Cross-sections
Solid cross-sections can be rectangular or circular, or are composed of several rectangles into shapes I, T or Pi. For these cross-sections calculation assumes integrity and doesn't consider any slip between the different parts of the section.
Built-up cross-sections consist of several rectangular parts. Sub-sections are either rigidly attached (glued) or are unconnected.
Coordinate Systems
Two coordinate systems are created for any cross-section: the local coordinate system of a member with axes marked 2 and 3 and cross-sectional coordinate system with axes marked y and z. Input of designing properties (buckling, LTB) is done mostly in the local coordinate system of the member. Thus rotation of the cross-section is measured relatively to the local axes 2 and 3. Internal forces are indicated by subscripts 2 and 3, as they are also related to the local coordinate system of the member. The verification is done in the coordinate system of the cross-section. Internal forces are always converted into the coordinate system of the cross-section before the verification.