AS 4100:2020

The AS 4100 engine implements AS 4100:2020 - Steel Structures, the Australian standard for the design of steel structures. The engine supports common hot-rolled, welded, and hollow section member-strength checks with AS 4100 residual stress categories and optional local bearing checks where the required bearing details are supplied.

Open AS 4100:2020 Calculator

Standard Reference

Supported Geometry Families

Six geometry families are supported; catalogue variants such as UB/UC and RHS/SHS are grouped within their respective families.

• I-Shapes (UB, UC - rolled and welded)
• Channels (PFC)
• Tees (BT / UBT beam tee catalogue sections; sideways orientation is controlled by the member orientation flag in the FEA workflow)
• Rectangular Hollow Sections (SHS, RHS - hot-formed and cold-formed)
• Circular Hollow Sections (CHS)
• Angles (EA, UA - equal and unequal)

Checks Performed

The design-check table shows the specific row and clause used for each member result. The documentation keeps the same clause groups at a summary level:

• 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.
• Compression (Cl 6.2 / Cl 6.3.3): Ordinary major/minor flexural buckling is checked. The additional 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.
• Flexure (Cl 5.2 / Cl 5.6): Section bending and LTB member bending checks use the selected section orientation and restraint inputs.
• Shear (Cl 5.11.3-Cl 5.11.5 / Cl 5.12.3): Shear, shear buckling, non-uniform shear, and shear-moment rows report the active local path.
• 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 are reported with the applicable compression or tension branch. Linear-analysis compression interactions use station-concurrent delta_b amplification; N*/Nomb at or above 1.0, or invalid amplification inputs, fail closed. P-Delta moments are not amplified again.

Calculator Inputs

The standalone AS4100 calculator accepts the following inputs. All values are in metric units.

Fabrication & Residual Stress

Two dropdowns control how residual stresses affect section classification and buckling:

The residual stress category determines the plate element yield slenderness limits (λ_ey) in Table 5.2. Fabrication provenance also controls the member section constant (α_b) in Table 6.3.3: generic welded or unknown plate provenance uses the as-rolled welded row, while the more favourable flame-cut row is used only when Welded (Flame-Cut Plates) is selected explicitly.

Generic welded fabrication defaults conservatively to HW. LW requires verified compressive residual stresses below the Table 5.2 threshold. Changing fabrication resets the residual-stress selection, and incompatible imported pairs are not used to publish capacity.

LTB Restraint Inputs

For I-shapes, channels, and RHS/SHS segments, including segments unrestrained at one end, lateral-buckling effective length can be built from the AS 4100 Table 5.6.3 inputs after the table-factor control is explicitly activated. Until activation, KLT is treated as the final L_e/L factor and hidden table/load-height values are not applied. Tees use final KLT only because the Table 5.6.3 web/flange-factor workflow is not exposed for that family.

• Load height: shear centre or top flange, setting k_l for gravity loading.
• Segment restraint: FF, FP, FL, PP, PL, LL, FU, or PU end-restraint arrangements.
• Load position: within segment or at segment end.
• Rotation restraint: neither end, one end, or both ends for the k_r reduction where Table 5.6.3(C) allows it.

For a cantilever (a segment unrestrained at one end), Table mode permits only FU or PU restraint arrangements and fixes k_r = 1.0. Top-flange gravity loading gives k_l = 2.0 in both longitudinal load-position rows. Table 5.6.2 independently supplies the selected cantilever moment modification factor.

Section Geometry

Select a shape group, then enter dimensions or pick from the built-in section library (Australian sections).

Material Properties

Member Lengths & Bracing

A Continuously Restrained checkbox bypasses bending LTB. L_b, load height, α_m, cantilever, and Table 5.6.3 controls are inactive while it is enabled; compression K_t remains independent where Clause 6.3.3 FTB applies.

Clause 6.3.3 ordinary major/minor flexural buckling is checked for supported compression members. For a hot-rolled channel, confirming minor-principal-axis bracing activates the additional flexural-torsional mode. The AS 4100 engine evaluates the referenced AS/NZS 4600 equations locally, then applies the AS 4100 reduction of 0.85 and capacity factor of 0.90. An unbraced hot-rolled channel remains on the ordinary flexural-buckling path.

Design Actions

Bearing Inputs

AS 4100 Clause 5.13 bearing is optional because it depends on local support or patch-load details that are not determined by the member force envelope alone.

I-shapes and channels report web bearing yield and bearing buckling. RHS/SHS sections report flat-wall bearing yield and buckling, plus Cl 5.13.5 bending-bearing interaction where bending demand is present. The interaction uses the moment at the entered bearing station on the selected local section axis, not an independently located member moment envelope. Sideways section mapping is automatic; horizontal, vertical, and sloped global member placement does not alter the selected physical face.

