Force gauge based on magnetic grid displacement meter and method for monitoring stress of concrete

Abstract

The application provides a force gauge based on a magnetic grating displacement meter, a mass concrete stress monitoring structure constructed by using the force gauge and a monitoring method. The force gauge is composed of upper and lower force collecting discs, upper and lower force transmitting sheets, a force measuring block and a magnetic grating displacement meter. The top and bottom surfaces of the force measuring block are coaxially fixedly connected with the upper and lower force collecting discs through the upper and lower force transmitting sheets. A through hole is formed in the center of the force measuring block, and the magnetic grating displacement meter is arranged in the through hole. The force gauge is arranged in an isolation cylinder with flexible structures at both ends, then the measured concrete is poured into the isolation cylinder, and finally the isolation cylinder is buried in the measured concrete. The deformation of the center points of the top and bottom surfaces of the force measuring block is measured by the magnetic grating displacement meter, and the stress value of the measured concrete is calculated. The stress value of the concrete measured by using the monitoring structure and method is close to the real stress value of the concrete, and the real and reliable stress data support is provided for the safe operation state of the mass concrete structure.

Description

A force gauge based on a magnetic grating displacement meter and a method for monitoring concrete stress. Technical Field

[0001] This invention relates to a force gauge and a method for monitoring concrete stress using the force gauge. More specifically, it relates to a force gauge based on a magnetic grating displacement meter and a method for monitoring concrete stress using the force gauge. Background Technology

[0002] The stress state of large-volume concrete is extremely complex, due to both the microscopic inhomogeneity of its internal structure and the influence of numerous factors such as internal temperature changes, autogenous volume deformation, and seepage pressure. The traditional method for monitoring the stress state of large-volume concrete is the "strain gauge flower" method, which involves embedding 5-9 strain gauges at measuring points in the large-volume concrete and arranging them in a flower shape. Because the strain gauges are installed in different directions, strain deformation in different directions of the concrete can be measured, and the stress state value of the concrete can then be calculated based on the measured values. The disadvantages of this monitoring method are: the calculated stress state value of the concrete based on the measured concrete strain values ​​has large errors and high dispersion. Reasons: 1) Because the strain gauges are directly embedded in the concrete, the measured values ​​are affected by factors such as concrete temperature changes and autogenous volume deformation during the measurement process, leading to inaccurate measurements and consequently inaccurate stress state values ​​calculated from the measured strain values. 2) The difference between the material properties of the strain gauges and the concrete material leads to inaccurate measured strain values, resulting in inaccurate calculated stress values. 3) Due to the need to assemble the strain gauges into a flower shape, the varying skill levels of the on-site installation personnel resulted in improper installation of the strain gauges, leading to inaccurate measurements. Based on current observations of the stress state of existing high concrete dams (large-volume concrete structures), it has been found that few dams yielded strain measurements that are reasonable, exhibit strong regularity, and can be directly used to calculate and evaluate the stress state of large-volume concrete.

[0003] Those skilled in the art have attempted to directly measure the force on concrete, i.e., the stress in concrete, using force sensors or dynamometers. This method requires selecting appropriate tensile and compressive force sensors based on the material properties of concrete; this is the first and most crucial step in accurately measuring concrete stress. However, most force sensors or dynamometers currently on the market are manufactured to meet the demands of high-precision measurement and high sensitivity in stress acquisition. The stiffness of these sensors is not important; on the contrary, the lower the stiffness of the sensor itself, the higher the measurement accuracy. Typically, their stiffness is 10-100 times lower than the stiffness of the hardened concrete being measured, making them unsuitable for directly measuring the stress in large volumes of concrete. Summary of the Invention

[0004] In order to address the problems existing in current methods and instruments for monitoring the stress state of large-volume concrete, the purpose of this invention is to provide a force gauge based on a magnetic grating displacement meter for monitoring the stress of large-volume concrete.

[0005] Another objective of this invention is to provide a monitoring structure for monitoring the stress of large-volume concrete using a force gauge based on a magnetic grating displacement meter.

