Cyclic shear test device for new and old concrete combined test block and test method of cyclic shear test device

Abstract

The invention relates to the technical field of concrete mechanical property testing, and particularly discloses a cyclic shear test device and method for a new and old concrete combined test block. The device comprises a base used for placing and supporting a combined test block. And the shear loading assembly comprises two loading mechanisms. The two loading mechanisms are respectively connected with the new concrete test block and the old concrete test block and are used for respectively and simultaneously applying alternating acting force parallel to the joint surface to the new concrete test block and the old concrete test block. And the normal loading assembly is used for applying normal pressure perpendicular to the combination surface to the combined test block. And the antifriction unit is arranged between the normal loading assembly and the combined test block and is used for reducing friction interference between the normal loading assembly and the combined test block. By means of the arrangement, the device can simulate the complex working condition of a shield tunnel double-layer lining scene, friction interference caused by normal pressure is reduced, and accurate testing of the anti-seismic performance of the joint surface is achieved.

Description

Technical Field

[0001] This invention relates to the field of concrete mechanical property testing technology, specifically to a cyclic shear test device and test method for a composite specimen of new and old concrete. Background Technology

[0002] The combination of old and new concrete structures is widely used in projects such as bridge reinforcement, building renovation and expansion, and double-layer lining of shield tunnels. Among these, the shear performance of the interface between the two layers of shield tunnel lining directly determines the seismic safety and long-term stability of the tunnel structure. During the operation of shield tunnels, the interface of the double-layer lining needs to withstand the combined effects of "dynamic contact pressure after the initial support of the tunnel segments and seismic cyclic shear load". The secondary lining is usually constructed after the tunnel segments have borne nearly 100% of the ground load. The interface pressure shows a local dynamic increase characteristic with the deformation of the tunnel segments. The cyclic shear under seismic loading can easily cause delamination failure of the interface. Therefore, accurate cyclic shear testing to simulate this combined working condition is crucial.

[0003] Existing technologies generally involve casting new concrete test blocks onto old concrete test blocks and anchoring them with anchor bolts, forming a bonding surface between the new and old concrete test blocks. These combined test blocks are then used to simulate the double-layer lining of shield tunnels. Taking patent CN202111493816.9, "A Shear Test Device for Concrete Anchor Bolts," as an example, this device is mainly used for shear tests on concrete anchor bolts. In terms of loading methods, it can only achieve simple shear force loading and cannot simulate the complex normal dynamic interface pressure changes in shield tunnels. Furthermore, it does not consider the effects of seismic reciprocating loads. These limitations in simulation result in low consistency between the test data and actual engineering conditions, failing to provide a reliable basis for the design and research of double-layer linings in shield tunnels.

[0004] Existing technologies have significant shortcomings in "double-layer lining scenario adaptation" and "composite working condition restoration", making it difficult to support accurate testing of the seismic performance of double-layer lining in shield tunnels. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a cyclic shear test device for composite new and old concrete blocks. This device can simulate the complex working conditions of a shield tunnel with double-layer lining, cyclically shearing the interface between the new and old concrete, and reducing frictional interference caused by normal pressure, thereby achieving accurate testing of the seismic performance of the interface.

[0006] To achieve the above objectives, the present invention provides a cyclic shear test apparatus for a composite specimen of old and new concrete, comprising: A base for placing and supporting the combined test block; The shear loading assembly includes two loading mechanisms; the two loading mechanisms are respectively connected to a new concrete test block and an old concrete test block, and are used to apply alternating forces parallel to the bonding surface of the combined test block to the new concrete test block and the old concrete test block, respectively; A normal loading component is used to apply a normal pressure perpendicular to the bonding surface to the combined test block; A friction reduction unit is disposed between the normal loading component and the combined test block to reduce frictional interference between the normal loading component and the combined test block.

