A steel cord for rubber reinforcement comprises a first group of core filaments (105) having a number of m and a second group of sheath filaments (110) having a number of n, m is three or four, the core filaments (105) are forming a helix, the core filaments (105) are not twisted together and being substantially parallel or the core filaments (105) have a twist pitch being more than 300 mm; the second group and the first group are twisted with each other, and the sheath filaments (110) are forming a flattened helix in the same direction of the helix of the core filaments (105), and the sheath filaments (110) have a cord twist pitch, at any cross-section of the steel cord, at least one interstice between two adjacent core filaments (105) is present. The steel cord has improved abrasion resistance and can contribute to the reduction of the weight of the tire.

A pre-stressed concrete structure comprises a steel wire or a steel strand. The steel wire or steel strand has been pre-tensioned before curing of the concrete or grout. The steel wire or steel strand is provided with a zinc coating. The zinc coating has a weight ranging between 70 g/m.sup.2 and 950 g/m.sup.2. The steel wire or steel strand has an outer surface that is provided with indentions to provide mechanical anchorage points in the concrete structure. The steel wire or steel strand is further provided with a passivation layer in the form of a metal oxide layer.

A pre-stressed concrete structure comprises a steel wire or a steel strand. The steel wire or steel strand has been pre-tensioned before curing of the concrete or grout. The steel wire or steel strand is provided with a zinc coating. The zinc coating has a weight ranging between 70 g/m.sup.2 and 950 g/m.sup.2. The steel wire or steel strand has an outer surface that is provided with indentions to provide mechanical anchorage points in the concrete structure. The steel wire or steel strand is further provided with a passivation layer in the form of a metal oxide layer.

A steel cord containing a core layer and an sheath layer, the core layer containing a plurality of core wires with a number of n and the sheath layer comprises a plurality of sheath wires with a number of m, and the steel cord has a flat cross-section with a major axis and a minor axis, the flat cross-section has a flat ratio being the ratio of the length of the major axis and the length of the minor axis, the flat ratio is more than 1.2, the steel cord has a breaking load being BL.sub.cord, the core wires and the sheath wires have a sum breaking load being Sum BL.sub.wires when the core wires and the sheath wires are un-twisted from the steel cord, BL.sub.cord and Sum BL.sub.wires satisfies the following formula: BL.sub.cord/Sum BL.sub.wires >96%. The steel cord has higher breaking load.

A steel cord containing a core layer and an sheath layer, the core layer containing a plurality of core wires with a number of n and the sheath layer comprises a plurality of sheath wires with a number of m, and the steel cord has a flat cross-section with a major axis and a minor axis, the flat cross-section has a flat ratio being the ratio of the length of the major axis and the length of the minor axis, the flat ratio is more than 1.2, the steel cord has a breaking load being BL.sub.cord, the core wires and the sheath wires have a sum breaking load being Sum BL.sub.wires when the core wires and the sheath wires are un-twisted from the steel cord, BL.sub.cord and Sum BL.sub.wires satisfies the following formula: BL.sub.cord/Sum BL.sub.wires >96%. The steel cord has higher breaking load.

A stranded wire having a plurality of steel wires twisted together includes, in its cross section perpendicular to its longitudinal direction, a central wire as the steel wire, a plurality of first circumferential wires as the steel wires arranged in contact with the central wire to surround an outer periphery side of the central wire, and a plurality of second circumferential wires as the steel wires arranged in contact with the first circumferential wires to surround an outer periphery side of a region where the first circumferential wires are arranged, the second circumferential wires being greater in yield stress than the central wire and the first circumferential wires. The central wire is in surface contact with the first circumferential wires. The first circumferential wires are in surface contact with the second circumferential wires.

A stranded wire having a plurality of steel wires twisted together includes, in its cross section perpendicular to its longitudinal direction, a central wire as the steel wire, a plurality of first circumferential wires as the steel wires arranged in contact with the central wire to surround an outer periphery side of the central wire, and a plurality of second circumferential wires as the steel wires arranged in contact with the first circumferential wires to surround an outer periphery side of a region where the first circumferential wires are arranged, the second circumferential wires being greater in yield stress than the central wire and the first circumferential wires. The central wire is in surface contact with the first circumferential wires. The first circumferential wires are in surface contact with the second circumferential wires.

Provided are: a rubber article-reinforcing steel cord having excellent corrosion resistance; and a method of producing the same with excellent productivity. In a rubber article-reinforcing steel cord (1), plural sheath strands (3) each formed by twisting together plural steel filaments are twisted together around at least one core strand (2) formed by twisting together plural steel filaments. Brass plating is performed on the steel filaments, and zinc plating is further performed on at least the outer circumference of the brass plating of outermost-layer steel filaments of the sheath strands (3).

Provided are: a rubber article-reinforcing steel cord having excellent corrosion resistance; and a method of producing the same with excellent productivity. In a rubber article-reinforcing steel cord (1), plural sheath strands (3) each formed by twisting together plural steel filaments are twisted together around at least one core strand (2) formed by twisting together plural steel filaments. Brass plating is performed on the steel filaments, and zinc plating is further performed on at least the outer circumference of the brass plating of outermost-layer steel filaments of the sheath strands (3).

Rubber article-reinforcing steel cord in which corrosion resistance is improved without an increase in weight. In a rubber article-reinforcing steel cord (1), plural sheath strands (3) each formed by twisting together plural steel filaments are twisted together around at least one core strand (2) formed by twisting together plural steel filaments. Core strand (2) and sheath strands (3) are each formed by twisting together one or two core filaments (2c) and (3c) and plural sheath filaments (2s) and (3s), respectively, and a relationship represented by the following Formula (1) is satisfied when a wire diameter of core filament(s) (2c) of core strand (2), a wire diameter of sheath filaments (2s), a wire diameter of core filaments (3c) of sheath strands (3), and a wire diameter of sheath filaments (3s) are defined as dcc, dcs, dsc and dss, respectively: dcc>dcsdsc>dss (1).