A steel bar connecting sleeve based on strong lap joint theory and a strength testing device thereof

Abstract

A reinforcing steel connecting sleeve based on strong lap joint theory, the sleeve body is a rectangular body structure, vertical through holes are symmetrically formed on both sides of the sleeve body, and the two vertical sides of the sleeve are symmetrically formed as convex arc surfaces, the sleeve tensile strength testing device comprises a base, a supporting pad, a steel box, a hollow jack and a through sensor, the base is provided with the supporting pad on the top, the steel box is fixed on the top surface of the middle part of the supporting pad, the hollow jack is fixed on the top surface of the steel box, and the sleeve is inserted into the steel box, the through sensor is fixed on the top of the hollow jack, and the through sensor is fixed on the top of the hollow jack. The steel reinforcing steel through holes on both sides of the sleeve penetrate the top surface of the through sensor and the bottom surface of the supporting pad respectively. The present application has the characteristics of good force transmission form, reduction of surrounding support, simple processing, convenient construction operation, and is not affected by the diameter of the reinforcing steel, and has wide application range, and provides a new idea and method for the connection of the assembled concrete structure from the practical engineering point of view.

Description

Technical Field

[0001] This invention belongs to the field of building structure connection technology, and particularly relates to a steel bar connection sleeve based on the strong lap splice theory and its strength testing device. Background Technology

[0002] Currently, with the continuous acceleration of social industrialization and the constant updating and improvement of construction technology, the application of traditional construction methods in the process of modern building industrialization is gradually decreasing, and prefabricated buildings are gradually becoming a new benchmark for the transformation and upgrading of the construction industry. Generally speaking, the prefabricated components required for prefabricated buildings are produced in factories in advance and then quickly assembled on site. In recent years, under the development of industrial policies and industry promotion, prefabricated buildings have been widely used.

[0003] In prefabricated building structures, the node connections between components are a crucial link in the entire prefabricated structure, and their connection strength and reliability restrict the development of prefabricated buildings. The node design of prefabricated concrete structures should follow the principle of "strong nodes, weak components," ensuring that they possess the same durability, stability, and overall performance as cast-in-place concrete structures. Therefore, safe and reliable rebar connections between components are an important prerequisite for the widespread application of prefabricated concrete structures, and the quality of the rebar connections directly affects the structural safety performance. Currently, commonly used rebar connection methods in prefabricated concrete structures include mechanical rebar connections, grouted lap splices, and grouted sleeve connections. Among them, the "Technical Specification for Prefabricated Concrete Structures" (JGJ1-2014) designates grouted lap splices and grouted sleeve connections as the main rebar connection methods for prefabricated buildings. However, these rebar connection methods generally suffer from problems such as the inability of prefabricated components to immediately participate in load-bearing after placement, and construction heavily relies on worker skills, making quality inspection difficult. To address these issues, some scholars have developed a rebar connection sleeve based on strong lap splices. Because this type of connecting sleeve is relatively novel and has a unique structure, existing methods for testing the tensile strength of sleeves are not applicable. Therefore, it is necessary to propose a tensile strength testing device for steel bar connecting sleeves based on strong lap splices to promote this connection method. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a steel bar connection sleeve based on the strong lap splice theory and its strength testing device. This testing device has the characteristics of good force transmission, reduced surrounding support, simple processing, and convenient construction operation. It is not affected by the diameter of the steel bar and has a wide range of applications. From the perspective of practical engineering, it provides a new idea and a new method for the connection of prefabricated concrete structures.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A steel bar connection sleeve based on the strong lap splice theory includes a cylinder body, characterized in that: the cylinder body is a rectangular structure, and vertical through holes for steel bars are symmetrically made on both sides of the cylinder body, and the two vertical sides of the sleeve are made into symmetrical convex arc surfaces.

[0007] The above-mentioned tensile strength testing device for rebar connection sleeves based on strong lap splice theory is characterized by comprising a base, a support plate, a steel box, a hollow jack, and a through-hole sensor. The support plate is provided on the top of the base, and the steel box is fixed on the top surface of the middle part of the support plate. The hollow jack is fixed on the top surface of the steel box, and the sleeve is inserted into the inside of the steel box. The through-hole sensor is fixed on the top of the hollow jack. The rebar through holes on both sides of the sleeve respectively penetrate the rebar and fix the top surface of the through-hole sensor and the bottom surface of the support plate.

