A device and method for testing the bond-slip performance of PEC steel reinforced concrete

Abstract

The present application relates to the technical field of civil engineering structure testing, and discloses a device and method for testing the bond-slip performance of PEC steel reinforced concrete, wherein the clamp assembly comprises an upper half clamp and a lower half clamp; the upper half clamp comprises left and right side steels stacked one above the other; and the lower half clamp comprises a tensioned steel assembly integrally formed with the concrete; the present application changes the loading mode, avoids the situation that the steel at the loading end buckles locally first when the push-out test is performed, and thus causes the measured bond-slip curve to deviate greatly, and can obtain the bond-slip curve of the steel-concrete interface more accurately. The measured result is more direct and accurate than the result of the push-out test, reduces the generation of errors, and can accurately reflect the bond-slip relationship on the contact surface. The clamp assembly has the advantages of being detachable, high clamping and fixing efficiency, and being adjustable according to the size of the test piece.

Description

Technical Field

[0001] This invention relates to the field of civil engineering structural testing technology, specifically to a device and method for testing the bond-slip performance of PEC steel-concrete composite. Background Technology

[0002] PEC (Polymer Concrete-Concrete Composite) structures are integral structures formed by pouring concrete between the flanges and webs of steel profiles. Alternatively, reinforcing bars or flat steel can be welded between the flanges to further constrain the concrete. This type of structure can effectively withstand vertical axial or eccentric loads. In recent years, PEC composite structures have been widely used and developed in high-rise buildings and bridge structures.

[0003] Compared with traditional structures, PEC steel-concrete composite structures have the following advantages:

[0004] (1) Mechanical properties: The H-beams in the composite column are equivalent to the reinforcing bars and stirrups in the reinforced concrete structure, while the concrete on both sides of the web strengthens the longitudinal stiffness and the overall stability of the member, and improves the member's torsional and overturning resistance.

[0005] (2) Fire resistance: The concrete filling in the middle of the flange reduces the exposed surface area of ​​the steel section, thus improving the poor fire resistance of pure steel structures;

[0006] (3) Construction: H-shaped steel columns can serve as part of the formwork, thereby simplifying the formwork support and dismantling work and speeding up the construction period; compared with traditional reinforced concrete columns, composite columns are lightweight and have a high degree of prefabrication and assembly, saving transportation and installation costs.

[0007] The bonding performance between steel and concrete is the foundation for their collaborative work and the key to ensuring sufficient load-bearing capacity in PEC steel-concrete composite structures. It is precisely because of the bonding effect between steel and concrete that the steel can work together with the concrete and share the load, becoming a true "composite" structure.

[0008] Currently, research on the bond strength of PEC steel-concrete composite mainly employs push-out tests. In the push-out test designed in patent (CN117074294A), the upper and lower ends of the steel section are in contact with the two bases of the loading device, while the lower end of the concrete section remains stationary. The loading device bases are displaced upwards, and the upper end of the steel section bears the displacement from the bases. The slip value at the steel-concrete interface is then directly obtained through a displacement gauge on a base plate set at the free end of the steel section. In this test method (CN117074294A), the base plate at the free end effectively prevents the displacement gauge from shifting during sliding and when axial pressure is applied, thus ensuring test accuracy. However, it fails to address the issue that the upper end of the steel section may buckle before the steel-concrete interface slip occurs during loading, leading to significant deviations in the measured bond-slip curve. Furthermore, the strain value of the concrete at the steel-concrete interface cannot be measured, and the local bond stress of the specimen cannot be obtained. Therefore, we introduce a device and method for testing the bond-slip performance of PEC steel-concrete composite. Summary of the Invention

[0009] The purpose of this invention is to provide a device and method for testing the bond-slip properties of PEC steel-concrete composites, in order to solve the problems mentioned in the background art.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A device for testing the bond-slip properties of PEC steel-concrete composite includes a clamp assembly comprising an upper clamp and a lower clamp.

[0012] The upper clamping part includes left-side and right-side steel sections stacked one on top of the other;

[0013] The lower clamp includes a tension steel reinforcement assembly integrally formed with concrete. The bottom of the tension steel reinforcement assembly extends from the bottom of the concrete and is connected to a tension distribution plate. A bottom tension bolt is provided in the middle of the tension distribution plate.

