Structural Steel - S235, S275, S355 Chemical Composition, Mechanical Properties and Common Applications

By Nick Gilbert

Topics Covered

Introduction
Chemical Composition of Structural Steels - S235, S275 and S355
Mechanical Properties of Structural Steel - S235, S275 and S355
Typical Structural Steel ‘Sections’ / Cross-sectional Shapes
Applications of Structural Steel

Introduction

Structural steel is a standard construction material, made from specific grades of steel and formed in a range of industry standard cross-sectional shapes (or ‘Sections’). Structural steel grades are designed with specific chemical compositions and mechanical properties formulated for particular applications.

In Europe, Structural Steel must comply with the European Standard EN 10025 a Governed by the ECISS (European Committee for Iron and Steel Standardization) a subset of CEN (European Committee for Standardization.

There are many examples of European grades of structural steel such as; S195, S235, S275, S355, S420, S460 etc. However, for the purposes of this article we will focus on the Chemical Composition, Mechanical Properties and Applications of S235, S275, S355. Three common structural steel grades used in all manner of Construction projects across the EU.

Inline with the European Standard classifications, Structural steels must be referenced using standard symbols including but not limited to: "S"235"J2’‘K2’’C’’Z’’W’’JR’’JO’’

Where:

  • S – denotes the fact that it is Structural Steel
  • 235 – related to the minimum yield strength of the steel (tested at a thickness of 16mm)
  • 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

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

The EU Standard classifications are inherently not a global standard and therefore a number of corresponding grades with the same Chemical and Mechanical properties may be used in other parts of the world. For example, Structural Steels fabricated for the US market must be specified in accordance with the ASTM (American Society for Testing and Materials) International guidelines and will be referenced with an ‘A’ and then the relevant Grade such as A36, A53 etc.

US Equivalent Grades

EU

US

S235

A283C

S275

A570Gr40

S355

A572Gr50

In most countries Structural Steel is regulated and must meet a minimum specific criterion for Shape, Size, Chemical Composition, strength etc.

Chemical Composition of Structural Steels - S235, S275 and S355

The Chemical composition of Structural Steel is extremely important and highly regulated. It is a fundamental factor which defines the Mechanical properties of the steel material. In the following table you can see the Max % 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

S275

0.25 max

1.60 max

0.04 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 incredibly important to the engineer and will change with specific Grades depending on their intended use. For Example; S355K2W is a Structural Steel that has been hardened (K2) and has been designed with a chemical composition to withstand increased weathering (W). Therefore, this grade of Structural Steel will have a slightly different chemical composition to the standard S355 grade.

Mechanical Properties of Structural Steel - S235, S275, S355

The Mechanical Properties of Structural Steel are fundamental to its classification and hence, application. Even though Chemical Composition is a dominant 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; Yield Strength and Tensile Strength.

Yield Strength

The yield strength of structural steel measures the minimum force required to create a permanent deformation in the steel. The naming convention used in European Standard EN10025 refers to the Minimum Yield strength of the steel grade tested at 16mm thick.

Structural Steel Grade at 16mm

Minimum Yield Strength at nominal thickness 16mm

ksi

N/mm2 (MPa)

S235

33 000 ksi

235 N/mm2

S275

36 000 ksi

275 N/mm2

S355

50 000 ksi

355 N/mm2

Tensile Strength

The Tensile Strength of Structural steel relates to the point at which permanent deformation occurs when the material is pulled or stretched laterally along its length.

Structural Steel Grade

Tensile Strength MPa at Nom thickness between 3mm and 16mm

S235

360 – 510 MPa

S275

370 – 530 MPa

S355

470 – 630 MPa

Typical Structural Steel ‘Sections’ / Cross-Sectional Shapes

Structural Steel comes in many Grades but is normally sold pre-formed with a defined cross-sectional shape, designed for specific applications. For example, it is common to find Structural Steel sold in: I-Beams, Z-beams, Box Lintels, HSS (Hollow Structural Section), L shaped, Steel Plate etc.

Depending on the desired application, an engineer will specify a grade of steel (Often to meet minimum strength, max weight and or weathering requirements) and the sectional shape, relative to the desired location and expected 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 diverse. They are particularly useful because they offer the unique combination of good welding properties with guaranteed strengths. Structural Steel is an extremely adaptable product and is often favoured by the engineer trying to maximise strength or s structure while minimising its weight.

It will come as no surprise that the construction industry is the biggest consumer of Structural Steel, where it is used for all manner of purposes and employed at diverse scales. Whether a small box lintel is used to carry 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 job.

  • High Rise Buildings / Skyscrapers
  • Houses
  • Factories
  • Offices
  • Shopping Malls
  • Train Tracks
  • Road barriers
  • Bridges

References

Date Added: May 11, 2012 | Updated: Jan 13, 2014
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