Value and development of the relaxation, with new test’s mode - under the influence of fatigue

Abstract

In the prestressed structures and elements, of important influence are the steel losses -of different nature, course, performance and value- during the time or as final value. One of these losses is from the relaxation of the prestressed steel, which function of development and progress on time, as well as the presumed final value, depends from the type of steel and used reinforcement, from its initial tension and variation on time, etc.. This loss is quantified through functions elaborated by expensive tests, which need long time -a minimum of 120 hours up to 1,000 hours- under continuous monitoring and constant conditions of temperature and tension value. For this the author, thought to realize such tests under fatigue, permitting to realized them in a very short time, reducing to the minimum tests difficulty and costs. In such a way one can be able to realize, for the same cost and less time, a greater number of these tests in order to know at the best the real behavior of prestressed steels under the action of various factors, both in its performance over time as well as in its last value. The first tests followed by the author in this direction, object of this article, gave results that validate the above idea and enable to correct the parameters and mode of future tests. This article presents the research program of losses on prestressed steels, in the study of the relaxation phenomenon, describing the terms and characteristics of the test, after been modified by introducing on it the fatigue influence. At the end, by the carried out tests, for the types of tested champions of steel, devices, methods and relative results, are illustrate the first considerations and formulas.