PZT-based random aggregate mesoscopic concrete external damage identification method

Abstract

The present application discloses a PZT-based random aggregate mesoscopic concrete external damage identification method, which relates to the field of civil engineering structure monitoring and simulation technology. A three-dimensional mesoscopic geometric model of concrete is established using an aggregate random generation and placement algorithm according to a target concrete mix ratio; a background grid method is used to assign material properties to units to establish a three-dimensional mesoscopic model of PZT concrete and verify its effectiveness; if the three-dimensional mesoscopic model of PZT concrete is effective, the influence of different damage conditions on the piezoelectric admittance curve of concrete is simulated and analyzed. A PZT concrete mesoscopic model of concrete heterogeneous characteristics is established, and the influence of concrete mesoscopic parameters on the piezoelectric admittance curve is considered, so that the numerical model is closer to the real structure. The changes in concrete performance are more clearly associated with the corresponding changes in the piezoelectric admittance curve, thereby more comprehensively revealing the mapping relationship between internal cracks in concrete and piezoelectric admittance, and improving the accuracy of the piezoelectric admittance method in damage identification.

Description

Technical Field

[0001] The present application relates to the technical field of civil engineering structure monitoring and simulation, and in particular to a PZT-based random aggregate micro-concrete external damage identification method. Background Art

[0002] Concrete materials have been widely used in highways, bridges, buildings and other fields due to their advantages such as affordability and ease of processing. In order to ensure structural safety, it is necessary to scientifically evaluate the safety status of concrete structures so as to take corresponding damage control and repair measures. Among them, the piezoelectric admittance method based on PZT (piezoceramic transducers) has broad application prospects in the field of concrete structure health monitoring due to its light weight, small impact on the main structure, high operating frequency, and sensitivity to initial structural damage.

[0003] At present, numerical studies of concrete based on the piezoelectric admittance method often simplify concrete as a homogeneous material. However, in reality, concrete is a multiphase composite material, so there are obvious differences between homogeneous models and heterogeneous models. In addition, the piezoelectric admittance method, as a high-frequency monitoring method, is very sensitive to changes in the internal properties of concrete structures, but these characteristics are difficult to observe in both experiments and homogeneous models.

[0004] Therefore, how to more clearly monitor the changes in concrete performance while taking into account the heterogeneous characteristics of concrete is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0005] In order to solve the above technical problems, this application proposes the following technical solutions:

[0006] In a first aspect, the present application provides a PZT-based random aggregate mesoscopic concrete external damage identification method, comprising:

[0007] According to the target concrete mix ratio, a three-dimensional mesoscopic geometric model of concrete is established using an aggregate random generation and placement algorithm;

[0008] The background grid method is used to assign material properties to the elements to establish a three-dimensional microscopic model of PZT concrete.

[0009] Verify the validity of the three-dimensional mesoscopic model of PZT concrete;

[0010] If the three-dimensional microscopic model of PZT concrete is valid, the influence of different damage conditions on the piezoelectric admittance curve of concrete is simulated and analyzed.

[0011] In a possible implementation, the method of establishing a concrete three-dimensional microscopic geometric model using a random aggregate generation and placement algorithm according to a target concrete mix ratio includes:

[0012] Fine aggregates with particle sizes smaller than the threshold are simplified as mortar matrix, and coarse aggregates with particle sizes larger than the threshold are simplified as spheres;

[0013] Determine the proportion of aggregates within various particle size ranges according to the target concrete mix ratio and gradation curve;

[0014] Divide the background grid in the aggregate placement area, and the grid size should be 1 / 5-1 / 10 of the smallest aggregate particle size;

[0015] Randomly place the centers of aggregate balls at the grid nodes;

[0016] When new aggregate is added, calculate the net distance between the new aggregate and the existing aggregate;

[0017] Generate the net distance vector between the new aggregate and the target area boundary and the existing aggregate ;

[0018] According to the Determine whether the new aggregate is successfully placed. If the new aggregate is successfully placed, delete all nodes within the minimum particle size range inside and around the aggregate. If the new aggregate fails to be placed, only delete the center node to avoid re-selection.

[0019] In a possible implementation, when new aggregate is added, calculating the net distance between the new aggregate and the existing aggregate includes:

[0020] Assume that the maximum aggregate size is , the coordinates of the center of the newly placed aggregate sphere are , the particle size range is , just calculate The net distance between the existing aggregate and the following formula:

[0021]

[0022] Calculate the new aggregate and the existing aggregate that meets the above requirements The net distance between , whose formula is:

[0023] .

