Sling Types and Load Distribution Flashcards

A two-leg bridle sling with equal-length legs is used to lift a 14,000 lb load. Each sling leg forms a 30° angle with the horizontal. Approximately how much tension is carried by each sling leg?

Answer: 14,000 lb

Tension per leg = (Total load ÷ 2) ÷ sin(30°) = 7,000 ÷ 0.5 = 14,000 lb per leg. At only 30° from horizontal, the mechanical disadvantage is severe enough that each sling leg must carry a tension equal to the entire load weight. This is why ASME B30.9 and rigging practice treat horizontal angles below 45° as high-hazard configurations requiring special review.

Per ASME B30.9, when a wire rope sling is used in a choker hitch and the measured angle of choke falls between 90° and 119°, the sling's rated choker capacity must be reduced to what percentage of its catalog choker rating?

Answer: 87%

ASME B30.9 specifies the following angle-of-choke reductions: 120° or greater = 100% (no reduction), 90°–119° = 87%, 60°–89° = 74%, 45°–59° = 62%, 30°–44° = 49%. The 90°–119° band is a common trap — many riggers assume any angle above 90° is penalty-free, but only 120° and above avoids a derating requirement.

A 1/2-inch diameter wire rope sling is used in a basket hitch around a lifting lug with a 1-inch pin diameter. What is the D/d ratio, and what does ASME B30.9 require regarding sling capacity in this situation?

Answer: D/d = 2; a bend efficiency reduction factor must be applied, significantly lowering the effective capacity

D (pin diameter) = 1 in, d (sling wire rope diameter) = 0.5 in, giving D/d = 2. ASME B30.9 recommends a D/d ratio of 25 or greater for full efficiency; at D/d = 2, a substantial bend reduction factor applies per the manufacturer's data or the standard's tables. Critically, the basket hitch configuration does not eliminate this penalty — both the hitch-type multiplier and the D/d reduction factor compound together, and ignoring the bend factor can result in a grossly overloaded sling.

A rigger rigs a four-leg wire rope sling to lift a structural beam whose center of gravity is significantly offset toward one end. Two legs attach near the heavy end; two attach near the light end. What is the most critical safety concern with this configuration?

Answer: A four-leg sling is statically indeterminate, so load distribution cannot be precisely calculated; legs on the heavy end may be overloaded beyond their individual rated capacity

A four-leg sling is a statically indeterminate system — there are more unknowns (four leg tensions) than independent equilibrium equations, so the exact load in each leg cannot be determined by statics alone. With an off-center center of gravity, the heavy-end legs experience disproportionately high tension that may exceed their rated capacity. ASME B30.9 addresses this by requiring each leg to be rated for the full load unless a certified equalizing device is used. Elastic stretch does not reliably equalize loads under real-world conditions; assuming equal distribution in a four-leg asymmetric lift is a recognized cause of sling failures.

A critical precision lift specification requires the wire rope sling end termination to have zero efficiency loss — that is, 100% mechanical efficiency. Which termination type meets this requirement per ASME B30.9?

Answer: Poured socket (spelter socket or resin-filled socket)

A poured socket — where molten zinc (spelter) or epoxy resin is poured into the conical socket around the broomed-out wire rope — is the only end termination recognized at 100% mechanical efficiency by ASME B30.9. The method anchors every individual wire in the rope, eliminating bending stress at the termination. By comparison, hand-tucked splices rate at approximately 90%, Flemish eyes with mechanical sleeves at roughly 90–95%, and U-bolt clips (acceptable only as field terminations) rate well below catalog efficiency. For certified critical lifts, poured sockets are the industry standard when maximum termination efficiency is mandatory.

A single wire rope sling rated at 6,000 lbs in a vertical hitch is rigged in a basket hitch. The two legs of the basket form an included angle of 120° between them. What is the maximum load this rigging arrangement can safely lift?

Answer: 6,000 lbs

With an included angle of 120° between the two legs, each leg is 60° from the vertical centerline, which means each leg makes only a 30° angle with the horizontal. Applying the sling tension formula: Maximum load = Vertical Rating × 2 × sin(horizontal angle) = 6,000 × 2 × sin(30°) = 6,000 × 2 × 0.5 = 6,000 lbs. The basket hitch advantage (factor of 2) is exactly cancelled by the severe sling angle penalty (factor of 0.5), leaving the effective capacity identical to a single vertical hitch. This is a common field error — riggers assume the basket always doubles capacity without accounting for the sling angle.