Concrete tensioning device capable of realizing compression-tension conversion
Patent Information
- Application Number
- CN202522294597.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-30
- Publication Date
- 2026-11-03
- Estimated Expiration
- 2035-10-30
AI Technical Summary
Existing concrete tensile testing devices suffer from low test success rates and large data dispersion due to insufficient stiffness and easy deformation of the rod structure. It is difficult to obtain the full stress-strain curve, especially for concrete without fiber or with a long service life. Existing devices have initial defects that affect stability and applicability.
A steel-bonded concrete tensioning device is designed. By combining a U-shaped lower clamping part and an N-shaped upper clamping part with an embedded steel plate, the compression-tension conversion is achieved using the compression program of a testing machine to stably apply tensile loads. The embedded steel plate is fixed with adhesive to ensure the rigidity and stability of the device.
It achieves stable measurement of concrete load-deformation curves, improves the success rate of tests, reduces the dispersion and variability of test results, and is applicable to axial tension tests under various observation methods and test conditions.
Smart Images
Figure CN224933735U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of concrete testing technology in civil engineering, and particularly relates to a steel-bonded concrete tensioning device that can realize compression-tension conversion. Background Technology
[0002] Concrete is a brittle material that often cracks during service due to its inherent defects such as low tensile strength, weak deformation capacity, and poor ductility, sometimes leading to serious quality accidents. Therefore, studying the tensile properties and constitutive relationship of concrete, especially the softening segment after the peak of the tensile stress-strain curve, is of great significance for the design and application of concrete structures.
[0003] There are three main methods for testing the tensile properties of concrete: direct tension test, splitting tension test, and bending tension test. Among them, the direct tension test, as the method that most directly reflects the tensile strength and deformation performance of concrete, is widely used to study the stress-strain constitutive relationship of concrete. However, due to the inherent brittleness of concrete, the direct tension test places high demands on the test method, test conditions, and testing machine. Currently, the testing machines commonly used for concrete tensile testing often lack rigidity. Their internal systems are prone to deformation in the opposite direction to the specimen's deformation during the tensile process, storing a large amount of elastic deformation energy. When the specimen reaches its maximum load-bearing capacity, the testing machine rapidly releases this energy due to the decrease in load, causing the specimen to suddenly fracture and making it impossible to measure the complete stress-strain curve of the concrete, thus hindering the comprehensive evaluation of the tensile properties of concrete. This is especially true for concrete without fiber incorporation and with a long service life, where obtaining the descending segment of the stress-strain curve through direct tension is extremely difficult. Therefore, a concrete tensile device capable of conversion between compression and tension is designed, allowing the testing machine to apply tensile loads to the specimens by executing a compression program. This reduces the impact of insufficient stiffness of the testing machine and the storage of elastic deformation energy during the tensile process, thereby improving the success rate of obtaining the full curve in direct tensile tests.
[0004] Most existing compression-tension conversion testing devices employ a rod-system reaction structure, which inevitably presents the following problems: ① The load-bearing rods in the rod system are prone to lateral bending deformation under large axial compressive loads, affecting the success rate and safety of the test. ② Insufficient overall stiffness of the device leads to reduced stability, resulting in significant dispersion and variability in the test data. ③ Initial defects and initial bending are unavoidable during the processing and installation of the load-bearing rods, and the larger the slenderness ratio of the load-bearing rods, the more significant the impact of these phenomena on the stability of the device, thus reducing its applicability. Utility Model Content
[0005] This invention addresses the shortcomings of existing technologies by comprehensively considering aspects such as test operability, ease of device assembly and disassembly, reusability, and data measurement stability. It develops a novel steel-bonded concrete tensile device that can achieve compression-tension conversion, thereby improving the success rate of obtaining the full curve in direct tensile tests and reducing test errors.
[0006] To solve the above-mentioned technical problems, this utility model provides the following technical solution: A steel-bonded concrete tensile testing device capable of conversion between compression and tension includes a U-shaped lower clamping part, an N-shaped upper clamping part, and two embedded steel plates. The U-shaped lower clamping part connects the upper loading end plate of the testing machine to the bottom end face of the concrete specimen, and the N-shaped upper clamping part connects the lower loading end plate of the testing machine to the top end face of the concrete specimen. The embedded steel plates are respectively bonded to both ends of the concrete specimen and detachably connected to the U-shaped lower clamping part and the N-shaped upper clamping part. When the testing machine executes a compression program, a tensile load is applied to the concrete specimen through the relative movement of the U-shaped lower clamping part and the N-shaped upper clamping part, thereby achieving the conversion between compression and tension.
