JT/T 1265-2019Method of tension detection for bridge prestressing fine-rolling screw-thread steel bars (English PDF)

Foreword

This standard is in accordance with GB/T Draft the rules given in 1-2009.

This standard is proposed and managed by the National Technical Committee for Standardization of Traffic Engineering Facilities (Highway) (SAC/T 223).

Introduction

The issuer of this document draws attention to the fact that when it declares compliance with this document, Chapter 4 may involve a patent number QL 10411 475 752. 8 "base "Patent for the detection system of the vertical prestressed tendons of the web of a concrete box girder bridge".

The issuing authority of this document has no position on the authenticity, validity and scope of the patent.

The patent holder has assured the publisher of this document that he is willing to work with any applicant on reasonable and non-discriminatory terms and conditions, Negotiating patent licenses. The patent holder's statement has been filed with the issuing authority of this document. Related information can be obtained through Contact.

Name of the patent holder. Zhong Xingu, et al. (Hunan University of Science and Technology, E-mail. 464397070 @ o.com) Address. Building of School of Civil Engineering, Hunan University of Science and Technology, Xiangtan City, Hunan Province Postcode. 411121 Please note that in addition to the above patents, some content of this document may still involve patents. The issuer of this document is not responsible for identifying these Li's responsibility.

JT/T 1265-2019

Method for detecting tensile force of pre-stressed finished rolled rebar for bridge

1 Scope

This standard specifies the tensile testing equipment, testing conditions, test pieces, testing procedures, and testing reports for prestressed precision rolled rebar for bridges.

And other requirements.

This standard is applicable to the detection of the tensile force of the pre-stressed anchoring system of the rolled rebars for bridges before grouting or sealing.

2 Normative references

The following documents are essential for the application of this document. For dated references, only the dated version applies to this article Pieces. For undated references, the latest version (including all amendments) applies to this document.

GB/T 14370 Anchors, clamps and connectors for prestressed tendons GB/T.20065 rebar for prestressed concrete JJG 676 Verification Regulations of Working Vibrometer JJG 834 Dynamic Signal Analyzer JT G 3362 Design Code for Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts JT G/T F50 Technical Specifications for Construction of Highway Bridges and Culverts

3 Terms and definitions, symbols

3.1 Terms and definitions the following terms and definitions apply to this document.

3. 1. 1

Pre-rolled rebar prestressed anchoring system the pressigning system symmetry offloorzrolling schrewing stell barr it consists of fine-rolled rebar, metal or plastic bellows, fixed-end anchorage, and tension-end anchorage.

Pre-stressed anchor system is obtained by tightening the tension-anchor anchor nut and pipe grouting.

3. 1. 2

Prestressed reinforcement bar Pre-rolled rebar that undergoes tensile forces in a pre-rolled rebar prestressed anchoring system.

3. 1. 3

Anchorage equipment

Assembly of pre-stressed tendon nut and anchor plate. The fixed-end anchorage is composed of a flat head nut and its supporting anchor pad, and the tensioned end the anchor is composed of a cone nut and a matching cone hole anchor pad.

3. 1. 4

Dynamic characteristic coefficient cofficient of off dynamic chracteristics A dimensionless coefficient describing the change in flexural stiffness of the anchoring section of the prestressed tendon nut at the tensioned end.

3.2 Symbol

The following symbols apply to this document.

JT/T 1265-2019

APV --- the cross-sectional area of the prestressed tendon, the unit is square millimeter (mm2);

a--the third-order fitting parameter of the relationship between the dynamic characteristic coefficient and the tensile stress of the prestressed tendon;

b--the fitting parameter of the quadratic term of the relationship curve between the dynamic characteristic coefficient and the tensile stress of the prestressed tendon;

c--the first-order fitting parameter of the relationship between the dynamic characteristic coefficient and the prestressed tendon tension;

d --- constant parameter fitting parameter of dynamic characteristic coefficient and prestressed tendon tension curve;

EP --- the elastic modulus of the prestressed tendon, the unit is Pascal (Pa);

er --- standard deviation of the relationship curve between the dynamic characteristic coefficient and the prestressed tendon tension;

f --- the natural frequency of the exposed section of the prestressed tendon, the unit is hertz (Hz);

k --- dynamic characteristic coefficient of flexural rigidity of prestressed tendon and nut anchoring section, dimensionless;