[0006] Another object of the present invention is to provide a method for monitoring the stress of large-volume concrete using a force gauge based on a magnetic grating displacement meter.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a force gauge based on a magnetic grating displacement meter, which consists of an upper force-collecting disk, an upper force-transmitting plate, a force-measuring block, a lower force-transmitting plate, a lower force-collecting disk, and a magnetic grating displacement meter; the top and bottom surfaces of the force-measuring block are respectively fixedly connected to the upper and lower force-collecting disks through the upper and lower force-transmitting plates, and the upper and lower force-collecting disks, the upper and lower force-transmitting plates, and the force-measuring block are coaxial;

[0008] The force measuring block is a regular-shaped body. At the center of the force measuring block, there is a through hole in a direction perpendicular to the longitudinal axis of the force measuring block. The magnetic grating displacement meter is built into the through hole, and the longitudinal axis of the magnetic grating displacement meter coincides with the longitudinal axis of the force measuring block.

[0009] The center point (u) on the top surface and the center point (d) on the bottom surface of the through hole are concrete deformation monitoring points; the height of the through hole is adapted to the magnetic grating displacement gauge, the center point of the bottom surface of the magnetic grating displacement gauge coincides with the center point (d) on the bottom surface of the through hole, and its deformation monitoring direction is parallel to the axis of the force measuring block; the displacement monitoring point of the magnetic grating displacement gauge is the center point (u) on the top surface of the through hole.

[0010] The deformation monitoring direction is parallel to the axial direction of the force measuring block;

[0011] The ratio of the height of the force measuring block to the height of the entire force gauge is 1:2 to 1:1.1; the ratio of the height of the through hole to the height of the force measuring block is 1:3 to 5:8.

[0012] The upper and lower force-gathering discs, upper and lower force-transmitting plates, and force-measuring blocks are all made of metal materials, and their equivalent elastic modulus is similar to that of the hardened concrete being tested, both being 15-40 GPa.

[0013] Preferably, the deformation range of the magnetic grating displacement gauge needs to be 0-1000µm, and its accuracy is 0.1µm-1µm.

[0014] Preferably, the force measuring block is a smooth-surfaced, regularly shaped cylinder.

[0015] Preferably, both the upper and lower force-collecting disks are circular disks with the same diameter as the force-measuring block; the diameters of the upper and lower force-transmitting plates are not less than 1 / 3 of the diameter of the force-collecting disk; the thickness of the upper and lower force-collecting disks is greater than 5mm, and the length of the upper and lower force-transmitting plates is not greater than 1cm.

[0016] Preferably, one or more threaded rods with a diameter greater than 1 cm and a length greater than 4 cm are welded to the top surface of the upper power collecting plate and the bottom surface of the lower power collecting plate.

[0017] The present invention also provides a concrete stress monitoring structure, which consists of a force gauge based on a magnetic grating displacement meter and an isolation cylinder with flexible structures at both ends;

[0018] The force gauge is built into the isolation cylinder, and the force gauge and the isolation cylinder are coaxial, forming a cylindrical structure;

[0019] The isolation cylinder is made of a material with an elastic modulus of 3 to 8 GPa.

[0020] The flexible structure at both ends of the isolation cylinder is composed of two layers of PP plastic sheets and modeling clay. The two layers of PP plastic sheets form a ring and are bonded to the ends of the isolation cylinder. The modeling clay is filled between the two layers of PP plastic sheets.

[0021] The sum of the lengths of the flexible structures at both ends of the isolation cylinder is 1 / 10 of the length of the isolation cylinder.

[0022] The present invention also provides a method for monitoring concrete stress using a concrete stress monitoring structure, which includes the following steps:

[0023] S1. The force gauge based on the magnetic grating displacement meter is built into an isolation cylinder with flexible structures at both ends, and the concrete to be tested is poured into it from both ends of the isolation cylinder.

[0024] S2. Embed the isolation cylinder containing the force gauge and the concrete to be tested from step S1 into the concrete to be tested. The axial direction of the isolation cylinder coincides with the axial direction of the concrete to be tested. Wait for the concrete to be tested to harden.

