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AustraliaAS 4100:2020

Steel Column

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Design hot-rolled steel columns and posts to AS 4100:2020 for Australian commercial, industrial, and residential projects. Checks cover axial section capacity, member buckling in compression, and combined axial-plus-bending interaction. Column loads link from beam reactions above to footing calculations below automatically.
(Note: The New Zealand Steel Column module also refers to this article. While New Zealand uses a different standard - NZS 3404.1:1997 - it is substantially similar to the Australian standard, and so this article is almost entirely applicable) The Calcs.com Steel Column Calculator allows users to design steel columns by specifying the desired load cases and dimensions of the column. In this article, each section of the calculator will be explained followed by a few worked examples. The Steel Column Calculator has 4 main sections
  1. Key Properties
  2. Design Criteria
  3. Loads
  4. Summary and Graphs

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Worked example

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Task 1

Design a steel stud with the following characteristics
  • for residential application
  • 4m in height with no lateral restraints and a braced frame
  • member type: 150 UB 14.0 - Gr. 300PLUS
  • fixed base and a roller support at the top
  • an axial load at the top: 6kN dead load and 10kN live load
  • assume zero eccentricity and therefore zero bending
  • include self-weight

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Method

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Summary & Graphs

Access the full PDF file here: Task 1

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Task 2

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Method & scope

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Design Criteria

Deflection Limit Absolute Criterion: This is the hard maximum deflection allowed for the column, regardless of span length, and applied to all load cases. Extension Limit Absolute Criterion: This is the hard maximum extension allowed for the column.

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See the exact clause

Every check in this calculator links back to its governing clause in AS 4100:1998. Open the Formula Reference panel on any result and select the clause reference to read it. See Viewing Clauses from Inside a Calculator.

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Calculation method

The Steel Column (AS 4100:2020) calculator designs hot-rolled steel columns and posts using limit state design per the current edition of AS 4100. It runs a first-order elastic analysis per Clause 4.4.2 to determine demands, then applies AS 4100:2020 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 evaluated at the maximum individual demand in each span regardless of load case.
Axial section capacity
Section capacity in compression is checked per AS 4100:2020 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 within the cross-section.
Member buckling capacity
Compression member buckling capacity follows AS 4100:2020 Section 6: utilization = N / (phi * Nc) ≤ 1.0* Nc is derived from the member slenderness reduction factor alphac, which depends on the modified slenderness lambda_n and the member section constant alphab from AS 4100 Table 6.3.3(1) and (2). Major- and minor-axis effective lengths are evaluated separately to identify the governing buckling axis.
Flexural capacity
Moment member capacity (lateral-torsional buckling) follows AS 4100:2020 Section 5: utilization = |M| / (phi * Mb) ≤ 1.0* Mb is determined from the reference buckling moment Ms and the slenderness reduction factor alphas per Section 5.6. Flange and web compactness classifications (compact, non-compact, slender) govern whether full plastic or reduced section capacity applies.
Combined axial and bending
Combined axial compression and biaxial bending is checked per AS 4100:2020 Section 8 interaction equations. Both major- and minor-axis moment demands are included. For beam-column configurations the amplified moment approach is applied consistent with the first-order analysis assumption.
Deflection
Lateral deflection under service loads is reported alongside strength checks. Limits are applied per the project’s serviceability requirements.
Outputs
Results are displayed as color-coded utilization ratios for each limit state with AS 4100:2020 clause references. Section properties, capacity factors, governing demands, and design actions are tabulated for straightforward report documentation.

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How to use it

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Key Properties

A. Member TypeCalcs.com gives the user the opportunity to use a custom member size if they wish. If ‘no’ is selected for the use of custom members, the user is provided with a drop-down list industry-standard size members from which a member can be selected.Alternatively, the member selector and autosize functions (circled in red in the above diagram) can also be used to select a member.B. Total Column HeightThe total height of the column needs to be given In millimeters (mm).C. Lateral and Torsional Unbraced and Effective LengthsThe first column of this table refers to the bracing type, which is of 3 categories. Torsional bracing restricts movement about the z-axis, while x-axis and y-axis lateral bracing restricts movement about the x and y-axes respectively. The orientation of the axes is given by the diagram on the left.The second column requires the user to input the unbraced length in mm for each of the bracing types. By default, this is set equal to the column height. However, if additional bracing is used, the unbraced length will be smaller than the column height. It may be useful to enter user formulas for these unbraced lengths, such as “L/2” if the column is braced at midheight.The third column is allocated for the effective length factor, which by default is assumed to be equal to 1; this is usually conservative, and is equal to assuming pin-type restraints. However, if the column’s restraints provide moment restraint (analogous to a fixed restraint), then this factor may be lower.Effective Unbraced Length = Unbraced Length x Effective Length FactorD. Position of Supports From BottomThis section prompts the user to select the support type from a drop-down menu and then specify the location of each support in millimeters(mm) as measured from the bottom of the column. The user then has to specify the restrain type of each support entered. A diagram of what is meant by the Full, Partial, and Lateral restraint types is available in the description if this field is expanded.E. Frame TypeIn this section, the user can choose between a braced frame and a sway frame for their design. In a sway frame, the structure as a whole is allowed to sway laterally while in a braced frame such movement is effectively restrained. See AS 4100:1998, Cl 4.1.2 for a more detailed definition.
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Loads

