Abstract: An optical fiber-embedded PC steel strand includes a PC steel strand in which a plurality of PC steel wires are twisted together, and an optical fiber. The optical fiber is fixed with a resin in a twist groove that is a groove between two PC steel wires of the PC steel wires, the two PC steel wires being disposed at an outer surface of the PC steel strand and being next to each other. A coefficient of variation in distance between a common tangent of the two PC steel wires that form the twist groove and are next to each other, and a center of the optical fiber is 0.5 or less, as measured in 10 cross sections of the PC steel strand that are perpendicular to a longitudinal direction of the PC steel strand.

Abstract: A tension measuring method installs a reel having a cylindrical coil forming part on a cable to be measured, forms a coil by winding a conductor around the coil forming part, measures a magnetic hysteresis loop of the cable by supplying a current to the coil to generate a magnetic field, and computes a tension of the cable using a parameter determined from the hysteresis loop. A magnetic field sensor and a magnetic flux sensor are provided inside a through hole in the coil forming part, and the cable is positioned inside the through hole. The magnetic field is varied so that the hysteresis loop includes a near-saturation magnetization region, to measure the hysteresis loop using the sensors. The parameter is selected from a magnetic flux or a magnetic flux density, a remanent magnetization, a coercivity, a magnetic permeability, and a hysteresis loss in the near-saturation magnetization region.

Abstract: A tension measuring method installs a reel having a cylindrical coil forming part on a cable to be measured, forms a coil by winding a conductor around the coil forming part, measures a magnetic hysteresis loop of the cable by supplying a current to the coil to generate a magnetic field, and computes a tension of the cable using a parameter determined from the hysteresis loop. A magnetic field sensor and a magnetic flux sensor are provided inside a through hole in the coil forming part, and the cable is positioned inside the through hole. The magnetic field is varied so that the hysteresis loop includes a near-saturation magnetization region, to measure the hysteresis loop using the sensors. The parameter is selected from a magnetic flux or a magnetic flux density, a remanent magnetization, a coercivity, a magnetic permeability, and a hysteresis loss in the near-saturation magnetization region.

Abstract: A coated PC steel stranded cable includes: a stranded cable in which a plurality of elemental wires each composed of steel are twisted together; an anti-corrosive coating having an outer circumferential portion that coats an outer circumference of the stranded cable; an outer coating that coats an outer circumference of the anti-corrosive coating; and an optical fiber provided at a position inwardly of an outer circumferential surface of the outer coating and corresponding to a strand groove in the stranded cable so as to follow expansion and contraction of the stranded cable.

Abstract: A coated PC steel stranded cable includes: a stranded cable in which a plurality of elemental wires each composed of steel are twisted together; an anti-corrosive coating having an outer circumferential portion that coats an outer circumference of the stranded cable; an outer coating that coats an outer circumference of the anti-corrosive coating; and an optical fiber provided at a position inwardly of an outer circumferential surface of the outer coating and corresponding to a strand groove in the stranded cable so as to follow expansion and contraction of the stranded cable.