Method for measuring strain associated with stress in a concrete structure

Abstract

The application discloses a kind of with the measurement method of concrete structure stress related strain, comprising the following steps: the measuring device is set in concrete pouring area;Synchronous pouring concrete outside shell and the concrete of second chamber, after the concrete in second chamber is poured, the top plate of second chamber is covered;The strain ε 测 Of concrete in shell is measured by sensor 外 ;The strain ε 应力相关 Related to concrete structure stress is calculated, wherein the measurement method directly embeds monitoring device in concrete, so that the concrete inside monitoring device is synchronous with the concrete outside monitoring device and has the same curing temperature and humidity, and also obtains concrete structure stress related strain by eliminating the strain that does not affect concrete stress, so that concrete quality and safety evaluation are more accurate.

Description

Technical Field

[0001] This invention relates to a method for measuring stress-related strain in concrete structures, belonging to the field of concrete strain monitoring technology. Background Technology

[0002] Cast-in-place concrete is the most widely used building material in civil engineering. During the hardening process of concrete, plastic shrinkage, temperature strain, autogenous shrinkage, drying shrinkage, creep strain, and load strain occur. Some of these strains can generate structural stress, while others do not. Only the strains that generate structural stress affect the stress state of the concrete.

[0003] The conventional method for monitoring stress and strain in concrete components involves embedding sensors within the concrete to directly read strain data. For example, patent application CN202311394858.6, entitled "Intelligent Sensing Method for Monitoring the Entire Process of Precast Prestressed Concrete Frames," describes embedding fiber optic composite cables and sensors within precast beams and columns. This allows for real-time monitoring of the structure and analysis and evaluation of the internal force state of the components. However, the data collected by strain sensors directly embedded in the concrete includes all strains, including plastic shrinkage, temperature strain, autogenous shrinkage, drying shrinkage, creep strain, and load strain. This data fails to reflect the true stress state of the structure, thus affecting the assessment results for structural quality and safety.

[0004] To monitor the stress and strain of concrete components, some methods involve casting a separate concrete component model with the same cross-sectional dimensions on-site and curing it under the same conditions. This concrete component model is a free member, with its ends unrestrained by loads. The strain value of the free concrete component is then subtracted from the strain value of the concrete structure; the result is the stress-related strain of the concrete structure. For example, patent document CN106524989A, entitled "Automatic Deformation Analysis System and Data Analysis Method for Large Foundation Pit Supports," uses this method. However, this method requires casting a separate concrete component model, and the temperature and humidity during curing directly affect the calculation results, increasing the difficulty of curing. Furthermore, this method is suitable for slender rod structures, but for large-volume concrete components, such as dams and large foundation slabs, it is difficult to establish an effective concrete component model. Summary of the Invention

[0005] To address the existing problems in monitoring stress and strain in concrete components, this invention provides a method for measuring stress-related strain in concrete structures. The monitoring device is directly embedded inside the concrete, and strains that do not affect the stress of the concrete can be eliminated to obtain stress-related strains of the concrete structure, thereby improving the accuracy of stress state monitoring of concrete structures.

[0006] To solve the above technical problems, the present invention includes the following technical solutions:

[0007] A method for measuring stress-related strain in concrete structures is disclosed, employing a measuring device comprising a cuboid outer shell, a partition plate, a strain sensor, and a sensor connector. The partition plate, disposed within the outer shell, divides the internal space of the outer shell into a first chamber and a second chamber along its length. The strain sensor connector, disposed within the first chamber, includes a connecting end plate fixedly connected to the outer shell. The strain sensor is located between the connecting end plate and the partition plate, with one end connected to the partition plate and the other end connected to the end plate. The side plate of the second chamber isolates the concrete inside and outside the outer shell and is permeable and thermally conductive. The top plate of the second chamber is detachably connected to the outer shell.

