The AS 4100 specification allows inelastic deformation of section elements. Thus, local buckling becomes an important criterion. Steel sections are classified as compact, noncompact, or slender; depending upon their local buckling characteristics. This classification is a function of the geometric properties of the section. The design procedures are different depending on the section class. STAAD determines the section classification for the standard shapes and user specified shapes. Design is performed for all three categories of section described above.