This standard delineates the specifications for uncoated, stress-relieved seven-ply steel strands exhibiting low relaxation, intended for use as prestressing tendons in prestressed concrete structures. It details manufacturing criteria, mechanical characteristics, testing protocols, and delivery conditions to guarantee high strength and minimal relaxation, essential for professionals in prestressed concrete construction and production.
This standard delineates the specifications for uncoated, stress-relieved seven-ply steel strands exhibiting low relaxation, intended for use as prestressing tendons in prestressed concrete structures. It details manufacturing criteria, mechanical characteristics, testing protocols, and delivery conditions to guarantee high strength and minimal relaxation, essential for professionals in prestressed concrete construction and production.
Audience
Who Uses This Standard
Structural design engineers
Civil engineering professionals
Prestressed concrete specialists
Steel strand fabricators
Quality assurance inspectors
Construction management personnel
Material testing experts
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Contents
Key Topics Covered
✓Production standards for seven-ply steel strands
✓Stress-relieving processes and low relaxation features
✓Mechanical attributes including tensile strength and proof load
✓Permissible chemical composition for steel wires
✓Sampling methodologies and testing procedures
✓Relaxation evaluation protocols and acceptance criteria
✓Dimensional accuracy, mass, and tolerances
✓Coiling, packaging guidelines, and marking rules
✓Surface quality and workmanship requirements
✓Authorized welding and strand joint regulations
✓Load application techniques and elongation measurement
✓Certification procedures and compliance validation
Structure
Table of Contents
1Scope and Applicability
2Referenced Standards and Essential Data
3Terminology and Definitions
4Manufacturing Processes and Requirements
5Chemical Composition Specifications
6Mechanical Performance Characteristics
7Sampling Procedures and Conformity Assessment
8Identification Marking and Packaging Instructions
9Certification Marking and Licensing
Annex ADetails of Committee Members
Frequently Asked
Popular Questions About IS 14268
?What mechanical performance criteria are specified for low relaxation seven-ply strands?▼
The standard mandates that when the strands are initially stressed to 70% of their specified minimum breaking strength (SMBS), the relaxation losses must not exceed 1.8% after 100 hours and 2.5% after 1000 hours. These limits ensure minimal loss of prestress over time, vital for structural longevity. Testing conditions and durations are prescribed in the relevant clauses to verify compliance.
?How is the low relaxation characteristic achieved and verified as per the standard?▼
Low relaxation in strands is attained through a hot stretching stabilization process where the strand undergoes tension during stress-relieving heat treatment, inducing linear hardening that enhances creep resistance and reduces relaxation. The relaxation is then measured over a test duration of up to 1000 hours or extrapolated from shorter tests, ensuring relaxation losses remain within defined limits.
?What are the chemical composition limits for steel wires used in these strands?▼
The steel wires must conform to maximum limits of 0.050% for sulphur and 0.050% for phosphorus, ensuring the use of high-quality plain carbon steel. The wires are cold drawn and must be free from surface defects. Chemical analyses follow IS 228 parts related to sulfur and phosphorus determination to maintain these standards.
?Are welding or joints permitted during the manufacturing of the strands?▼
Welding is allowed only in individual wires prior to or during the final heat treatment stage, with a restriction of one butt weld per 45 meters of wire length. No joints or splices are permitted in the finished strand unless explicitly authorized by the purchaser, preserving strand integrity and performance.
?What requirements govern the packaging and marking of the strands upon supply?▼
Strands must be delivered in reels or reelless packs with a minimum core diameter of 600 mm, as agreed between supplier and purchaser. Each unit must be clearly labeled with the manufacturer’s identification, coil number, nominal strand diameter, and strand class if applicable. Additionally, coils may bear the BIS Standard Mark to certify compliance, facilitating traceability and quality assurance.
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