Análise experimental do efeito de fadiga em vergalhões de 7 mm de aço CA-60 em barras isoladas e telas soldadas para aplicação em concreto armado

Abstract

This paper presents a comparative study between isolated bars and welded mesh of CA-60 steel rebar used in reinforced concrete structures in relation to fatigue behavior. In reinforced concrete structures subjected to mobile loads, the fatigue effect is relevant and can cause the structural element to collapse. Therefore, it is of utmost importance to check the fatigue resistance of the steel to guarantee the safety of the structure during its lifespan. An experimental analysis of specimens of CA-60 steel rebar, 7 mm diameter, in an isolated form and with a welded mesh, was submitted to air fatigue tests. From the results obtained in the tests, Wöhler curves were generated, relating three levels of tension fluctuation and the number of rupture cycles, for each of the two forms of execution of the bars. In addition, the nominal mass was checked and hardness, X-ray fluorescence and tensile tests were carried out, as well as the microstructural analysis of the material. One of the main reasons that led to the development of this experimental research was the lack of a standardization that could prescribe the behavior of steel bars and welded mesh of CA-60 steel subjected to cyclical actions. It is noteworthy that this type of steel is produced through cold treatment, with the compression of the grains mechanically, resulting in greater hardness and resistance to requests, and less ductility and resistance to the aggressiveness of the environment. In the case of screen-shaped bars, the spot welding process had an influence on the microstructure and the resistance to fatigue was changed. Therefore, this work will contribute to an improvement of the normative statements for the dimensioning and verification of fatigue in reinforced concrete structures.