Regular versus thin-walled cross-sections

Eurocode makes a distinction between:

1. Regular steel cross-sections who can have the production methods: hot rolled, welded or cold formed
   These cross-sections have a thickness t >= 3mm and are designed using EN 1993-1-1.
2. Thin walled steel cross-section who have the production method: cold-formed
   These cross-sections have a thickness t < 3mm and are designed using EN 1993-1-3.

Diamonds contains a library of common thin walled cross-sections (MRP, Brause, Joris Ide, Sadef). For those sections, Diamonds will automatically apply EN 1993-1-3.

Any other type of cross-section is default calculated according to EN 1993-1-1. However, if the thickness < 3mm and the production method is defined as ‘cold formed’, you can impose Diamonds to use EN 1993-1-3 by checking this option. The parameters VzRd, VyRd and fya required for the design, need to be imposed by the user.

Effective properties

Eurocode organizes cross-sections into four classes that describe the behaviour of that cross-section.

1. Class 1 & 2 are plastic cross-sections
2. Class 3 are elastic cross-sections
3. And Class 4 are slender cross-sections.

For classes 1 to 3, it’s easy to determine the section properties required to do a design according to EN 1993. Class 4 on the other hand, requires effectieve properties to do a design according to EN 1993… which are much harder to determine.
‘Regular’ steel cross-sections can be of class 1 to 4. Thin walled cross-sections are almost always of class 4.

The table below gives an overview for which cross-sections Diamonds has these effective properties.

		Parameters for elastic analysis	Parameters for unity check (Eurocode 3)
	Cross-section procceded by	✓	✓
		✓	✓, until class 3 For class 4, you should impose the effective properties
		✓	✓
		✓	✓, until class 3 For class 4, you should impose the effective properties. Also for class 4, EN 1993-1-6: Strength and stability of shell structures applies. Diamonds does not support this part of Eurocode.
		✓	not possible [1]
		✓	not possible [2]
	(for Section Utility manual, click here)	✓	you should impose additional properties For class 4, you should also impose the effective properties.

^[1] For the cold formed cross-sections in the library, the effective properties have been provided by the manufacturers. If you select one of these cross-section shapes and change its dimensions or impose them from zero, Diamonds is not capable of recalculating these effective properties! Therefor you cannot run a unity check on these cross-sections
^[2] These cross-sections shapes are intended for concrete design.

Which commercial thin walled cross-sections are in Diamonds

The table below gives an overview of all commercial thin walled cross-sections in Diamonds:

[NL]: Voor bepaalde staven kon de normcontrole niet uitgevoerd worden. De rekenkundige bewerking heeft geresulteerd in een overloop.

[FR]: La vérification ne pourraît pas être exécuté pour certaines barres. De objectverwijzing is niet op een exemplaar van een object ingesteld.

Cause (in general)

This error is always related to an inconsistency in the dimensions of the used cross-section(s). Resulting in cross-section classifications, imperfection factors, effective properties, … not being calculated automatically.

Example 1:

An RHS-section is used to create an elliptical cross-section. But because r0 (=25mm) equals B/2 (=50mm/2), the cross-section classification in the weak direction cannot be performed.
Solution: set B= 51mm or set r0 to 24mm.

Example 2:

Some cross-section shapes are associated with cold-formed sections, like these in the list below:

When the option ‘Automatic calculation’ is selected, Diamonds calculates the general, elastic (except T_wm) and the plastic properties of the cross-section.
But Diamonds cannot calculate the effective and design properties for these cross-section shapes. These shapes are in Diamonds because manufacturers (Joris Ide, Brausa, Sadef, …) provided us with lists of common cross-sections with their dimensions and effective properties. So although you can play around with the dimensions, Diamonds is not capable of calculating the effective properties!

So if you want to perform a steel verification on these cross-section shapes, you should:

• Check the option ‘Automatic Calculation’. This way the general, elastic and plastic properties are calculated.
• Uncheck the option ‘Automatic calculation’. This way you can adjust the value of T_wm in the tab page ‘Elastic’.
• Define all the properties in the tab page ‘Effective’.
• Define all the properties in the tab page ‘Design’.