Method for measuring strain related to stress of concrete structure

Abstract

The invention discloses a method for measuring strain related to stress of a concrete structure. The method comprises the following steps: arranging a measuring device in a concrete pouring area; concrete outside the shell and concrete in the second cavity are poured synchronously, and after concrete in the second cavity is poured, a top plate of the second cavity is covered; the concrete strain epsilon in the shell is measured through a sensor, and the concrete strain epsilon outside the shell is measured through another sensor; according to the measuring method, the monitoring device is directly buried in concrete, the concrete inside the monitoring device and the concrete outside the monitoring device are made to be poured synchronously and have the same curing temperature and humidity, the strain which does not affect the stress of the concrete is eliminated, and the stress correlation of the concrete structure is calculated. The stress-related strain of the concrete structure is obtained, so that the concrete quality and safety evaluation is more accurate.

Description

Technical Field

[0001] The invention relates to a method for measuring strain related to concrete structure stress, belonging to the technical field of concrete strain monitoring. Background Art

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

[0003] The conventional monitoring method for stress and strain of concrete components is to bury sensors in concrete and directly read strain data. For example, in the patent document with patent application number CN202311394858.6 and titled "Full-process Monitoring Method for Prefabricated and Prestressed Concrete Frames with Intelligent Sensing", optical fiber composite strands and sensors are placed in prefabricated beams and prefabricated columns, and the structure is monitored in real time through optical fiber composite strands and sensors, and the internal force state of the components is analyzed and evaluated. However, the monitoring data of strain sensors directly buried in concrete includes all strains of concrete plastic shrinkage, temperature strain, autogenous shrinkage, drying shrinkage, creep strain, and load strain, and cannot reflect the true stress state of the structure, thus affecting the evaluation results of structural quality and safety.

[0004] In order to monitor the stress and strain of concrete components, some methods also cast concrete component models of the same cross-sectional dimensions at the construction site and perform the same curing conditions. The concrete component model is a free component, and the ends are not subject to load constraints. Then, the concrete structure strain value is subtracted from the concrete free component strain value, and the result is the strain related to the concrete structure stress. For example, the patent document with the publication number CN106524989A and the name "Automatic Analysis System and Data Analysis Method for Deformation of Large Foundation Pit Support Body" adopts this method. However, this method requires the casting of a concrete component model separately, and the temperature and humidity of the curing directly affect the calculation results, increasing the difficulty of curing. Moreover, this method is suitable for slender rod structures, but for large-volume concrete components, such as dam bodies, large bottom plates, etc., it is difficult to establish an effective concrete component model. Summary of the invention

[0005] In response to the problems existing in the existing stress and strain monitoring of concrete components, the present invention provides a method for measuring strains related to concrete structure stress. The monitoring device is directly buried in the concrete, and the strains that have no effect on the concrete stress can be eliminated to obtain strains related to the concrete structure stress, thereby improving the accuracy of concrete structure stress state monitoring.

[0006] In order to solve the above technical problems, the present invention includes the following technical solutions:

[0007] A method for measuring strain associated with stress of a concrete structure, using a measuring device for measurement, the measuring device comprising a rectangular shell, a partition plate, a strain sensor and a sensor connector, the partition plate being arranged in the shell, dividing the inner space of the shell into a first chamber and a second chamber along the length direction; the strain sensor connector being arranged in the first chamber, comprising a connecting end plate fixedly connected to the shell; the strain sensor being located between the connecting end plate and the partition plate, one end of the strain sensor being connected to the partition plate, and the other end being connected to the end plate; the side plate of the second chamber isolating the concrete inside and outside the shell, and having water permeability and thermal conductivity; the top plate of the second chamber being detachably connected to the shell;

[0008] The measuring method comprises the following steps:

[0009] Step 1: Setting the measuring device in the concrete pouring area, opening the top plate of the second chamber, and setting an isolation layer on the inner sides of the top plate, bottom plate, and side plates of the outer shell;

[0010] Step 2: pouring concrete outside the shell and concrete in the second chamber simultaneously. After the concrete in the second chamber is poured, cover the top plate of the second chamber.

[0011] Step 3: Measure the concrete strain ε in the shell through the strain sensor 测 , the concrete strain ε outside the shell is measured by another strain sensor 外 ;

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

[0013]

[0014] Wherein, L is the initial length of the second cavity, and N is the gauge length of the strain sensor, which is a known number.

