"Sling Angles and the Multiple-Lift Rules" is lesson 4 of 6 in the Structural Steel (C-51) Learning Hub. It opens with "Sling Tension Depends on the Angle" and works through 5 short steps, then a worked example you can check yourself against.
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Steps in this lesson
Sling Tension Depends on the Angle
Find the Angle, Then Check the Marking
The Multiple-Lift Rules in California
Capacity Limits: 5-to-1 and 75 Percent
Rigging Order, Spacing, and Who Stands Under the Load
The worked example in the course applies this lesson to a realistic job in 6 steps, from "Weight of the beams" through "Crane limit".
What you'll be able to do
Explain the main idea of "Sling Angles and the Multiple-Lift Rules" in plain language you can use on the exam.
Apply this step with confidence: "The Multiple-Lift Rules in California".
Apply this step with confidence: "Capacity Limits: 5-to-1 and 75 Percent".
Apply this step with confidence: "Rigging Order, Spacing, and Who Stands Under the Load".
Test yourself on the worked example and the quick-check quiz inside the classroom.
The diagram for this lesson, exactly as it appears in the Learning Hub.
The first steps of this lesson
Step 1: Sling Tension Depends on the Angle
When a load hangs from a two-leg sling, each leg carries more than half the load unless the legs are vertical. Measured from horizontal, tension per leg is T = W / (n x sin θ), with n legs. At 90° each leg of a two-leg bridle carries 0.50 W; at 60° it is 0.577 W; at 45° it is 0.707 W; at 30° each leg carries 1.00 W, the whole load. That relationship is geometry (statics), not a number printed in a California code. What the code does print is the definition of the angle: the inclination of a sling leg may be measured from the horizontal or vertical plane, and when the angle of loading is less than 5 degrees from the vertical the load may be considered a vertical load. Source: statics; 8 CCR §5041 (Angle of Loading).
Step 2: Find the Angle, Then Check the Marking
You rarely measure the angle with a protractor. Measure the vertical height from the load attachment points up to the hook (H) and the sling leg length (L): sin θ = H / L. A 10 ft leg hanging 8.66 ft below the hook gives sin θ = 0.866, which is 60°. California then controls the rating: alloy steel chain slings and wire rope slings must carry permanent legible markings that give the safe working load for the type of hitch used, the angle that load is based on, and the number of legs if more than one. A sling may not be loaded beyond the rated capacity on its markings, may not be used without legible markings, and must be inspected each day before use by a qualified person. Source: 8 CCR §5044(a), §5045(g), §5042(a)(4) and (a)(15), and §5043.
The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.
Independent exam preparation. Contractors Classroom is not affiliated with the Contractors State License Board, and no course can guarantee a passing result.
