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# Design a Steel Member (Design Only) to AS 4100:2020
> Fast capacity design of steel members to AS 4100:2020 when analysis results are available. Input forces directly and choose from thousands of AU sections.
Member reactions link to connected column or footing calculations automatically, change a load and everything downstream updates. Design steel members to AS 4100:2020 where analysis results are already available, choosing from thousands of Australian sections. Checks combined axial and bending interaction, shear, lateral-torsional buckling, and flexural buckling.
The Steel Member Design Only calculator to AS 4100:2020, is perfect for the fast capacity design of steel members where engineers already have analysis results available (for example, when forces are being taken from a 3D analysis model of a steel structure). By enabling easy input of analysis forces on the member, the steel member calculator enables the fast, optimized selection of steel members from our library of thousands of Australian steel sections.
## Method & scope
| Property | Detail |
| ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| Design standards | AS 4100:2020 |
| Regions | Australia & New Zealand |
| Presets | Manual Input, (BETA) Link to Analysis Module |
| What it checks | Section classification, Bending capacity and lateral-torsional buckling, Compression and flexural buckling, Tension capacity, Shear capacity, Combined actions interaction equations |
#### Calculation method
The Steel Member (Design Only) calculator to AS 4100:2020 accepts analysis forces directly and evaluates all member capacity limit states for the selected Australian steel section. It is designed for design-only use: engineers provide forces from their own analysis model or from a linked analysis calculator in Calcs.com.
##### Section classification
Plate elements, flanges and webs, are classified using the element slenderness ratios and the compact and non-compact limits from AS 4100 Table 5.2. Compact sections can reach the full plastic moment. Non-compact sections are limited by first yield with an effective section modulus. Slender sections use an effective section with reduced plate areas. The "flange" and "web" terminology always refers to the element orientation if the member were bent about its X-axis, regardless of the actual bending direction.
##### Bending capacity and lateral-torsional buckling
Section moment capacity Ms is the lesser of the yield moment and plastic moment, scaled by the section form factor kf. Member moment capacity Mbx for major-axis bending accounts for lateral-torsional buckling between restraint points. The reference buckling moment Mo is computed from:
* The segment length Ls between lateral restraints
* Twist restraint factor kt (accounts for end connection stiffness)
* Load height factor kl (accounts for load application point relative to shear center)
* Lateral rotation restraint factor kr (accounts for restraint against lateral rotation at ends)
The slenderness reduction factor αs is then applied to give the member moment capacity Mbx, modified by the moment modification factor αm for non-uniform bending diagrams. For minor-axis bending, lateral-torsional buckling does not apply and the section capacity governs directly.
##### Compression and flexural buckling
Section 6 compression checks apply. An effective area reduction factor kf is applied for sections with slender plate elements. The member compression capacity Nc is derived from the section compression capacity Ns reduced by the member slenderness reduction factor αc (Clause 6.3.3). The slenderness ratio is computed for both major and minor axis using the effective lengths:
**αc** depends on the section slenderness and the member slenderness ratio λn = (Le/r) × sqrt(kf × fy / 250)
Residual stress category (hot-rolled, welded, etc.) influences the imperfection factor used in αc.
##### Tension capacity
Section 7 tension checks cover the gross section yield capacity (Ag × fy) and, where holes or reduced net sections are present, the net section fracture capacity (0.85 × kt × An × fu). By default the net area equals the gross area assuming maximum permissible holes.
##### Shear capacity
Section 5.11 shear checks apply. For compact webs (dp/tw ≤ 82/sqrt(fy/250)) the full plastic shear capacity governs. For slender webs, shear buckling reduces the capacity using the shear buckling coefficient. Bending-shear interaction and bending-bearing interaction checks are applied when significant shear or bearing coincides with high moment.
##### Combined actions interaction equations
The critical check is from AS 4100 Section 8. For members with combined compression and bending:
**In-plane interaction ratio** = N\*/φNs + Mx\*/φMix ≤ 1.0
**Out-of-plane interaction ratio** = N\*/φNcy + Mx\*/φMbx ≤ 1.0
Where N\* is design axial force, Ns is section axial capacity, Ncy is the minor-axis buckling capacity, Mix is the in-plane member moment capacity, and Mbx is the lateral-torsional buckling member moment capacity. The βm distribution factor and δs amplification factor are entered manually by the engineer based on the moment diagram shape and frame context. Both interaction ratios are shown with full code references.
## How to use it
Open it from **Run calc** in the About this calculator panel above. To start from a typical setup, choose one of the presets listed there.
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](/docs/running-calculations/checking-results/checks-references-conditions-assumptions).
Check the utilization of each governing check in the summary, then export a PDF report. See [Views and Export](/docs/running-calculations/exporting-reports/views-and-export).
## Available presets
Each preset opens the calculator with a typical setup already entered.
| Preset | Open in Calcs.com |
| ------------------------------------------------------- | ------------------------------------------------------------------------------------------------ |
| Manual Input | [Run with preset](https://app.calcs.com/new/sheet/steelMemberAS4100-2020?presetCode=manualInput) |
| (BETA) Link to Analysis Module | [Run with preset](https://app.calcs.com/new/sheet/steelMemberAS4100-2020?presetCode=elementLink) |
## Common questions
This calculator uses AS 4100:2020, the current Australian standard for steel structures. It supersedes AS 4100:1998 and includes updated provisions for stability, section properties, and combined actions. Engineers on older projects requiring AS 4100:1998 should use the steelMember calculator.
You enter the steel section (selected from the Australian section library including universal beams, columns, welded sections, channels, angles, and hollow sections), member length, restraint conditions, and the analysis forces, axial load, bending moments about both axes, and shear. Forces can be manually entered or linked from a frame analysis or beam analysis calculator.
The calculator checks member bending capacity including lateral-torsional buckling (AS 4100 Section 5), compression capacity including flexural buckling (Section 6), tension capacity (Section 7), shear capacity (Section 5.11), bearing, and the combined actions interaction equations from Section 8.
Yes. The Section 8 combined actions equations check both in-plane and out-of-plane interaction for members with simultaneous axial force and bending about one or both axes. Both interaction ratios are reported alongside the governing equation reference.
You specify restraint conditions at each end of the member and at any intermediate brace points. The calculator uses the twist restraint factor kt, load height factor kl, and lateral rotation restraint factor kr to derive the effective length for LTB checks. Effective lengths for flexural buckling are set by the end restraint conditions.
Yes, the member calc receives reactions from upstream calculations (e.g. frame analysis) and passes base reactions to footing or base plate calculations. Changes propagate automatically through the load path.
## Next steps
Design steel beams to AS 4100:2020 with multiple supports and loads. Floor- and roof-beam presets cut repetitive entry.
Complete list of Calcs.com design calculators available for Australian and New Zealand projects (AS 3600, AS 4100, AS 1720, AS/NZS 1170, and related standards).
Design steel lintels supporting masonry, as an angle, a T-lintel, or a PFC with plate, to AS 4100:2020.
Design cold-formed steel members to AS/NZS 4600:2018 by the Direct Strength Method. Input analysis forces to check moment, shear, bearing, and combined actions.
Guide to the Steel Lintel calculator for steel angle lintels to AS 4100:2020.
Design hot-rolled steel columns and posts to AS 4100:2020. Checks axial section capacity, member buckling and combined axial and bending.
Link Design Only calculators to Truss Analysis and Portal Frame Analysis results to check member capacity against the analysis forces.
