Steel Angle Design (BS5950) - Zx_max & Zx_min values

The section properties for Zx & Zy max are based upon the whole section working as a single element where the neutral axis passes through the leg/section itself at the and Zx & Zy min value are based the section where the neutral axis of the whole section is considered. This then allows the calculation to assume that the load applied to the leg is along the top edge of the leg so the load is transfer directly into the element rather than in the position of the neutral axis and therefore assumes that the larger section modulus is considered

Solution

The calculation of the section modulus is as indicated below;

Zx_min = Zxx
Zx_max = Ixx/Cx
Zy_min = Zyy
Zy_max = Iyy/Cy

Refer to Blue Book for position of Cx & Cy