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GB/T 21839-2019 (GBT 21839-2019)

GB/T 21839-2019_English: PDF (GBT21839-2019)
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BASIC DATA
Standard ID GB/T 21839-2019 (GB/T21839-2019)
Description (Translated English) Test methods of steel for prestressing concrete
Sector / Industry National Standard (Recommended)
Classification of Chinese Standard H49
Classification of International Standard 77.140.65
Word Count Estimation 30,367
Date of Issue 2019-06-04
Date of Implementation 2020-05-01
Older Standard (superseded by this standard) GB/T 21839-2008
Drafting Organization China Metallurgical Construction Research Institute Co., Ltd., Changshu Longteng Rolling Body Manufacturing Co., Ltd., Liaoning Tongda Building Materials Industry Co., Ltd., Tianjin Yinlong Prestressed Material Co., Ltd., Tianjin Metallurgical Group Zhongxing Shengda Steel Co., Ltd., Beijing Tieke Shougang Track Technology Co., Ltd., Huludao North Metal Products Co., Ltd., Tianjin Iron and Steel Group Co., Ltd., Metallurgical Industry Information Standards Institute
Administrative Organization National Steel Standardization Technical Committee (SAC/TC 183)
Regulation (derived from) National Standard Announcement No.7 of 2019
Proposing organization China Iron and Steel Association
Issuing agency(ies) State Administration of Markets and China National Standardization Administration

GB/T 21839-2019
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.140.65
H 49
Replacing GB/T 21839-2008
Test methods of steel for prestressing concrete
(ISO 15630-3:2010, Steel for the reinforcement and prestressing of concrete –
Test methods – Part 3: Prestressing steel, MOD)
ISSUED ON: JUNE 04, 2019
IMPLEMENTED ON: MAY 01, 2020
Issued by: State Administration for Market Regulation;
Standardization Administration of PRC.
Table of Contents
Foreword ... 4 
1 Scope ... 6 
2 Normative references ... 6 
3 Symbols and description ... 7 
4 General requirements for specimen ... 9 
5 Tensile test ... 9 
6 Bending test ... 12 
7 Repeated bending test ... 13 
8 Torsion test ... 14 
9 Winding and coating adhesion test ... 15 
10 Isothermal relaxation test ... 15 
11 Axial force fatigue test ... 20 
12 Stress corrosion test in thiocyanate solution ... 22 
13 Deflection tensile test ... 25 
14 Chemical analysis ... 29 
15 Geometry measurement ... 29 
16 Determination of relative rib area (fR) ... 32 
17 Determination of the deviation of nominal mass per meter ... 34 
18 Testing of anti-corrosion grease content ... 35 
19 Sheath thickness measurement ... 36 
20 Coating uniformity test ... 36 
21 Zinc layer quality test ... 36 
22 Test report ... 37 
Appendix A (Informative) List of comparisons between this standard and ISO
15630-3:2010 ... 38 
Appendix B (Informative) The technical differences between this standard and
ISO 15630-3:2010 and their reasons ... 39 
Appendix C (Informative) Tensile test method of steel strand for prestressed
concrete ... 40 
Test methods of steel for prestressing concrete
1 Scope
This standard specifies the test methods for the tensile, bending, repeated
bending, torsion, winding and coating adhesion, isothermal relaxation, axial
force fatigue, stress corrosion in thiocyanate solution, deflection tensile,
chemical analysis, measurement of geometric dimensions, determination of
relative rib area, determination of nominal mass deviation per meter, detection
of anti-corrosion grease content, measurement of sheath thickness, coating
uniformity, zinc layer quality and so on, of the steel for prestressing concrete.
This standard applies to the determination of the relevant properties of
prestressed steel wires, prestressed steel rods, prestressed steel bars,
prestressed steel strands.
2 Normative references
The following documents are essential to the application of this document. For
the dated documents, only the versions with the dates indicated are applicable
to this document; for the undated documents, only the latest version (including
all the amendments) are applicable to this standard.
