Eccentricity test piece for steel bar connection joint and eccentricity test method

Abstract

The invention discloses an eccentric test piece of a steel bar connection joint and an eccentric test method. The eccentric test piece of the steel bar connection joint comprises: a steel bar connection sleeve, a tensioned steel bar, a connector fixed end and an eccentric tensioned end. The two ends of the steel bar connection sleeve are respectively connected to the center axis of the tensioned steel bar and the connector fixed end. The eccentric tensioned end is arranged at the other end of the tensioned steel bar. The center axis of the eccentric tensioned end and the center axis of the tensioned steel bar are staggered and connected together by fillet welds on both sides. The connection length of the eccentric tensioned end and the tensioned steel bar is not less than 6 times the diameter d of the tensioned steel bar. The tensioned ends of the connector fixed end and the eccentric tensioned end are both reserved with a test machine clamping section. The eccentric test method comprises an eccentric tensile test method and an eccentric low-cycle load test method.

Description

Technical Field

[0001] The invention relates to the technical field of steel bar connection performance detection, and in particular to an eccentric test piece for a steel bar connection joint and an eccentric test method. Background Art

[0002] At present, the standards related to the performance of steel bar connection joints in building structures mainly include China's "Mechanical Connection Test Methods for Steel Bars" GB / T 42901-2023, "Test Methods for Steel for Reinforced Concrete" GB / T 28900-2022 and the United States' "Types of Mechanical Splices for Reinforcing Bars" ACI 439.3R-07, etc., all of which test the performance of connection joints through central tensile tests. In prefabricated concrete structures, the interconnected parts such as precast columns, precast wall edge components, and precast beams often have 100% steel bar connection joints for the entire cross-section. Under the action of rare earthquakes, these connection parts are often the parts where plastic hinges are generated. The plastic rotation deformation of the node area causes the steel bar to deform together with the bending member, making the actual stress state of the steel bar with the connection joint complicated, and it is actually in an eccentric tension state. The most common ones are the full-section threaded sleeve connection between the longitudinal reinforcement of reinforced concrete beams and steel columns, and patent CN108060746A discloses a prestressed press-fit assembly frame beam-column joint method. The failure mode of the two under earthquake action is different from that of cast-in-place concrete beam-column joints. The deformation is mainly concentrated near the beam-column joint surface. The steel bar straight threaded connection joints set near the beam-column joint surface are subjected to axial and bending forces at the same time. Only using conventional center tensile test detection methods may not guarantee the safety of the joints. In order to ensure the safety and reliability of such joints, an effective method is needed to inspect and evaluate the bearing performance of eccentric steel bar joints to promote the development of high-performance steel bar connection joints. Summary of the invention

[0003] The object of the present invention is to provide an eccentric test piece and an eccentric test method for a steel bar connection joint, so as to solve the problems raised in the above-mentioned background technology.

[0004] To achieve the above-mentioned purpose, the present invention provides an eccentric test piece for a steel bar connection joint, comprising: a steel bar connection sleeve, a tensioned steel bar, a connecting piece fixed end and an eccentric tensioned end, wherein the two ends of the steel bar connection sleeve are respectively connected to the central axis of the tensioned steel bar and the fixed end of the connecting piece, the eccentric tensioned end is arranged at the other end of the tensioned steel bar, the central axis of the eccentric tensioned end is staggered with the central axis of the tensioned steel bar, and are connected together by fillet welds on both sides, and the connection length of the eccentric tensioned end and the tensioned steel bar is Not less than 6 times the diameter d of the tensile steel bar; both the fixed end of the connector and the eccentric tensile end are equipped with a clamping section for the testing machine.

[0005] In a preferred embodiment, the total length of the assembled tensile steel bar and the steel bar connecting sleeve is not less than , where when the steel bar connection sleeve is a mechanical connection sleeve, the fixed end of the connector and the mechanical connection sleeve are integrally formed, and L is the sum of 1 / 2 the length of the standard mechanical connection sleeve and the length of the section where the tensile steel bar cross section changes; when the steel bar connection sleeve is a grouting sleeve, the fixed end of the connector is an ordinary steel bar, and L is the length of the grouting sleeve. , L 1 、βd They are the first test section, the second test section and the third test section of the tensile reinforcement. Take 2, L 1 The minimum length is 100mm, β Use a value not less than 2.