L1 --- length of exposed section of prestressed tendon, unit is millimeter (mm);

L2 --- the height of pre-stressed anchor nut in millimeters (mm);

L3 --- Length of prestressed tendon anchoring tension section, unit is meter (m);

Mgf --- mass of anchor nut, unit is kilogram (kg);

Mgg --- mass of acceleration sensor, unit is gram (g);

Mgs --- the unit length mass of the prestressed tendon, the unit is kilogram per meter (kg/m);

PIPd --- Tension control force of the design of the prestressed tendon, the unit is kilonewton (kN);

PIPT-the effective tensile force of the prestressed tendon without considering creep loss, the unit is kilonewton (kN);

PcIPy --- fitting the tensile stress of the prestressed tendon, the unit is kilonewton (kN);

S11 --- Readout of dial indicator before jack unloading, unit is millimeter (mm);

S12 --- B dial indicator before jack unloading, unit is millimeter (mm);

S21 --- A dial indicator reading after the jack is unloaded, the unit is millimeter (mm);

S22 --- B dial indicator reading after the jack is unloaded, the unit is millimeter (mm);

T1 --- the tensile force of the prestressed tendon before tightening the nut, the unit is kilonewton (kN);

T2 --- Tension of the exposed section after tightening the nut with the prestressed tendon, the unit is kilonewton (kN);

T3 --- Tension of the anchored tensioning section L3 after tightening the nut with the prestressed tendon, the unit is kilonewton (kN);

deltaS --- Retraction value of prestressed tendon, unit is millimeter (mm);

deltaT --- Retraction loss of pre-stressed tendons in millimeters (mm).

4 Testing equipment

4.1 Structure

The pre-stressed precision rolled threaded steel bar tensile tester for the bridge is composed of an acceleration sensor, a data acquisition and analysis system, and an impact hammer.

Composition, see Figure 1.

Explanation.

1 --- vibrating hammer; 4 --- exposed section of prestressed tendon; 7 --- charging interface;

2 --- acceleration sensor with magnetic base and connecting line; 5 --- LCD touch screen of signal acquisition and analysis system; 8 --- data output interface.

3 --- signal acquisition and analysis system; 6 --- signal acquisition interface;

Figure 1 Schematic diagram of the tension tester

5.3 The following operations should be performed before testing.

a) The physical and mechanical parameters required to measure the tensile force according to the requirements in Table 1 are recorded in Table 2, and the obtained physical and mechanical parameters are entered into the data.

Acquisition and analysis system (only one input is required for each type of prestressed tendons and supporting anchors).

b) Calibration of the relationship between the dynamic characteristic coefficient and the tension curve of the prestressed tendons (see Appendix A), and input the calibrated parameters to the data acquisition and analysis system (you only need to enter it once for each type of prestressed tendon and supporting anchors).

Table 1 Physical and mechanical parameter measurement requirements for tensile testing

Three random rebars of the same specification were randomly selected and cut at the ends. After 3m, cut again. 5m length Used to measure the mass per unit length, take the arithmetic average, and measure the steel bars of the same specification at least once.

Accuracy is ± 1g

Randomly select 3 nuts of the same specification, measure the mass and height of each nut, and take the arithmetic average Value, the nut of the same specification shall be measured no less than once, the mass accuracy of the nut shall be ± 1g, and the height accuracy shall be ± 1mm

Table 2 Record of physical and mechanical parameters

6 Test piece

6.1 The prestressed tendons to be tested shall meet the following requirements.

a) The top of the exposed section of the prestressed tendon is mechanically cut, and there should be no burrs or slips.

b) The exposed length (L1) of the prestressed tendon should not be less than 0. 5 times (connector length should meet the requirements of GB/T 14370) should not be less than 80mm and not more than 300mm.

c) The size of the anchor nut complies with the requirements of GB/T.20065.