[0008] The measurement method includes the following steps:

[0009] Step 1: Set up the measuring device in the concrete pouring area, open the top plate of the second chamber, and set up an isolation layer on the inside of the top plate, bottom plate, and side plate of the outer shell;

[0010] Step 2: Simultaneously pour concrete for the outer shell and the second chamber. After the concrete in the second chamber is poured, cover it with the top plate.

[0011] Step 3: Obtain the strain ε from the strain sensor. 测 ;

[0012] Step 4: Calculate the strain ε related to the stress in the concrete structure. 应力相关 ,in,

[0013] (1)

[0014] In the formula, L is the initial length of the second cavity, N is the gauge length of the strain sensor, and N is a known value.

[0015] Furthermore, the measurement method also includes:

[0016] Step 5: Based on the difference in thermal expansion coefficients between the strain sensor material and concrete, measure the strain ε of the concrete inside the outer shell. 测 The correction was made, and the strain ε of the concrete inside the shell after the correction was determined. 修 for:

[0017] ε 修 = ;

[0018] In the formula, The coefficient of thermal expansion of steel. The coefficient of thermal expansion of concrete. The temperature difference between the two measurements;

[0019] Corrected ε 应力相关 The calculation formula is:

[0020] .

[0021] Furthermore, a force transmission key is provided on the outer side of the outer shell, with one end of the force transmission key fixed to the outer wall of the outer shell and the other end pointing outwards from the outer shell.

[0022] Furthermore, anchor bars are installed on the side of the partition plate facing the second chamber. After the concrete is poured, the anchor bars are embedded in the concrete, so that the partition plate and the concrete are integrated.

[0023] Furthermore, the connecting end plate is fixed to the outer shell by an L-shaped connecting plate, and a flexible sealing material is provided between the L-shaped connecting plate and the partition plate.

[0024] By employing the above technical solutions, this invention has the following advantages and positive effects compared with existing technologies: The method for measuring stress-related strain in concrete structures provided by this invention directly embeds the monitoring device inside the concrete, allowing the concrete inside the monitoring device to be poured synchronously with the concrete outside the monitoring device. This ensures that the concrete inside and outside the monitoring device have the same curing temperature and humidity. Furthermore, this invention obtains stress-related strain in concrete structures by eliminating strains that do not affect concrete stress, reducing interference from non-stress strains and making the assessment of concrete quality and safety more accurate. Attached Figure Description

[0025] Figure 1 This is a flowchart of a method for measuring stress-related strain in concrete structures according to an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the measuring device in one embodiment of the present invention;

[0027] Figure 3 for Figure 2 A sectional view along the middle AA;

[0028] Figure 4 for Figure 2 A magnified view of a portion of region G in the middle.

[0029] The numbers in the diagram are as follows:

[0030] 10-Outer shell; 11-Side panel; 12-End panel; 13-Top panel; 14-Bottom panel; 15-Isolation layer; 16-Force transmission key;

[0031] 20 - Partition plate; 21 - Flexible sealing material;

[0032] 30 - Sensor connector; 31 - Connecting end plate; 32 - L-shaped connecting plate;

[0033] 40 - Strain sensor;

[0034] 50 - Concrete; 51 - Anchor bar. Detailed Implementation

[0035] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a method for measuring stress-related strain in concrete structures according to the present invention. The advantages and features of the present invention will become clearer from the following description. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise scales, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0036] First, it is necessary to explain the stress and strain of concrete. Considering the hardening process of concrete, the strain of a concrete structure under load mainly includes: plastic shrinkage, temperature strain, autogenous shrinkage strain, drying shrinkage strain, creep strain, and load strain. Strain sensors (such as strain gauges) within the concrete measure strain values, which are the external manifestation of the comprehensive strain of the concrete. However, the measured strain values ​​cannot explain the stress state of the structure because some strains do not necessarily generate structural stress, and the absence of strain does not necessarily mean the absence of structural stress. For example, the strain generated by temperature difference and shrinkage only generates stress in the structure when the deformation is constrained. The magnitude of the stress generated depends on the degree of constraint. When the deformation is not constrained, although strain is generated, no structural stress is generated. Regarding creep, in statically determinate structures without reinforcement, creep has no effect on the structural stress. However, in structures with reinforcement or that are statically indeterminate, creep causes a redistribution of structural stress, thus affecting the structural stress. Therefore, this patent classifies creep as a type that affects structural stress. In summary, the strain ε that affects concrete stress... 应力相关 Including ε 荷载 ε 受约束温度应变 ε 受约束收缩应变 ε 徐变 The strain ε that has no effect on concrete stress 应力不相关 Including ε 未受约束温度应变 ε 未受约束收缩应变 .