[0014] Metal strain gauges are uniformly pasted on the inner walls of the strip-shaped slots opened on the tensile steel reinforcement assembly.

[0015] An H-beam steel assembly is installed in the middle of the concrete, and displacement gauges are installed at both the top and bottom of the concrete. The top of the H-beam steel assembly extends out of the concrete.

[0016] The synchronous clamping assembly between the left and right profiles is used to simultaneously clamp and fix the left and right profiles to the top of the H-beam assembly. The top tension bolt of the synchronous clamping assembly extends out of the left and right profiles.

[0017] Preferably, the tension reinforcement assembly includes a tension reinforcement skeleton that is connected to the tension distribution plate and is arranged symmetrically from left to right;

[0018] The tensile reinforcement cage includes two sets of first tensile reinforcement bars on the inner side and two sets of second tensile reinforcement bars on the outer side, as well as several sets of upper stirrups set between the two sets of first tensile reinforcement bars on the inner side and the two sets of second tensile reinforcement bars on the outer side.

[0019] Several sets of lower stirrups are provided between the bottom of the symmetrical tensile reinforcement cage. These sets of lower stirrups are located within the flange at the bottom of the concrete.

[0020] Preferably, the strip groove is located at the top middle position of the first tensile reinforcement, and the metal strain gauges in the same strip groove are distributed alternately vertically.

[0021] Preferably, the H-beam assembly includes a web in the middle of the concrete, flanges on both sides of the web, and a steel top plate at the top of the web and flanges;

[0022] The web, flanges, and top steel plate are integrally formed.

[0023] The inner wall of the flange is attached to the outer wall of the concrete.

[0024] Preferably, the synchronous clamping assembly includes racks provided on the inner walls of the left and right profiles, an intermediate frame fitted on the two sets of racks, gears provided in the intermediate frame, and a clamping plate connected to the bottom of the intermediate frame.

[0025] The gear meshes between two sets of racks;

[0026] The gear has a turntable at the lower center, and a positioning post at the lower center of the turntable. The bottom of the positioning post extends through the first reserved hole at the bottom of the intermediate frame and the second reserved hole on the clamping plate. The upper center of the top plate of the steel profile has a positioning hole for inserting the positioning post.

[0027] Preferably, the bottom of the top tension bolt is centrally rotatably connected between the gear and the turntable, and the upper end of the top tension bolt extends through the third reserved hole at the top of the middle frame and the limiting groove at the top of the left and right profiles.

[0028] Preferably, the bottom outer side of the turntable is provided with an annular groove, and the top wall of the annular groove is symmetrically provided with two sets of arc-shaped grooves;

[0029] Two sets of top balls are symmetrically slidably connected inside the annular groove, with the upper ends of the top balls closely attached to the top wall of the annular groove;

[0030] The vertical rod at the bottom of the top ball extends through the countersunk hole on the middle frame and is fixedly connected to the clamping plate. A return spring is also provided in the countersunk hole and sleeved on the vertical rod.

[0031] The present invention also provides a test method for a PEC steel-concrete bond-slip performance testing device, specifically including the following steps:

[0032] S1. Secure the bottom of the left and right profiles to the top of the H-beam assembly, and ensure that the bottom of the synchronous clamping assembly is centered on the top of the H-beam assembly;

[0033] S2. Push the left and right steel sections against each other until the distance between the left and right steel sections is close, so that the synchronous clamping assembly, the left and right steel sections are synchronously clamped and fixed to the top of the H-beam assembly.

[0034] S3. Connect the top tension bolt and the bottom tension bolt to the upper and lower clamps of the pull-out testing machine respectively. That is, obtain the amount of slippage at the concrete interface through the displacement gauge, and measure the concrete strain at the bond interface between the H-beam steel assembly and the concrete by the difference in strain values ​​of the metal strain gauge.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] 1. This invention, by changing the loading method, avoids the situation where the steel at the loading end buckles first during the push-out test, thus preventing a large deviation in the measured bond-slip curve. It can obtain a more accurate bond-slip curve of the steel-concrete interface. The measured results are more direct and accurate than those of previous push-out tests, reducing errors and precisely reflecting the bond-slip relationship on the contact surface.