GB/T 228.1 Metallic materials - Tensile testing - Part 1 : Method of test at
room temperature (GB/T 228.1-2010, ISO 6892-1:2009, MOD)
GB/T 230.1 Metallic materials - Rockwell hardness test - Part 1: Test method
(GB/T 230.1-2018, ISO 6508-1:2016, MOD)
GB/T 232 Metallic materials - Bend test (GB/T 232-2010, ISO 7438:2005,
MOD)
GB/T 238 Metallic materials – Wire - Reverse bend test (GB/T 238-2013,
ISO 7801:1984, MOD)
GB/T 239.1 Metallic materials - Wire - Part 1: Simple torsion test (GB/T
239.1-2012, ISO 7800:2003, MOD)
GB/T 1839 Test method for gravimetric determination of the mass per unit
area of galvanized coatings on steel products (GB/T 1839-2008, ISO
1460:1992, MOD)
accordance with the requirements of GB/T 228.1.
When measuring the total elongation at maximum force (Agt) of steel wire and
steel rod by manual method, draw equidistant marks on the free length of the
specimen (see GB/T 228.1); the distance between the marks is determined
according to the diameter of the sample, which can be 20 mm, 10 mm or 5 mm.
5.2 Test equipment
The test equipment shall be checked and calibrated according to GB/T 16825.1.
It shall have at least level 1 accuracy.
When measuring E, Fp0.1 or Fp0.2, the accuracy of the extensometer shall be
level 1 (see GB/T 12160); the extensometer used to determine Agt can be level
2 (see GB/T 12160).
Appropriate fixtures shall be used to prevent the specimen from breaking in or
near the fixture.
5.3 Test procedure
5.3.1 Overview
5.3.1.1 The tensile test shall be performed in accordance with the requirements
of GB/T 228.1. The tensile test procedure of multi-wire steel strands for
prestressed concrete can be performed with reference to Appendix C.
5.3.1.2 An extensometer shall be used to determine the modulus of elasticity
(E), 0.1% yield strength, 0.2% yield strength (Fp0.1 and Fp0.2), total elongation at
maximum force (Agt). The gauge distance of the extensometer is determined in
accordance with the requirements of relevant product standards.
5.3.1.3 The precise value of Agt can only be measured by the use of an
extensometer. If the extensometer on the specimen cannot be maintained until
the specimen breaks, the Agt can be determined as follows:
- Continue loading until the elongation recorded by the extensometer is
slightly greater than the elongation at Fp0.2. At this time, remove the
extensometer and record the distance between the upper and lower
working platforms of the testing machine. Continue to load until the
specimen breaks; record the final distance between the upper and lower
working platforms of the testing machine at this time.
- Calculate the difference of the distance between the upper and lower
working platforms of the two testing machines; add the ratio of this
difference to the initial distance between the upper and lower working
platforms of the testing machine and the percentage measured with the
D - Diameter of the mandrel.
Figure 1 -- Principle of bending equipment
6.2.2 The bending test can also be carried out according to GB/T 232 by a
device which is equipped with a support and a mandrel.
6.3 Test procedure
The bending test shall be carried out at a temperature of 10 °C ~ 35 °C; the
specimen shall be bent along the mandrel.
The bending angle and mandrel diameter shall meet the requirements of
relevant product standards.
6.4 Judgment of test results
The determination of the results of the bending test shall meet the requirements
of the relevant product standards.
When the product standard does not specify, if there are no visible cracks in the
bent part, the specimen is judged to be qualified.
Surface cracks produced on the roots of ribs or notches are valid tests. The
crack depth shall not be greater than the crack width.
7 Repeated bending test
7.1 Specimen
In addition to complying with the provisions of Chapter 4, the preparation of
specimen shall comply with the relevant requirements in GB/T 238.
7.2 Test equipment
The test equipment shall meet the relevant requirements in GB/T 238.
For steel wire with a nominal diameter of 10 mm < d ≤ 12.5 mm, the instrument
shall meet the following conditions: r = (30 ± 1) mm, h = 125 mm, dg = 11 mm
or 13 mm, as shown in Figure 2.
8.3.1 Torsion test shall be carried out in accordance with GB/T 239.1.
8.3.2 The torsion rate used is not more than 30 r/min.
8.3.3 The axial tension used is 0.5% ~ 2% of the corresponding tensile load of
the nominal tensile strength of the specimen.
9 Winding and coating adhesion test
9.1 Specimen
The specimen shall meet the requirements of Chapter 4.
9.2 Test equipment
The test equipment shall comply with the relevant requirements in GB/T 2976.
9.3 Test procedure
The winding and coating adhesion test shall be carried out in accordance with
the requirements of GB/T 2976.
10 Isothermal relaxation test
10.1 Test principle
The isothermal stress relaxation test is to keep the specimen at a certain length
(L0 + ΔL0) at a given temperature (unless otherwise specified, usually 20 °C);
starting from the initial force F0, measure the change of the force on the
specimen (see Figure 3).
