UK Steel Charpy V-Notch Values — BS EN 10025-2 Subgrades JR/J0/J2/K2

Charpy V-notch (CVN) impact energy requirements for UK structural steel grades per BS EN 10025-2:2019, covering subgrades JR, J0, J2, and K2 for S275 and S355. Includes UK National Annex modifications from BS EN 1993-1-10 and guidance for fracture-critical applications in UK building and bridge construction.

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Charpy Impact Requirements — BS EN 10025-2

The subgrade designation indicates the guaranteed Charpy V-notch impact energy at a specified test temperature. This is critical for fracture-safe design per EN 1993-1-10 and is mandatory for all primary structural steel in UK construction.

Subgrade Test Temp Min Energy Equivalent BS 4360 UK Application
JR +20°C 27 J 43A / 50A Interior members, secondary steel, non-fracture-critical
J0 0°C 27 J 43B / 50B Standard building frames, exterior members in mild UK climate
J2 -20°C 27 J 43C / 50C Primary members, bridges, crane girders, UK standard specification
K2 -20°C 40 J 43D / 50D Fracture-critical bridges, fatigue-loaded, cold climate

UK NA Modifications per BS EN 1993-1-10

The UK National Annex to BS EN 1993-1-10 provides fracture toughness requirements based on minimum service temperature, steel grade, thickness, and stress level:

Minimum Air Temperature Subgrade for S355, t ≤ 25 mm, σEd ≤ 0.75fy Subgrade for S355, t > 25 mm
-5°C (most UK lowlands) J0 J2
-10°C J2 J2
-15°C (Scotland, exposed) J2 K2
-20°C (highlands, bridges) K2 K2*

*For t > 50 mm in K2 applications, consider S355NL (EN 10025-3) as an alternative.

Charpy Values by Grade and Thickness

While the minimum energy is 27 J for J0/J2 and 40 J for K2, typical achieved values for UK-rolled sections are significantly higher:

Grade Guaranteed Min Typical Achieved (UK mill data)
S275JR 27 J at +20°C 80-120 J at +20°C
S275J2 27 J at -20°C 60-100 J at -20°C
S355JR 27 J at +20°C 70-110 J at +20°C
S355J2 27 J at -20°C 50-90 J at -20°C
S355K2 40 J at -20°C 60-100 J at -20°C

The typical achieved values reflect the inherent toughness of UK-manufactured structural sections. Actual values vary by heat, section size, and rolling practice. Mill certificates from British Steel (Scunthorpe) provide the verified test results for each cast.

Charpy Testing Requirements per BS EN 1090-2

For UK fabrication to BS EN 1090-2 execution classes, Charpy testing frequency depends on the execution class (EXC):

The test results must be traceable to the cast, heat, and section delivered to site. UK fabricators maintain test records for the design life of the structure.

Worked Example — Fracture Toughness Check for Welded Beam Connection

Given: Beam 533×210 UB 92, S355J2, flange thickness 15.6 mm. Welded moment connection. Site location: Edinburgh (minimum service temperature −12°C). Stress level at connection: σ_Ed = 0.6 f_y.

UK NA requirement (EN 1993-1-10): For S355, t = 15.6 mm ≤ 25 mm, and −12°C service temperature, the required subgrade is S355J2 (27J at −20°C). This provides an 8°C margin below the service temperature, satisfying the UK NA requirements.

If the same beam were in Glasgow (min −15°C) at σ_Ed = 0.8 f_y, the UK NA would require S355K2 (40J at −20°C) for t > 25 mm. At t = 15.6 mm, S355J2 would still be adequate.

Design Resources

Frequently Asked Questions

What Charpy subgrade is standard for UK building structures?

S355J2 (27 J at -20°C) is the standard specification for primary structural steel in UK multi-storey buildings. For internal secondary members in heated buildings, S275JR (27 J at +20°C) is sometimes accepted. For bridges, fracture-critical members, and exposed structures in Scotland, S355K2 (40 J at -20°C) or S355NL (EN 10025-3, 27 J at -50°C) is typically specified.

What is the difference between JR, J0, J2, and K2 subgrades?

All indicate Charpy V-notch impact properties. JR guarantees 27 J at +20°C (room temperature), J0 guarantees 27 J at 0°C, J2 guarantees 27 J at -20°C, and K2 guarantees 40 J at -20°C. The yield and tensile strength are identical across subgrades for a given grade (e.g., all S355 subgrades have fy = 355 MPa for t ≤ 16 mm). The cost premium for J2 over JR is approximately 5-8 %.

How does the UK National Annex modify EN 1993-1-10 Charpy requirements?

The UK NA to BS EN 1993-1-10 provides simplified tables relating minimum service temperature, steel grade, thickness, and stress level to the required subgrade. For most UK lowland sites (-5°C minimum), S355J2 is adequate for t ≤ 25 mm at stress levels up to 0.75fy. For exposed Scottish sites (-15°C), K2 is the minimum for primary members.

What Charpy values should I specify for UK bridges?

For UK highway bridges designed to BS EN 1993-2 and BS EN 1993-1-10, the minimum Charpy requirement is typically S355K2 (40 J at -20°C) for main girders and cross-girders. For welded tension members in fracture-critical locations, S355NL (27 J at -50°C) may be required per the UK NA to BS EN 1993-2. The weld metal must also meet matching Charpy requirements per BS EN 1090-2.

Related Pages

Educational reference only. All design values are per BS EN 1993-1-1:2005 + UK National Annex and BS EN 10025-2:2019. Verify all values against the current editions of the standards and the applicable National Annex for your project jurisdiction. Designs must be independently verified by a Chartered Structural Engineer registered with the Institution of Structural Engineers (IStructE) or the Institution of Civil Engineers (ICE). Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent professional verification.