What is effective length and why does it matter?

Effective length is the actual column height multiplied by a factor that accounts for end conditions. A column fixed at both ends (factor 0.7) can carry more load than one pinned at both ends (factor 1.0) because the fixed ends resist rotation. The effective length directly affects the slenderness ratio, which determines how prone the column is to buckling.

What slenderness ratio is acceptable for a steel column?

BS EN 1993-1-1 limits the slenderness ratio to 200 for members in compression. In practice, most columns have slenderness ratios between 30 and 120. Below 30, the column behaves almost as a pure compression member. Above 120, buckling dominates and capacity drops significantly. Aim for below 100 for efficient design.

What is the difference between a UC and a UB used as a column?

Universal Columns (UC) have a nearly square cross-section with roughly equal flange width and depth, making them efficient in compression as they resist buckling equally in both axes. Universal Beams (UB) are deeper and narrower, so they buckle easily about the weak axis. UCs are the standard choice for columns unless lateral restraint is provided.

How do I determine the axial load on my column?

The axial load is the total factored load from all floors, roof, and any beams that frame into the column. Add up the unfactored dead loads and imposed loads from each level, then apply load factors (typically 1.35 for dead and 1.5 for imposed under BS EN 1990). Include the self-weight of the column itself and any eccentric moments from beam connections.

Do I need a structural engineer to specify a steel column?

Yes, for any structural steel column in a building, Building Regulations require the design to be carried out or checked by a competent structural engineer. This calculator provides a preliminary size for budgeting and discussion, but the final specification must account for eccentricity, combined loading, fire protection, and connection details that require professional engineering judgement.

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Steel Column Calculator — Axial Load & Buckling Check

Select the right UC section for your steel column. Checks buckling resistance based on effective length and end conditions per BS EN 1993-1-1.

Axial Compressive Load

Total factored load on the column

Column Height

Storey height between restraint points

End Conditions

Determines the effective length factor

Price Per kg (optional)

Enter your steel price per kg for a cost estimate

How We Calculate This

This calculator selects a Universal Column (UC) section to resist an axial compressive load, checking buckling resistance based on the effective length and slenderness ratio per BS EN 1993-1-1.

Design process

Effective length: LE = k × L, where k depends on end fixity (0.7 to 2.0)
Slenderness ratio: λ = LE / ry (radius of gyration about weak axis)
Compressive resistance: Reduced from full squash load based on slenderness and buckling curve

The calculator works through the UC catalogue from lightest to heaviest, finding the first section whose buckling resistance exceeds the applied load at the given effective length.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.