Self-adjusting load-bearing device and loading method for concrete durability testing

Abstract

A self-adjusting holding device and loading method for concrete durability testing belongs to a concrete durability testing device and loading method. In order to solve the problem that the stress level of the load during the freeze-thaw cycle test will produce large fluctuations and distort the test results, the device described in the present invention includes a specimen loading mechanism for applying an axial load to the concrete test piece, a load compensation mechanism for realizing the axial movement and locking of the load adjustment member on each slide rod, and a stress detection mechanism for measuring the stress on each slide rod. The method described in the present invention uses a stress detection mechanism to measure the stress on each high-strength screw and convert it into an electrical signal. During the freeze-thaw test, the load compensation mechanism detects the loss of holding pressure stress in real time and compensates it in real time according to the preset load value. When the external environment changes and the load applied by the specimen loading mechanism changes, the applied load is corrected to the predetermined load by the load compensation mechanism to achieve self-compensation of the holding load.

Description

Technical field:

[0001] The invention belongs to a concrete durability test device and a loading method, and particularly relates to a self-adjusting load-bearing device and a loading method for concrete durability testing under freeze-thaw cycles. Background technology:

[0002] As the most common building material, concrete is used in a variety of environments. Buildings in cold northern regions and low-temperature plateau areas are often subject to repeated erosion by freeze-thaw cycles. Currently, most freeze-thaw durability tests for concrete materials involve placing concrete specimens in freeze-thaw cycle test chambers for accelerated testing to test their durability. However, this test method is very different from the actual service conditions of the material. The concrete in most concrete structures is often exposed to the combined effects of multiple factors such as load and environmental corrosion during its service. In order to obtain the durability of the material in a real service environment, it is in line with actual engineering practices to apply a continuous load to the concrete material while conducting a durability test on it. Currently, there are generally two ways that load-bearing devices apply loads: one uses a lever to amplify the weight of a counterweight to achieve the load-bearing effect. For example, Chinese patent "CN215574197U" discloses a "Long-term load test frame with a secondary lever," which uses the weight of the counterweight and a force-transmitting lever to amplify the force and apply it to the concrete test piece to achieve the load-bearing effect. The other uses spring compression and fasteners to apply prestress. For example, Chinese patent "CN107543755B" discloses a "Concrete durability test device and evaluation method under load and freeze-thaw cycle coupling," which uses a load-bearing device composed of springs and nuts to conduct durability tests and uses strain gauges to measure the strain of the concrete to determine the magnitude of the applied load. However, neither of these methods can stably maintain the load stress level during long-term durability tests. Commonly used load-bearing devices mostly use manual loading, which results in large errors in load application and large fluctuations in load levels during the test. They primarily apply axial compressive loads and are unable to accurately apply eccentric loads. Moreover, during the freeze-thaw cycle test, the ambient temperature often changes, which can cause the load-bearing device to deform due to temperature. Along with the degradation of material properties, the load stress level will fluctuate greatly, causing the test results to be distorted. Current technology cannot solve this problem well. Summary of the invention:

[0003] In order to solve the problems mentioned in the above background technology, the purpose of the present invention is to provide a self-adjusting loading device and loading method for concrete durability test under freeze-thaw cycles.

[0004] A stress self-adjusting loading device for concrete durability testing under freeze-thaw cycles, comprising a specimen loading mechanism, a load compensation mechanism, and a stress detection mechanism; the specimen loading mechanism applies an axial load to the concrete specimen, and comprises N sliding rods, three high-strength steel plates, N load adjustment members, an elastic compression assembly, and N locking members; the three high-strength steel plates are arranged side by side in a transverse direction relative to each other, the concrete specimen is axially arranged between and clamped by two adjacent high-strength steel plates, and the elastic compression assembly is arranged between and clamped by another two adjacent high-strength steel plates; the N sliding rods are evenly arranged circumferentially around the concrete specimen and the elastic compression assembly, and are respectively axially slidably connected to the three high-strength steel plates; The N load adjustment parts are located on one side of the high-strength steel plate and are respectively mounted on one end of the N sliding rods, and the load adjustment parts abut against the plate surface of the high-strength steel plate adjacent to it; the N locking parts are located on the other side of the high-strength steel plate and are respectively mounted on the other end of the N sliding rods, and the locking parts are locked on the sliding rod and abut against the plate surface of the high-strength steel plate adjacent to it; the load compensation mechanism includes N driving ends, each driving end corresponds to a load adjustment part, which is used to realize the axial movement and locking of the load adjustment part on the respective sliding rod, and the stress detection mechanism is used to measure the stress on each sliding rod; the linear expansion coefficients of the sliding rod, high-strength steel plate, load adjustment part, elastic compression assembly and locking part are different.

[0005] A method for axial loading of a self-adjusting stress holding device for concrete durability testing under freeze-thaw cycles is disclosed. The method implements axial loading based on the self-adjusting stress holding device for concrete durability testing under freeze-thaw cycles. The specific loading process is as follows:

[0006] Step 1: Install and debug the holding device with the concrete test piece;

[0007] Step 1.1: Place the concrete specimen and several disc springs between three high-strength steel plates, ensuring the coaxiality of the concrete specimen, disc springs, and high-strength steel plates.

[0008] Step 1.2: Insert N high-strength screws into three high-strength steel plates, and screw 2N high-strength nuts onto both ends of the N high-strength screws. Use a torque wrench to pre-tighten the high-strength nuts at both ends of the high-strength screws to an initial torque of 1 N·m.

[0009] Step 1.3: Install a backstop on the high-strength nut serving as a locking member to limit the rotation of the high-strength nut;

[0010] Step 1.4: Install a load compensation mechanism on the high-strength nut serving as a load adjustment member, so that N nut sleeves are respectively sleeved on their corresponding high-strength nuts;

[0011] Step 1.5, stick the strain gauge on the high-strength screw;

[0012] Step 2: The load-carrying device automatically applies the predetermined load to the axis. The specific application process is as follows:

[0013] Step 2.1. Enter the initial torque T1 into the load compensation mechanism. Assume the tightening torque coefficient is K. Calculate the initial preload force F1 on each high-strength screw using the tightening torque calculation formula T = KFd. Here, F represents the preload force on the high-strength screw, F1 is the initial preload force on the high-strength screw, T represents the tightening torque, T1 is the initial tightening torque, and d is the diameter of the high-strength screw.

[0014] Initial strain of each high-strength screw Among them, σ' is the screw stress; G1 is the elastic modulus of the high-strength screw; S1 is the cross-sectional area of the high-strength screw;

[0015] By combining the above formulas, the relationship between the high-strength nut torque and the high-strength screw strain is:

[0016]

[0017] Wherein, γ is the conversion coefficient between the high-strength screw strain ε and the high-strength nut torque T;

[0018]

[0019] Initial stress of concrete specimen S is the cross-sectional area of the test piece;

[0020] Step 2.2: At room temperature of 20°C,

[0021] The conversion relationship between screw strain ε and screw stress is:

[0022] The conversion relationship between screw strain ε and screw preload is:

[0023] The conversion relationship between the stress of the concrete specimen and the screw preload is: σ represents the stress of the concrete specimen;

[0024] The relationship between the screw strain and the concrete specimen stress can be obtained by combining β is the conversion coefficient between the strain ε of a high-strength screw and the stress σ of the concrete specimen during axial load loading. d is the screw diameter, d7 is the test piece diameter;

[0025] Step 2.3: Enter the stress σ to be applied in the load compensation mechanism e, start the axial load loading program in the load compensation mechanism, the system automatically calculates the set values of high-strength screw strain and high-strength nut torque, and the conversion coefficient derived in step 2.2 is used to obtain the set value ε of high-strength screw strain e =βσ e , σ e is the stress setting value of the concrete test piece; according to the conversion coefficient derived in step 2.1, the torque setting value that the high-strength nut torque needs to reach is obtained

[0026] Step 2.4: The signal processor controls the torque motor inside the load compensation mechanism through an electrical signal to simultaneously turn N nut sleeves at a torque of 5 N·m until the torque of the torque motor reaches 5 N·m.

[0027] Step 2.5: At this time, the load compensation mechanism detects the strain value ε of the high-strength screw and converts the current concrete test piece stress σ according to the conversion coefficient in step 2.1. According to the conversion formula in step 2.1, the strain value of the high-strength screw should be ε = γT. The current concrete test piece stress is calculated based on the high-strength screw strain and the conversion coefficient.

[0028] Step 2.6: The signal processor continues to control the torque motor to rotate the N nut sleeves at a torque of 10 N·m until the high-strength nut can no longer be tightened. The load compensation mechanism detects the strain value ε of the high-strength screw and calculates the current concrete specimen stress σ based on the conversion factor in step 2.1.

