ISO 6934-5:1991

Overview

ISO 6934-5:1991 is an international standard published by the International Organization for Standardization (ISO) that specifies the technical requirements for hot-rolled steel bars used in the prestressing of concrete. This part of the ISO 6934 series focuses on round high tensile steel bars with either plain or ribbed surfaces, applicable for nominal bar diameters ranging from 15 mm up to 40 mm. The steel bars covered by this standard can be supplied either as hot-rolled alone or hot-rolled with subsequent mechanical processing to enhance their properties.

The standard ensures consistent quality, mechanical characteristics, and surface configuration essential for the structural integrity and durability of prestressed concrete applications.

Key Topics

• Steel Quality and Manufacture
  Bars must be produced from steel meeting the general requirements of ISO 6934-1 and manufactured by hot rolling. They may undergo further mechanical processing as agreed between purchaser and manufacturer.

• Surface Configuration
  The surface of the bars can be plain or ribbed. For ribbed bars, ribs must be transverse with uniform spacing not exceeding 0.8 times the nominal bar diameter. Rib dimensions are defined to provide adequate bonding with concrete.

• Mechanical Properties
  Bars are required to meet minimum tensile strength, 0.1% proof stress, and elongation values. A characteristic total elongation of at least 3.5% is specified, ensuring ductility.

• Relaxation and Fatigue
  Relaxation limits are set at a maximum of 4.0% after 1000 hours at 70% of the characteristic maximum force, critical for long-term prestressing performance. Fatigue resistance is also considered, with some bars able to withstand 2 million loading cycles without failure.

• Designation and Marking
  Bars must be clearly designated including the standard reference, bar type, nominal diameter, nominal tensile strength, and surface type (plain or ribbed), facilitating traceability and specification compliance.

• Delivery Conditions
  Delivery must follow ISO 6934-1 with adequate protection against damage. Bars may have threaded ends cold-rolled to agreed profiles if necessary.

Applications

ISO 6934-5 steel bars are primarily used in prestressed concrete construction, where high tensile strength and reliable mechanical properties are essential to resist stresses and improve the performance of concrete structures such as:

• Bridges
• High-rise buildings
• Parking garages
• Industrial floors and slabs
• Parking structures and infrastructure elements requiring high durability and load-bearing performance

Their ribbed or plain surfaces enhance the bond strength between steel and concrete, optimizing prestressing efficiency.

Related Standards

ISO 6934-5 is part of the broader ISO 6934 series, which addresses various types of steel components used for prestressing concrete. Relevant related parts include:

• ISO 6934-1: General requirements for steel used in prestressing concrete
• ISO 6934-2: Cold-drawn wire
• ISO 6934-3: Quenched and tempered wire
• ISO 6934-4: Strand

Additional related standards often referenced include:

• ISO 10065: Steel bars for reinforcement - Bend and rebend tests, ensuring bending ductility
• National or regional standards that complement ISO 6934 series in specific construction practices

Summary

ISO 6934-5:1991 provides a comprehensive framework for the specification, quality control, designation, and delivery of hot-rolled steel bars for prestressed concrete. By standardizing the mechanical properties, surface texture, and production requirements, this standard supports the production of reliable prestressing steels essential for modern civil engineering and infrastructure projects. Adherence to ISO 6934-5 results in enhanced structural safety, durability, and performance of prestressed concrete members worldwide.

Keywords: prestressing steel, hot-rolled steel bars, iso 6934-5, prestressed concrete, high tensile steel bars, ribbed steel bars, steel specifications, concrete reinforcement steel, steel bar tensile strength, relaxation of prestressing steel.