BIZOMAT MAKEOS · Strength
Lifting Lug Design (Plate, Pin and Bearing Checks)
Is this pinned lifting lug strong enough for the sling load: net tension, tear-out, bearing and pin shear?
Check of a plate lifting lug with a pin or shackle: the load per sling leg from the total load, number of legs, sling angle and a dynamic factor, net-section tension across the hole, shear tear-out beyond the hole, bearing of the pin on the plate, double-shear stress in the pin (as the bolt and pin shear tool), utilisation of each against your allowables and the hole clearance.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Total load lifted | kN | Total weight of the load (as force). |
| Sling legs sharing the load | Number of sling legs that share the load (use fewer if the slings may not share evenly). | |
| Sling angle from vertical | ° | Angle of each sling leg from vertical. |
| Dynamic factor | Factor for snatch and acceleration during the lift (your value from the lifting code). | |
| Lug plate thickness | mm | Thickness of the lug plate at the hole. |
| Distance from hole centre to the plate edge (in the load direction) | mm | Distance from the hole centre to the plate edge in the direction of the pull (the edge radius for a round-ended lug). |
| Hole diameter | mm | Diameter of the pin hole. |
| Pin diameter | mm | Diameter of the pin or shackle pin. |
| Allowable tensile stress | MPa | Allowable tensile stress of the plate (your design value). |
| Allowable shear stress (plate) | MPa | Allowable shear stress of the plate. |
| Allowable bearing stress | MPa | Allowable bearing stress between pin and plate. |
| Allowable shear stress (pin) | MPa | Allowable shear stress of the pin. |
| Largest hole clearance | mm | Largest clearance you accept between hole and pin (larger clearance concentrates bearing stress). |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Total load lifted
- What it is
- The total weight of the load being lifted, expressed as a force, shared between the sling legs.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0.000001 kN to 1000000 kN. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The load per lug and every stress rise in direct proportion.
- Get it right
- Enter kN: a mass in tonnes times 9.81 gives kN. Include rigging and attachments.
What this means: Sling legs sharing the load
- What it is
- How many sling legs, each attached to its own lug, share the load.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 8. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The load per lug is inversely proportional to the number of legs.
- Get it right
- With four legs, slings rarely share evenly; count fewer if your lifting code says so.
What this means: Sling angle from vertical
- What it is
- The angle of each sling leg measured from the vertical. Wider angles raise the force in each leg for the same load.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0° to 60°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The load per lug rises as 1 ÷ cos of the angle.
- Get it right
- Measure from vertical, not from horizontal; mixing them up badly underestimates the leg force.
What this means: Dynamic factor
- What it is
- A multiplier for snatch, acceleration and uneven lifting on top of the static weight.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 3. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.25 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The load per lug and every stress rise in direct proportion.
- Get it right
- Take it from the lifting code that applies to your lift.
What this means: Lug plate thickness
- What it is
- The thickness of the lug plate at the pin hole, excluding any cheek plates.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 300 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- All three plate stresses are inversely proportional to thickness.
- Get it right
- If cheek plates are welded on, this simple check does not include them; use the main plate only.
What this means: Distance from hole centre to the plate edge (in…
- What it is
- The distance from the hole centre to the plate edge in the direction of pull, the edge radius on a round-ended lug.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 55 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More edge distance lowers both net tension and tear-out stress.
- Get it right
- The tool also takes the plate width across the hole as twice this distance, as for a round-ended lug.
What this means: Hole diameter
- What it is
- The diameter of the hole in the lug plate that the pin or shackle passes through.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 34 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger hole raises net tension and tear-out stresses.
- Get it right
- It must not be smaller than the pin. Use the finished hole size, not the drill size before reaming.
What this means: Pin diameter
- What it is
- The diameter of the pin or shackle pin that bears on the lug plate.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 32 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger pin lowers bearing stress and pin shear stress.
- Get it right
- Use the pin body diameter where it bears, not the shackle’s nominal size code.
What this means: Allowable tensile stress
- What it is
- The tensile stress you allow across the net section of plate either side of the hole, from your design code.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 2000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 150 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- It does not change the stress, only the net tension utilisation.
- Get it right
- Use the allowable working stress, not the yield or tensile strength.
What this means: Allowable shear stress (plate)
- What it is
- The shear stress you allow in the plate for tear-out beyond the hole, from your design code.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 2000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- It does not change the stress, only the tear-out utilisation.
- Get it right
- Use the allowable for the plate material, not the pin material.
What this means: Allowable bearing stress
- What it is
- The bearing stress you allow where the pin presses on the inside of the hole, from your design code.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 3000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 225 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- It does not change the stress, only the bearing utilisation.
- Get it right
- Bearing acts on pin diameter times plate thickness, not on the hole area.
What this means: Allowable shear stress (pin)
- What it is
- The shear stress you allow in the pin material. The tool treats the pin as in double shear, as in a shackle or clevis.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 2000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 120 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- It does not change the stress, only the pin shear utilisation.
- Get it right
- Use the pin’s own material allowable; a shackle maker’s working load limit is a separate check.
What this means: Largest hole clearance
- What it is
- The largest difference between hole and pin diameter you accept, since more clearance concentrates the bearing stress.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 50 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- It does not change the stresses, only the hole clearance check.
- Get it right
- This is the diametral clearance, hole minus pin, not the gap on one side.
Method and formulas
- Load per lug F = W × dynamic factor ÷ (legs × cos θ).
- Net tension σ = F ÷ [(2R − d_h) t]; tear-out τ = F ÷ [2 t (R − d_h ÷ 2)].
- Bearing σ_b = F ÷ (d_p t); pin in double shear τ_p = F ÷ (2 × π d_p² ÷ 4).
- Example: 200 kN on 2 legs at 30° puts 144.34 kN on each lug; the highest utilisation is 80.188%.
Limitations
- Simplified lug checks; lifting codes add out-of-plane loads, cheek plates and weld checks.
- The lug weld to the structure needs its own check.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a lifting lug on a fabricated frame
- Size a padeye for a new lift
- Review a lug when sling angles change
Who it is for
- Structural engineers
- Rigging supervisors
- Fabrication supervisors
What you get
- Design load per lug
- Net tension, tear-out and bearing stresses
- Pin shear and utilisations
Interpreting the result
- Tear-out usually governs short lugs: increase the edge distance before the plate thickness.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1535, 1720–1735. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
The plate list, mass and lifting
What it covers: Bring the bin together on one plate list: net and gross mass, plate cost with GST, centre of gravity from its parts, sling loads for planning, and a lift plan that assumed the load was shared evenly.
BIZOMAT 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 Lifting Lug Design (Plate, Pin and Bearing Checks) calculator