A method for monitoring early-age strain of mass concrete under multi-field coupling conditions

Abstract

The present invention discloses a method for monitoring the early-stage strain of large-volume concrete under a multi-field coupling state, comprising: S1, assembling a strain gauge; S2, calibrating the sensitivity of the assembled strain gauge; S3, conducting a temperature sensitivity test on the base of the strain gauge in a standard temperature chamber to simulate the temperature rise and fall characteristics of the concrete hydration process before the strain gauge is embedded and installed, specifically establishing a correlation between the thermal strain and temperature during the temperature rise and temperature drop process; S4, simultaneously installing a temperature monitoring sensor at the strain gauge installation point to obtain a temperature monitoring value synchronized with the concrete and the strain gauge; S5, after the strain gauge is embedded and installed, connecting to an automatic data acquisition and remote transmission system to realize key-controlled remote terminal data storage; S6, constructing a remote data synchronization processing system to realize automatic and synchronous acquisition, analysis and processing of strain and temperature at each measuring point. According to the present invention, the method is suitable for in-situ automatic monitoring of strain during the entire maintenance process of large-volume concrete structures.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete monitoring, and in particular to a method for monitoring the early-age strain of large-volume concrete under a multi-field coupling state. Background Art

[0002] Rapid changes in temperature and moisture content within large-volume concrete structures at early ages can cause non-uniform structural deformation, crack initiation, and internal damage due to the coupled temperature, humidity, and stress fields. This poses significant risks to the safety and durability of engineering structures. Therefore, accurately detecting and scientifically evaluating deformation and damage in large-volume concrete structures at early ages is a crucial technical step in all concrete structure engineering projects.

[0003] Due to the low stiffness of early-stage concrete (generally ranging from 1MPa to 10GPa), the strain gauges used in traditional monitoring (detection) methods are too stiff to match the stiffness of the concrete medium and accurately transmit deformation. The monitored strain data is far less than the actual deformation of the concrete structure, resulting in data distortion and even erroneous results. Secondly, the strain sensor substrate (base) material undergoes volumetric deformation due to high temperatures during the concrete hydration process, resulting in the inclusion of substrate deformation information in the detection (monitoring) results. Traditional detection methods do not consider the influence of thermal strain on the strain gauge substrate and effectively eliminate it, which seriously affects the accuracy and even correctness of the detection data.

[0004] In summary, there is an urgent need to develop a multi-field coupled strain monitoring method for early-age concrete (with high fidelity). This method can obtain high-precision strain data during the early-age concrete curing process, so as to scientifically and accurately evaluate the internal quality of large-volume concrete. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention aims to provide a method for monitoring the early-stage strain of mass concrete under a multi-field coupling state. To achieve the above-mentioned purpose and other advantages according to the present invention, a method for monitoring the early-stage strain of mass concrete under a multi-field coupling state is provided, comprising:

[0006] S1, assemble strain gauge;

[0007] S2. Calibrate the sensitivity of the assembled strain gauge, specifically by establishing the correlation between strain and potential;

[0008] S3. Before pre-installation of the strain gauge, a temperature sensitivity test of the base of the strain gauge is conducted in a standard temperature chamber to simulate the temperature rise and fall characteristics of the concrete hydration process. Specifically, the correlation between the thermal strain and temperature during the temperature rise and temperature drop process is established.

[0009] S4. Install a temperature monitoring sensor at the strain gauge installation point to obtain a temperature monitoring value of the concrete that is synchronized with the strain gauge;

[0010] S5. After the strain gauge is pre-buried and installed, it is connected to the automatic data collection and remote transmission system based on the 4G network to realize remote terminal data storage controlled by the key;

[0011] S6. Build a remote data synchronization processing system to realize the automatic and synchronous collection, analysis and processing of strain and temperature at each measuring point.

[0012] Preferably, in the present application, the elastic modulus of early-age concrete is low, i.e., 1 MPa to 10 GPa, and the axial elastic modulus of the strain gauge main structure is less than 1.0 MPa, thereby achieving stiffness matching of early-age concrete strain measurement and fidelity transmission of structural strain.