[0006] In a preferred embodiment, the eccentric tension end is a common ribbed steel bar or a steel rod, and the diameter of the eccentric tension end is 1.1 to 1.3 times the diameter of the tension steel bar.

[0007] In a preferred embodiment, the fixed end of the connector is an ordinary ribbed steel bar or a steel rod. When it is an ordinary ribbed steel bar, the diameter of the fixed end of the connector is 2mm-5mm larger than the diameter of the tensile steel bar. When it is other forms, the tensile section strength of the fixed end of the connector is not less than the tensile strength of the tensile steel bar.

[0008] The present invention also provides an eccentric test method using the above-mentioned eccentric test piece of the steel bar connection joint, which includes an eccentric tensile test method and an eccentric low-cycle load test method, wherein the eccentric tensile test method includes the following steps:

[0009] S11. Cut all the tensile steel bars on the same steel bar and make no less than 3 steel bar mechanical connection eccentricity test pieces;

[0010] S12. Check and ensure that the eccentric test piece of the steel bar connection joint meets the test size requirements. Fix the two ends of the eccentric test piece of the steel bar connection joint in the clamp of the mechanical properties testing machine. When the diameter of the tensile steel bar is greater than 20 mm, use the clamp to ensure that the clamp of the testing machine is centered and ensure that the clamping is uniform and does not slip.

[0011] S13. Install the extensometer and mark the measuring area with a thin line on the tensile reinforcement;

[0012] S14, start the testing machine and gradually apply the tensile load until failure;

[0013] S15. Record the ultimate tensile strength at break, export the measured data, and analyze the total elongation at maximum force.

[0014] In a preferred embodiment, the eccentric low cycle load test method comprises the following steps:

[0015] S21. Cut all the tensile steel bars on the same steel bar and make no less than 6 eccentricity test pieces of steel bar connection joints;

[0016] S22. Check and ensure that the eccentric test piece of the steel bar connection joint meets the test size requirements. Fix the two ends of the eccentric test piece of the steel bar connection joint in the clamp of the testing machine. When the diameter of the tensile steel bar is greater than 20 mm, use the clamp to ensure that the clamp of the testing machine is centered and ensure that the clamping is uniform and does not slip.

[0017] S23. Install the extensometer and mark the measuring area with a thin line on the tensile reinforcement;

[0018] S24. Select no less than 3 eccentric test pieces of steel bar connection joints and conduct high stress tension and compression tests and large deformation tension and compression tests according to the following steps:

[0019] S241, high stress tension and compression test: Start the testing machine and control the load from zero stress to 0.9 , The standard value of the yield strength of the tensile steel bar specified in the specification is the eccentric test piece of the tensile steel bar connection joint, and then it is reduced to 0.5 Compress the eccentric test piece of the steel bar connection joint, repeat 20 times, and finally gradually apply tensile load until failure;

[0020] S242, large deformation tension and compression test: Start the testing machine, first, according to the strain control mode from zero strain to 2 , To meet the requirements of the specification for the yield strain of the tensile reinforcement, the tensile test piece is subjected to compression to 0.5 , repeated 4 times, then the strain was controlled from zero to 5 Tensile test piece, compress the test piece to 0.5 in load control mode , repeat 4 more times, and finally gradually apply tensile load until failure;

[0021] S25. Record the ultimate tensile strength at break, export the measured data, and analyze the residual deformation after 20 times of tension and compression in the case of high stress tension and compression test. When the large deformation tension and compression test is performed, the residual deformation after 4 and 8 times of tension and compression is analyzed. and .

[0022] In a preferred embodiment, the method further includes: dividing the performance of the steel bar connection joint into two levels, T1 and T2, according to the measured test results. When the eccentric connection joint is used in a location where bending deformation is concentrated, its performance should reach T2 level. The performance indicators of T1 and T2 levels are as follows:

[0023] T1: The measured ultimate tensile strength of all eccentric test pieces calculated based on the minimum net cross-section is not less than 1.25 times the standard value of the yield strength of the tensile steel bars specified in the specification; the average value of the measured total elongation of the three eccentric tensile test pieces is not less than 3%, and the residual deformation of the three high-stress tension and compression test pieces after 20 tension and compression cycles ... The average value is less than or equal to 0.3 mm, and the residual deformation of the three large deformation tension and compression test pieces after four times of tension and compression The average value is no more than 0.6 mm;

