Unlike the more commonly known W20 hot rolled steel framing systems available, iSteel has developed a more economical system offering maximum glass area, thin sections and exceptional performance. The iSteel system utilises traditional steel box sections with small add-ons and alterations to accommodate all internal glazing requirements, from 4mm toughened right up to 12.8mm acoustic laminated glass – as we have developed and are using our own system, we are able to offer the best prices in the UK and an almost limitless choice of design. The system works extremely well for all types of internal partitioning. Internal systems offer the designer, architect or client even more freedom of expression to create truly bespoke solutions by just contacting iSteel and letting our in-house design and technical team do the hard work – so you don’t have to!


About Structural Steel

Structural steel is a basic construction material, made from specific grades of steel and manufactured in a variety of industry standard cross-sectional shapes (or ‘sections’). Structural steel grades are engineered with specific chemical compositions and mechanical properties formulated for specific applications.

In Europe, Structural Steel must adhere to the European Standard EN 10025, governed by the European Committee for Iron and Steel Standardisation (ECISS), a subset of CEN (European Committee for Standardisation).

  • 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

Based on the manufacturing process, chemical composition and applicable application, further letters and classifications might be used to reference particular grades/products of structural steel.

Chemical Composition of Structural Steels – S235 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.

Grade C% Mn% P% S% Si%
S235 0.22 max 1.60 max 0.05 max 0.05 max 0.05 max
S355 0.23 max 1.60 max 0.05 max 0.05 max 0.05 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, 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 mm Minimum Yield Strength at nominal thickness 16 mm
ksi N/mm2 (MPa)
S235 33 000 ksi 235 N/mm2
S355 50 000 ksi 355 N/mm2

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.

Applications of Structural Steel

Structural steels are used in many ways and their application can be varied. They are particularly beneficial because they offer the unique combination of good welding properties with assured strengths. Structural steel is a very adaptable product and is frequently favoured by the engineer trying to maximise strength or structure while reducing its weight.

It is a fact that the construction sector is the biggest consumer of structural steel, where it is used for all manner of purposes and used at diverse scales. Whether a small box lintel is used to hold the load of a structural wall in a residential property or a vast I-beam is bolted in place to hold the road surface on a bridge, structural steel can be specified, designed, and fabricated for the application.

  • High rise buildings/skyscrapers
  • Factories
  • Houses
  • Shopping malls
  • Offices
  • Road barriers
  • Train tracks
  • Bridges