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GB/T 28900-2022 English PDF (GBT28900-2022)

GB/T 28900-2022 English PDF (GBT28900-2022)

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GB/T 28900-2022: Test methods of steel for reinforcement of concrete

This document specifies the test methods of tensile test, bending test, rebending test, axial force fatigue test, chemical analysis, geometric dimension measurement, determination of specific projected rib area, determination of weight deviation and cyclic inelastic load test of steel for reinforcement of concrete. This document applies to steel for reinforcement of concrete. This document does not apply to prestressed steel products.
GB/T 28900-2022
GB
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 77.140.60
CCS H 44
Replacing GB/T 28900-2012
Test methods of steel for reinforcement of concrete
(ISO 15630-1:2019, Steel for the reinforcement and prestressing of
concrete - Test methods - Part 1: Reinforcing bars, rods and wire, MOD) ISSUED ON: OCTOBER 12, 2022
IMPLEMENTED ON: OCTOBER 12, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of the PEOPLE Republic of China.
Table of Contents
Foreword ... 4
1 Scope ... 6
2 Normative references ... 6
3 Terms and definitions ... 7
4 Symbols and descriptions ... 7
5 General provisions concerning the test piece ... 8
5.1 Preparation ... 8
5.2 Straightening ... 8
5.3 Artificial aging ... 9
6 Tensile test ... 9
6.1 Test piece ... 9
6.2 Test equipment ... 10
6.3 Test procedure ... 10
7 Bending test ... 12
7.1 Test piece ... 12
7.2 Test equipment ... 13
7.3 Test procedure ... 13
7.4 Interpretation of test results ... 14
8 Rebending test ... 14
8.1 Test piece ... 14
8.2 Test equipment ... 14
8.3 Test procedure ... 15
8.4 Interpretation of test results ... 16
9 Axial force fatigue test ... 16
9.1 Test principle ... 16
9.2 Test piece ... 17
9.3 Test equipment ... 17
9.4 Test procedure ... 17
10 Chemical analysis ... 19
11 Dimension measurement ... 19
11.1 Test piece ... 19
11.2 Test equipment ... 19
11.3 Test procedure ... 20
12 Determination of the specific projected rib area (fR) ... 23
12.1 General ... 23
12.2 Measurement ... 23
12.3 Calculation ... 23
13 Determination of weight deviation ... 25
13.1 Test piece ... 25
13.2 Accuracy of measurement ... 25
13.3 Calculation ... 25
14 Cyclic inelastic load test ... 26
14.1 Test principle ... 26
14.2 Test piece ... 26
14.3 Test equipment ... 27
14.4 Test procedure ... 27
Appendix A (Informative) Comparison table of structure between this document and ISO 15630-1:2019 ... 29
Appendix B (Informative) Technical differences and reasons between this document and ISO 15630-1:2019 ... 31
Test methods of steel for reinforcement of concrete
1 Scope
This document specifies the test methods of tensile test, bending test, rebending test, axial force fatigue test, chemical analysis, geometric dimension measurement, determination of specific projected rib area, determination of weight deviation and cyclic inelastic load test of steel for reinforcement of concrete.
This document applies to steel for reinforcement of concrete.
This document does not apply to prestressed steel products.
2 Normative references
The following documents are normatively referenced in this document and are indispensable for its application. For dated references, only the version corresponding to that date is applicable to this document; for undated references, the latest version (including all amendments) is applicable to this document.
