engineering team began by first calculating the load through each of the six lifters. The next step for the team was to calculate the tension through each individual rigging element. Once this was checked against the capacity of each rigging element, the calculations were overlaid onto our rigging diagram for full transparency. Having a vast array of in-house rigging equipment was crucial for this lift; each of the slings and chains had to be of varying lengths and capacities due to the CoG.
With the aid of our skilled crew, the plan was implemented, and the load was lifted safely and successfully.
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