Method for correcting measured values of cylinder-type concrete stress meter

Abstract

This invention provides a method for correcting the measured values ​​of a cylindrical concrete stress gauge. It measures the axial deformation of concrete using a monitoring device with a built-in magnetic displacement gauge, then calculates the stress value of the measured concrete. Finally, considering the influence of the measuring device, concrete temperature changes, and its own volume deformation on the measurement results, the calculated concrete stress value is corrected to make the calculated result closer to the actual concrete stress value. Finite element simulation analysis verifies that the concrete stress value monitored using the method disclosed in this invention has a very small error compared to the actual value.

Description

Technical Field

[0001] This invention relates to a method for obtaining the stress of large-volume concrete, specifically, to a method that not only monitors the stress of large-volume concrete, but also corrects the monitoring results to make the obtained concrete stress closer to the true value. 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 differences between the strain gauge material properties and the concrete material properties result in inaccurate measured strain values ​​and 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. Summary of the Invention

[0003] For the reasons mentioned above, the purpose of this invention is to provide a method for correcting the measured values ​​of a cylindrical concrete stress gauge.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a method for correcting the measured values ​​of a cylindrical concrete stress gauge, comprising the following steps:

[0005] S1. Prepare a monitoring device for monitoring the stress of large-volume concrete;

[0006] The monitoring device includes a force gauge and an isolation cylinder. The force gauge is vertically built into the isolation cylinder and is coaxial with the isolation cylinder.

[0007] The force gauge includes a cylindrical force measuring block. At the center of the force measuring block, a through hole is opened in a direction perpendicular to the longitudinal axis of the force measuring block. A magnetic grating displacement meter is fixed in the through hole, and the longitudinal axis of the magnetic grating displacement meter coincides with the longitudinal axis of the force measuring block.

[0008] The top center point (u) and bottom center point (d) of the through hole are concrete deformation monitoring points; the height of the through hole is adapted to the magnetic grating displacement meter, the bottom center point of the magnetic grating displacement meter coincides with the bottom center point (d) of the through hole, and its deformation monitoring direction is parallel to the normal of the bottom surface of the through hole; the displacement monitoring point of the magnetic grating displacement meter coincides with the top center point (u) of the through hole, and its deformation monitoring direction is parallel to the normal of the top of the force measuring block; the ratio of the height of the through hole to the height of the force measuring block is 1:3 to 5:8;

[0009] The force measuring block is made of metal material, and its equivalent elastic modulus is similar to that of the hardened concrete being tested, both being 15-40 GPa.

[0010] The isolation cylinder is made of a material with an elastic modulus of 3~8 GPa;

[0011] S2. Fill the isolation cylinder of the monitoring device with the concrete to be tested, forming concrete force transmission columns at both ends of the force gauge, and wait for the concrete force transmission columns to harden.

[0012] S3. Vertically embed the monitoring device after the concrete force transmission column in step S2 has hardened into the large volume of concrete to be tested, with the axial direction of the monitoring device coinciding with the axial direction of the concrete to be tested.

[0013] If the large volume of concrete to be monitored has not yet formed, the monitoring device is directly embedded vertically in the casting mold of the large volume of concrete to be measured, and the concrete to be measured is poured. After the concrete to be measured hardens, the monitoring is carried out.

[0014] If the monitored object is a hardened large volume of concrete, a rectangular trench is dug at the designated measurement location of the concrete. The length of the trench is twice the length of the isolation cylinder, and the width and height of the trench are twice the diameter of the isolation cylinder. The entire monitoring device is placed at the measurement location, and the isolation cylinder is adjusted so that its axis is aligned with the direction of the concrete being monitored. The cable of the magnetic grating displacement meter is led out and connected to the data acquisition unit. Then, the stress change of the concrete at the measurement location can be monitored for a long period of time.

[0015] S4. Measure the deformation values ​​of the top center point (u) and bottom center point (d) of the through hole of the force measuring block using the force gauge in the monitoring device;

[0016] S5. Calculate the stress value σ of the concrete being tested by measuring the deformation difference between the top center point (u) and the bottom center point (d) of the through hole of the force measuring block.

