When this situation occurs, the load distribution will change as the load tips up. In Figures 1 and 2, the lugs are at different heights and if we drew a line between the lug holes, the CG does not lie on that line. How much the distribution changes will depend on the geometry of the load. Once we begin tipping up the load, we may find that the load distribution between the cranes changes. Also, where the distance between the lugs gets smaller, the accuracy of our guess makes a lot more difference to our assumed load distribution. Obviously, the worse our guess, the more inaccurate our assumed load distribution. This is a difference of 8.3% which can be significant when working near the limits of the load chart. If the actual CG is 6” closer to the right side than is shown in figure 3, then load 2 will increase to 6,500 lbs from the 6,000 lbs we calculated based on our assumed CG. This might seem like a lot, but taking all measurements in feet for Figure 3, the discrepancy is only 6 inches.

Assume again that we miss our guess by 5% of the distance between the lugs. As mentioned above, we are left to guessing its location. Let’s assume for a moment that the CG is not given. In this case, the relative height of the lugs and CG is not a factor in the calculations.

These calculations assume that the crane’s load line is plumb with no side loading. Note that distances are measured to the lift lug holes from the CG. Once we have the necessary data, the load share for each crane can be determined. Remember, if we guess at the CG location, we are guessing at the load weight which can lead to accidents. However, the load distribution cannot be calculated accurately without it and this must be impressed upon the owner of the load if the lift is to be done safely. Of these three factors, the hardest to get is usually the CG. These are the load weight, the load center of gravity (CG), and in some cases, the load geometry.

To obtain this most basic piece of information for a multi-crane lift, three factors must be known first. This is generally due to the load interaction between the cranes.ĭespite the risks, it is not uncommon for multi-crane lifts to be conducted without the operator’s knowing the exact load that will be lifted by his/her crane. One source described two crane lifts as being more than twice as risky as single crane lifts with even more disproportionate increases in risk as more cranes are added. Multiple crane lifts can be tricky business. January 2005 Understanding Load Sharing In Multi-Crane Lifts Sudbury Non Destructive Testing Services.Lift Equipment Inspection & Engineering.

Crane lifting plan calculation