Fiber composite tendon bond-slip online monitoring system and method based on built-in OFDR distributed optical fiber

Abstract

This invention relates to the field of online bond-slip monitoring technology for reinforced concrete structures, specifically a bond-slip monitoring system and method for fiber composite reinforcement based on embedded OFDR distributed optical fibers. It includes: a fiber composite reinforcement assembly comprising multiple embedded OFDR distributed optical fiber-fiber composite reinforcements disposed within the concrete matrix, with distributed monitoring optical fibers and distributed temperature compensation optical fibers internally arranged within each fiber composite reinforcement; a light source emitting device for emitting laser light into the distributed monitoring and distributed temperature compensation optical fibers in the fiber composite reinforcement assembly and for receiving the returned scattered light; an OFDR sensing and measurement system for acquiring the optical fiber monitoring signals transmitted back from the distributed monitoring and distributed temperature compensation optical fibers; and a data acquisition instrument for processing the signals acquired by the OFDR sensing and measurement system.

Description

Technical Field

[0001] This invention relates to the field of online bond-slip monitoring technology for reinforced concrete structures, specifically an online bond-slip monitoring system and method for fiber composite reinforcement based on built-in OFDR distributed optical fiber. Background Technology

[0002] With the rapid expansion of construction projects, the reliability and safety of engineering structures are receiving increasing attention, making structural health monitoring a key focus. For reinforced concrete structures, load transfer between the reinforcing bars and concrete is primarily achieved through interfacial bond stress, aiming to ensure the reinforcing bars and concrete work together under stress. However, numerous studies have shown that reinforcing bar-concrete failure often occurs at the bond interface rather than within the materials themselves. At this point, neither the reinforcing bars nor the concrete have reached their strength limits, and the material properties are not fully realized, yet the structure already exhibits potential defects, rapidly and severely impacting its lifespan and reliability. Therefore, the bond interface is a weak point in reinforced concrete structures. To address this issue, extensive research has used bond-slip constitutive mathematical models to represent the performance of this weak interface, with interfacial slip being a crucial parameter. Thus, real-time monitoring of the bond-slip between the reinforcing bars and concrete is of great significance for the health monitoring of reinforced concrete structures.

[0003] Currently, engineering considerations regarding bond-slip performance mostly focus on the material properties of reinforcing bars and concrete, or on obtaining average parameters of bond-slip performance through laboratory tests, which then guide the design of projects. However, for practical engineering applications, there is still a lack of direct and effective methods for real-time monitoring of bond-slip. In real-world engineering projects under complex conditions, it is easy to miss crucial early warning signs that could lead to timely repairs, ultimately resulting in structural failure and significant losses and consequences.

[0004] OFDR (Optical Fiber Resonance Distribution) distributed fiber optic sensing technology, as a distributed monitoring technology, uses optical fiber as both a signal transmission medium and a sensing element. It can acquire specific physical quantities along the sensing direction of the fiber. Through the proper deployment of the fiber optic network, continuous spatial measurements can be performed, enabling large-scale health monitoring of the measured structure. However, while this technology boasts advantages such as high precision and high sensitivity, it also suffers from disadvantages such as low strength, low stiffness, fragile materials, and high requirements for the operating environment. The construction and service environments of reinforced concrete engineering are harsh, resulting in an extremely low survival rate for fiber optic installations within them. Therefore, this significantly limits the application of optical fibers in concrete engineering.

[0005] As a traditional reinforcing material, steel bars have long been used in concrete structures. However, their poor corrosion and rust resistance significantly affect the durability of the structure, and their heavy weight and long weld length also affect construction efficiency. As a fiber-derived product that my country has consistently prioritized for development, fiber-reinforced composite bars possess significant advantages such as high strength, rust resistance, corrosion resistance, light weight, and ease of processing. With continuous improvement and development in recent years, the use of fiber-reinforced composite bars to replace steel bars in concrete engineering construction has shown a certain development trend. Furthermore, compared to steel bars, the constituent materials and corresponding manufacturing processes of fiber-reinforced bars exhibit diversified and step-by-step characteristics, providing a convenient inherent basis for changing or adding / reducing the types of materials used to improve their function. Summary of the Invention

[0006] This invention aims to address the existing problems of lacking effective engineering means to obtain the bond-slip value between fiber-reinforced reinforcing bars and concrete in real time, non-destructively, accurately, and continuously, and lacking a quantitative calculation method between the measured data of embedded fiber-optic intelligent composite bars and the actual mechanical state parameters of the composite bars. It provides an online bond-slip monitoring system and method for fiber-reinforced composite bars based on built-in OFDR distributed optical fibers.