[0017] Under the action of axial force on a large volume of concrete, the displacements of the top center point (u) and bottom center point (d) of the through hole of the force measuring block are w, respectively. u w d The deformation value w between the two points is:

[0018]

[0019] Let the overall stiffness of the force gauge be K, then the axial force F acting on the force gauge is:

[0020]

[0021] The measured stress value σ of the concrete is:

[0022]

[0023] In the formula, σ is the measured concrete stress value, r0 is the radius of the inner diameter of the isolation cylinder, E1 is the equivalent elastic modulus of the force gauge, and α s The linear expansion coefficient of the force gauge is... This represents the temperature change value of the concrete.

[0024] S6. Modify the measured concrete stress value σ obtained in step S5:

[0025] S6.1 Considering the influence of the isolation cylinder on the concrete force transmission column inside the cylinder and the difference between the force gauge and the elastic modulus of the concrete, the measured concrete stress value σ obtained in step S5 is corrected as follows:

[0026] The correction factor is:

[0027]

[0028] 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;

[0029] The overall equivalent elastic modulus E of the monitoring device for the τ-year after concrete pouring inside the isolation cylinder cs (τ) is:

[0030]

[0031] In the formula, h1 is the total height of the force gauge inside the monitoring device, h0 is the total height of the monitoring device, and h c E represents the total height of the concrete force-transfer columns inside the isolation cylinder. c (τ) represents the elastic modulus of concrete at age τ, and E1 represents the equivalent elastic modulus of the force gauge when no concrete is poured inside the isolation cylinder.

[0032] The corrected measured concrete stress value σ'(τ) at age τ is:

[0033]

[0034] In the formula: E cs (τ) represents the overall equivalent elastic modulus of the age-τ monitoring device, E cσ(τ) is the elastic modulus of concrete at age τ, σ(τ) is the measured stress value of concrete at age τ obtained by actual measurement calculation, and σ'(τ) is the corrected measured stress value of concrete at age τ.

[0035] S6.2 Considering the impact of the change in elastic modulus of large-volume concrete during hydration on stress monitoring, the stress value of the measured concrete obtained in step S6.1 is further corrected.

[0036] The corrected formula is as follows:

[0037]

[0038] In the formula: σ1(τ) is the measured concrete stress value at age τ after correction of the elastic modulus, E c (τ) represents the elastic modulus of the concrete outside the cylinder at age τ, E c (∞) represents the elastic modulus of the concrete outside the cylinder after hydration and stabilization;

[0039]

[0040]

[0041] In the above formula, α c Let α be the coefficient of linear expansion of the concrete being tested. s E is the linear expansion coefficient of the force gauge, E1 is the equivalent elastic modulus of the force gauge, and E c This refers to the elastic modulus of the concrete outside the cylinder. Due to changes in concrete temperature, ε' represents the change in volumetric deformation of concrete at age τ, ε' represents the coefficient of linear expansion and the additional strain caused by its volumetric deformation, and σ2(τ) represents the additional stress generated by the coefficient of linear expansion and its volumetric deformation at age τ.

[0042] The above formula can be used to obtain the measured concrete stress value at age τ after correcting for the influence of the main material parameters. The calculation formula is as follows:

[0043] .

[0044] In a preferred embodiment of the present invention, the deformation range of the magnetic grating displacement gauge is 0-1000µm, and its accuracy is 0.1µm-1µm.

[0045] The force gauge also includes an upper force-collecting plate, an upper force-transmitting plate, a lower force-transmitting plate, and a lower force-collecting plate; the top and bottom surfaces of the force-measuring block are fixedly connected to the upper and lower force-collecting plates respectively through the upper and lower force-transmitting plates, and the upper and lower force-collecting plates, the upper and lower force-transmitting plates, and the force-measuring block are coaxial; the upper and lower force-collecting plates and the upper and lower force-transmitting plates 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.

[0046] 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 disks; 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; 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.

[0047] The two ends of the isolation cylinder are flexible structures, which are 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. 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.

