## Emh

4 Local buckling

4.1 General

(1)P The effects of local buckling shall be taken into account in determining the resistance and stiffness of cold formed members and sheeting.

(2)P This may be done by using effective cross-sectional properties, calculated on the basis of the effective widths of those elements that are prone to local buckling.

(3)P The possible shift of the centroidal axis of the effective cross-section relative to the centroidal axis of the gross cross-section shall be taken into account.

(4) In determining resistance to local buckling, the yield strength fy should be taken as /yb.

(5) In determining the resistance of a cross-section, the effective width of a compression element should be based on the compressive stress acom Ed in the element when the cross-section resistance is reached.

(6) For serviceability verifications, the effective width of a compression element should be based on the compressive stress ^com,Ed,ser m the element under the serviceability limit state loading.

### 4.2 Plane elements without stiffeneirs

(1)P The effective widths of compression elements shall be obtained from table 4.1 for doubly supported compression elements or table 4.2 for outstand compression elements.

(2)P The notional flat width bp of a plane element shall be determined as specified in 3.3.4. In the case of plane elements in a sloping web, the appropriate slant height shall be used.

NOTE: In ENV 1993-1-1 the symbol b is used for the notional flat width of a plane element.

(3)P The reduction factor p used in tables 4.1 and 4.2 to determine beff shall be based on the largest compressive stress acom Ed in the relevant element (calculated on the basis of the effective cross-section and taking account of possible second order effects), when the resistance of the cross-section is reached.

(4) If ocom Ed = /yb^TMi the reduction factor p should be obtained from the following:

- if Xp > 0,673: p = (1,0-0,22/Xp)/Xp in which the plate slenderness Xp is given by:

where:

ka is the relevant buckling factor from table 4.1 or 4.2;

Table 4.1 : Doubly supported compression elements

Stress distribution [compression positive]

Effective width beff ct2

¿eff =

pbc

¿el =

0,4Z>eff

¿e2 =