125PFC AS/NZS 3679.1 Grade 300 — Australian Parallel Flange Channel Section Properties
125PFC is an Australian PFC (Parallel Flange Channel) per AS/NZS 3679.1 hot-rolled structural steel section. Standard Australian PFC dimensions. Verify against Liberty OneSteel / InfraBuild section catalog.
Dimensions (Metric)
| Property | Value | Unit |
|---|---|---|
| Depth (d) | 125 | mm |
| Flange Width (bf) | 60 | mm |
| Flange Thickness (tf) | 7.5 | mm |
| Web Thickness (tw) | 4.5 | mm |
| Cross-Sectional Area (A) | 13.9 | cm² |
| Mass | 14.0 | kg/m |
Elastic Section Properties (Metric)
| Property | Strong Axis (X-X) | Weak Axis (Y-Y) | Unit |
|---|---|---|---|
| Moment of Inertia (I) | 361 | 27 | cm⁴ |
| Elastic Section Modulus (S) | 58 | 9 | cm³ |
| Plastic Section Modulus (Z) | 66 | 14 | cm³ |
| Radius of Gyration (r) | 5.09 | 1.39 | cm |
Torsional Properties
| Property | Value | Unit |
|---|---|---|
| Torsional Constant (J) | 2 | cm⁴ |
| Distance Between Flange Centroids (ho) | 11.75 | cm |
Section Profile Summary
Unlike doubly-symmetric sections, channel bending about the weak axis produces twist. Where weak-axis flexure is unavoidable, provide torsional restraint at close intervals or switch to a hollow section.
At 125 mm deep — a shallow section suitable for girts, rails, struts, and mild-load secondary members.
Key Design Checks (AS 4100)
| Check | Formula | This Section |
|---|---|---|
| Plastic moment | Mp = Zx × Fy | 20 kNÃÂ÷m |
| Deflection | Δ = 5wL⁴/(384EIx) | Use Ix = 361 cm⁴ |
| Torsion | St. Venant = GJ/L | J = 2 cm⁴ |
| Column buckling | KL/r → Fcr | r_x = 5.09 cm |
Design Notes
- Section asymmetry: The shear center lies outside the web. Loads not applied through the shear center produce torsion. Provide intermediate torsional restraints or stiffeners when the load eccentricity is significant.
- Lateral-torsional buckling: Check Cb (moment modification factor) per AS 4100 Chapter F — channels are more sensitive to load height effects than doubly-symmetric sections.
- Web crippling at supports: For channels used as beams, bearing stiffeners may be needed at concentrated load points per AS 4100 Section J10.
Verification (AS 4100): All designs using this section must be verified by a licensed Professional Engineer. Before finalizing member selection, check beam-column interaction (P-M), lateral-torsional buckling, serviceability deflections, and all connection limit states. See Engineering Disclaimer.
Worked Example: Industrial floor beam — 125pfc
Scenario: Light industrial floor — forklift traffic and storage considerations. Simply supported channel, 2.3 m span, 3 m tributary width. Service loads: 5.0 kPa dead + 7.5 kPa live (37.5 kN/m total).
Given:
- Span L = 2250 mm (2.3 m)
- Total service load w = 37.5 kN/m
- Live load portion w_L = 22.5 kN/m
- Section 125pfc: Ix = 3.6 × 10⁶ mm⁴, Sx = 58,000 mm³, Zx = 66,000 mm³
- Steel: fy = 300 MPa, E = 200,000 MPa
- Design moment resistance: φMn = 0.9 × Zx × fy = 18 kNÃÂ÷m
Step 1 — Live load deflection:
Δ_LL = 5 w_L L⁴ / (384 E Ix)
Δ_LL = 5 × 22.5 × (2250)⁴ / (384 × 200000 × 3,610,000)
Δ_LL = 10.4 mm
Step 2 — Deflection limit (L/250):
Δ_limit = L / 250 = 2250 / 250 = 9.0 mm
Step 3 — Dead + live deflection:
Δ_total = 17.3 mm
Step 4 — Design check:
⚠ Live load deflection exceeds L/250 — consider a deeper section, reduce tributary, or shorten the span.
Verify the design moment M*_Ed (from factored loads 1.35G + 1.5Q per AS 4100) does not exceed φMn = 18 kNÃÂ÷m. Also confirm shear resistance and bearing details at the supports.
Related Resources
- Steel Beam Capacity Calculator
- Column Capacity Calculator
- Beam Deflection Calculator
- Section Properties Calculator
- Steel Grades Reference
- Section Comparison Tool
Design Resources
- Section Properties Lookup — Compare with similar sections
- Steel Beam Sizes Reference — Standard beam dimensions
Educational reference only. Verify all section properties against the current AS 4100 Manual and mill certificates before design. Results are PRELIMINARY — NOT FOR CONSTRUCTION.