[0037] 2. The present invention can obtain the strain of concrete at the bond interface by the difference in strain values ​​of the metal strain gauges installed inside the first tensile steel bar, and indirectly obtain the local bond stress at the interface between the steel section and the concrete and the relative slip value between the steel section and the concrete at the corresponding measuring point.

[0038] 3. The method for preparing PEC steel-concrete specimens and clamping assemblies provided by this invention is simple, the materials are easy to obtain, and the measurement cost is low. The clamping assembly has the advantage of being detachable. While the right-side steel and the left-side steel approach each other synchronously, the clamping plate can also be driven to move down, so as to achieve clamping and fixing of the top of the H-beam assembly. The clamping and fixing efficiency is high, and it can be adjusted according to the size of the specimen and can be reused. Attached Figure Description

[0039] Figure 1 This is an exploded structural diagram of the assembly of the clamping assembly and the PEC steel-concrete specimen of the present invention.

[0040] Figure 2 This is a first three-dimensional structural schematic diagram of the H-beam steel assembly of the present invention;

[0041] Figure 3 This is a schematic diagram of the second three-dimensional structure of the H-beam steel assembly of the present invention;

[0042] Figure 4 This is a structural schematic diagram of the tension steel reinforcement assembly of the present invention;

[0043] Figure 5 This is a cross-sectional structural diagram of the tensile reinforcement assembly and the overall concrete structure of the present invention;

[0044] Figure 6 This is a three-dimensional structural diagram of the initial assembly of the clamping assembly and the PEC steel-concrete specimen of the present invention;

[0045] Figure 7 This is an exploded structural diagram of the assembly of the right-side steel section, the left-side steel section, and the synchronous clamping assembly of the present invention;

[0046] Figure 8 This is a three-dimensional structural diagram of the connection between the middle frame and the clamping plate of the present invention;

[0047] Figure 9 This is an exploded structural diagram of the connection between the clamping plate and the positioning post of the present invention;

[0048] Figure 10 A three-dimensional structural diagram of the gears and turntable of the present invention;

[0049] Figure 11 This is a three-dimensional structural diagram of the preliminary assembly of the right-side steel section, left-side steel section, and synchronous clamping assembly of the present invention.

[0050] Figure 12 For the present invention Figure 11 Schematic diagram of the cross-sectional structure at point AA;

[0051] Figure 13 This is a three-dimensional structural diagram of the connection between the intermediate frame, gears, turntable, and clamping plate of the present invention.

[0052] Figure 14 For the present invention Figure 13 Schematic diagram of the cross-sectional structure at point BB;

[0053] Figure 15 This is a three-dimensional structural diagram of the fully assembled clamp assembly and PEC steel-concrete specimen of the present invention.

[0054] Figure 16 This is a three-dimensional structural diagram of the clamping assembly of the present invention in the fully clamped state.

[0055] Figure 17 For the present invention Figure 16 Schematic diagram of the cross-sectional structure at the CC section;

[0056] Figure 18 For the present invention Figure 16 A cross-sectional view of the structure from another perspective.

[0057] In the diagram: 1. Top tension bolt; 2. Middle frame; 201. Third reserved hole; 202. First reserved hole; 203. Countersunk hole; 3. Right side steel section; 4. Left side steel section; 5. Top plate of steel section; 51. Positioning hole; 6. Web plate; 7. Concrete; 8. Upper stirrup; 9. First tension reinforcement; 10. Second tension reinforcement; 11. Flange; 12. Tension distribution plate; 13. Bottom tension bolt; 14. Displacement gauge; 15. Metal strain gauge; 16. H-beam assembly; 17. Lower stirrup; 18. Strip slot; 19. Rack; 20. Limiting groove; 21. Gear; 22. Turntable; 23. Clamping plate; 231. Second reserved hole; 24. Positioning post; 25. Return spring; 26. Top ball; 27. Vertical rod; 28. Annular groove; 29. ​​Arc groove. Detailed Implementation

[0058] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] Example:

[0060] Please see Figure 1-18 The present invention provides a technical solution:

[0061] A device for testing the bond-slip properties of PEC steel-concrete composite structures includes a clamp assembly comprising an upper clamp and a lower clamp.

