Compound sections are two or more chords connected by battens or lattice. These sections are used as sections of column piers (C-sections, I-sections, and angles) and sections of truss bars (usually, a set of angles). Static calculations for these section types are the same as for solid sections. Structural properties are calculated based on the actual section without battens and lattice.
To avoid analysis errors that result from an incorrect definition of a compound section, the software verifies whether the section geometry is correct. It checks whether the sections of a compound section overlap. If it finds such errors, you cannot save the compound section.