[0007] Furthermore, the device also includes a limiting component for limiting the displacement of the combined test block in the direction perpendicular to the alternating force; The limiting component includes two opposing limiting plates, which are tunably connected to the base; the two limiting plates and the base together form an adjustable-width test channel; the test channel is used to accommodate the combined test block and restrict the displacement of the combined test block in the direction perpendicular to the alternating force. The limiting assembly also includes a guide member, which is disposed on the side of the limiting plate near the test channel and is fixedly connected to the limiting plate.

[0008] The base is provided with at least two parallel sliding grooves that extend in a direction perpendicular to the alternating force, and the limiting plate is adjustablely connected to the sliding grooves by bolts.

[0009] Furthermore, the friction reduction unit includes two guide plates arranged opposite to and parallel to the mating surface, and a plurality of rolling elements disposed between the two guide plates; The rolling element is a roller, and several of the rolling elements are spaced apart along the direction of the alternating force. Furthermore, the normal loading component is provided with a first pressure sensor for detecting the normal pressure exerted on the combined test block; The shear loading assembly is equipped with a second pressure sensor and a displacement sensor, which are used to detect the alternating force on the combined test block and the shear displacement of the joint surface, respectively.

[0010] Furthermore, the two loading mechanisms are a second actuator and a reaction seat, respectively; The loading end of the second actuator is connected to the new concrete test block, and the fixing end of the second actuator is fixedly connected to the external reaction carrier; one end of the reaction seat is connected to the old concrete test block, and the other end is fixedly connected to the external reaction carrier. The device further includes an extension component for adapting to the combined test blocks of different lengths; the extension component is disposed between the second actuator and the new concrete test block; one end of the extension component is fixedly connected to the loading end of the second actuator, and the other end of the extension component is fixedly connected to the new concrete test block.

[0011] This invention also provides a method for cyclic shear testing of composite specimens of old and new concrete, comprising the following steps: S1. Prepare the combined test block; S2. Apply a normal pressure perpendicular to the joint surface of the combined test block to the combined test block; S3. Simultaneously apply alternating forces parallel to the bonding surface to the new concrete test block and the old concrete test block, so that the bonding surface is subjected to cyclic shear load. S4. During step S3, the values ​​of the alternating force and the dynamic shear displacement of the joint surface are collected in real time. S5. Stop applying the normal pressure and the alternating force; S6. Collect the residual deformation of the bonding surface, including at least one of the following: residual shear displacement, maximum crack width, and peeling area; S7. Based on the collected values ​​of the alternating forces and the shear displacement, calculate the shear stiffness of the joint surface; and characterize the seismic performance of the joint surface based on the shear stiffness and the residual deformation.

[0012] Furthermore, the method also includes: S8. Prepare multiple sets of the combined test blocks; S9. Perform steps S2 to S7 on each group of combined test blocks, wherein the number of cycles in step S3 performed on each group of combined test blocks is different; S10. Compare the seismic performance of different combined test blocks to obtain the trend of the seismic performance of the joint surface with the number of cycles.

[0013] Further, step S1 includes: S1.1 Prepare old concrete test blocks and cure them for no less than 28 days; S1.2. Pre-set anchor holes on the joint surface; inject anchoring adhesive into the anchor holes, insert anchor bars, and perform curing for no less than 2 days; S1.3. A new concrete test block is poured at the end of the old concrete test block where the anchor bar is not inserted, and it is bonded to the old concrete test block to form a bonding surface; and it is cured for no less than 28 days.

[0014] Further, step S2 includes: the normal pressure is gradually increased to a preset normal pressure value at a preset loading rate and kept constant.

[0015] Further, step S5 includes: first stopping the application of the alternating force to the combined test block; and after a first preset time, gradually reducing the normal pressure to zero at a preset unloading rate.

