KEVOS® MAKEOS · Mechanics
Shear Legs (A-Frame) Check (Geometry, Leg Force, Foot Thrust, Buckling)
For a pair of shear legs (an A-frame) lifting this load, what is the head height and leg angle, what force does each leg carry, how hard do the feet push apart, and will the tube legs buckle?
Check of shear legs or an A-frame of two equal legs with the load hung from the apex: the triangle of legs and foot spread, apex angle and head height (as the triangle solver tool), the compression in each leg and the outward thrust at each foot, and Euler or Johnson buckling of each round-tube leg (as the column buckling tool), checked against your factor of safety and the foot tie or anchor capacity.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Leg length (foot to head) | mm | Length of each leg from foot to the head pin. |
| Spread between the feet | mm | Distance between the two feet. |
| Load at the head (with hook block) | kN | Load hung from the head, including the hook block and slings. |
| Leg tube | ||
| Tube outside diameter | mm | Outside diameter of the tube legs. |
| Wall thickness | mm | Wall thickness of the legs. |
| Elastic modulus | GPa | Elastic modulus. |
| Yield strength | MPa | Yield strength of the tube. |
| Effective length factor | Effective length factor for the leg ends (1 for pinned). | |
| Required safety factor on buckling | Factor against buckling you need. | |
| Foot tie or anchor capacity | kN | Capacity of the tie between the feet, or of each foot anchor against sliding outwards. |
Method and formulas
- Triangle with sides L, L and s: apex angle and base angles by the law of cosines (as the triangle solver tool); head height = √(L² − (s ÷ 2)²).
- Each leg carries W ÷ (2 cos θ) with θ the half apex angle; thrust at each foot = W tan θ ÷ 2.
- Leg buckling by Euler or Johnson for the tube section (as the column buckling tool).
- Example: the head stands 3,815.8 mm high; each leg carries 5.2414 kN and the feet push out with 1.5724 kN; buckling factor 13.9.
Limitations
- Load hung centrally at the apex in the plane of the legs; shear legs also need back guys against falling over.
- Pinned leg ends; foot slipping and ground bearing are checked separately.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check improvised lifting shear legs
- Size the tube for an A-frame hoist
- Find the foot tie force
Who it is for
- Riggers
- Maintenance engineers
- Lifting supervisors
What you get
- Apex angle, leg angle and head height
- Leg force and foot thrust
- Leg buckling factor
Interpreting the result
- Spreading the feet wider lowers the head and raises both the leg force and the foot thrust.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 95–102, 281–287. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Shear Legs (A-Frame) Check (Geometry, Leg Force, Foot Thrust, Buckling) calculator