[0007] Furthermore, the U-shaped lower clamping part includes an upper steel wing plate, a lower steel plate, steel column plates on both sides, and a first stiffening rib; the upper steel wing plate is provided with a first through hole for connecting with the loading end plate on the testing machine; the lower steel plate is provided with a groove for accommodating the embedded steel plate and a through hole for connecting with the embedded steel plate.
[0008] Furthermore, the N-shaped upper clamping part includes an upper steel plate, two side steel column plates, left and right second stiffening ribs, and front and rear steel box plates; the upper steel plate is provided with a groove for accommodating the embedded steel plate and a second through hole for connecting with the embedded steel plate; the two side steel column plates are provided with observation holes for observation during the test, and the bottom surface is in contact with the lower loading end of the testing machine; the bottom surface of the embedded steel plate is provided with a threaded blind hole for bolt connection with the U-shaped lower clamping part or the N-shaped upper clamping part; the boltless end face of the embedded steel plate is bonded to the end face of the concrete specimen with adhesive.
[0009] Furthermore, the U-shaped lower clamping part and the N-shaped upper clamping part are welded parts.
[0010] Furthermore, the diameter of the first through hole on the upper steel wing plate of the U-shaped lower clamping part is the same as the diameter of the corresponding through hole on the loading end plate of the testing machine.
[0011] Furthermore, the observation holes on the steel column plates on both sides of the N-type upper clamping part are not less than 40mm wide and not less than the height of the concrete specimen, for use in conjunction with DIC technology observation.
[0012] Furthermore, the outer periphery shape of the embedded steel plate cross section is the same as that of the outer periphery shape of the concrete specimen cross section, which is a circle, square, rectangle or N-sided shape, where N≥5; the dimensions of each side are 1~3mm larger than the corresponding dimensions of the concrete specimen.
[0013] Furthermore, the boltless end face of the embedded steel plate is bonded to the end face of the concrete specimen using epoxy resin-based structural adhesive.
[0014] Furthermore, the length of the lower steel plate of the U-shaped lower clamping part is not less than the width of the upper steel plate of the N-shaped upper clamping part, and the U-shaped lower clamping part and the N-shaped upper clamping part are interlocked.
[0015] Furthermore, the center point of the lower end steel plate of the U-shaped lower clamping part and the center point of the upper end steel plate of the N-shaped upper clamping part are both located on the central axis of the embedded steel plate and coincide with the central axis of the concrete specimen.
[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention relates to a novel steel-bonded concrete tensile device that enables compression-tension conversion. It can convert the concrete specimen into a tensile load by executing the compression program of the testing machine, stably measure the load-deformation curve of the concrete, and especially obtain the curve of the descent segment after the peak.
[0017] The device has a clear force transmission, simple structure, convenient operation, and is detachable and reusable. It is suitable for axial tensile tests under various observation methods, including DIC technology, various test conditions, including presses, and various types of concrete specimens.
[0018] The device has high overall stiffness and stability, which improves the success rate of tensile tests and reduces the dispersion and variability of test results. Attached Figure Description
[0019] To more clearly illustrate the technical solutions in this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0020] Figure 1 This is a schematic diagram of an embodiment of the concrete stretching device of this utility model.
[0021] Figure 2 This is a schematic diagram of a concrete tensioning device according to an embodiment of the present invention.
[0022] In the figure: 1 – U-shaped lower clamping part; 1a – steel wing plate; 1b – steel plate; 1c – steel column plate; 1d – first stiffening rib; 1e – first through hole; 1f – groove; 2 – N-shaped upper clamping part; 2a – steel plate; 2b – steel column plate; 2c – second stiffening rib; 2d – steel box plate; 2e – second through hole; 2f – observation hole; 3 – embedded steel plate; 3a – threaded blind hole; 4 – concrete specimen; 5 – bolt; 6 – bolt. Detailed Implementation
[0023] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.
