Steel grades for framing

What the designation says

The raw material of framing profiles is continuously coated structural steel coil, designated according to EN 10346. In the designation:

• the letter and number combination gives the structural purpose and the nominal yield strength,
• the coating designation gives the type and amount of metallic coating on the sheet.

In practice the typical structural grades sit in the medium and high yield ranges; which one suits depends on the role of the section.

Why higher yield strength is not always better

This is one of the most important things to understand about the technology.

On a thick section, higher yield strength means directly higher capacity. On a thin plate element, however, the material is often not what gives up first — stability is: the plate buckles before it reaches the yield strength.

In that case the more expensive, higher-strength steel brings no proportional gain. What has to change is the geometry: a larger section, a stiffening lip, or a different arrangement.

Where the cross-section is stocky, or where the connection governs, higher yield strength does pay.

What the design has to state

• the steel grade and nominal yield strength,
• the nominal thickness, and whether it includes the coating,
• the type and amount of coating,
• the geometry of the section.

Together these determine the capacity. If the material installed differs, the assumption behind the design is broken — which is why the CE marking and declaration of performance matter.

Formability and strength

Higher-strength steel is less formable: with a sharper bend the edge can crack. The manufacturer therefore matches the bend radius to the grade. For the designer this means section geometry is not arbitrary — the corners are rounded, and that is built into the effective cross-section calculation.

The effect of cold forming

During forming the material work-hardens in the corners, which raises strength locally. Design may take this into account to a limited extent. What cold forming does to steel.

The point

Steel grade only means something together with the section geometry. On thin sheet the shape is usually worth more than higher strength.