[0029] Step 2.7: Following the process of steps 2.3 to 2.6, the torque motor loads the concrete specimen step by step with an increment of 5 N·m, gradually increasing the stress of the concrete specimen until the nth loading. After the load is applied, tighten the nut with a torque of 5 N, and the step-by-step loading process is completed. e -5≤5n≤T e , T e is the torque setting value;

[0030] Step 2.8: After the step-by-step loading is completed, the compensation system automatically enters the fine-tuning stage. The signal processor controls the torque motor to set the torque value T e Fine-tune and twist N nuts and sleeves in turn to make N strain values ε of the high-strength screw reach the set value ε=ε e , at this time the concrete specimen stress σ=σ e , σ e Set the stress value for the concrete test piece; when the concrete test piece reaches the predetermined load, the device automatically applies the predetermined load and the function is completed;

[0031] Step 3: Place the loaded concrete specimen and the load-holding device in a freeze-thaw cycle tester, set corresponding freeze-thaw parameters, and conduct a freeze-thaw cycle test in accordance with the corresponding specifications;

[0032] Step 4: The load compensation mechanism realizes self-compensation of the load according to the strain value of the high-strength screw;

[0033] During the test, when the strain value of the four screws rises to ε=ε3, it can be seen from step 2.5 that the torque of the nut at this time is The signal processor controls the torque motor to loosen the nut with a torque of T=T3+1, and fine-tune the nut to make the strain value of the high-strength screw ε=γT e =ε e , at this time the test piece reaches the predetermined load σ=σ e ;

[0034] When the strain value of the four screws drops to ε=ε4, it can be seen from step 2.5 that the torque of the nut is The signal processor controls the torque motor with T=T e Tighten the nut with the torque of , and fine-tune the nut to make the high-strength screw strain value ε=γT e =ε e , at this time the test piece reaches the predetermined load σ=σ e .

[0035] An eccentric loading method for a stress self-adjusting loading device for concrete durability testing under freeze-thaw cycles is disclosed. Axial loading is achieved based on the stress self-adjusting loading device for concrete durability testing under freeze-thaw cycles. The specific loading process is as follows:

[0036] Step 1: Install and debug the holding device with the concrete test piece;

[0037] Step 1.1. Place the concrete specimen and several disc springs between three high-strength steel plates, ensuring the coaxiality of the concrete specimen, the disc springs, and the high-strength steel plates.

[0038] Step 1.2: Insert N high-strength screws into three high-strength steel plates, and screw 2N high-strength nuts onto both ends of the N high-strength screws. Use a torque wrench to pre-tighten the high-strength nuts at both ends of the high-strength screws to an initial torque of 1 N·m.

[0039] Step 1.3: Install a backstop on the high-strength nut serving as a locking member to limit the rotation of the high-strength nut;

[0040] Step 1.4: Install a load compensation mechanism on the high-strength nut serving as a load adjustment member, so that N nut sleeves are respectively sleeved on their corresponding high-strength nuts;

[0041] Step 1.5, stick the strain gauge on the high-strength screw;

[0042] Step 2: The load-carrying device automatically applies an eccentric predetermined load. The specific application process is as follows:

[0043] Step 2.1. Enter the initial torque T in the load compensation mechanism. Assume the tightening torque coefficient is K. Calculate the initial preload force on each high-strength screw using the tightening torque calculation formula T = KFd. Calculate the initial preload force F1 = T1 / Kd on each high-strength screw. Where F represents the preload force on the high-strength screw, F1 is the initial preload force on the high-strength screw, T represents the tightening torque, T1 is the initial tightening torque, and d is the diameter of the high-strength screw.

[0044] Initial strain of each high-strength screw G1 is the elastic modulus of the high-strength screw; S1 is the cross-sectional area of the high-strength screw; σ' is the screw stress;

[0045] By combining the above formulas, the relationship between nut torque and screw strain is:

[0046]

[0047] Wherein, γ is the conversion coefficient between the high-strength screw strain ε and the high-strength nut torque T;

[0048]

[0049] Initial stress of concrete specimen S is the cross-sectional area of the test piece;

[0050] Step 2.2: Start the eccentric load loading program of the load compensation mechanism, set the eccentricity to e0, and the predetermined compressive stress of the concrete specimen to σ e , the system automatically calculates the set value that the screw strain needs to reach, and the bending moment should be M=σ e Se0; by conversion factor d1 should be the screw diameter, d7 should be the test piece diameter, and the set value ε that the average strain of the high-strength screw needs to reach is obtained e =βσ e , σ e is the stress setting value of the concrete specimen; when the strains of any two adjacent high-strength screws among the N high-strength screws are not equal to the strains of the other two screws, the load applied by the loading device is an eccentric load; let any two adjacent high-strength screws be numbered as screw X1, and the other two high-strength screws be numbered as X2;

[0051] Step 2.3: Eccentricity e of the holding device a It is half of the center distance between two adjacent high-strength screws. According to the relationship between screw stress and concrete specimen stress, pressure difference and strain difference Formula combination:

[0052]

[0053] ε e1 +ε e2 =2βσ e

[0054] Simplified to:

[0055]

[0056] The set values of the strain of both screws of screw X1 should be The set value of screw X2 strain should be The setting values of the torque of the two screws of screw X1 should be The setting value of the torque of the two screws of screw X2 should be

[0057] Step 2.4: The signal processor controls the torque motor inside the load compensation mechanism through an electrical signal to simultaneously turn the four nut sleeves at a torque of 5 N·m until the torque of the torque motor reaches 5 N·m.

[0058] Step 2.5: At this time, the load compensation mechanism detects the strain value ε of the high-strength screw and converts the current concrete test piece stress σ according to the conversion coefficient in step 2.1. According to the conversion formula in step 2.1, the strain value of the high-strength screw in this embodiment should be ε = γT. The current concrete test piece stress is calculated based on the screw strain and the conversion coefficient. where ε 11 is the strain corresponding to screw X1, ε 12 is the strain corresponding to screw X2;

[0059] Step 2.6: The signal processor continues to control the torque motor to rotate the four nut sleeves at a torque of 10 N·m until the high-strength nut can no longer be tightened. The load compensation mechanism detects the strain value ε of the high-strength screw and calculates the current concrete specimen stress σ based on the conversion factor β from step 2.2.

[0060] Step 2.7: Following the process of steps 2.3 to 2.6, the torque motor is loaded step by step with an increment of 5 N·m, gradually increasing the stress of the concrete specimen until the nth loading, tightening the nut T with a torque of 5 N·m. e2 -5≤5n≤T e2 At this time, the torque motor corresponding to screw X2 enters the fine-tuning stage, and the torque motor corresponding to screw X1 continues to load step by step; until the mth loading, tighten the nut with a torque of 5m, T e1 -5≤5m≤T e1, at this time, the torque motor corresponding to screw X2 enters the fine-tuning stage;

[0061] Step 2.8: After the step-by-step loading is completed, the compensation system automatically enters the fine-tuning stage. The signal processor controls the torque motor to fine-tune the four nut sleeves in turn with their respective torque setting values, so that the strain value ε of the screw X1 is 11 Both reach the set value ε e1 , the strain value ε of screw X2 12 Both reach the set value ε e2 , at this time the concrete specimen stress σ=σ e , the concrete test piece reaches the predetermined load, and the device automatically applies the predetermined load function; at this time, the strains of screw X1 and screw X2 are different, and the tension provided is also different;

[0062] Step 3: Place the loaded concrete specimen and the load-holding device in a freeze-thaw cycle tester, set corresponding freeze-thaw parameters, and conduct a freeze-thaw cycle test in accordance with the corresponding specifications;

[0063] Step 4: Under eccentric load, the load compensation mechanism realizes self-compensation of the load according to the strain value of the high-strength screw;

[0064] During the test, the strain value of screw X1 increased to ε 21 , the screw X2 strain value rises to ε 22 From step 2.5, we can see that the torque of the nut of screw X1 is Torque of the nut of screw X2 The signal processor controls the torque motor, and the signal processor controls the torque motor, respectively. 21 The torque is used to loosen the nut of screw X1, so that the strain value of screw X1 is ε 11 =ε e1 ;T 22 The torque is used to loosen the nut of screw X2, so that the strain value of screw X2 is ε 12 =ε e2 ;

[0065] At this time, the loading eccentricity of the concrete specimen The overall stress level of the concrete specimen σ=σ e , so as to achieve the self-compensation effect of eccentric load of the load-bearing device under the freeze-thaw test environment.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] 1. The present invention first uses the temperature deformation formula to calculate the linear expansion coefficient of the steel required for each component of the holding device, so that the temperature deformation of the holding device and the concrete during the change of ambient temperature is self-balanced, thereby avoiding the stress change of the holding device due to temperature deformation. Secondly, the stress on each high-strength screw is measured by a stress detection mechanism and converted into an electrical signal, and the electrical signal is transmitted to the load compensation mechanism. During the freeze-thaw test, the load compensation mechanism detects the holding stress loss of the holding device due to the fatigue of the disc spring and the degradation of the performance of the concrete test piece in real time, and performs real-time compensation according to the preset load value. When the external environment changes and the load applied by the specimen loading mechanism changes, the applied load can be quickly corrected to the predetermined load through the load compensation mechanism, realizing self-compensation of the load under extreme test conditions.

[0068] 2. The present invention can simulate the freeze-thaw durability changes of concrete materials under continuous load to the greatest extent, making the results of freeze-thaw tests closer to the actual service environment of concrete materials. Description of the drawings:

[0069] For ease of explanation, the present invention is described in detail with reference to the following specific implementations and accompanying drawings.

[0070] Figure 1 Schematic diagram of the structure of the slider;

[0071] Figure 2 Schematic diagram of the structure of high-strength steel plate;

[0072] Figure 3 Schematic diagram of the structure of the disc spring;

[0073] Figure 4 A schematic diagram of the structure of the elastic compression assembly composed of disc springs;

[0074] Figure 5 A schematic diagram of the structure of the backstop;

[0075] Figure 6 It is a side view of the present invention.

[0076] Figure 7 It is an axonometric view of the present invention.