[0024] T2: The measured ultimate tensile strength of all eccentric test pieces calculated according to the minimum net cross-section is not less than the standard value of the ultimate tensile strength of the tensile steel bar specified in the specification; the average value of the measured total elongation of the three eccentric tensile test pieces is not less than 6%, and the residual deformation of the three high-stress tension and compression test pieces after 20 tension and compression cycles is not less than 6%. The average value is less than or equal to 0.3 mm. The residual deformation of the three large deformation tensile and compressive test pieces after 4 and 8 times of tension and compression is and The average values ​​are less than or equal to 0.3 mm and 0.6 mm respectively.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention converts the axial tension of the testing machine into eccentric tension of the mechanical connection joint by arranging an eccentric tension end welded to the side of the tensioned steel bar, and provides a detection method, which is more in line with the stress state of the joint in actual engineering. The eccentric tensile test and eccentric low-cycle load test of the steel bar connection joint can be completed on a conventional mechanical property testing machine, and an index of performance grading is given. The test method of the present invention is simple and reliable, and has good economic benefits and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of an eccentric test piece when the steel bar connection sleeve of the present invention adopts a mechanical connection sleeve;

[0028] Figure 2 yes Figure 1 Schematic diagram along the AA direction;

[0029] Figure 3 is a schematic diagram of an eccentric test piece when the tensile steel bar is partially weakened in the present invention;

[0030] Figure 4Schematic diagram of an eccentric test piece when the steel bar connection sleeve of the present invention adopts a grouting sleeve;

[0031] Figure 5 yes Figure 4 Schematic diagram along the BB direction;

[0032] Figure 6 It is a schematic diagram of a prefabricated beam-column node in Embodiments 1 and 2 of the present invention;

[0033] Figure 7 This is a schematic diagram of a steel tube column concrete beam connection node in Example 1 of the present invention;

[0034] Figure 8 This is a schematic diagram of a bending-resistant column base node in Example 3 of the present invention.

[0035] Description of reference numerals:

[0036] 1-rebar connection sleeve, 2-tension steel bar, 21-thin line of measurement area, 22-local weakened section of tension steel bar, 3-fixed end of connector, 4-eccentric tension end, 5-fillet weld, 6-clamping section of testing machine, 71-straight thread sleeve, 72-tension steel bar at beam end, 73-precast concrete column, 74-precast concrete beam, 75-prestressed steel bar, 81-grouting sleeve, 82-tension steel bar in foundation, 83-precast concrete column, 831-possible joint surface opening area, 832-possible plastic hinge area, 84-concrete foundation, 91-straight thread sleeve, 92-longitudinal reinforcement of concrete beam, 93-concrete-filled steel tube column, 94-concrete beam. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention are described clearly and completely below. The embodiments of the present invention and all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0038] Embodiment 1:

[0039] like Figure 1 , Figure 2 , Figure 6 and Figure 7 As shown, Figure 6 A beam-column joint is provided in which a precast concrete column 73 and a precast concrete beam 74 are crimped together by prestressed steel bars 75. When the beam end rotates under the action of an earthquake or wind load, the joint surface between the precast column and the precast beam opens significantly, causing eccentric tension to occur in the tensile steel bars 72 and the straight threaded sleeve 71 connecting the beam end. Figure 7A connection node of a steel tube concrete column 93 and a concrete beam 94 is provided, wherein the longitudinal reinforcement 92 of the concrete beam is connected to the steel tube concrete column 93 through a full-section straight threaded sleeve 91. When the beam end rotates under the action of an earthquake and concrete damage occurs, the connection joint between the longitudinal reinforcement 92 of the concrete beam and the straight threaded sleeve 91 is also in an eccentric tension state. In order to ensure the engineering quality of this type of steel bar connection joint, it is necessary to test the eccentric force performance of the connection joint.

