--------------------- | ----------- | ----------- | ----------- | ----------- | | Yield fy (t <= 16 mm) | 235 MPa | 275 MPa | 355 MPa | 460 MPa | | Yield fy (16 < t <= 40 mm) | 225 MPa | 265 MPa | 345 MPa | 440 MPa | | Yield fy (40 < t <= 63 mm) | 215 MPa | 255 MPa | 335 MPa | 430 MPa | | Yield fy (63 < t <= 80 mm) | 215 MPa | 245 MPa | 325 MPa | 410 MPa | | Tensile fu (t <= 16 mm) | 360-510 MPa | 410-560 MPa | 470-630 MPa | 520-670 MPa | | Typical Elongation A% | 26% | 23% | 22% | 17% | | Modulus of Elasticity E | 210 GPa | 210 GPa | 210 GPa | 210 GPa | | Carbon equivalent CEV (max) | 0.35% | 0.40% | 0.45% | 0.53% | | Poisson's ratio nu | 0.30 | 0.30 | 0.30 | 0.30 | | Shear modulus G | 81 GPa | 81 GPa | 81 GPa | 81 GPa |

S235 - Mild Steel

S235 is the lowest strength structural grade, comparable to the former Grade 43 steel under BS 4360. It is used for:

• Light-duty structural members where strength is not critical
• Non-structural components (handrails, platforms, stairs)
• Secondary steelwork in buildings
• Cold-formed sections and thin-gauge members

S235JR is the most common subgrade. It offers excellent weldability due to the low carbon content (max 0.22% for thickness <= 16 mm) and is suitable for all conventional welding processes without preheat for thicknesses up to 30 mm. In design per EN 1993-1-1, the design yield strength fy = 235 MPa gives relatively low member capacities, so S235 is rarely used for primary beams or columns in multi-storey construction.

S275 - General Structural Steel

S275 replaced Grade 43 as the general-purpose structural steel in the UK following the withdrawal of BS 4360. It is widely specified for:

• Steel-framed agricultural and industrial buildings
• Portal frame structures
• Lattice towers and transmission poles
• Light commercial buildings and extensions

S275JR is the standard subgrade for internal members. For external exposed steelwork, S275J2 or S275J0 provides guaranteed Charpy impact toughness. The slightly higher carbon content (max 0.25%) compared to S235 still permits good weldability without preheat for most thicknesses.

S355 - The UK Standard Structural Grade

S355 is the default structural steel grade for most UK building and civil engineering works. It replaced Grade 50 in the BS 4360 system. S355 is specified for:

• Primary beams, columns, and bracing in multi-storey buildings
• Bridge girders (typically S355J2 or S355K2)
• Offshore and marine structures
• Heavy civil engineering works
• Crane beams and heavily loaded frames

S355J2 is the most common specification for structural steelwork in the UK. The 355 MPa yield strength (at t <= 16 mm) provides efficient member sizes - a 20% increase over S275 and 50% over S235. The weldability is good for most thicknesses; preheat may be required above 30 mm depending on the CEV.

Thickness Effects on S355

The yield strength of S355 reduces with thickness:

• t <= 16 mm: fy = 355 MPa
• 16 < t <= 40 mm: fy = 345 MPa
• 40 < t <= 63 mm: fy = 335 MPa
• 63 < t <= 80 mm: fy = 325 MPa
• 80 < t <= 100 mm: fy = 315 MPa

When designing to EN 1993-1-1, use the fy value corresponding to the nominal thickness of the element - for flanges, this is the flange thickness tf, not the overall section depth.

S460 - High-Strength Steel

S460 is the entry-level high-strength structural steel under EN 10025-3 (thermomechanical rolled) or EN 10025-4 (normalised/normalised rolled). It offers:

• 30% higher strength than S355 for same-weight sections
• Reduced member sizes and foundation loads
• Lower carbon equivalent for better weldability than older high-strength grades
• Applications in long-span roofs, heavy trusses, and columns in tall buildings

S460 is less commonly stock-held in UK fabrication shops than S355, so availability and lead time should be verified early in design. Welding requires a qualified WPS with controlled heat input and preheat.