[0007] This invention adopts the following technical solution: an online monitoring system for bond-slip of fiber composite reinforcement based on built-in OFDR distributed optical fibers, comprising: a fiber composite reinforcement assembly, the fiber composite reinforcement assembly including multiple built-in OFDR distributed optical fibers-fiber composite reinforcements disposed inside a concrete matrix, wherein distributed monitoring optical fibers and distributed temperature compensation optical fibers are disposed inside the built-in OFDR distributed optical fibers-fiber composite reinforcements; a light source emitting device, the light source emitting device being used to emit laser light to the distributed monitoring optical fibers and distributed temperature compensation optical fibers in the fiber composite reinforcement assembly and to receive the returned scattered light; an OFDR sensing and measurement system, the OFDR sensing and measurement system being used to collect the optical fiber monitoring signals returned by the distributed monitoring optical fibers and distributed temperature compensation optical fibers; and a data acquisition instrument, used to process the signals collected by the OFDR sensing and measurement system.

[0008] In some embodiments, the two ends of the fiber composite rib assembly are respectively connected to adapter wires, the adapter wire at the input end is connected to the OFDR sensing and measurement system and the light source emitting device, and the adapter wire at the output end is connected to the tail end eliminator.

[0009] In some embodiments, the fiber composite reinforcement assembly includes a distributed monitoring fiber, a distributed temperature compensation fiber, epoxy resin, and a fiber composite reinforcement. The epoxy resin is wrapped around the outside of the distributed monitoring fiber and the distributed temperature compensation fiber, and the fiber composite reinforcement is wrapped around the outside of the epoxy resin.

[0010] In some embodiments, the distributed monitoring optical fiber includes an optical fiber core, a coating layer, a cladding layer, and a sheath arranged sequentially from the inside out.

[0011] In some embodiments, the distributed temperature compensation optical fiber includes an optical fiber core, a coating layer, a cladding layer, a tight sheath, and a loose sheath arranged sequentially from the inside out, with a gap provided between the tight sheath and the loose sheath.

[0012] A monitoring method for an online monitoring system of bond-slip of fiber composite reinforcement based on built-in OFDR distributed optical fiber includes the following steps:

[0013] S100: The light source emitting device emits laser light into the distributed monitoring fiber and the distributed temperature compensation fiber. The OFDR sensing and measurement system collects the optical signals transmitted back from the distributed monitoring fiber and the distributed temperature compensation fiber (the collected optical signal is the internal fiber spectral shift; the Rayleigh scattering spectral shift is proportional to the fiber strain and temperature, and the OFDR sensing and measurement system can directly perform this conversion and transmit the result to the data acquisition instrument), converting the optical signal into an electrical signal and transmitting it to the data acquisition instrument; the measured axial strain value ε of the distributed monitoring fiber is also transmitted. fx1 Subtract the measured axial strain value ε of the distributed temperature-compensated fiber optic cable fx2 To eliminate errors caused by external temperature changes in fiber optic monitoring results, the axial strain ε of the distributed monitoring fiber optic cable due to substrate deformation is obtained. fx This is referred to as distributed fiber optic axial strain.

[0014] S200: Establish the axial strain ε on the surface of the fiber composite reinforcement px (x) and the axial strain ε of the internally distributed optical fiber f The second-order linear nonhomogeneous differential equation (x) is solved by combining the boundary conditions to obtain the particular solution at coordinate x. f With ε px The calculation relationship;

[0015]

[0016]

[0017] In the formula, denoted as x, where x is the axial strain of the internal distributed fiber; p is the proportion of the residual strain inside the distributed fiber; L is half the bonding length of the distributed fiber; