The influence of the process-induced deformed state on straightness of prestressing strands after manufacture

Abstract

Based on the study of elastic-plastic deformation, the expressions of longitudinal force Nt , bending Mb and torque Mt moments in wire-cross sections subject to the process parameters of rope torsion are obtained: wire tensioning efforts, untwisting and preformation.A technique for determining the technological internal force factors (TIFF) in the rope cross-sections: the longitudinal forces ; bending and torque moments. Being guided by the theorem on unloading and FEM, the external deformed state of the rope unloading from TIFF is studied. The expression of the rope unloading deformations vector as a function of the TIFF vector using the global stiffness matrix of 4×4 rope cross-section corresponding to the elastic deformation is obtained.Based on the bending deformations, an expression was χ and ζ obtained, the parameter h (h is the segment arrow at the chord length of 1 m), which, according to the regulatory standard, characterizes the degree of the rope straightness after manufacture. The connection between the parameters of torsion (tension, untwisting, and preformation) and the parameter h of straightness is established. It is determined that the unstraightness is directly affected only by the deviation from the uniformity of tension. The developed theory allows to determine the permissible deviation from the non-uniformity of tension with the permissible value of the parameter h of straightness. For example, a prestressing strand of a structure 1+6, having a diameter of 6.9 mm is considered to be of high quality according to the standard, if h ≤ 25mm. This value h corresponds to the deviation of the tension of Δκ = 0,8 one of the 6 wires of the layer. With an increase in deviation of tension, h increases almost rectilinearly to Δκ ≃3. With further increase, a loop is Δκ formed – the loss of stability.The obtained theory of the external deformed state of unloading provides further opportunity to study the internal deformed-stress state of the rope wires due to process-induced forces, which opens the prospect of even a deeper study of operational strength and durability of ropes.