Intelligent FRP-concrete composite structure deflection identification method based on resistance change

Abstract

The invention discloses an intelligent FRP-concrete composite structure deflection identification method based on resistance change. The method comprises the following steps: determining composite structure and intelligent FRP material information; arranging transverse electrodes along the length direction of the FRP, and collecting resistance change data of each electrode by using a resistance acquisition system; resistance change rate multi-point smooth fitting is carried out, and a polynomial mathematical model is established; and inputting a kernel function based on resistance change, and calculating the real-time deflection of any position point of the composite structure. According to the method, the real-time deflection of any position point of the structure can be monitored and reflected in a nondestructive mode under the condition that normal operation of the structure is not affected, and the method has the advantages of being real-time, comprehensive, high in accuracy, high in adaptability and nondestructive in monitoring and can be applied to deflection monitoring of structures such as bridges and tunnels.

Description

Technical Field

[0001] The present invention relates to the field of intelligent materials and structural health monitoring in civil engineering, and in particular to a method for identifying the deflection of an intelligent FRP-concrete composite structure based on resistance change. Background Art

[0002] Structural health monitoring is a key technology to ensure the long-term safe operation of buildings and infrastructure. With the rapid development of urbanization and industrialization, the stability and durability of structures such as bridges and tunnels have become an important part of public safety. Among the many structural performance parameters, deflection is an important indicator to measure structural deformation, which is crucial for evaluating the safety and functionality of the structure. Traditional deflection measurement methods, such as contact displacement meters and optical measurement equipment, are usually costly, complex to install, and may cause damage to the structure in some cases. In addition, these methods are often difficult to achieve continuous monitoring, limiting real-time understanding and rapid response to changes in structural performance.

[0003] Fiber reinforced polymer (FRP) materials are widely used in civil engineering to reinforce concrete structures due to their light weight, high strength and corrosion resistance. FRP reinforcement is usually applied to the concrete surface by gluing or winding to improve its bending, shear and seismic properties. For example, FRP reinforcement can significantly improve the bearing capacity of beams, slabs and columns, extend their service life, and achieve rapid reinforcement of structures in some cases. In particular, carbon fiber reinforced polymer (CFRP) can be used as a self-sensing material due to its piezoresistive effect and has the potential for self-monitoring of structures.

[0004] The piezoresistive effect refers to the phenomenon that the resistance of a material changes when it is subjected to pressure. CFRP exhibits a significant piezoresistive effect due to the characteristics of its microstructure. When CFRP is applied to a concrete structure and subjected to load, the contact resistance between its internal fibers and the matrix changes, and this change is proportional to the stress. By accurately measuring the resistance change of CFRP, the stress and deformation information of the structure can be indirectly obtained. This method has the advantages of easy installation, low cost, and continuous data acquisition, and provides a new technical approach for structural health monitoring.

[0005] Although there are many patent technologies dedicated to the monitoring of structural deflection, they still have some limitations in practical applications. For example, some patents rely on external sensors and complex data acquisition systems, such as the utility model patents with announcement numbers CN205426061U and CN204007499U, which not only increase costs but may also be interfered by environmental factors. In addition, some technologies may require invasive modifications to the structure, such as the utility model patent with announcement number CN202255273U, which discloses a strain sensor for measuring structural deflection, one end of which needs to be welded to the tested structure, and the other end passes through the mounting hole and is fixed at the mounting hole by a self-locking nut, affecting the integrity of the structure. In addition, the existing technology also has challenges in data analysis and long-term stability, which limits its wide application in complex engineering environments. Therefore, based on the self-sensing characteristics of CFRP, the present invention proposes an intelligent FRP-concrete composite structure deflection identification method without the need for additional sensors, which is highly integrated and non-destructive real-time monitoring of structural deflection. Summary of the invention

