This standard establishes the criteria for uncoated, stress-relieved high-strength steel strands utilized in prestressed concrete construction. It details specifications regarding manufacturing processes, dimensions, mechanical characteristics, testing procedures, and quality assurance for two-wire, three-wire, and seven-wire strands, ensuring their reliability and performance in structural applications.
Overview
This standard establishes the criteria for uncoated, stress-relieved high-strength steel strands utilized in prestressed concrete construction. It details specifications regarding manufacturing processes, dimensions, mechanical characteristics, testing procedures, and quality assurance for two-wire, three-wire, and seven-wire strands, ensuring their reliability and performance in structural applications.
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Frequently Asked
Per the standard, seven-wire strands have defined nominal diameters, cross-sectional areas, and masses detailed in a reference table. The tolerances for nominal diameters vary by class: Class 1 permits ±0.4 mm, while Class 2 allows an asymmetric tolerance of +0.66 mm and -0.15 mm. For example, a 6.3 mm seven-wire strand has a nominal diameter of 6.3 mm with ±0.4 mm tolerance and a nominal mass of 0.195 kg/m. These parameters ensure consistency in design and manufacturing.
The breaking load is determined through tensile testing of randomly sampled strands from coil batches. Sampling quantity depends on the lot size and strand type. During the test, the maximum load before failure is recorded as the breaking load. This value must meet or exceed the minimum breaking load specified in the standard’s reference table to ensure strength adequacy.
The component wires must be cold-drawn plain carbon steel with sulfur and phosphorus content not exceeding 0.05%. After stress relieving, these wires must satisfy prescribed mechanical property criteria, including tensile strength and elongation. Dimensional tolerances for wire diameter are also stipulated to maintain strand quality. Additionally, the material should be certified, preferably bearing the ISI mark, to verify compliance.
Relaxation is defined as the reduction in stress under a constant strain over time. The standard specifies a relaxation test where an initial stress equal to 70% of the minimum tensile strength is applied gradually over 5 minutes and held for 1 minute at a temperature of 20 ± 2°C. Relaxation measurements begin 6 minutes after loading. The relaxation stress after 1000 hours must not exceed 5% of the initial stress; alternatively, a 100-hour test with stricter limits and correlation to the 1000-hour value is acceptable. This ensures strands maintain prestress levels over time.
Each coil must be marked to allow traceability back to its original cast. Markings should include the strand size, coil number, and applicable class. Manufacturers are required to provide certification documents detailing manufacturing processes, mechanical test outcomes including proof load, chemical composition if applicable, and identification numbers matching the coil labels. Secure packaging and clear labeling ensure quality control and traceability throughout the supply chain.
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