GB/T 228.1, Metallic materials - Tensile testing - Part 1: Method of test at room temperature (GB/T 228.1-2021, ISO 6892-1:2019, MOD)
GB/T 232, Metallic materials - Bend test (GB/T 232-2010, ISO 7438:2005, MOD) GB/T 4336, Carbon and low-alloy steel - Determination of multi-element contents - Spark discharge atomic emission spectrometric method (routine method)
GB/T 11170, Stainless steel. Determination of multi-element contents - Spark discharge atomic emission spectrometric method (Routine method)
GB/T 12160, Metallic materials - Calibration of extensometers systems used in uniaxial testing (GB/T 12160-2019, ISO 9513:2012, IDT)
GB/T 16825.1, Metallic materials - Calibration and verification of static uniaxial testing machines - Part 1: Tension/compression testing machines - Calibration and verification of the force-measuring system (GB/T 16825.1-2008, ISO 7500-1:2004, IDT)
GB/T 25917.1, Uniaxial fatigue testing systems - Part 1: Calibration of dynamic force (GB/T 25917.1-2019, ISO 4965-1:2012, IDT)
GB/T 25917.2, Uniaxial fatigue testing systems - Part 2: Dynamic calibration device (DCD) instrumentation (GB/T 25917.2-2019, ISO 4965-2:2012, IDT)
Note 1: For tensile test at room temperature, axial force fatigue test, cyclic inelastic load test, bending test, rebending test, and determination of weight deflection, the straightening of the test piece is critical.
Note 2: Excessive straightening can easily cause changes in mechanical and process properties. Use a rubber hammer or a wooden hammer for slight knock, or a special device for straightening. On the basis of ensuring the minimum plastic deformation, try to make the axis of the test piece coincident with or in the same plane as the line of action of the force.
5.3 Artificial aging
When determining the performance indicators in the tensile test at room temperature, bending test, rebending test, axial force fatigue test and cyclic inelastic load test, the straightened test piece can be artificially aged according to the requirements of the product standard.
When the artificial aging process is not specified in the product standard, the following process conditions can be used: heat the test piece to 100 ??C; keep it warm at 100 ??C ?? 10 ??C for 60 min ~ 75 min; then, cool it naturally in still air to room temperature. Note: Different test conditions (including quantity and size of test pieces and type of heating equipment) require different heating durations. It is generally believed that the best effect is achieved when the heating duration is not less than 40 min. If the test pieces are artificially aged, the process conditions of artificial aging shall be recorded in the test report.
6 Tensile test
6.1 Test piece
In addition to the general provisions given in Chapter 5, the parallel length of the test piece shall be long enough to meet the requirements for the determination of elongation after break (A) or total elongation at maximum force (Agt) in 6.3.
When the elongation after break (A) is determined manually, the test piece shall be marked with the original gauge length according to the provisions of GB/T 228.1. When the total elongation at maximum force (Agt) is determined manually, equidistant marks shall be marked on the parallel length of the test piece, where the length between the marks shall be selected from 20 mm, 10 mm or 5 mm according to the diameter of the test piece.
6.2 Test equipment
The testing machine shall be checked and calibrated according to GB/T 16825.1, and its accuracy shall reach at least grade 1.
When an extensometer is used to measure ReL or Rp0.2, it shall be a grade 1 extensometer (GB/T 12160); when it is used to measure Agt, it can be a grade 2 extensometer (GB/T 12160).
The extensometer which is used to determine the total elongation at maximum force (Agt) shall have a gauge length of at least 100 mm, and the gauge length shall be recorded in the test report.
6.3 Test procedure
6.3.1 General requirements
6.3.1.1 The tensile test shall be carried out in accordance with GB/T 228.1. 6.3.1.2 Unless otherwise specified in the relevant product standards, for the calculation of tensile properties (ReL or Rp0.2, Rm), the original cross-sectional area shall be the nominal cross-sectional area.
6.3.1.3 If the break occurs at a distance less than 20 mm from the clamping part or at the nominal diameter d (whichever is greater) or on the clamping part, the test may be considered invalid.
6.3.2 Determination of specified plastic elongation strength (Rp0.2)
When the yield is not obvious, Rp0.2 shall be measured instead of ReL. When the elastic straight-line segment of the force-extension curve is short or not obvious, one of the following methods shall be used to determine the valid straight-line segment: a) Recommended procedure specified in GB/T 228.1;
b) The straight-line segment of the force-extension curve shall be regarded as the straight-line segment connecting the two points of 0.2Fm and 0.5Fm.
Note 1: Fm can be pre-defined as the force corresponding to the specified tensile strength given in the product standard.
Note 2: The above-mentioned range values are only applicable to carbon steel. For stainless steel, the appropriate values given in the product standard or agreed by the relevant parties can be used instead.