[0024] In a possible implementation, the net distance vector for:

[0025] ;

[0026] Where L is the length of the target area boundary.

[0027] In a possible implementation, the Determining whether the new aggregate is successfully placed includes:

[0028] if , new aggregate particle size , the new aggregate was put into use successfully;

[0029] if , new aggregate particle size , the new aggregate was put into use successfully;

[0030] if , then the new aggregate placement fails, among which is a random number uniformly distributed in the interval [0,1].

[0031] In a possible implementation, the method of using the background grid method to assign material properties to units to establish a three-dimensional mesoscopic model of PZT concrete includes:

[0032] According to the frequency range of the piezoelectric admittance curve, the appropriate mesh size is selected to divide the concrete three-dimensional micro-geometric model, where: the concrete mesh size directly below the PZT should be the same as that of the PZT to ensure that the PZT unit is coupled with the underlying bonding layer and concrete nodes;

[0033] Assign values ​​to unit materials based on the coordinate information of the eight nodes of the unit;

[0034] If the coordinates of all the nodes of the unit are in the aggregate, it is an aggregate unit; if the coordinates of all the nodes of the unit are in the mortar, it is a mortar unit; if the coordinates of the node of the unit are both in the aggregate and in the mortar, it is a mortar interface unit.

[0035] In a possible implementation, verifying the validity of the PZT concrete three-dimensional mesoscopic model includes:

[0036] Collect the piezoelectric admittance curve of the target concrete structure;

[0037] Compare the curve shape, resonant frequency, and resonant peak of the piezoelectric admittance data calculated by the model with the collected piezoelectric admittance curve;

[0038] If the number of resonance peaks is consistent and the difference between the resonance frequency and the resonance peak does not exceed a preset range, the model is considered valid.

[0039] In a possible implementation, if the three-dimensional mesoscopic model of PZT concrete is valid, the influence of different damage conditions on the piezoelectric admittance curve of concrete is simulated and analyzed, including:

[0040] A three-dimensional microscopic model of PZT concrete with damage was established, and the piezoelectric admittance curve was calculated.

[0041] The root mean square deviation RMSD of the conductivity signal and the baseline conductivity data is calculated as follows:

[0042]

[0043] Where: For the The damage condition was measured The data values, The baseline conductivity signal is measured The data Values;

[0044] The calculated RMSD value is used to identify concrete damage.

[0045] In the embodiment of the present application, a PZT concrete micro-model considering the heterogeneous characteristics of concrete is established, and the influence of concrete micro-parameters on the piezoelectric admittance curve is considered, so that the numerical model is closer to the real structure. Compared with the existing homogeneous model results, it is more in line with the actual results, and more clearly associates the changes in concrete performance with the corresponding changes in the piezoelectric admittance curve, thereby more comprehensively revealing the mapping relationship between internal cracks in concrete and piezoelectric admittance, and improving the accuracy of the piezoelectric admittance method in damage identification. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A schematic diagram of a PZT-based random aggregate mesoscopic concrete external damage identification method provided in an embodiment of the present application;

[0047] Figure 2 A schematic diagram of a unit material assignment process for a construction provided in an embodiment of the present application;

[0048] Figure 3 A schematic diagram of the results of placing different aggregate contents provided in the embodiments of the present application;

[0049] Figure 4 A comparison diagram of the actual aggregate gradation and the preset gradation provided in the embodiment of the present application;

[0050] Figure 5 A schematic diagram of a three-dimensional mesoscopic model of PZT concrete provided in an embodiment of the present application;

[0051] Figure 6 A comparison diagram of the heterogeneous model, homogeneous model and experimental conductivity curves under different aggregate volume fractions provided in the embodiments of the present application;

[0052] Figure 7 A comparison diagram of the resonance peak and resonance frequency of the heterogeneous model, homogeneous model and experimental conductivity curves under different aggregate volume fractions provided in the embodiments of the present application;

[0053] Figure 8 Schematic diagram of different damage conditions provided in the embodiments of the present application;

[0054] Fig. 9 This is a comparison chart of the RMSD values ​​of the inhomogeneous model, homogeneous model and experimental conductivity curves under different damage conditions provided in the embodiments of the present application. DETAILED DESCRIPTION

[0055] The present solution is described below in conjunction with the accompanying drawings and specific implementation methods.