[0016] Applying one of the above-mentioned technical solutions of the present invention has the following effects: The base provides stable support. Two loading mechanisms simultaneously apply equal and time-varying, opposite forces to the composite test block, simulating the cyclic shear load on the joint surface during an earthquake. Simultaneously, the normal loading component applies pressure perpendicular to the joint surface to replicate the actual pressure state experienced by the composite test block in actual engineering. The friction reduction unit reduces frictional interference between the normal loading component and the composite test block, ensuring accurate transmission of normal pressure to the joint surface while avoiding additional friction affecting the test results. Through the above setup, the device can simulate the complex working conditions of a double-layer lining in a shield tunnel, cyclically shearing the interface between new and old concrete, and reducing frictional interference from normal pressure, achieving accurate testing of the seismic performance of the joint surface and improving the reliability and repeatability of the test.

[0017] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0018] Figure 1 This is an overall schematic diagram of the device in this invention; Figure 2 This is a schematic diagram of the combined test block in this invention; Figure 3 This is a schematic diagram of the extended component in this invention; Figure 4 This is a schematic diagram of the clamping component in this invention; Figure 5 This is a schematic diagram of the device in this invention; Figure 6 This is a schematic diagram of the limiting component in this invention; Figure 7 This is a schematic diagram of the base in this invention; Figure 8 This is a schematic diagram of the friction reduction unit in this invention; Figure 9 This is a flowchart of the experimental method in this invention; Figure 10 This is another flowchart of the experimental method in this invention; Figure 11 This is a flowchart of step S1 in this invention.

[0019] Explanation of reference numerals in the attached figures 1-First actuator; 2-Second actuator; 3-Reaction seat; 4-New concrete test block; 5-Old concrete test block; 6-Anchor bar; 7-Clamping assembly; 71-Force-bearing component; 72-Clamping component; 8-Limiting plate; 9-Guide component; 10-Friction reduction unit; 101-Upper guide plate; 102-Lower guide plate; 103-Rolling component; 11-Base; 12-Slide groove; 13-Leveling component; 14-Extension assembly; 141-Extension rod; 142-Positioning flange; 15-Positioning pin. Detailed Implementation

[0020] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0021] In this invention, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the orientation in the assembled and used state. "Inner" and "outer" refer to the inner and outer sides relative to the outline of each component itself.

[0022] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of the invention described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0023] like Figure 1 and Figure 2As shown, this invention provides a device for cyclic shear testing of new and old concrete. The device is adapted to use a composite specimen, comprising a new concrete specimen 4 and an old concrete specimen 5. The new concrete specimen 4 is cast onto the old concrete specimen 5, forming a bonding surface between them. The new concrete specimen 4 and the old concrete specimen 5 are also connected by anchor bars 6. The device includes: a base 11, a shear loading assembly, a normal loading assembly, and a friction reduction unit 10. The base 11 is used to place and support the composite specimen. The shear loading assembly includes two loading mechanisms. The two loading mechanisms are respectively connected to the new concrete specimen 4 and the old concrete specimen 5, and are used to simultaneously apply alternating forces parallel to the bonding surface to the new concrete specimen 4 and the old concrete specimen 5. The normal loading assembly is used to apply a normal pressure perpendicular to the bonding surface to the composite specimen. The friction reduction unit 10 is disposed between the normal loading assembly and the composite specimen, and is used to reduce frictional interference between the normal loading assembly and the composite specimen. It should be noted that the projection lines of the lines of action of the two alternating forces on the joint surface coincide with each other, and the projection point of the line of action of the normal pressure on the joint surface falls on the projection line.

[0024] In the above scheme, the base 11 provides stable support. Two loading mechanisms simultaneously apply equal and time-varying, opposite forces to the composite test block to simulate the cyclic shear load on the joint surface during an earthquake. Simultaneously, the normal loading component applies pressure perpendicular to the joint surface to replicate the actual pressure state experienced by the composite test block in real engineering. The friction reduction unit 10 reduces frictional interference between the normal loading component and the composite test block, ensuring accurate transmission of normal pressure to the joint surface while preventing additional friction from affecting the test results.

