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steelColumnAS4100-1998

Run the calc
Design hot-rolled steel columns and posts to AS 4100:1998 (R2016) for legacy Australian projects. Checks cover axial section capacity, member buckling, and combined axial-plus-bending interaction. Column axial load links from beam reactions above and passes down to footing calculations below so changes propagate automatically.
This calculator uses an earlier code edition (AS 4100:1998 (R2016)). It stays available for existing projects. For new designs, check the Calculator Library for the current edition.

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Method & scope

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Calculation method

The Steel Column (AS 4100:1998) calculator designs hot-rolled steel columns and posts using limit state design per AS 4100:1998 (R2016). It runs a first-order elastic analysis per Clause 4.4.2 to determine demands, then applies AS 4100:1998 capacity equations for all relevant limit states.
Structural analysis
The calculator performs FEA on the column as a beam-column, resolving axial forces, bending moments, and deflections under applied loads. End conditions (pinned, fixed, roller) are specified at each support. Concentrated axial loads and distributed lateral loads can be applied at any height. The member is assumed to be of uniform cross-section along its full length. Interaction limit states are conservatively based on the maximum individual demands in each span regardless of load case.
Axial section capacity
Section capacity in compression is checked per AS 4100:1998 Section 6: utilization = N / (phi * Ns) ≤ 1.0* where phi = 0.90 and Ns = kf * An * fy. The form factor kf accounts for local buckling of slender plate elements in the cross-section.
Member buckling capacity
Compression member buckling capacity is checked per AS 4100:1998 Section 6: utilization = N / (phi * Nc) ≤ 1.0* Nc is determined from the member slenderness reduction factor alphac, which depends on the modified slenderness lambda_n and the member section constant alphab from Table 6.3.3. Major- and minor-axis effective lengths are entered separately to capture the governing buckling axis.
Flexural capacity
Moment member capacity (lateral-torsional buckling) is checked per AS 4100:1998 Section 5: utilization = |M| / (phi * Mb) ≤ 1.0* Mb is determined from the reference buckling moment Ms and the slenderness reduction factor alphas. Flange and web compactness classifications govern whether the full plastic, compact, or slender section capacity applies.
Combined axial and bending
Combined axial compression and biaxial bending is checked per AS 4100:1998 Section 8 interaction equations. The interaction checks account for amplified moments where first-order analysis is used for design.
Outputs
Results are displayed as color-coded utilization ratios for each limit state with AS 4100:1998 clause references. Section properties, governing demands, and capacity factors are tabulated for report documentation.

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How to use it

1

Open the calculator

Open it from Run calc in the About this calculator panel above.
2

Enter your inputs

Work through the input sections from top to bottom. Click any input label to see its reference explanation, clause, conditions and assumptions. See Checks, References, Conditions and Assumptions.
3

Review the results and export

Check the utilization of each governing check in the summary, then export a PDF report. See Views and Export.

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Common questions

The calculator designs to AS 4100:1998 (Reconfirmed 2016). This is the predecessor to AS 4100:2020 and is still referenced by some state and project-specific documentation. The design method is limit state design with capacity factors phi.
Key inputs include column height, end conditions (pinned, fixed, roller), axial loads, distributed lateral loads, and effective length factors for major- and minor-axis buckling. The steel section is selected from the Australian hot-rolled section database covering UB, UC, RHS, SHS, CHS, and angle sections.
The calculator checks axial section capacity (phi * Ns), member buckling capacity in compression (phi * Nc) for both major and minor axis, major- and minor-axis moment member capacity (phi * Mbx, phi * Mby), and combined axial compression plus biaxial bending interaction per AS 4100:1998 Section 8.
AS 4100:2020 introduced revised member slenderness reduction factors and updated references to Australian section properties aligned with current manufacturer data. For most common column configurations the calculated capacity difference is small. New projects in most jurisdictions should use AS 4100:2020; this calculator is provided for legacy project continuity and reference-checking.
Effective length factors for major and minor axis bending are entered directly. AS 4100 Table 4.6.3 provides reference values for standard end conditions. For columns within continuous frames, a rational buckling analysis or the effective length nomograph from the code commentary should be used.
Yes, column axial load can be linked from beam reaction outputs above, and the resulting column base reaction links to a footing or base plate calculation below. Changes propagate automatically across the full load path.

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Next steps

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