[0048] 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. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the monitoring device for monitoring stress in large-volume concrete according to the present invention.

[0050] Figure 2 This is a schematic diagram of the force gauge structure based on the magnetic grating displacement meter of the present invention;

[0051] Figure 3 This is a front view of the force gauge based on the magnetic grating displacement meter of the present invention;

[0052] Figure 4 for Figure 1 A magnified view of section B;

[0053] Figure 5 for Figure 1 AA cross-section diagram;

[0054] Figure 6 This is a schematic diagram of the structure of embodiment 2 of the force gauge based on the magnetic grating displacement meter of the present invention;

[0055] Figure 7 A comparison chart of the actual concrete stress obtained by FEM when Ec does not change with age and the monitored stress obtained by monitoring using the present invention.

[0056] Figure 8The error diagram between the concrete stress monitored using this invention and the actual stress obtained by FEM analysis when Ec does not change with age is shown.

[0057] Figure 9 This is a simplified diagram of the internal structure of the monitoring device of the present invention;

[0058] Figure 10 A comparison diagram of the actual concrete stress obtained by FEM and the monitored stress obtained by monitoring using the present invention when Ec changes with age;

[0059] Figure 11 This is an error diagram of the concrete stress monitored using this invention and the actual stress obtained by FEM analysis when Ec changes with age.

[0060] Figure 12 A comparison chart of the actual concrete stress obtained by FEM and the monitored stress corrected by the algorithm of this invention when Ec changes with age;

[0061] Figure 13 This is an error diagram of the monitored stress and the actual stress obtained by FEM analysis when Ec changes with age, after correction using the algorithm of this invention. Detailed Implementation

[0062] 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.

[0063] To obtain the stress of large-volume concrete, this invention designs a monitoring device for monitoring the stress of large-volume concrete, such as... Figures 1-5 As shown, it consists of a force gauge 1 and an isolation cylinder 2. The force gauge 1 is built into the isolation cylinder 2, and the force gauge 1 and the isolation cylinder 2 are coaxial.

[0064] The force gauge 1 consists of an upper force-collecting plate 11, an upper force-transmitting plate 12, a force-measuring block 13, a lower force-transmitting plate 14, a lower force-collecting plate 15, and a magnetic grating displacement meter 16. The top and bottom surfaces of the force-measuring block 13 are fixedly connected to the upper force-collecting plate 11 and the lower force-transmitting plate 15 through the upper force-transmitting plate 12 and the lower force-transmitting plate 14, respectively, and the upper and lower force-collecting plates, the upper and lower force-transmitting plates, and the force-measuring block are coaxial.

[0065] At the center of the force-measuring block 13, a through hole 131 is formed perpendicular to the longitudinal axis of the force-measuring block. The magnetic grating displacement meter 16 is installed inside the through hole, and the longitudinal axis of the magnetic grating displacement meter 16 coincides with the longitudinal axis of the force-measuring block 13. The force-measuring block 13 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.

[0066] The function of the upper and lower force-collecting plates is to collect the stress of the concrete being tested; the function of the upper and lower force-transmitting plates is to transfer the stress collected by the force-collecting plates to the center of the top and bottom surfaces of the force-measuring block, so that the deformation of the force-measuring block mainly occurs at the center of the top and bottom surfaces of the force-measuring block.

[0067] The force-measuring block 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 at the center of the force-measuring block are the concrete deformation monitoring points. The magnetic grating displacement gauge monitors the deformation values ​​at points u and d, which are the axial deformation values ​​of the large-volume concrete. When manufacturing the through hole 131, it is necessary to adapt the height of the through hole 131 to the magnetic grating displacement gauge 16. The center point of the bottom surface of the magnetic grating displacement gauge coincides with the deformation monitoring point d, and the deformation monitoring direction of the magnetic grating displacement gauge is parallel to the normal of the bottom surface of the through hole; 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 normal of the upper force-collecting plate.

[0068] The ratio of the height h2 of the force measuring block 13 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 13 is 1:3 to 5:8.