[0024] Example 1 This embodiment provides a novel steel-bonded concrete tensile device that can realize compression-tension conversion. It mainly includes a U-shaped lower clamping part 1, an N-shaped upper clamping part 2, and an embedded steel plate 3, which are installed at both ends of the concrete specimen 4 to fix the concrete specimen between the two loading ends of the tensile test loading device. When the compression program of the testing machine is executed, a tensile load can be applied to the concrete specimen to realize compression-tension conversion. In this embodiment, the tensile device is installed at both ends of the concrete specimen. The upper loading end plate of the testing machine is connected to the bottom end face of the specimen 4 through the U-shaped lower clamping part 1 and the embedded steel plate 3, and the lower loading end plate of the testing machine is connected to the top surface of the specimen 4 through the N-shaped upper clamping part 2 and the embedded steel plate 3. The compression-tension conversion process is as follows: When the testing machine executes the compression program, the loading end plate on the testing machine causes the bottom end of the concrete specimen 4 to move downward, and the lower end plate of the testing machine causes the top end of the concrete specimen 4 to move upward or not move, so that a tensile load can be applied to the concrete specimen 4 to complete the direct tensile test of concrete.
[0025] In one specific embodiment, the U-shaped lower clamping part 1 includes an upper steel wing plate 1a, a lower steel plate 1b, two steel column plates 1c on both sides, and a first stiffening rib 1d; the U-shaped lower clamping part 1 is a welded part, and the verticality and parallelism are ensured after the whole welding is performed. The thickness of the steel wing plate 1a at the upper end of the U-shaped lower clamping part and the steel column plates 1c on both sides shall be determined according to the actual test conditions and shall not be less than 20mm. The upper steel wing plate 1a of the U-shaped lower clamping part is provided with a first through hole 1e for connecting with the upper end plate of the testing machine. The size of the first through hole is determined according to the actual reserved through hole diameter of the testing machine. The steel wing plate 1a and the upper end plate of the testing machine have four bolt holes for accommodating the same bolt. The bolts 5 are inserted into the through holes of the steel wing plate and the upper end plate of the testing machine for fixing. The lower end steel plate 1b of the U-shaped lower clamping part is provided with a groove 1f for accommodating the embedded steel plate 3 and a second through hole 2e for connecting with the embedded steel plate; the size of the groove 1f is the same as that of the embedded steel plate 3; the size of the second through hole 2e is the same as that of the blind hole thread of the embedded steel plate. The first stiffening ribs 1d on the left and right sides of the U-shaped lower clamping part are right-angled trapezoids, with two in total, located at the center of the steel column plates 1c on both sides respectively; the size of the first stiffening ribs 1d is determined according to the actual test situation, with the short side length not less than 10mm and the thickness not less than 12mm; they are welded and fixed to the upper steel wing plate 1a and the steel column plates 1c on both sides. In one specific embodiment, the N-shaped upper clamping part 2 is a welded component, including a steel plate 2a at the upper end, steel column plates 2b on both sides, second stiffening ribs 2c on the left and right sides, and steel box plates 2d at the front and rear; the N-shaped upper clamping part 2 is a welded component, and the verticality and parallelism are ensured after the whole is welded and processed. The thickness of the steel column plates 2b on both sides of the upper clamping part of the N-type is determined according to the actual test situation, and shall not be less than 25mm; The upper end steel plate 2a of the N-type upper clamping part is provided with a groove 1f for accommodating and embedding the embedded steel plate 3 and a second through hole 2e for connecting with the embedded steel plate 3; the size of the groove 1f is the same as that of the embedded steel plate 3; the size of the second through hole 2e is the same as that of the threaded blind hole 3a of the embedded steel plate. The bottom surface of the steel column plate 2b on both sides of the upper clamping part of the N-type contactes the lower loading end plate of the testing machine. The second stiffening ribs 2c on the left and right sides of the N-type upper clamping part are right-angled trapezoids, with a total of four, located on both sides of the observation holes 2f set on the steel column plates 2b for observation during the test. The distance between the central axis of the second stiffening rib 2c and the edge of the observation hole 2f is not less than 30mm. The size of the second stiffening rib 2c is determined according to the actual test conditions, with a short side length of not less than 10mm and a thickness of not less than 12mm. It is welded and fixed to the upper steel plate 2a and the steel column plates 2b on both sides. The steel box plates 2d at the front and rear of the N-type upper clamping part are rectangular, and there are two in total. The steel box plates 2d are flush with the outer edge of the upper steel plate 2a. They are welded and fixed to the upper steel plate 2a and the two side steel column plates 2b. The size of the rectangle is determined according to the actual test situation, with a height of not less than 50mm and a thickness of not less than 30mm. In the aforementioned N-type upper clamping part 2, the two side steel column plates are provided with observation holes 2f for experimental observation. The upper edge of the observation holes 2f is flush with the bottom surface of the upper steel plate 2a of the N-type upper clamping part. The size of the observation holes 2f is determined according to the actual experimental conditions, with a width of not less than 40mm and a height of not less than the height of the concrete specimen 4.
