Influence of Atmospheric Humidity on the Critical Buckling Load of Reinforced Concrete Columns

In this paper, an evaluation of the influence of atmospheric humidity on the critical buckling load of reinforced concrete columns is performed. A particular case consisting of a real, extremely slender reinforced concrete pole was taken for the study. The chosen mathematical procedure for calculating the critical load is based on the Mechanics of Deformable Solids due to variations of structure vibration frequency over time. The rheological behavior of concrete related to creep and shrinkage, which illustrates the time-dependent aspect of the problem, was also considered in the analysis following normative recommendations from the Brazilian Association of Technical Standards (ABNT). In order to evaluate value changes of critical buckling loads, different time instants after loading the structure as well as different relative humidity from 0% to 100%, in 10% increments were considered. According to the selected criteria, it was possible to verify that a higher atmospheric humidity decreases the water transport from the interior out to the exterior surfaces of concrete, hence positively influencing structure stiffness. Therefore, the lowest reduction on critical buckling was 41.9% at 100% relative atmospheric humidity, versus the highest 60.7% at 0% relative humidity. A period of 7500 days after loading the structure was considered in the analysis.

GENERAL STRUCTURE OF TILLAGE DRAFT FORCE. CONSEQUENCES IN EXPERIMENTAL AND APPLICATIVE RESEARCHES

The empirical and theoretical estimation of the draft force of agricultural machinery for soil tillage, has been the target of scientific research for about one hundred years. The results obtained so far may seem contradictory or divergent. The article presents the results of some research on the usual calculation formulas of the draft force of agricultural machines for soil tillage. Although apparently these formulas are different, analyzing the structure of the formula, we find cohesion and coherence embodied in a simple generalization and easy to use both theoretical and experimental. Moreover, the formulas are convertible between them, the two languages used for their definition (the mechanics of deformable solids and that of the phenomenological description), are only different forms of expression for the same phenomenon. Another problem that is addressed in the research whose results are presented in this article is that of highlighting the dependence of the draft force on the tool speed (in the field) of the soil tillage machine. Exposure is complemented by an algorithm that highlights the dependence of the draft force on the tillage tool speed. Also like a consequences of the draft tillage force structure, finally, a third problem addressed in these researches and whose results and perspectives are given in this paper is that of optimizing the working processes of agricultural machinery for soil tillage. The treatment of the problem starts from the hypothesis of the most general formula of the traction resistance force and proposes some ways to solve the optimal problem.

THE SOLUTION OF PHYSICALLY NONLINEAR PROBLEMS OF BENDING VALVE PLATES

The algorithm of Kantorovich gradient method applied to nonlinear problems of construction mechanics and mechanics of deformable solids, proposed in [1], is applied to the study of the bending of physically nonlinear plates of variable thickness. This article should be considered as a logical development of the content of the work [2]