[0069] To improve the measurement accuracy of the monitoring device, the upper and lower force-collecting discs, upper and lower force-transmitting plates, and force-measuring blocks are all made of metallic materials (such as stainless steel, iron, copper, etc.), with an equivalent elastic modulus similar to that of the hardened concrete being measured, ranging from 15 to 40 GPa. This further results in smaller deformation of the force-measuring block under the same axial force, thus requiring the accuracy of the deformation monitoring device to be compatible with the deformation of the force gauge. Based on this requirement, the present invention selects a magnetic grating displacement gauge 16 as the core component of the deformation monitoring device, with a deformation range of 0-1000 μm and an accuracy of 0.1 μm-1 μm.

[0070] In a preferred embodiment of the present invention, the force measuring block 13 is a smooth, regularly shaped cylinder with a diameter of 8 mm. A through hole with a diameter of 5 mm, perpendicular to the longitudinal axis of the force measuring block, is formed at the center of the force measuring block. Both the upper and lower force collecting disks are circular, 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. To prevent self-compression deformation of the force collecting disks and force transmitting plates, the thickness of the upper and lower force collecting disks must be greater than 5 mm, and the length of the upper and lower force transmitting plates must not exceed 1 cm.

[0071] When monitoring the stress state of concrete, the monitoring device needs to be embedded in the concrete. To accurately measure the stress state of the concrete, such as... Figure 1 As shown, in this invention, the force gauge 1 is placed inside the isolation cylinder 2. The force gauge 1 and the isolation cylinder 2 are coaxial, forming a cylindrical structure, so as to eliminate the stress interference of the surrounding concrete circumferential stress on the entire force gauge.

[0072] The isolation cylinder 2 is made of a material with an elastic modulus of 3-8 GPa, such as polyvinyl chloride. It has a cable hole 21 with a diameter less than 1 cm at its center along its length, from which the cable of the magnetic grating displacement gauge exits. Both ends of the isolation cylinder are flexible structures, such as... Figure 4 , Figure 5 As shown, it consists of two layers of PP plastic sheets 22 and modeling clay 23. The two layers of PP plastic sheets form a ring and are bonded to the end of the isolation cylinder. The modeling clay is filled between the two layers of PP plastic sheets. The sum of the lengths of the flexible structures at both ends is 1 / 10 of the length of the isolation cylinder.

[0073] 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.

[0074] 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.

[0075] To better measure the tensile stress in concrete, such as Figure 6 As shown, one or more threaded rods 17 with a diameter greater than 1 cm and a length greater than 4 cm can be welded to the top surface of the upper force-collecting plate 11 and the bottom surface of the lower force-collecting plate 15 of the force gauge. If only one threaded rod is welded, it can be welded at the center of the top surface of the upper force-collecting plate 11 and the bottom surface of the lower force-collecting plate 15. If multiple threaded rods are welded, the threaded rods can be evenly arranged in a ring on the top surface of the upper force-collecting plate 11 and the bottom surface of the lower force-collecting plate 15.

[0076] The method for monitoring and correcting the obtained concrete stress using the aforementioned large-volume concrete stress monitoring device is as follows:

[0077] S1. Fill the isolation cylinder of the large-volume concrete stress monitoring device with the concrete to be tested, forming concrete force transmission columns 3 at both ends of the force gauge (see...). Figure 1 (Wait for the concrete to harden.)

[0078] S2. Vertically embed the monitoring device, which has been hardened in step S1, into the large-volume concrete 4 to be measured (see...). Figure 1In the middle, the large volume of concrete to be tested is waiting to harden.

[0079] If the large-volume concrete to be monitored by this invention has not yet been formed, the monitoring device is directly embedded in the casting mold of the large-volume concrete to be tested, and the concrete to be tested is poured. After the concrete to be tested hardens, monitoring is carried out.

