Structural steel acts as the backbone of modern construction, assembled in shapes compliant with standard industry profiles. This material sports a specific grade variety, purpose-built with particular compositions and mechanical traits to serve distinct structural roles.
        Europe mandates structural steel conformity with EN 10025 from the European Committee for Iron and Steel Standardization wing of CEN. This includes a spectrum of European structural steel grades like S195 to S460. Nonetheless, our discourse zeros in on the nuances of S235, S275, and S355 compositions, their mechanical properties, and their prevalent construction uses within the EU.
        Structural steel acts as the backbone of modern construction, assembled in shapes compliant with standard industry profiles. This material sports a specific grade variety, purpose-built with particular compositions and mechanical traits to serve distinct structural roles.
Europe mandates structural steel conformity with EN 10025 from the European Committee for Iron and Steel Standardization wing of CEN. This includes a spectrum of European structural steel grades like S195 to S460. Nonetheless, our discourse zeros in on the nuances of S235, S275, and S355 compositions, their mechanical properties, and their prevalent construction uses within the EU.
These denote:
  • S – denotes the fact that it is structural steel
  • 235 – related to the minimum yield strength of the steel (tested at a thickness of 16 mm)
  • J2/K2/JR/JO – material toughness in relation to the Charpy impact or ‘V’notch test methodology
  • W – Weathering steel (atmospheric corrosion resistant)
  • Z – Structural steel with improved strength perpendicular to the surface
  • C – Cold-formed
        Beyond construction methods and elemental composition, various symbols and designations may arise to qualify unique steel types or products.
        EU classifications don't necessarily correlate globally. In the US, for instance, equivalent ASTM International standards apply, with the American system labeling A36, A53, and similar.

EU to US Equivalent Grades:

EUUS
S235A283C
S275A570Gr40
S355A572Gr50

Globally, structural steel requires adherence to precise criteria for its chemical makeup and physical shape and strength.

Chemical Composition of Structural Steels - S235, S275 and S355

The chemical composition of structural steel is very important and highly regulated. It is a central factor which defines the mechanical properties of the steel material. In the following table, one can see the maximum % levels of certain regulated elements present in European structural steel grades S235, S275 and S355.

GradeC%Mn%P%S%Si%
S2350.22 max1.60 max0.05 max0.05 max0.05 max
S2750.25 max1.60 max0.04 max0.05 max0.05 max
S3550.23 max1.60 max0.05 max0.05 max0.05 max

The chemical composition of structural steel is extremely important to the engineer and will change with specific grades based on their intended use. For instance; S355K2W is a structural steel that has been hardened (K2) and has been designed with a chemical composition to endure increased weathering (W). Thus, this grade of structural steel will have a marginally different chemical composition to the standard S355 grade.

Mechanical Properties of Structural Steel - S235, S275, S355

The mechanical properties of structural steel are central to its classification and hence, application. Although, chemical composition is a governing factor of the mechanical properties of steel, it is also very important to understand the minimum standards for the mechanical properties (performance characteristics) such as tensile strength and yield strength.

Yield Strength

The structural steel’s yield strength measures the minimum force needed to create a permanent deformation in the steel. The naming convention used in European Standard EN10025 relates to the minimum yield strength of the steel grade tested at 16 mm thick.

Structural Steel Grade at 16 mmMinimum Yield Strength at nominal thickness 16 mm
ksiN/mm2 (MPa)
S23533 000 ksi235 N/mm2
S27536 000 ksi275 N/mm2
S35550 000 ksi355 N/mm2

Tensile Strength

The tensile strength of structural steel relates to the point at which permanent deformation takes place when the material is stretched or pulled laterally along its length.

Structural Steel GradeTensile Strength MPa at Nom thickness between 3 mm and 16 mm
S235360 – 510 MPa
S275370 – 530 MPa
S355470 – 630 MPa

Typical Structural Steel ‘Sections’/Cross-Sectional Shapes

Structural steel is supplied in many grades but is typically sold pre-formed with a defined cross-sectional shape, engineered for specific applications. For instance, it is common to find structural steel sold in: I-Beams, Z-beams, Box Lintels, hollow structural section (HSS), L-shaped, steel plate etc.

Depending on the preferred application, an engineer will specify a grade of steel (frequently to meet minimum strength, maximum weight, and/or weathering requirements) and the sectional shape, relative to the preferred location and anticipated load to be carried or job to be performed.

Multifaceted Structural Steel Application
From welding benefits to strength guarantees, structural steel manifests as a malleable force in engineering. Widely employed for its strength-to-weight efficiency, it scales from minor residential fixtures to immense infrastructure support systems such as high buildings, industrial setups, malls, offices, and bridges.