[0040] According to the beam-column node drawings, make no less than 9 Figure 1 The steel bar mechanical connection eccentric test piece shown, of which 3 are used for unidirectional tensile test, 3 are used for high stress tension and compression test, and 3 are used for large deformation tension and compression test. The steel bar mechanical connection eccentric test piece comprises: a mechanical connection sleeve 1, a tension steel bar 2, a connector fixed end 3 and an eccentric tension end 4, and the two ends of the mechanical connection sleeve 1 are respectively connected to the center axis of the tension steel bar 2 and the connector fixed end 3. The mechanical connection sleeve 1 and the connector fixed end 3 are processed and formed together, and one end thereof is provided with an internal thread. The eccentric tension end 4 is arranged at the other end of the tension steel bar 2, and the center axis of the eccentric tension end 4 is staggered with the center axis of the tension steel bar 2, and is connected together by a double-sided fillet weld 5. The connection length between the eccentric tension end 4 and the tension steel bar 2 is not less than 6 times the diameter d of the tension steel bar, and the tension ends of the connector fixed end and the eccentric tension end are both reserved with a test machine clamping section 6.

[0041] In this embodiment, the total length of the assembled tensile steel bar 2 and the mechanical connection sleeve 1 is not less than The diameter d of the tension steel bar 2 is 25 mm. The tension steel bars 2 of the 9 specimens are all taken from the same steel bar. The connection length between the eccentric tension end 4 and the tension steel bar 2 of this embodiment is Take 170 mm, the eccentric tension end 4 is a 28 mm diameter ordinary ribbed steel bar. One end of the mechanical connection sleeve 1 is provided with an internal thread, L is 1 / 2 the length of the standard mechanical connection sleeve, L is 70 mm, , L 1 、βd They are the first test section, the second test section and the third test section for tensile reinforcement, which are used to ensure the consistency of the test. Take 2, L 1 Take 100 mm, Take 2. HRB400 steel bars are used for both the eccentric tension end 4 and the tension reinforcement 2, and the length of the clamping section 6 of the testing machine is 150 mm. The total length of the assembled tension reinforcement 2 and the mechanical connection sleeve 1 is .

[0042] Take 3 test pieces and use a mechanical properties testing machine to perform an eccentric tensile test: 1. Check and ensure that the test pieces meet the test size requirements, fix the two ends of the test pieces in the fixture of the testing machine, use a special fixture to ensure that the chuck of the testing machine is centered, and ensure that the clamping is uniform and does not slide; 2. Mark the measurement area fine line 21 on the tensile steel bar 2; 3. Start the testing machine and gradually apply the tensile load until it fails using a load control method; 4. Record the ultimate tensile strength at the time of fracture , measure the gauge length between the thin lines of the tensile reinforcement 2 again, derive the measured data, and analyze the total elongation under the maximum force. Calculate according to the following formula: (where L 10 L is the gauge length between thin lines before the test begins. 11 is the gauge length between the fine lines after the specimen breaks, and E is the elastic modulus of the tensile reinforcement given in the specification):

[0043] .

[0044] Take 3 test pieces for high stress tension and compression test: 1. Check and ensure that the test pieces meet the test size requirements, fix the two ends of the test pieces in the fixture of the test machine, use a special fixture to ensure the centering of the test machine chuck, ensure uniform clamping and no slip; 2. Install the extensometer and mark the measurement area fine line 21 on the tensile steel bar 2; 3. Start the test machine and control the load from zero stress to 0.9 Tensile test piece, then dropped to 0.5 Compress the test piece, repeat 20 times, and finally gradually apply tensile load until it breaks; 4. Record the ultimate tensile strength at break, export the measured data, and analyze the residual deformation after 20 times of tension and compression .

[0045] Take 3 test pieces for large deformation tension and compression test: 1. Check and ensure that the test pieces meet the test size requirements, fix the two ends of the test pieces in the fixture of the testing machine, use a special fixture to ensure the centering of the testing machine chuck, ensure uniform clamping and no slip; 2. Install the extensometer and mark the measurement area fine line 21 on the tensile steel bar 2; 3. Start the testing machine, first, according to the strain control mode from zero strain to 2 Tensile test piece, compress the test piece to 0.5 in load control mode , repeated 4 times, then the strain was controlled from zero to 5 Tensile test piece, compress the test piece to 0.5 in load control mode , repeat 4 times, and finally gradually apply tensile load until failure; 4. Record the ultimate tensile strength at break, derive the measured data, and analyze the residual deformation of 4 and 8 times of tension and compression and .