[0056] See also Figure 1 The random aggregate mesoscopic concrete external damage identification method based on PZT provided in this embodiment includes:

[0057] S101, establishing a concrete three-dimensional micro-geometric model using an aggregate random generation and placement algorithm according to a target concrete mix ratio.

[0058] In this embodiment, the concrete three-dimensional micro-geometric model establishment process is as follows:

[0059] Fine aggregates with a particle size smaller than the threshold are simplified as mortar matrix, and coarse aggregates with a particle size larger than the threshold are simplified as spheres, and the proportion of aggregates within various particle size ranges is determined according to the target concrete mix ratio and gradation curve. Specifically, in this embodiment, the threshold is set to 5 mm, and the gradation curve adopts Fuller gradation.

[0060] Divide the background grid in the aggregate placement area, and the grid size is 1 / 5-1 / 10 of the smallest aggregate particle size. Randomly place the center of the aggregate sphere at the grid node, and when new aggregate is placed, calculate the net distance between the new aggregate and the existing aggregate.

[0061] In order to reduce the number of aggregate determinations, only the net distance of aggregates that may cross or overlap is calculated. Assuming the maximum aggregate size is Assuming the maximum aggregate size is , the coordinates of the center of the newly placed aggregate sphere are , the particle size range is , then we only need to calculate The net distance between the existing aggregate and the following formula:

[0062]

[0063] Calculate the new aggregate and the existing aggregate that meets the above requirements The net distance between , whose formula is:

[0064] .

[0065] Generate the net distance vector between the new aggregate and the target area boundary and the existing aggregate , the net distance vector for:

[0066] ;

[0067] Where L is the length of the target area boundary.

[0068] According to the Determine whether the new aggregate is successfully placed. If the new aggregate is successfully placed, delete all nodes within the minimum particle size range inside and around the aggregate. If the new aggregate fails to be placed, only delete the center node to avoid re-selection.

[0069] In this embodiment, according to Determining whether the new aggregate is successfully placed includes:

[0070] if , new aggregate particle size , the new aggregate is put into place successfully. , new aggregate particle size , the new aggregate is put into place successfully. , then the new aggregate placement fails, among which is a random number uniformly distributed in the interval [0,1].

[0071] S102, using the background grid method to assign material properties to the elements to establish a three-dimensional microscopic model of PZT concrete.

[0072] The PZT in the model can be pasted on the surface of the model or buried in the model. In this embodiment, the PZT is pasted in the middle of the model surface. Figure 2 ,The process of establishing the three-dimensional mesoscopic model of PZT concrete specifically includes:

[0073] According to the frequency range of the piezoelectric admittance curve, the appropriate mesh size is selected to divide the concrete three-dimensional micro-geometric model. The concrete mesh size directly below the PZT should be the same as that of the PZT to ensure that the PZT unit is coupled with the underlying bonding layer and concrete nodes.

[0074] The unit material is assigned values ​​according to the coordinate information of the eight nodes of the unit. If the coordinates of all the nodes of the unit are in the aggregate, it is an aggregate unit; if the coordinates of all the nodes of the unit are in the mortar, it is a mortar unit; if the coordinates of the nodes of the unit are both in the aggregate and in the mortar, it is an ITZ unit.

[0075] S103, verifying the validity of the PZT concrete three-dimensional microscopic model.

[0076] In this embodiment, the process of verifying the validity of the PZT concrete three-dimensional mesoscopic model specifically includes:

[0077] Collect the piezoelectric admittance curve of the target concrete structure; compare the curve shape, resonant frequency, and resonant peak of the piezoelectric admittance data calculated by the model with the collected piezoelectric admittance curve; if the number of resonant peaks is consistent and the difference between the resonant frequency and the resonant peak does not exceed a preset range, the model is considered valid. In this embodiment, the preset range is set to 5%.

[0078] S104, if the PZT concrete three-dimensional microscopic model is valid, simulate and analyze the influence of different damage conditions on the concrete piezoelectric admittance curve.

[0079] In this embodiment, the process of simulating and analyzing the influence of different damage conditions on the concrete piezoelectric admittance curve specifically includes:

[0080] A three-dimensional microscopic model of PZT concrete with damage was established, and the piezoelectric admittance curve was calculated.

[0081] The root mean square deviation RMSD of the conductivity signal and the baseline conductivity data is calculated as follows:

[0082]

[0083] Where: For the The damage condition was measured The data values, The baseline conductivity signal is measured The data Values;

[0084] The calculated RMSD value is used to identify concrete damage.

