steelComplexBeam

Beam reactions link to the columns and footings below, so load changes propagate downstream automatically. Design steel beams to AS 4100:1998 (R2016) with multiple spans and load cases. For projects that require compliance with the superseded code edition.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 | | -------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | What it checks | Structural model, Load combinations (AS/NZS 1170.0), Section compactness (Clause 5.2), Design moment capacity (Clauses 5.1 to 5.3), Shear capacity (Clause 5.11), Bearing capacity (Clause 5.13), Deflection checks (Clause 2.3), Section properties | #### Calculation method ##### Structural model The calculator uses a finite element method (FEM) engine to model the steel beam. Supports are defined at any position along the member as pins or rollers. The FEM solver produces moment, shear, and deflection diagrams for every AS/NZS 1170.0 load case combination, and the governing case for each check is reported. ##### Load combinations (AS/NZS 1170.0) Loads are entered by type: permanent action (G), imposed action (Q), wind (W), and earthquake (E). The character of Q (floor, roof, storage) determines the combination factors psi\_s and psi\_l. The calculator generates all required strength and serviceability load case combinations and evaluates every check against each. ##### Section compactness (Clause 5.2) For bending about the major and minor axes, flange and web element slenderness ratios (lambda\_e) are compared to the yield limit (lambda\_ey) and plastic limit (lambda\_ep) from AS 4100:1998. The section is classified as compact, non-compact, or slender in each axis: * **Compact** (lambda\_s ≤ lambda\_sp): effective section modulus Z\_e = S (plastic) * **Non-compact**: Z\_e interpolated between S and Z\_11 * **Slender**: Z\_e = Z\_11 reduced by the slenderness ratio ##### Design moment capacity (Clauses 5.1 to 5.3) **Section moment capacity (phiM\_s):** the product of phi, Z\_e, and yield stress f\_y. **Member moment capacity (phiM\_bx):** reduced from phiM\_s to account for lateral torsional buckling. The calculation uses: * Restraint classification for each segment (F, P, L, or U type at each end) * Moment modification factor alpha\_m, computed from the quarter-point moment values M2, M3, M4 across the segment * Slenderness reduction factor alpha\_s, derived from the reference buckling moment M\_oa **Proportioning method:** For sections with a slender compression flange (AS 4100:1998 Cl. 5.2.4), the calculator computes the effective compression flange area A\_fc, effective tension flange area A\_ft, the minimum flange effective area A\_fm, and the moment capacity of the flanges alone M\_f. This is an important check for asymmetric sections including PFC profiles. **Utilization:** **moment utilization** = M\*x / phiM\_sx ≤ 1.0 ##### Shear capacity (Clause 5.11) Nominal shear yield capacity V\_w is derived from the web area A\_w and yield stress. The shear buckling capacity V\_b accounts for panel aspect ratio via the buckling coefficient alpha\_v. The governing shear capacity V\_v is the lesser of V\_w and V\_b. A combined shear-moment interaction check is performed where both M\* and V\* are significant. ##### Bearing capacity (Clause 5.13) Bearing capacity at each support is checked in two modes: end bearing and interior bearing. The calculation includes the web buckling contribution via the member section constant alpha\_b, the form factor k\_f, and the member slenderness reduction factor alpha\_c. The bending-bearing interaction is then checked at each support. ##### Deflection checks (Clause 2.3) Three deflection limits are checked independently per span: 1. **Short-term deflection** (delta\_s), under short-term service load case 2. **Long-term deflection** (delta\_l), accounting for creep and shrinkage 3. **Imposed load deflection** (delta\_Q), Q component only Each is compared to the user-defined L/n criterion or optional absolute limit. ##### Section properties Section properties (I\_11, I\_22, Z\_11, S\_11, J, I\_w, A\_g, A\_w, f\_y, f\_u) are drawn from the AU/NZ hot-rolled steel section database. The principal axis angle alpha and centroid offsets x\_L, y\_L handle asymmetric sections such as angles and PFCs. ##### Load linking Support reactions are made available for linking to downstream column and footing calculations. Changing any load input propagates updated reactions automatically through the project. ## How to use it Open it from **Run calc** in the About this calculator panel above. 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 The calculator designs steel beams to AS 4100:1998 (R2016) using limit states design. Load cases follow AS/NZS 1170.0 and 1170.1. Both strength and serviceability limit states are checked. This is the legacy edition of the standard, new projects should use the AS 4100:2020 calculator. Key inputs include the steel section and grade, total beam length, lateral restraint classification and spacing, support positions, distributed and point loads by load type (G, Q, W, E), height of load application relative to the shear center, and per-span deflection limit criteria. Outputs include: design moment demand M*x vs. member moment capacity phiM\_sx, shear demand V* vs. capacity phiV\_v, shear-moment interaction, bearing demand R\* vs. capacity phiR\_b at each support, bending-bearing interaction, and short-term, long-term, and imposed-load deflections. The proportioning method for calculating tension flange effective area is available where applicable. For sections where the compression flange is slender, the calculator applies the AS 4100:1998 proportioning method: it computes the effective compression flange area A\_fc, the effective section modulus, and the factored moment capacity of the flanges alone phiM\_f. This applies to PFC, UA, and custom sections where relevant. Yes. The FEM engine supports unlimited spans, multiple supports, and any combination of distributed and point loads on individual spans. The governing load case for each check (moment, shear, bearing, deflection) is identified automatically across all combinations. Yes, beam reactions link directly to connected column and footing calculations. When inputs change, all downstream calcs update automatically. ## 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). Design steel beams to AS 4100:2020 with multiple supports and loads. Floor- and roof-beam presets cut repetitive entry. Design steel beams to NZS 3404.1:1997 (Amdt 2) with multiple supports and loads. Checks compactness, LTB, shear, bearing and deflection. Design cold-formed steel beams to AS/NZS 4600:2018 using the Direct Strength Method, with a built-in database of Australian CFS sections. Analyze simple and continuous beams under AS/NZS 1170.0:2002 (Amdt 5) load combinations, with governing demands identified by load case.