[0025] With the above setup, the device can simulate the complex working conditions of a shield tunnel with double-layer lining, perform cyclic shearing on the interface between the new and old concrete, reduce frictional interference caused by normal pressure, achieve accurate testing of the seismic performance of the interface, and improve the reliability and repeatability of the test.

[0026] Specifically, the normal loading component includes a first actuator 1. The first actuator 1 is positioned above the combined test block. The loading end of the first actuator 1 is connected to the combined test block via a friction-reducing unit 10, and the fixed end of the first actuator 1 is fixedly connected to an external reaction carrier. A base 11 is mounted on the external reaction carrier. The normal pressure applied to the combined test block by the first actuator 1 is counteracted by the external reaction carrier through the base 11, thus forming a complete closed-loop force system. The bearing capacity of the base 11 on the combined test block and the normal pressure applied to the combined test block by the first actuator 1 constitute a pair of balanced forces (ignoring the weight of the combined test block).

[0027] The two loading mechanisms are a second actuator 2 and a reaction seat 3. The loading end of the second actuator 2 is connected to the new concrete specimen 4, and the fixed end of the second actuator 2 is fixedly connected to the external reaction carrier. One end of the reaction seat 3 is connected to the old concrete specimen, and the other end is fixedly connected to the external reaction carrier. The external reaction carrier is used to withstand high-intensity loads from all directions and provide corresponding reaction forces. The alternating force from the second actuator 2 and the reaction force from the reaction seat 3 on the composite specimen together constitute a pair of shear forces, causing the bonding surface to be subjected to shear action along the bonding surface direction.

[0028] In this embodiment, the first actuator 1 is configured as a hydraulic loading cylinder to apply a constant normal pressure. The second actuator 2 is configured as an electro-hydraulic servo loading cylinder to precisely control the magnitude of the alternating force and apply alternating cycles. The external reaction carrier is a reaction system composed of a strong base, a reaction wall, and ground anchors to withstand high-intensity loads from all directions.

[0029] In one possible implementation, a leveling component 13 is also provided at the lower part of the base 11. The base 11 is leveled by adjusting the leveling component 13.

[0030] like Figure 1 and Figure 3 As shown, in one possible implementation, the device further includes an extension component 14 to accommodate composite test blocks of different lengths. The extension component 14 is positioned between the second actuator 2 and the new concrete test block 4, with one end fixedly connected to the loading end of the second actuator 2 and the other end fixedly connected to the new concrete test block 4. In this embodiment, the extension component 14 includes multiple extension rods 141 of uniform length, each extension rod 141 having positioning flanges 142 at both ends. The extension rods 141 and the positioning flanges 142 are integrally formed. The positioning flanges 142 have positioning holes and positioning pins 15 that match the positioning holes, used to position and center the extension component 14, preventing force axis deviation. Multiple extension rods 141 are aligned through the positioning holes and positioning pins 15 and then fixedly connected by bolts. By selecting different numbers of extension rods 141 and connecting them sequentially, it is possible to adapt to composite test blocks of different lengths.

[0031] like Figure 1 and Figure 4As shown, in one possible implementation, the device further includes a clamping assembly 7 for positioning and applying force to the composite test block. The clamping assembly 7 includes a clamping member 72 and a force-receiving member 71. The clamping member 72 is fixedly connected to the force-receiving member 71. The clamping member 72 and the force-receiving member 71 cooperate to form a receiving space. The receiving space is adapted to the size of the composite test block and is used to accommodate and fix the new concrete test block 4 or the old concrete test block 5. The force-receiving member 71 is connected to a shear loading assembly to withstand alternating forces and transmit them to the composite test block. The force-receiving member 71 is also provided with at least two positioning holes for positioning the composite test block. Through the above configuration, the composite test block can be fixed and accurately positioned, facilitating the test. Specifically, the clamping member 72 and the force-receiving member 71 are fastened together by bolts. The clamping member 72 has a hollow section for observing the condition of the composite test block during the test. Furthermore, the hollow section reduces the overall weight of the device, facilitating transportation.