In case of dispute, method b) shall be adopted.
The angle of bend (??) and the diameter of the bending indenter (D) shall comply with the relevant product standards.
Test pieces shall be carefully inspected for cracks by visual inspection. 8.3.3 Artificial aging steps
The temperature and time of artificial aging shall meet the requirements of relevant product standards.
When it is not specified in the product standard, the artificial aging process conditions in 5.3 shall be used.
8.3.4 Rebending steps
After naturally cooling to 10 ??C ~ 35 ??C in still air, the test piece shall be rebent to the corresponding angle (??) at the bending origin (the middle point of the arc section with the largest radius of curvature) according to the relevant product standards. 8.4 Interpretation of test results
The results of the rebending test shall be judged in accordance with the provisions of the relevant product standards.
When it is not specified the product standard, if there is no visual crack on the rebending test piece, judge the test piece as qualified.
9 Axial force fatigue test
9.1 Test principle
The axial force fatigue test is such that the test piece is subjected to an axial tensile force with a fixed frequency (f) sinusoidal periodical variation (see Figure 5) within the range of elastic deformation, and the test is carried out until the test piece is damaged OR the number of cycles stipulated in the relevant product standards is reached and the test piece is not damaged.
During the test and during a series of tests, the cycle frequency shall remain constant. The frequency shall be 1 Hz ~ 200 Hz.
9.4.6 Temperature
During the whole process of the test, the temperature of test piece shall not exceed 40 ??C. Unless otherwise specified, the test ambient temperature shall be 10 ??C ~ 35 ??C. To ensure that the test is carried out under controllable conditions, the test temperature shall be (23??5) ??C.
9.4.7 Test termination
Where the test piece is damaged before the specified number of cycles is reached, or where the specified number of cycles is reached and the test piece is not damaged, the test shall be terminated.
9.4.8 Validity of the test
If the failure occurs on the clamping part or within a distance of 2d from the clamping part, or if the failure is caused by abnormal characteristics of the test piece, the test may be considered invalid.
10 Chemical analysis
In general, use the spectrometric method of GB/T 4336 or GB/T 11170 to determine the chemical composition.
In case of dispute over the analytical result, the chemical composition shall be arbitrated by chemical analysis methods.
11 Dimension measurement
11.1 Test piece
The test piece shall comply with the provisions of Chapter 5.
The length of the test piece shall meet the measurement requirements of 11.3. 11.2 Test equipment
The geometric dimension accuracy of the measuring equipment shall at least meet the following requirements:
-- 0.01 mm for the measurements of the height of transverse or longitudinal ribs less than or equal to 1 mm;
-- 0.02 mm for the measurements of the height of transverse or longitudinal ribs greater than 1 mm;
-- 0.05 mm for the measurement of the gap between two adjacent transverse ribs; -- 0.05 mm for the measurement of the width of transverse ribs;
-- 0.5 mm for the measurement of transverse rib spacing (see 11.3.3);
-- 1?? for the inclination between the transverse rib and the longitudinal axis of the steel or the rib inclination.
In case of dispute, traditional direct-reading instruments, such as caliper, depth gauge, shall be used.
11.3 Test procedure
11.3.1 Height of transverse ribs
11.3.1.1 Maximum value (hmax)
For the maximum height (hmax) of transverse ribs, at least three maximum values shall be measured on each row of the transverse ribs, and the average value shall be calculated. These transverse ribs used for measurement shall not have the product identification of the reinforcement.
If there are different angles (??) between the axis of a transverse rib and the steel axis in a row, for each ??, at least three measurements shall be performed on the individual transverse ribs.
11.3.1.2 Value at a given position
The height of transverse ribs at a given position, for example, at the points of 1/4, 1/2 and 3/4, defined as h1/4, h and h3/4 respectively, shall be determined on different transverse ribs. For each row, at least 3 values shall be measured at this position, and the average value shall be calculated. These transverse ribs used for measurement shall not have the product identification of steel bars.
If there are different angles (??) between the axis of a transverse rib and the steel axis in a row, for each ??, at least three measurements shall be performed on the individual transverse ribs.
