To ensure that compression flange of a beam is restrained from moving laterally, the cross section must be ____

To ensure that the compression flange of the beam is restrained from moving laterally, the cross-section must be plastic or compact. If significant ductility is required, the section must invariably be plastic.

The different types of the section are as follows:

1. Plastic - Cross-sections, which can develop plastic hinges and have, the rotation capacity required for the failure of the structure by formation of a plastic mechanism, are called plastic sections. The stress distribution for these sections is rectangular.

2. Compact - Cross-sections, which can develop the plastic moment of resistance, but have inadequate plastic hinge rotation capacity for the formation of a plastic mechanism before buckling classed as compact sections. These cross-sections may develop fully plastic stress distribution across the entire cross-section but do not have adequate ductility. The stress distributions for these sections are rectangular.

3. Semi-compact– Cross sections, in which the extreme fiber in compression can reach yield stress but cannot develop the plastic moment of resistance due to local buckling are called semi-compact or non-compact sections. These sections are used in the elastic design and the stress distribution for such sections is triangular.

4. Slender – Cross sections in which the elements buckle locally even before the attainment of yield stress are classed as slender sections.