6.2 The prestressed tendons to be tested shall be in accordance with 5. 3a) Perform measurements and records.

JT/T 1265-2019

7 Detection steps

Follow these steps to check the tension of the prestressed tendons.

a) The acceleration sensor with magnetic base is installed on the unthreaded surface of the exposed section of the prestressed tendon, and the top of the exposed section of the sensor and the prestressed tendon the faces are flush, as shown in Figure 3.

b) Measure the length L1 (Figure 3) of the exposed section of the prestressed tendon at two symmetrical non-threaded surfaces in the circumferential direction of the cross section of the prestressed tendon.

The average value is input to the data acquisition and analysis system of the tensile tester. The accuracy of the measuring gage is ± 1mm. Two positions the maximum difference between the measured values should not exceed 2mm. If the value exceeds this value, the top surface shall be smoothed by a grinder until the maximum difference is less than 2mm.

c) Trigger signal acquisition in the data acquisition and analysis system of the tensile tester.

d) As shown in Figure 3, hold the vibrating hammer in hand, 220mm away from the top surface of the exposed section of the prestressed tendon, and there is no threaded surface between the end of the hammer handle and the prestressed tendon.

In the same straight line, relax the vibrating hammer and make the vibrating hammer rotate around the end of the hammer handle to strike the top of the exposed section of the prestressed tendon.

e) The tensile tester displays the acceleration time history signal and frequency power spectrum of the exposed section of the prestressed tendon in the signal display window.

Read the natural frequency (f) and calculate the dynamic characteristic coefficient (k) and tensile force of the prestressed tendon to be measured, and display it in the signal display window its value forms a tension test data file.

f) Record the test results of the pre-stressed tensile test (PPIy) (see Table B.1 for the form style).

Figure 3.

8 Test report

8.1 Cover

The cover should include the following.

a) (Project name) Pre-stressed finishing rolled rebar tensile test report;

JT/T 1265-2019

b) the name of the testing unit;

c) measurement certification number;

d) date;

e) official seal of the unit;

f) Measurement certification chapter.

8.2 Front page

The cover page should include the following.

a) Names of entrusted units, design units, supervision units, and construction units;

b) Signature of the person in charge of inspection, the main inspector, the report writer, the report reviewer, and the report approver;

c) testing unit;

d) Date of test.

8.3 Text

The text should include the following.

a) project introduction;

b) testing basis;

c) Information of the measured prestressing tendons (span number, pier number, axial position, lateral position), tensile force, and the recording format, see Table B. 1;

d) Description of the test situation. the total number of test roots, the proportion that meets the design requirements, etc .;

e) Summary of test results (see Table B.2).

Appendix A

(Normative appendix) Calibration of Control Parameters for Curves of Dynamic Characteristic Coefficient and Tension of Prestressed Tendons A. 1 General requirements for each type of anchorage and prestressed tendons, a calibration test of the relationship between the dynamic characteristic coefficient and the tensile stress of the prestressed tendons is required;

Prestressed tendons and supporting anchors shall meet the requirements of GB/T.20065.

A. 2 Equipment and instruments the supporting equipment and instruments during the test should meet the following technical requirements.

a) The jack meets the requirements of JT G/T F50;

b) During the effective inspection period, the maximum range of the load cell is greater than the design tensile control force (PIPd). 2 times;

c) two dial indicators within the effective inspection period;

d) the measuring tool is within the effective inspection period;

e) According to Table A. 1 Fill in the data such as the equipment model, parameter, measurement number and so on.

Table A. 1 Equipment and instrument records

A. 3 Test preparation Select three prestressed tendons to be calibrated that meet the requirements of Chapter 6, and complete the following tasks.

a) Consult the design drawing to obtain the length L3 of the anchoring tension section of the prestressed tendon to be calibrated, and enter the corresponding data in the data acquisition and analysis system.

Value

b) According to Table A. 2 Fill in engineering information such as the project name, the location of the prestressed tendons to be calibrated, and the length of the anchor tension section L3.

A. 4 Calibration steps Perform calibration according to the following steps, record the data of the calibration process and enter it in Table A. 2.

a) Install the reaction force device according to normal construction, tension the jack, connect the pre-stressed tendons to be tensioned with a connector, and connect the self-locking nut to the jack.