[0006] The purpose of the present invention is to provide an intelligent FRP-concrete composite structure deflection identification method based on resistance change to address the limitations of structural deflection monitoring methods in terms of real-time performance, cost-effectiveness, and possible damage to structural integrity, so as to achieve continuous and non-destructive monitoring of structural deflection, enhance the accuracy and timeliness of structural performance evaluation, thereby ensuring structural safety and extending its service life.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A method for identifying the deflection of an intelligent FRP-concrete composite structure based on resistance change includes determining the composite structure and intelligent FRP material information; arranging transverse electrodes along the length direction of the FRP and using a resistance acquisition system to collect resistance change data of each electrode; performing multi-point smooth fitting of the resistance change rate and establishing a polynomial mathematical model; inputting a core function based on resistance change and calculating the real-time deflection of any position point of the composite structure.

[0008] The FRP is CFRP or mixed with other non-conductive FRPs. The non-conductive FRP may be GFRP (glass fiber reinforced composite material), BFRP (basalt fiber reinforced composite material), or AFRP (aramid fiber reinforced composite material).

[0009] Furthermore, the number of FRP layers is single layer or multiple layers.

[0010] Furthermore, the hybrid method is that CFRP is in the middle layer, other non-conductive FRP is in the outer layer, and the FRP layers are impregnated and cured with epoxy resin.

[0011] The electrode is a conductive copper sheet or a conductive copper wire, wherein the width of the conductive copper sheet is 3 to 5 mm. The electrode is fixed between CFRP layers or between CFRP and non-conductive FRP layers by silver paste or conductive glue, and is connected to an external resistance acquisition system to achieve an end-to-end or multi-point series connection.

[0012] The resistance acquisition system is a sophisticated electronic device that can record and store the resistance value of each electrode in the FRP in real time, with an accuracy requirement of at least four decimal places to meet the standard of high-precision measurement.

[0013] The function based on the resistance change is:

[0014] Where: a is the parameter of FRP resistance change rate; y is the distance from the outer surface of the FRP of the structural cross section to the neutral axis; is a polynomial based on the resistance change rate, x The value of is the effective length of the structure L Within the range, that is, 0 ≤ x ≤ L .

[0015] Furthermore, the parameter of the FRP resistance change rate is a is the inherent property of the material to conduct electricity, and the relationship satisfies:

[0016] Where: ε is the FRP tensile strain.

[0017] The polynomial function mathematical model is in the form of:

[0018] Where: ∑ represents summation; subscript k =1 indicates the starting point of the summation, the superscript n Indicates the end point of the summation; α k It is k The coefficient of the term, x k yes x of k Power.

[0019] The smooth fitting adopts the least square method.

[0020] Furthermore, the theoretical formula of the core function based on resistance change is: Any cross section x Deflection f ( x) and bending moment M ( x ) is calculated as:

[0021] Where: E is the elastic modulus of the structural material, I is the moment of inertia of the structural cross section.

[0022] Any structure bottom x The strain at ε ( x ):

[0023] Furthermore, the resistance change rate of FRP at any point on the bottom of the structure and bending moment M ( x ) is:

[0024] Where: is the length of FRP x The resistance change rate at R 0 is the initial resistance of each FRP electrode, Δ R is the length of FRP x Resistance at any time R t With initial resistance R 0 The difference, Δ R = R t - R 0 ; Furthermore, the deflection at any point on the bottom of the structure f ( x ) and the resistance change rate of FRP The relationship is:

[0025] The beneficial effects of the present invention are: (1) Through the multi-point smoothing fitting technology, the noise and random fluctuations in the resistance change data are effectively reduced, and the accuracy and reliability of deflection identification are improved.

[0026] (2) By monitoring the structural deflection through resistance changes, the present invention does not require additional sensors or equipment, greatly reducing the monitoring cost and avoiding intrusive detection methods that cause additional damage to the structure, such as drilling or adding weight, thereby protecting the integrity and safety of the structure.

[0027] (3) The method of the present invention is applicable to FRP-concrete composite structures in different environments and working conditions, including but not limited to high temperature, low temperature, humid, dry and chemically corrosive environments; it has good adaptability and versatility under both static and dynamic load conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention is further described below using the accompanying drawings, but the embodiments in the accompanying drawings do not constitute any limitation to the present invention.