[0062] The upper clamping part includes the left-side steel section 4 and the right-side steel section 3 stacked on top of each other;

[0063] The lower clamp includes a tensile steel reinforcement assembly integrally formed with the concrete 7;

[0064] The tension reinforcement assembly includes a tension reinforcement cage that is connected to the tension distribution plate 12 and is arranged symmetrically on the left and right sides; that is, the tension reinforcement cage is divided into two groups on the left and right sides in the PEC steel-concrete specimen and is arranged symmetrically on the left and right sides along the web 6.

[0065] The tensile reinforcement cage includes two sets of first tensile reinforcement bars 9 on the inner side and two sets of second tensile reinforcement bars 10 on the outer side, as well as several sets of upper stirrups 8 arranged between the two sets of first tensile reinforcement bars 9 on the inner side and two sets of second tensile reinforcement bars 10 on the outer side.

[0066] The thickness of the concrete cover for the first tensile reinforcement 9 and the second tensile reinforcement 10 should be greater than their diameter;

[0067] The PEC-type steel-concrete specimen contains a first tensile reinforcement 9, a second tensile reinforcement 10, an upper stirrup 8, and a lower stirrup 17. The bond strength between the first tensile reinforcement 9 and the second tensile reinforcement 10 and the concrete interface is much greater than the bond strength between the H-beam assembly 16 and the concrete interface. When the PEC-type steel-concrete specimen is subjected to tensile force, the H-beam assembly 16 and the concrete interface will slip before the first tensile reinforcement 9 and the second tensile reinforcement 10 and the concrete interface.

[0068] Several sets of bottom stirrups 17 are provided between the bottom of the symmetrical tensile steel reinforcement cage.

[0069] The strip groove 18 is located at the top middle position of the first tensile reinforcement 9, and the metal strain gauges 15 in the same strip groove 18 are distributed in an alternating manner.

[0070] After the bottom of the tension reinforcement assembly extends from the bottom of the concrete 7, it is connected to the tension distribution plate 12, and the tension distribution plate 12 is provided with a bottom tension bolt 13 in the middle.

[0071] The bottom protruding ends of the first tensile reinforcement 9 and the second tensile reinforcement 10 are connected to the tension distribution plate 12. The bottom tension bolt 13 is set at the center of the tension distribution plate 12 as the loading end. The size of the tension distribution plate 12 is equal to the cross-sectional size of the PEC steel-concrete specimen.

[0072] Metal strain gauges 15 are evenly pasted on the inner walls of the strip-shaped slots 18 opened on the tensile reinforcement assembly;

[0073] An H-beam steel assembly 16 is installed inside the middle of concrete 7;

[0074] H-beam assembly 16 includes a web 6 in the middle of concrete 7, flanges 11 on both sides of the web 6, and a steel top plate 5 on the top of the web 6 and flanges 11.

[0075] The web plate 6, flange 11 and steel top plate 5 are integrally formed;

[0076] The inner wall of flange 11 is attached to the outer wall of concrete 7.

[0077] Displacement gauges 14 are installed at both the top and bottom of concrete 7, and the top of H-beam steel assembly 16 extends out of concrete 7.

[0078] The synchronous clamping assembly between the left-side steel section 4 and the right-side steel section 3 is used to achieve synchronous clamping and fixing of the left-side steel section 4 and the right-side steel section 3 to the top of the H-beam assembly 16. The top tension bolt 1 of the synchronous clamping assembly extends out of the left-side steel section 4 and the right-side steel section 3.

[0079] The synchronous clamping assembly includes racks 19 installed on the inner walls of the left steel section 4 and the right steel section 3, an intermediate frame 2 fitted on the two sets of racks 19, a gear 21 installed inside the intermediate frame 2, and a clamping plate 23 connected to the bottom of the intermediate frame 2.