[0025] S3. Measure the deformation of the center point (u) on the top surface and the center point (d) on the bottom surface of the inner wall of the through hole of the force measuring block using the magnetic grating displacement gauge inside the force measuring gauge;

[0026] S4. Calculate the concrete stress value σ by measuring the deformation difference between the center point (u) on the top surface and the center point (d) on the bottom surface of the inner wall of the through hole of the force measuring block;

[0027] Under the action of axial force on a large volume of concrete, the displacements of the center points (u) on the top surface and (d) on the bottom surface of the inner wall of the force measuring block are w, respectively. u w dThe deformation difference w between the two points is:

[0028] w = w u -w d (1)

[0029] Let the overall stiffness of the force gauge be K, then the axial force F acting on the force gauge is:

[0030] F = Kw (2)

[0031] The concrete stress value σ is then:

[0032]

[0033] In the formula, σ is the concrete stress, r0 is the radius of the force-collecting disk, E1 is the equivalent elastic modulus of the force gauge, and α s ΔT is the coefficient of linear expansion of the force gauge, and ΔT is the temperature change of the concrete.

[0034] Preferably, if the large volume of concrete to be monitored has not yet formed, the two ends of the isolation cylinder containing the force gauge are filled with the concrete to be tested. Then, it is embedded in the concrete pouring mold, the concrete to be tested is poured, and monitoring is carried out after the concrete to be tested has hardened.

[0035] Preferably, if the concrete to be monitored has hardened, the isolation cylinder needs to be filled with the concrete to be tested first. After the concrete has hardened for 28 days, a rectangular trench is dug at the designated measurement location of the concrete to be tested. The length of the trench is twice the length of the isolation cylinder, and the width and height of the trench are both twice the diameter of the isolation cylinder. The isolation cylinder containing the hardened concrete and the force gauge is placed at the measurement location. At the same time, the position of the isolation cylinder is adjusted so that the cylinder axis is consistent with the direction of concrete monitoring. The cable of the magnetic grating displacement gauge is led out and connected to the data acquisition device to monitor the stress change of the concrete at the measurement location.

[0036] Considering the difference in elastic modulus between the isolation cylinder structure and the monitoring structure and the surrounding concrete, and its impact on concrete stress, the concrete stress value calculated in step S4 is corrected. The specific method is as follows:

[0037] The correction factor is:

[0038]

[0039] In the formula, r0 is the radius of the inner diameter of the isolation cylinder, and r1 is the radius of the outer diameter of the isolation cylinder;

[0040] The overall equivalent elastic modulus E of the monitoring device after the concrete to be tested is poured inside the isolation cylinder CS (τ) is:

[0041] E cs (τ)=Ec (τ)E1h0 / (E c (τ)h1+E1h c (7)

[0042] The corrected concrete stress is:

[0043]

[0044] In the formula: E CS (τ) represents the overall equivalent elastic modulus of the monitoring device after concrete is poured inside the isolation cylinder at time τ, E c (τ) represents the elastic modulus of concrete at age τ, σ(τ) represents the concrete stress value obtained by actual measurement and calculation at time τ, and σ′(τ) represents the corrected concrete stress value at time τ. Attached Figure Description

[0045] Figure 1 is a schematic diagram of the force gauge structure based on the magnetic grating displacement meter of the present invention;

[0046] Figure 2 is a front view of the force gauge based on the magnetic grating displacement meter of the present invention;

[0047] Figure 3 is a schematic diagram of the structure of the force gauge embodiment 2 based on the magnetic grating displacement meter of the present invention;

[0048] Figure 4 is a front view of the monitoring structure of the present invention used for monitoring stress in large-volume concrete;

[0049] Figure 5 is the AA section view of Figure 4;

[0050] Figure 6 is a magnified view of part B in Figure 4;

[0051] Figure 7 is a schematic diagram of the principle of monitoring the stress state of large-volume concrete using a force gauge based on a magnetic grating displacement meter according to the present invention.

[0052] Figure 8 shows the actual stress of large-volume concrete analyzed by finite element simulation and the stress diagram of concrete obtained by monitoring using the present invention.

[0053] Figure 9 shows the concrete stress error detected by the present invention in finite element simulation analysis. Detailed Implementation

[0054] The structure and features of the present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that various modifications can be made to the embodiments disclosed herein; therefore, the embodiments disclosed in this specification should not be considered as limitations on the present invention, but merely as examples to make the features of the present invention readily apparent.

