Plane Elements with Edge Stiffeners

The procedure for determining the effective width/thickness of elements with edge stiffeners is given in EN 1993-1-3 art. 5.5.3.2 and art. 5.5.3.1.

This applies to elements of type RUO and DEF

General remarks regarding the stiffness K of the edge stiffener given in formula (5.10b) .

h_w is taken as l_c (centreline length) of the biggest adjacent element. Adjacent elements are those elements connected to the flange. For typical cross-sections, there is only one adjacent element, the web.

For Sigma sections, h_w is taken as the sum of the centreline lengths of the web elements.

This concerns the following form codes:

FC 121 Cold formed Sigma section

FC 124 Cold formed Sigma section eaves beam

FC 122 Cold formed Sigma section stiffened

FC 123 Cold formed Sigma-Plus section

FC 125 Cold formed Sigma-Plus section eaves beam

FC 128 Cold formed IS-Plus section

FC 129 Cold formed Sigma section asymmetric

General Cross-section: h_w for stiffener:

• Elements connected to the stiffener are not accounted for since they are considered as flanges
• Elements connected to those flanges are all accounted for in case they are of type I and the summation is made of the lengths of these elements
• Roundings are not accounted for

General Cross-section: In case there is only one edge stiffener

k_f is taken as zero. (i.e. no interaction between two flanges since there is only one flange).

General Cross-section: In case there are two edge stiffeners

k_f is determined by default. (i.e. interaction between the two flanges is accounted for).

General Cross-section: In case there are more than two edge stiffeners

The same logic is followed as for a single stiffener. The factor k_f is thus taken as zero.

The formula for K given in the EN 1993-1-3 is based purely on simple sections with two flanges. In case of more complex cross-sections, the only exact procedure is to perform a numerical analysis (finite strip method) to determine the critical stresses for local and distortional buckling. This is referenced as the ‘Advanced Procedure’ given in art. 5.5.1(7).

Critical stresses for local and distortional buckling obtained from a numerical analysis can be inputted in the cross-section manager.

The reduced effective area of the stiffener A_s,red according to art 5.5.3.2(11) is calculated using σ_com,Ed = f_yb/γ_M0.