[0029] Figure 1 It is a schematic diagram of the structural deflection identification method of the present invention.

[0030] Figure 2 Schematic diagram of the electrode arrangement of the present invention.

[0031] Figure 3 It is a schematic diagram of the FRP hybrid method of the present invention.

[0032] Figure 4 Schematic diagram of calculation of an embodiment of the present invention.

[0033] Figure 5 It is a schematic cross-sectional view of an FRP-concrete composite structure according to an embodiment of the present invention.

[0034] exist Figures 1 to 5 It includes: 1. concrete structure, 2. load, 3. test point, 4. FRP, 5. deflection curve, 6. resistance test system, 7. electrode, 8. CFRP, 9. non-conductive FRP. DETAILED DESCRIPTION

[0035] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not limited to the scope of the present invention.

[0036] like Figures 1 to 5 As shown, a method for identifying the deflection of an intelligent FRP-concrete composite structure based on resistance change includes the following steps: Step 1: The composite structure is a simply supported beam or an outrigger beam at the bottom of the intelligent FRP reinforced concrete structure. Determine the effective length of the composite structure L and the cross-sectional form, which can determine the required structural length and the distance of the cross-sectional FRP outer surface from the neutral axis in the solution process; Specifically, the FRP is CFRP or mixed with other non-conductive FRP. The non-conductive FRP can be GFRP (glass fiber reinforced composite material), BFRP (basalt fiber reinforced composite material), AFRP (aramid fiber reinforced composite material), and the number of FRP layers is single or multi-layer. The mixing method is that CFRP is in the middle layer and other non-conductive FRP is in the outer layer. The FRP layers are impregnated and cured with epoxy resin. Effective length L is the distance between the supports at both ends of the structure. For rectangular cross-sections, the distance between the outer surface of the FRP and the neutral axis is half the height of the rectangle; for complex cross-sections, the position of the neutral axis is calculated using a graphical method, and the formula is: (1) In formula (1), A i It is i The area of ​​the part, y i It is i Partial Centroid y coordinate.

[0037] Step 2: Test the tensile strain and resistance change rate of the smart FRP sample. The specific operations are as follows: S1. Cut the smart FRP sample, make sure the surface is clean and the conductive fibers are exposed. Install the electrodes and connect the wires to the conductive fibers of the sample with conductive glue or clamps. Fix the sample to the fixture of the tensile tester, connect the resistance acquisition system and strain gauge, and make sure all connections are firm.

[0038] S2. Calibrate the tensile tester, strain gauge and resistance acquisition system to test the initial resistance of FRP R 0 Start the tensile tester and gradually apply the tensile load. At different stretching stages, record the corresponding strain value ε t And the resistance value of the sample R t .

[0039] S3. Use the data acquisition system to record the strain and resistance changes in real time. After the test, analyze the recorded data, draw a curve of the relationship between strain and resistance change rate, and calculate the resistance change rate. The relationship is: (2) In formula (2): Δ R = R t - R 0 , a is the resistance change rate parameter, ε is the FRP tensile strain.

[0040] Step 3: Arrange transverse electrodes along the length direction of the existing intelligent FRP, connect each electrode to the outermost electrode at one end, and use the resistance acquisition system to test the initial resistance and resistance change data of each electrode. The specific operations are as follows: S1. Cut a conductive copper sheet or conductive copper wire as an electrode with a width of 3~5mm. Fix the electrode between the CFRP layers or between the CFRP and non-conductive FRP layers with silver paste or conductive glue. Ensure that each electrode is evenly arranged along the length of the smart FRP sample and connected to the outermost electrode at one end.

[0041] S2. Connect the wires to each electrode, making sure the connections are secure. Connect the other end of the wires to the resistance acquisition system. Make sure all connections are secure and calibrate the resistance acquisition system to ensure the accuracy of the initial resistance measurement.

