Class 1 (plastic)

Cross section which can be develop in plastic hinges and rotation capacity required for failure of the structure by formation of plastic mechanism. The width to thickness ratio is less than that specified under class 1 (plastic)

2 Class 2 (compact)

Cross section which can develop plastic moment of resitance but have inadequate plastic hinge rotation capacity for formation of plastic mechanism due to local buckling. The width to thickness ratio of plate element shall be less than that specified under class 2 (compact) but better than that specified under class 1 plastic

3 Class 3 (Semi-compact)

Cross section in which the extreme fibre in compression can reach yield stress but cannot develop plastic moment of resistance due to local buckling. The width to thickness ratio less than that specified under class 3(semi compact) but greater than that specified under class 2 (compact)

4 Class 4 (Slender)

Cross-section in which the element buckle locally even befire raaching yield stress, The width to thickn ratio of plate element shall be greater than the specific under class 3 (semi compact)