[0080] If the present invention monitors a large volume of hardened concrete, the test concrete needs to be filled into the isolation cylinder first, and then the concrete needs to be hardened for 28 days. A rectangular trench is dug at the designated measurement location of the large volume of concrete to be tested. The length of the trench is twice the length of the isolation cylinder of the monitoring device, and the width and height of the trench are twice the diameter of the isolation cylinder. The monitoring device is placed at the measurement location, and the position of the monitoring device is adjusted so that the axial direction of the isolation cylinder constituting the monitoring device is consistent with the direction of concrete monitoring. The cable of the magnetic grating displacement meter is led out and connected to the data acquisition device. Then, the stress change of the concrete at the measurement location can be monitored for a long time.

[0081] During the implementation of 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.

[0082] S3. Measure the deformation of the top center point u and bottom center point d of the through hole of the force measuring block by measuring the force gauge in the monitoring device.

[0083] S4. Calculate the stress value σ of the concrete being measured by measuring the deformation difference between the top center point u and the bottom center point d of the through hole of the force measuring block.

[0084] The axial force F of the large-volume concrete 4 is transmitted through the concrete force transmission column 3 inside the isolation cylinder 2 to the upper and lower force-collecting disks 11 and 15 on the top and bottom surfaces of the force gauge 1, and then through the upper and lower force transmission plates 12 and 14 to the deformation monitoring point u at the top center and the deformation monitoring point d at the bottom center of the through hole 131 of the force measuring block. When the force measuring block is subjected to axial force, the through holes u and d of the force measuring block will deform. The magnetic grating displacement gauge 16 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.

[0085] Under the action of axial force on a large volume of concrete, the displacements of points u and d at the center of the through hole 131 of the force measuring block are w, respectively. u w d The deformation value w between the two points is:

[0086] (1)

[0087] Let the overall stiffness of the force gauge be K, then the axial force F acting on the force gauge is:

[0088] (2)

[0089] The concrete stress value σ is then:

[0090] (3)

[0091] 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 The linear expansion coefficient of the force gauge is... This represents the temperature change value of the concrete.

[0092] 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 w at point u and d of the through-hole of the force gauge 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:

[0093] (4)

[0094] (5)

[0095] 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.

[0096] S5. Modify the concrete stress value σ calculated in step S4:

[0097] S5.1 Considering the influence of the isolation cylinder on the concrete force transmission column inside the cylinder, the concrete stress value σ obtained in step S4 is corrected.

[0098] analyze Figure 1 The structure of the monitoring device shown is used to monitor concrete stress. When the external axial force of the concrete 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 to be corrected. The correction factor is:

[0099] (6)

[0100] 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. (See [reference needed]) Figure 5 Let the total height of the force gauge inside the monitoring device be h1 ( Figure 3 The total height of the force gauge is h1), and the total height of the concrete force transmission column inside the isolation cylinder is h. c The total height of the monitoring device is h0, and the elastic modulus of the concrete at age τ 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 the concrete is poured inside the isolation cylinder, the overall equivalent elastic modulus of the monitoring device at age τ is E1. CS (τ) is:

[0101] (7)

[0102] Therefore, the measured stress value of concrete at age τ after simultaneously correcting for the influence of the monitoring device structure and the difference in elastic modulus is:

[0103] (8)

[0104] In the formula: E CS (τ) represents the overall equivalent elastic modulus of the age-τ monitoring device, E c (τ) represents the elastic modulus of concrete at age τ, σ(τ) represents the concrete stress value obtained from actual measurement at age τ, and σ' (τ) represents the corrected concrete stress value at age τ.

[0105] Given a force gauge material elastic modulus of 208 GPa and a concrete elastic modulus of 41 GPa, the stress value of the large-volume concrete monitored by the device of this invention, calculated using a finite element model (FEM), yields an equivalent elastic modulus of 15.4 GPa. Through finite element simulation analysis, when the elastic modulus of the measured concrete remains constant, the measured results and the actual stress values ​​are as follows: Figure 7 As shown, the measurement error is less than 0.01 MPa. Figure 8 As shown.

[0106] S5.2. Considering the change in the elastic modulus of large-volume concrete during hydration and the influence of the main material properties of concrete on stress monitoring, the concrete stress value σ obtained in step S4 is corrected.