[0037] Then, the strain measured by the strain sensor embedded in the concrete structure is analyzed. The strain measured by the strain sensor is ε. 砼 ,in,

[0038] ;

[0039] ε is the strain directly measured by the strain sensor. 未受约束温度应变 ε 未受约束收缩应变It has no effect on concrete stress, and the strain ε is omitted when used as a basis for crack assessment. 受约束温度应变 ε 受约束收缩应变 Therefore, using measured stress as the basis for concrete stress assessment has the problem of insufficient accuracy.

[0040] Assuming the concrete at the location where the strain sensor is placed is unconstrained by surrounding elements and does not bear external loads, and can freely deform under temperature and shrinkage conditions, then the strain sensor measurement at that location is defined as follows: ,satisfy:

[0041] .

[0042] Then there is,

[0043] - = -(

[0044] = + +( ) + ( ).

[0045] When concrete strength and curing conditions are the same, the total temperature strain ε of concrete is... 温度总应变 Subtract the unconstrained temperature strain ε 未受约束温度应变 The resulting values ​​are the same in magnitude as the values ​​for strain under constraint without strain, but in the opposite direction. For example, if expansion is constrained, the structure is actually under compressive stress, but after the constraint is released, the structural strain is positive; therefore, the strain sign needs to be reversed. Contraction strain is the same as temperature strain. Therefore, we can obtain:

[0046] =

[0047] )=

[0048] therefore,

[0049] = + + ;

[0050] ε 荷载 ε 徐变 ε 受约束温度应变 ε 受约束收缩应变 Both are strains that cause stress.

[0051] Therefore: ε 砼 -ε 自由 =ε 应力相关 .

[0052] As can be seen from the above formula, the result obtained by subtracting the strain value of the free concrete component from the strain value of the concrete structure under the same curing conditions is the stress-related strain of the concrete structure.

[0053] This embodiment requires the construction of a measuring device that ensures the concrete inside the device has the same curing temperature and humidity as the concrete outside the device, and that the concrete inside the device has free expansion and contraction ends. For example... Figure 2 As shown, the measuring device includes a cuboid housing 10, a partition plate 20, a strain sensor 40, and a sensor connector 30.

[0054] Combination Figures 2 to 4 As shown, the outer shell 10 has a cuboid structure, including two side plates 11, two end plates 12, a bottom plate 13, and a top plate 14. The partition plate 20 is disposed inside the outer shell 10, dividing it into two parts along its length: a first chamber and a second chamber. The first chamber is used to house the strain sensor 40 and the sensor connector 30, while the second chamber is used for pouring concrete 50. The sensor connector 30 is disposed in the first chamber, and the strain sensor 40 is disposed between the sensor connector 30 and the partition plate 20. One end of the strain sensor 40 is connected to the sensor connector 30, and the other end is connected to the partition plate 20. The end of the concrete in the second chamber connected to the partition plate 20 is a free-expanding end, capable of moving along the length of the outer shell 10 and causing the partition plate 20 to move, thus synchronously generating strain in the strain sensor.

[0055] To ensure that the concrete in the second chamber can expand and contract freely, an isolation layer 15 is provided on the inner side of the outer shell 10 of the second chamber. For example, the isolation layer is a thin film structure with air permeability and low frictional resistance, which isolates the concrete from the outer shell 10 and reduces the resistance of concrete expansion and contraction.