[0026] The dimensions of the steel plate 1b at the lower end of the U-shaped lower clamping part and the steel plate 2a at the upper end of the N-shaped upper clamping part are determined according to the actual test conditions. The thickness at the thickest part is not less than 60mm and the thickness at the thinnest part is not less than 30mm. The length of the lower end steel plate 1b of the U-shaped lower clamping part shall not be less than the width of the upper end steel plate 2a of the N-shaped upper clamping part; The U-shaped lower clamping part 1 and the N-shaped upper clamping part 2 are interlocked; the center of the lower end steel plate 1b of the U-shaped lower clamping part and the center of the upper end steel plate 2a of the N-shaped upper clamping part are located on the central axis of the embedded steel plate 3 and coincide with the central axis of the concrete specimen 4. In one specific embodiment, the embedded steel plate 3 is a casting, and there are two of them; the bottom surface is provided with a threaded blind hole 3a for connecting with the U-shaped lower clamping part 1 and the N-shaped upper clamping part 2; the diameter of the threaded blind hole 3a is determined according to the actual test situation, and is not less than 13mm; its boltless end face is glued to the end face of the concrete specimen 4, and the boltless end face is connected to the U-shaped lower clamping part 1 or the N-shaped upper clamping part 2; The outer perimeter shape of the cross section of the embedded steel plate 3 is the same as that of the cross section of the concrete specimen 4, which is circular, square, rectangular or N-sided, where N≥5; the dimensions of each side are 1~3mm larger than those of the concrete specimen 4; the thickness is determined according to the actual test conditions, and is not less than 30mm.
[0027] The first embedded steel plate 3 is embedded in the groove 1f of the lower end steel plate of the U-shaped lower clamping part. The embedded steel plate 3 and the lower end steel plate 1b of the U-shaped lower clamping part have four second through holes 2e and threaded blind holes 3a for accommodating the same bolt. It is fixed by inserting four bolts 6 into the embedded steel plate 3, the lower end steel plate 1b of the U-shaped lower clamping part, the second through holes 2e, and the threaded blind holes 3a. The second embedded steel plate 3 is embedded in the groove 1f of the upper end steel plate of the N-shaped upper clamping part. The embedded steel plate 3 and the upper end steel plate 2a of the N-shaped upper clamping part have four second through holes 2e for accommodating the same bolt. It is fixed by inserting four bolts 6 into the embedded steel plate 3, the upper end steel plate 2a of the N-shaped upper clamping part, the second through holes 2e, and the threaded blind holes 3a.
[0028] The U-shaped lower clamping part 1, the N-shaped upper clamping part 2, and the embedded steel plate 3 are made of the same material. Bolts 5 and 6 are made of the same material as described above or have higher strength properties than the steel materials mentioned above.
[0029] The boltless end face of the embedded steel plate 3 is bonded to the end face of the concrete specimen 4 using adhesive. The room temperature curing time of the adhesive should not exceed 24 hours, the tensile strength of the adhesive should not be less than 30 MPa, the shear strength should not be less than 18 MPa, and the tensile bond strength between the steel and the concrete specimen 4 should meet the ultimate tensile strength of the specimen in the test. The adhesive used should preferably be a cyclic resin-based structural steel bonding adhesive with the following bonding capabilities: steel-to-steel shear strength standard value >15 MPa, steel-to-steel butt joint tensile bond strength >33 MPa, and steel-to-C40 concrete tensile bond strength >4 MPa.
[0030] When the boltless end face of the embedded steel plate 3 is separated from the concrete specimen 4, the side of the concrete specimen can be struck with a hammer to remove most of the concrete specimen, and then the end face concrete can be cleaned with a drill.
[0031] As attached Figure 1 and 2 The concrete specimens were cylinders with a diameter of 100 mm and a height of 200 mm.