[0107] In the later stages of concrete hydration, stress monitoring is highly accurate and can represent the true stress value of concrete. However, to monitor the stress changes of concrete throughout its entire life cycle, it is necessary to consider the impact of changes in the elastic modulus of concrete during hydration on stress monitoring. Simultaneously, the influence of stress-free deformation caused by temperature changes and its own volume deformation on concrete stress monitoring needs to be eliminated. Therefore, the concrete stress value calculated in step S5.1 needs to be corrected. The specific correction method is as follows:

[0108] First, since the isolation cylinder contains a combination of the concrete being measured and a force gauge, and the force gauge is made of metal, its elastic modulus does not change with age. The measurement error of the cylinder-type force gauge is minimized when the equivalent elastic modulus E1 of the force gauge 1 inside the isolation cylinder is equal to the elastic modulus Ec of the concrete force transmission column 3. Concrete undergoes a hydration and hardening process, and the concrete elastic modulus changes from Ec(0) to Ec(∞), making it difficult to achieve E1=Ec(τ). This leads to a difference between the overall average elastic modulus of the monitoring device and the external concrete being measured. When the concrete structure is subjected to external forces, the hydration characteristics of the concrete cause the equivalent elastic modulus inside the isolation cylinder to be higher than that outside in the early age and lower than that outside in the later age (because the elastic modulus solution of the metal sensor is higher than that of the concrete in the early age, and lower than that of the concrete in the later age). The stress inside the cylinder differs from that outside. Therefore, the elastic modulus needs to be corrected, and the correction formula is as follows:

[0109] (9)

[0110] In the formula: σ1(τ) is the measured concrete stress value at age τ after correction of the elastic modulus, E c (τ) represents the elastic modulus of the concrete outside the cylinder at age τ, E c (∞) represents the elastic modulus of the concrete outside the cylinder after hydration and stabilization.

[0111] Secondly, the linear expansion coefficient and volume deformation of concrete are inherent properties of the material. These two factors will cause strain in the concrete force transmission column inside the isolation cylinder during temperature changes and concrete hydration. The strain, combined with the elastic modulus of the material, will generate stress. This additional stress is generated during the concrete hydration period and will continue to exist in the stress monitoring process for a long time, so it needs to be corrected.

[0112] The isolation cylinder is divided into two parts: a concrete force transmission column and a metal force gauge. This simplifies the internal structure of the monitoring device. Figure 9 As shown, it is divided into two parts: a metal force transmission plate and a concrete force transmission column.

[0113] (10)

[0114] (11)

[0115] In the above formula, α c Let α be the coefficient of linear expansion of the concrete being tested. s E is the linear expansion coefficient of the force gauge, E1 is the equivalent elastic modulus of the force gauge, and E c This refers to the elastic modulus of the concrete outside the cylinder. Due to changes in concrete temperature, ε' represents the volumetric deformation of the concrete at age τ, ε' represents the coefficient of linear expansion and the additional strain caused by its volumetric deformation, and σ2(τ) represents the additional stress generated by the coefficient of linear expansion and its volumetric deformation at age τ.

[0116] The above formula can be used to obtain the measured concrete stress value at age τ after correcting for the influence of the main material parameters. The calculation formula is as follows:

[0117] (12).

[0118] The accuracy of the algorithm was verified using finite element simulation analysis. Given a material elastic modulus of 208 GPa and a concrete elastic modulus of Ec(τ) = 41*(1-e^(-0.4τ^0.5)), the concrete elastic modulus varies from 0 to 41 GPa over the specified age τ. c α is 0.000006 (1 / ℃). s The value is 0.000012 (1 / ℃). The finite element method (FEM) calculation shows the force gauge elastic modulus to be 15.4 GPa. The calculation result without algorithm correction is as follows: Figure 10 As shown, its error is as follows Figure 11 As shown, the calculation results when using the algorithm for correction are as follows: Figure 12 As shown, its error is as follows Figure 13 As shown.

[0119] Finite element simulation verification shows that when considering the changes in concrete material properties with age, the measurement method described in this patent, after correction by the above algorithm, reduces the error from 2.5 MPa before correction to 0.1 MPa after correction.

