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 Section Types

• 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; fastener-hole deductions are not inferred.
• Compression (Cl 6.2 / Cl 6.3.3): Section and member flexural-buckling capacities are reported for the supported axes.
• 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 8.3 / Cl 8.4): Section and member axial-plus-bending checks are reported with the applicable compression or tension branch.

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 and the member section constant (α_b) in Table 6.3.3.

LTB Restraint Inputs

For I-shapes, channels, and tees, the lateral-torsional buckling length factors can use the AS 4100 Table 5.6.3 inputs:

• 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.

In the FEA Design Check tab, when the Cantilever toggle is enabled with top flange loading, k_l is automatically increased to 2.0 per Table 5.6.3(B).

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 sets L_b = 0, bypassing the LTB check.

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.

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

• 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: LTB for supported monosymmetric shapes uses the AS 4100 member-stability path. A separate flexural-torsional compression-member check is not performed; fabricated or non-standard monosymmetric/non-symmetric compression members outside the Clause 6.3.3 exceptions should verify FTB separately.
• Net sections and connection force distribution: Tension fracture under Cl 7.2 uses gross section area unless a user-supplied tension-factor input is provided. Fastener holes, penetrations, staggered hole paths, and detailed Clause 7.3 connection layouts should be checked separately with Clause 9.1.10 hole deductions where relevant.
• 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 location, and web restraint are not inferred automatically from reactions or point loads. 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%.