[0008] Preferably, the base is U-shaped with an opening at the top and a support pad that can be movably covered within the opening.

[0009] Preferably, the reinforcing bar includes an upper section and a lower section. The bottom end of the upper section is inserted into one of the reinforcing bar through holes of the sleeve from top to bottom and is axially fixedly connected to the bottom surface of the sleeve. The middle part of the upper section extends upward and slides through the sleeve, the steel box, the hollow jack, and the through-hole sensor. The top end of the upper section is axially fixedly connected to the top surface of the through-hole sensor. The top end of the lower section is inserted into another reinforcing bar through hole of the sleeve from bottom to top and is axially fixedly connected to the top surface of the sleeve. The middle part of the lower section extends downward and slides through the sleeve, the steel box, and the support pad. The bottom end of the lower section is axially fixedly connected to the bottom surface of the support pad.

[0010] Preferably, a rigid top block is fixed on each of the two opposing inner walls of the steel box, and the side wall of the rigid top block is made into a concave arc surface of the convex arc surface on both sides of the sliding constraint sleeve.

[0011] Preferably, a washer D and a rolled straight thread sleeve are provided at the top end of the upper section of the reinforcing bar and the bottom end of the lower section of the reinforcing bar, wherein the rolled straight thread sleeve is threadedly connected to the top end of the upper section of the reinforcing bar and the bottom end of the lower section of the reinforcing bar, so that the upper section of the reinforcing bar is axially fixedly connected to the top surface of the through-core sensor, and the bottom end of the lower section of the reinforcing bar is axially fixedly connected to the bottom surface of the support plate.

[0012] The advantages and technical effects of this invention are:

[0013] 1. This invention uses a sleeve as the load-bearing connection between the upper and lower sections of reinforcing bars, and uses a tensile strength testing device to verify the deformation of the sleeve to validate the feasibility of the sleeve connection. Specifically, through-holes in the reinforcing bars on both sides of the sleeve penetrate the upper and lower sections of reinforcing bars, respectively. The nut on the upper section of the reinforcing bar is connected to the top of a through-hole sensor, which is supported upwards by a hollow jack, applying an upward pulling force to the sleeve via the upper section of the reinforcing bar. The nut on the lower section of the reinforcing bar is connected to the bottom surface of a support plate, applying an upward reaction force to the sleeve via the lower section of the reinforcing bar.

[0014] 2. The present invention simulates the compression and positioning constraint of the sleeve inside the precast concrete block. Rigid top blocks with convex arc surfaces are fixed on both sides of the steel box to prevent the sleeve from twisting when under tensile load. Under the premise of simulating the non-load-bearing direction constraint condition when the sleeve is embedded in the concrete block, the load-bearing direction constraint condition under actual working conditions is eliminated, which facilitates the testing of the sleeve's load-bearing limit and deformation. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the tensile strength testing device in this invention;

[0016] Figure 2 for Figure 1 A partial structural diagram (diagram of connecting and supporting components);

[0017] Figure 3 for Figure 1 Sectional view of section AA;

[0018] Figure 4 This is a three-dimensional structural diagram of the sleeve in this invention;

[0019] Figure 5 This is the Mises stress cloud diagram of sleeves DSPC-1 to DSPC-4 under the ultimate load of steel reinforcement, obtained by finite element analysis in this invention.

[0020] Figure 6 This is the Mises deformation cloud diagram of sleeves DSPC-1 to DSPC-4 under the ultimate load of steel reinforcement, obtained by finite element analysis in this invention.

[0021] Figure 7 This is a schematic diagram showing the bonding positions of strain gauges A1-A5 in the sleeve tensile test of this invention;

[0022] Figure 8 This is a schematic diagram of the load-strain relationship curves of the four sets of specimens in this invention.

[0023] In the diagram: 1-Through-through sensor; 2-Hollow jack; 3-Rebar; 4-Sleeve; 5-Rigid top block; 6-U-shaped base; 7-Support plate; 8-Steel box; 9-Concave arc surface; 10-Convex arc surface; 11-Rebar through hole; 12-Rolled straight thread sleeve; 13-Shim. Detailed Implementation

[0024] To further understand the content, features, and effects of this invention, the following embodiments are provided, and detailed descriptions are given below in conjunction with the accompanying drawings. It should be noted that these embodiments are descriptive, not limiting, and should not be construed as limiting the scope of protection of this invention.

