# Steel Checks to EN 1993

The steel design check supports the EN 1993-1-1:2005 edition. EN 1993 or Eurocode 3 provides the basic code and is supplemented by National Annexes to allow for variations from one country to another.

## Input data

All cases provided to the checker are assumed to be ultimate limit state (i.e. the member forces are fully factored). Any non ULS cases – e.g. unfactored wind load – will be treated as if they are ULS, and so will result in non-conservative utilizations.

**Effective net area factor (β)**

For angles connected through one leg, the tensile strength of a section is affected by shear lag. To comply with EN 1993-1-8:2005 3.10.3 the Effective net area factor (Beta) is used to compute the design tensile strength. This factor is calculated for a single bolt. The effect of shear lag in tension is ignored for members with other section shapes.

**Single Angle Struts**

When considering Member Restraints for angle sections EC3 interprets restraint settings “A” and “B” as relating to the longer and shorter leg respectively. Where both legs are connected, both “A” and “B” should be set.

## Local Checks

Sections are checked at the ends of every sub-span of the member for the moments and forces acting on it.

Checks are carried out for Class 1, Class 2, Class 3 and Class 4 sections. Local buckling effects for Class 4 sections are included by an effective width in accordance with EN 1993-1-5.

For Class 4 CHS sections a reduced yield stress is used to account for local buckling.

For Channel and Tee sections elastic section verification is used.

**Shear**

Shear is checked according to EN 1993-1-1:2005 clause 6.2.6 if the section’s web(s) are not slender. A warning is given if the section is slender in shear.

**Bending moment**

Moment capacity is calculated in accordance with EN 1993-1-1:2005 clause 6.2.5 and compared with the applied moments. Allowance is made for shear and torsion in moment capacity according to EN 1993-1-1:2005 6.2.8.

Moment capacities are reduced for Class 1 and Class 2 sections to account for axial force as per EN 1993-1-1:2005 6.2.9.1.

**Axial force**

Compression and tension capacities are calculated in accordance with EN 1993-1-1:2005 6.2.4 and 6.2.3 respectively and compared with the applied axial force. For sections in tension the user defined ‘Net Area Ratio’ and ‘Effective net area factor (Beta)’ are used to determine tension capacity.

**Torsion**

At present, any significant torsional moment (greater than 5% of the torsional capacity) produces a warning. See BS5950-1:2000 for more details.

**Combined local effects**

The section is checked against all the applied forces using the equations in EN 1993-1-1:2005 6.2.9 and 6.2.10. The choice of equations depends on the section shape and the section’s local buckling class.

## Buckling Checks

The member is checked along its length for major axis axial buckling, minor axis axial buckling, torsional buckling, flexural torsional buckling and lateral torsional buckling. Interaction checks are carried out according to EN 1993-1-1:2005 6.3.3; see National Annexes for interaction factors. See BS5950-1:2000 for more details on buckling checks.

If a member has an Equivalent Uniform Moment Factor override specified, this is used in place of $C_1$ for lateral torsional buckling check and design.

## Limitations

- Section classification is based on axial force and major axis bending moment. Minor axis bending moment is disregarded.
- Shear lag effects are not considered in bending.
- Elastic critical moment for lateral-torsion buckling is calculated in accordance with Annex I of EN 1999-1-1:2007. When the loads on the member are not found in the appropriate table of Annex I of EN 1999-1-1:2007, the worst values of C1, C2 and C3 are taken from the appropriate table assuming the ends are pinned.
- Transverse load checks not yet supported.
- Slender Angle sections not yet supported.
- Refer BS5950-1:2000 for other limitations.