[0032] like Figure 1 as well as Figure 5-7 As shown, in one possible implementation, to prevent lateral slippage of the test block during the loading experiment, the device further includes a limiting component to restrict the displacement of the combined test block in the direction perpendicular to the alternating force. The limiting component includes two opposing limiting plates 8, which are adjustablely connected to the base 11. The two limiting plates 8 and the base 11 together form an adjustable-width test channel. The test channel is used to accommodate the combined test block and restrict its displacement in the direction perpendicular to the alternating force. The limiting component also includes a guide 9, which is disposed on the side of the limiting plate 8 near the test channel and fixedly connected to the limiting plate 8. The base 11 has at least two parallel grooves 12 extending in the direction perpendicular to the alternating force, and the limiting plates 8 are adjustablely connected to the grooves 12 by bolts.

[0033] In the above scheme, the limiting component is adjustablely connected to the base 11 via two opposing limiting plates 8, forming an adjustable-width test channel. This channel accommodates the combined test block and restricts its displacement perpendicular to the direction of alternating force, ensuring that the shear load is accurately applied to the mating surface. The guide 9 is fixed to the side of the limiting plate 8 near the test channel to guide the combined test block, reducing off-center loading or torsional interference, thereby ensuring that the shear load is accurately transferred to the mating surface. The limiting component is adjustablely connected to the slide 12 via bolts, allowing the position of the limiting plate 8 to be freely adjusted according to the width of the test block to accommodate combined test blocks of different sizes. Through the above settings, the lateral disturbance of the combined test block under cyclic shear loading can be significantly reduced, significantly improving the control accuracy and result consistency during the test process; the slide 12 cooperates with the limiting plate 8 to form an adjustable-width test channel, adapting to combined test blocks of different specifications, and possessing good versatility and reusability.

[0034] like Figure 8As shown, in one possible implementation, the friction reduction unit 10 includes two guide plates arranged opposite to and parallel to the mating surface, and at least two rolling elements 103 disposed between the two guide plates.

[0035] The rolling element 103 is a roller, which can roll along the direction of the alternating force, and several rolling elements 103 are spaced apart along the direction of the alternating force. The two force guide plates are the upper force guide plate 101 and the lower force guide plate 102.

[0036] In the above scheme, the friction reduction unit 10 is arranged parallel to the mating surface via guide plates to ensure that the normal pressure is uniformly transmitted to the combined test block. Simultaneously, rolling elements 103 are spaced apart between the guide plates, allowing the guide plates to roll relative to each other in the direction of alternating force, reducing sliding friction interference between the normal loading components and the combined test block. Through this arrangement, the friction reduction unit 10 can ensure accurate application of normal pressure while minimizing friction interference to avoid affecting the transmission of shear load, thus improving the accuracy and repeatability of the test.

[0037] In this embodiment, the rolling element 103 is a cylindrical steel bar, and four of them are provided. It is understood that the rolling element 103 can also be other shapes such as balls. Preferably, the guide plate also has positioning grooves for accommodating the rolling elements 103. The positioning grooves are arranged along the direction of the alternating force, and their outline dimensions are slightly larger than the outer outline of the rolling element 103. This is used to constrain the position of the rolling element 103 without affecting its rolling performance, preventing lateral displacement or accidental detachment of the rolling element 103 during loading, further improving the structural stability and reliability of the friction-reducing unit 10.

[0038] In one possible implementation, the normal loading assembly is equipped with a first pressure sensor for detecting the normal pressure acting on the composite specimen. The shear loading assembly is equipped with a second pressure sensor and a displacement sensor for detecting the alternating force acting on the composite specimen and the shear displacement of the mating surface, respectively.

