The occurrence of local buckling of the compression elements of a cross-section prevents the development of full section capacity. It is therefore imperative to establish this possibility prior to determining the section capacities. Cross sections are classified in accordance with their geometrical properties and the stress pattern on the compression elements. For each load case considered in the design process, STAAD determines the section class and calculates the capacities accordingly.

The EC3 DD design module in STAAD can design members with all section profiles that are of Class 1 2 or 3 as defined in section 5.3.2 of the code. However, the design of members that have a "Class 4" section profile are limited to WIDE FLANGE, TEE, SINGLE CHANNEL, SINGLE ANGLE, and RECTANGULAR HOLLOW SECTIONS. Also built-up user sections that are class 4 sections are not dealt with in the current version of EC3 design in STAAD.Pro.

Laced and battened members are not considered in the current version of EC3 DD design module in STAAD.Pro.