Two-Leg Bridle at a Flattening Angle, With Damaged Gear
A crew is setting a 2,400 lb packaged rooftop unit. The lift plan calls for a two-leg bridle of synthetic web slings, each with a vertical working load limit of 2,000 lb, shackled to the unit's two lifting eyes. The rigger sets the legs so each makes about 45° with the horizontal. Rigging hardware adds 250 lb. The telehandler's load chart shows 3,000 lb capacity at a 12-foot radius in the planned boom configuration and 2,400 lb at 16 feet. The only setup spot puts the load center about 12 feet from the handler. During the pre-lift inspection the rigger finds a 1-inch cut through the jacket of one sling and a hook whose latch is bent and will not close.
1. Compute the tension in each sling leg at 45° and at 30° from horizontal, and decide what the rigger can and cannot do.
Read the worked answer
For a symmetric two-leg bridle, each leg carries half the load divided by the sine of the angle from horizontal:
Tension per leg = W ÷ (2 × sin θ)
At 45°:
- T = 2,400 ÷ (2 × 0.707) = 2,400 ÷ 1.414 = about 1,700 lb per leg
- Against a 2,000 lb vertical WLL, that is roughly 85% of capacity - acceptable, but with little margin.
At 30°:
- T = 2,400 ÷ (2 × 0.500) = 2,400 lb per leg
- That is above the 2,000 lb WLL. The lift is not permitted at that angle.
What this means:
- The 45° rigging shown is allowable on sling capacity only.
- If the load must be spread wider or the hook height forces the legs flatter, the rigger cannot simply "spread them a bit more." Options are a spreader bar (which removes the horizontal component from the slings entirely) or larger slings.
- The WLL of each leg is a vertical rating; the angle is what converts it, and the tension grows fast as the angle flattens - 30° costs about 40% more per leg than 45°.
Also note the sling angle is measured to the horizontal, and a leg angle quoted from vertical gives the same tension with cosine instead - mixing the two conventions is a common and expensive error.
2. The handler is set up at 12 feet. Is the lift within capacity, and what changes if the setup has to move back to 16 feet?
Read the worked answer
Compare total weight, not the unit's shipping weight.
- Unit: 2,400 lb
- Rigging hardware: 250 lb
- Total suspended load: 2,650 lb
At 12 feet: chart capacity is 3,000 lb. 2,650 lb is about 88% of capacity. It is within the chart, so the lift can proceed - but only if the radius, boom configuration, and outrigger setup are exactly what the chart was read for. Any change in boom angle, extension, or outrigger spread means re-reading the chart, because capacity falls steeply with radius.
At 16 feet: capacity drops to 2,400 lb, which is less than the 2,650 lb total load. The lift cannot be made from that position. The 2,400 lb figure equals the bare unit weight, which is exactly the arithmetic trap: forgetting the rigging makes an over-capacity lift look like a perfect match.
What to do if the setup must move:
- Do not creep the load in at a longer radius "just this once."
- Reposition the handler, reduce the radius, use a different machine, or have the lift re-planned by a qualified person.
- Confirm ground bearing at any new setup location - a handler on disturbed fill or over a septic tank has no chart at all.
3. What does the pre-lift inspection require for the cut sling and the bent hook latch, and what should happen to the lift today?
Read the worked answer
Both items are out of service. The lift does not proceed on those components.
Cut web sling:
- A 1-inch cut through the jacket is damage to the load-bearing fibers. Removal criteria for synthetic web slings include cuts, snags, tears, burns, ultraviolet degradation, and broken stitching - this meets the criteria.
- Remove it from service, tag it, and destroy it so it cannot return to the gang box. Do not "use it on the light lifts" and do not tape the jacket.
Bent hook latch:
- A latch that will not close means the hook can roll out of the eye or shackle under a slack condition or a shifting load. The latch must close and seat freely.
- Tag the hook out and replace it. Never lift on a hook with a missing or defeated latch, and never let the load bear on the tip or the latch itself.
For today's lift:
- Hold the lift and notify the supervisor and the lift director.
- Replace both items with inspected, rated components of adequate capacity for the computed leg tension.
- Verify shackles are rated, pins are fully engaged, and the shackle is loaded on the bow, not side-loaded.
- Re-inspect the entire sling assembly, re-verify the sling angle, and confirm the load's center of gravity is between the eyes so the unit does not tilt when it comes off the ground.
Inspecting rigging is not a formality before a lift; it is the part of the lift that decides whether there is one.