Capacity Reduction Factor

A single capacity reduction factor of φ = 0.9 is used across all member checks covered here (tension, compression, bending, shear, and bearing) per AS 4100:2020 Table 3.4.

Limitations & Notes

• Analysis and amplification basis: In the Structural FEA Design tab, linear/general compression interaction applies Clause 4.4.2 δ_b at each concurrent station. N*/N_omb at or above 1.0 gives an axis-specific FAIL; invalid E/I/K/L inputs give INCOMPLETE, and the affected compression interaction is suppressed. P-Delta moments are not amplified again. The standalone calculator has no frame-analysis basis and treats entered M* as design moments; it does not add δ_b, so include any required second-order/amplification effects in those entered actions.
• Custom-section axis convention: The engine expects section properties in the AutoCalcs strong/weak convention: Izz is major/strong-axis inertia and Iyy is minor/weak-axis inertia. In raw section-library files, Szz/Syy are plastic section modulus values; AS4100 standalone/PDF output displays those plastic values as Pzz/Pyy and derives displayed/report elastic Szz/Syy separately. Custom or imported sections with these axes swapped can produce incorrect bending, buckling, and LTB axis assignments.
• Single-element Z_e: Effective section modulus uses the governing slender element for the reported stress state. Rare edge cases with multiple slender elements may need separate review.
• Non-uniform shear distribution: Clause 5.11.3 distribution handling is selected by section type and shear direction for the supported member families.
• Cold-formed design thickness: The AS/NZS 1163 design-thickness convention is applied to slenderness calculations for cold-formed hollow sections, but not to gross area.
• Sideways members: For members marked sideways=true, AS4100 major/minor design actions and capacities are reported after the section orientation mapping is applied. These design-axis results may not line up one-for-one with raw local My/Mz result component labels for mono-symmetric sections (tees, channels, angles), even when the governing capacities match.
• Imported design metadata: Imported replay models may carry explicit AS4100 metadata such as kf, alpha_b, or beta_x. These are not ordinary required calculator inputs; they preserve known section metadata when an import source supplies it.
• Flexural-torsional buckling: Bending LTB and compression FTB are distinct checks. The additional compression FTB mode required by Clause 6.3.3 is numerical for fabricated unequal-flange I-sections, fabricated equal-flange channels, and confirmed minor-axis-braced hot-rolled channels. Unequal-flange fabricated channels remain incomplete because validated principal-axis and two-coordinate shear-centre properties are unavailable.
• Net sections and connection force distribution: Tension fracture under Cl 7.2 uses entered A_n and k_t; blank A_n defaults to A_g and blank k_t defaults to 1.0. Fastener holes, staggered paths, and detailed Clause 7.3 connection layouts are not inferred.
• Bearing and stiffeners (Cl 5.13-5.16): Cl 5.13 bearing is checked only when local bearing inputs are supplied. R*, bearing length, bearing station/loaded face, and web restraint are not inferred automatically from reactions or point loads. RHS/SHS bending-bearing interaction fails closed without a valid station when bending is present. Load-bearing stiffeners, end posts, and transverse or longitudinal web stiffeners remain separate checks.
• Bracing and restraint systems: Effective lengths, unbraced lengths, load height, cantilever load type, and continuous restraint are design inputs. The engine does not design brace members, restraint connections, diaphragms, anchorage, or the Clause 6.6 restraint forces for compression members.
• Built-up and compound members: Laced, battened, back-to-back, and multi-component tension or compression member detailing in Clauses 6.4-6.5 and 7.4 is outside the automatic member check.
• Connection-region checks: Section 9 bolt, weld, pin, ply bearing, block shear, prying, and minimum connection action checks are separate from the member-strength result.
• α_m computation: Auto-computed from the quarter-point moment distribution. For specific loading patterns, the manual override is available.
• Torsion (Bredt-Batho): Not an input in the standalone calculator. In the FEA tool, torsion is checked for closed hollow sections (RHS/SHS/CHS) only. Warping torsion for open sections (I-beams, channels, angles, tees) is not performed.
• Serviceability and special design states: Structural analysis results may report displacements separately, but the AS 4100 design engine does not perform serviceability limit comparisons, vibration checks, bolt slip checks, corrosion protection, brittle fracture, lamellar tearing, fatigue, fire, or earthquake detailing unless handled by a separate workflow.

Verification

The engine is benchmarked against 60 independent test cases from the Steel Structures Sample Worked Problems, the Design Manual by Kirke and Al-Jamel, ASI/ATM Design Capacity Tables, and independent benchmark cases, with an average difference of 0.17%.