[0013] Preferably, in order to obtain the strain change state of the entire concrete curing process, the present invention adopts a monitoring method of pre-embedded strain gauges. Considering that the hydration process after the pouring of large-volume concrete generates high temperatures (the peak temperature may reach above 60°C) and changes rapidly in a relatively short period of time, and the thermal strain effect on the base of the strain gauge, before the pre-embedded installation of the strain gauge, the temperature rise and fall process of the large-volume concrete hydration reaction is simulated to perform indoor test calibration of the thermal strain-temperature correlation, so as to eliminate the influence of the base thermal strain caused by the hydration heat during the monitoring process.

[0014] Preferably, in the present application, a temperature sensor is embedded at each strain monitoring point to synchronously monitor the concrete temperature, and obtains temperature change measured data corresponding to the strain at the measuring point and synchronized with time, which is used to calculate the real-time thermal strain value of the strain gauge base, thereby improving the reliability of eliminating the thermal strain of the base.

[0015] Preferably, the strain gauge reading data ε of each measuring point is obtained by monitoring m Its time-varying curve ε m (t), thermal strain of the strain gauge base ε T Its time-varying curve ε T (t), the error caused by thermal strain is eliminated by using the pre-calibrated thermal strain-temperature function relationship of the strain gauge base to obtain the concrete strain value ε at the measuring point c (t). At the same time, the quadratic spline interpolation and display ε i -t i Dynamic time-varying curve, and real-time reconstruction of the strain spatial distribution of the concrete structure in the detection area based on Gaussian interpolation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A graph showing changes in the elastic modulus of early-age concrete over time according to the method for monitoring the early-age strain of mass concrete under a multi-field coupling state according to the present invention;

[0017] Figure 2 Schematic diagram of a calculation method for base thermal strain correction in a method for monitoring early-age strain of mass concrete under multi-field coupling conditions according to the present invention;

[0018] Figure 3 A diagram showing a quadratic spline interpolation method for strain data series of a method for monitoring early-age strain of mass concrete under a multi-field coupling state according to the present invention;

[0019] Figure 4 Flow chart of the method for monitoring early-age strain of mass concrete under multi-field coupling conditions according to the present invention;

[0020] Figure 5 This is an example diagram of the strain gauge sensitivity calibration of the method for monitoring the early-age strain of mass concrete under multi-field coupling conditions according to the present invention;

[0021] Figure 6 The thermal strain rate diagram of the strain gauge base in the method for monitoring the early-age strain of mass concrete under multi-field coupling conditions according to the present invention;

[0022] Figure 7 Schematic diagram of the three-dimensional strain monitoring arrangement of the early-age strain monitoring method of mass concrete under multi-field coupling conditions according to the present invention. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] Reference Figure 4 A method for monitoring the early-age strain of mass concrete under multi-field coupling conditions includes:

[0025] S1. Assemble the strain gauge. In this application, the elastic modulus of the strain gauge is 1.0-2.0 MPa. Matching the strain gauge with the concrete medium stiffness during monitoring ensures faithful transmission of concrete deformation and displacement, improving the reliability and accuracy of monitoring data. Figure 7 This is a pre-embedded strain gauge arrangement method. i) A single strain gauge can be arranged in any direction to obtain axial strain data; ii) Strain gauges can be arranged in planes, such as the xoy plane, xoz plane, and yoz plane, to obtain corresponding plane strain states; iii) Strain gauges can be arranged in three dimensions to obtain 3D strain states.

[0026] S2. Perform sensitivity calibration on the assembled strain gauge, specifically to establish the correlation between strain and potential.

[0027] S3. Before pre-installation of the strain gauge, a temperature sensitivity test of the base of the strain gauge is conducted in a standard temperature chamber to simulate the temperature rise and fall characteristics of the concrete hydration process. Specifically, the correlation between the thermal strain and temperature during the temperature rise and temperature drop process is established. The strain gauge base thermal strain-temperature function addresses the adverse effects of rapid temperature fluctuations in early-stage concrete (0-170 hours) on the accuracy and reliability of strain monitoring results, resulting in corresponding thermal strain in the strain gauge base. Prior to pre-installation of the strain gauge, this application must conduct thermal strain-temperature correlation tests in a simulated environment using a controllable temperature chamber, based on the temperature variations during concrete curing. This establishes a thermal strain-temperature function for the strain gauge base, eliminating the effects of thermal strain caused by hydration heat during the monitoring process and ensuring the reliability and high accuracy of the monitoring data.