[0055] As shown in Figures 1 and 2, the force gauge based on a magnetic grating displacement meter disclosed in this invention consists of an upper force-collecting plate 1, an upper force-transmitting plate 2, a force-measuring block 3, a lower force-transmitting plate 4, a lower force-collecting plate 5, and a magnetic grating displacement meter 6. The top and bottom surfaces of the force-measuring block 3 are fixedly connected to the upper force-collecting plate 1 and the lower force-transmitting plate 5 through the upper force-transmitting plate 2 and the lower force-transmitting plate 4, respectively, and the upper and lower force-collecting plates, the upper and lower force-transmitting plates, and the force-measuring block are coaxial.

[0056] At the center of the force measuring block 3, a through hole 31 is formed perpendicular to the longitudinal axis of the force measuring block. The magnetic grating displacement meter 6 is installed inside this through hole, and the longitudinal axis of the magnetic grating displacement meter 6 coincides with the longitudinal axis of the force measuring block 3. The force measuring block 3 is a regular-shaped body. The advantage of this design is that when the force measuring block is in direct or indirect contact with the concrete being measured, it can effectively avoid stress concentration inside the concrete caused by the force measuring block itself and stress interference to the surrounding concrete.

[0057] The upper and lower force-collecting plates 1 and 5 of this invention are used to collect the stress of the concrete being tested; the upper and lower force-transmitting plates 2 and 4 are used to transfer the stress collected by the force-collecting plates to the center of the top and bottom surfaces of the force-measuring block 3, so that the load deformation of the force-measuring block mainly occurs at the center of the top and bottom surfaces of the force-measuring block.

[0058] The force-measuring block 3 is the main structure of the entire force gauge that bears stress and deforms. The top and bottom center points u and d of the through hole 31 at the center of the force-measuring block are concrete deformation monitoring points. The magnetic grating displacement gauge 6 monitors the deformation values ​​at points u and d, which are the deformation values ​​of the force-measuring block and the force-collecting disk in the coaxial direction. When manufacturing the through hole 31, the height of the through hole 31 needs to be matched with that of the magnetic grating displacement gauge 6. The center point of the bottom surface of the magnetic grating displacement gauge 6 coincides with the deformation monitoring point d, and the deformation monitoring direction of the magnetic grating displacement gauge 6 is parallel to the axis of the force-measuring block 3. The displacement monitoring point of the magnetic grating displacement gauge coincides with the deformation monitoring point u, and its deformation monitoring direction is parallel to the axis of the force-measuring block.

[0059] The ratio of the height h2 of the force measuring block 3 constituting the present invention to the height h1 of the entire force gauge is 1:2 to 1:1.1; the ratio of the height h3 of the through hole 31 to the height h2 of the force measuring block 3 is 1:3 to 5:8.

[0060] To improve the measurement accuracy of the force gauge in this invention, the upper and lower force-collecting disks 1 and 5, the upper and lower force-transmitting plates 2 and 4, and the force-measuring block 3 are all made of metallic materials (such as stainless steel, iron, copper, etc.), and their equivalent elastic modulus is similar to that of the hardened concrete being measured, both being 15-40 GPa. However, this also leads to a smaller deformation of the force-measuring block under the same axial force, thus requiring the accuracy of the deformation monitoring structure to be compatible with the deformation of the force gauge. Based on this requirement, this invention selects a magnetic grating displacement gauge 6 as the main component of the deformation monitoring structure, with a deformation range of 0-1000 μm and an accuracy of 0.1 μm-1 μm.

[0061] In a preferred embodiment of the present invention, the force measuring block 3 is a smooth-surfaced, regularly shaped cylinder with a diameter of 8 mm. A through hole 31 with a diameter of 5 mm and perpendicular to the longitudinal axis of the force measuring block is opened at the center of the force measuring block. A magnetic grating displacement meter 6 is fixed in the through hole 31, and the magnetic grating displacement meter 6 is coaxially arranged with the force measuring block 3.

[0062] Both the upper force-collecting disk 1 and the lower force-collecting disk 5 are circular disks with the same diameter as the force-measuring block 3. The diameters of the upper and lower force-transmitting plates 2 and 4 are not less than 1 / 3 of the diameter of the force-collecting disk. To avoid self-compression deformation of the force-collecting disk and the force-transmitting plates, the thickness of the upper and lower force-collecting disks must be greater than 5mm, and the length of the upper and lower force-transmitting plates 2 and 4 must not be greater than 1cm.