[0056] To ensure that the concrete 50 inside the second chamber has the same curing temperature and humidity as the concrete outside the outer shell 10, the side plate 11 of the second chamber is made of a permeable and heat-conducting material, such as a ceramic permeable plate or a magnesium oxide plate.

[0057] To ensure the measurement accuracy of the strain sensor in the first chamber, the outer shell 10 of the first chamber is made of a waterproof material, or a sealing plate is installed in the first chamber for sealing. The connection between the partition plate 20 and the outer shell 10 is sealed with a flexible sealing material 21 to prevent concrete and water in the concrete from entering the first chamber.

[0058] The measuring device is cast in concrete. In order to facilitate the synchronous casting of the concrete in the second chamber and the concrete outside the outer shell 10, the top plate 14 of the outer shell 10 is detachably connected to the side plate 11 and the end plate 12. The top plate 14 is removed before the concrete is poured and then reinstalled after the concrete is poured.

[0059] In order to ensure that the outer shell 10 and the concrete outside the outer shell 10 expand and contract synchronously, a force transmission key 16 is provided on the outer side of the outer shell 10. The force transmission key 16 can be made of steel structure, with one end fixedly connected to the outer shell 10 and the other end cast in the concrete outside the outer shell 10, thereby ensuring that the outer shell 10 and the concrete outside the outer shell deform synchronously.

[0060] To ensure synchronous movement between the partition plate 20 and the concrete 50, anchor bars 51 are provided on the side of the partition plate 20 facing the second chamber. After the concrete is poured, the anchor bars 51 are embedded in the concrete 50, thus making the partition plate 20 and the concrete an integral unit. When the concrete in the second chamber expands and contracts freely, it will synchronously drive the partition plate 20 to move, causing the strain sensor to deform synchronously. Anchor bars 51 can also be provided on the inner side of the end plate 12 of the second chamber to firmly connect the concrete components in the second chamber with the end plate.

[0061] In one specific embodiment, the sensor connector 30 includes a connecting end plate 31 and an L-shaped connecting plate 32. The connecting end plate 31 is arranged parallel to the end plate of the housing 10 and the partition plate 20. One end of the L-shaped connecting plate 32 is fixedly connected to the connecting end plate 31, and the other end is fixedly connected to the side plate of the housing 10. A flexible sealing material 21 is provided between the L-shaped connecting plate 32 and the partition plate 20 to ensure the movement of the partition plate 20. Due to the L-shaped connecting plate 32, the distance between the connection position of the connecting end plate 31 on the housing 10 and the partition plate 20 can be reduced. When calculating strain, the distance between the connection position of the connecting end plate 31 on the housing 10 and the end plate of the second chamber can be approximately equal to the initial distance of the second chamber, which facilitates calculation.

[0062] This embodiment provides a method for measuring stress-related strain in concrete structures. The following section discusses this method in conjunction with Embodiment 1. Figures 1 to 4 The measurement method is further described below. The measurement method includes the following steps:

[0063] Step 1: Set up a measuring device in the concrete pouring area. The structure of the measuring device is as described above. Open the top plate 14 of the second chamber and set up an isolation layer 15 on the inner side of the top plate 14, bottom plate 13 and side plate 11 of the outer shell 10.

[0064] Step 2: Simultaneously pour concrete on the outside of the outer shell 10 and concrete in the second chamber. After the concrete 50 in the second chamber is poured, cover the top plate 14 of the second chamber.

[0065] Step 3: Obtain the strain ε from the strain sensor. 测 ;

[0066] Step 4: Calculate the strain ε related to the stress in the concrete structure. 应力相关 ,in,

[0067] (1)

[0068] In the formula, L is the initial length of the second cavity, and N is the gauge length of the strain sensor 40, which is a known value.