[0085] This embodiment also carried out a series of example experiments according to the above method. In the example experiments, the test pieces were a series of cubic concrete test blocks with a size of 100 mm×100 mm×100 mm. Figure 3 , volume fraction of coarse aggregate The values ​​are 10%, 20%, 30% and 40% respectively. The particle size of coarse aggregate is between 5 and 20 mm, which conforms to the Fuller gradation. The Aglient 4294A impedance meter is used to collect the admittance signals under different damage conditions.

[0086] in: Figure 3 (a) is is 10% coarse aggregate, (b) is is 20% coarse aggregate, (c) is is 30% coarse aggregate, (d) is The red spheres represent aggregates with a particle size of 5-7.5 mm, the yellow spheres represent aggregates with a particle size of 7.5-10 mm, the cyan spheres represent aggregates with a particle size of 10-15 mm, and the blue spheres represent aggregates with a particle size of 15-20 mm.

[0087] See also Figure 4 and Figure 5 , Figure 4 This is a comparison chart between the actual aggregate gradation and the preset gradation. Figure 5 (a) is the three-dimensional microscopic model of PZT concrete, and (b) is the model section of the three-dimensional microscopic model of PZT concrete. The model section contains mortar, aggregate, and the interface transition zone ITZ between aggregate and mortar. It can be seen that all the aggregates put in are inside the test block, and the boundaries of the aggregates and test blocks do not intersect, and there is no intersection or overlap between the aggregates. Under the low aggregate condition ( ), the aggregates placed were randomly distributed in various positions of the test block, and there was no aggregate concentration. The gradation of the aggregates placed was almost consistent with the Fuller gradation. Figure 5 (a) is the overall model, and (b) is the model section. The model section contains mortar, aggregate, and the interface transition zone ITZ between aggregate and mortar.

[0088] See also Figure 6 , Figure 6 (a) is a comparison of the conductivity curves of the heterogeneous model, homogeneous model and test when the aggregate volume fraction is 10%; (b) is a comparison of the conductivity curves of the heterogeneous model, homogeneous model and test when the aggregate volume fraction is 20%; (c) is a comparison of the conductivity curves of the heterogeneous model, homogeneous model and test when the aggregate volume fraction is 30%; (d) is a comparison of the conductivity curves of the heterogeneous model, homogeneous model and test when the aggregate volume fraction is 40%. Figure 7 , (a) is a comparison diagram of the resonance frequencies of the constructed heterogeneous model, homogeneous model and experimental conductivity curve under different aggregate volume fractions; (b) is a comparison diagram of the resonance peaks of the constructed heterogeneous model, homogeneous model and experimental conductivity curve under different aggregate volume fractions.

[0089] Depend on Figure 6 and Figure 7It can be seen that the simulation results of this embodiment are compared with the existing homogeneous model simulation results and test results. When the aggregate content exceeds 30%, the simulated admittance curve of this embodiment is closer to the experimental value, because the higher aggregate content increases the heterogeneity of concrete, so that the model proposed in this embodiment more accurately reflects the real structure of concrete. With the increase of coarse aggregate content, the frequency of the resonance peak regularly moves to the right (i.e., the resonance frequency increases) due to the change of mass and elastic modulus. The numerical value and change trend of the model proposed in this embodiment are closer to the measured results than the existing homogeneous model. The resonance peak amplitude of the heterogeneous model and the experiment regularly moves downward (i.e., the resonance peak decreases), while the resonance peak amplitude of the homogeneous model is almost unchanged. These results show that the homogeneous model can hardly predict the performance changes of the concrete specimen caused by the aggregate volume content, which may be because the aggregate content enhances the heterogeneity of concrete and amplifies the dispersion and attenuation of stress waves, which cannot be reflected in the homogeneous model. Considering that coarse aggregate usually accounts for 30%-50% of the concrete volume, a model considering this heterogeneity can produce more accurate predictions.

[0090] like Figure 8 and Fig. 9 As shown in the figure, in order to quantify the change in the conductivity curve caused by damage, the conductivity characteristics of the undamaged state are used as a reference to calculate the root mean square deviation of each damage condition. It can be seen that the RMSD value increases with the increase in the severity of the damage. In addition, the RMSD value of the mesoscopic model under each damage state is closer to the experimental results, which once again proves that the model proposed in this embodiment can provide more accurate structural damage identification results.