[0063] To better measure the tensile stress in concrete, as shown in Figure 3, this invention welds one or more threaded rods 7 with a diameter greater than 1 cm and a length greater than 4 cm to the top surface of the upper concentrator 1 and the bottom surface of the lower concentrator 5. If only one is welded, it can be welded at the center of the top surface of the upper concentrator 1 and the bottom surface of the lower concentrator 5. If multiple are welded, the threaded rods can be evenly arranged in a ring on the top surface of the upper concentrator 1 and the bottom surface of the lower concentrator 5.

[0064] When monitoring the stress state of concrete, the force gauge based on the magnetic grating displacement meter of this invention needs to be embedded in the concrete. To accurately measure the stress state of the concrete, as shown in Figure 4, the monitoring structure for monitoring concrete stress of this invention includes the aforementioned force gauge based on the magnetic grating displacement meter and an isolation cylinder 8 with flexible structures at both ends. The force gauge, which houses the magnetic grating displacement meter 6, is built into the isolation cylinder 8, and the force measuring block 3 and the isolation cylinder 8 are coaxial, forming a cylindrical structure to eliminate the stress interference of the surrounding concrete circumferential stress on the entire force gauge.

[0065] The isolation cylinder 8 is made of a material with an elastic modulus of 3-8 GPa, such as polyvinyl chloride. There is a cable hole 81 with a diameter of less than 1 cm at the center of its length direction, from which the cable of the magnetic grating displacement meter is led out.

[0066] As shown in Figures 4-6, the two ends of the isolation cylinder are flexible structures, consisting of two layers of PP plastic sheets 82 and modeling clay 83. The two layers of PP plastic sheets 82 form a ring and are bonded to the ends of the isolation cylinder, while the modeling clay 83 is filled between the two layers of PP plastic sheets 82. The sum of the lengths of the flexible structures at both ends is 1 / 10 of the length of the isolation cylinder.

[0067] In a preferred embodiment of the present invention, a PP plastic sheet with a thickness of 0.1-1mm is selected, and it is glued into a ring with PP plastic special adhesive and glued to the end of the isolation cylinder. Then, modeling clay is filled between the two layers of PP plastic sheets to wrap the end of the isolation cylinder.

[0068] Conventional modeling clay with an elastic modulus of approximately 0.0078 GPa is used to fill the space between two layers of PP plastic sheets. The overall elastic modulus of the flexible structure is almost the same as that of conventional modeling clay, allowing it to deform freely and reducing stress interference to the surrounding concrete at both ends of the isolation cylinder.

[0069] Figure 7 is a schematic diagram of the monitoring structure constructed using a force gauge based on a magnetic grating displacement meter to monitor concrete stress according to the present invention. The method of the present invention for monitoring the stress of large-volume concrete using a force gauge based on a magnetic grating displacement meter is as follows:

[0070] S1. The force gauge based on the magnetic grating displacement meter is built into an isolation cylinder with flexible structures at both ends, and the concrete to be tested is poured into it from both ends of the isolation cylinder.

[0071] S2. Embed the isolation cylinder containing the force gauge and the concrete to be tested from step S1 into the concrete to be tested. The axial direction of the isolation cylinder coincides with the axial direction of the concrete to be tested, and wait for the concrete to harden.

[0072] If the large volume of concrete to be monitored by this invention has not yet been formed, the two ends of the isolation cylinder containing the force gauge are filled with the concrete to be tested. Then, it is embedded in the concrete pouring mold, and the concrete to be tested is poured. After the concrete to be tested hardens, monitoring is carried out.

[0073] If the present invention monitors hardened concrete, the isolation cylinder needs to be filled with the concrete to be tested first, and then the concrete needs to harden for 28 days. A rectangular trench is dug at the designated measurement location of the concrete to be tested. The length of the trench is twice the length of the isolation cylinder, and the width and height of the trench are both twice the diameter of the isolation cylinder. The isolation cylinder containing the hardened concrete and the force gauge is placed at the measurement location, and the position of the isolation cylinder is adjusted so that the cylinder axis is consistent with the direction of concrete monitoring. The cable of the magnetic grating displacement gauge is led out, and then the concrete to be tested is filled in. The cable of the magnetic grating displacement gauge is connected to the data acquisition device, and then the stress change of the concrete at the measurement location can be monitored for a long time.