[0046] According to the measured test results, the performance of steel bar connection joints can be divided into two levels, T1 and T2. When the eccentric connection joint is used in a location with concentrated bending deformation, its performance should reach T2 level. The performance indicators of T1 and T2 are as follows: T1 level: the measured ultimate tensile strength of all eccentric test pieces calculated according to the minimum net cross-section is not less than 1.25 times the standard value of the yield strength of the tensile steel bar 2 specified in the specification; the average value of the measured total elongation of the three eccentric tensile test pieces is not less than 3%, and the residual deformation of the three high-stress tension and compression test pieces after 20 times of tension and compression ... residual deformation of the three high-stress tension and compression test pieces after 20 times of tension and compression is not less than 1.25 times the standard value of the yield strength of the tensile steel bar 2 specified in the specification; the residual deformation of the three high The average value is less than or equal to 0.3 mm, and the residual deformation of the three large deformation tension and compression test pieces after four times of tension and compression The average value is not greater than 0.6 mm. T2 grade: The measured ultimate tensile strength of all eccentric test pieces calculated according to the minimum net section is not less than the standard value of the ultimate tensile strength of the tensile steel bar 2 specified in the specification; the average value of the measured total elongation of the three eccentric tensile test pieces is not less than 6%, and the residual deformation of the three high-stress tension and compression test pieces after 20 times of tension and compression is not less than 6%. The average value is less than or equal to 0.3 mm. The residual deformation of the three large deformation tensile and compressive test pieces after 4 and 8 times of tension and compression is and The average values ​​are less than or equal to 0.3 mm and 0.6 mm, respectively.

[0047] By collating the test data, the performance of the connection joint is evaluated. If it meets the above T2 performance indicators, it can be evaluated as a T2 joint and can be used in Figure 6 It should be noted that when the failure occurs in the tensile reinforcement 2 section, the measured ultimate tensile strength of all test pieces is not less than the ultimate tensile strength of the tensile reinforcement 2 specified in the specification; when the failure occurs in the mechanical connection sleeve 1 section, the measured ultimate tensile strength of all test pieces is not less than 1.1 times the ultimate tensile strength of the tensile reinforcement 2 specified in the specification.

[0048] Embodiment 2:

[0049] like Figure 3 As shown, when Figure 6 When the tensile reinforcement 72 at the end of the beam is partially weakened, a thin line 21 of the measuring area should be set in the weakened section 22 of the tensile reinforcement 2, and the total length of the weakened section 22 is 150 mm. Other dimensions, test methods and evaluation methods are the same as those in Example 1.

[0050] Embodiment 3:

[0051] like Figure 4 , Figure 5 and Figure 8As shown, this embodiment provides a bending-resistant column foot node of a precast concrete column 83 and a concrete foundation 84. After the precast column 83 rotates under the action of an earthquake, the joint surface between the precast column and the foundation may open (corresponding to the possible joint surface opening area 831), so that the tensile steel bars 82 at the connecting column end and the grouting sleeve 81 are eccentrically tensile. In order to ensure the engineering quality of the connection joint of the grouting sleeve 81, it is necessary to perform an eccentric tensile test on this type of connection joint.

[0052] According to the column foot node drawing, make no less than 9 Figure 3 The eccentric tensile test pieces of the connection joint shown in the figure are used for unidirectional tensile test, 3 for high stress tension and compression test, and 3 for large deformation tension and compression test. The eccentric test piece of the steel connection joint includes: a steel bar connection sleeve 1, a tensioned steel bar 2, a connection piece fixed end 3 and an eccentric tensile end 4. The two ends of the steel bar connection sleeve 1 are respectively connected to the center axis of the tensioned steel bar 2 and the connection piece fixed end 3. The steel bar connection sleeve 1 is a grouting sleeve, and the connection piece fixed end 3 is an ordinary steel bar. One end of the grouting sleeve is connected to the connection piece fixed end 3, and the other end is connected to the tensioned steel bar 2. The eccentric tensile end 4 is arranged at the other end of the tensioned steel bar 2. The center axis of the eccentric tensile end 4 and the center axis of the tensioned steel bar 2 are staggered with each other, and are connected together by double-sided fillet welds 5. The connection length of the eccentric tensile end 4 and the tensioned steel bar 2 is not less than the diameter of the tensioned steel bar. d The fixed end of the connector and the eccentric tensile end are both provided with a clamping section 6 for the testing machine.