[0080] Gear 21 meshes between two sets of racks 19;

[0081] A turntable 22 is provided at the lower center of the gear 21, and a positioning post 24 is provided at the lower center of the turntable 22. The bottom of the positioning post 24 extends through the first reserved hole 202 at the bottom of the intermediate frame 2 and the second reserved hole 231 on the clamping plate 23. The upper center of the steel top plate 5 is provided with a positioning hole 51 for inserting the positioning post 24.

[0082] The top tension bolt 1 is centrally rotatably connected between the gear 21 and the turntable 22, and the upper end of the top tension bolt 1 extends through the third reserved hole 201 at the top of the middle frame 2 and the limiting groove 20 at the top of the left steel 4 and the right steel 3.

[0083] The bottom outer side of the turntable 22 is provided with an annular groove 28, and the top wall of the annular groove 28 is provided with two sets of arc grooves 29 symmetrically.

[0084] Two sets of top balls 26 are symmetrically slidably connected inside the annular groove 28, with the upper ends of the top balls 26 closely attached to the top wall of the annular groove 28;

[0085] The vertical rod 27 at the bottom of the top ball 26 extends through the countersunk hole 203 on the middle frame 2 and is fixedly connected to the clamping plate 23. A return spring 25 sleeved on the vertical rod 27 is also provided in the countersunk hole 203.

[0086] The steel top plate 5, web plate 6, flange 11 and concrete 7 together constitute a PEC steel-concrete specimen for pull-out testing.

[0087] The method for preparing PEC-type steel-concrete composite specimens includes the following steps:

[0088] (a) When pouring concrete on both sides of the web plate 6, the operation is carried out in two stages, and the other side is poured after one side is completed;

[0089] (b) Its single-sided casting process is as follows: the first tensile reinforcement 9, the second tensile reinforcement 10 and the upper stirrup 8 form a tensile reinforcement skeleton and keep it horizontal, and fix it in the concrete casting area, wherein the bottom of the first tensile reinforcement 9 and the second tensile reinforcement 10 extends beyond the outer surface of the concrete cast inside the H-beam assembly 16.

[0090] (c) A steel top plate 5 is installed 50 mm away from the top of the web 6 to form a reserved area for installing the upper part of the clamp;

[0091] (d) After completing steps (b) and (c) above, pour concrete between the flanges 11 of the H-beam steel assembly 16, and pour concrete on the other side after curing is completed;

[0092] (e) Use the tension distribution plate 12 to connect the bottom protruding parts of the first tension steel bar 9 and the second tension steel bar 10 to complete the fabrication of the PEC steel-concrete specimen.

[0093] A 50mm gap is left between the top of the PEC steel-concrete specimen and the bottom of the steel top plate 5.

[0094] Displacement gauges 14 are symmetrically installed on the loading end and the free end of the PEC steel-concrete specimen.

[0095] When conducting a pull-out test, the PEC steel-concrete specimen, after being combined with the clamp assembly, is placed into the pull-out testing machine. The top tension bolt 1 and the bottom tension bolt 13 are connected to the upper and lower clamps of the pull-out testing machine, respectively. The amount of interface slippage of the PEC steel-concrete specimen can be obtained by the displacement gauges 14 set at the loading end and the free end of the PEC steel-concrete specimen.

[0096] The preparation steps for the first tensile reinforcement 9 are as follows:

[0097] (1) Cut the first tensile steel bar 9 into two symmetrical halves to form a strip groove 18. Then, make strip grooves on the opposite sides of the cut first tensile steel bar 9 (i.e., the opposite sidewalls of the strip groove 18).

[0098] (2) Metal strain gauges 15 are evenly pasted in the two strip grooves in step (1). The metal strain gauges 15 in the two strip grooves are staggered. Then, the two strip grooves are filled with epoxy resin. After the epoxy resin dries, the cut first tensile steel bar 9 is assembled into a whole and spot-welded along the cut end of the first tensile steel bar 9 near the top plate 5 of the steel section. The two leads of each metal strain gauge 15 are led out from the end of the first tensile steel bar 9 near the top plate 5 of the steel section and are numbered accordingly.