[0069] The derivation of Formula 1 is as follows:

[0070] Assume the external concrete strain is ε 外 The strain of the concrete inside the second cavity is ε. 内 The strain of strain sensor 40 is The initial length of the second cavity is L, the gauge length of the strain sensor 40 is N, and the strain of the outer shell 10 is the same as the strain of the external concrete. According to deformation compatibility, it can be known that:

[0071] ×L= ×N+ ×L; (2)

[0072] available:

[0073] (3)

[0074] Since the measuring device is embedded in concrete, the strain of the concrete outside its casing is equal to the strain measured by the strain sensor embedded in the concrete, ε. 外 This refers to ε mentioned earlier. 砼 The concrete inside the second cavity has free expansion and contraction ends, ε 内 This refers to ε mentioned earlier. 自由 ,therefore, .

[0075] In one specific embodiment, the measurement method further includes the following steps:

[0076] Step 5: Based on the difference in thermal expansion coefficients between the strain sensor 40 material and concrete, measure the concrete strain ε inside the outer shell 10. 测 The correction was made, and the concrete strain ε inside the outer shell 10 was adjusted. 修 for:

[0077] ε 修 = ;

[0078] In the formula, The coefficient of thermal expansion of steel. The coefficient of thermal expansion of concrete. The temperature difference between the two measurements;

[0079] The revised formula 1 is:

[0080] .

[0081] in addition, = , The measured value is from strain sensor 40. The initial value is for strain sensor 40.

[0082] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0083] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for measuring stress-related strain in concrete structures, characterized in that, Measurements are performed using a measuring device comprising a cuboid outer shell, a partition plate, a strain sensor, and a sensor connector. The partition plate is disposed within the outer shell, dividing the internal space of the outer shell into a first chamber and a second chamber along its length. The sensor connector is disposed within the first chamber and includes a connecting end plate fixedly connected to the outer shell. The strain sensor is located between the connecting end plate and the partition plate, with one end of the strain sensor connected to the partition plate and the other end connected to the end plate. The side plate of the second chamber isolates the concrete inside and outside the outer shell and is permeable and thermally conductive. The top plate of the second chamber is detachably connected to the outer shell. The measurement method includes the following steps: Step 1: Set up the measuring device in the concrete pouring area, open the top plate of the second chamber, and set an isolation layer on the inner side of the top plate, bottom plate and side plate of the outer shell; Step 2: Simultaneously pour concrete for the outer shell and the second chamber. After the concrete in the second chamber is poured, cover it with the top plate. Step 3: Obtain the strain ε from the strain sensor. 测 ; Step 4: Calculate the strain ε related to the stress in the concrete structure. 应力相关 ,in, ； In the formula, L is the initial length of the second cavity, N is the gauge length of the strain sensor, and N is a known value; Step 5: Based on the difference in thermal expansion coefficients between the strain sensor material and concrete, measure the strain ε of the concrete inside the outer shell. 测 The correction was made, and the strain ε of the concrete inside the shell after the correction was determined. 修 for: e 修 = ; In the formula, The coefficient of thermal expansion of steel. The coefficient of thermal expansion of concrete. The temperature difference between the two measurements; Corrected ε 应力相关 The calculation formula is: 。 2. The method for measuring stress-related strain in concrete structures as described in claim 1, characterized in that, A force transmission key is provided on the outside of the outer shell. One end of the force transmission key is fixed to the outer wall of the outer shell, and the other end points out of the outer shell.

3. The method for measuring stress-related strain in concrete structures as described in claim 1, characterized in that, Anchor bars are installed on the side of the partition plate facing the second chamber. After the concrete is poured, the anchor bars are embedded in the concrete, so that the partition plate and the concrete are integrated.

4. The method for measuring stress-related strain in concrete structures as described in claim 1, characterized in that, The connecting end plate is fixed to the outer shell by an L-shaped connecting plate, and a flexible sealing material is provided between the L-shaped connecting plate and the partition plate.

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