[0077] In the figure, 1-specimen loading mechanism; 1-1-slide rod; 1-2-high-strength steel plate; 1-2-1-circular groove; 1-2-2-slide hole; 1-3-load adjustment member; 1-4-elastic compression assembly; 1-4-1-disc spring; 1-5-locking member; 2-load compensation mechanism; 2-1-housing; 2-2-sleeve; 3-backstop; 3-1-center connection part; 3-2-hexagonal wrench head; 4-test piece. Specific implementation method:

[0078] To make the objectives, technical solutions, and advantages of the present invention more clearly apparent, the present invention is described below using specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely illustrative and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0079] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, the accompanying drawings only show structures and / or processing steps closely related to the solutions according to the present invention, while other details that are not closely related to the present invention are omitted.

[0080] Specific implementation method 1: Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 and Figure 5 As shown, this specific embodiment adopts the following technical scheme, which includes a specimen loading mechanism 1, a load compensation mechanism 2 and a stress detection mechanism; the specimen loading mechanism 1 applies an axial load to the concrete specimen 4, which includes N slide bars 1-1, three high-strength steel plates 1-2, N load adjustment members 1-3, an elastic compression assembly 1-4 and N locking members 1-5; the three high-strength steel plates 1-2 are arranged side by side relative to each other in the transverse direction, the concrete specimen 4 is axially arranged between two adjacent high-strength steel plates 1-2 and clamped, and the elastic compression assembly 1-4 is arranged between the other two adjacent high-strength steel plates 1-2 and clamped; the N slide bars 1-1 are evenly arranged circumferentially around the concrete specimen 4 and the elastic compression assembly 1-4, and are respectively connected to the three high-strength steel plates 1-2. The high-strength steel plate 1-2 is axially slidably connected; the N load adjustment members 1-3 are located on one side of the high-strength steel plate 1-2 and are respectively sleeved on one end of the N slide bars 1-1, and the load adjustment members 1-3 abut against the plate surface of the high-strength steel plate 1-2 adjacent to it; the N locking members 1-5 are located on the other side of the high-strength steel plate 1-2 and are respectively sleeved on the other end of the N slide bars 1-1, and the locking members 1-5 are locked on the slide bar 1-1 and abut against the plate surface of the high-strength steel plate 1-2 adjacent to it; the load compensation mechanism 2 includes N driving ends, each driving end corresponds to a load adjustment member 1-3, which is used to realize the axial movement and locking of the load adjustment member 1-3 on the respective slide bar 1-1, and the stress detection mechanism is used to measure the stress on each slide bar 1-1.

[0081] In this embodiment, the linear expansion coefficients of the sliding rod 1-1, the high-strength steel plate 1-2, the load adjustment member 1-3, the elastic compression assembly 1-4 and the locking member 1-5 are different.

[0082] In this embodiment, steels with different linear expansion coefficients are selected according to the temperature variation range of the freeze-thaw test environment, thereby reducing the temperature deformation difference between the holding device and the concrete test piece 4 during the temperature variation process and effectively reducing the loss of sustained load.

[0083] In this embodiment, during the freeze-thaw test, the load compensation mechanism 2 automatically calibrates the load level of the concrete test piece 4 under axial compression or eccentric compression, so that the load level of the concrete test piece 4 remains unchanged.

[0084] In this embodiment, the linear expansion coefficient of the steel required for each component of the holding device is first calculated using a temperature-deformation formula. This ensures that the axial temperature deformation of the holding device and concrete is zero during ambient temperature fluctuations, achieving internal self-balancing within the device. This prevents stress changes in the holding device caused by temperature deformation and ensures test accuracy. Next, a stress detection mechanism measures the stress on each slide bar 1-1 and converts it into an electrical signal. This signal has high transmission speed and is less affected by environmental changes. This signal is then transmitted to a load compensation mechanism 2. During the freeze-thaw test, the load compensation mechanism 2 detects the loss of compressive stress in the holding device caused by fatigue of the elastic compression components 1-4 and degradation of the concrete specimen 4 in real time, and compensates for this stress in real time according to a preset load value. When environmental changes cause the load applied by the specimen loading mechanism 1 to change, the load compensation mechanism 2 can quickly correct the applied load to the predetermined value, achieving self-compensation for the load under extreme test conditions. This invention can closely simulate the freeze-thaw durability changes of concrete materials under continuous load, making the freeze-thaw test results more closely resemble the actual service environment of concrete materials.

[0085] Specific implementation method 2: Figure 2 As shown, this embodiment is a further limitation of the specific embodiment one. On the two high-strength steel plates 1-2 on the outside, a circular groove 1-2-1 is opened at the center position of one side of the plate surface; on the high-strength steel plate 1-2 in the middle, a circular groove 1-2-1 is opened at the center position of both side plates; the two adjacent high-strength steel plates 1-2 are arranged with the sides having the circular groove 1-2-1 opposite to each other, and the two ends of the concrete test piece 4 are respectively located in the circular grooves 1-2-1 of the two high-strength steel plates 1-2; the two ends of the elastic compression component 1-4 are respectively located in the circular grooves 1-2-1 of the two high-strength steel plates 1-2.

[0086] Furthermore, the inner diameter of the circular groove 1-2-1 is consistent with the outer diameter of the concrete test piece 4 and the elastic compression component 1-4, ensuring the coaxiality of the high-strength steel plate 1-2, the concrete test piece 4 and the elastic compression component 1-4.

[0087] Specific implementation method three: Figure 2 As shown, this embodiment is a further limitation of the specific embodiment one or two, and each of the high-strength steel plates 1-2 is provided with N sliding holes 1-2-2 uniformly opened in the circumference with the circular groove 1-2-1 as the center; the sliding rod 1-1 is inserted into the high-strength steel plate 1-2 through the sliding hole 1-2-2, and the three high-strength steel plates 1-2 are all located at the optical axis section of the sliding rod 1-1.

[0088] Furthermore, the sliding rod 1-1 and the sliding hole 1-2-2 are clearance-fitted.

[0089] Specific implementation method four: Figure 3 As shown, this embodiment is a further limitation of specific embodiments one, two or three. In this embodiment, the elastic compression assembly 1-4 is composed of a plurality of disc springs 1-4-1 stacked together, and the disc springs 1-4-1 are divided into two groups of equal number. The disc springs 1-4-1 in each group are stacked together in the same direction, and the two groups of disc springs are then stacked in opposite directions.

[0090] Furthermore, the number of the disc springs 1-4-1 is six.

[0091] Specific implementation method five: Figure 5 As shown, this embodiment is a further limitation of specific embodiments one, two, three or four, and the load compensation mechanism 2 includes a housing 2-1, N torque motors, N sleeves 2-2 and a signal processor; the N torque motors are installed in the housing 2-1, and the N sleeves 2-2 are evenly inserted on the same side of the housing 2-1 in the circumferential direction and rotate relative to the housing 2-1. The sleeves 2-2 are arranged in a one-to-one correspondence with the torque motors and the load adjustment members 1-3, one end of the sleeve 2-2 is connected to the output end of the torque motor, and the other end of the sleeve 2-2 is sleeved on the load adjustment member 1-3 and pushes the load adjustment member 1-3 to move axially; the signal processor is installed in the housing 2-1, and the signal receiving end of the signal processor is connected to the signal output end of the stress detection mechanism, and the signal output ends of the signal processor are respectively connected to the signal receiving ends of the N torque motors.

[0092] In this embodiment, when the stress detection mechanism detects the stress change of one or more high-strength screws and converts it into a corresponding electrical signal, which is transmitted to a signal processor, the signal processor has the function of setting a predetermined load and storing it as a corresponding electrical signal. The signal processor quickly calculates the strain size that needs to be compensated based on the received electrical signal and the stored electrical signal, and controls the operation of the torque motor; the torque motor generates a corresponding torque based on the incoming electrical signal, and the generated torque is transmitted to the corresponding sleeve 2-2. The sleeve 2-2 drives the load adjustment member 1-3 to move toward the high-strength steel plate 1-2 to achieve the application of the load. Since the sleeve 2-2 and the load adjustment member 1-3 are individually adjustable, or four sleeves 2-2 can be adjusted simultaneously, the load compensation mechanism 2 can accurately apply axial loads and eccentric loads, and the scope of application is more diverse. The controller and the torque motor automatically control the torque change in real time to control the stability of the screw stress and eliminate stress fluctuations.

[0093] In this embodiment, the housing 2-1 has a length b1 of 100 mm, a width h1 of 100 mm, and a height t5 of 50 mm. The sleeve 2-2 is embedded within the housing 2-1 to a depth t6 of 10 mm. The sleeve 2-2 has a length L3 of 40 mm, a depth L4 of 30 mm, an outer diameter d5 of 25.7 mm, and an inner diameter d6 of 18 mm. The sleeve transmits the torque generated by the torque motor to the corresponding loading end nut.

[0094] Specific embodiment six: This embodiment is a further limitation of specific embodiments one, two, three, four or five. The stress detection mechanism includes a strain collector and N strain gauges. A strain gauge is pasted on the surface of each sliding rod 1-1 and is sealed and protected with 703 silicone rubber and insulating tape.

[0095] In this embodiment, the strain collector has the function of collecting the strain of the strain gauge in real time and converting it into a corresponding electrical signal.

