Study of the structure of steel strand K-12 (3+3+6) according to the criterion of using the strength properties of steel

An analytical study of the complex stress-strain state of steel spiral strand with linear contact of wires K-12 (3 + 3 + 6) used as a prestressed reinforcement of reinforced concrete structures is presented. There is not a single straight wire in K-12 (3+3+6), it consists only of spiral winding wires. The three layer-forming wires of the first layer can be conventionally called the core or the central three-wire strand. In the spiral strand with linear contact of wires, the length of the wires of the outer layer always exceeds the length of the wires of the inner layer located under them. That is, the wires of the outer layer have the maximum deformation properties and, therefore, the minimum stresses occur in them. The wires of the central strand in K-12 (3 + 3 + 6), being the shortest wires, have minimal deformation properties and, therefore, maximum stresses occur in them. Moreover, their strength is not the greatest since their diameter is not the smallest (the smaller the wire diameter, the higher its strength). Thus, the design of the K-12 (3 + 3 + 6) strand is not optimal in terms of the maximum use of the strength properties of steel in the wires of the strand. The author has developed a new steel spiral strand with linear contact of wires K-6 (3+3), which has an optimal structure according to the criterion of maximum use of the strength properties of steel in the wires of the strand. K-6 (3 + 3) is a strand with an incomplete external layer and improved technological characteristics.