[0053] The diameter d of the tensile steel bar 2 is 25 mm. The tensile steel bars 2 of the nine specimens are all taken from the same steel bar. The fixed end 3 of the connector is an ordinary steel bar with a diameter of 28 mm. L is the length of the grouting sleeve, which is 430 mm. Other dimensions and specifications of the test pieces are the same as those in Example 1.

[0054] Three test pieces were taken for eccentric tensile test, and the test method was the same as that of Example 1. When the fracture of the test piece occurred within the second test section L1 of the tensile steel bar 2, a new test piece was selected for tensile test to obtain the total elongation under the maximum force.

[0055] Then, three test pieces were taken to carry out high stress tension and compression test and large deformation tension and compression test respectively, and the test method was the same as that of implementation example 1.

[0056] The test data are collated to evaluate the performance of the connection joints. If all the joints meet the criteria described in Example 1, they can be evaluated as T2 grade joints and can be used in Figure 7 In the column foot node shown.

[0057] In addition, the steel bar connection sleeve 1 of the present invention can also be selected from a standard straight thread sleeve, a flared straight thread sleeve, a tapered thread sleeve or an extruded steel bar connection sleeve.

[0058] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A steel bar connection joint eccentricity test piece, characterized in that: include: A steel bar connection sleeve (1), a tensioned steel bar (2), a connector fixed end (3), and an eccentric tensioned end (4), wherein the two ends of the steel bar connection sleeve (1) are respectively connected to the center axis of the tensioned steel bar (2) and the connector fixed end (3), the eccentric tensioned end (4) is arranged at the other end of the tensioned steel bar (2), the center axis of the eccentric tensioned end (4) is staggered with the center axis of the tensioned steel bar (2), and the eccentric tensioned end (4) is connected together by fillet welds (5) on both sides, and the connection length of the eccentric tensioned end (4) and the tensioned steel bar (2) is The diameter of the tensioned steel bar (2) is not less than 6 times the diameter d of the tensioned steel bar (2), and the tensioned ends of the connecting piece fixed end (3) and the eccentric tensioned end (4) are both reserved with a testing machine clamping section (6).

2. The eccentric test piece for a steel bar connection joint according to claim 1, characterized in that: The total length of the assembled tensile steel bar (2) and the steel bar connecting sleeve (1) is not less than , wherein, when the steel bar connection sleeve (1) is a mechanical connection sleeve, the connection piece fixed end (3) and the mechanical connection sleeve are integrally formed, and L is the sum of 1 / 2 the length of the standard mechanical connection sleeve and the length of the section where the tensile steel bar cross section changes; when the steel bar connection sleeve (1) is a grouting sleeve, the connection piece fixed end (3) is an ordinary steel bar, and L is the length of the grouting sleeve. , L 1 、 They are the first test section, the second test section and the third test section of the tensile reinforcement. Take 2, L 1 The minimum length is 100 mm, Use a value not less than 2.

3. The eccentric test piece for a steel bar connection joint according to claim 1, characterized in that: The eccentric tension end (4) is an ordinary ribbed steel bar or a steel rod, and the diameter of the eccentric tension end (4) is 1.1 to 1.3 times the diameter of the tension steel bar (2).

4. The eccentric test piece for a steel bar connection joint according to claim 1, characterized in that: The connecting piece fixed end (3) is an ordinary ribbed steel bar or a steel bar. When the connecting piece fixed end (3) is an ordinary ribbed steel bar, the diameter of the connecting piece fixed end (3) is 2 mm to 5 mm larger than the diameter of the tensile steel bar (2). When the connecting piece fixed end (3) is a steel bar, the tensile section strength of the connecting piece fixed end (3) is not less than the tensile strength of the tensile steel bar (2).

5. The eccentric test piece for a steel bar connection joint according to claim 1, characterized in that: The steel bar connection sleeve (1) is one of a standard straight thread sleeve, a flared straight thread sleeve, a tapered thread sleeve, an extruded steel bar connection sleeve or a grouting sleeve.

6. The eccentric test piece for a steel bar connection joint according to claim 1, characterized in that: The length of the clamping section (6) of the testing machine is not less than 50 mm.

