GB/T 5224-2023Steel strand for prestressed concrete (English PDF)

3.1 standard strand

The steel strand twisted from cold-drawn round steel wires.

3.2 indented strand

The steel strand twisted from steel wires containing indentations.

3.3 helical rib strand

The steel strand twisted from steel wires containing helical ribs.

3.4 compact strand

The steel strand that is twisted, and then, cold-compacted.

3.5 nominal diameter

The nominal dimension of the diameter of the circumscribed circle of the steel strand.

3.6 stabilizing treatment

In order to reduce stress relaxation during application, the steel strand is subject to heat treatment under a certain tension for a short period of time.

4.1 Classification and Code

The general structure of the steel strand is classified into the following 9 categories, and the structure codes are.

4.2 Labeling

The labeling of products delivered in accordance with this document shall include the following content.

6.1 The dimensions and allowable deviations, nominal cross-sectional area, and theoretical

weight per meter of the 1  2 structured steel strands are shown in Table 1, and the schematic diagram of the cross-sectional shape is shown in Figure 1.

6.2 The dimensions and allowable deviations, nominal cross-sectional area, and theoretical

weight per meter of the 1  3 structured steel strands are shown in Table 2, and the schematic diagram of the cross-sectional shape is shown in Figure 2.

6.9 The weight of each coil of the steel strands is not less than 1,000 kg. When there are no less

than 10 coils, 10% of the number of coils of the steel strands is allowed to be less than 1,000 kg, but not less than 300 kg.

7.1 Manufacturing

7.1.1 The steel strands should be manufactured by wire rods of designations that comply with

the stipulations of GB/T 24238 or GB/T 24242.2 and GB/T 24242.4.Wire rods of other designations can also be adopted. The manufacturer does not provide the chemical composition.

7.1.2 The steel strands shall be manufactured with wire rods as the raw material, which are

subject to surface treatment and cold-drawing, and then, twisted into steel strands. After twisting, the steel strands shall undergo continuous stabilizing treatment.

7.1.4 The twist direction of the helical rib steel strands shall be the same as the helical ribs.

7.1.6 There shall be no broken, transverse cracks or intersecting wires in the steel strands.

7.1.7 The twist direction of the steel strands is generally left (S) twist, and right (Z) twist shall

be indicated in the contract.

7.2.5 The elastic modulus of the steel strands is (195  10) GPa, which is not required as a

delivery condition. When required by the demand-side, this range shall be satisfied. If it exceeds this range, with reference to the stipulations of GB/T 21839, in the stress - strain curve, the slope value of the straight-line segment within the range of 0.2Fm ~ 0.7Fm can be re-corrected and select the best fit to obtain it.

7.2.6 In accordance with the agreement between the demand-side and the supply-side, steel

strands with strength levels other than Table 7 ~ Table 10 can be provided.

7.2.7 If there are no special requirements, only the relaxation test with an initial force of 70%

Fma is performed, and the reckoning algorithm is allowed to be used to conduct a 120-h relaxation test to determine the 1,000-h relaxation rate. There is no requirement for the relaxation rate of the steel strands used for mine support.

7.3 Surface Quality

7.3.1 Unless the user has special requirements, there shall be no oil, grease and other substances

on the surface of the steel strands.

7.3.2 There shall be no detrimental defects that may affect the performance on the surface of

the steel strands. Axial surface defects are allowed, but their depth shall be less than 4% of the diameter of a single steel wire.

7.3.4 Tempering color is allowed on the surface of the steel strands.

7.4 Straightness of Steel Strands

The straightness of the steel strands shall not be greater than 25 mm.

7.5 Fatigue Properties, Deflection Tensile Properties and Stress Corrosion Properties

Through negotiation between the demand-side and the supply-side, and statement in the contract, axial fatigue test, deflection tensile test and stress corrosion test can be carried out.

8.1 Surface Inspection

Conduct visual inspection on the surface quality.

8.2 Inspection of Overall Dimensions

8.2.1 The diameter of the steel strands shall be measured with a measuring tool with a division

value of not greater than 0.02 mm. The distance between the measurement position and the end shall not be less than 300 mm.

8.4 Tensile Test

8.4.1 General requirements

In accordance with the stipulations of GB/T 21839, anchor clamps for prefabricated field-tensioned steel strands shall not be used for the tensile test on the steel strands.

The design of the clamping device shall ensure that during the test, the load is distributed along the entire clamping length, and the minimum effective clamping length shall not be less than one lay length of the steel strands.

8.4.2 Maximum force

The maximum force test of the whole steel strands shall be carried out in accordance with the stipulations of GB/T 21839.When calculating the tensile strength, take the nominal cross-sectional area value of the steel strands.

8.4.4 Total elongation of maximum force

The total elongation Agt of the maximum force is determined in accordance with the stipulations of GB/T 21839.If a computer is used to collect data or an electronic tensile equipment is used, when measuring the elongation, the elongation caused by the preload on the specimen shall be added to the total elongation.

8.4.5 Elastic modulus

The elastic modulus is determined in accordance with the stipulations of GB/T 21839.

8.5 Straightness

The straightness measurement of the steel strands shall be carried out in accordance with the stipulations of GB/T 21839.

8.6 Measurement and Calculation of Nominal Weight Deviation per Meter

8.6.3 The measured unit weight is the average value of three calculated values.

8.6.4 To calculate the nominal weight deviation per meter, the difference between the average

measured unit weight of the specimens and the corresponding nominal weight per meter provided in this document shall be divided by the corresponding nominal weight per meter. The percentage of the calculation result is the nominal weight deviation per meter.

8.7 Test of Stress Relaxation Properties

8.7.1 The test of stress relaxation properties of the steel strands shall be carried out in

accordance with the stipulations of GB/T 21839.

8.7.2 The test gauge length shall not be less than 60 times the nominal diameter.

8.8 Fatigue Test

8.8.1 The specimens used for the fatigue test are specimens taken directly from the finished

steel strands. The length of the specimens shall ensure that the distance between the two clamps is not less than 500 mm or twice the lay length (whichever is the larger value).

8.8.4 The fatigue test shall be carried out in accordance with the stipulations of GB/T 21839.

8.9 Deflection Tensile Test

The deflection tensile coefficient D of the general-purpose steel strands shall be  28%; the deflection tensile coefficient D of the steel strands used for stay cables shall be  20%. The deflection tensile test shall be carried out in accordance with the stipulations of GB/T 21839.

8.11 Numerical Rounding

The numerical rounding and judgement of the inspection results shall comply with the stipulations of YB/T 081.

9.1 Classification of Inspection

The inspection of the steel strands is classified into delivery inspection and eigenvalue inspection.

9.2 Delivery Inspection

9.2.1 Inspection and acceptance

The factory inspection of the product is carried out by the supply-side’s quality inspection department in accordance with Table 12, and the demand-side may conduct inspection and acceptance in accordance with this document.

9.2.2 Batch rules

The steel strands shall be inspected and accepted in batches. Each batch is composed of steel strands of the same designation, same diameter and twisted by the same production process.

The weight of each batch shall not exceed 100 t.

9.2.3 Inspection items and sampling size

The requirements for the inspection items and sampling size are as follows.

9.3 Eigenvalue Inspection

9.3.1 The eigenvalue inspection is applicable to the following circumstances.

9.3.2 The eigenvalue inspection shall be performed in accordance with the rules in Appendix A.