[0015] Furthermore, the measuring method further comprises:

[0016] Step 5: Based on the different thermal expansion coefficients between the strain sensor material and concrete, the strain ε of the concrete in the shell is 测 After correction, the concrete strain ε in the shell is 修 for:

[0017] ε 修 =ε 测 +ΔT(α s -α c );

[0018] In the formula, αs is the thermal expansion coefficient of steel, α c is the thermal expansion coefficient of concrete, ΔT is the temperature difference between two measurements;

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

[0020]

[0021] Furthermore, a force transmission key is arranged on the outer side of the shell, one end of the force transmission key is fixed on the outer wall of the shell, and the other end points to the outside of the shell.

[0022] Furthermore, anchor bars are arranged on one 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 connected as one.

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

[0024] Due to the adoption of the above technical scheme, the present invention has the following advantages and positive effects compared with the prior art: the measurement method of strain related to stress of concrete structure provided by the present invention directly buries the monitoring device inside the concrete, so that the concrete inside the monitoring device and the concrete outside the monitoring device are cast synchronously, and it can be ensured that the concrete inside the monitoring device and the concrete outside the monitoring device have the same curing temperature and humidity. The present invention also obtains strain related to stress of concrete structure by eliminating strain that has no effect on concrete stress, thereby reducing the interference of non-stress strain and making concrete quality and safety assessment more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of a method for measuring strain associated with stress in a concrete structure in one embodiment of the present invention;

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

[0027] Figure 3 for Figure 2 Sectional view along AA;

[0028] Figure 4 for Figure 2 A partial enlarged view of the middle G area.

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

[0030] 10-housing; 11-side plate; 12-end plate; 13-top plate; 14-bottom plate; 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 reinforcement. DETAILED DESCRIPTION

[0035] The following is a further detailed description of a method for measuring strain related to stress in a concrete structure provided by the present invention in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer with the following description. It should be noted that the accompanying drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0036] First of all, it is necessary to explain the stress and strain of concrete. Taking into account the hardening process of concrete, the strain of concrete structure after bearing load mainly includes: plastic shrinkage, temperature strain, autogenous shrinkage strain, drying shrinkage strain, creep strain and load strain and other strains. The strain sensor (such as strain gauge) in the concrete measures the strain value, which is the external manifestation of the comprehensive strain of concrete, but the measured strain value cannot explain the stress state of the structure. The reason is that some strains do not necessarily produce structural stress, and there is no strain. There is no structural stress. For example, the strain caused by temperature difference and shrinkage. This part of the strain will only produce stress in the structure when the deformation is constrained. The magnitude of the stress generated is related to 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 steel bars, creep has no effect on the stress of the structure, but in structures containing steel bars or over-static structures, creep causes redistribution of structural stress and affects the structural stress. Therefore, this patent classifies creep as a type of structure 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] ε 砼 =ε 荷载 +ε 未受约束温度 +ε 未受约束收缩+ε 徐变 ;

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

[0040] Assuming that the concrete at the location where the strain sensor is placed is not subject to surrounding constraints and external loads, and can deform freely under the action of temperature and shrinkage, the strain sensor measurement value at this location is defined as ε 自由 ,satisfy:

[0041] ε 自由 =ε 温度总应变 +ε 收缩总应变 .

[0042] Then there is,

[0043] ε 砼 -ε 自由 =(ε 荷载 +ε 未受约束温度应变 +ε 未受约束收缩应变 +ε 徐变 )-(ε 温度总应变 +ε 收缩总应变 )

[0045] =ε 荷载 +ε 徐变 +(ε 未受约束温度应变 -ε 温度总应变 )+(ε 未受约束收缩应变 -ε 收缩总应变 ).

[0046] When the concrete strength and curing conditions are the same, the total temperature strain of concrete ε 温度总应变 Subtract the unconstrained temperature strain ε 未受约束温度应变 The value after the contraction is the same as the value without strain under constraint, but the direction of the strain is opposite. For example, if the expansion is constrained, the structure is actually compressive stress, and after the constraint is released, the structural strain is positive, so the strain needs to be opposite in sign. Contraction strain is the same as temperature strain. Therefore, we can get:

[0047] -(ε 温度总应变 -ε 未受约束温度应变 )=ε 受约束温度应变

[0048] -(ε 收缩总应变 -ε 未受约束收缩应变 )=ε 受约束收缩应变

[0049] therefore,

[0050] ε 砼 -ε 自由 =ε 荷载 +ε 徐变 +ε 受约束温度应变 +ε 受约束收缩应变 ;

[0051] ε 荷载 , ε 徐变 , ε 受约束温度应变 , ε 受约束收缩应变 are strains that cause stress.

