FEM research of internal stresses evolution in the prestressing strand production

Abstract

The article presents the finite-element modeling results of stranding, reduction, straightening and mechanicalthermal treatment (MTT) of prestressing strand (PSC strand). Computer models took into account the distribution of residual stresses formed at the preliminary stage of wire drawing. During the simulation, the effect of MTT on the internal stresses of the wires was studied: residual stresses after the drawing process and additional stresses after the stranding. All studied methods demonstrated a positive effect not only from the point of eliminating internal stresses, but also from the point of view of their favorable redistribution. The reduction of PSC strand in a monolith tool with strain degree 1-3% allows to minimize tensile stresses on the surface of the wires and save compressive stresses in the center of the wires. The straightening by a group of 5 rolls made it possible to reduce the tension of outer wires twice. The MTT application, combining the effects of various physical nature, made it possible to control over a wide range the redistribution of residual stresses in the wires after high strain degrees and the additional stresses created during the stranding, which affect the preservation of the geometric parameters of the PSC strand. The study showed that to eliminate longitudinal residual stresses, the magnitude of the tension in the MTT is the most important parameter. Therefore, with a minimum value of tension, the residual stresses are not redistributed either in the central or in the surface layers, regardless of the temperature of the MTT. However, with tension above 70 kN and a temperature of 380-400°C, the residual stresses in the center and on the surface of the wires are balanced or almost completely eliminated.