ISO 6934-4:2020

Overview

ISO 6934-4:2020 - "Steel for the prestressing of concrete - Part 4: Strand" specifies technical requirements for steel strand used in prestressed concrete. It covers strand that has undergone a stress‑relieving heat treatment in accordance with ISO 6934-1 and defines strand types, dimensions, mechanical properties, manufacturing conditions and delivery requirements. The standard addresses 2-, 3-, 7- and 19-wire strand configurations and covers ten grades of strand for prestressed concrete construction.

Key Topics

• Scope and manufacture
  • Applies to stress‑relieved steel strand produced by continuous linear heat treatment and rewound into reels.
  • Requirements for compacted strand (7‑wire), finishing, appearance and protection against mechanical damage.
• Strand configurations and lay
  • 2‑ and 3‑wire, 7‑wire (including compacted) and 19‑wire (Seale or Warrington patterns) with specified pitch ranges (e.g., 2–3 wire: 12–22 × nominal diameter; 7‑wire: 12–18 × nominal diameter).
• Welds and joints
  • No welds permitted in 2‑ or 3‑wire strand; limited welding of individual wires during manufacture of 7‑ and 19‑wire strand only by agreement (butt welds limited to specified frequency).
• Mechanical properties
  • Dimensions, mass per length and characteristic tensile forces are tabulated (see Table 1 in the standard).
  • Minimum total elongation (Agt) of 3.5%.
  • Nominal modulus of elasticity may be taken as 195 GPa.
• Relaxation and durability
  • Two relaxation classes (Relax 1 and Relax 2) with maximum relaxation values specified (example: at 70% initial force - Relax 1: 8.0%; Relax 2: 2.5%; at 80% - Relax 1: 12.0%; Relax 2: 4.5%).
  • Optional stress corrosion testing and guidance (Annex A) and purchaser can require corrosion‑resistance measures.
• Testing
  • Optional fatigue and deflected tensile tests (Annex B) can be required by the purchaser; the standard specifies a stress range of 195 MPa for fatigue testing when requested.
• Delivery
  • Reel dimensions, curvature limits to ensure strand is reasonably straight on unreeled, packing and protection per ISO 6934-1.

Applications and Users

• Relevant for manufacturers and suppliers of prestressing strand, precast concrete producers, bridge and building contractors, structural engineers, specifiers and quality assurance teams.
• Used to specify material for tendons, post-tensioning and pre-tensioning systems in bridges, buildings, parking structures and other prestressed concrete works.
• Helpful for procurement, production acceptance testing, design verification and durability assessment in corrosive or fatigue‑sensitive environments.

Related Standards

• ISO 6934-1 - General requirements for steel for prestressing of concrete (normative reference).
• Other parts of the ISO 6934 series detail wires, ropes and related requirements for prestressing steel.

Keywords: ISO 6934-4, steel strand, prestressing of concrete, stress‑relieving heat treatment, 7‑wire strand, 19‑wire strand, relaxation class, fatigue test, stress corrosion, strand configuration.