[0099] The left-side steel section 4 and the right-side steel section 3 can slide closer to each other until they reach the required size for anchoring the PEC steel-concrete specimen. The top plate 5 of the steel section is respectively secured to the inner walls of the left-side steel section 4 and the right-side steel section 3. The rack 19 drives the gear 21 to rotate clockwise, and the turntable 22 at the bottom of the gear 21 also rotates clockwise until the top ball 26 is removed from the arc-shaped groove 29 (i.e., from...). Figure 14 Transformation to Figure 17 and Figure 18 (as shown in the diagram), causing the top ball 26, vertical rod 27 and clamping plate 23 to move downwards, with clamping plate 23 clamping onto the top of the steel top plate 5.

[0100] The present invention also provides a test method for a PEC steel-concrete bond-slip performance testing device, specifically including the following steps:

[0101] S1. Secure the bottom of the left-side steel section 4 and the right-side steel section 3 to the top of the H-beam assembly 16, and ensure that the bottom of the synchronous clamping assembly is centered on the top of the H-beam assembly 16.

[0102] S2. Push the left-side steel section 4 and the right-side steel section 3 against each other until the distance between the left-side steel section 4 and the right-side steel section 3 is close, so that the synchronous clamping assembly, the left-side steel section 4 and the right-side steel section 3 are synchronously clamped and fixed to the top of the H-section steel assembly 16.

[0103] S3. Connect the top tension bolt 1 and the bottom tension bolt 13 to the upper and lower clamps of the pull-out tester, respectively. That is, obtain the slippage of the concrete 7 interface through the displacement gauge 14, and measure the concrete strain at the bond interface between the H-beam steel assembly 16 and the concrete by the difference in strain values ​​of the metal strain gauge 15.

[0104] If the tension steel reinforcement assembly and concrete 7 are identified as working together, then the measured value of the metal strain gauge 15 in the first tension steel reinforcement 9 is the concrete strain value at the interface between the H-beam steel assembly 16 and the concrete. The local bond stress at the interface between the H-beam steel assembly 16 and the concrete and the relative slip value between the H-beam steel assembly 16 and the concrete at the corresponding measuring point can be obtained.

[0105] The PEC steel-concrete composite specimen consists of an H-beam steel assembly (web 6, flange 11, steel top plate 5) and concrete 7, with internally embedded tensile reinforcement assemblies (first tensile reinforcement 9, second tensile reinforcement 10, upper stirrup 8, lower stirrup 17).

[0106] During testing:

[0107] The upper clamp (left steel section 4, right steel section 3) is fixed to the top plate 5 of the H-beam assembly by a synchronous clamping assembly. The top tension bolt 1 is connected to the clamp on the tensile testing machine as the force-bearing end of the H-beam.

[0108] In the lower part of the clamp, the bottom of the tensioned steel reinforcement assembly extends out of the concrete 7 and is connected to the bottom tension bolt 13 through the tension distribution plate 12. The bottom tension bolt 13 is connected to the lower clamp of the pull-out test machine and serves as the force-bearing end of the concrete.

[0109] Pull-out test and force transmission:

[0110] When the pull-out testing machine applies tension, the tension is transmitted to the H-beam assembly through the top tension bolt 1, and to the tension reinforcement assembly through the bottom tension bolt 13 (which in turn drives the concrete 7). Since the interfacial bond between the tension reinforcement assembly and the concrete is much greater than the interfacial bond between the H-beam assembly 16 and the concrete, the tension will preferentially cause relative slippage between the H-beam assembly 16 and the concrete (rather than between the reinforcement and the concrete), simulating the interfacial behavior of PEC steel-concrete composite under actual stress.

[0111] During the tensile testing process, the H-beam steel assembly 16 causes the concrete 7 in contact with it to deform upwards. At this time, the tensile steel reinforcement assembly has not yet caused the concrete 7 in contact with it to deform. This causes the top of the concrete 7 to move upwards, thereby increasing the distance between the displacement gauge 14 at the upper end and the displacement gauge 14 at the lower end of the concrete 7. The increased distance is the interface slip of the PEC steel-concrete specimen. This allows us to "obtain the interface slip of the PEC steel-concrete specimen by means of the displacement gauges 14 set at the loading end and the free end of the PEC steel-concrete specimen."

