Specialised steel checks

CivilKit Studio includes specialised design checks beyond the standard AS 4100 member capacities. These run independently of the analysis: you enter dimensions (or fill them from a selected member) and the engine computes the check directly.

How to use

1. Open the panel - click Special steel checks (fire, fatigue, cellular) in the Tools menu, Section & member column.
2. Select check type - choose from the dropdown.
3. Enter inputs - either manually or:
   • Select a member in the model.
   • Click Fill from member to auto-populate section dimensions.
4. Run check - click Run check.
5. Add to report - click Add to report to save a calc card to the PDF report.

A refused check is never a silent zero

If a value cannot be computed, the result shows the reason instead of a passing number. A stamped calculation must never show a passing result for something that was never actually checked.

Check types

Check	Standard	Purpose
Fire	AS 4100-1998 Section 12	Temperature-dependent capacity for fire resistance
Fatigue	AS 4100 Section 11	S-N curve fatigue with Palmgren-Miner damage
Cellular beam	AS 4100 + SCI P355	Castellated/cellular beam net/gross properties
Tapered member	AS 4100 Sections 5 & 6	Web-tapered I-section member design
Composite beam	AISC 360-16 Chapter I	Steel-concrete composite member design

Verification status

The fire and fatigue checks follow AS 4100 directly. The cellular, tapered and composite checks are intentionally conservative first-pass methods (see the per-check notes below) and are not yet calibrated against a published worked example. Treat all results as first-pass checks and verify restraints, detailing and material grades before professional use.

Fire check

Temperature-dependent yield and modulus reduction under standard fire exposure, using the limiting-temperature method from AS 4100 Section 12.

Inputs

Field	Description	Units
Ambient capacity	Design capacity at ambient temperature	MPa
Fire demand	Required capacity at fire temperature	MPa
Fire duration	Standard fire exposure time	minutes
Section factor	Hp/A (heated perimeter / area)	m^-1
Exposure	Four-sided or three-sided	-

Outputs

• Steel temperature at fire time
• Limiting temperature
• Temperature margin
• Load ratio
• OK/OVER status

Valid range

The calculation is valid for section factors 15 - 275 m^-1 (2 - 35 m^2/tonne) and steel temperatures up to 905 degrees C. Values outside this range are clamped.

Code reference: rust_solver/fem-core/src/as4100_fire.rs

Fatigue check

S-N curve fatigue assessment for normal-stress details, with Palmgren-Miner damage summation across a stress spectrum.

Inputs

Field	Description	Units
Stress spectrum	Stress range pairs (cycles, MPa)	-
Detail category	Cat160-Cat36 per Table 11.5.1	-
Thickness t	Thickness at detail location	mm
Yield strength fy	Steel yield strength	MPa
Capacity factor phi	Typically 0.7	-
Apply beta_tf	Thickness correction for welds	-

Outputs

• Damage sum
• Applicable flag
• OK/OVER status

Thickness correction

Beta_tf = (25/t)^0.25 applies for transverse welds when t > 25 mm. Toggle this with the Apply thickness fatigue reduction checkbox.

Code reference: rust_solver/fem-core/src/as4100_fatigue.rs

Cellular beam check

Geometry and capacity calculations for fabricated cellular (circular web openings) and castellated (hexagonal web openings) beams. The checks follow AS 4100 for section and member capacity, supplemented by SCI P355 concepts for Vierendeel bending and web-post buckling.

Inputs

Field	Description	Units
Depth d	Overall beam depth	mm
Flange bf	Flange width	mm
Flange tf	Flange thickness	mm
Web tw	Web thickness	mm
Hole do	Opening diameter	mm
Spacing s	Hole centre-to-centre	mm
Length	Member length	mm
Effective length Le	For LTB	mm
fy	Yield strength	MPa
Alpha m	Moment gradient case (0-4)	-
Alpha b	Section constant	-

Outputs

Output	Meaning
phi M gross	Full-section flexural capacity
phi M net	Net-section moment capacity
phi M b	LTB capacity
phi V net	Net vertical shear
phi M vierendeel	Vierendeel moment capacity
phi V web post	Web-post shear capacity

Conservative web-post model

Web-post buckling uses a strut-on-elastic-foundation model, a deliberately conservative first pass following SCI P355 guidance. It is not yet calibrated against a published SCI P355 worked example. Verify against SCI P355 for your specific geometry.

