Effect of Creep on Stability of Structural Elements

Creep, which represents the gradual increase of deformation over time, is a typical phenomenon of viscoelastic materials. Its consideration is necessary in the stability verification of compressed slender pieces in ultimate limit state because these pieces can have their stiffness modified as a function of the rheology of the material. Mathematically, creep can be characterized by models where the immediate elastic deformation is increased by viscous deformation, resulting in a temporal function. Although the first postulations for the understanding of stability (or buckling) have been solved statically, the phenomenon penetrates the field of structural dynamics since it involves the concept of the vibration of mechanical systems. In both cases, whether static or dynamic, it is necessary to consider the total stiffness of the structural element as composed of two terms, the conventional stiffness portion and the geometric stiffness portion. In this way, it is possible to include in the first plot a modulus of elasticity variable in time, that allows to follow the increase of the deformations, according to the model adopted for their representation, even under constant tension.

Keywords: Creep; Stability; Critical buckling load; Slender elements; Viscoelastic materials