In a given time, the loss of force is expressed as a percentage of the initial force.
10.3.1 Frame
Any deformation of the frame shall be within the limit that does not affect the
test results.
10.3.2 Force measuring device
10.3.2.1 Coaxial load cells or other suitable devices can be used. (Example:
Lever type loading system)
10.3.2.2 The load cell shall be calibrated in accordance with GB/T 16825.1; its
accuracy is ±1% when it is not greater than 1000 kN and ±2% when it is greater
than 1000 kN. Any other suitable device shall have the same accuracy as
specified for the load cell above.
10.3.2.3 The output resolution of the force measuring device shall not be less
than 5 × 10-4F0.
10.3.3 Length measuring device (extensometer)
The gauge length L0 is not less than 200 mm, especially for steel strands, when
the actual length L0 + ΔL0 of the same steel wire in the steel strand is measured,
the gauge length should be 1000 mm or an integer multiple of the strand lay
length.
The accuracy of the extensometer shall be level 1.
10.3.4 Clamping device
The clamping device shall ensure that the specimen does not slide or rotate
during the test.
10.3.5 Loading device
The loading device shall load the specimen smoothly without oscillation. During
the test, as the force on the specimen decreases, the loading device shall
ensure that the length of the specimen (L0 + ΔL0) remains within the range as
specified in 10.4.5.
10.4 Test procedure
10.4.1 Specimen
Before the test, the specimen shall be placed at least 24 h in the relaxation test
chamber.
The specimen shall be clamped with a fixture to ensure that the specimen does
not slide during loading and testing.
kept within the range of 10 °C ~ 35 °C.
11.4.6 Test termination
The test shall be terminated when the specimen is damaged or one or more
steel wires in the steel strand are broken, or when the number of cycles
specified in the product standard is reached without damage.
11.4.7 Validity of the test
If the specimen breaks in the clamp or within 2 d from the clamp or the specimen
is defective, the test shall be deemed invalid.
12 Stress corrosion test in thiocyanate solution
12.1 Test principle
This test is used to determine the time the when the specimen is immersed in
a given isothermal thiocyanate solution (see 12.3.5) until it breaks under a
constant tensile force.
12.2 Samples and specimens
The specimens shall meet the requirements of Chapter 4; no less than 6
specimens shall be provided for the stress corrosion test. When the initial force
is expressed as a percentage of , such as 80% ; 2 specimens are used
to determine through the axial tensile test.
The specimen length Lt shall be long enough to minimize the bending caused
by the clamping end; the Lt shall be twice the length of L0.
12.3 Test equipment
12.3.1 Frame
A rigid frame shall be used; a lever device or hydraulic device or mechanical
device shall be used for loading. The load acts on the horizontal or vertical
direction of the enclosed frame.
12.3.2 Force measuring device
The force measuring device shall be calibrated according to GB/T 16825. The
accuracy during calibration and use shall be at least ±2%.
12.3.3 Time measuring device
chemicals used for testing shall be treated after use.
12.4 Test procedure
12.4.1 Preparation of specimens
The specimens shall be wiped with a soft cloth and degreased with acetone
(CH3COCH3) and dried in the air.
The part of the specimen at least 50 mm long that enters the container shall be
protected by painting or other methods to prevent corrosion. The test length (L0)
is the length of the specimen in contact with the solution.
12.4.2 Loading and holding
The specimen passes through the container. It is placed in the rack. Load the
specimen until reaching to F0.
The variation of the test force F0 as displayed during the entire test period shall
be kept within ±2%.
The F0 value shall be recorded at the time t0 and the force value shall be
confirmed. If necessary, it shall be adjusted at appropriate time intervals during
the test.
12.4.3 Filling of the container
After loading, the container shall be sealed to prevent leakage. The solution
shall be replaced every time the test is performed. The test solution shall be
preheated to 50 °C ~ 55 °C and then poured into the container. The volume V0
of the solution shall ensure that there is at least 5 mL per square centimeter of
the surface along the length L0 of the specimen. The filling of the solution shall
be completed within 1 min; then the timing device starts timing t0.
During the test, the solution cannot circulate.
12.4.4 Temperature during test
In the time t0 to (t0 + 5) min, for the temperature of the steel wire and steel strand,
the solution shall be adjusted to (50 ± 1) °C; for the steel rod, the solution
temperature shall be adjusted to (50 ± 2) °C; during the test, the temperature
shall be kept within the corresponding range.
