GOST 28334-89

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  ГОСТ 28334-89

GOST 28334−89 (ST SEV 6433−88) Wire and wire ropes for reinforcement of prestressed concrete structures. Test method for relaxation at constant strain

GOST 28334−89
Group B09

INTERSTATE STANDARD

WIRE AND STEEL WIRE FOR THE REINFORCEMENT PREVIOUSLY
PRESTRESSED CONCRETE STRUCTURES

Test method for relaxation at constant strain

Steel wire and ropes for reinforcement
of prestressed concrete constructions.
Method of relaxation test at constant deformation

ISS 77.140.65
AXTU 0809

Date of introduction 1990−07−01

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the Ministry of ferrous metallurgy of the USSR, the USSR State Committee for construction

2. APPROVED AND put INTO EFFECT by Decision of the USSR State Committee on management of quality and standards from 17.11.89 N 3396

3. INTRODUCED FOR THE FIRST TIME

4. The standard complies ST SEV 6433−88 in part test method, relaxation at constant strain

5. Limitation of actions taken by Protocol No. 4−93 of the Interstate Council for standardization, Metrology and certification (ICS 4−94)

6. REISSUE


This standard specifies the test method for the relaxation at temperature (20±1) °C wire ropes of carbon steel for reinforcement of prestressed concrete structures.

The terms and definitions given in Annex 1.

The method is based on determining the dependence of the voltage drop samples from time to time while maintaining the specified deformation.

1. THE SELECTION AND PREPARATION OF SAMPLES

1.1. For the test selected samples from one piece of no longer than 20 m, with end and mid-cut test for the determination of mechanical properties. The remainder of the piece is to determine the relaxation resistance. Minimum gauge length of the specimen for the test of relaxation (part between the jaws of the grips) should be not less than 40 diameters of the sample or the three steps of lay of rope.

1.2. Samples cut from the tested wire or rope without any additional processing.

1.3. The test is carried out on three samples in the delivery condition.

1.4. The curved sample of short-term load until voltage greater than 0.3 strength of the sample.

2. EQUIPMENT

2.1. Test set, providing the impact on the sample continuous static tensile load. Clamping device test set-up should preserve the constant length of the specimen during the test. The deviation from the calculated length must not exceed ±0,001%. Clamping in the grips should not cause additional effort in the sample (unicentro stretching and stress concentration) and vibration, while the difference between the deformations measured on two diametrically opposite sides of the sample should not exceed ±5% of the arithmetic mean. Initial load should not differ from the specified by more than 1% at a voltage of 1000 MPa and 2% — at a voltage of more than 1000 MPa.

2.2. Instruments for measuring deformation, ensuring the accuracy not less than 0.001% of the measured length of the specimen.

3. PREPARING FOR THE TEST

Before the test, alignment and stabilization of the temperature, the samples were kept for days in the workroom at the test temperature and relative air humidity not more 75%.

4. TESTING

4.1. When testing a sample load of the initial load of 0.01 corresponding temporary resistance to rupture, and the sample is fixed strain gauges.

4.2. Loading of the specimen to the initial loading is carried out at a speed corresponding to the elongation of the sample in the range of (0.2±0,025)% per minute or the voltage gain in the range (400±50) MPa per minute. Loading the sample should be smooth or stepped through 1/10 of the temporary tear resistance of the sample.

4.3. The test is carried out at an initial load corresponding to 0,6; 0,7 and 0,8 temporary tear resistance of the sample.

4.4. Voltage drop start to measure after (60±2) after the initial load.

4.5. After finishing the test count the value of the load of the sample and unload the specimen to the initial loading. Measure permanent deformation and determine the voltage drop.

In the absence of the test setup the device for automatic starting of the voltage drop measurement is carried out at the following intervals of time:

1, 3, 6, 9, 15, 30, 45, 60, 90 min;

2, 4, 8, 24, 48, 72, 100 and 120 hours and then to 1000 hours every 48 hours.

When testing new materials with low relaxation test duration shall be not less than 5000 hours.

5. PROCESSING OF THE RESULTS

5.1. The test results Express the curve of fall of load or stress from the relaxation time of one of the following ways:

1) in a linear coordinate ();

2) in semi-logarithmic coordinates ();

3) in logarithmic coordinates ().

Extrapolation of test results allowed for tests of a duration of not less than 1000 hours.

An example of extrapolation and interpolation of the relaxation given in Appendix 2.

5.2. The test results are entered into the record, which must contain the following information:

1) the type and marking of wire or rope;

2) the shape and dimensions of samples;

3) type test unit;

4) the way of clamping the specimen in the grips of the test unit;

5) the type of device for measuring the strain with an indication of the accuracy of measurement;

6) the initial load or stress;

7) the loading rate of the sample;

8) fall characteristic load depending on time when recording drop load or drop a load at the set interval time.

ANNEX 1 (reference). TERMS AND DEFINITIONS

ANNEX 1
Reference

1. Initial load — the load that causes the sample of the source voltage.

2. Initial load — the load that causes in a sample of primary voltage.

3. The initial voltage at test for relaxation  — the stress corresponding to the initial loading of the specimen.

4. Residual stress relaxation is sensitive to the voltage of the sample after a certain period of time elapsed since the beginning of the test, provided that the total length of the sample did not change during the test. The residual voltage is calculated for the actual cross-sectional area of the sample measured before the test.

5. Relaxation  — difference initial and residual stresses in the sample.

APPENDIX 2 (recommended). EXAMPLE EXPRESSIONS TEST RESULTS

ANNEX 2
Recommended

The nature of the change relationship of the voltage drop to the primary voltage depending on time in a logarithmic scale, after a certain time stabiliziruemost and further has a linear relationship expressed by the equation

,

where  — relaxation, MPa;

 — the initial voltage of the test sample, MPa;

the coefficients and depend on the type of the tested products determined according to the schedule (see drawing), it should be observed that the condition h;

 — the time h

The text of the document is verified by:
the official publication of the
Wire metal. Part 3: Sat. Standards. -
M.: IPK Publishing house of standards, 2003