In this paper, the induced stress in longitudinal reinforcement bars with cross sections subjected to concrete creep and shrinkage was evaluated. The study was performed for a reinforced concrete column, with loading varying from zero-in which the structure is exclusively subjected to self-weight-to forces close to the loss of stability by bifurcation of equilibrium. A real precast concrete pole, extremely slender, with geometry varying lengthwise, was the structure chosen for the analysis. The aspects related to the material nonlinearity, as well as creep, shrinkage and the development of characteristic concrete strength, were taken into account following Brazilian normative recommendations in NBR 6118:2014 (Design of structural concrete-Procedure) by the Brazilian Association of Technical Standards (ABNT). The critical buckling load was defined according to the structural frequency by using particularly nonlinear formulations. The results were obtained for different instants without exceeding the expected time for convergence of results. The maximum relative value found for the reinforcement stress was 1.24% of the steel yield strength, eliminating the possibility of yielding material.

The effects of axial compressive forces on free vibration frequencies of rotating machine support beams are investigated taking into account their geometric stiffness. One class of structures that has economic and strategic importance is the base of machines, which is excited by vibrations induced by the supported equipment. These vibrations can affect the structures or, more generally, may generate damage to the supported equipment and the quality of production. They may also render human working conditions difficult. In the current work, these effects are studied via mathematical modeling, numerical simulation and experimental evaluation.

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