[0032] The upper steel wing plate of the U-shaped lower clamping part is 118.5mm long, 200mm wide, and 20mm thick. A through hole of the same size is provided at the pre-drilled hole position on the loading end plate of the testing machine. M30 bolts are used to fix the upper steel wing plate of the U-shaped lower clamping part to the loading end plate of the testing machine. The lower steel plate is 213mm long, 200mm wide, and 60mm thick. A groove for accommodating the embedded steel plate and a through hole for connecting with the embedded steel plate are provided at the center of the lower steel plate. The groove has a diameter of 104mm and a height of 30mm, and four symmetrically arranged through holes with a diameter of 13mm are provided in the groove. The steel column plates on both sides are 200mm long, 440mm high, and 20mm thick. The stiffening ribs on both sides are right-angled trapezoids with a short side length of 10mm, a long side length of 98.5mm, a height of 440mm, and a thickness of 12mm. They are located at the center of the steel column plates on both sides and are welded and fixed to the upper steel wing plate and the steel column plates on both sides.
[0033] The upper steel plate of the N-type clamping part is 270mm long, 200mm wide, and 60mm thick, with wing plates extending from both sides, each 45mm long, 200mm wide, and 30mm thick. A groove for accommodating an embedded steel plate and a through hole for connection are provided at the center of the upper steel plate. The groove has a diameter of 104mm and a height of 30mm, and four symmetrically arranged through holes with a diameter of 13mm are located within the groove. The steel column plates on both sides are 200mm long, 320mm high, and 25mm thick, with their bottom surfaces directly contacting the lower loading end plate of the testing machine. An observation hole for experimental observation is provided between the two steel column plates, with a width of 40mm and a height of 260mm, and the upper edge of the hole is flush with the bottom surface of the upper steel plate. The stiffening ribs on both sides are right-angled trapezoids, with a short side length of 10mm, a long side length of 45mm, a height of 350mm, and a thickness of 12mm. They are located 30mm from both sides of the test hole and are welded and fixed to the upper steel wing plate and the steel column plates on both sides. The front and rear steel box plates are rectangular, with a width of 220mm, a height of 100mm, and a thickness of 30mm. They are flush with the outer edge of the upper steel plate and are welded and fixed to the upper steel plate and the steel column plates on both sides.
[0034] The embedded steel plate is cylindrical with a diameter of 102mm and a thickness of 30mm. The bottom surface is provided with threaded blind holes corresponding to the through holes of the grooves of the lower end steel plate of the U-shaped lower clamping part and the upper end steel plate of the N-shaped upper clamping part. The blind holes have a diameter of 13mm and a depth of 25mm.
[0035] The boltless end face of the embedded steel plate is bonded to the end face of the concrete specimen using epoxy resin-based structural steel adhesive. The bolt-hole end face is connected to the U-shaped lower clamping part or the N-shaped upper clamping part; the first embedded steel plate is embedded in the groove of the lower steel plate of the U-shaped lower clamping part and fixed by inserting four M12 bolts into the bolt holes of the embedded steel plate and the lower steel plate of the U-shaped lower clamping part; the second embedded steel plate is embedded in the groove of the upper steel plate of the N-shaped upper clamping part and fixed by inserting four M12 bolts into the bolt holes of the embedded steel plate and the upper steel plate of the N-shaped upper clamping part.
[0036] The U-shaped lower clamping part, the N-shaped upper clamping part, and the embedded steel plate are made of the same material. The bolt material is the same as that described above or has higher strength properties than the steel materials mentioned above.
[0037] The strength grade of the steel, the thickness of the steel components, and the cross-sectional dimensions are all determined based on the design requirements of the concrete specimens and the stiffness requirements of the tensile device in the actual test.
[0038] The U-shaped lower clamping part and the N-shaped upper clamping part are interlocked; the center of the lower end steel wing plate of the U-shaped lower clamping part and the center of the upper end steel plate of the N-shaped upper clamping part are located on the central axis of the embedded steel plate and coincide with the central axis of the concrete specimen.
[0039] The tensile test uses DIC non-contact measurement technology. A camera is set up in front of the test observation hole of the N-type clamp to measure the deformation of the concrete specimen. The testing machine is used to execute the compression program. The upper end plate of the testing machine drives the bottom end plate of the concrete specimen to move downward, and the lower end plate of the testing machine drives the top end plate of the concrete specimen to move upward or not move. That is, a tensile load is applied to the concrete specimen to complete the direct tensile test of concrete and measure the descending segment of the tensile stress-strain curve of concrete.
[0040] It should be understood that any parts not described in detail in this specification belong to the prior art.
