AS 4100:2020 Steel Member Design
Evaluate structural steel member capacities according to AS 4100:2020. This calculator automates section slenderness, member stability, and combined action interactions.
Design Check Overview
The calculator classifies your cross-section as Compact, Non-compact, or Slender based on plate width-to-thickness ratios and residual stress category. It then determines section capacities (tension, compression, bending, shear) and member stability accounting for effective lengths, buckling curves, and lateral-torsional buckling. Where multiple actions are present, combined interaction checks are performed automatically.
Clause Compliance Coverage:
- Section classification (Table 5.2 / Cl 6.2.4): Bending classification and compression form-factor effects are selected from the active section state.
- Tension (Cl 7.2): Gross yielding and net-section fracture are checked using optional member An; blank An defaults to Ag because fastener-hole geometry is not inferred. Blank kt uses the Table 7.3.2 value for the section family. A valid tensile strength is required for fracture and dependent tension interactions.
- Compression (Cl 6.2 / Cl 6.3.3): Ordinary major/minor flexural buckling is checked. The additional flexural-torsional buckling (FTB) mode is numerical for fabricated unequal-flange I-sections, fabricated equal-flange channels, and minor-axis-braced hot-rolled channels; unequal-flange fabricated channels remain incomplete. Design checks use E = 200,000 MPa and G = 80,000 MPa under Clause 2.2.4.
- Flexure (Cl 5.2 / Cl 5.6): Unequal-I section bending uses each flange's geometry. Supported sharp-cornered (no root fillet) segments restrained at both ends use Cl 5.6.1.2 monosymmetric LTB and applicable Cl 8.4 interactions. Reverse curvature uses the lower flange elastic buckling moment and a moment modification factor of 1. With continuous restraint, sagging uses section moment capacity and hogging is checked for member LTB; other configurations or missing properties explicitly omit member LTB while preserving section checks.
- Shear (Cl 5.11.3-Cl 5.11.5 / Cl 5.12.3): Shear, shear buckling, non-uniform shear, and shear-moment checks are reported for the governing local case.
- Bearing (Cl 5.13 / Cl 6.3.3): Optional local bearing checks are reported when R*, bearing length, distance from the member end, and restraint inputs are supplied; RHS/SHS bending-bearing interaction is included where applicable.
- Combined actions (Cl 4.4.2 / Cl 8.3 / Cl 8.4): Section and member axial-plus-bending checks use the applicable compression or tension provisions. With first-order moments, compression-bending checks apply Clause 4.4.2 member amplification; a factor above 1.4 requires an Appendix E second-order analysis. The External second-order moments option uses the entered moments directly. Frame sway effects are not calculated here and must be included in the entered moments. Invalid amplification prevents completion of the affected interaction.
Supported Section Types
I-Shapes - UB, UC, WB, WC
Channels - PFC
Tees - BT, CT
RHS / SHS
CHS
Angles - EA, UA
Current Limitations
- Tension fracture under Cl 7.2 uses the entered An and kt. Blank An defaults to Ag because holes are not inferred; blank kt takes the Table 7.3.2 eccentric-connection value for the section family (enter 1.0 when the connection satisfies Cl 7.3.1).
- Single member analysis only: no automatic frame buckling analysis or system-level effects.
- The standalone calculator does not run a frame or second-order analysis. For first-order moments, it applies Clause 4.4.2 δb to compression-bending checks and marks the result incomplete when δb exceeds 1.4 or cannot be calculated. For external second-order moments, it uses the entered moments directly without further amplification. Obtain those moments from a separate Appendix E analysis; the calculator does not verify that analysis or system-level effects.
- No connection design, no composite construction (AS 2327), and no fatigue checks.
- Check the compression effective length factors (default 1.0) and the LTB restraint, load-position and load-height settings (default Table 5.6.3 factors with top-flange gravity loading) against the actual member. For segments restrained at both ends, the moment modification factor may be entered or filled from the beam statics helper. Cantilevers require an applicable Table 5.6.2 load case; a manual factor alone does not complete LTB. CHS and SHS are not susceptible to lateral-torsional buckling, so Mb = Ms (Clause 5.3.2.1) and no LTB inputs are shown.
- Resistance and stability checks use E = 200,000 MPa and G = 80,000 MPa under Clause 2.2.4.
- The calculator assumes the default section orientation shown in the preview. Major and minor axis inputs are relative to that orientation. Rotated or sideways mono-symmetric members, such as channels, tees, and angles, should be checked in the FEA workflow.
- Clause 6.3.3 ordinary major/minor flexural buckling is checked for all supported compression members. Its additional flexural-torsional mode is evaluated locally for fabricated unequal-flange I-sections, fabricated equal-flange channels, and hot-rolled channels with confirmed minor-principal-axis bracing, using the referenced AS/NZS 4600 equations, the AS 4100 reduction of 0.85, and phi = 0.90. Fully non-symmetric fabricated sections remain incomplete where validated principal-axis and shear-centre properties are unavailable.
- Optional Cl 5.13 bearing checks are available for I-shapes, channels, and RHS/SHS when local bearing inputs are supplied. The calculator does not infer R*, bearing length, bearing location, or web restraint from V*; load-bearing stiffeners, end posts, and web stiffener detailing remain separate checks.
- Torsion is not an input in the standalone calculator. Use the 3D FEA design check for torsion on closed hollow sections (RHS/SHS/CHS). Applied torsion on open sections requires separate warping verification.
Benchmarks: 38 published comparisons, 0.09% average numerical difference
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