A. Axial, Point & Moment LoadsTo enter an axial, point or moment load, one needs to fill out the above table. The first column refers to the name of the load, which can be decided by the user. Then the location at which the load acts on the column as measured from the bottom of the column (in millimeters) needs to be entered. The third column refers to the axial eccentricity of the load; this is set according to the “Default Axial Load Eccentricity” by default. Axial eccentricity will be discussed in detail in part C of this section. When one clicks on the fourth column the following table will appear.In this table, the user can select the load type from the drop-down menu shown, and specify the magnitude of the load in the x and y directions in kilo Newtons(kN) and enter any moment loads in kilo Newton Meters(kNm).B. Lateral Distributed LoadsThis table is applicable to distributed loads that act in the x-direction (i.e. perpendicular to the column). Similar to the Point Loads table, the first column of the lateral distributed loads table prompts the user to name the load. Then the start and end location of the distributed load must be specified, as measured from the bottom of the column. Then the start and end width of the load must be entered in millimeters(mm). To enter the load magnitudes, the following table must be filled out.The load type must be selected from the drop-down menu in the first column, then the load magnitude must be specified per area in units of kilo Pascals(kPa).C. Default Axial Load EccentricityWhat is Axial Load Eccentricity?Generally, axial loads (i.e. loads acting vertically downwards) act through the center of a column. However, in some cases, the load can act off the center of the column and cause bending in addition to compression of the column. Axial load eccentricity refers to the horizontal distance between the center of the column and the line of action of the axial load.Axial Load Eccentricity Options in Calcs.com
  • ‘Corner Face’ assumes default eccentricity to be the corner of the member plus a 100mm (not common in steel)
  • ‘Capped’ assumes default eccentricity to be equal to the face of the member
  • ‘Pure Compression’ assumes zero eccentricity. The calculator is set to pure compression by default
  • ‘Custom’ allows the user to specify the default eccentricity as needed
  • ‘X-axis Face’ assumes default eccentricity to be the face of the flange plus a 100mm
  • ‘Y-axis Face’ assumes default eccentricity to be the face of the web plus a 100mm
D. Include Self-WeightThe user can choose whether or not they include the self-weight of the column in their calculations. The calculator is set to include the self-weight by default unless the user specifies otherwise.E. Character of Imposed LoadThe character of imposed loads that is most applicable to the intended use of the column can be selected from this drop-down menu.
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Summary & Graphs

The summary section the key parameters of your calculation will be outlined.In the graphs section, the user can select whether or not they include the load duration factor k1 in the plots and select the load case that they would like the see in their graph (e.g.: 1.2G 1.5Q). The user can also specify whether they want the axial compression capacity graphed on the plot.A sample of the summary and graphs produced during calculations can be seen in the examples given below.

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AU Steel Column: Overview

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AU Steel Column: Example

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Available presets

Each preset opens the calculator with a typical setup already entered.

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Common questions

The calculator designs to AS 4100:2020, the current edition of the Australian Steel Structures standard. It uses limit state design with capacity factors per the AS 4100:2020 provisions.
Key inputs include column height, end conditions (pinned, fixed, roller), axial design loads, distributed lateral loads, and effective length factors for major- and minor-axis buckling. Sections are selected from the current Australian database of UB, UC, RHS, SHS, CHS, WB, WC, and angle sections.
The calculator checks axial section capacity (phi * Ns), member buckling capacity in compression (phi * Nc) for both axes, major- and minor-axis moment member capacity (phi * Mb), and combined axial compression plus biaxial bending interaction per AS 4100:2020 Section 8.
Yes. When lateral loads or eccentric axial loads produce moment demands, the combined axial compression plus biaxial bending interaction checks per AS 4100:2020 Section 8 are performed. The calculator handles beam-column configurations where both compression and moment demands coexist.
Major- and minor-axis effective length factors are entered directly. AS 4100:2020 Table 4.6.3 provides reference values for standard end conditions. For columns in moment frames, a rational buckling analysis or the effective length nomograph from the AS 4100 commentary should be used to determine appropriate values.
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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