Steel strand & wire
High-strength steel wire is available (with a characteristic strength in the order of 1800 N/mm2) may be used for prestressing. However, it is more usual for several wires to be formed into a strand, the most common being 7-wire strand although 5-wire and 19-wire are available from some suppliers.
A range of strand diameters is available, from about 8 mm to 18 mm with corresponding characteristic strengths from about 70 kN to 380 kN. Tendons may have ‘normal relaxation’ characteristics under load or may be treated so that they have ‘low relaxation’. For large structures it is common to form a groups of strands into tendons.
The relevant British Standard is BS 5896, Specification for high tensile steel wire and strand for the prestressing of concrete.