[0028] S4. Install temperature monitoring sensors at the strain gauge installation points to obtain temperature monitoring values ​​synchronized with the time of the concrete and the strain gauge; considering that the concrete strain and temperature are both time-varying, synchronize the concrete temperature monitoring at each strain monitoring point to obtain temperature variation data corresponding to the strain. At the same time, in order to avoid data loss and mismatch between temperature data and strain data, different sequence data are regressed into continuous functions of time ε(t) and T(t) respectively to ensure the feasibility of thermal strain elimination operation. The base thermal strain elimination is based on the strain and temperature sequence functions ε(t) and T(t) obtained by actual regression, and the thermal strain-temperature functional relationship ε is used. T and Figure 2 The calculation method shown is ε c (T,t)=ε(t)-ε T (T, t), we can get the concrete strain and its change with time ε c (T,t).

[0029] S5. After the strain gauge is pre-buried and installed, it is connected to the automatic data acquisition and remote transmission system based on the 4G network to realize key-controlled remote terminal data storage; when the concrete pouring begins, the monitoring system is started to read the initial reading of the strain gauge, and the acquisition system is placed in the monitoring mode of timed acquisition-transmission-storage in the database to guide the test to completion.

[0030] S6. Build a remote data synchronization processing system to achieve automatic collection, analysis and processing of strain and temperature at each measuring point. Perform quadratic spline interpolation analysis on the data sequence after thermal strain elimination and display ε i -t i Dynamic time-varying curves (such as Figure 3The strain spatial distribution of the concrete structure in the detection area is reconstructed in real time based on Gaussian interpolation.

[0031] Example 1

[0032] The specific implementation is as follows:

[0033] (1) Use an assembled resistance strain gauge with an axial stiffness less than or equal to the stiffness of the early-age concrete structure. The strain gauge is required to use an axially symmetrical arrangement of two strain gauges and a full bridge connection method.

[0034] (2) After the strain gauge is assembled, the sensitivity of the assembled strain gauge is calibrated to establish the strain-potential correlation and to test the linearity and repeatability of the reciprocating deformation. Figure 5 shown.

[0035] (3) The strain gauge is installed in a pre-buried manner. Before the pre-buried installation, the temperature sensitivity test of the strain gauge base must be carried out in a standard temperature box to simulate the temperature rise and fall characteristics of the concrete hydration process, and the correlation between the thermal strain and temperature in the temperature rise and temperature fall process should be established respectively. Each strain gauge should be subjected to no less than 3 reciprocating temperature rise and fall simulation tests, and the average value should be taken to establish the functional relationship between the thermal strain and temperature as the reference calibration relationship of the strain gauge. Figure 6 shown.

[0036] (4) Before the strain gauge is embedded and installed, the measuring distance and measuring point positions shall be set according to the reinforced concrete design data, engineering or scientific research objectives, and the strain gauge shall be installed at the corresponding measuring point position in the predetermined position and direction as the on-site steel bar bundling progresses.

[0037] (5) A temperature monitoring sensor must be installed at the strain gauge installation point to obtain a temperature monitoring value synchronized with the strain gauge time. The thermal strain-temperature functional relationship can be used to effectively eliminate the influence of the concrete hydration process temperature on the strain gauge base.

[0038] (6) In actual measurement, the strain gauge can be arranged in any direction to obtain the strain value in that direction; for any monitoring section, the strain gauge can be arranged in the orthogonal direction and the 45° angle direction to obtain ε x ,ε y and ε 45 , according to formula (1), the principal strain on the section is obtained, and the combination method is as follows Figure 7 Similarly, this method can be directly extended to monitor any 3D orthogonal strain inside concrete.

[0039] (7) After the strain gauge is embedded and installed, it is connected to the automatic data acquisition and remote transmission system based on the 4G network to realize key-controlled remote terminal data storage. When the concrete pouring begins, the monitoring system is started to read the initial reading of the strain gauge, and the acquisition system is placed in the monitoring mode of timed acquisition-transmission-storage in the database to guide the test to completion.

