What develops in a beam when the plastic moment is removed?

When the plastic moment is removed from a beam, the structure no longer experiences the fully plastic behavior it exhibited at that moment. The plastic moment represents the maximum moment a beam can resist due to plastic deformation, meaning that the sections have yielded, and the material behavior has transitioned into a plastic state.

Once the plastic moment is no longer acting, the beam is assumed to revert to an elastic state, which typically results in the formation of residual stresses within the material. These residual stresses are internal forces that are locked within the beam even when it is unloaded, arising due to differential yielding, temperature changes, or changes in support conditions, and they counteract external loads to some extent. They can be tensile or compressive depending on the specific conditions of the beam and the loading history.

Identifying the development of residual stress is crucial for understanding the long-term performance of structural elements, as these stresses can influence both stability and material fatigue over time.