[0039] like Figure 9 As shown, the present invention also provides a method for cyclic shear testing of composite specimens of old and new concrete, comprising the following steps: S1. Prepare the combined test block.

[0040] The composite test block is obtained by casting a new concrete test block 4 onto an old concrete test block 5, with a bonding surface formed between the new concrete test block 4 and the old concrete test block 5. The composite test block is used to simulate the double-layer lining of a shield tunnel in actual engineering. In this embodiment, the old concrete test block 4 has dimensions of 500mm*200mm*150mm, and the new concrete test block 5 also has dimensions of 500mm*200mm*150mm. The area of ​​the bonding surface is 500mm*200mm, or 0.1m².

[0041] S2. Apply a normal pressure perpendicular to the joint surface of the combined test block to the combined test block.

[0042] The normal pressure is used to simulate the static pressure at the normal interface of the double-layer lining. In this embodiment, to simulate the extreme pressure under an 8-degree earthquake, the corresponding normal pressure is taken as 3 MPa, and the normal pressure is calculated to be 300 kN according to the formula F1=P*S. Where F1 is the normal pressure, P is the normal pressure, and S is the interface area.

[0043] S3. Simultaneously apply alternating forces parallel to the bonding surface to the new concrete test block 4 and the old concrete test block 5, so that the bonding surface is subjected to cyclic shear load.

[0044] Alternating forces are used to simulate the seismic cyclic loads on the double-layer lining. The frequency range of the alternating forces is 0.1 to 5 Hz. In this embodiment, the waveform of the alternating forces is a sine wave with a frequency of 1 Hz. To obtain the peak value of the alternating forces, a target shear stress of 4 MPa is taken, and the peak value of the alternating forces is calculated to be 400 kN according to the formula F2 = τ * S. Here, F2 is the peak value of the alternating forces, τ is the target shear stress, and S is the area of ​​the joint surface.

[0045] S4. During step S3, the values ​​of the alternating force and the dynamic shear displacement of the bonding surface are collected in real time. The dynamic shear displacement is the real-time shear displacement of the composite specimen, which changes with the alternating force.

[0046] S5. Stop applying the normal pressure and the alternating force.

[0047] S6. Collect the residual deformation of the bonding surface, including at least one of the following: residual shear displacement, maximum crack width, and peeling area.

[0048] The residual shear displacement is the final shear displacement of the composite specimen after the force is removed, which can be measured by a laser rangefinder to ensure accuracy. The maximum crack width is the maximum width of the crack formed on the joint surface of the composite specimen in the direction perpendicular to the joint surface, which can be measured by a crack width meter. The peeling area is the area peeled off from the joint surface of the composite specimen due to damage.

[0049] S7. Based on the collected values ​​of the alternating forces and the shear displacement, calculate the shear stiffness of the joint surface; and characterize the seismic performance of the joint surface based on the shear stiffness and the residual deformation.

[0050] The formula for calculating shear stiffness is: K = ΔF / Δu. Where K is the shear stiffness, ΔF is the change in alternating force per unit time, and Δu is the change in dynamic shear displacement per unit time.

[0051] The above methods can simulate the complex working conditions of double-layer lining in shield tunnels. By accurately testing the seismic performance of the composite test blocks, the seismic performance of the double-layer lining interface under seismic cyclic loads in actual engineering can be analyzed, providing key experimental data and theoretical support for the seismic design and safety assessment of shield tunnels.

[0052] like Figure 9 and Figure 10 As shown, in one possible implementation, the method further includes: S8. Prepare multiple sets of the combined test blocks.

[0053] Multiple sets of combined test blocks are made with identical specifications and from the same batch to reduce errors.

[0054] S9. Perform steps S2 to S7 on each group of combined test blocks, wherein the number of cycles in step S3 performed on each group of combined test blocks is different.