7. An eccentricity test method using the eccentricity test piece of a steel bar connection joint according to any one of claims 1 to 6, characterized in that: It includes an eccentric tensile test method and an eccentric low-cycle load test method, wherein the eccentric tensile test method includes the following steps: S11. Cut the tensile steel bars (2) on all the test pieces from the same steel bar and make no less than 3 steel bar mechanical connection eccentricity test pieces; S12. Check and ensure that the eccentricity test piece of the steel bar connection joint meets the test size requirements. Fix the two ends of the eccentricity test piece of the steel bar connection joint in the clamp of the mechanical properties testing machine. When the diameter of the tensile steel bar (2) is greater than 20 mm, use the clamp to ensure that the clamp of the testing machine is centered and that the clamping is uniform and does not slip. S13, installing an extensometer and marking a thin line (21) of the measuring area on the tensioned steel bar (2); S14, start the testing machine and gradually apply the tensile load until failure; S15. Record the ultimate tensile strength at break, export the measured data, and analyze the total elongation at maximum force.

8. The eccentricity test method according to claim 7, characterized in that: The eccentric low cycle load test method comprises the following steps: S21. Cut the tensile steel bars (2) on all the test pieces from the same steel bar and make no less than 6 steel bar connection joint eccentricity test pieces; S22. Check and ensure that the eccentricity test piece of the steel bar connection joint meets the test size requirements. Fix the two ends of the eccentricity test piece of the steel bar connection joint in the clamp of the testing machine. When the diameter of the tensile steel bar (2) is greater than 20 mm, use the clamp to ensure that the clamp of the testing machine is centered and ensure that the clamping is uniform and does not slip. S23, installing an extensometer and marking a thin line (21) of the measuring area on the tensioned steel bar (2); S24. Select no less than 3 eccentric test pieces of steel bar connection joints and conduct high stress tension and compression tests and large deformation tension and compression tests according to the following steps: S241, high stress tension and compression test: Start the testing machine and control the load from zero stress to 0.9 , The standard value of the yield strength of the tensile steel bar specified in the specification is the eccentric test piece of the tensile steel bar connection joint, and then it is reduced to 0.5 Compress the eccentric test piece of the steel bar connection joint, repeat 20 times, and finally gradually apply tensile load until failure; S242, large deformation tension and compression test: Start the testing machine, first, according to the strain control mode from zero strain to 2 , To meet the requirements of the specification for the yield strain of the tensile reinforcement, the tensile test piece is subjected to compression to 0.5 , repeated 4 times, then the strain was controlled from zero to 5 Tensile test piece, compress the test piece to 0.5 in load control mode , repeat 4 more times, and finally gradually apply tensile load until failure; S25. Record the ultimate tensile strength at break, export the measured data, and analyze the residual deformation after 20 times of tension and compression in the case of high stress tension and compression test. When the large deformation tension and compression test is performed, the residual deformation after 4 and 8 times of tension and compression is analyzed. and .

9. The eccentricity test method according to claim 8, characterized in that: Also includes: According to the measured test results, the performance of the steel bar connection joint is divided into two levels: T1 and T2. When the eccentric connection joint is used in a location with concentrated bending deformation, its performance should reach T2 level. The performance indicators of T1 and T2 are as follows: T1: The measured ultimate tensile strength of all eccentric test pieces calculated based on the minimum net cross-section is not less than 1.25 times the standard value of the yield strength of the tensile steel bar (2) specified in the specification; the average value of the measured total elongation of the three eccentric tensile test pieces is not less than 3%; the residual deformation of the three high-stress tension and compression test pieces after 20 tension and compression cycles ... The average value is less than or equal to 0.3 mm, and the residual deformation of the three large deformation tension and compression test pieces after four times of tension and compression The average value is no more than 0.6 mm; T2: The measured ultimate tensile strength of all eccentric test pieces calculated based on the minimum net cross-section is not less than the standard value of the ultimate tensile strength of the tensile steel bar (2) specified in the specification; the average value of the measured total elongation of the three eccentric tensile test pieces is not less than 6%, and the residual deformation of the three high-stress tension and compression test pieces after 20 tension and compression cycles is not less than 6%. The average value is less than or equal to 0.3 mm. The residual deformation of the three large deformation tensile and compressive test pieces after 4 and 8 times of tension and compression is and The average values ​​are less than or equal to 0.3 mm and 0.6 mm, respectively.

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