Steel sections are classified as plastic (Class 1), compact (Class 2), noncompact (Class 3), or slender element (Class 4) sections depending upon their local buckling characteristics (See Clause 11 and Tables 1 & 2 of CAN/CSA-S16-09, S16-14, or S16-19). The design procedures are different depending on the section class. STAAD.Pro determines the section classification for the standard shapes and user specified shapes.