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ISO 15630-3 Testing of Prestressing Steel Strands Relaxation, Fatigue, Tensile testing

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ISO 15630-3 Steel for the reinforcement and prestressing of concrete — Test methods — Part 3: Prestressing steel

This standard specifies test methods applicable to prestressing steel (bar, wire or strand) for concrete.


ISO 15630-3, ASTM A416 and ASTM A1061 test standards offer guidelines for testing steel strands. Manufacturers of steel strands are required, through product standards, to test their products using both static and dynamic conditions.

ASTM A416Standard Specification for Low-Relaxation, Seven-Wire Steel Strand for Prestressed Concrete
ASTM A1061Standard Test Methods for Testing Multi-Wire Steel Prestressing Strand
XP A 35-045PRESTRESSING STEELS - PART 1: GENERAL REQUIREMENTS
EN 10138-3Prestressing steels. - Part 3: Bars



Static Tensile test of steel strands: 

In static tensile tests according to ISO 15630-3, ASTM A416, and ASTM A1061, the steel strand undergoes elongation until it fractures. Steel strands are composed of multiple wires twisted together, and they tend to untwist when subjected to tensile loads.

Throughout the tensile test, both the force applied to the specimen and its elongation are measured. Testing machines designed for high test loads are predominantly utilized because prestressing steel is a high-strength steel.

ISO 15630-3 Testing of Prestressing Steel Strands Relaxation, Fatigue, Tensile testing

Dynamic Tests on Prestressing Steel Strands:

In the high cycle fatigue test (for example, according to ISO 15630-3, XP A 35-045-2011, EN 10138-3:2009) on steel strands, the specimen must withstand two million test cycles at a maximum frequency of 20 Hz without fracturing.

specimen fractures near or in the grip, the test is considered invalid and needs to be repeated. Invalid tests are very costly, as the fatigue test lasts several days. Prestressing steel strands, being highly stiff, are particularly sensitive to notching.


Steel Strands Relaxation Testing

Test principle: 

The relaxation test of steel strands is a test to measure the degree of deformation of steel strands after long-term stable loading. In this experiment, the steel strand first needs to be subjected to a constant load to ensure that it reaches a "steady state". After being subjected to a certain amount of load for a certain period of time, measuring the elongation generated by the steel strand can determine its performance under that load. This experiment can simulate actual usage conditions, thereby more accurately evaluating the service life and safety performance of steel strands.


Test steps: 

1. Pre treat the steel strand to achieve a stable state.

2. Apply a constant load to achieve a stable state.

3. Maintain a specified time under a constant load.

4. After stopping the load, record the length change of the steel strand.

5. Calculate the stress relaxation rate of steel strands based on experimental data.


Key words: 

ISO 15630-3 - British Standard 15630-3 - Mechanical Testing - Dimensional Measurement - Corrosion Tests - Prestressing Steels - Concretes - Reinforcing Materials - Stress Corrosion - Reinforcing Steels - Prestressed Concrete - Construction Materials - Steels - Reinforced Concrete - Modulus of Elasticity - Wires - Bars (Materials) - Bend Testing - Stress Relieving - Fatigue Testing - Tensile Testing

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