KEVOS® MAKEOS · Strength
Steel Column Safe Stress (Classic AISC Formulas)
What safe unit stress and load do the classic AISC column formulas give for this slenderness?
Safe unit stress for steel compression members by the classic AISC working-stress formulas quoted in the handbook — parabolic up to l/r 120, and the secant-type formula above 120 for bracing and secondary members, reduced for main members — with the safe concentric load for a given section area.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Effective length | mm | Effective (unbraced) length of the member. |
| Least radius of gyration | mm | Least radius of gyration of the section. |
| Cross-section area | mm² | Gross area of the section. |
| Member type | choice | Main members above l/r 120 take a further reduction. |
| Applied concentric load | kN | Axial load to check. |
Method and formulas
- l/r ≤ 120: safe stress = 17,000 − 0.485 (l/r)² psi.
- l/r > 120, bracing and secondary members: 18,000 ÷ [1 + (l/r)² ÷ 18,000] psi; main members: that value × (1.6 − l/r ÷ 200).
- Converted to MPa (1 psi = 0.0068948 MPa); safe load = stress × area.
- Example: l/r = 100 gives a safe stress of 83.772 MPa.
Limitations
- Historic working-stress formulas for mild structural steel; current design uses AISC 360 or the local steel code.
- Concentric loads only; main members are limited to l/r 200 here.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check an existing or historic steel strut or column
- Compare older design calculations with current methods
- Quick sizing of light bracing
Who it is for
- Structural engineers
- Maintenance engineers
- Design engineers
What you get
- Slenderness ratio
- Safe unit stress
- Safe concentric load
Interpreting the result
- Use for comparison and older structures; confirm new work to the current code.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 281–285. Topic reference; no source tables or recommended settings are reproduced.
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Open the Steel Column Safe Stress (Classic AISC Formulas) calculator