[0096] Specific implementation method seven: Figure 1 As shown, this embodiment is a further limitation of specific embodiments one, two, three, four, five or six, the sliding rod 1-1 is a high-strength screw, both ends of the high-strength screw are provided with external threads, and the optical axis section is between the two threaded sections; the load adjustment member 1-3 is screwed onto the threaded section of the high-strength screw.

[0097] In this embodiment, the value of N is 4.

[0098] Specific embodiment eight: This embodiment is a further limitation of specific embodiments one, two, three, four, five, six or seven, in which the load adjustment member 1-3 is a high-strength nut, and the sleeve 2-2 is a nut sleeve.

[0099] In this embodiment, since the positions of the nut sleeve and the high-strength screw are fixed, in order to generate axial thrust on the high-strength steel plate 1-2, the high-strength nut needs to move axially along the nut sleeve and the high-strength screw, and the high-strength nut cannot be separated from the drive of the nut sleeve, so the length of the high-strength nut is greater than the length of its maximum axial displacement; the nut sleeve is driven to rotate by the torque motor, and the nut sleeve drives the high-strength nut to rotate, and the high-strength nut moves axially along the nut sleeve and the high-strength screw, thereby realizing the extrusion of the high-strength nut on the high-strength steel plate 1-2.

[0100] Specific implementation method nine: Figure 4 As shown, this embodiment is a further limitation of specific embodiments one, two, three, four, five, six, seven or eight, and the locking member 1-5 is a high-strength nut, and the locking member 1-5 is screwed onto the threaded section of the high-strength screw; the holding device also includes a backstop 3, and the backstop 3 includes a central connecting portion 3-1 and N hexagonal wrench heads 3-2, and the N hexagonal wrench heads 3-2 are installed on the central connecting portion 3-1 and are arranged one-to-one with the locking member 1-5, and the hexagonal wrench heads 3-2 are sleeved on the locking member 1-5.

[0101] In this embodiment, during the freeze-thaw cycle test, concrete, a non-homogeneous, anisotropic material, shrinks unevenly in different directions and is prone to localized damage. During the freezing process, the free water within the concrete freezes and expands, causing the concrete volume to expand, increasing the reaction force on the supporting device. During the thawing process, the frozen water within the concrete melts and contracts, causing the concrete volume to shrink, reducing the reaction force on the supporting device. Significant and repetitive changes in the stress of the supporting device will cause the high-strength nuts in the supporting device to slip and retreat, further causing stress loss in the supporting device and distorting the test results. Furthermore, as the freeze-thaw cycle test progresses, significant damage occurs on the surface and interior of the concrete specimen 4. The change in the load-bearing area causes localized bias in the supporting device, resulting in significant dispersion in the test data.

[0102] Therefore, this loading device is designed with a backstop 3 fastening a high-strength nut at one end of the device, and the backstop 3 is used to lock the high-strength nut to prevent the high-strength nut from slipping back due to temperature changes and causing fluctuations in the load size; at the same time, the nut sleeve connected to the load compensation mechanism 2 is controlled by the torque motor and will not rotate freely, which can limit the high-strength nut from slipping back during the freeze-thaw process; at the same time, the load compensation mechanism 2 detects the high-strength screw strain data in real time, adjusts the tightness of the high-strength nut, and automatically compensates for the stress loss of the loading device, so that the strain value of the high-strength screw is always maintained at the set value, thereby keeping the test piece at a constant load and achieving a stable pressure-holding loading effect for concrete under a freeze-thaw environment.

[0103] Specific embodiment ten: This embodiment is a further limitation of specific embodiments one, two, three, four, five, six, seven, eight or nine. The following relationship exists between the high-strength screw, high-strength steel plate, high-strength nut, disc spring and the test piece, which can ensure that the holding device can achieve temperature deformation self-balance under temperature changes:

[0104] Among them, α1 and L are the linear expansion coefficient and length of the high-strength screw, respectively; α2 and t1 are the linear expansion coefficient and thickness of the high-strength steel plate, respectively; α5 and t3 are the linear expansion coefficient and thickness of the high-strength nut, respectively; α3 and t4 are the linear expansion coefficient and thickness of the disc spring, respectively; α4 and L5 are the linear expansion coefficient and axial length of the concrete specimen, respectively; the unit of the linear expansion coefficient is mm / °C, and the unit of the length is mm.

[0105] The specific verification process is as follows:

[0106] Step 1, preparing the concrete required for the test piece;

[0107] Step 2: preparing a concrete cylindrical test piece;

[0108] Step 3, determining the linear expansion coefficient of the concrete test piece;

[0109] Step 4, obtaining the linear expansion coefficient of the sliding rod;

[0110] According to the material temperature deformation calculation formula ΔL=α×L×ΔT, the deformation of the concrete specimen ΔL5, the deformation of the high-strength steel plate ΔL2, the deformation of the high-strength nut ΔL3 and the deformation of the disc spring ΔL4 are obtained;

[0111] Concrete specimen deformation ΔL5 = α4 × L5 × ΔT;

[0112] High-strength steel plate deformation ΔL2 = α2 × t1 × ΔT;

[0113] High-strength nut deformation ΔL3=α5×t3×ΔT;

[0114] Disc spring deformation ΔL4 = α3 × t4 × ΔT;

[0115] When testing different types of concrete, if the linear expansion coefficient α4 changes, the axial temperature deformation formula ΔL1=ΔL5+ΔL2+ΔL3+ΔL4 can be used to deduce:

[0116]

[0117] Example 1:

[0118] Step 1, prepare concrete:

[0119] The components of concrete are configured according to the following mass ratios:

[0120] P.042.5 Ordinary Portland cement: medium sand: 5-20mm crushed stone: water: air-entraining agent = 1:1.64:2.92:0.52:0.079, design strength grade C25, measured compressive strength is 33.6MPa, slump is 70mm, and air content is 4.26%.

[0121] Step 2: Use a steel mold to prepare a concrete cylindrical specimen (4φ76×300mm) to be tested and evaluated. One day after the concrete is formed, remove the mold and cure it to the predetermined age.

[0122] Step 3: Obtain the linear expansion coefficient of the concrete specimen:

[0123] Since the linear expansion coefficient of ordinary concrete ranges from 10 to 12.00×10 -6 mm / ℃, the linear expansion coefficient of common steel materials ranges from 8 to 20.00×10 -6 mm / ℃, the linear expansion coefficients of the two are similar. At the same time, steels with different linear expansion coefficients can be obtained by controlling the content of trace elements in steel, such as carbon, chromium, nickel, and manganese. Therefore, the linear expansion coefficient of the required steel can be calculated based on the linear expansion coefficient of the concrete to be tested, so that the overall temperature deformation of the entire load-bearing device is zero when the temperature changes, thereby reducing the impact of temperature deformation on the applied load.

[0124] The linear expansion coefficient of concrete specimen 4 under freeze-thaw cycle temperature of -20 to 20°C was measured by material mechanics experiments, as shown in Table 1 below:

[0125] Table 1 Linear expansion coefficient of concrete at freeze-thaw cycle temperature measured in the experiment

[0126]

[0127] The elastic modulus and linear expansion coefficient of the sliding rod under the freeze-thaw cycle temperature of -20 to 20°C were measured through material mechanics experiments, as shown in Table 2 below:

[0128] Table 2 Elastic modulus and linear expansion coefficient of the sliding bar under freeze-thaw cycle temperature

[0129]

[0130] Since the elastic modulus and linear expansion coefficient of the concrete test piece and the slide rod do not change by more than 1% in an environment of -20 to 20°C, which is within the error control range, the elastic modulus and linear expansion coefficient of the concrete and the screw rod at room temperature of 20°C can be used for calculation in this embodiment. In this embodiment, after the concrete is cured to a predetermined age, its linear expansion coefficient is measured according to the material mechanics test to be α4 = 11.00 × 10 -6 mm / ℃.

[0131] Step 4: Get the linear expansion coefficient of the slider:

[0132] The high-strength steel plate and high-strength nut are made of 45# carbon steel, with a yield strength greater than 345MPa, a tensile strength greater than 600MPa, and a linear expansion coefficient α2 of 12.00×10 -6 mm / °C, and the surface of the part is galvanized. The dimensions of the high-strength steel plate are as follows: length b is 100 mm, width h is 100 mm, thickness t1 is 16 mm, with 13.5 mm bolt holes on all four sides and a central circular groove with a diameter d2 of 78 mm and a depth t2 of 1 mm. The dimensions of the high-strength nut are as follows: opposite side h1 is 18 mm, opposite corner h2 is 20 mm, thickness t3 is 10.8 mm, and the thread pitch P has a coarse thread of 1.75 mm.

[0133] The disc spring is made of 60Si2Mn spring steel, with a yield strength greater than 1176MPa, a tensile strength greater than 1274MPa, and a linear expansion coefficient α3 of 15.80×10 -6 The disc spring has an oxidized blue surface. The disc spring dimensions are as follows: inner diameter d3 is 41 mm, outer diameter d4 is 80 mm, disc spring thickness t4 is 5 mm, and disc spring inner height h3 is 1.7 mm.

[0134] The dimensions of the high-strength screw are as follows: diameter d1 is 12 mm, length L1 is 423 mm, and both ends have coarse threads with length L2 of 50 mm and pitch P of 1.75 mm.