[0112] Parameter monitoring and data calculation:

[0113] Slip measurement: Displacement gauges 14 at the upper and lower ends of concrete 7 record the relative displacement between H-beam assembly 16 and concrete 7 in real time, i.e., interface slip.

[0114] Bond stress calculation: Metal strain gauges 15 with alternating vertical spacing are pasted in the strip groove 18 of the first tensile steel bar 9. By measuring the strain difference of the steel bar, the local bond stress at the interface between the H-beam steel component 16 and the concrete is calculated by combining the material mechanics formula (based on the principle that "when steel bars and concrete work together, the strain of the steel bars can reflect the strain of the concrete").

[0115] Finally, by analyzing the relationship between slip and bond stress, a complete bond-slip curve is obtained, enabling a quantitative evaluation of the interface performance.

[0116] Synergistic advantages of synchronous clamping components:

[0117] Synchronization of gear-rack transmission: The racks 19 on the inner walls of the left steel section 4 and the right steel section 3 mesh with the gears 21 in the middle frame 2. When the top tension bolt 1 is rotated, the gears 21 drive the racks 19 on both sides to move synchronously, so that the left steel section 4 and the right steel section 3 symmetrically clamp the top plate 5 of the steel section, avoiding the H-section steel assembly 16 from being subjected to uneven load (traditional asynchronous clamps are prone to causing the H-section steel to tilt, increasing the error by more than 20%).

[0118] Dual protection of positioning and pre-tightening: The turntable 22 at the lower end of the gear 21 is inserted into the positioning hole 51 of the top plate 5 of the steel section through the positioning pin 24 to ensure that the clamp is aligned with the center of the H-beam assembly 16; at the same time, the top ball 26 at the bottom of the turntable 22 presses against the clamping plate 23 under the action of the return spring 25 to achieve pre-clamping and avoid slippage in the initial loading stage.

[0119] Layout advantages of tension-reinforced steel components:

[0120] Symmetrical arrangement of force balance: The tensile reinforcement components are symmetrically distributed along the web 6, and the concrete cover thickness of the first tensile reinforcement 9 and the second tensile reinforcement 10 is greater than their diameter, ensuring that the tensile force is evenly transmitted to the concrete 7, avoiding premature cracking of the concrete due to local stress concentration, and ensuring that slippage only occurs at the interface between the H-beam and the concrete.

[0121] The restraining effect of the stirrups: The upper stirrup 8 and the lower stirrup 17 enhance the bond between the tensile steel bars and the concrete (by limiting the lateral deformation of the concrete), ensuring that "the steel bar-concrete interface does not fail before the H-beam-concrete interface", which is in line with the force transmission logic of the test design.

[0122] The load distribution advantages of a tension distribution plate:

[0123] The tension distribution plate 12 is the same size as the concrete cross-section and is connected to the bottom protruding ends of the first tension reinforcement 9 and the second tension reinforcement 10. It evenly distributes the concentrated tension of the bottom tension bolt 13 to multiple tension reinforcements and then to the concrete 7, avoiding local compression failure of the concrete and ensuring the validity of the test.

[0124] Measurement advantages of metal strain gauge 15:

[0125] The metal strain gauges 15 inside the strip slot 18 are staggered vertically, which can simultaneously measure the strain at different positions of the tensile steel bar. By calculating the difference, interference factors such as temperature and overall deformation are eliminated, thus improving the accuracy of strain measurement.

[0126] Advantages of specimen preparation:

[0127] The concrete was poured in two stages (first one side and then the other), and a 50mm gap was left at the bottom of the top steel plate 5. This ensured the tight bond between the H-beam steel component 16 and the concrete 7, and also provided space for the installation of the upper clamps, thus solving the problem of "poor compatibility between the specimen and the clamps".

[0128] The cutting and spot welding process of the first tensile reinforcement 9 ensures that the metal strain gauge 15 in the strip groove 18 is not damaged, while ensuring that the overall stress performance of the reinforcement is not affected.

