180x20FL Flat Bar
AS/NZS 3679.1Grade 300The 180x20FL is a flat bar to AS/NZS 3679.1. It is 180 × 20 mm, has a mass of 28.3 kg/m and a gross area of 3600 mm². Its major-axis second moment of area is Ix = 0.120 × 10⁶ mm⁴ and in Grade 300 (fy = 280 MPa) its section moment capacity is φMsx = 4.5 kNm. Download its free DXF drawing (a true-scale CAD outline) below, or print the dimensioned drawing sheet.
Also written as: 180 x 20 flat bar, 180x20 FL
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Dimensions
| Symbol | Property | Value | Unit |
|---|---|---|---|
| b | Width | 180 | mm |
| t | Thickness | 20 | mm |
Section properties
| Symbol | Property | Value | Unit |
|---|---|---|---|
| m | Mass per metre (nominal) | 28.3 | kg/m |
| Ag | Gross cross-section area | 3600 | mm² |
| Ix | Second moment of area about x-axis | 0.120 | 10⁶ mm⁴ |
| Zx | Elastic section modulus, x-axis | 12.0 | 10³ mm³ |
| Sx | Plastic section modulus, x-axis | 18.0 | 10³ mm³ |
| rx | Radius of gyration, x-axis | 5.8 | mm |
| Iy | Second moment of area about y-axis | 9.72 | 10⁶ mm⁴ |
| Zy | Elastic section modulus, y-axis | 108 | 10³ mm³ |
| Sy | Plastic section modulus, y-axis | 162 | 10³ mm³ |
| ry | Radius of gyration, y-axis | 52.0 | mm |
| J | Torsion constant | 446 | 10³ mm⁴ |
| As | External surface area per metre | 0.400 | m²/m |
| As/t | External surface area per tonne | 14.2 | m²/t |
Axes: x-x is parallel to the wide face (weak axis); y-y is the strong axis.
Design capacities to AS 4100
| Symbol | Property | Value | Unit |
|---|---|---|---|
| Steel grade | 300 (AS/NZS 3679.1) | ||
| fy | Yield stress used | 280 | MPa |
| fu | Tensile strength | 440 | MPa |
| kf | Form factor (Cl. 6.2.2) | 1.000 | |
| Section class, x-axis (Cl. 5.2) | Compact | ||
| Zex | Effective section modulus, x-axis | 18.0 | 10³ mm³ |
| φMsx | Section moment capacity, x-axis | 4.5 | kNm |
| Section class, y-axis | Compact | ||
| Zey | Effective section modulus, y-axis | 162 | 10³ mm³ |
| φMsy | Section moment capacity, y-axis | 40.8 | kNm |
| φNs | Section compression capacity (Cl. 6.2.1) | 907 | kN |
| φNt | Tension capacity, gross section (Cl. 7.2, kt=1, An=Ag) | 907 | kN |
| αb | Compression member section constant (Table 6.3.3) | 0.5 |
For restraint types, ktklkr and αm, use the lateral restraint calculator.
Instant check only. Effective lengths and moment modification factors must be determined by the designer in accordance with AS 4100 Cl. 4.6, 5.6.3 and 6.3.2. Not a substitute for a qualified engineer: see the disclaimer.
Other flat bars
Relevant Australian Standards
- AS/NZS 3679.1:2016 Structural steel – Part 1: Hot-rolled bars and sections
Specifies chemical composition, mechanical properties and tolerances for hot-rolled universal beams and columns, channels, angles, flats and bars in Grades 300 and 350. - AS 4100:2020 Steel structures
The Australian design Standard for steel members and connections. Covers section classification (Section 5), member moment capacity including lateral-torsional buckling (5.6), shear (5.11), axial compression (Section 6), tension (Section 7) and combined actions (Section 8).
See all Australian Standards for structural steel.
Properties are calculated from nominal dimensions, including root and toe radii, as described in notation & method. Mass is the nominal catalogue mass; the calculated mass at 7850 kg/m³ is 28.26 kg/m. Verify against current manufacturer literature before use in design. Spotted an error? Report it.