BIZOMAT MAKEOS · Mechanics
Lifting Beam and Spreader Beam Check
Is this lifting beam or spreader bar strong and stiff enough for the load, and what are the sling tensions?
Check of a below-the-hook beam: a lifting beam (one top lug, load hung from two points, beam in bending) for bending stress and deflection, or a spreader beam (top slings to the ends, beam in compression) for the compression from the sling angle and Euler buckling, with the sling leg tensions, using a dynamic factor on the load.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Beam type | choice | A lifting beam carries the load in bending from one central lug; a spreader beam keeps slings apart and is in compression. |
| Load mass | kg | Mass of the load (plus rigging below the beam). |
| Dynamic factor | Factor for lifting dynamics (from the lifting standard; about 1.1–1.3). | |
| Spacing of the load lift points | mm | Distance between the two load lift points. |
| Top sling angle from vertical (spreader) | ° | Angle of each top sling leg from vertical (spreader beams). |
| Section | ||
| Elastic section modulus | mm³ | Section modulus of the beam about the bending axis. |
| Second moment of area (least, for buckling) | mm⁴ | Second moment of area (the least one for spreader buckling). |
| Elastic modulus | GPa | Elastic modulus of the beam. |
| Allowable bending or compressive stress | MPa | Allowable stress from the lifting equipment standard. |
| Section area (spreader) | mm² | Cross-section area of a spreader. |
| Required buckling factor (spreader) | Factor required against Euler buckling. | |
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: Beam type
- What it is
- Whether the beam is a lifting beam hung from one central lug that carries the load in bending, or a spreader beam that holds two slings apart and is in compression.
- Units and format
- Choose one of 2 options from the list: Lifting beam (bending); Spreader beam (compression).
- Example
- The form opens with “Lifting beam (bending)” selected as a worked example. Choose the option that matches your case.
- Get it right
- The sling angle, section area and buckling factor apply only to spreaders; the section modulus only to lifting beams.
What this means: Load mass
- What it is
- Mass of the load being lifted, plus any rigging hanging below the beam.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0.000001 kg to 10000000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5000 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Design load, stress and compression rise in proportion.
- Get it right
- Use the verified mass of the load, including slings and shackles below the beam.
What this means: Dynamic factor
- What it is
- Multiplier on the static weight to allow for the dynamic effects of hoisting, such as starting, stopping and swinging.
- 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
- Design load rises in proportion.
- Get it right
- Take it from the applicable lifting equipment standard for your crane and duty.
What this means: Spacing of the load lift points
- What it is
- Distance between the two points where the load is attached to the beam.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3000 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- For a lifting beam moment rises with spacing and deflection with its cube; for a spreader buckling load falls with its square.
- Get it right
- Measure between the centres of the load lugs or shackle holes.
What this means: Top sling angle from vertical (spreader)
- What it is
- Angle of each top sling leg measured from vertical, for a spreader beam hung from two slings.
- 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
- A larger angle raises sling tension and spreader compression.
- Get it right
- Measure from vertical, not from horizontal; used only for spreader beams.
Section
What this means: Elastic section modulus
- What it is
- Elastic section modulus of the beam about its bending axis, used to turn the bending moment into stress for a lifting beam.
- Units and format
- Enter a number in mm³: mm³. The form accepts 0.000001 mm³ or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 300000 mm³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Bending stress falls in proportion as section modulus rises.
- Get it right
- Use the value about the axis that bends under load, from the section table.
What this means: Second moment of area (least, for buckling)
- What it is
- Second moment of area of the beam section. For a lifting beam it sets deflection; for a spreader the smallest value sets buckling.
- Units and format
- Enter a number in mm⁴: millimetres to the fourth power (second moment of area). The form accepts 0.000001 mm⁴ or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20000000 mm⁴ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Deflection falls and buckling load rises in proportion.
- Get it right
- For spreaders use the least second moment of area (weak axis), as buckling happens about that axis.
What this means: Elastic modulus
- What it is
- Elastic (Young’s) modulus of the beam material, used for deflection and buckling.
- Units and format
- Enter a number in GPa: gigapascals (1 GPa = 1000 MPa). The form accepts 0.000001 GPa to 500 GPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 206 GPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Deflection falls and buckling load rises in proportion.
- Get it right
- Enter gigapascals; 1 GPa = 1,000 MPa.
What this means: Allowable bending or compressive stress
- What it is
- Allowable bending stress (lifting beam) or compressive stress (spreader) for the beam material, from the lifting equipment standard.
- 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 160 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from the lifting equipment standard, which may be lower than for ordinary structures.
What this means: Section area (spreader)
- What it is
- Cross-section area of the spreader beam, used to work out its compressive stress.
- Units and format
- Enter a number in mm²: square millimetres. The form accepts 0.000001 mm² to 100000000 mm². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4000 mm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Compressive stress falls in proportion as area rises.
- Get it right
- Used only for spreader beams; take it from the section table.
What this means: Required buckling factor (spreader)
- What it is
- Lowest acceptable ratio of the Euler buckling load to the actual compression in a spreader beam.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 10. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from the lifting equipment standard; used only for spreader beams.
Method and formulas
- Design load W = mass × g × dynamic factor; each load point carries W ÷ 2.
- Lifting beam: M = W S ÷ 4; stress = M ÷ Z; deflection = W S³ ÷ 48 E I (central lug, end loads, equivalent to a centrally loaded simple span).
- Spreader: top sling tension = W ÷ (2 cos θ); compression = (W ÷ 2) tan θ; buckling P_cr = π² E I ÷ S² (pinned ends).
- Example: a 5000 kg load on a 3000 mm lifting beam gives 153.23 MPa bending stress.
Limitations
- Lifting equipment must be designed, proof-tested and certified to the applicable standard.
- Lug, weld and local flange checks are separate.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a fabricated lifting beam before use
- Choose a section for a spreader bar
- Find sling tensions for a two-point lift
Who it is for
- Rigging supervisors
- Structural engineers
- Lifting equipment designers
What you get
- Design load and sling tension
- Bending stress and deflection (lifting beam)
- Compression and buckling factor (spreader)
Interpreting the result
- Flatter top slings (larger angles) raise both sling tension and spreader compression quickly.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2613–2625, 281–285. 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
Lifting magnets
In Magnetic Workholding by the Numbers
What it covers: Plan a lift with lifting magnets: rated loads and their conditions, derating for thickness, surface and material, plate mass and centre of gravity, lifting beams, plate flex and safe use.
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.