[0025] See appendix Figure 1-4 The present invention provides a rebar connection sleeve based on the strong lap splice theory. The sleeve 4 has a rectangular structure. The sleeve has vertically penetrating rebar through holes 11 symmetrically formed on both sides of the sleeve. The two vertical sides of the sleeve are formed with symmetrical convex arc surfaces 10. The double holes (rebar through holes) are used for the penetration and fixing of the upper and lower sections of rebar.

[0026] The aforementioned tensile strength testing device for rebar connection sleeves based on the strong lap joint theory includes a U-shaped base 6, a support plate 7, a steel box 8, a hollow jack 2, and a through-hole sensor 1. The top of the U-shaped base is open, and the support plate is movable within the opening. A steel box is fixed to the top surface of the middle of the support plate. A hollow jack is fixed to the top surface of the steel box, and the interior of the steel box moves vertically to constrain the insertion sleeve. A through-hole sensor is fixed to the top of the hollow jack. The upper and lower sections of the rebar are penetrated through the rebar through-holes 11 on both sides of the sleeve, respectively. The bottom end slides through one of the steel bar through holes in the sleeve from top to bottom and is axially fixedly connected to the bottom surface of the sleeve. The middle part of the upper steel bar extends upward and slides through the sleeve, steel box, hollow jack and through-hole sensor. The top end of the upper steel bar is axially fixedly connected to the top surface of the through-hole sensor. The top end of the lower steel bar slides through another steel bar through hole in the sleeve from bottom to top and is axially fixedly connected to the top surface of the sleeve. The middle part of the lower steel bar extends downward and slides through the sleeve, steel box and support pad. The bottom end of the lower steel bar is axially fixedly connected to the bottom surface of the support pad.

[0027] Preferably, a rigid top block 5 is fixed on each of the two opposing inner walls of the steel box, and the side wall of the rigid top block is made into a concave arc surface 9 of the convex arc surface on both sides of the sliding constraint sleeve.

[0028] Preferably, the top end of the upper section of the reinforcing bar and the bottom end of the lower section of the reinforcing bar are each equipped with a washer 13 and a rolled straight thread sleeve 12, wherein the rolled straight thread sleeve is threadedly connected to the top end of the upper section of the reinforcing bar and the bottom end of the lower section of the reinforcing bar, so that the upper section of the reinforcing bar is axially fixedly connected to the top surface of the through-core sensor, and the bottom end of the lower section of the reinforcing bar is axially fixedly connected to the bottom surface of the support pad.

[0029] The testing process of the pull-out strength testing device for the rebar connection sleeve based on the strong lap splice theory described in this invention is as follows:

[0030] 1. The strength test procedure is as follows:

[0031] A. Place the U-shaped base on the ground or table before testing;

[0032] B. Place a support pad on top of the U-shaped base;

[0033] C. Place the steel box on the support plate;

[0034] D. Place a hollow jack on the steel box;

[0035] E. Install a through-hole sensor on the upper part of the hollow jack;

[0036] F. Install the upper steel bars from top to bottom. After the lower end passes through the reserved hole on the left side of the steel bar connecting sleeve based on strong lap splice, first install the rolled straight thread sleeve at the end of the upper steel bar, and then install the shim at the lower end.

[0037] G. The lower reinforcing bars are installed from bottom to top. After the upper end passes through the reserved hole on the right side of the reinforcing bar connecting sleeve based on strong lap splice, the rolled straight thread sleeve is first installed at the upper end of the lower reinforcing bar.

[0038] H. Use a hydraulic pump to drive the hollow jack until the reinforcing bar is broken or the reinforcing bar connecting sleeve based on the strong lap joint is damaged, and record the output force of the hollow jack at that moment.

[0039] 2. Comparative analysis of simulation results, such as... Figure 4 and Figure 5 As shown:

[0040] (1) The DSPC-1 model (inner diameter 19mm, outer diameter 28mm) is suitable for steel bar connecting sleeves with nominal diameters of {12mm and 14mm}. The designed sleeve lengths are 20mm, 30mm and 50mm respectively, the connection width is 4mm, and a 14mm steel bar breaking force is applied to the upper surface of the sleeve.