[0120] This invention is based on a monitoring device for monitoring the stress of large-volume concrete using a force gauge based on a magnetic grating displacement meter. It proposes a stress measurement error correction algorithm for this structure. This algorithm considers and corrects the differences in material properties between the concrete and the monitoring device, as well as the interference of temperature changes and volume deformation of the large-volume concrete on the concrete stress measurement. This invention is applicable to monitoring concrete stress during hydration and under complex conditions such as temperature changes, obtaining the stress value of the concrete in the measured direction under real conditions. It solves the problems of difficulty in traditional stress monitoring, the complexity of secondary stress calculation using strain gauge groups, and the difficulty in obtaining the true stress state of concrete. This provides reliable technical support for concrete stress monitoring and provides reliable stress state data support for the safe operation of large-volume concrete structures.

[0121] 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 correcting the measured values ​​of a cylindrical concrete stress gauge, characterized in that: S1. Prepare a monitoring device for monitoring the stress of large-volume concrete; The monitoring device includes a force gauge and an isolation cylinder. The force gauge is vertically built into the isolation cylinder and is coaxial with the isolation cylinder. The force gauge includes a cylindrical force measuring block. At the center of the force measuring block, a through hole is opened in a direction perpendicular to the longitudinal axis of the force measuring block. A magnetic grating displacement meter is fixed in the through hole, and the longitudinal axis of the magnetic grating displacement meter coincides with the longitudinal axis of the force measuring block. The top center point (u) and bottom center point (d) of the through hole are concrete deformation monitoring points; the height of the through hole is adapted to the magnetic grating displacement gauge, the bottom center point of the magnetic grating displacement gauge coincides with the bottom center point (d) of the through hole, and its deformation monitoring direction is parallel to the axial direction of the force measuring block; the displacement monitoring point of the magnetic grating displacement gauge coincides with the top center point (u) of the through hole, and its deformation monitoring direction is parallel to the normal direction of the axial direction of the force measuring block; the ratio of the height of the through hole to the height of the force measuring block is 1:3 to 5:8; The force measuring block is made of metal material, and its equivalent elastic modulus is similar to that of the hardened concrete being tested, both being 15-40 GPa. The isolation cylinder is made of a material with an elastic modulus of 3~8 GPa; S2. Fill the isolation cylinder of the monitoring device with the concrete to be tested, forming concrete force transmission columns at both ends of the force gauge, and wait for the concrete force transmission columns to harden. S3. Vertically embed the monitoring device after the concrete force transmission column in step S2 has hardened into the large volume of concrete to be tested, with the axial direction of the monitoring device coinciding with the axial direction of the concrete to be tested. If the large volume of concrete to be monitored has not yet formed, the monitoring device is directly embedded vertically in the casting mold of the large volume of concrete to be measured, and the concrete to be measured is poured. After the concrete to be measured hardens, the monitoring is carried out. If the monitored object is a hardened large volume of concrete, a rectangular trench is dug at the designated measurement location of the concrete. The length of the trench is twice the length of the isolation cylinder, and the width and height of the trench are twice the diameter of the isolation cylinder. The entire monitoring device is placed at the measurement location, and the isolation cylinder is adjusted so that its axis is aligned with the direction of the concrete being monitored. The cable of the magnetic grating displacement meter is led out and connected to the data acquisition unit. Then, the stress change of the concrete at the measurement location can be monitored for a long period of time. S4. Measure the deformation values ​​of the top center point (u) and bottom center point (d) of the through hole of the force measuring block using the force gauge in the monitoring device; S5. Calculate the stress value σ of the concrete being tested by measuring the deformation difference between the top center point (u) and the bottom center point (d) of the through hole of the force measuring block. Under the action of axial force of mass concrete, the displacement of the top center point (u) and the bottom center point (d) of the through hole of the force block is w u , w d , and the deformation value w between the two points is: Let the overall stiffness of the force gauge be K, then the axial force F acting on the force gauge is: The measured stress value σ of the concrete is: In the formula, σ is the measured concrete stress value, r0 is the radius of the inner diameter of the isolation cylinder, E1 is the equivalent elastic modulus of the force gauge, and α s The coefficient of linear expansion of the force gauge is . This represents the temperature change value of the concrete. S6. Modify the measured concrete stress value σ obtained in step S5: S6.1 Considering the influence of the isolation cylinder on the concrete force transmission column inside the cylinder and the difference between the force gauge and the elastic modulus of the concrete, the measured concrete stress value σ obtained in step S5 is corrected as follows: The correction factor 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 device for monitoring the post-aging period τ of cast-in-place concrete in the isolation cylinder cs (τ) is: where h1 is the total height of the load cell inside the monitoring device, h0 is the total height of the monitoring device, h c E0 is the total height of the concrete transfer column in the isolation cylinder, E c (τ) is the elastic modulus of concrete at age τ, and E1 is the equivalent elastic modulus of the load cell when no concrete is poured in the isolation cylinder. The corrected measured concrete stress value σ'(τ) at age τ is: In the formula: E cs (τ) represents the overall equivalent elastic modulus of the age-τ monitoring device, E c σ(τ) is the elastic modulus of concrete at age τ, σ(τ) is the measured stress value of concrete at age τ obtained by actual measurement calculation, and σ'(τ) is the corrected measured stress value of concrete at age τ. S6.2 Considering the impact of the change in elastic modulus of large-volume concrete during hydration on stress monitoring, the stress value of the measured concrete obtained in step S6.1 is further corrected. The corrected formula is as follows: In the formula: σ1(τ) is the measured concrete stress value at age τ after correction of the elastic modulus, E c (τ) represents the elastic modulus of the concrete outside the cylinder at age τ, E c (∞) represents the elastic modulus of the concrete outside the cylinder after hydration stabilization at age τ; In the above formula, α c Let α be the coefficient of linear expansion of the concrete being tested. s E is the linear expansion coefficient of the force gauge, E1 is the equivalent elastic modulus of the force gauge, and E c This refers to the elastic modulus of the concrete outside the cylinder. Due to changes in concrete temperature, ε' represents the change in volumetric deformation of concrete at age τ, ε' represents the coefficient of linear expansion and the additional strain caused by its volumetric deformation, and σ2(τ) represents the additional stress generated by the coefficient of linear expansion and its volumetric deformation at age τ. The above formula can be used to obtain the measured concrete stress value at age τ after correcting for the influence of the main material parameters. The calculation formula is as follows: 。 2. The method for correcting the measured values ​​of a cylindrical concrete stress gauge according to claim 1, characterized in that: The deformation range of the magnetic grating displacement gauge is 0-1000µm, and its accuracy is 0.1µm-1µm.