[0074] In steps S1 and S2 above, if the concrete gradation to be tested is three-grade or higher, the concrete to be tested needs to be wet-sieved before being filled into the isolation cylinder.

[0075] S3. Measure the deformation of the center point u on the top surface and the center point d on the bottom surface of the inner wall of the through hole of the force measuring block using the magnetic grating displacement gauge inside the force measuring gauge;

[0076] S4. Calculate the concrete stress value σ by measuring the deformation difference between the center point u on the top surface and the center point d on the bottom surface of the inner wall of the through-hole of the force measuring block.

[0077] The axial force of the large-volume concrete 9 is transmitted through the concrete force transmission column 10 inside the isolation cylinder 8 to the upper and lower force-collecting disks 1 and 5 on the top and bottom surfaces of the force gauge, and then through the upper and lower force transmission plates 2 and 4 to the deformation monitoring point u at the top center and the deformation monitoring point d at the bottom center of the through hole 31 of the force measuring block 3. When the force measuring block is subjected to axial force, points u and d on the inner wall of the through hole of the force measuring block will deform. The magnetic grating displacement gauge 6 can measure the deformation difference w between the two points. Then, the stress value σ of the large-volume concrete is obtained by solving the algorithm.

[0078] Under the action of axial force on a large volume of concrete, the displacements of the center points u and d on the inner wall of the through hole of the force measuring block are w, respectively. u w d The deformation difference w between the two points is:

[0079] w = w u -w d (1)

[0080] Let the overall stiffness of the force gauge be K, then the axial force F acting on the force gauge is:

[0081] F = Kw (2)

[0082] The concrete stress value σ is then:

[0083]

[0084] In the formula, σ is the concrete stress value, r0 is the radius of the force-collecting plate (i.e., the radius of the inner diameter of the isolation cylinder), E1 is the equivalent elastic modulus of the force gauge, and α s ΔT is the coefficient of linear expansion of the force gauge, and ΔT is the temperature change of the concrete.

[0085] The overall stiffness K and equivalent elastic modulus E1 of the force gauge need to be obtained through actual measurement. A load P is applied to the force gauge using a universal press, and the deformation difference w at points u and d on the inner wall of the force-measuring block is measured using a magnetic displacement gauge. The equivalent elastic modulus E1 and overall stiffness K of the force gauge are calculated using the following formulas:

[0086]

[0087] In the formula, P is the load applied to the force gauge, r0 is the radius of the force collecting plate, i.e. the radius of the inner diameter of the isolation cylinder, w is the deformation difference between point u and point d at the center of the through hole of the force measuring block, and h3 is the height of the through hole of the force measuring block.

[0088] Analyzing the monitoring structure shown in Figure 4 for monitoring concrete stress, when the external concrete axial force acts on the isolation cylinder and the internal concrete force-transfer column, the isolation cylinder experiences almost no force due to its low elastic modulus and the presence of flexible materials at both ends. However, the cross-sectional area of ​​the concrete force-transfer column is weakened by the cylinder wall and needs correction. The correction factor is:

[0089]

[0090] In the formula, r0 is the radius of the inner diameter of the isolation cylinder, and r1 is the radius of the outer diameter of the isolation cylinder, as shown in Figure 5.

[0091] Let the total height of the force gauge be h1, and the total height of the concrete force transmission column inside the isolation cylinder be h. c The total height of the monitored structure is h0, and the elastic modulus of concrete at different ages is E. c (τ), when no concrete is poured inside the isolation cylinder, the overall equivalent elastic modulus of the monitoring device is E1. Then, after concrete is poured inside the isolation cylinder, the overall equivalent elastic modulus of the monitoring device is E1. CS (τ) is:

[0092] E cs (τ)=E c (τ)E1h0 / (E c (τ)h1+E1h c (7)

[0093] Therefore, the concrete stress value after simultaneously correcting for structural effects and elastic modulus differences is:

[0094]

[0095] In the formula: E cs (τ) represents the overall equivalent elastic modulus of the monitoring device after concrete is poured inside the isolation cylinder at time τ, E c (τ) represents the elastic modulus of concrete at age τ, σ(τ) represents the concrete stress value obtained by actual measurement and calculation at time τ, and σ′(τ) represents the corrected concrete stress value at time τ.

