Canadian Steel Fy/Fu — Yield and Tensile Strength per CSA G40.21 by Thickness

Complete reference for CSA G40.21 yield strength (Fy) and tensile strength (Fu) for Canadian structural steel grades. Includes thickness-dependent reductions, complete grade tables, design implications, and worked examples for the commonly specified grades 300W, 350W, 350WT, 400W, and 700Q.

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CSA G40.21 Fy/Fu Table — Complete Strength Properties

Per CSA G40.21-18, yield strength decreases with increasing thickness due to reduced through-thickness rolling reduction during plate manufacture. Tensile strength is specified as a range with minimum and maximum values.

Full Grade Table

Design Values for Common Applications

For CSA S16-19 limit states design, the factored material resistance uses:

phi = 0.90 for steel (member resistance) phi_u = 0.75 for fracture at net section

The design values used in Canadian practice:

Thickness Brackets — Yield Strength Reduction Mechanism

CSA G40.21 defines four thickness brackets for yield strength. The reduction in Fy for thicker sections occurs because:

1. Less rolling reduction: Thicker plates undergo fewer rolling passes, resulting in less grain refinement
2. Slower cooling rate: Thicker sections cool more slowly after rolling, producing coarser grain structures
3. Through-thickness constraint: Mechanical property testing of thicker sections samples material with less cumulative deformation

Yield Reduction Percentage by Grade

Higher-strength grades (480W, 700Q) experience larger percentage reductions because their strength depends more heavily on the thermomechanical processing that is less effective in thick sections.

Design Implications of Thickness-Dependent Fy

Column Design

When selecting a W-shape column, the flange thickness determines the applicable Fy:

For heavy column sections (W360×262 and above), the yield strength reduction must be included in the design calculation. The CISC Handbook of Steel Construction provides pre-computed capacities accounting for these reductions.

Beam Design

For flexural members, the flange thickness is typically the controlling factor:

The reduction is typically small (3-8%) for common W-shapes, meaning most Canadian beam designs can conservatively use Fy = 350 MPa without significant error.

Worked Example — Fy Reduction for W360×382 Column

Given: W360×382 Grade 350W column, flange thickness = 65 mm.

Step 1 — Determine thickness bracket: t = 65 mm → 65 < t ≤ 100 mm bracket → Fy = 320 MPa.

Step 2 — Calculate factored axial resistance (simplified, assuming KL/r = 30):

For Fy = 350 MPa: Cr = phi × A × Fy × (1 - 0.5 × (KL/r)/(pi × sqrt(E/Fy))) = 0.90 × 48,700 × 350 × 0.954 / 1000 = 14,620 kN

For Fy = 320 MPa: Cr = 0.90 × 48,700 × 320 × 0.951 / 1000 = 13,340 kN

Reduction: (14,620 - 13,340) / 14,620 = 8.8% — significant and must be included in design.

Tensile Strength Fu and Its Role

The tensile strength Fu is used for:

1. Bolt bearing and tearout: Br = 3.0 × phi_br × t × d_hole × Fu
2. Net section fracture: Tr = phi_u × An × Fu
3. Weld strength: Matching electrode strength to base metal Fu
4. Block shear: Combined shear and tension rupture

Fu by Grade — Design Values

Weldability and Fy/Fu Ratio

The Fy/Fu ratio affects weldability and connection ductility:

A lower Fy/Fu ratio provides greater strain-hardening capacity and ductility. The ratio of 0.78 for 350W is considered optimal for structural applications, providing adequate ductility for plastic hinge formation while maintaining high strength.

Frequently Asked Questions

What is the yield strength of CSA G40.21 Grade 350W steel at 50 mm thickness? For 350W with thickness 40 < t ≤ 65 mm, CSA G40.21 specifies Fy = 340 MPa. This is a 10 MPa reduction from the 350 MPa value for t ≤ 20 mm. The reduction applies to both flanges in W-shapes — if the flange thickness is 50 mm, use Fy = 340 MPa for the entire section. The tensile strength remains Fu = 450-620 MPa regardless of thickness.

How does CSA G40.21 350W yield compare to ASTM A992 steel? ASTM A992 (standard US W-shape specification) has Fy = 345 MPa with no thickness reduction up to 75 mm flange thickness. CSA G40.21 350W matches closely at 350 MPa for thin sections but reduces to 340 MPa at 40-65 mm and 320 MPa at 65-100 mm. For sections with moderate thickness (t ≤ 40 mm), 350W equals or exceeds A992 strength. For very heavy sections, A992 maintains its strength whereas 350W reduces.

What Fu value should be used for bolt bearing calculations in 350W steel? For CSA G40.21 350W, use Fu = 450 MPa (the minimum specified tensile strength) for bearing and tear-out calculations in bolted connections. This is conservative. The actual mill Fu is typically 480-520 MPa, but design must use the specified minimum per CSA S16-19. For 350WT, also use Fu = 450 MPa. For 300W, use Fu = 440 MPa.

Is the yield strength reduction for thickness cumulative with other reductions? No. The thickness-based Fy reduction per CSA G40.21 is the yield strength for that thickness bracket. It already accounts for the material properties. No additional reduction is applied for member size effects. For columns, the overall Cr uses Fy (thickness-adjusted) combined with the buckling reduction factor per CSA S16 Clause 13.3. The two factors are multiplicative: reduced Fy × buckling factor, not additive.

Related Pages

• Canadian Steel Grades — CSA G40.21 Reference
• Canadian Steel Chemical Composition
• Canadian Steel Charpy Values
• CSA S16 Beam Design
• CSA S16 Column Design
• Canadian Beam Sizes
• Beam Capacity Calculator
• Column Capacity Calculator

This page is for educational reference. Strength data per CSA G40.21-18. Verify yield and tensile values against current mill certificates. Thickness-dependent Fy reductions apply per CSA G40.21 Clause 6.2. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent PE/SE verification.

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