Calculating Sling Legs
At our organization, we offer in-depth rigging courses led by experienced instructors who guide participants through the essential rigging calculations for determining the minimum sling lengths necessary for safely handling various loads. This important process is streamlined by employing a specialized formula, conveniently located on our rated capacity card. By mastering these rigging calculations, participants not only enhance their load management capabilities but also significantly improve safety practices during rigging operations.
Scenario: In this case, we need to set up a pair of slings between the crane hook and a spreader bar, ensuring that the angle does not exceed 90 degrees.
Question #1: What size wire rope slings are necessary for this setup?
Facts: The spreader bar measures 8 feet in length, and the total weight of the load, bar, and rigging gear is 12,000 lbs.
Solution #1: To rig the load at a 90-degree angle or less, we can refer to the 90-degree column on our rated capacity card. Here, we find that for the sling weight capacity the sling legs must be made of at least ¾” wire rope to safely support the weight of 12,000 lbs.
Question #2: What is the minimum length required for these slings?
Facts: A practical calculating formula is included at the bottom of the rated capacity card.
SLING LENGTH represents the minimum distance from the crane hook to the sling’s connection point on the load.
LOAD WIDTH (or length) refers to the space between the load’s shackle connection points or edges.
MULTIPLIER is the value found at the bottom of each degree angle column, which is used in the formula based on the angle formed by the slings (60, 90, or 120 degrees).
Sling Length = Load Width x Multiplier
Solution #2: Given that the pad eyes are 8 feet apart, we can consider 8 as the LOAD WIDTH. The MULTIPLIER for a 90-degree angle is 0.75, as indicated in the 90-degree column.
SLING LENGTH CALCULATION = 8’ x 0.75
SLING LENGTH = 6’
Now, it's your turn to apply your sling length calculation skills.
What size and length of slings would you require between the hook and a 20-foot spreader bar? (Total weight of load and rigging = 25,000 lbs)
Angle Size Length
60 ______ x ______
90 ______ x ______
120 _____ x ______
(Solutions are provided below, so proceed with caution if you wish to avoid seeing the answers).
Solution: Angle Size Length
60 1” x 20’
90 1 1/8” x 15’
120 1 ¼” x 12’
Wishing you successful rigging projects, Mike Parnell.
For additional resources on rigging safety and techniques, consider ordering the Journeyman Rigger's Reference Card, an essential tool for professional riggers utilized in our training workshops.
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