[0096] Given that the elastic modulus of the force gauge material is 208 GPa and the elastic modulus of concrete is 41 GPa, the stress in the large-volume concrete monitored by the force gauge based on the magnetic grating displacement gauge of this invention is calculated to be 15.4 GPa by finite element method. Through finite element simulation analysis, when the elastic modulus of the measured concrete remains unchanged, the measurement results and the actual stress values ​​are shown in Figure 8, and the measurement error is less than 0.01 MPa, as shown in Figure 9.

[0097] The monitoring structure and method for monitoring stress in large-volume concrete provided by this invention have the following advantages compared with traditional measuring devices and methods:

[0098] 1. First, the structural design and material selection of the force gauge based on the magnetic grating displacement meter that constitutes the monitoring structure make the equivalent elastic modulus E1 of the force gauge relatively large, ranging from 15-40 GPa, which is similar to the elastic modulus of the large volume concrete being measured. Therefore, the equivalent elastic modulus E1 of the measuring device is similar to the elastic modulus of the concrete, which can ensure that the monitored stress value obtained by the monitoring equipment is similar to the actual stress value of the concrete.

[0099] 2. This invention takes into account the influence of differences in the structure and elastic modulus of the monitoring materials on the measurement of the stress in the concrete being tested, and makes corrections accordingly, thus ensuring the feasibility of monitoring the stress in concrete using the monitoring structure in principle.

[0100] 3. From the perspective of monitoring accuracy, the deformation caused by external forces on the force gauge is on the same order of magnitude as the concrete deformation. Accurate monitoring of even the minute deformations caused by external forces is crucial for obtaining precise stress measurements. This invention uses a force gauge based on a magnetic grating displacement meter, which boasts micron-level monitoring accuracy and is also waterproof, heat-resistant, and oil-resistant. This ensures both high accuracy and the durability of the monitored structure. It provides reliable equipment support for concrete stress monitoring and provides accurate and reliable stress data to support the safe operation of large-volume concrete structures.