[0135] According to the material temperature deformation calculation formula ΔL=α×L×ΔT, we can get:

[0136] Concrete specimen deformation ΔL5=α4×L5×ΔT=11×10 -6 ×300×ΔT=0.0033ΔT;

[0137] High-strength steel plate deformation ΔL2=α2×t1×ΔT=12×10 -6 ×16×3×ΔT=0.000576ΔT;

[0138] High-strength nut deformation ΔL3=α5×t3×ΔT=12×10 -6 ×10.8×2×ΔT=0.000259ΔT;

[0139] Disc spring deformation ΔL4=α3×t4×ΔT=15.8×10 -6 ×33.4×ΔT=0.000528ΔT;

[0140] When testing different types of concrete, if the linear expansion coefficient α4 changes, the axial temperature deformation formula ΔL1=ΔL5+ΔL2+ΔL3+ΔL4 can be used to deduce:

[0141]

[0142] Therefore, only the linear expansion coefficient of the steel material used in the slide bar is required (α4 is the linear expansion coefficient of concrete measured experimentally), which can ensure that the holding device can achieve temperature deformation self-balance under temperature changes.

[0143] The linear expansion coefficient of the sliding rod 1-1 in this embodiment is 11.02×10 -6 When the slide rod 1-1 is a high-strength screw, the high-strength screw is made of high-strength chromium steel, with a yield strength greater than 345MPa, a tensile strength greater than 600MPa, and an elastic modulus G1 of 2.0×10 5 MPa, the linear expansion coefficient α1 is 11.02×10 -6 mm / ℃.

[0144] Steps 1 through 3 primarily determine the material properties of the high-strength screw and test piece, which are required for subsequent calculations. Step 4 determines the linear expansion coefficient of the high-strength screw, primarily to ensure zero temperature deformation of the device and test piece in a freeze-thaw environment, achieving self-balanced temperature changes across the entire system.

[0145] Specific embodiment 11: This embodiment provides an axial loading method of a stress self-adjusting loading device for concrete durability testing under freeze-thaw cycles. The specific loading process is as follows:

[0146] Step 1: Install and debug the holding device with the concrete test piece 4;

[0147] Step 1.1, place the concrete specimen 4 and the 6 disc springs between the three high-strength steel plates 1-2, respectively, and ensure the coaxiality of the concrete specimen 4 and the 6 disc springs with the high-strength steel plates 1-2;

[0148] Step 1.2: Insert four high-strength screws onto three high-strength steel plates 1-2, and screw eight high-strength nuts onto the four high-strength screws. Use a torque wrench to pre-tighten the high-strength nuts at both ends of the high-strength screws to an initial torque of 1 N·m.

[0149] Step 1.3: Install a backstop 3 on the high-strength nut serving as a locking member to limit the rotation of the high-strength nut;

[0150] Step 1.4: Install the load compensation mechanism 2 on the high-strength nut serving as the load adjustment member, so that the four nut sleeves are respectively sleeved on the corresponding high-strength nuts;

[0151] Step 1.5: Attach the strain gauge to the high-strength screw and seal it with 703 silicone rubber and insulating tape.

[0152] Step 2: The load-carrying device automatically applies the predetermined load to the axis:

[0153] Currently, commonly used methods of loading and holding pressure, such as jacks, lever-amplified counterweights, and manual tightening of bolts, generally have disadvantages such as low loading accuracy and large workload. This loading device adopts an automated loading control method. By detecting the strain of high-strength screws, it regulates the load application in real time, keeping the holding pressure error within 1%, meeting the error control requirements of conventional concrete tests. The specific application process is as follows:

[0154] Step 2.1: Input an initial torque of 1 N·m into the load compensation mechanism 2. The high-strength nut used in this embodiment has a galvanized, non-lubricated thread, and the tightening torque coefficient is K = 0.22. According to the tightening torque calculation formula T = KFd, it can be calculated:

[0155] Initial preload on each high-strength screw Where, d is the diameter of the high-strength screw, in mm; F1 is in N; T1 is the initial tightening torque, in N·m;

[0156] Initial strain of each high-strength screw G1 is the elastic modulus of the high-strength screw. In this embodiment, G1 is 2×10 5 MPa, S1 is the cross-sectional area of the high-strength screw, unit is mm 2 ;σ' is the screw stress, unit is MPa;

[0157] By combining the above formulas, the relationship between the high-strength nut torque and the high-strength screw strain is:

[0158]

[0159] Wherein, γ is the conversion coefficient between the high-strength screw strain ε and the high-strength nut torque T;

[0160] From this embodiment, it can be obtained that: Initial stress of concrete specimen 4 S is the cross-sectional area of the test piece, in mm 2 .

[0161] Step 2.2: At room temperature of 20°C,

[0162] The conversion relationship between screw strain and screw stress is:

[0163] The conversion relationship between screw strain and screw preload is:

[0164] The conversion relationship between the stress of concrete specimen 4 and the screw preload is: S is the cross-sectional area of the test piece;

[0165] The relationship between the screw strain and the concrete specimen stress can be obtained by combining

[0166] β is the conversion coefficient between the strain ε1 of a screw and the stress σ1 of the concrete specimen 4. From this embodiment, it can be obtained that

[0167] Step 2.3: Enter the stress σ to be applied in the load compensation mechanism 2 e =16.8MPa, start the axial load loading program in the load compensation mechanism 2, the system automatically calculates the set values that the screw strain and nut torque need to reach, and the conversion coefficient derived in step 2.2 is used to obtain the set value ε that the high-strength screw strain needs to reach e =βσ e =5.0139×10 -5 ×16.8=842.335×10 -6 ; According to the conversion coefficient derived in step 2.1, the set value of the high-strength nut torque needs to be obtained It should be noted that the torque setting value should be rounded up and not down. For example, the setting value calculated by this formula is 50.3006N·m. Considering the torque control accuracy and other reasons later, it is uniformly rounded up and used to tighten with 51N·m.

[0168] Step 2.4: The signal processor controls the torque motor inside the load compensation mechanism 2 through an electrical signal to simultaneously turn the four nut sleeves at a torque of 5 N·m until the torque of the torque motor reaches 5 N·m.

[0169] Step 2.5: At this time, the load compensation mechanism 2 detects the strain value ε of the high-strength screw and converts the current stress σ of the concrete test piece 4 according to the conversion coefficient in step 2.1. According to the conversion formula in step 2.1, the strain value of the high-strength screw in this embodiment should be ε = γT = 1.6746 × 10 -5 ×5=(83.73±5)×10 -6 The current concrete specimen stress is calculated from the screw strain and conversion coefficient

[0170] Step 2.6: The signal processor continues to control the torque motor to rotate the four nut sleeves at a torque of 10 N·m until the high-strength nut can no longer be tightened. The load compensation mechanism 2 detects the strain value ε of the high-strength screw and calculates the current stress σ of the concrete specimen 4 according to the conversion factor in step 2.1.

[0171] Step 2.7: Following the process of steps 2.3 to 2.6, the load compensation mechanism 2 is loaded step by step with an increment of 5 N·m, gradually increasing the stress of the concrete specimen 4 until the 10th loading. After the load is applied by tightening the nut with a torque of 50 N·m, the step-by-step loading process is completed.

[0172] Step 2.8: After the step-by-step loading is completed, the compensation system automatically enters the fine-tuning stage. The signal processor controls the torque motor to fine-tune the four nut sleeves in turn at a torque setting of 51 N·m, so that the four strain values ε of the high-strength screw all reach the set value ε = (842.335 ± 5) × 10 -6 =ε e , at this time the stress of concrete specimen 4 Error accuracy The concrete test piece 4 reaches the predetermined load, and the stress error is controlled within 1%, and the device automatically applies the predetermined load function.

[0173] Step 3: Place the loaded concrete test piece 4 and the load-holding device in a freeze-thaw cycle tester, set corresponding freeze-thaw parameters, and conduct a freeze-thaw cycle test in accordance with corresponding specifications;

[0174] Step 4: The load compensation mechanism 2 realizes self-compensation of the load according to the strain value of the high-strength screw.

[0175] The load compensation mechanism 2 detects the strain values of the four high-strength screws in real time through strain gauges. When the strain value of a high-strength screw decreases, the signal controller controls the torque motor to rotate the nut sleeve to tighten the high-strength nut; when the strain value of a screw increases, the signal controller controls the torque motor to rotate the nut sleeve to loosen the high-strength nut.

[0176] During the test, when the strain value of the four screws rises to ε = ε3, it can be seen from step 2.5 of (1) that the torque of the nut at this time is The signal processor controls the torque motor to loosen the nut with a torque of T=T3+1, and fine-tune the nut to make the strain value of the high-strength screw ε=γT e =ε e , at this time the test piece reaches the predetermined load σ=σ e .

[0177] When the strain value of the four screws drops to ε = ε4, it can be seen from step 2.5 of (1) that the torque of the nut is The signal processor controls the torque motor with T=T e Tighten the nut with the torque of , and fine-tune the nut to make the high-strength screw strain value ε=γT e =ε e , at this time the test piece reaches the predetermined load σ=σ e .

[0178] Specifically, during the freezing process of the freeze-thaw cycle test, the free water inside the concrete freezes and expands, causing the concrete volume to expand by 9%, and the strain value of the four screws rises to ε = (870.000 ± 5) × 10 -6 , from step 2.5 of (1), we can know that the torque of the nut is The signal processor controls the torque motor to loosen the nut with a torque of 52.95 N·m and fine-tune the nut to make the strain value of the high-strength screw ε=γT=1.6746×10 -5 ×51=(842.335±5)×10 -6 =ε e , at this time the test piece reaches the predetermined load The device achieves load self-compensation effect in the freeze-thaw test environment.

