For a centered static load carried by two identical, symmetrically arranged tension-only legs, equilibrium resolves the load into equal vertical components. The required leg tension rises as the included angle between the legs approaches 180 degrees.
Resolution of Suspension Interactive Calculator
Enter a static load and the included angle between two identical symmetric legs. The calculator resolves the ideal equilibrium forces only; it is not a sling-rating, hardware-selection or lift-planning tool.
Equation Used
- The entered angle is the full included angle between two identical legs.
- Both anchors are level, the load acts through the symmetry line and each leg remains in tension.
- Leg and attachment weight, stretch, friction, dynamics, shock, wind, out-of-plane forces, unequal lengths, tolerances and hardware ratings are omitted.
Symmetric Two-Leg Equilibrium
A centered load W acts downward at the common point. Each identical leg carries tension T along its own axis. Symmetry cancels the two horizontal components, while the two vertical components add to W.
This page defines theta as the full included angle between the legs. Each leg is therefore theta/2 from vertical. Keeping that definition explicit avoids confusing included angle with the angle measured from the horizontal.
What the Idealization Can Show
OSHA sling tables and official rigging training material show the same geometric trend: shallower sling angles increase leg loading. The calculator makes that trend visible for an ideal two-leg symmetric case.
It does not determine a safe working load, select a sling, establish a design factor or approve a lift. Actual work must follow the applicable regulation, manufacturer tables and qualified-person planning.
Force Resolution with Included Angle
Veach = T cos(theta/2) = W/2
Heach = T sin(theta/2)
The two vertical components sum to the entered load. The horizontal components are equal and opposite only under the stated symmetric geometry.
Worked Ideal Example
For W = 1000 N and an included angle of 120 degrees, each leg is 60 degrees from vertical. The ideal result is T = 1000 N per leg, Veach = 500 N and Heach ≈ 866 N.
This verifies the equilibrium arithmetic; it is not a rigging recommendation or a rated-capacity check.
Model Boundary
- Calculated: ideal equal leg tension plus per-leg vertical and horizontal components.
- Required conditions: centered static load, two identical legs, equal anchor height, planar symmetry and tension-only members.
- Not calculated: center-of-gravity offset, unequal leg lengths or angles, three- or four-leg load sharing, acceleration, shock, wind, friction, stretch, bending, fatigue, connector geometry, sling rating, design factor, inspection status or lift safety.
Frequently Asked Questions
What angle does this calculator use?
The full included angle between the two legs.
Why is each vertical component always half the load?
In this ideal symmetric case the equal vertical components must sum to W.
Why does tension rise near 180 degrees?
The vertical component of each nearly horizontal leg becomes a small fraction of its tension.
Does the horizontal component act on the anchors?
Each tensioned leg pulls its upper support toward the suspended load, giving an inward horizontal component in this geometry. The support supplies the opposing reaction; real connection loads require the actual geometry.
Can I use the result to choose slings or anchors?
No. Use applicable standards, manufacturer ratings and a qualified lift plan.
Does the formula cover an off-center load?
No. An asymmetric system needs separate equilibrium equations and may have unequal leg tensions.
References
- U.S. Occupational Safety and Health Administration, Guidance on Safe Sling Use: angle-dependent multi-leg sling tables and figures.
- Los Alamos National Laboratory, Crane: Qualified Classroom Instruction: load share, load-angle factor and sling-leg tension.
- Naval Facilities Engineering Systems Command, Rigging Practices Student Guide: sling geometry and angle-factor method.
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