[0042] S3. Use the resistance acquisition system to test the initial resistance value of each electrode During the load application or environmental changes, the resistance change data of each electrode is recorded in real time. The resistance acquisition system should have an accuracy requirement of at least four decimal places to meet high-precision measurement standards. Real-time recording and storage of the resistance value of each electrode in the FRP, and calculation of the resistance change rate of each distributed electrode , the relationship is: (3) Step 4: Use the least squares method to smooth the resistance change rate of the electrodes at different positions at different times. x The resistance change rate of the electrode The polynomial is: (4) In formula (4): is the length of FRP x The resistance change rate at R 0 is the initial resistance of each FRP electrode, Δ R is the length of FRP x Resistance at any time R t With initial resistance R 0 The difference, Δ R = R t - R 0 ;∑ represents summation; subscript k =1 indicates the starting point of the summation, the superscript n Indicates the end point of the summation; α k It is kThe coefficient of the term, x k yes x of k Power.

[0043] Step 5: Based on the theoretical formula of material mechanics and boundary conditions, establish a core function based on resistance change, and input the structural information in step 1, the material information in step 2, and the polynomial mathematical model in step 4 to calculate the real-time deflection of any position of the composite structure. The core function based on resistance change is: (5) In formula (5): a is the parameter of FRP resistance change rate; y is the distance from the outer surface of the FRP of the structural cross section to the neutral axis; is a polynomial based on the resistance change rate, x The value of is the effective length of the structure L Within the range, that is, 0 ≤ x ≤ L .

[0044] Specifically, the theoretical formula based on material mechanics is: Any cross section x Deflection f ( x ) and bending moment M ( x ) is calculated as: (6) In formula (6): E is the elastic modulus of the structural material, I is the moment of inertia of the structural cross section.

[0045] Any structure bottom x The strain at ε ( x )for: (7) Combining formula (2) and formula (4), the resistance change rate of FRP at any point on the bottom of the structure can be obtained: and bending moment M ( x ) is: (8) Combining formula (6) and formula (8), the deflection at any point on the bottom of the structure is f ( x ) and the resistance change rate of FRP The relationship is: (9) Formula (9) is integrated twice and the boundary conditions are introduced: f (0) = f ( L ) = 0, the core function based on resistance change is: (10) Example

[0046] like Figure 4 As shown, an effective span L The cross-section of the reinforced concrete beam is 3.6m long and the cross-section size is 0.15m×0.3m. A vertical concentrated load is applied at the three equal points, and displacement meters are arranged at the support, loading point and mid-span. At the same time, transverse electrodes are arranged at the support, loading point and mid-span of the FRP within the effective span. The resistance change rate of the FRP is . Measure the resistance between the electrode and the leftmost support. Define the initial resistance between each electrode and the leftmost support electrode before the test starts. , i Take 0, 1, 2, 3, 4; test until t At this moment, the resistance between the electrodes is , then in t At this moment, the rate of change of distributed resistance Start testing, t 1 At this moment, the FRP distributed resistance change rate is ; t 2 At this moment, the FRP distributed resistance change rate is .

[0047] According to the above theoretical derivation, the results of the change of simply supported beam deflection in two aspects of theory and actual measurement are compared and analyzed, as shown in Table 1 and Table 2 Table 1 t 1 Comparison of calculation data of deflection change of simply supported beam at time

[0048] Table 2 t 2 Comparison of calculation data of deflection change of simply supported beam at time

[0049] It can be seen from Table 1 and Table 2 that the calculation results based on resistance change have a smaller deviation than the actual measured value, and its relative error is less than 2%. As the power of the fitting function increases, the deviation percentage decreases. It can be seen that the method based on resistance change to calculate the deflection of the intelligent FRP-concrete composite structure has a high accuracy and has good application value in the field of non-destructive monitoring.

[0050] The above contents are only preferred embodiments of the present invention. For ordinary technicians in this field, according to the concept of the present invention, there will be changes in the specific implementation methods and application scopes. The content of this specification should not be understood as limiting the present invention.