[0179] During the freezing and thawing cycle test, the frozen water inside the concrete melted, causing the concrete volume to shrink by 8.8%. The strain values of the four screws suddenly dropped to ε = (820.000 ± 5) × 10 -6 , from step 2.5, we can know that the torque of the nut is The signal processor controls the torque motor to tighten the nut with a torque of 51 N·m, making the strain value of the high-strength screw ε=γT=1.6746×10 -5 ×50=(842.335±5)×10 -6 At this time, the concrete specimen 4 reaches the predetermined load The device achieves load self-compensation effect in the freeze-thaw test environment.

[0180] It should also be noted that: in the present invention, generally no superscript indicates the current state, a superscript indicates a process quantity, a superscript 1 indicates the initial value corresponding to the parameter, and a superscript e indicates the set value corresponding to the parameter. For example, the stress with a superscript 1 is the initial stress, and the stress with a superscript e is the set stress.

[0181] Specific embodiment 12: This embodiment provides an eccentric loading method of a stress self-adjusting loading device for concrete durability testing under freeze-thaw cycles. The specific loading process is as follows:

[0182] Step 1: Install and debug the holding device with the concrete test piece 4;

[0183] Step 1.1, place the concrete specimen 4 and 8 disc springs between the three high-strength steel plates 1-2, respectively, and ensure the coaxiality of the concrete specimen 4 and 8 disc springs with the high-strength steel plates 1-2;

[0184] Step 1.2: Insert four high-strength screws onto three high-strength steel plates 1-2, and screw eight high-strength nuts onto the four high-strength screws. Use a torque wrench to pre-tighten the high-strength nuts at both ends of the high-strength screws to an initial torque of 1 N·m.

[0185] Step 1.3: Install a backstop 3 on the high-strength nut serving as a locking member to limit the rotation of the high-strength nut;

[0186] Step 1.4: Install the load compensation mechanism 2 on the high-strength nut serving as the load adjustment member, so that the four nut sleeves are respectively sleeved on the corresponding high-strength nuts;

[0187] Step 1.5: Attach the strain gauge to the high-strength screw and seal it with 703 silicone rubber and insulating tape.

[0188] Step 2: The load-carrying device automatically applies an eccentric predetermined load:

[0189] Step 2.1: Input an initial torque of 1 N·m into the load compensation mechanism 2. This embodiment uses a high-strength nut with a galvanized, non-lubricated thread. The tightening torque coefficient is K = 0.22. According to the tightening torque calculation formula T = KFd, it can be calculated:

[0190] Initial preload on each screw Where, d is the diameter of the high-strength screw, in mm; F1 is in N; T1 is the initial tightening torque, in N·m;

[0191] Initial strain of each screw G1 is the elastic modulus of the high-strength screw, which is 2×10 5 MPa; S1 is the cross-sectional area of the high-strength screw, in mm 2 ;σ' is the screw stress, unit is MPa;

[0192] By combining the above formulas, the relationship between nut torque and screw strain is:

[0193] γ is the conversion coefficient between the screw strain ε and the nut torque T; from this embodiment, it can be obtained that: Initial stress of concrete specimen 4 0.334MPa. S is the cross-sectional area of the test piece, in mm 2 .

[0194] Step 2.2: Start the eccentric load loading program of the load compensation mechanism 2, set the eccentricity e0 = 10 mm, and the system automatically calculates the set value that the screw strain needs to reach. The concrete test piece 4 has a predetermined compressive stress σ e=35.00MPa, eccentricity e0 = 10mm, the device should provide axial compressive stress σ = 35.00MPa, and bending moment The conversion factor derived from step 2.1 gives the set value ε that the average strain of the high-strength screw needs to reach. e =βσ e =5.0139×10 -5 ×35.00=1754.865×10 -6 , when the strains of any two adjacent high-strength screws among the four high-strength screws are not equal to the strains of the other two screws, the load applied by the loading device is an eccentric load; let any two adjacent high-strength screws be numbered as screw X1, and the other two high-strength screws be numbered as X2;

[0195] Step 2.3: Eccentricity e of the holding device a is half of the center distance between two adjacent high-strength screws, then The relationship between the screw stress and the concrete specimen stress is: pressure difference and strain difference Formula combination:

[0196]

[0197] ε e1 +ε e2 =2βσ e

[0198] Simplifying, we can get:

[0199]

[0200] The set values of the strain of both screws of screw X1 should be The set value of screw X2 strain should be The torque setting values of the nuts corresponding to the two screws of screw X1 should be The set value of screw X2 strain should be

[0201] Step 2.4: The signal processor controls the torque motor inside the load compensation mechanism 2 through an electrical signal to simultaneously turn the four nut sleeves at a torque of 5 N·m until the torque of the torque motor reaches 5 N·m.

[0202] Step 2.5: At this time, the load compensation mechanism 2 detects the strain value ε of the high-strength screw and converts the current stress σ of the concrete test piece 4 according to the conversion coefficient in step 2.1. According to the conversion formula in step 2.1, the strain value of the high-strength screw in this embodiment should be ε = γT = 1.6746 × 10 -8 ×5×10 3 =(83.73±5)×10 -6 The current concrete specimen stress is calculated from the screw strain and conversion coefficient Here, because the four screws are all tightened to a torque of 5 N·m in the initial stage, this formula can be used for calculation here. However, this formula cannot be used for calculation later when the torque is different.

[0203] Step 2.6: The signal processor continues to control the torque motor to rotate the four nut sleeves at a torque of 10 N·m until the high-strength nut can no longer be tightened. The load compensation mechanism 2 detects the strain value ε of the high-strength screw and calculates the current stress σ of the concrete specimen 4 according to the conversion factor in step 2.1.

[0204] Step 2.7. According to the process of steps 2.3 to 2.6, the load compensation mechanism 2 loads step by step with an increment of 5 N·m, gradually increasing the stress of the concrete specimen 4 until the 15th loading, tightening the nut corresponding to the screw X2 with a torque of 75 N·m. After the load is applied, the step-by-step loading process of the screw X2 is completed; the load compensation mechanism 2 continues to tighten the screw X1 step by step with an increment of 5 N·m until the 26th loading, tightening the nut corresponding to the screw X1 with a torque of 130 N·m. After the load is applied, the step-by-step loading process of the screw X1 is completed.

[0205] Step 2.8: After the step-by-step loading is completed, the compensation system automatically enters the fine-tuning stage. The signal processor controls the torque motor corresponding to the screw X1 to fine-tune the two nut sleeves corresponding to the screw X1 with a torque setting value of 133 N·m, so that the strain value ε of the high-strength screw X1 is 11 Reach the set value ε e1 =2216.672±5×10 -6 The signal processor controls the torque motor corresponding to the screw X2, and fine-tunes the two nut sleeves corresponding to the screw X2 with a torque setting value of 78N·m, so that the strain value of the high-strength screw X2 is ε 12 Reach the set value ε e2 =1293.058±5×10 -6 At this time, the strains of screw X1 and screw X2 are different, and the tensions they provide are also different. The strain of screw X1 is ε 11 =(2216.672±5)×10 -6 , screw X2 strain ε 12 =(1293.058±5)×10-6 , loading eccentricity The overall stress level of concrete specimen 4 σ = Error accuracy The concrete test piece 4 reaches the predetermined load, and the stress error is controlled within 1%, thereby achieving the effect of implementing eccentric load.

[0206] Step 3: Place the loaded concrete test piece 4 and the load-holding device in a freeze-thaw cycle tester, set corresponding freeze-thaw parameters, and conduct a freeze-thaw cycle test in accordance with corresponding specifications;

[0207] Step 4: Under eccentric load, the load compensation mechanism 2 realizes self-compensation of the load according to the strain value of the high-strength screw:

[0208] When concrete specimen 4 was subjected to eccentric loading, the concrete on the side with greater compressive stress suffered greater damage, while the concrete on the side with less compressive stress suffered less damage. During the freeze-thaw cycle test, damage to concrete specimen 4 caused the loading level to fluctuate. This device automatically compensated for stress losses in the holding device by detecting high-strength screw strain data in real time and adjusting the tightness of the high-strength nut, ensuring that the stress of concrete specimen 4 was always maintained at the set value.

[0209] During the test, the strain value of screw X1 suddenly increased to ε 11 =ε 21 , the strain value of screw X2 suddenly rises to ε 12 =ε 22 From step 2.5, we can see that the torque of the nut of screw X1 is Torque of the nut of screw X2 The signal processor controls the torque motor, and the signal processor controls the torque motor, respectively. 21 The torque is used to loosen the nut of the screw X1, so that the strain value of the high-strength screw X1 is ε 11 Reach the set value ε e1 =2216.672×10 -6 ;T 22 The torque is used to loosen the nut of screw X2, so that the strain value of high-strength screw X2 is ε 12 Reach the set value ε e2 =1293.058×10 -6 .

[0210] At this time, the loading eccentricity of the concrete specimen 4 The overall stress level of concrete specimen 4 is σ = σ e , so as to achieve the self-compensation effect of eccentric load of the load-bearing device under the freeze-thaw test environment.