Impact Testing Requirements (UK NA to EN 1993-1-1)

The UK National Annex specifies Charpy V-notch impact requirements based on service temperature and stress category:

In the UK, S355J2 is the minimum specification for external steelwork exposed to winter temperatures. For internal steelwork in heated buildings, S355JR may be acceptable.

Design Values per EN 1993-1-1

When using these grades in EN 1993-1-1 design with UK NA:

• gamma_M0 = 1.00 (cross-section resistance)
• gamma_M1 = 1.00 (member buckling resistance)
• gamma_M2 = 1.25 (cross-section in tension / bolt resistance)
• E = 210 000 N/mm2 (modulus of elasticity)
• G = 81 000 N/mm2 (shear modulus)

Which Grade Should You Use?

• S235 - Very light secondary steelwork, non-structural components, low-cost applications
• S275 - General-purpose agricultural/light industrial buildings, lattice structures
• S355 - Default for all building structures in the UK. Best balance of strength, weldability, and cost
• S460 - Long-span or heavily loaded members where weight reduction offsets the material premium

For most building structures designed to EN 1993-1-1, S355J2 is the most economical and widely available grade in UK sections (UB, UC, PFC, CHS, SHS).

Try the Calculator

Use the Beam Capacity Calculator to check member capacities with the correct grade strength. Select EN 1993 and enter your grade (S235, S275, S355, or S460).

Frequently Asked Questions

What is the yield strength of S355 steel in EN 1993-1-1 design? S355 has a minimum yield strength fy = 355 MPa for thicknesses up to 16 mm, reducing to 345 MPa for 16-40 mm, 335 MPa for 40-63 mm, and 315 MPa for 80-100 mm. Always use the thickness-appropriate fy value per EN 1993-1-1 Table 3.1.

What is the difference between S355JR, S355J0, and S355J2? The subgrade specifies Charpy impact energy and test temperature: JR = 27 J at +20degC, J0 = 27 J at 0degC, J2 = 27 J at -20degC. S355J2 is the standard for UK external steelwork. For internal heated buildings, S355JR may be acceptable.

Can S275 be used for primary beams and columns? Yes, but S275 gives 23% lower yield strength than S355, requiring heavier sections for the same load. For spans over 6 m or heavily loaded members, S355 is typically more economical despite the slightly higher material cost per tonne.

Try it now: Check your steel grades with our free Steel Grade Selection calculator →

See Also

• Beam Capacity Calculator
• Beam Deflection Calculator
• Steel Beam Sizes Reference
• Beam Design Guide
• Beam Span Reference [object Object]

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Frequently Asked Questions

What is the recommended design procedure for this structural element?

The standard design procedure follows: (1) establish design criteria including applicable code, material grade, and loading; (2) determine loads and applicable load combinations; (3) analyse the structure for internal forces; (4) check member strength for all applicable limit states; (5) verify serviceability requirements; and (6) detail connections. Computer analysis is recommended for complex structures, but hand calculations should be used for verification of critical elements.

How do different design codes compare for this calculation?

AISC 360 (US), EN 1993 (Eurocode), AS 4100 (Australia), and CSA S16 (Canada) follow similar limit states design philosophy but differ in specific resistance factors, slenderness limits, and partial safety factors. Generally, EN 1993 uses partial factors on both load and resistance sides (γM0 = 1.0, γM1 = 1.0, γM2 = 1.25), while AISC 360 uses a single resistance factor (φ). Engineers should verify which code is adopted in their jurisdiction.

Design Resources

Calculator tools

• Steel Grade Calculator
• Steel Weight Calculator
• Steel Material Takeoff Calculator

Reference pages

• UK Steel Properties