[0041] Maximum required load. Through simulation and comparative analysis, the 30mm long sleeve did not yield under the ultimate load of the reinforcing steel, and did not fail under 1.5 times the ultimate load.

[0042] (2) Applicable to steel bar connecting sleeves with nominal diameters of {16mm and 18mm}, model number:

[0043] The DSPC-2 sleeve (inner diameter 24mm, outer diameter 34mm) is designed with sleeve lengths of 30mm, 50mm, and 60mm, and a connection width of 4mm. The maximum load required for failure of an 18mm rebar is applied to the upper surface of the sleeve. Through simulation and comparative analysis, the 50mm long sleeve did not yield under the ultimate load of the rebar and did not fail under 1.5 times the ultimate load.

[0044] (3) The DSPC-3 (inner diameter 28mm, outer diameter 40mm) sleeve is suitable for steel bar connecting sleeves with nominal diameters of {20mm and 22mm}. The designed sleeve lengths are 50mm, 60mm and 80mm respectively, the connection width is increased to 8mm, and a 22mm steel bar is applied to the upper surface of the sleeve.

[0045] The maximum load required for failure. Through simulation and comparative analysis, the 60mm long sleeve did not yield under the ultimate load of the reinforcing steel, and did not fail under 1.5 times the ultimate load.

[0046] (4) Applicable to steel bar connecting sleeves with nominal diameters of {25mm and 28mm}, model number:

[0047] The DSPC-4 (inner diameter 34mm, outer diameter 50mm) sleeve is designed with sleeve lengths of 60mm, 80mm, and 100mm, and a connection width of 8mm. The maximum load required for failure of a 28mm steel reinforcement is applied to the upper surface of the sleeve. Through simulation and comparative analysis, the 80mm long sleeve did not yield under the ultimate load of the steel reinforcement and did not fail under 1.5 times the ultimate load.

[0048] 3. Analysis of the actual stress on the reinforcing steel:

[0049] To obtain the required yield load and ultimate load of the steel bars in the tensile test, three HRB400 grade hot-rolled ribbed threaded steel bars with diameters of 12mm-28mm were selected and subjected to material property tests on a 2000kN universal testing machine according to the prescribed method.

[0050] The measured yield load and ultimate load of the reinforcing steel are shown in the table below:

[0051]

[0052] 4. Analysis of experimental results:

[0053] (1) DS30-1: The main body height of this sleeve connector is 30mm. At the start of the test, the static strain testing system began to collect data, and the non-contact strain-displacement video measurement system began to measure. In the initial stage of specimen loading, the specimen showed a slight deflection. As the load continued to increase, the deflection angle of the specimen increased slightly. The test was stopped when the load reached the ultimate load value of 96kN for the 14mm steel reinforcement. The sleeve connector did not suffer any obvious damage.

[0054] (2) DS50-1: The main body height of this sleeve connector is 50mm. At the start of the test, the static strain testing system began to collect data, and the non-contact strain-displacement video measurement system began to measure. As the load began to increase, the specimen showed a slight deflection. The test was stopped when the load reached the ultimate load value of 153kN for the 18mm steel bar. The right side of the sleeve connector showed slight deformation under tension, but the specimen as a whole did not suffer any significant damage.

[0055] (3) DS60-1: The main body height of this sleeve connector is 60mm. At the start of the test, the static strain testing system began to collect data, and the non-contact strain-displacement video measurement system began to measure. As the load began to increase, the specimen showed a slight deflection, and the side of the specimen rubbed against the support plate, producing a slight sound. The test was stopped when the load reached the ultimate load value of 228kN for the 22mm steel bar. The sleeve connector tilted significantly, and the lower part of the right-side through hole deformed slightly during the tensile process due to the resistance of the internal high-strength bolts. The specimen as a whole did not suffer any significant damage.

[0056] (4) DS80-1: The main body height of this sleeve connector is 80mm. At the start of the test, the static strain testing system began to collect data, and the non-contact strain-displacement video measurement system began to measure. As the load began to increase, the specimen showed a slight deflection. When the load was increased to 190kN, a slight sound was produced by the friction between the side of the specimen and the support plate. When the load was increased to 279kN, the friction sound increased, and the deflection of the specimen became obvious. The test was stopped when the load reached the ultimate load value of 374kN for the 28mm steel reinforcement. The through hole on the right side of the sleeve connector was slightly deformed by the pressure of the support plate. The wall of the through hole did not break, and the specimen as a whole did not show obvious damage.

