Question

The ultimate moment capacity of a mild steel section is usually
1. Equal to the plastic moment capacity
2. More than the yield moment capacity
3. Less than the plastic moment capacity but more than the yield moment capacity
4. More than the plastic moment capacity

Answer 1

Correct Answer - Option 1 : Equal to the plastic moment capacity

If the cross –section of beam is subjected to yield stresses throughout the depth, it cannot take further loads. If any additional load is applied, then the beam rotates at that section. Since, the beam rotates due to moment; we call it plastic moment capacity. This will be the ultimate moment capacity as such beam is not able to resist further any load.

The yield moment of a cross section is defined as the moment that will just produce the yield stress in

the outer most fibres of the section only. It is always less than plastic or ultimate moment capacity of section.