Steel Member (Design Only - old AS 4100:1998)

Member reactions link to connected column or footing calculations automatically, change a load and everything downstream updates. Design steel members to AS 4100:1998 where analysis results are already available, choosing from thousands of Australian sections. For projects still on the earlier code edition.

This calculator uses an earlier code edition (AS 4100:1998 (R2016)). It stays available for existing projects. For new designs, check the [Calculator Library](/docs/calculators/au) for the current edition. ## Method & scope | Property | Detail | | ---------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Design standards | AS 4100:1998 (R2016) | | 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, βm and stability factors | #### Calculation method The Steel Member (Design Only) calculator to AS 4100:1998 accepts analysis forces directly, axial load, biaxial bending moments, and shear, and checks the selected Australian steel section against all relevant member capacity limit states. ##### Section classification Before capacity checks run, the calculator classifies each plate element of the cross-section (flange and web) as compact, non-compact, or slender using the slenderness limits from AS 4100 Table 5.2. The section slenderness determines which effective section properties apply to bending and local buckling checks. The web and flange are always referred to by reference to the X-axis orientation, regardless of the actual bending axis, so the terminology stays consistent across all section orientations. ##### Bending capacity and lateral-torsional buckling The nominal section moment capacity Ms is calculated as the lesser of the first yield moment and the plastic moment, scaled by the section form factor. For bending about the X axis (major axis), the calculator determines the member moment capacity Mbx accounting for lateral-torsional buckling. The reference buckled moment Mo is derived from the geometry of the segment between lateral restraints, using the segment length Ls, the twist restraint factor kt, the load height factor kl, and the lateral rotation restraint factor kr (AS 4100 Clause 5.6). The slenderness reduction factor is then applied to give Mbx, with the moment modification factor αm amplifying capacity when the bending moment is non-uniform along the segment. ##### Compression and flexural buckling Compression capacity checks follow AS 4100 Section 6. An effective area reduction factor is applied for slender sections. The member slenderness ratio Le/r is computed for both major- and minor-axis buckling using the effective lengths set by the restraint conditions. The section compression capacity is reduced by the member slenderness reduction factor αc (AS 4100 Clause 6.3.3) to give the nominal member capacity Nc. Residual stress category, as assigned by section type, influences the imperfection factor used in αc. ##### Tension capacity Tension capacity follows AS 4100 Section 7. The calculator checks the gross section yield capacity and, where holes are declared, the net section fracture capacity. By default the net area is assumed equal to the gross area with the maximum code-permitted holes. ##### Shear capacity Web shear capacity follows AS 4100 Section 5.11. For compact webs the capacity is the full plastic shear capacity of the web element. For slender webs the shear buckling reduction applies. Shear capacity is checked independently, and bending-shear and bending-bearing interaction checks are applied when significant shear or bearing coincides with high moment. ##### Combined actions interaction equations The critical output is the combined actions check from AS 4100 Section 8. For members carrying both axial compression and bending: **In-plane interaction ratio** = N\*/φNs + Mx\*/φMix ≤ 1.0 **Out-of-plane interaction ratio** = N\*/φNcx + Mx\*/φMbx ≤ 1.0 Where N\* is the design axial force, Ns the section axial capacity, Ncy the member buckling capacity about the minor axis, and Mix the in-plane member moment capacity. For biaxial bending, an additional interaction check combines moments about both axes at the section level. Each interaction ratio is shown with the governing equation reference, making it straightforward to see which limit state controls and by how much capacity remains. ##### βm and stability factors The moment distribution factor βm and the amplification factor δs for compression-bending interaction are entered manually by the engineer, as they depend on the broader frame context and moment diagram shape. The calculator provides clear input fields for these values with code guidance notes. ## 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). ## Common questions This calculator uses AS 4100:1998 (Reconfirmed 2016), the superseded Australian steel structures standard. It is provided for projects and checking exercises that must remain on the earlier code edition. Engineers starting new projects should use the AS 4100:2020 version instead. You enter the steel section (chosen from the Australian section library), member length, support and bracing conditions, and the analysis forces, axial load, bending moments about both axes, and shear. Forces can be entered manually or linked directly from a frame analysis or beam analysis calculator. The calculator checks member capacity in bending (including lateral-torsional buckling via the reference buckled moment), compression (flexural buckling), tension, shear, bearing, and the combined bending plus compression or tension interaction equations from AS 4100 Section 8. Yes. The calculator evaluates the combined actions interaction equations for members subject to simultaneous axial force and bending about one or both axes. Both the in-plane and out-of-plane interaction ratios are checked and reported with code references. You specify the member length and select the restraint conditions at each end. The calculator derives the effective length factor for flexural buckling and the segment length between lateral restraints for lateral-torsional buckling checks. These can also be overridden directly. 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 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). 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. Design steel beams to AS 4100:2020 with multiple supports and loads. Floor- and roof-beam presets cut repetitive entry. 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. Link Design Only calculators to Truss Analysis and Portal Frame Analysis results to check member capacity against the analysis forces.