Nominal Yield Strength fy by Thickness

EN 10025-2 defines yield strength that varies by product thickness. The nominal yield strength fy is the minimum specified value at the smallest thickness bracket.

Grade t ≤ 16 mm fy 16 < t ≤ 40 mm fy 40 < t ≤ 63 mm fy 63 < t ≤ 80 mm fy 80 < t ≤ 100 mm fy 100 < t ≤ 150 mm fy
S235 235 MPa 225 MPa 215 MPa 215 MPa 215 MPa 195 MPa
S275 275 MPa 265 MPa 255 MPa 245 MPa 235 MPa 225 MPa
S355 355 MPa 345 MPa 335 MPa 325 MPa 315 MPa 295 MPa
S420 420 MPa 400 MPa 390 MPa 370 MPa — —
S460 460 MPa 440 MPa 430 MPa 410 MPa — —

Key observation: Yield strength reduces with increasing thickness. The reduction is approximately 15-20% from the thinnest to the thickest bracket depending on grade. For S355, fy drops from 355 MPa at t ≤ 16 mm to 295 MPa at 100 < t ≤ 150 mm, a 17% reduction.

Ultimate Tensile Strength fu by Thickness

S235 Series

Grade t ≤ 40 mm fu 40 < t ≤ 63 mm fu 63 < t ≤ 100 mm fu 100 < t ≤ 150 mm fu
S235 360-510 MPa 360-510 MPa 350-500 MPa 350-500 MPa

S275 Series

Grade t ≤ 40 mm fu 40 < t ≤ 63 mm fu 63 < t ≤ 100 mm fu 100 < t ≤ 150 mm fu
S275 370-530 MPa 370-530 MPa 360-520 MPa 350-510 MPa

S355 Series

Grade t ≤ 40 mm fu 40 < t ≤ 63 mm fu 63 < t ≤ 100 mm fu 100 < t ≤ 150 mm fu
S355 470-630 MPa 470-630 MPa 450-610 MPa 440-600 MPa

S420 and S460 Series

Grade t ≤ 40 mm fu 40 < t ≤ 63 mm fu 63 < t ≤ 100 mm fu
S420 520-680 MPa 520-680 MPa 500-660 MPa
S460 540-720 MPa 540-720 MPa 530-710 MPa

fy/fu Ratio and Ductility

EN 1993-1-1 Clause 3.2 specifies ductility requirements for structural steels. The fy/fu ratio and elongation must satisfy:

Parameter EN 1993-1-1 Requirement Typical S235 Typical S275 Typical S355 Typical S460
fu/fy ratio ≥ 1.10 (recommended) 1.35-1.55 1.35-1.55 1.30-1.45 1.15-1.30
Elongation at break ≥ 15% (recommended) 24-28% 22-26% 20-24% 17-22%
fy/E — 0.00112 0.00131 0.00169 0.00219

The fu/fy ratio is important for:

Design Values per EN 1993-1-1

For EN 1993 design, use the following partial factors:

The design yield strength is fy_d = fy / γ_M0 for most limit states. For net section fracture at bolt holes, use fu / γ_M2.

International Grade Comparisons

European AISC (US) AS/NZS (Australia) CSA G40.21 (Canada)
S235JR A36 Grade 250 260W
S275JR A572 Gr 42 Grade 300 300W
S355JR A572 Gr 50 Grade 350 350W
S420JR A572 Gr 60 Grade 400 400W
S460JR A572 Gr 65 — —

Note that A572 Grade 50 has fy = 345 MPa versus S355's 355 MPa — these are closely comparable. However, A36 (fy = 250 MPa) and S235JR (fy = 235 MPa) have a slight difference, so substitution requires a 6% area increase for equivalent axial capacity.

Worked Example — Strength Selection for Bolted Connection Plate

Problem: A tension splice connection uses S355 plate, 28 mm thick. The connection is designed per EN 1993-1-8 with M24 Grade 10.9 bolts in 26 mm clearance holes. Determine fy and fu for cross-section checks (γ_M0) and net section fracture (γ_M2).

