KEVOS® MAKEOS · Strength
Thin-Walled Closed Tube in Torsion
What shear stress and twist does torque cause in this thin-walled round or rectangular tube?
Shear stress (Bredt’s formula), torsional constant and twist of a closed thin-walled round or rectangular tube under torque.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Section | choice | Round or rectangular hollow section. |
| Outside diameter or width | mm | Outside diameter (round) or outside width (rectangular). |
| Outside height (rectangular only) | mm | Outside height (rectangular only). |
| Wall thickness | mm | Wall thickness. |
| Torque | N·m | Torque. |
| Length | mm | Length for twist. |
| Shear modulus | GPa | Shear modulus. |
| Allowable shear stress | MPa | Allowable shear stress from your design code. |
Method and formulas
- Mid-line dimensions: outside minus t. Enclosed area Am; mid-line perimeter s.
- Bredt: τ = T ÷ (2 Am t).
- J = 4 Am² t ÷ s; twist θ = T L ÷ (G J).
- Example: 1500 N·m on a 100 × 50 × 4 RHS gives τ = 42.459 MPa.
Limitations
- Thin walls (t well under a tenth of the size); corner radii ignored.
- Open sections (with a slit) are far weaker and need a different method.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check RHS and box frames in torsion
- Compare open and closed sections
- Size a torque tube
Who it is for
- Design engineers
- Structural and mechanical engineers
- Engineering students
What you get
- Enclosed mid-line area
- Shear stress
- Torsional constant J
- Angle of twist
Interpreting the result
- Closing a section (welding a slit shut) multiplies torsional stiffness many times.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 295–303. Topic reference; no source tables or recommended settings are reproduced.
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