[0211] Specifically, after multiple freeze-thaw cycle tests, local spalling of cement paste occurred on the side of the concrete with greater compressive stress, and the strain value of screw X1 suddenly increased to ε 21 =(2500.000±5)×10 -6 , the strain value of screw X2 suddenly rises to ε 22 =(1400.000±5)×10 -6 From step 2.5, we can see that the torque of the nut of screw X1 is Torque of the nut of screw X2 The signal processor controls the torque motor, and the signal processor controls the torque motor to tighten the nut of the screw X1 with a torque of 133N·m, which will make the strain value of the screw X1 ε 11 =ε e1 =(2216.672±5)×10 -6 ; Loosen the nut of screw X2 with a torque of 84 N·m, so that the strain value of screw X2 ε 12 =ε e2 =(1293.058±5)×10 -6 .

[0212] At this time, the loading eccentricity of the concrete specimen 4

[0213] Overall stress level of concrete specimen 4 The eccentric load self-compensation effect of the load-bearing device is achieved in the freeze-thaw test environment.

[0214] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A stress self-adjusting loading device for concrete durability testing under freeze-thaw cycles, characterized by: It comprises a specimen loading mechanism (1), a load compensation mechanism (2) and a stress detection mechanism; the specimen loading mechanism (1) applies an axial load to a concrete specimen (4), and comprises N sliding rods (1-1), three high-strength steel plates (1-2), N load adjustment members (1-3), an elastic compression assembly (1-4) and N locking members (1-5); the three high-strength steel plates (1-2) are arranged side by side in a transverse direction, the concrete specimen (4) is axially arranged between two adjacent high-strength steel plates (1-2) and clamped, and the elastic compression assembly (1-4) is arranged between the other two adjacent high-strength steel plates (1-2) and clamped; the N sliding rods (1-1) are uniformly arranged circumferentially around the concrete specimen (4) and the elastic compression assembly (1-4), and are respectively axially slidably connected to the three high-strength steel plates (1-2); the N load adjustment members (1-3) are located between the high-strength steel plates (1-2) and the elastic compression assembly (1-4). On one side of the N slide bars (1-1), and respectively sleeved on one end of the N slide bars (1-1), the load adjustment member (1-3) abuts on the plate surface of the adjacent high-strength steel plate (1-2); the N locking members (1-5) are on the other side of the high-strength steel plate (1-2), and respectively sleeved on the other end of the N slide bars (1-1), the locking members (1-5) are locked on the slide bars (1-1) and abut on the plate surface of the adjacent high-strength steel plate (1-2); the load The compensation mechanism (2) includes N driving ends, each driving end corresponding to a load adjustment member (1-3) for realizing axial movement and locking of the load adjustment member (1-3) on the respective slide rod (1-1); the stress detection mechanism is used to measure the stress on each slide rod (1-1); the linear expansion coefficients of the slide rod (1-1), the high-strength steel plate (1-2), the load adjustment member (1-3), the elastic compression assembly (1-4) and the locking member (1-5) are different; The elastic compression assembly (1-4) is formed by stacking a plurality of disc springs (1-4-1), wherein the plurality of disc springs (1-4-1) are divided into two groups of equal number, wherein the disc springs (1-4-1) in each group are stacked together in the same direction, and the two groups of disc springs are then stacked in opposite directions; The load compensation mechanism (2) comprises a housing (2-1), N torque motors, N sleeves (2-2) and a signal processor; the N torque motors are mounted in the housing (2-1), the N sleeves (2-2) are circumferentially and evenly inserted on the same side of the housing (2-1) and rotate relative to the housing (2-1), the sleeves (2-2) are arranged in a one-to-one correspondence with the torque motors and the load adjustment member (1-3), one end of the sleeve (2-2) is connected to the output end of the torque motor, the other end of the sleeve (2-2) is sleeved on the load adjustment member (1-3) and promotes the axial movement of the load adjustment member (1-3); the signal processor is mounted in the housing (2-1), the signal receiving end of the signal processor is connected to the signal output end of the stress detection mechanism, and the signal output end of the signal processor is respectively connected to the signal receiving ends of the N torque motors; The sliding rod (1-1) is a high-strength screw, and both ends of the high-strength screw are provided with external threads, and an optical axis section is located between the two threaded sections; the high-strength steel plate (1-2) is located on the optical axis section of the high-strength screw, and the load adjustment member (1-3) is a high-strength nut, which is screwed onto the threaded section of the high-strength screw, and the sleeve (2-2) is a nut sleeve; The locking member (1-5) is a high-strength nut, and the locking member (1-5) is screwed onto the threaded section of the high-strength screw; the holding device further comprises a backstop (3), and the backstop (3) comprises a central connecting portion (3-1) and N hexagonal wrench heads (3-2), the N hexagonal wrench heads (3-2) being mounted on the central connecting portion (3-1) and arranged in one-to-one correspondence with the locking member (1-5), and the hexagonal wrench heads (3-2) being sleeved on the locking member (1-5); The following relationship exists between the high-strength screw, the high-strength steel plate (1-2), the high-strength nut, the disc spring (1-4-1) and the concrete test piece (4), which can ensure that the holding device can achieve temperature deformation self-balance under temperature changes: Among them, α1 and L are the linear expansion coefficient and length of the high-strength screw, respectively; α2 and t1 are the linear expansion coefficient and thickness of the high-strength steel plate, respectively; α5 and t3 are the linear expansion coefficient and thickness of the high-strength nut, respectively; α3 and t4 are the linear expansion coefficient and thickness of the disc spring, respectively; α4 and L5 are the linear expansion coefficient and axial length of the concrete specimen, respectively.

2. A stress self-adjusting loading device for concrete durability testing under freeze-thaw cycles according to claim 1, characterized in that: On the two high-strength steel plates (1-2) on the outside, a circular groove (1-2-1) is opened at the center position of one side of the plate surface; on the high-strength steel plate (1-2) in the middle, a circular groove (1-2-1) is opened at the center position of both side plates; the two adjacent high-strength steel plates (1-2) are arranged with the sides having the circular groove (1-2-1) facing each other, and the two ends of the concrete test piece (4) are respectively located in the circular grooves ( 1-2-1); the two ends of the elastic compression component (1-4) are respectively located in the circular grooves (1-2-1) of the two high-strength steel plates (1-2); each of the high-strength steel plates (1-2) is uniformly provided with N sliding holes (1-2-2) in the circumferential direction with the circular groove (1-2-1) as the center; the sliding rod (1-1) passes through the sliding hole (1-2-2) and is inserted into the high-strength steel plate (1-2), and the sliding rod (1-1) and the sliding hole (1-2-2) are in clearance fit.

3. The self-adjusting stress holding device for concrete durability testing under freeze-thaw cycles according to claim 1, characterized in that: The stress detection mechanism comprises a strain collector and N strain gauges, and a strain gauge is pasted on the surface of each sliding rod (1-1).

4. An axial loading method for a stress self-adjusting loading device for concrete durability testing under freeze-thaw cycles, characterized by: Axial loading is achieved based on the stress self-adjusting loading device for concrete durability test under freeze-thaw cycles described in claim 1. The specific loading process is as follows: Step 1: Install and debug the holding device with the concrete test piece (4); Step 1.1, placing the concrete test piece (4) and a plurality of disc springs (1-4-1) between three high-strength steel plates (1-2), respectively, to ensure the coaxiality of the concrete test piece (4) and the disc springs with the high-strength steel plates (1-2); Step 1.2: Insert N high-strength screws onto three high-strength steel plates (1-2), and screw 2N high-strength nuts onto both ends of the N high-strength screws. Use a torque wrench to pre-tighten the high-strength nuts at both ends of the high-strength screws to an initial torque of 1 N·m. Step 1.3, install a backstop (3) on the high-strength nut serving as a locking member to limit the rotation of the high-strength nut; Step 1.4, installing the load compensation mechanism (2) on the high-strength nut serving as the load adjustment member, so that N nut sleeves are respectively sleeved on the corresponding high-strength nuts; Step 1.5, stick the strain gauge on the high-strength screw; Step 2: The load-carrying device automatically applies the predetermined load to the axis. The specific application process is as follows: Step 2.

1. Input the initial torque T1 into the load compensation mechanism (2), set the tightening torque coefficient as K, and calculate the initial pre-tightening force F1 = T1 / Kd on each high-strength screw according to the tightening torque calculation formula T = KFd; wherein F represents the pre-tightening force on the high-strength screw, F1 is the initial pre-tightening force on the high-strength screw; T represents the tightening torque, T1 is the initial tightening torque; d is the diameter of the high-strength screw; Initial strain of each high-strength screw Among them, σ' is the screw stress; G1 is the elastic modulus of the high-strength screw; S1 is the cross-sectional area of the high-strength screw; Therefore, the relationship between the high-strength nut torque and the high-strength screw strain is: Wherein, γ is the conversion coefficient between the high-strength screw strain ε and the high-strength nut torque T; Initial stress of concrete specimen (4) S is the cross-sectional area of the test piece; Step 2.2: At room temperature of 20°C, The conversion relationship between screw strain ε and screw stress is: The conversion relationship between screw strain ε and screw preload is: The conversion relationship between the stress of concrete specimen (4) and the screw preload is: σ represents the stress of the concrete specimen; The relationship between the screw strain and the concrete specimen (4) stress is obtained by combining β is the conversion factor between the strain ε of a high-strength screw and the stress σ of the concrete specimen (4) during axial load loading. d is the screw diameter, d7 is the test piece diameter; Step 2.3: Enter the stress σ to be applied in the load compensation mechanism (2) e , start the axial load loading program in the load compensation mechanism (2), the system automatically calculates the set values that the high-strength screw strain and high-strength nut torque need to reach, and the conversion coefficient derived from step 2.2 is used to obtain the set value ε that the high-strength screw strain needs to reach e =βσ e , σ e is the stress setting value of the concrete test piece; according to the conversion coefficient derived in step 2.1, the torque setting value that the high-strength nut torque needs to reach is obtained Step 2.4, the signal processor controls the torque motor inside the load compensation mechanism (2) through an electrical signal to simultaneously turn N nut sleeves at a torque of 5 N·m until the torque of the torque motor reaches 5 N·m; Step 2.5: At this time, the load compensation mechanism (2) detects the strain value ε of the high-strength screw and converts the current stress σ of the concrete test piece (4) according to the conversion coefficient of step 2.1; the strain value of the high-strength screw is ε=γT, and the current stress of the concrete test piece is calculated from the strain of the high-strength screw and the conversion coefficient. Step 2.6: The signal processor continues to control the torque motor to rotate the N nut sleeves in turn at a torque of 10 N·m until the high-strength nut cannot be tightened any further. The load compensation mechanism (2) detects the strain value ε of the high-strength screw and calculates the current stress σ of the concrete test piece (4) according to the conversion coefficient in step 2.