Code reference: rust_solver/fem-core/src/as4100_cellular.rs

Tapered member check

Capacity checks for linearly web-tapered doubly-symmetric I-section members. The check evaluates at the shallowest section along the member, matching the conservative approach documented in STAAD.Pro for AS 4100 tapered design.

Inputs

Field	Description	Units
Length	Member length	mm
Depth dA	Depth at end A	mm
Depth dB	Depth at end B	mm
Flange bf	Flange width	mm
Flange tf	Flange thickness	mm
Web tw	Web thickness	mm
Effective length Le	For buckling	mm
fy	Yield strength	MPa
Alpha m	Moment gradient case (0-4)	-
Alpha b	Section constant	-

Outputs

Output	Meaning
Governing x	Position of governing section
Governing d	Depth at governing section
phi Ms	Section capacity at shallowest
phi Mb	Member LTB capacity
phi Nc	Compression capacity
Taper ratio	(dA - dB) / dA

Shallowest-section approach

This check evaluates capacity at the shallowest cross-section, which is conservative where the governing limit state is at the deep end. It matches the conservative shallowest-section approach documented for STAAD.Pro AS 4100 tapered design, and is not yet quantified against a published worked example.

Code reference: rust_solver/fem-core/src/as4100_tapered.rs

AISC 360 composite beam check

Steel-concrete composite beam design under positive bending, using the AISC 360-16 Chapter I method. Covers effective slab width, headed-stud shear strength, fully-composite plastic moment capacity, and partial-composite interpolation.

Inputs

Field	Description	Units
As	Steel area	mm^2
Depth d	Steel section depth	mm
fy	Steel yield strength	MPa
Slab tc	Concrete thickness	mm
f'c	Concrete strength	MPa
Effective width b	Tributary width	mm
Stud diameter	Shear stud diameter	mm
Stud fu	Stud ultimate strength	MPa
Number of studs	Stud count	-
phi	Capacity factor (0.9)	-

Outputs

Output	Meaning
phi Mn full	Full shear connection moment
phi Mn partial	Partial shear connection moment
Degree of shear connection	Ratio of actual to full
Horizontal shear	Vh from composite action
Stud shear	Total stud shear capacity

Known simplifications

Solid flat slab only (no ribbed metal deck). Positive bending only. The plastic moment uses a simplified stress block rather than full plastic-neutral-axis location logic, so results are conservative; this has not yet been quantified against a published worked example.

Code reference: rust_solver/fem-core/src/aisc360_composite.rs

AS 2327 composite beam

For Australian composite beam design to AS 2327, see Concrete & composite design which covers the AS 2327 check integrated into the member inspector.

Report integration

Each successful check adds a calculation card to the report with all inputs and outputs, the applicable standard header (AS 4100 or AISC 360), and an OK/OVER verdict. Cards are exported via File ▸ Report (PDF).

Verify before professional use

All steel checks use simplifying assumptions and simplified calculation methods. Confirm section data, material grades, restraint conditions, and the governing load combination against the applicable standard before relying on these numbers for professional design.

What is not covered yet

• AISC DG31 and DG25 specific methods - the cellular and tapered checks follow AS 4100 supplemented by SCI P355 and STAAD.Pro approaches, not the AISC design-guide tapered-beam or cellular-beam methods directly, and are not yet calibrated against a published worked example.
• Eurocode 4 composite - no EC4 composite beam check (AS 2327 and AISC 360-16 are covered).
• Ribbed metal deck composite - the AISC 360 composite check assumes a solid flat slab only.
• Negative bending composite - no composite check for negative moment regions with slab rebar.
• Shear-stress fatigue - fatigue check covers normal-stress detail categories only (Cat36 - Cat160). Shear-stress fatigue (limited to categories 80 and 100 in AS 4100) is not yet implemented.
• Protection design for fire - the fire check covers the structural adequacy limit state only, not the insulation or integrity criteria that form part of a full fire resistance level assessment.