Design checks (AS 4100)

CivilKit Studio computes AS 4100 steel member capacities automatically when you solve, and reports per-member utilisation - turning the analysis into a design tool.

How to get a design check

1. Assign a real section. Open a member's inspector → Browse sections and pick a catalogue section (the check needs section geometry - depth, flange, web, Zx/Sx - that the catalogue carries). The gallery's "real section" models already have these.
2. Solve (S) with Linear static or P-Delta.
3. Read the results in the Design (AS 4100) tab of the results panel, or select a member to see its check in the inspector ("Result · AS 4100 design").

What's reported

Column	Meaning
Class	Section compactness - compact / non-compact / slender (Cl 5.2)
φMsx	Design section moment capacity (Cl 5.2), kN·m
φMbx	Design member moment capacity - lateral-torsional buckling (Cl 5.6), kN·m
M*x	Design bending moment from the analysis (max over the member), kN·m
φNc	Design member compression capacity (Cl 6.3), governing axis, kN
N*c	Design compression from the analysis, kN
Utilisation	Governing demand/capacity ratio
Status	OK (≤ 1) or OVER (> 1)

Utilisation is the worst of the bending (M*/φMb) and compression (N*/φNc) ratios.

What governs each ratio

Hover a utilisation cell to see what drives it, e.g. "0.77 - governed by combined M-N (Cl 8.3/8.4)" or "...governed by shear V*/φVv" - so you can read the design table without opening each member's inspector.

Working the design table

The Design (AS 4100) tab has a few controls for working through a real model:

• Failures only - filter the table to members failing the check (utilisation

  1), so you fix the red ones first.

• Group by section - engineers design to the worst member of each section (a "design member"), not member by member. This toggle collapses the per-member table to one row per distinct section, showing the section name, the member count, and the governing (worst) member with its utilisation and status. Click a row to select that governing member. Toggle off to return to the full per-member table. It also carries the steel mass per section group (kg / t), which drives cost and take-off.
• Gov. case - with load combinations, this column shows which Σ combination governs each member's utilisation, so you can see the driving case at a glance.

Serviceability

Alongside strength, the panel reports a serviceability deflection check: the worst-member span / deflection ratio against a configurable limit, stated with a verdict, e.g. "L/δ = 1/108 vs L/250 ✗" (✓ when within limit). The pass test uses the unrounded ratio so a borderline case is not masked by rounding.

The limit is set in Settings → Deflection limit (SLS) - L/180, L/250 (default), L/300 or L/360 - to suit the member and finish (e.g. L/180 for cantilevers, L/360 for brittle finishes). The chosen limit applies live in the design panel and the PDF report, which always agree, and persists across a refresh.

Scope & assumptions (read before professional use)

This is an early, transparent slice - the capacities are validated against the ASI/OneSteel Design Capacity Tables (see AS 4100 API), but the member-design inputs use simplifying assumptions, shown in the panel footnote:

• Steel grade: AS/NZS 3679.1 Grade 300, with fy by flange thickness (320 / 300 / 280 MPa for ≤11 / ≤17 / >17 mm).
• Effective length Le = the member's length - no intermediate restraints are modelled. If your member is restrained between ends, φMb / φNc are conservative; a restraint editor is planned.
• αm = 1.0 (uniform-moment, conservative) for φMb.
• φNc uses r = √(I/A) per axis (minor axis usually governs).
• Combined actions (Cl 8.3/8.4) are applied - the reported Utilisation is the M-N interaction, evaluated on both axes (major φMbx and minor φMby), and the worse axis governs. φNt (tension) and φVv (shear) are also shown.
• Biaxial note: the per-axis combined checks each use the full axial force; the full Cl 8.4.5 biaxial interaction (combined Mx+My in one inequality) is a planned refinement, so for members with large moments about both axes the utilisation is slightly non-conservative versus that interaction.

Verify before professional use

Always confirm restraints, section data, steel grade and the governing load combination against the standard and a manufacturer catalogue before relying on these numbers.