Determining Lifting Load Capacity of a Sling
As the horizontal angle of a sling decreases, the load on each leg increases. The effect is the same whether a single sling is used as a basket, or two slings are used with each in a straight pull, as with a 2-legged bridle.
Anytime pull is exerted at an angle on a leg - or legs - of a sling, the load per leg can be determined by using the data in the table at right. Proceed as follows to calculate this load - and determine the rated capacity required of the sling, or slings, needed for a lift.
- Divide the total load to be lifted by the number of legs to be used. This provides the load per leg if the lift were being made with all legs lifting vertically.
- Determine the angle between the legs of the sling and the horizontal.
- MULTIPLY the load per leg (as computed in No. 1) by the Load Factor for the leg angle being used (from the table at right) - to compute the actual load on each leg for this lift and angle. The angle load must NOT exceed the rated sling capacity.
Thus in drawing #3, (sling angle at 30 degrees): 1000 / 2 = 500 (Load Per Leg is a vertical lift)
500 x 1.154 = 577 lbs. = ACTUAL LOAD on each leg at the 60 degree included angle being used.
In drawing #4 (sling angle at 45 degrees): 1000 / 2 =500 (Load Per Leg if a vertical lift)
500 x 1.414 = 707 lbs. = ACTUAL LOAD on each leg at the 45 degree horizontal angle being used.
Angle of Bridles
The horizontal angle of bridles with 3 or more legs is measured the same as the horiztontal slign angle of 2-legged hitches. In this case where a bridle designed with tdifferent leg lengths results in horizontal angles, the leg with the smallest horizontal angle will carry the greatest load. Therefore, the smallest horizontal angle is used in calculating actual leg load and evaluating the rated capacity of the sling proposed.