11.3.2 Height of longitudinal ribs (hl)
The height of longitudinal ribs (hl) shall be the calculated average value obtained from at least three measurements of individual longitudinal ribs at three different locations of the product.
Unless otherwise specified in the product standard, the transverse rib top width (b) shall be the average value of the three measurements for each rib, and shall be measured at the midpoint of the rib, which is perpendicular to the axis of the rib. These transverse ribs for measurement shall not have the product identification of the reinforcement. 12 Determination of the specific projected rib area (fR)
12.1 General
The bond between steel and concrete allows the transfer of shared loads. The main factor affecting the bond comes from the shear bond produced by the ribs on the surface of the reinforcing steel.
When the steel for reinforced concrete is ribbed, the bond properties can be determined by different methods:
a) Determination of geometric dimensions of the rib;
b) Measurement of the bond between concrete and reinforcing steel in pull-out or beam tests.
On the basis of the data of geometrical dimensions, calculate the bond factor, which is also called the specific projected rib area (fR).
12.2 Measurement
The determination of the specific projected rib area (fR) shall be carried out using the results of the geometric dimensions measured in Chapter 11.
12.3 Calculation
12.3.1 General formulae
The specific projected rib area (fR) is defined by Formula (5):
Where:
fR ?€? specific projected rib area, dimensionless;
?€ ?€? Pi, dimensionless;
d ?€? nominal diameter of reinforcing bars, rods or wire, in millimeters (mm); Where:
h1/4 ?€? height of the transverse rib at the quarter point, in millimeters (mm); h ?€? height of the transverse rib at the half point, in millimeters (mm); h3/4 ?€? height of the transverse rib at the three-quarter point, in millimeters (mm); ??ei ?€? part of the circumference without indentation or rid, in millimeters (mm). 12.3.3 Others
The formula used to calculate fR shall comply with the relevant product standards and shall be stated in the test report.
13 Determination of weight deviation
13.1 Test piece
The determination of the weight deviation shall be carried out on the test piece with a vertically cut end face; the sampling position, quantity and length of test pieces shall comply with the relevant product regulations.
13.2 Accuracy of measurement
The length measurement of the test piece is accurate to 1 mm, and the measurement accuracy of weight shall not be less than 1%.
13.3 Calculation
The deviation We between the actual weight and the theoretical weight is calculated according to Formula (10):
Where:
WT ?€? actual total weight of the test piece, in kilograms (kg);
LT ?€? total length of the test piece, in meters (m);
Wt ?€? theoretical weight, in kilograms per meter (kg/m).
14.3 Test equipment
The force value detection system of the testing machine shall be checked and calibrated according to GB/T 16825.1, and its static accuracy grade shall be at least grade 1. For each cyclic inelastic load testing machine, the test conditions (initial force, clamping force, test control of the unsupported length between clamps) for each nominal diameter of the steel, as well as the necessary length of the test piece shall be recorded.
Note: Refer to GB/T 228.1 for regulations on initial force and beam separation rate control.
14.4 Test procedure
14.4.1 Provisions concerning the test piece
The test piece shall be clamped in the testing equipment so as to transmit the load axially. Clamps used shall ensure that the test piece does not bend during the test. The clamping force perpendicular to the test axis shall be at a minimum, so as to ensure that no displacement of the test piece occurs.
14.4.2 Upper and lower limits of strain
The upper and lower limits of strain shall comply with the provisions in Table 2. The loading direction shall be properly controlled to achieve the change process from tension to compression and then reverse loading, so as to accurately reach the maximum and minimum points of the cycle of hysteresis (see Figure 7) specified by the test conditions (see Table 2).
14.4.3 Interruption
During the entire test, the cyclic loading shall not be interrupted, otherwise, the test shall be considered invalid.
14.4.4 Number of cycles
The number of cycles shall be counted from the first complete force-displacement cycle. 14.4.5 Frequency
During the test, the force cycle frequency shall be stably controlled within the range specified in Table 2.
14.4.6 Temperature
Unless otherwise specified, the test shall be performed at a temperature of 10 ??C ~ 35 ??C.

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