[0040] (8) By building a remote data synchronization processing system, the strain and temperature of each measuring point can be automatically collected and analyzed synchronously. This includes: i) synchronous collection and remote storage; ii) data fault tolerance processing and reliability testing; iii) based on the synchronous measurement values ​​of strain and temperature at each measuring point, the error caused by thermal strain is eliminated by using the pre-calibrated thermal strain-temperature function relationship of the strain gauge base to obtain the concrete strain value at the measuring point. Figure 3 As shown, iv) quadratic spline interpolation and display ε i -t i Dynamic time-varying curve, and real-time reconstruction of the strain spatial distribution of the concrete structure in the detection area based on Gaussian interpolation.

[0041] Figure 2 The diagram shows the concept of thermal strain elimination for the strain gauge base. For the strain raw data sequence ε(t) obtained at any measuring point, the thermal strain ε of the strain gauge base at the monitoring point is calculated based on the concrete temperature data sequence T(t) measured at the same measuring point and time and the pre-calibrated strain gauge thermal strain-temperature function relationship. T (t), then the concrete strain ε at the measuring point is c (t)=ε(t)-ε T (t).

[0042] The number of devices and processing scales described herein are intended to simplify the description of the present invention, and the application, modification, and variation of the present invention will be apparent to those skilled in the art. Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiment. They can be applied to various fields suitable for the present invention. For those skilled in the art, additional modifications can be easily implemented. Therefore, the present invention is not limited to the specific details and figures shown and described herein without departing from the general concept defined by the claims and their equivalents.

Claims

1. A method for monitoring the early-age strain of mass concrete under multi-field coupling conditions, characterized in that: include: S1, assemble strain gauge; The axial stiffness of the strain gauge is less than or equal to the stiffness of the early-age concrete structure; S2. Calibrate the sensitivity of the assembled strain gauge, specifically by establishing the correlation between strain and potential; S3. Before pre-installation of the strain gauge, a temperature sensitivity test of the base of the strain gauge is conducted in a standard temperature chamber to simulate the temperature rise and fall characteristics of the concrete hydration process. Specifically, the correlation between the thermal strain and temperature of the base of the strain gauge during the temperature rise and temperature fall processes is established. S4. Install a temperature monitoring sensor at the strain gauge installation point to obtain a temperature monitoring value of the concrete that is synchronized with the strain gauge; S5. After the strain gauge is pre-buried and installed, it is connected to the automatic data collection and remote transmission system based on the 4G network to realize remote terminal data storage controlled by the key; S6. Build a remote data synchronization processing system to achieve automatic and synchronous collection, analysis and processing of strain and temperature at each measuring point; The step S6 specifically includes the following steps: 1) The strain and temperature of each measuring point are automatically collected and stored remotely; 2) Perform fault tolerance processing and reliability testing of data; 3) Based on the synchronous measurement values ​​of strain and temperature at each measuring point, the error caused by thermal strain is eliminated by using the pre-calibrated thermal strain-temperature function relationship of the strain gauge base to obtain the concrete strain value at the measuring point; for the strain original data sequence ε(t) of any measuring point obtained by actual measurement, the thermal strain ε of the strain gauge base at the monitoring point is calculated based on the concrete temperature data sequence T(t) measured at the same measuring point and time and the pre-calibrated thermal strain-temperature function relationship of the strain gauge. T (t), then the concrete strain ε at the measuring point is c (t)=ε(t)-ε T (t); 4) Quadratic spline interpolation and display Dynamic time-varying curve, and real-time reconstruction of the strain spatial distribution of the concrete structure in the detection area based on Gaussian interpolation.

2. The method for monitoring early-age strain of mass concrete under multi-field coupling conditions as claimed in claim 1, characterized in that: In step S3, each strain gauge should be subjected to no less than three reciprocating temperature increase-reduction simulation tests, and an average value is taken to establish a functional relationship between thermal strain and temperature, which serves as a reference calibration relationship for the strain gauge.

3. The method for monitoring early-age strain of mass concrete under multi-field coupling state according to claim 1, characterized in that: In actual measurements, strain gauges are arranged in any direction along the concrete to obtain the strain value in the corresponding direction. For any monitoring section, the strain gauges are arranged in the orthogonal direction and the 45° angle direction of the strain gauge itself to obtain the principal strain on the corresponding section.

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