12.4.5 Termination of the test
When a break occurs or the specified time ta is reached, the test is considered
complete.
the sum of the average gap between the ends of two adjacent ribs.
The average gap (е) shall be the average of at least 3 measurements.
15.3.1.5 Inclination angle β of lateral rib
The inclination angle (β) of the lateral ribs shall be determined by calculating
the average value of the inclination angle measurements for each row of ribs.
15.3.1.6 Lateral rib width b
The section M-M represents the width of the lateral rib b, as shown in Figure 9.
The width of the lateral rib is measured at the middle point of the rib along the
axis, taking the average value of 3 measurements in each line.
15.3.2 Measurement of notch size
15.3.2.1 Overview
The measurement of the notch size of the notched steel strand shall be
performed on the monofilament as removed from the steel strand specimen.
Before the measurement, the wire shall be removed from the steel strand and
straightened under the premise that the surface of the steel wire will not change.
The notched steel wire that has not been straightened during the production
process shall be straightened under the premise that the surface of the steel
wire will not change before measurement.
15.3.2.2 Depth of the deepest point (amax)
To determine the depth of the notch at the deepest point amax, measure the
depth of n (n ≥ 5) points on each row of marks and calculate the average value.
15.3.2.3 Notch spacing (c)
The notch spacing (c) shall be the measured length divided by the number of
ribs in the length.
The measured length shall be the distance from the center of one notch to the
center of another notch on a line parallel to the centerline of the steel wire on
the same row of notches. The measured distance is the length of at least 10
notches.
15.3.2.4 Length of notch (l)
The length of the notch shall be the average of 3 measurements on the same
row of notches, parallel to the longitudinal axis of the steel wire and passing
through the center of the notch.
19 Sheath thickness measurement
19.1 Specimen
According to the provisions of Chapter 4, take the sheath after removing the
anti-corrosion grease in the anti-corrosion grease content testing.
19.2 Test equipment
The accuracy of the thickness measuring equipment is not less than 0.02 mm.
19.3 Test procedure
The thickness is measured once by a measuring tool at the thinnest position on
each end's cross-section of the sheath, the minimum value is taken.
20 Coating uniformity test
20.1 Specimen
The specimen shall meet the requirements of Chapter 4.
20.2 Test equipment
The test equipment shall meet the relevant requirements in GB/T 2972.
20.3 Test procedure
The uniformity test shall be performed according to the requirements of GB/T
2972.
21 Zinc layer quality test
21.1 Specimen
The specimen shall meet the requirements of Chapter 4.
21.2 Test equipment
The test equipment shall comply with relevant requirements in GB/T 1839.
21.3 Test procedure
The quality test of the zinc layer shall be carried out in accordance with the
requirements of GB/T 1839.
Appendix C
(Informative)
Tensile test method of steel strand for prestressed concrete
C.1 Overview
This method specifies the tensile test procedure of multi-wire steel strands for
prestressed concrete. This method is intended to be used to evaluate the
characteristics of steel strands described in the standard specification for
prestressed steel strands.
C.2 Precautions
C.2.1 If the specimen has any notches, cuts or bends as caused by the
clamping device of the testing machine, it may cause early damage to the
specimen.
C.2.2 If the seven-wire structure steel strand is not uniformly stressed, it will
lead to test errors.
C.2.3 Additional heating during specimen preparation may have a significant
impact on the mechanical properties of the steel strand.
C.2.4 There will be deviations in the clamping method as recommended in C.4.
C.3 Clamping device
C.3.1 When the rupture of the steel strand specimen occurs in the free span
part between the fixtures of the testing machine, the true mechanical properties
of the steel strand can be determined. Therefore, appropriate test equipment
should be used, and a complete set of test procedures shall be established to
obtain stable test results.
Since each testing machine has inherent characteristics, the laboratory shall
choose a clamping method that is most suitable for the test equipment used
from C.3.2 ~ C.3.8.
C.3.2 Standard V-shaped fixture with teeth.
Note: The number of teeth is about 5 teeth/cm ~ 10 teeth/cm; the minimum effective
clamping length is about 102 mm.
C.3.3 Standard V-shaped fixture with teeth and use of gasket material. This
method is to place some material between the fixture and the specimen, to
minimize the impact of tooth bite. The available materials include lead foil,