[0057] In addition, such as Figure 5 As shown, to analyze the strain of the sleeve connector during the tensile test loading process, strain gauges were attached to the middle of the outer surface of the specimen and both sides of the sleeve wall, as shown. Figure 5 As shown, the load-strain relationship curves on the surfaces of the four sleeve connector specimens are as follows: Figure 6 As shown in the figure, the curve values ​​at each measuring point generally exhibit a linear increase. The strain growth rate is relatively faster in the central region of the specimen. The strain values ​​at A3 and A4 are both positive, indicating that the outer surface of the specimen is under axial tension. At A5, the load-strain curve initially falls on the negative half of the horizontal axis and then tends towards the positive half, indicating that the surface strain at this point gradually changes from compressive strain to tensile strain as the load increases. The absolute strain value at A2 is greater than that at A1 and A3, indicating that the absolute strain value is largest along the 45° direction at the same measuring point. Under load, the strain values ​​at the five measuring points on the cylinder wall are relatively small and the growth rate is slow, indicating that the new sleeve connector can effectively transfer stress, has good mechanical properties, and meets the strength requirements.

[0058] This invention can quickly determine the reliability of force transmission in steel bar connecting sleeves based on strong lap joints. It has low environmental requirements, is fast, and is suitable for rapid installation and testing on construction sites, thereby improving work efficiency. It has high application value and broad prospects for promotion.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

[0060] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A tensile strength testing device for a rebar connection sleeve based on the strong lap splice theory, the testing device being used to test the lap splice strength of the rebar connection sleeve, wherein the sleeve is a rectangular structure, with vertically penetrating rebar through holes symmetrically formed on both sides of the sleeve, and the two vertical sides of the sleeve being symmetrical convex arc surfaces. Its features are: The testing device includes a base, a support plate, a steel box, a hollow jack, and a through-hole sensor. The support plate is set on the top of the base. The steel box is fixed on the top surface of the middle part of the support plate. The hollow jack is fixed on the top surface of the steel box, and a sleeve is inserted into the inside of the steel box. The through-hole sensor is fixed on the top of the hollow jack. The steel bars through holes on both sides of the sleeve respectively penetrate the steel bars and fix the top surface of the through-hole sensor and the bottom surface of the support plate. Rigid top blocks are fixed on both opposing inner walls of the steel box, and the side walls of the rigid top blocks are made into concave arc surfaces of the convex arc surfaces on both sides of the sliding constraint sleeve.

2. The tensile strength testing device for rebar connection sleeves based on strong lap splice theory according to claim 1, characterized in that: The base is U-shaped with an opening at the top and a support pad that can be moved inside the opening.

3. The tensile strength testing device for rebar connection sleeves based on strong lap splice theory according to claim 1, characterized in that: The reinforcing bars include an upper section and a lower section. The bottom end of the upper section is inserted through one of the reinforcing bar through holes in the sleeve from top to bottom and is axially fixedly connected to the bottom surface of the sleeve. The middle part of the upper section extends upward and slides through the sleeve, the steel box, the hollow jack, and the through-hole sensor. The top end of the upper section is axially fixedly connected to the top surface of the through-hole sensor. The top end of the lower section is inserted through another reinforcing bar through hole in the sleeve from bottom to top and is axially fixedly connected to the top surface of the sleeve. The middle part of the lower section extends downward and slides through the sleeve, the steel box, and the support plate. The bottom end of the lower section is axially fixedly connected to the bottom surface of the support plate.

4. The tensile strength testing device for rebar connection sleeves based on strong lap splice theory according to claim 3, characterized in that: The top end of the upper section of the reinforcing bar and the bottom end of the lower section of the reinforcing bar are both provided with a washer and a rolled straight thread sleeve. The rolled straight thread sleeve is threadedly connected to the top end of the upper section of the reinforcing bar and the bottom end of the lower section of the reinforcing bar, so that the upper section of the reinforcing bar is axially fixedly connected to the top surface of the through-core sensor, and the bottom end of the lower section of the reinforcing bar is axially fixedly connected to the bottom surface of the support plate.

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