Claims

1. A method for identifying the deflection of an intelligent FRP-concrete composite structure based on resistance change, characterized in that: The steps include: Step 1: The composite structure is a simply supported beam or an outrigger beam at the bottom of the intelligent FRP reinforced concrete structure, and the effective length and cross-sectional form of the composite structure are determined; Step 2: Test the tensile strain and resistance change rate of the smart FRP sample; Step 3: Arrange transverse electrodes along the length direction of the existing intelligent FRP, connect each electrode to the outermost electrode at one end, and use a resistance acquisition system to test the initial resistance and resistance change data of each electrode; Step 4: Polynomial smoothing fitting of the resistance change rate of electrodes at different positions at different times; Step 5: Establish a core function based on resistance change, and input the structural information in step 1, the material information in step 2, and the polynomial mathematical model in step 4 to calculate the real-time deflection of any position point of the composite structure.

2. According to claim 1, a method for identifying the deflection of an intelligent FRP-concrete composite structure based on resistance change is characterized in that: The FRP is CFRP or mixed with other non-conductive FRPs. The non-conductive FRP may be GFRP (glass fiber reinforced composite material), BFRP (basalt fiber reinforced composite material), or AFRP (aramid fiber reinforced composite material).

3. According to claim 2, a method for identifying the deflection of an intelligent FRP-concrete composite structure based on resistance change is characterized in that: The number of FRP layers is single layer or multi-layer.

4. According to claim 2, a method for identifying the deflection of an intelligent FRP-concrete composite structure based on resistance change is characterized in that: The hybrid method is that CFRP is in the middle layer, other non-conductive FRP is in the outer layer, and the FRP layers are impregnated and cured with epoxy resin.

5. The method for identifying the deflection of an intelligent FRP-concrete composite structure based on resistance change according to claim 1 is characterized in that: The parameter of the FRP resistance change rate a is the inherent property of the material to conduct electricity, and the relationship satisfies: , where: ε is the FRP tensile strain.

6. The method for identifying the deflection of an intelligent FRP-concrete composite structure based on resistance change according to claim 1 is characterized in that: The electrode is a conductive copper sheet or a conductive copper wire, wherein the width of the conductive copper sheet is 3 to 5 mm. The electrode is fixed between CFRP layers or between CFRP and non-conductive FRP layers by silver paste or conductive glue, and is connected to an external resistance acquisition system to achieve an end-to-end or multi-point series connection.

7. The method for identifying the deflection of an intelligent FRP-concrete composite structure based on resistance change according to claim 1 is characterized in that: The resistance acquisition system is a sophisticated electronic device that can record and store the resistance value of each electrode in the FRP in real time, with an accuracy requirement of at least four decimal places to meet the standard of high-precision measurement.

8. The method for identifying the deflection of an intelligent FRP-concrete composite structure based on resistance change according to claim 1 is characterized in that: The different positions x The resistance change rate of the electrode The polynomial is: , where: is the length of FRP x The resistance change rate at R 0 is the initial resistance of each FRP electrode, ∆ R is the length of FRP x Resistance at any time R t With initial resistance R 0, that is, ∆ R = R t - R 0; ∑ means sum; subscript k =1 indicates the starting point of the summation, the superscript n Indicates the end point of the summation; α k It is k The coefficient of the term, x k yes x of k Power.

9. The method for identifying the deflection of an intelligent FRP-concrete composite structure based on resistance change according to claim 1 is characterized in that: The smooth fitting adopts the least square method.

10. The method for identifying the deflection of an intelligent FRP-concrete composite structure based on resistance change according to claim 1, characterized in that: The core function based on resistance change is: , where: a is the parameter of FRP resistance change rate; y is the distance from the outer surface of the FRP of the structural cross section to the neutral axis; is a polynomial based on the resistance change rate, x The value of is the effective length of the structure L Within the range, that is, 0 ≤ x ≤ L .

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