GB/T 40029-2021Steel strand for prestressed concrete of LNG (English PDF)

3.1 Cold drawn round wire

smooth round steel wire formed by cold drawing of wire rod

3.2 Strand

5.1 Codes

For the strand that is twisted by six cold drawn round wires, around a cold drawn round wire, according to the same twist direction, the same twist distance, its structure code is: 1×7.

5.2 Marks

Products are marked with product name, structure code, nominal diameter, strength level, and file number. Example:

The steel strand of which the nominal diameter is 15.70mm, tensile strength is 1860MPa, is marked as: prestressed steel strand 1×7-15.70-1860-GB/T 40029-2021

7.1 Shape, size, weight and allowable deviation

The size and allowable deviation of the steel strand shall meet the requirements […]

7.2

7.2.4 The lay length of the steel strand shall be 12 to 16 times the nominal diameter of the steel strand.

7.2.5 The diameter of the center wire shall not be less than 1.03 times the diameter of the outer wire.

7.2.6 There shall be no broken, cross-cracked and intersecting steel wires in the steel strand.

7.2.7 The twist direction of the steel strand is right twist or left twist.

7.2.8 The steel strand shall be cut with a grinding wheel saw. It shall not be loose after cutting. If it leaves the original position, it shall be manually restored to the original position.

7.2.9 There shall be no welding points on the steel strand, including the welding points before drawing.

7.3 Properties

7.3.1 The mechanical properties of steel strand shall meet the requirements of Table 3.

7.3.2 The steel strand is drawn and fractured. The steel wire fracture shall be plastic fracture.

7.3.3 The rate of reduction in area Z of the central steel wire of the strand is not less than 25%.

7.3.4 The elastic modulus E of the steel strand is (195±10) GPa, which cannot be used as a delivery condition. When requested by the purchaser, the range value shall be met.

8.3.2 0.2% yield strength

The 0.2% yield strength test of the steel strand is carried out in accordance with the provisions of GB/T 21839. The 0.2% yield force is the force (Fp0.2) when the non-proportional extension of the extensometer gauge length (not less than 500mm) reaches 0.2% of the extensometer gauge length. When measuring Fp0.2, the preload is 10% of the nominal maximum force.

8.3.3 Maximum force total elongation

The determination of the maximum force total elongation Agt is carried out in accordance with the provisions of GB/T 21839. If it uses a computer to collect data or use electronic stretching equipment, the extension of the specimen caused by the preload when measuring the elongation shall be added to the total extension.

8.3.4 Elastic modulus

The determination of elastic modulus is carried out according to GB/T 21839.

8.3.5 Steel wire section shrinkage rate

The rate of reduction in area of steel wire shall be determined in accordance with the provisions of GB/T 228.1. After the wire is broken, the diameter of the wire is measured in two mutually perpendicular directions at the smallest point of the necking (if necessary, the broken part of the specimen shall be butted together at the break). Take the average value d1. The rate of reduction in area of steel wire is calculated according to formula (2):

Where, Z - Rate of reduction in area, %; d1 - Average diameter after breaking, in millimeters (mm); d0 - Original average diameter, in millimeters (mm).

8.4 Stress relaxation performance test

8.4.1 The stress relaxation performance test of steel strand shall be carried out according to GB/T 21839.

8.4.2 The test gauge length is not less than 60 times of the nominal diameter.

8.4.3 No heat treatment or cold working shall be carried out after specimen […]

10.2 Labeling

Each steel strand coil shall be attached with a sign, indicating supplier name, product name, mark, exit-factory number, specification, strength level, furnace batch number, execution document number, weight and number of pieces.

10.3 Transportation

The steel strand shall be transported in a closed type. Pay attention to waterproof. Avoid contact with all objects that may cause mechanical or chemical damage to the steel strand. Be careful when loading and unloading to prevent damage to the steel strand and its packaging.

10.4 Storage

10.4.1 Steel strands shall be stored indoors. Set up support pads to prevent the steel strand from contacting the ground.

10.4.2 Pay attention to ventilation during storage of steel strands and prevent atmospheric corrosion to the steel strands.

10.4.3 During storage, all steel strands shall be protected with water-soluble anti-rust oil or similar products every 10d~12d if they are unpacked.

10.5 Quality certificate

Each batch shall be accompanied by a quality certificate, indicating the supplier's name, product name, specification, mark, strength level, implementation standard, weight, number of pieces, purchaser's name, test results, delivery date, and quality inspection department's imprint. […]