Step 1 — Determine fy by Thickness per EN 10025-2 Table 7: Plate thickness 28 mm falls in the 16 < t ≤ 40 mm bracket. For S355: fy = 345 MPa (minimum guaranteed per standard). Design yield strength: fy_d = fy / γ_M0 = 345 / 1.00 = 345 MPa per EN 1993-1-1 Clause 6.2.

Step 2 — Determine fu per EN 10025-2: For S355 at t ≤ 40 mm: fu = 470-630 MPa. Use the minimum value (fu = 470 MPa) for conservative design. This is the value required by EN 1993-1-8 Clause 3.6 for bolt bearing resistance calculations.

Step 3 — Gross Section Tension Resistance per EN 1993-1-1 Clause 6.2.3: N_pl,Rd = A × fy / γ_M0 For a 200 mm wide × 28 mm plate: A = 200 × 28 = 5600 mm² N_pl,Rd = 5600 × 345 / 1.00 = 1932 kN.

Step 4 — Net Section Fracture per EN 1993-1-1 Clause 6.2.2.2: For a section with 2 bolt holes (d0 = 26 + 2 = 28 mm allowance per EN 1993-1-8 Clause 3.6): A_net = (200 - 2 × 28) × 28 = 144 × 28 = 4032 mm² N_u,Rd = 0.9 × A_net × fu / γ_M2 = 0.9 × 4032 × 470 / 1.25 = 1365 kN.

Step 5 — fu/fy Ratio Check per EN 1993-1-1 Clause 3.2: fu/fy = 470 / 345 = 1.362 > 1.10 (minimum required). Ductility requirement satisfied.

Step 6 — Bearing Resistance per EN 1993-1-8 Table 3.4: End distance e1 = 40 mm, edge distance e2 = 35 mm, bolt pitch p1 = 70 mm. For M24 bolts in 28 mm plate: α_d = min(e1/3d0, p1/3d0 - 1/4, fub/fu, 1.0) = min(40/84, 70/84 - 0.25, 1000/470, 1.0) = min(0.476, 0.583, 2.13, 1.0) = 0.476. k1 = min(2.8×e2/d0 - 1.7, 1.4×p2/d0 - 1.7, 2.5) = min(2.8×35/28 - 1.7, ..., 2.5) = min(1.80, ..., 2.5) = 1.80. F_b,Rd = k1 × α_d × fu × d × t / γ_M2 = 1.80 × 0.476 × 470 × 24 × 28 / 1.25 = 217 kN per bolt.

Result: Gross section governs (1932 kN). Net section (1365 kN) provides adequate capacity with margin. Bearing per bolt = 217 kN.

Frequently Asked Questions

What is the yield strength of S355 steel at 50 mm thickness?

S355 steel at 50 mm thickness falls in the 40 < t ≤ 63 mm bracket. Per EN 10025-2, the minimum yield strength is 335 MPa at this thickness range. The tensile strength remains 470-630 MPa.

What is the difference between S235JR and S235J2 mechanical properties?

S235JR and S235J2 have identical yield strength (235 MPa for t ≤ 16 mm) and tensile strength (360-510 MPa for t ≤ 40 mm). The difference is in Charpy impact testing only: JR requires 27 J at 20°C, J2 requires 27 J at -20°C.

What fu value should I use for bolt bearing resistance per EN 1993-1-8?

For bolt bearing resistance per EN 1993-1-8 Clause 3.6, use the ultimate tensile strength fu of the connected plate (not the bolt). For S355 steel, use fu = 470 MPa (minimum for t ≤ 40 mm). Include the partial factor γ_M2 = 1.25 in the resistance calculation.

Related Pages

Educational reference only. Mechanical properties per EN 10025-2:2019. Design partial factors per EN 1993-1-1:2005 + A1:2014. Verify fy and fu against mill certificates per EN 10204 Type 3.1. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent verification.

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