3. The method for correcting the measured values ​​of a cylindrical concrete stress gauge according to claim 1, characterized in that: The force gauge also includes an upper force-collecting plate, an upper force-transmitting plate, a lower force-transmitting plate, and a lower force-collecting plate; The top and bottom surfaces of the force measuring block are fixedly connected to the upper and lower force collecting plates via the upper and lower force transmitting plates, respectively, and the upper and lower force collecting plates, the upper and lower force collecting plates, the upper and lower force transmitting plates, and the force measuring block are coaxial. The upper and lower force-concentrating plates, as well as the upper and lower force-transmitting plates, are all made of metal materials, and their equivalent elastic modulus is similar to that of the hardened concrete, which is 15-40 GPa.

4. The method for correcting the measured values ​​of a cylindrical concrete stress gauge according to claim 3, characterized in that: 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 disks. The thickness of the upper and lower force-collecting plates is greater than 5mm, and the length of the upper and lower force-transmitting plates is no greater than 1cm. The ratio of the height of the force measuring block to the height of the entire force gauge is 1:2 to 1:1.

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5. The method for correcting the measured values ​​of a cylindrical concrete stress gauge according to claim 4, characterized in that: The two ends of the isolation cylinder are flexible structures, which are 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. 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.

6. The method for correcting the measured values ​​of a cylindrical concrete stress gauge according to any one of claims 3-5, 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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