1. Step 2.7: According to the process of step 2.3 to step 2.6, the torque motor loads step by step with an increase of 5N·m, gradually increasing the stress of the concrete test piece (4) until the nth loading. After the load is applied by tightening the nut with a torque of 5N, the step-by-step loading process is completed. e -5≤5n≤T e , T e is the torque setting value; Step 2.8: After the step-by-step loading is completed, the compensation system automatically enters the fine-tuning stage. The signal processor controls the torque motor to set the torque value T e Fine-tune and twist N nuts and sleeves in turn to make N strain values ε of the high-strength screw reach the set value ε=ε e At this time, the stress of the concrete specimen (4) σ=σ e , σ e The stress of the concrete test piece is set to a value; when the concrete test piece (4) reaches a predetermined load, the device automatically applies the predetermined load and the function is completed; Step 3, placing the concrete test piece (4) after the load is applied and the load-holding device in a freeze-thaw cycle test machine, setting corresponding freeze-thaw parameters, and conducting a freeze-thaw cycle test according to corresponding specifications; Step 4: The load compensation mechanism (2) realizes self-compensation of the load according to the strain value of the high-strength screw; During the test, when the strain value of the four screws rises to ε=ε3, the torque of the nut is The signal processor controls the torque motor to loosen the nut with a torque of T=T3+1, and fine-tune the nut to make the strain value of the high-strength screw ε=γT e =ε e , at this time the test piece reaches the predetermined load σ=σ e ; When the strain value of the four screws drops to ε=ε4, the torque of the nut is The signal processor controls the torque motor with T=T e Tighten the nut with the torque of , and fine-tune the nut to make the high-strength screw strain value ε=γT e =ε e , at this time the test piece reaches the predetermined load σ=σ e .

5. An eccentric loading method for a stress self-adjusting loading device for concrete durability testing under freeze-thaw cycles, characterized by: Axial loading is achieved based on the stress self-adjusting loading device for concrete durability test under freeze-thaw cycles described in claim 1. The specific loading process is as follows: Step 1: Install and debug the holding device with the concrete test piece (4); Step 1.1, placing the concrete test piece (4) and the plurality of disc springs (1-4-1) between three high-strength steel plates (1-2), respectively, to ensure the coaxiality of the concrete test piece (4) and the plurality of disc springs (1-4-1) and the high-strength steel plates (1-2); Step 1.2: Insert N high-strength screws onto three high-strength steel plates (1-2), and screw 2N high-strength nuts onto both ends of the N high-strength screws. Use a torque wrench to pre-tighten the high-strength nuts at both ends of the high-strength screws to an initial torque of 1 N·m. Step 1.3, install a backstop (3) on the high-strength nut serving as a locking member to limit the rotation of the high-strength nut; Step 1.4, installing the load compensation mechanism (2) on the high-strength nut serving as the load adjustment member, so that N nut sleeves are respectively sleeved on the corresponding high-strength nuts; Step 1.5, stick the strain gauge on the high-strength screw; Step 2: The load-carrying device automatically applies an eccentric predetermined load. The specific application process is as follows: Step 2.

1. Input the initial torque T into the load compensation mechanism (2), set the tightening torque coefficient as K, and calculate the initial pre-tightening force F1 = T1 / Kd on each high-strength screw using the tightening torque calculation formula T = KFd; where F represents the pre-tightening force on the high-strength screw, F1 is the initial pre-tightening force on the high-strength screw; T represents the tightening torque, T1 is the initial tightening torque; and d is the diameter of the high-strength screw; Initial strain of each high-strength screw G1 is the elastic modulus of the high-strength screw; S1 is the cross-sectional area of the high-strength screw; σ' is the screw stress; Therefore, the relationship between nut torque and screw strain is: Wherein, γ is the conversion coefficient between the high-strength screw strain ε and the high-strength nut torque T; Initial stress of concrete specimen (4) S is the cross-sectional area of the test piece; Step 2.2: Start the eccentric load loading program of the load compensation mechanism (2), set the eccentricity to e0, and the predetermined compressive stress of the concrete specimen (4) to σ e , the system automatically calculates the set value that the screw strain needs to reach, and the bending moment should be M=σ e Se0; by conversion factor d1 is the screw diameter, d7 is the test piece diameter, and the set value ε that the average strain of the high-strength screw needs to reach is obtained e =βσ e , σ e is the stress setting value of the concrete specimen; when the strains of any two adjacent high-strength screws among the N high-strength screws are not equal to the strains of the other two screws, the load applied by the loading device is an eccentric load; let any two adjacent high-strength screws be numbered as screw X1, and the other two high-strength screws be numbered as X2; Step 2.3: Eccentricity e of the holding device a It is half of the distance between the centers of two adjacent high-strength screws. According to the relationship between the screw stress and the stress of the concrete specimen (4), pressure difference and strain difference Joint: e e1 +e e2 =2βσ e Simplified to: The set values of the strain of the two screws of screw X1 are The set value of screw X2 strain is The setting values of the torque of the two screws of screw X1 are The setting value of the torque of the two screws of screw X2 is Step 2.4, the signal processor controls the torque motor inside the load compensation mechanism (2) through an electrical signal to simultaneously turn the four nut sleeves at a torque of 5 N·m until the torque of the torque motor reaches 5 N·m; Step 2.5: At this time, the load compensation mechanism (2) detects the strain value ε of the high-strength screw and converts the current stress σ of the concrete test piece (4) according to the conversion coefficient of step 2.1; the strain value of the high-strength screw is ε=γT, and the current stress of the concrete test piece is calculated from the screw strain and the conversion coefficient. where ε 11 is the strain corresponding to screw X1, ε 12 is the strain corresponding to screw X2; Step 2.6: The signal processor continues to control the torque motor to rotate the four nut sleeves in turn at a torque of 10 N·m until the high-strength nut cannot be tightened any further. The load compensation mechanism (2) detects the strain value ε of the high-strength screw and converts the current stress σ of the concrete test piece (4) according to the conversion coefficient β in step 2.

2. Step 2.7: According to the process of step 2.3 to step 2.6, the torque motor is loaded step by step with an increase of 5N·m, gradually increasing the stress of the concrete test piece (4) until the nth loading, tightening the nut T with a torque of 5N e2 -5≤5n≤T e2 At this time, the torque motor corresponding to screw X2 enters the fine-tuning stage, and the torque motor corresponding to screw X1 continues to load step by step; until the mth loading, tighten the nut with a torque of 5m, T e1 -5≤5m≤T e1 , at this time, the torque motor corresponding to screw X2 enters the fine-tuning stage; Step 2.8: After the step-by-step loading is completed, the compensation system automatically enters the fine-tuning stage. The signal processor controls the torque motor to fine-tune the four nut sleeves in turn at their respective torque setting values, so that the strain value ε of the screw X1 is 11 Both reach the set value ε e1 , the strain value ε of screw X2 12 Both reach the set value ε e2 At this time, the stress of the concrete specimen (4) σ=σ e , the concrete test piece (4) reaches the predetermined load, and the device automatically applies the predetermined load function; at this time, the strains of the screw X1 and the screw X2 are different, and the tension provided is also different; Step 3, placing the concrete test piece (4) after the load is applied and the load-holding device in a freeze-thaw cycle test machine, setting corresponding freeze-thaw parameters, and conducting a freeze-thaw cycle test according to corresponding specifications; Step 4: Under eccentric load, the load compensation mechanism (2) realizes self-compensation of the load according to the strain value of the high-strength screw; During the test, the strain value of screw X1 increased to ε 21 , the screw X2 strain value rises to ε 22 , at this time the torque of the nut of screw X1 Torque of the nut of screw X2 The signal processor controls the torque motor, and the signal processor controls the torque motor, respectively. 21 The torque is used to loosen the nut of screw X1, so that the strain value of screw X1 is ε 11 =ε e1 ; T 22 The torque is used to loosen the nut of screw X2, so that the strain value of screw X2 is ε 12 =ε e2 ; At this time, the concrete test piece (4) is loaded with an eccentricity of Concrete specimen (4) overall stress level σ=σ e , so as to achieve the self-compensation effect of eccentric load of the load-bearing device under the freeze-thaw test environment.

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