[0129] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A device for testing the bond-slip properties of PEC steel-concrete composite, comprising a clamp assembly, characterized in that: The clamp assembly includes an upper clamp and a lower clamp; The upper clamping part includes left-side and right-side steel sections stacked one on top of the other; The lower clamp includes a tension steel reinforcement assembly integrally formed with concrete. The bottom of the tension steel reinforcement assembly extends from the bottom of the concrete and is connected to a tension distribution plate. A bottom tension bolt is provided in the middle of the tension distribution plate. Metal strain gauges are uniformly pasted on the inner walls of the strip-shaped slots opened on the tensile steel reinforcement assembly. An H-beam steel assembly is installed in the middle of the concrete, and displacement gauges are installed at both the top and bottom of the concrete. The top of the H-beam steel assembly extends out of the concrete. The synchronous clamping assembly between the left and right profiles is used to simultaneously clamp and fix the top of the H-beam assembly with the left and right profiles. The top tension bolt of the synchronous clamping assembly extends out of the left and right profiles. The H-beam assembly includes a web in the middle of the concrete, flanges on both sides of the web, and a steel top plate at the top of the web and flanges. The web, flanges, and top steel plate are integrally formed. The inner wall of the flange is attached to the outer wall of the concrete; The synchronous clamping assembly includes racks installed on the inner walls of the left and right steel sections, an intermediate frame fitted on the two sets of racks, gears installed inside the intermediate frame, and a clamping plate connected to the bottom of the intermediate frame. The gear meshes between two sets of racks; The gear has a turntable at the lower center, and a positioning post at the lower center of the turntable. The bottom of the positioning post extends through the first reserved hole at the bottom of the intermediate frame and the second reserved hole on the clamping plate. The upper center of the top plate of the steel profile has a positioning hole for inserting the positioning post.

2. The device for testing the bond-slip properties of PEC steel-concrete composite as described in claim 1, characterized in that: The tension reinforcement assembly includes a tension reinforcement skeleton that is connected to the tension distribution plate and is arranged symmetrically on the left and right sides. The tensile reinforcement cage includes two sets of first tensile reinforcement bars on the inner side and two sets of second tensile reinforcement bars on the outer side, as well as several sets of upper stirrups set between the two sets of first tensile reinforcement bars on the inner side and the two sets of second tensile reinforcement bars on the outer side. Several sets of bottom stirrups are provided between the bottom of the symmetrical tensile steel reinforcement cage.

3. The device for testing the bond-slip properties of PEC steel-concrete composite as described in claim 2, characterized in that: The strip groove is located at the top center of the first tensile reinforcement, and the metal strain gauges in the same strip groove are staggered vertically.

4. The device for testing the bond-slip properties of PEC steel-concrete composite as described in claim 1, characterized in that: The top tension bolt is centrally rotatably connected between the gear and the turntable, and the upper end of the top tension bolt extends through the third reserved hole at the top of the middle frame and the limiting groove at the top of the left and right steel sections.

5. The device for testing the bond-slip properties of PEC steel-concrete composite as described in claim 1, characterized in that: The turntable has an annular groove on the outer side of its bottom, and two sets of arc grooves are symmetrically arranged on the top wall of the annular groove. Two sets of top balls are symmetrically slidably connected inside the annular groove, with the upper ends of the top balls closely attached to the top wall of the annular groove; The vertical rod at the bottom of the top ball extends through the countersunk hole on the middle frame and is fixedly connected to the clamping plate. A return spring is also provided in the countersunk hole and sleeved on the vertical rod.

6. A test method for the bond-slip performance testing device for PEC steel-concrete composite structures based on any one of claims 1-5, characterized in that: Specifically, the following steps are included: S1. Secure the bottom of the left and right profiles to the top of the H-beam assembly, and ensure that the bottom of the synchronous clamping assembly is centered on the top of the H-beam assembly; S2. Push the left and right steel sections against each other until the distance between the left and right steel sections is close, so that the synchronous clamping assembly, the left and right steel sections are synchronously clamped and fixed to the top of the H-beam assembly. S3. Connect the top tension bolt and the bottom tension bolt to the upper and lower clamps of the pull-out testing machine respectively. That is, obtain the amount of slippage at the concrete interface through the displacement gauge, and measure the concrete strain at the bond interface between the H-beam steel assembly and the concrete by the difference in strain values ​​of the metal strain gauge.

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