[0052] Therefore: 砼 -ε 自由 =ε 应力相关 .

[0053] It can be seen from the above formula that the strain value of the concrete structure under the same curing conditions minus the strain value of the concrete free member is the strain related to the stress of the concrete structure.

[0054] This embodiment requires the construction of a measuring device so that the concrete inside the measuring device and the concrete outside the measuring device have the same curing temperature and humidity, and the concrete inside the measuring device has a free telescopic end. Figure 2 As shown, the measuring device includes a rectangular parallelepiped housing 10 , a partition plate 20 , a strain sensor 40 and a sensor connector 30 .

[0055] Combination Figures 2 to 4 As shown, the housing 10 is a rectangular parallelepiped structure, including two side plates 11, two end plates 12, a bottom plate 13 and a top plate 14. The partition plate 20 is arranged in the housing 10, and the housing 10 is divided into two parts along the length direction, namely a first chamber and a second chamber. The first chamber is used to set the strain sensor 40 and the sensor connector 30, and the second chamber is used to pour concrete 50. The sensor connector 30 is arranged in the first chamber, and the strain sensor 40 is arranged 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 telescopic end, which can move along the length direction of the housing 10 and drive the partition plate 20 to move, so that the strain sensor generates strain synchronously.

[0056] In order to ensure that the concrete in the second chamber can expand and contract freely, an isolation layer 15 is provided inside the shell 10 of the second chamber. For example, the isolation layer is a thin film structure with air permeability and low friction resistance, which isolates the concrete from the shell 10 and reduces the resistance of the concrete to expansion and contraction.

[0057] In order to ensure that the concrete 50 in the second chamber has the same curing temperature and humidity as the concrete outside the housing 10, the side panels 11 of the second chamber are made of water-permeable and heat-conductive materials, such as ceramic water-permeable panels or magnesium oxide panels.

[0058] In order to ensure the measurement accuracy of the strain sensor in the first chamber, the outer shell 10 of the first chamber is made of impermeable material, or a sealing plate is set in the first chamber for sealing, and the connection between the partition plate 20 and the outer shell 10 is sealed by a flexible sealing material 21 to prevent concrete and water in the concrete from entering the first chamber.

[0059] 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 shell 10, the top plate 14 of the shell 10 is detachably arranged between the side plates 11 and the end plates 12. The top plate 14 is removed before building the concrete and then installed after casting.

[0060] In order to ensure that the shell 10 and the concrete outside the shell 10 expand and contract synchronously, a force transmission key 16 is provided on the outside of the shell 10. The force transmission key 16 can be made of a steel structure, one end of which is fixedly connected to the shell 10, and the other end is cast in the concrete outside the shell 10, thereby ensuring that the shell 10 and the concrete outside the shell deform synchronously.

[0061] In order to ensure the synchronous movement between the partition plate 20 and the concrete 50, an anchor bar 51 is provided on the side of the partition plate 20 facing the second chamber. After the concrete is poured, the anchor bar 51 is buried in the concrete 50, so that the partition plate 20 and the concrete are connected as one. When the concrete in the second chamber is free to expand and contract, the partition plate 20 will be driven to move synchronously, so that the strain sensor is deformed 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 component in the second chamber with the end plate.

[0062] In a 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 and the partition plate 20 of the housing 10. 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 arranged between the L-shaped connecting plate 32 and the partition plate 20 to ensure the movement of the partition plate 20. Due to the arrangement of the L-shaped connecting plate 32, the distance between the connecting position of the connecting end plate 31 on the housing 10 and the partition plate 20 can be reduced. When calculating the strain, the distance between the connecting 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 is convenient for calculation.

[0063] This embodiment provides a method for measuring strain related to concrete structure stress. Figures 1 to 4The measurement method is further described. The measurement method comprises the following steps:

[0064] Step 1: Set 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 an isolation layer 15 on the inner side of the top plate 14, the bottom plate 13, and the side plate 11 of the shell 10.

[0065] Step 2: Concrete outside the shell 10 and concrete inside the second chamber are poured simultaneously. After the concrete 50 inside the second chamber is poured, the top plate 14 of the second chamber is covered.

