Tandem lifting calculations

Tandem lifting calculations – WikiLogistics

When you are considering to lift an special piece in tandem lift with 2 cranes, some quick calculations are needed to know in advance what will be the weight at each crane will be working.

Knowing the length, weight and position of the cog (center of gravity) we can easy calculate the weight soported by each crane at diferent positions where the slings are placed.

General example:

Tandem lifting calculations – WikiLogistics

P is the weight of the piece (Kgs)
F1 is the weight soported by crane number 1 (Kgs)
F2 is the weight soported by crane number 2 (Kgs)
l is the length of the piece (mm)
a is the distance between the leftmost to the position of the sling from crane number 1 (mm)
b is the distance between the rightmost to the position of the sling from crane number 2 (mm)
c is the distance between the leftmost to the position of the cog (center of gravity) (mm)

Equilibrium condition says that:
1.- The resultant force acting on the object is zero.
F1 + F2 = P so F2 = P – F1

2.- The sum of the moments acting on an object must be zero.
F1 x (c-a) = F2 x (l-b-c)
F1 x (c-a) = (P – F1) x (l-b-c)
F1 x (c-a) = (P x (l-b-c)) – (F1 x (l-b-c))
F1 x (c-a+l-b-c) = P x (l-b-c)
F1 = P x (l-b-c) / (-a+l-b)

Weblink if you want to calculate F1 and F2 automatically:
https://docs.google.com/spreadsheets/d/1pLk_5cSmGhnlEqXum9I9WvDfig2DnEngN3BNSCPhpHA/edit?usp=sharing

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