NCCCO Sling Types and Load Distribution 2

Question 1

What is the D/d ratio for a wire rope sling and why is it important?

Accepted Answer

It is the ratio of the bend radius (D) around a hook, shackle, or fitting to the rope diameter (d), which determines the efficiency loss — smaller D/d ratios cause greater bending stress and capacity reduction

Answer

The D/d ratio is the diameter of the bend (fitting or object the sling wraps around) divided by the rope diameter. Small D/d ratios create sharp bends that reduce wire rope sling capacity by a rated derating factor.

Question 2

A rigging crew is using a two-leg bridle sling to lift a horizontal beam. The horizontal angle of each sling leg from vertical is 30 degrees. What effect does this angle have on the tension in each sling leg?

Accepted Answer

The tension in each sling leg is greater than half the load weight — the more horizontal the angle, the greater the tension in each leg

Answer

In a bridle sling, as the sling legs angle out from vertical, the tension in each leg increases. At 30 degrees from vertical (60 degrees from horizontal), each leg carries approximately 57.7% of the total load weight.

Question 3

Under ASME B30.9, what is the minimum allowable horizontal sling angle for a wire rope sling in a two-leg bridle configuration?

Accepted Answer

30 degrees from horizontal

Answer

ASME B30.9 establishes 30 degrees from horizontal as the minimum sling angle for wire rope slings in bridle configurations. Below this angle, the increased tension in the slings creates a risk of overload.

Question 4

What is the difference between a vertical hitch, a choker hitch, and a basket hitch for a single sling?

Accepted Answer

Vertical hitch suspends the load from the end of the sling; choker hitch wraps around the load and passes through itself, reducing capacity; basket hitch wraps under the load with both ends attached to the hook, increasing capacity

Answer

These three hitches have different geometries and capacity ratings: Vertical hitch equals 100% capacity; Choker hitch equals approximately 75-80% (due to the bend at the choke point); Basket hitch equals approximately 200% (load shared across two legs).

Question 5

A synthetic web sling has a working load limit (WLL) of 10,000 lbs in a vertical hitch. What is the approximate WLL in a basket hitch with a 45-degree horizontal sling angle?

Accepted Answer

14,140 lbs

Answer

Basket hitch WLL = 2 x Vertical WLL x sin(horizontal angle). At 45 degrees: WLL = 2 x 10,000 x sin(45) = 2 x 10,000 x 0.707 = 14,140 lbs.

NCCCO (National Commission for the Certification of Crane Operators) Practice Test

NCCCO (National Commission for the Certification of Crane Operators) Practice Test

NCCCO Sling Types and Load Distribution 2