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FlounderUM
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I am lifting a rectangular structure, all lift points on the same elevation. However, the 4 lift points are not evenly distributed around the CoG AND we have an intended 10 degree tilt on the structure being lifted to facilitate installation. I have attached a spreadsheet/dwg in PDF
This leads to 4 different length slings to the single lift point. In order to determine the lengths of these slings we have drawn a line in the direction of gravity up to our intended hook height and connected the hook point to the 4 lifting points.
My question specifically is: How do I know the ratio of the load that each sling carries?
Please let me be clear that I understand how the angle of the sling to horizontal effects the tension in the sling. It does not, in my understanding, effect the percentage of the load of the structure being lifted that sling carries.
In order to calculate the amount of the structure weight each sling carries we find the distances between the lifting points and the CoG (L) along the plane of the structure being lifted. We take the inverse of those distances (1/L) and sum them (sum(L)). The load taken by each sling in our theory in terms of the weight (W) of the structure is:
load in individual sling (W*) = W x (1/L*)/sum(L)
In this case the load in the sling is an inverse function of its distance away from the CoG, that is, the closer the sling is to the CoG in plan, the higher percentage of the total weight of the structure being lifted it takes.
Does anyone know if this is an appropriate method?
After that is determined I am able to apply dynamics and other amplifications including angle of sling to horizontal to determine max tension in each sling.
This leads to 4 different length slings to the single lift point. In order to determine the lengths of these slings we have drawn a line in the direction of gravity up to our intended hook height and connected the hook point to the 4 lifting points.
My question specifically is: How do I know the ratio of the load that each sling carries?
Please let me be clear that I understand how the angle of the sling to horizontal effects the tension in the sling. It does not, in my understanding, effect the percentage of the load of the structure being lifted that sling carries.
In order to calculate the amount of the structure weight each sling carries we find the distances between the lifting points and the CoG (L) along the plane of the structure being lifted. We take the inverse of those distances (1/L) and sum them (sum(L)). The load taken by each sling in our theory in terms of the weight (W) of the structure is:
load in individual sling (W*) = W x (1/L*)/sum(L)
In this case the load in the sling is an inverse function of its distance away from the CoG, that is, the closer the sling is to the CoG in plan, the higher percentage of the total weight of the structure being lifted it takes.
Does anyone know if this is an appropriate method?
After that is determined I am able to apply dynamics and other amplifications including angle of sling to horizontal to determine max tension in each sling.