[0091] In the embodiments of the present application, "at least one" refers to one or more, and "plurality" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent the existence of A alone, the existence of A and B at the same time, and the existence of B alone. Among them, A and B can be singular or plural. The character " / " generally indicates that the previous and subsequent associated objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b and c can be represented by: a, b, c, ab, ac, bc, or abc, where a, b, c can be single or multiple.

[0092] The above is only a specific implementation of the present application. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. The protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A PZT-based random aggregate mesoscopic concrete external damage identification method, characterized in that: include: According to the target concrete mix ratio, a random aggregate generation and placement algorithm is used to establish a concrete three-dimensional micro-geometric model, including: Fine aggregates with particle sizes smaller than the threshold are simplified as mortar matrix, and coarse aggregates with particle sizes larger than the threshold are simplified as spheres; Determine the proportion of aggregates within various particle size ranges according to the target concrete mix ratio and gradation curve; Divide the background grid in the aggregate placement area, and the grid size should be 1 / 5-1 / 10 of the smallest aggregate particle size; Randomly place the centers of aggregate balls at the grid nodes; When new aggregate is added, calculate the net distance between the new aggregate and the existing aggregate; Generate the net distance vector between the new aggregate and the target area boundary and the existing aggregate ; According to the Determine whether the new aggregate is successfully placed. If the new aggregate is successfully placed, delete all nodes within the minimum particle size range inside and around the aggregate. If the new aggregate fails to be placed, only delete the sphere center node to avoid re-selection. When new aggregate is added, the net distance between the new aggregate and the existing aggregate is calculated, including: Assume that the maximum aggregate size is , the coordinates of the center of the newly placed aggregate sphere are , the particle size range is , just calculate The net distance between the existing aggregate and the following formula: Calculate the new aggregate and the existing aggregate that meets the above requirements The net distance between , whose formula is: The net distance vector for: ； Where L is the length of the target area boundary; According to the Determining whether the new aggregate is successfully placed includes: if , new aggregate particle size , the new aggregate was put into use successfully; if , new aggregate particle size , the new aggregate was put into use successfully; if , then the new aggregate placement fails, among which is a random number uniformly distributed in the interval [0,1]; The background grid method is used to assign material properties to the elements to establish a three-dimensional microscopic model of PZT concrete. Verify the validity of the three-dimensional mesoscopic model of PZT concrete; If the three-dimensional microscopic model of PZT concrete is valid, the influence of different damage conditions on the piezoelectric admittance curve of concrete is simulated and analyzed.

2. The PZT-based random aggregate mesoscopic concrete external damage identification method according to claim 1 is characterized in that: The method of using the background grid method to assign material properties to the unit to establish a three-dimensional microscopic model of PZT concrete includes: According to the frequency range of the piezoelectric admittance curve, the appropriate mesh size is selected to divide the concrete three-dimensional micro-geometric model, where: the concrete mesh size directly below the PZT should be the same as that of the PZT to ensure that the PZT unit is coupled with the underlying bonding layer and concrete nodes; Assign values ​​to unit materials based on the coordinate information of the eight nodes of the unit; If the coordinates of all the nodes of the unit are in the aggregate, it is an aggregate unit; if the coordinates of all the nodes of the unit are in the mortar, it is a mortar unit; if the coordinates of the node of the unit are both in the aggregate and in the mortar, it is a mortar interface unit.

3. The PZT-based random aggregate mesoscopic concrete external damage identification method according to claim 1 is characterized in that: The verification of the validity of the PZT concrete three-dimensional mesoscopic model includes: Collect the piezoelectric admittance curve of the target concrete structure; Compare the curve shape, resonant frequency, and resonant peak of the piezoelectric admittance data calculated by the model with the collected piezoelectric admittance curve; If the number of resonance peaks is consistent and the difference between the resonance frequency and the resonance peak does not exceed a preset range, the model is considered valid.

4. The PZT-based random aggregate mesoscopic concrete external damage identification method according to claim 1 is characterized in that: If the three-dimensional microscopic model of PZT concrete is valid, the influence of different damage conditions on the piezoelectric admittance curve of concrete is simulated and analyzed, including: A three-dimensional microscopic model of PZT concrete with damage was established, and the piezoelectric admittance curve was calculated. The root mean square deviation RMSD of the conductivity signal and the baseline conductivity data is calculated as follows: Where: For the The damage condition was measured The data values, The baseline conductivity signal is measured The data Values; The calculated RMSD value is used to identify concrete damage.

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