Steel strands have different types according to their different uses, with the most common being aluminum coated and galvanized. Today, we will refer to the standard GB/T 33363-2016 to discuss the testing items and standards for prestressed hot-dip galvanized steel strands

Testing items and standards

1. Materials and manufacturing

1) The wire rods used for manufacturing steel strands should comply with the provisions of GB/T24238

2) Zinc ingots used for heat should comply with the provisions of GB/T470, and the minimum zinc content of zinc ingots should not be less than 99.95%

3) The steel wires that make up galvanized steel strands should be hot-dip galvanized before being twisted; The steel strand should undergo continuous stabilization treatment after being twisted During the production of a single steel wire for steel strands, only wire rod joints are allowed, and any other type of joint should be cut off. The steel wire in the galvanized steel strand used for cables should have no joints. Within a length range of 45m, there should not be more than one wire rod joint in a single wire for the use of Ferrasol After the steel strand is cut without binding, the steel wire should not be loose or dislodged, or it can be manually restored after being dislodged

6) Take a steel strand with a chord length of 1m and place it freely on a plane, with the maximum natural vector height between the chord and arc not exceeding 25mm The lay length of the steel strand should be uniform, with a range of 12 to 16 times the nominal diameter D of the steel strand If there are no special regulations, the twisting direction of the steel strand is left twisting, and the right twisting should be specified in the contract

2. Mechanical Properties

1) Mechanical Property Requirements

The mechanical properties of hot-dip galvanized steel strands should comply with the provisions of Table 2 in GB/T33363

2) Elastic modulus requirement

The elastic modulus of steel strand is (195 ± 10) GPa

3) Relaxation test requirements

70% of the nominal breaking force of hot-dip galvanized steel strands shall be used as the initial force for the relaxation test.

4) Deviation tensile coefficient

For general purpose hot-dip galvanized steel strands, the deviation tensile coefficient should not exceed 28% The deflection tensile coefficient of hot-dip galvanized steel strands used for cables should not exceed 20%

5) Fatigue performance

Calculate according to the requirements and formulas in GB/T33363

3. Performance of Galvanized Layer

1) Weight of Zinc Layer per Unit Area

The weight of zinc layer per unit area of galvanized steel wire composed of steel strands should be 190g/m ²~ 350g/m ²

2) Adhesion of Zinc Layer

At least two steel wires that make up the finished hot-dip galvanized steel strand have undergone winding tests. After 6 rounds of winding, the outer zinc layer of the spiral coil should not peel off or friction with fingers should not cause peeling.

3) Uniformity of zinc layer

Immerse sample 2 of the galvanized wire that constitutes the steel strand into a copper sulfate solution. If there is no bright deposition layer or adhesion of orange red copper at any point more than 25mm from the submerged end of the sample, it is considered qualified.

4. Surface Quality

The steel wires that make up the steel strand should have a continuous zinc layer surface, and there should be no defects such as local dezincification or exposed iron. However, slight scratches that do not affect the quality of the zinc layer are allowed locally

5. Tensile test

1) The maximum force test of the entire strand shall be carried out in accordance with the provisions of GB/T21839. When calculating the strength of the stranded wire, the nominal cross-sectional area is used In the tensile test, if the maximum compliance and elongation of the steel strand meet the requirements of GB/T33363 before a steel wire breaks If the sample breaks within the range of 2 times the nominal diameter of the stranded wire from the jaws, and the breaking force, elongation, and specified non proportional extension force do not meet the standard requirements, the test is invalid and another sample should be taken for retesting

2) Prescribed non proportional extension force

The determination of non proportional extension force shall be carried out in accordance with the provisions of GB/T21893, using the force applied when the non proportional extension of the extensometer gauge length reaches 0.2% of the extensometer gauge length.

3) Elastic modulus

The determination of elastic modulus shall be carried out in accordance with the provisions of GB/T21839

6. Relaxation test

The stress relaxation test of steel strands shall be carried out in accordance with the provisions of GB/T21839 Before testing, the galvanized layer on the surface of the sample held by the anchor should be cleaned with dilute acid to avoid corrosion of the steel substrate

7. Bias tensile test

Bias tensile test shall be conducted in accordance with the provisions of GB/T21839

8. Pulse tensile fatigue test

Pulse tensile fatigue test shall be conducted in accordance with the provisions of GB/T21939

9. Zinc layer weight

The zinc layer weight test shall be conducted in accordance with the provisions of GB/T1839

10. Zinc layer adhesion

The zinc layer adhesion should be subjected to winding test in accordance with GB.T2976

11. Zinc layer uniformity

The zinc layer uniformity test shall be conducted in accordance with the provisions of GB/T2972

12. Dimension measurement

Use a caliper with an accuracy of 0.02mm to measure the diameter of the steel strand, and measure the lay distance of the steel strand in accordance with the provisions of GB/T21839 The diameter measurement should be based on the two opposite flat wire flanges crossing the diameter direction, and measured three times in different directions on the same section, taking the average value

13. Surface quality

Visual inspection of surface quality.