[0055] The number of cycles refers to the number of cycles in which alternating forces are applied to the combined test block, with one complete cycle of alternating force change considered as a cycle.

[0056] S10. Compare the seismic performance of different combined test blocks to obtain the trend of the seismic performance of the joint surface with the number of cycles.

[0057] In this embodiment, three sets of combined test blocks were prepared, each set comprising several test blocks. The first set of test blocks was subjected to 5 cycles of alternating force, the second set to 25 cycles, and the third set to 50 cycles. The seismic performance of these three sets of test blocks represents the seismic performance of double-layer linings during the initial, middle, and final stages of an earthquake, respectively. By comparing and analyzing the seismic performance of these three sets of test blocks, the degradation law of the seismic performance of the double-layer lining interface under repeated seismic loads can be systematically analyzed.

[0058] like Figure 11 As shown, in one possible implementation, step S1 includes: S1.1 Prepare 5 old concrete test blocks and cure them for no less than 28 days.

[0059] Old concrete specimen 5 was prepared using grade C60.

[0060] S1.2. Pre-set anchor holes on the joint surface; inject anchoring adhesive into the anchor holes, insert anchor bars 6, and perform curing for no less than 2 days.

[0061] In this embodiment, the surface of the old concrete test block 5 needs to be mechanically roughened before pre-drilling the anchoring holes. Two anchoring holes are drilled, and two anchor bars 6 are inserted. High-strength epoxy anchoring adhesive is used.

[0062] S1.3. A new concrete test block 4 is poured at the end of the anchor bar 6 where the old concrete test block 5 is not inserted, and it is bonded to the old concrete test block 5 to form a bonding surface; and it is cured for no less than 28 days.

[0063] New concrete test block 4 was prepared using grade C40.

[0064] In one possible implementation, step S2 includes: gradually increasing the normal pressure at a preset loading rate to a preset normal pressure value, and keeping it constant. In this embodiment, the preset loading rate is 20 kN / s, and the preset normal pressure value is 300 kN.

[0065] In one possible implementation, step S5 includes: first, stopping the application of the alternating force to the combined test block; and after a first preset time, gradually reducing the normal pressure to zero at a preset unloading rate. In this embodiment, the first preset time is 2 minutes, and the preset unloading rate is 5 kN / min. By setting the above parameters, unloading the normal pressure after a first preset time following the cessation of the alternating force can stabilize the residual stress of the combined test block, ensuring the accuracy of subsequent data acquisition; and the slow reduction of the normal pressure at the preset unloading rate can prevent impact damage to the combined test block due to sudden load changes.

[0066] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0067] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0068] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A cyclic shear test device for a composite specimen of old and new concrete, characterized in that, include: Base (11) for placing and supporting the combined test block; The shear loading assembly includes two loading mechanisms; the two loading mechanisms are respectively connected to a new concrete test block (4) and an old concrete test block (5) for applying alternating forces parallel to the bonding surface of the combined test block to the new concrete test block (4) and the old concrete test block (5); A normal loading component is used to apply a normal pressure perpendicular to the bonding surface to the combined test block; The friction reduction unit (10) is disposed between the normal loading component and the combined test block to reduce frictional interference between the normal loading component and the combined test block.

2. The cyclic shear test device for composite new and old concrete blocks according to claim 1, characterized in that, The device also includes a limiting component for limiting the displacement of the combined test block in the direction perpendicular to the alternating force; The limiting component includes two opposing limiting plates (8), which are tunably connected to the base (11); the two limiting plates (8) and the base (11) together form a test channel with adjustable width; the test channel is used to accommodate the combined test block and restrict the displacement of the combined test block in the direction perpendicular to the alternating force. The limiting component also includes a guide (9), which is disposed on the side of the limiting plate (8) near the test channel and is fixedly connected to the limiting plate (8). The base (11) is provided with at least two sliding grooves (12) that extend in a direction perpendicular to the alternating force and are parallel to each other, and the limiting plate (8) is adjustablely connected to the sliding grooves (12) by bolts.