[0041] It should be understood that the above description of the preferred embodiments is quite detailed, but this should not be construed as limiting the scope of protection of this utility model patent. It is neither necessary nor possible to exhaustively describe all possible implementations. Those skilled in the art, under the guidance of this utility model, can make substitutions or modifications without departing from the scope of protection of the claims of this utility model, and all such substitutions or modifications fall within the scope of protection of this utility model. The scope of protection of this utility model should be determined by the appended claims.
Claims
1. A steel-bonded concrete tensioning device capable of conversion between compression and tension, characterized in that: It includes a U-shaped lower clamping part, an N-shaped upper clamping part, and two embedded steel plates; the U-shaped lower clamping part is used to connect the upper loading end plate of the testing machine and the bottom end face of the concrete specimen, the N-shaped upper clamping part is used to connect the lower loading end plate of the testing machine and the top end face of the concrete specimen, and the embedded steel plates are respectively bonded to both ends of the concrete specimen and detachably connected to the U-shaped lower clamping part and the N-shaped upper clamping part; when the testing machine executes the compression program, the relative movement of the U-shaped lower clamping part and the N-shaped upper clamping part applies a tensile load to the concrete specimen, realizing the conversion between compression and tension.
2. The steel-bonded concrete tensioning device capable of conversion between compression and tension according to claim 1, characterized in that: The U-shaped lower clamping part includes an upper steel wing plate, a lower steel plate, steel column plates on both sides, and a first stiffening rib; the upper steel wing plate is provided with a first through hole for connecting with the loading end plate on the testing machine; the lower steel plate is provided with a groove for accommodating the embedded steel plate and a through hole for connecting with the embedded steel plate.
3. The steel-bonded concrete tensioning device capable of conversion between compression and tension according to claim 2, characterized in that: The N-shaped upper clamping part includes an upper steel plate, two side steel column plates, left and right second stiffening ribs, and front and rear steel box plates; the upper steel plate is provided with a groove for accommodating the embedded steel plate and a second through hole for connecting with the embedded steel plate; the two side steel column plates are provided with observation holes for observation during the test, and the bottom surface is in contact with the lower loading end of the testing machine; the bottom surface of the embedded steel plate is provided with a threaded blind hole for bolt connection with the U-shaped lower clamping part or the N-shaped upper clamping part; the boltless end face of the embedded steel plate is bonded to the end face of the concrete specimen with adhesive.
4. A steel-bonded concrete tensioning device capable of conversion between compression and tension according to claim 1, characterized in that: The U-shaped lower clamping part and the N-shaped upper clamping part are welded parts.
5. A steel-bonded concrete tensioning device capable of conversion between compression and tension according to claim 1, characterized in that: The diameter of the first through hole on the upper steel wing plate of the U-shaped lower clamping part is the same as the diameter of the corresponding through hole on the loading end plate of the testing machine.
6. A steel-bonded concrete tensioning device capable of conversion between compression and tension according to claim 1, characterized in that: The observation holes on the steel column plates on both sides of the N-type upper clamping part are not less than 40mm wide and not less than the height of the concrete specimen, and are used for observation with DIC technology.
7. A steel-bonded concrete tensioning device capable of conversion between compression and tension according to claim 1, characterized in that: The outer periphery shape of the embedded steel plate cross section is the same as that of the concrete specimen cross section, which is a circle, square, rectangle or N-sided polygon, where N≥5; the dimensions of each side are 1~3mm larger than the corresponding dimensions of the concrete specimen.
8. A steel-bonded concrete tensioning device capable of conversion between compression and tension according to claim 1, characterized in that: The boltless end face of the embedded steel plate is bonded to the end face of the concrete specimen using epoxy resin-based structural adhesive.
9. A steel-bonded concrete tensioning device capable of conversion between compression and tension according to claim 1, characterized in that: The length of the lower steel plate of the U-shaped lower clamping part is not less than the width of the upper steel plate of the N-shaped upper clamping part, and the U-shaped lower clamping part and the N-shaped upper clamping part are interlocked.
10. A steel-bonded concrete tensioning device capable of conversion between compression and tension according to claim 1, characterized in that: The center point of the lower end steel plate of the U-shaped lower clamping part and the center point of the upper end steel plate of the N-shaped upper clamping part are both located on the central axis of the embedded steel plate and coincide with the central axis of the concrete specimen.