Why does Steel Member for Combined Stress not allow me to design an angle section?
The Steel Member for Combined Stress is bound by the limitations of the various design codes. The codes typically provide design procedures for double-symmetical sections like I-beams and rectangular hollow sections, and also channels. Most design codes do not give guidance for designing sections like angles for combined bending moment and axial force; these sections do not perform well in flexure.
The Steel Member for Combined Stress supports only those section types supported by the design codes. Updated design procedures that support more section types have become available in recent years (e.g. AS 4100), and these procedures will be included in the program over time.
You can design a custom steel section that conforms to one of the supported the shapes. For a welded I-section, for example, add the section to the Section Database under the standard I-sections and design it like any other rolled I-section.