3. The cyclic shear test device for composite new and old concrete blocks according to claim 1, characterized in that, The friction reduction unit (10) includes two guide plates arranged opposite to and parallel to the mating surface, and a plurality of rolling elements (103) disposed between the two guide plates. The rolling element (103) is a roller, and a plurality of the rolling elements (103) are arranged at intervals along the direction of the alternating force.

4. The cyclic shear test device for composite new and old concrete blocks according to claim 1, characterized in that, The normal loading component is equipped with a first pressure sensor for detecting the normal pressure on the combined test block; The shear loading assembly is equipped with a second pressure sensor and a displacement sensor, which are used to detect the alternating force on the combined test block and the shear displacement of the joint surface, respectively.

5. The cyclic shear test device for composite new and old concrete blocks according to claim 1, characterized in that, The two loading mechanisms are the second actuator (2) and the reaction seat (3), respectively. The loading end of the second actuator (2) is connected to the new concrete test block (4), and the fixing end of the second actuator (2) is fixedly connected to the external reaction carrier; one end of the reaction seat (3) is connected to the old concrete test block (5), and the other end is fixedly connected to the external reaction carrier. The device also includes an extension component (14) for adapting to the combined test blocks of different lengths; the extension component (14) is disposed between the second actuator (2) and the new concrete test block (4); one end of the extension component (14) is fixedly connected to the loading end of the second actuator (2), and the other end of the extension component (14) is fixedly connected to the new concrete test block (4).

6. A method for cyclic shear testing of composite specimens of new and old concrete, characterized in that, Includes the following steps: S1. Prepare the combined test block; S2. Apply a normal pressure perpendicular to the joint surface of the combined test block to the combined test block; S3. Simultaneously apply alternating forces parallel to the bonding surface to the new concrete test block (4) and the old concrete test block (5) to subject the bonding surface to cyclic shear load. S4. During step S3, the values ​​of the alternating force and the dynamic shear displacement of the joint surface are collected in real time. S5. Stop applying the normal pressure and the alternating force; S6. Collect the residual deformation of the bonding surface, including at least one of the following: residual shear displacement, maximum crack width, and peeling area; S7. Based on the collected values ​​of the alternating forces and the shear displacement, calculate the shear stiffness of the joint surface; and characterize the seismic performance of the joint surface based on the shear stiffness and the residual deformation.

7. The cyclic shear test method for composite new and old concrete blocks according to claim 6, characterized in that, The method further includes: S8. Prepare multiple sets of the combined test blocks; S9. Perform steps S2 to S7 on each group of combined test blocks, wherein the number of cycles in step S3 performed on each group of combined test blocks is different; S10. Compare the seismic performance of different combined test blocks to obtain the trend of the seismic performance of the joint surface with the number of cycles.

8. The cyclic shear test method for composite new and old concrete blocks according to claim 6, characterized in that, Step S1 includes: S1.1 Prepare old concrete test blocks (5) and cure them for no less than 28 days; S1.

2. Pre-set anchor holes on the joint surface; inject anchoring adhesive into the anchor holes, insert anchor bars (6), and perform curing for no less than 2 days; S1.

3. A new concrete test block (4) is poured at the end of the anchor bar (6) where the old concrete test block (5) is not inserted, and it is bonded to the old concrete test block (5) to form a bonding surface; and it is cured for no less than 28 days.

9. The cyclic shear test method for composite new and old concrete blocks according to claim 6, characterized in that, Step S2 includes: the normal pressure is gradually increased to a preset normal pressure value at a preset loading rate and then kept constant.

10. The cyclic shear test method for composite new and old concrete blocks according to claim 6, characterized in that, Step S5 includes: first stopping the application of the alternating force to the combined test block; and after a first preset time, gradually reducing the normal pressure to zero at a preset unloading rate.

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