UK Steel Properties — BS EN 10025 Material Data

This reference covers steel properties for UK steel design per BS EN 10025-2:2019 and UK NA to EN 1993-1-1. Material selection for UK structural steelwork depends on yield strength, tensile strength, ductility, and toughness requirements determined by the design loads, fabrication methods, and service conditions.

Design requirements, worked examples, and practical design guidance are provided for common design office applications.

Code Reference: BS EN 10025-2:2019 and UK NA to EN 1993-1-1

Yield Strength vs Thickness (BS EN 10025-2:2019)

Yield strength reduces with increasing thickness due to the reduced cooling rate in thicker sections during rolling. The table below applies to all three impact quality classes (JR, J0, J2).

Grade t ≤ 16 mm 16 < t ≤ 40 mm 40 < t ≤ 63 mm 63 < t ≤ 80 mm 80 < t ≤ 100 mm 100 < t ≤ 150 mm
S235 235 225 215 215 215 195
S275 275 265 255 245 235 225
S355 355 345 335 325 315 295
S420 420 400 390 370 360 340
S460 460 440 430 410 400 380

All values in N/mm² (MPa). Nominal thickness in mm. For product thicknesses outside these ranges, consult the manufacturer's mill certificate.

Tensile Strength Ranges

Grade t ≤ 3 mm 3 < t ≤ 100 mm 100 < t ≤ 150 mm Min Elongation (%) Min CVN at 20°C (J)
S235JR 360-510 360-510 350-500 24 27
S275JR 370-530 370-530 360-510 22 27
S355JR 470-630 470-630 450-600 21 27
S355J2 470-630 470-630 450-600 21 27 at -20°C
S460J2 520-680 520-680 500-650 17 27 at -20°C

Impact Quality Classes

Quality class suffixes indicate Charpy V-notch impact energy requirements:

Suffix Test Temperature Min Energy (J) — Longitudinal Application
JR +20°C 27 Internal buildings, warm environments
J0 0°C 27 Heated external, covered structures
J2 -20°C 27 External exposed, bridges, cold environments
K2 -20°C 40 Critical welded connections in cold regions

For UK practice, S355J2 is commonly specified for external steelwork and bridges. S355JR is acceptable for internal heated buildings.

Material Selection Guide for UK Practice

Application Typical Grade Quality Rationale
Multi-storey office beams S355 JR or J2 Strength for spans, JR adequate for internal
Multi-storey columns S355 JR or J2 Same as beams for economy
Industrial portal frames S355 J2 External environment, welded connections
Bridges S355 or S460 J2 or K2 Fatigue, low-temperature toughness
Stadium canopies S460 J2 Long spans, weight saving
Secondary steel (stairs) S275 JR Lightly loaded, cost-effective
Cold-formed purlins S350GD+Z — Pre-galvanised, BS EN 10326

UK NA Modifications to EN 1993-1-1 Material Factors

The UK National Annex specifies the following partial factors:

No modification factors for material overstrength (fy,act/fy,nom) are required by the UK NA — the nominal yield strength is used directly in design.

Stress-Strain Parameters for Design

For elastic design to EN 1993-1-1:

Parameter Value Notes
Modulus of elasticity E 210,000 N/mm² Same for all grades
Shear modulus G 81,000 N/mm² G = E / [2(1+ν)]
Poisson's ratio ν 0.3 Elastic range
Density ρ 78.5 kN/m³ 7850 kg/m³
Coefficient of thermal expansion α 12 × 10⁻⁶ /K Per EN 1993-1-2
ε (S275) 0.92 √(235/fy)
ε (S355) 0.81 √(235/fy)
ε (S460) 0.71 √(235/fy)

Design Example — Grade Selection for a 533×210 UB 92 Beam

Given:

Yield strength: For S355 with tf = 15.6 mm (t ≤ 16 mm range): fy = 355 N/mm² If the flange were 18 mm: fy = 345 N/mm² (16 < t ≤ 40 range)

Design effect — moment capacity: Mc,Rd (S355, t ≤ 16) = Wpl × 355/1.0 = 2616 × 355 × 10⁻³ = 929 kNm Mc,Rd (S355, 16 < t ≤ 40) = 2616 × 345 × 10⁻³ = 903 kNm (3% reduction)

S275 would give: Mc,Rd = 2616 × 275 × 10⁻³ = 719 kNm (23% reduction)

The choice between S275 and S355 is driven by span, load, and deflection requirements. For typical 6-9 m span floor beams, S355 is standard in UK practice.

Design Resources

Frequently Asked Questions

What are the standard UK steel grades per BS EN 10025?

Common UK structural steel grades: S235JR (fy = 235 MPa), S275JR (fy = 275 MPa), S355JR (fy = 355 MPa), S355J2 (fy = 355 MPa with improved notch toughness). S355 is dominant for building structures, representing approximately 80% of UK structural steel consumption. S275 is used for secondary steel, lighter loaded members, and cost-sensitive applications. S460 is growing in use for heavily loaded columns and long-span trusses where weight savings offset the higher material cost.

How does yield strength vary with thickness per BS EN 10025?

Yield strength reduces with increasing thickness: for S355 — t ≤ 16 mm: fy = 355 MPa, 16 < t ≤ 40: fy = 345 MPa, 40 < t ≤ 63: fy = 335 MPa, 63 < t ≤ 80: fy = 325 MPa, 80 < t ≤ 100: fy = 315 MPa, 100 < t ≤ 150: fy = 295 MPa. This thickness effect is critical to consider when designing with heavy UC sections (254×254 UC 89 has flange thickness 17.3 mm, so uses fy = 345 MPa) or thick base plates.

What is the difference between S355JR and S355J2?

Both have identical yield and tensile strength. The difference is in Charpy V-notch impact toughness: JR requires 27J at +20°C, J2 requires 27J at -20°C. For internal heated buildings, JR is sufficient. For external steelwork, bridges, and structures subject to low-temperature service, J2 is required. The UK NA to EN 1993-1-1 recommends J2 for all welded connections in tension where the minimum service temperature is below 0°C.

What partial factors does the UK NA specify for steel design?

The UK NA to EN 1993-1-1 specifies: γM0 = 1.00 (cross-section resistance), γM1 = 1.00 (buckling resistance), γM2 = 1.25 (tension and connection resistance), γM3 = 1.25 (slip resistance at ULS), γM3,ser = 1.10 (slip resistance at SLS). These match the Eurocode recommended values, which simplifies UK design using European-standard software and design tables.

What steel grade is used for cold-formed sections in UK?

Cold-formed sections use structural grades with zinc coating per BS EN 10326: S320GD+Z (fy = 320 MPa), S350GD+Z (fy = 350 MPa), S390GD+Z (fy = 390 MPa). These are not covered by BS EN 10025-2. The coating class (Z180, Z275, Z350) indicates the zinc mass in g/m². Z275 is standard for internal, Z350 for external applications. Cold-formed design follows EN 1993-1-3 and is covered in the UK cold-formed steel guide.

Reference only. Verify all values against the current edition of BS EN 10025-2:2019 and UK NA to EN 1993-1-1. This information does not constitute professional engineering advice.