Install a load cell between them and record the initial value of the load cell, as shown in Figure A. 1 shown. Connectors, pre-stressed anchors the requirements of GB/T 14370.

b) Install two dial indicator magnetic bearings symmetrically at a distance of 10 mm from the top surface of the anchor nut. The magnetic bearings are installed in Figure A. 1 shown Unthreaded surface, and fix the dial indicator, record the initial value of the dial indicator.

c) Start the oil pump tensioning jack and divide it into four levels of tensioning (30%, 50%, 80%, 100%) according to the design tension control (PIPd).

PIPd), record the value displayed by the corresponding load cell.

d) Record the value displayed by the corresponding load cell after tightening the anchor nut (the nut will be unloaded by about 2% after tightening the nut), and read Dial indicator value, relax the jack, read the dial indicator value after all unloading.

e) Remove the reaction force nut, jack, reaction force frame, dial indicator, magnetic base, etc.

f) Perform the test according to Chapter 7 to obtain the dynamic characteristic coefficient.

g) Repeat a) to f) to obtain four levels of tensile force of a single prestressed tendon and the corresponding dynamic characteristic coefficients, and complete 3 prestresses.

In the tendon test, a total of 12 pairs of data were obtained for the tensile force and the corresponding dynamic characteristic coefficient.

Explanation.

Figure A. 1 Pretensioned Tension Retraction Value Measurement and Tension Measurement

A. 5 data processing A. 5. 1 Tension Retraction Loss Calculation the tensile retraction value is calculated according to formula (A.1).

deltaS = [(S11-S21) + (S12-S22)]/2 (A. 1) the tensile retraction loss is calculated according to formula (A.2).

deltaT = deltaS × Ep × Apv/L3 (A. 2) A. 5. 2 tension calculation After tightening the nut, the tensile force T3 of the anchor tensioning section L3 is calculated according to formula (A.3).

The effective tensile force of the prestressed tendon anchored tensile section is calculated according to formula (A.4).

In the formula, i = 1,2,3,4, corresponding to four-level tension (30%, 50%, 80%, 100% of PId).

A. 6 Curve fitting of dynamic characteristic coefficient and prestressed tendon tension A. 6. 1 The relationship curve should be calculated using the regression equation of formula (A.5), and the calculation method is the least square method.

In the formula. a, b, c, d --- curve control parameters.

A. 6. 2 The relative standard deviation of the relationship curve is calculated according to formula (A.6).

A. 6. 3 Press a, b, c, and d. 2 Requires input data acquisition and analysis system.

A. 6. 4 See Appendix C for examples of curve fitting of dynamic characteristic coefficients and prestressed tendons.

Appendix B

(Informative appendix) Record form, test results B. 1 On-site inspection records of prestressed tendons See Table B for the on-site test records of the pre-stressed tendons. 1.

Table B. 1 On-site inspection records of prestressed tendons

The design effective tension is equal to the design tension control force minus the retraction loss and friction loss. For calculation of the retraction loss and friction loss, see JT G 3362, JT G/T F50.

Regulations.

B. 2 Tension test results of prestressed finishing rolled rebar the results of the tensile test of the prestressed finished rolled rebar are shown in Table B. 2.

Table B. 2 Tension test results of prestressed finishing rolled rebar

No. Detect Prestressed Bar Position Description Detection of tension (KN) Design effective tension (KN) Whether to meet the design requirements Appendix C (Informative appendix) Calibration Example of Control Parameters for Curve of Relationship between Dynamic Characteristic Coefficient and Prestressed Tension C. 1 Test preparation the physical and mechanical parameters of the prestressed tendons and nuts are recorded in Table C. 1. Records of instruments and equipment are shown in Table C. 2.

Table C. 1 Record of physical and mechanical parameters

C. 2 Test data

Press A. 4. A. 5 Get the test data and fill in Table C. 3.

C. 3 curve fitting and control parameters from Table C. 3 The curve equation fitted to the data listed in "Actual Tension" and "Dynamic Characteristic Coefficient k" is.

PcIPT = 4 597. 0k3-5 731. 0k2 + 2376. 0k-83. 2 Relative standard deviation of the curve er = 4. 2%, the correlation coefficient is 0. 979. The curve control parameters are. a = 4 597. 0, b =-5 731. 0, c = 2 376. 0, d =-83. 2. The relationship curve between the dynamic characteristic coefficient and the tensile force of the prestressed tendons is shown in Figure C. 1 shown.