[0101] Finally, it should be noted that the above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for monitoring concrete stress, characterized in that: The process includes the following steps: S1. A force gauge based on a magnetic grating displacement meter is embedded within an isolation cylinder with flexible ends. The concrete to be measured is then poured into the isolation cylinder from both ends. Specifically, the force gauge is embedded within the isolation cylinder, and the force-transmitting block and the isolation cylinder are coaxial, forming a cylindrical structure to eliminate stress interference from the surrounding concrete's circumferential stress on the entire force gauge. The force gauge based on the magnetic grating displacement meter consists of an upper force-transmitting plate, an upper force-transmitting plate, a force-transmitting block, a lower force-transmitting plate, a lower force-transmitting plate, and a magnetic grating displacement meter. The top and bottom surfaces of the force-transmitting block are respectively... The upper and lower force transmission plates are fixedly connected to the upper and lower force collection disks, and the upper and lower force collection disks, upper and lower force transmission plates, and force measuring block are coaxial. The force measuring block is a regular-shaped body, and a through hole is opened at the center of the force measuring block along a direction perpendicular to the longitudinal axis of the force measuring block. The magnetic grating displacement gauge is built into the through hole, and the longitudinal axis of the magnetic grating displacement gauge coincides with the longitudinal axis of the force measuring block. For the isolation cylinder with flexible structures at both ends, the force measuring gauge is built into the isolation cylinder, and the force measuring gauge and the isolation cylinder are coaxial, forming a cylindrical structure. The isolation cylinder is made of a material with an elastic modulus of 3-8 GPa; the flexible structure at both ends of the isolation cylinder consists of two layers of PP plastic sheets and modeling clay, with the two layers of PP plastic sheets forming a ring and bonded to the ends of the isolation cylinder, and the modeling clay filling the space between the two layers of PP plastic sheets; the sum of the lengths of the flexible structures at both ends of the isolation cylinder is 1 / 10 of the length of the isolation cylinder; S2, embed the isolation cylinder containing the force gauge and the concrete to be tested from step S1 into the concrete to be tested, with the axial direction of the isolation cylinder coinciding with the axial direction of the concrete to be tested, and wait for the concrete to harden; S3, measure the deformation of the center point (u) on the top surface and the center point (d) on the bottom surface of the inner wall of the through hole of the force measuring block using the magnetic grating displacement gauge inside the force gauge; the through hole The center point (u) on the top surface and the center point (d) on the bottom surface of the hole are concrete deformation monitoring points; the height of the through hole is adapted to the magnetic grating displacement gauge, the center point of the bottom surface of the magnetic grating displacement gauge coincides with the center point (d) on the bottom surface of the through hole, and its deformation monitoring direction is parallel to the axis of the force measuring block; the displacement monitoring point of the magnetic grating displacement gauge coincides with the center point (u) on the top surface of the through hole, and its deformation monitoring direction is parallel to the axis of the force measuring block; S4, calculate the concrete stress value σ by measuring the deformation difference between the center point (u) on the top surface and the center point (d) on the bottom surface of the inner wall of the through hole of the force measuring block; under the action of the axial force of the large volume concrete, the displacements of the center point (u) on the top surface and the center point (d) on the bottom surface of the inner wall of the through hole of the force measuring block are respectively w u w d The deformation difference w between the two points is: w = w u -w d (1) Let the overall stiffness of the force gauge be K, then the axial force F on the force gauge is: F = Kw (2) Then the concrete stress value σ is: In the formula, σ is the concrete stress, r0 is the radius of the force-collecting disk, E1 is the equivalent elastic modulus of the force gauge, and α s ΔT is the linear expansion coefficient of the force gauge, and ΔT is the concrete temperature change value. If the large volume of concrete to be monitored has not yet formed, first fill both ends of the isolation cylinder containing the force gauge with the concrete to be tested, then embed it in the concrete casting mold, pour the concrete to be tested, and monitor it after the concrete to be tested hardens. If the concrete to be monitored has hardened, first fill the isolation cylinder with the concrete to be tested, and after the concrete has hardened for 28 days, dig a rectangular trench at the designated measurement position of the concrete to be tested. The length of the trench is twice the length of the isolation cylinder, and the width and height of the trench are both twice the diameter of the isolation cylinder. Place the isolation cylinder containing the hardened concrete and the force gauge at the measurement position, and adjust the position of the isolation cylinder so that the cylinder axis is consistent with the direction of concrete monitoring. Lead out the cable of the magnetic grating displacement meter and connect it to the data acquisition device to monitor the concrete stress change at the measurement position. Considering the difference between the structure of the isolation cylinder and the elastic modulus of the monitoring structure and the surrounding concrete, the concrete stress value calculated in step S4 is corrected. The specific method is as follows: the correction coefficient is: In the formula, r0 is the radius of the inner diameter of the isolation cylinder, and r1 is the radius of the outer diameter of the isolation cylinder; the overall equivalent elastic modulus E of the monitoring device after the concrete to be tested is poured into the isolation cylinder. CS (τ) is: E cs (τ)=E c (τ)E1h0 / (E c (τ)h1+E1h c (7) The corrected concrete stress is: In the formula: E CS (τ) represents the overall equivalent elastic modulus of the monitoring device after concrete is poured inside the isolation cylinder at time τ, E c σ(τ) represents the elastic modulus of concrete at age τ, σ(τ) represents the concrete stress value calculated from actual measurements at time τ, and σ′(τ) represents the corrected concrete stress value at time τ. The ratio of the height of the force-measuring block to the height of the entire force gauge is 1:2 to 1:1.1; the ratio of the height of the through hole to the height of the force-measuring block is 1:3 to 5:8; the upper and lower force-collecting plates, upper and lower force-transmitting plates, and the force-measuring block are all made of metal, and their equivalent elastic modulus is equal to the elastic modulus of the hardened concrete. The magnitudes are similar, both ranging from 15-40 GPa; the deformation range of the magnetic grating displacement gauge must meet the requirement of 0-1000 μm, with an accuracy of 0.1 μm-1 μm; the force measuring block is a smooth-surfaced, regularly shaped cylinder; both the upper and lower force collecting disks are circular disks with the same diameter as the force measuring block; the diameters of the upper and lower force transmitting plates are not less than 1 / 3 of the diameter of the force collecting disk; the thickness of the upper and lower force collecting disks is greater than 5 mm, and the length of the upper and lower force transmitting plates is not greater than 1 cm; 2. The method according to claim 1, characterized in that: One or more threaded rods with a diameter greater than 1 cm and a length greater than 4 cm are welded to the top surface of the upper power collecting plate and the bottom surface of the lower power collecting plate.

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