About thin-walled sections for Eurocode3

The section 10 of the EN 1993-1-3 code introduces additional regulations allowing more accurate verification of elements protected against lateral displacements in the upper part and compressed in the lower part.

You can design members for which one of the predefined types of thin-walled sections has been used; as specified in section 10, additional analysis are performed for thin-walled Z-sections, C-sections and Sigma sections. The scope of the code includes calculations of steel members loaded with an arbitrary set of internal forces (N,Vy,Vz,Mx,My,Mz). NOTE: Possible bimoments are not taken into account in the current program version.

Calculations according to EN 1993-1-3 do not take account of the design of closed sections (pipes - rectangular, square, etc.) for which calculations are performed based on the principles of the general code EC3 (EN 1993-1-1:2005)

Buckling / lateral buckling parameters are defined exactly the same for both thin-walled members and solid sections.

An analyzed thin-walled member will be checked (apart from standard code-specified verifications) due to the loss of capacity and stability of the lower compression flange.

Besides standard verifications, the following verifications can be performed:

• Verification of resistance of the section of the lower (unstiffened) flange according to point 10.1.4.1.(2) of the code (when a bending moment causes compression of the lower flange)
• Verification of stability of the lower (unstiffened) flange according to point 10.1.4.2.(1) of the code (when a bending moment causes compression of the lower flange).

It is assumed that the sheeting is always connected with the UPPER flange of a purlin. The sheeting appropriately connected with the purlin is usually treated as a stiff membrane which sufficiently protects the upper flange of the purlin against lateral displacements. Parameters of the cross-section of corrugated sheeting are taken from the sheet database. Moreover, the user determines additional information concerning mutual positions of the sheeting and the purlin, the model for calculating and the how the sheet is fastened to the purlin.

The Thin-walled section dialog holds options used to determine the method of forming a thin-walled section in the production stage. This information is necessary to evaluate an average material resistance f _ya according to section 3.2.2.(3) of the code.

Calculations of thin-walled sections are performed for the following thin-walled sections included in Robot databases:

• SIGMA sections
• Z-sections
• open C-sections
• half-closed C-sections
• angles
• OMEGA sections
• C-sections with stiffeners of flanges.

Code verification for bars with thin-walled sections is performed as follows:

• Calculation of gross sectional properties
• Calculation of the yield strength f _ya of a cold-rolled section taking account of an increase in section mechanical strength resulting from cold-work during cold-rolling (EN 1993-1-3 & 3.2.2)
• Calculation of effective section parameters
  • evaluation of stresses in individual section walls
  • evaluation of slenderness of elements in compression
  • determining sections of effective walls
• Calculation of individual resistances considering effective parameters of thin-walled sections (points 6.1.1 to 6.1.6)
• Member verification according to principles given in point 6.1 (section check) and 6.2 (global stability check).