What each leg of a sling is really carrying SLING
A two-leg sling at sixty degrees from vertical puts the whole weight of the load into each leg. Not half of it. That is why sixty degrees is the limit.
The lift
What it comes to
The same lift at five angles
The working
EN 13414 and EN 1492 mode factors and the sixty degree limit. The sling, its condition, its certificate and the lift plan are a competent person’s.
How it works
Each leg never carries the load divided by the number of legs
Two things make it more than that, and both are routinely ignored at the hook.
The angle. A leg at an angle carries the load divided by the cosine of that angle. At 30° from vertical a two-leg sling puts about 58% of the load into each leg; at 45°, 71%; at 60°, a full 100%: each leg is carrying the entire weight of the load, not half of it. Sixty degrees is the limit in the standard, and that is exactly why: at that point a two-leg sling has stopped sharing anything at all.
The count. A four-leg sling is rated as though three legs are working. On a rigid load with fixed-length legs, three of them find the load first and the fourth is along for the ride, which three depends on how the load sits and can change during the lift. The mode factors in EN 13414 and EN 1492 build that in, which is why a four-leg sling is not rated at twice a two-leg one.
The squeeze nobody calculates
The same angle that increases the tension also pulls the top of the load inwards, and that horizontal component is often what actually breaks something. At 60° the inward force is about 1.7 times the load, applied to the lifting points and to whatever is between them.
On a crate, a frame, a cabinet or anything with a hollow section, that is frequently the failure: the load is not overloaded vertically, it is crushed sideways. A spreader beam removes it entirely by taking the horizontal force into the beam instead of into the load, which is what a spreader is for, not to make the sling reach.
Working within it
Measure the angle rather than estimating it. People consistently underestimate angles at the hook, in the direction that matters, and the error is largest exactly where the cosine is changing fastest.
Shorter legs mean bigger angles. The instinct to shorten a sling so it is tidier is the instinct that pushes the angle past the limit, and the honest answer to a sling that is too long is a longer hook height or a spreader, not a tighter angle.
Check the lifting points as well as the sling. The rating you looked up is for the sling; the eyebolt, the shackle and the point it is welded to have ratings of their own, and an eyebolt loaded at an angle is derated sharply, often to a quarter of its straight pull.
And treat this as the arithmetic, not the plan. The lift plan, the condition of the gear, the examination record, and whether the weight you were given is the real weight are all outside anything a calculator can see. The weight in particular: a figure from a drawing is a figure for the thing as drawn, without the contents, the water in it, or the frame it is bolted to.
Nothing is uploaded. Nearby: TORQUE on what a bolt is really being tightened to, AXLE and BALANCE for the vehicle it goes on, and PALLET for how it is stacked.
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