[0066] Step 3: Measure the concrete strain ε in the housing 10 by using a strain sensor 测 ;

[0067] Step 4: Calculate the strain ε related to the concrete structure stress 应力相关 ,in,

[0068]

[0069] Wherein, L is the initial length of the second cavity, and N is the gauge length of the strain sensor 40, which is a known number.

[0070] The derivation process of formula 1 is as follows:

[0071] Assume that the external concrete strain is ε 外 , the strain of the concrete inside the second cavity is ε 内 , the strain of the strain sensor 40 is ε 测 , the length of the second cavity is initially L, the gauge length of the strain sensor 40 is N, the strain of the housing 10 is the same as the strain of the external concrete, and according to the deformation coordination, it can be known that:

[0072] ε 外 ×L=ε 测 ×N+ε 内 ×L; (2)

[0073] available:

[0074]

[0075] Since the measuring device is buried in concrete, the strain of the concrete outside its shell is equal to the strain measured by the strain sensor buried in the concrete, ε 外 This is the ε mentioned above. 砼 , the concrete in the second cavity has a free telescopic end, ε 内 This is the ε mentioned above. 自由 ,therefore,

[0076] In a specific embodiment, the measuring method further comprises the following steps:

[0077] Step 5: Based on the different thermal expansion coefficients between the strain sensor 40 and the concrete, the concrete strain ε 测 After correction, the concrete strain ε in the shell 10 is 修 for:

[0078] ε 修 =ε 测 +ΔT(α s -α c );

[0079] In the formula, α s is the thermal expansion coefficient of steel, α c is the thermal expansion coefficient of concrete, ΔT is the temperature difference between two measurements;

[0080] The corrected formula 1 is:

[0081]

[0082] In addition, ε 测 =ε 1 -ε 0 , ε 1 is the measured value of the strain sensor 40, ε 0 is the initial value of the strain sensor 40.

[0083] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0084] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for measuring strain related to stress in concrete structures, characterized in that: The measurement is performed using a measuring device, which includes a rectangular shell, a partition plate, a strain sensor and a sensor connector. The partition plate is arranged in the shell to divide the inner space of the shell into a first chamber and a second chamber along the length direction; the sensor connector is arranged in the first chamber and includes a connecting end plate fixedly connected to the shell; the strain sensor is located between the connecting end plate and the partition plate, one end of the strain sensor is connected to the partition plate, and the other end is connected to the end plate; the side plate of the second chamber isolates the concrete inside and outside the shell and has water permeability and thermal conductivity; the top plate of the second chamber is detachably connected to the shell; The measuring method comprises the following steps: Step 1: The measuring device is arranged in the concrete pouring area, the top plate of the second chamber is opened, and an isolation layer is arranged on the inner sides of the top plate, the bottom plate and the side plate of the outer shell; Step 2: pouring concrete outside the shell and concrete in the second chamber simultaneously. After the concrete in the second chamber is poured, cover the top plate of the second chamber. Step 3: Measure the concrete strain ε in the shell through the strain sensor 测 , the concrete strain ε outside the shell is measured by another strain sensor 外 ; Step 4: Calculate the strain ε related to the concrete structure stress 应力相关 ,in, Wherein, L is the initial length of the second cavity, and N is the gauge length of the strain sensor, which is a known number.

2. The method for measuring strain related to stress in concrete structure according to claim 1, characterized in that: The measuring method further comprises: Step 5: Based on the different thermal expansion coefficients between the strain sensor material and concrete, the strain ε of the concrete in the shell is 测 After correction, the concrete strain ε in the shell is 修 for: e 修 =e 测 +ΔT ( a s -a c ) ; In the formula, α s is the thermal expansion coefficient of steel, α c is the thermal expansion coefficient of concrete, ΔT is the temperature difference between two measurements; Modified ε 应力相关 The calculation formula is:

3. The method for measuring strain related to stress in concrete structure according to claim 1 or 2, characterized in that: A force transmission key is arranged on the outer side of the shell, one end of the force transmission key is fixed on the outer wall of the shell, and the other end points to the outside of the shell.

4. The method for measuring stress-related strain of concrete structure according to claim 1 or 2, characterized in that: Anchor bars are arranged on one 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 connected as a whole.

5. The method for measuring strain related to stress in concrete structure according to claim 1 or 2, characterized in that: The connecting end plate is fixed on the outer shell through an L-shaped connecting plate, and a flexible sealing material is arranged between the L-shaped connecting plate and the partition plate.

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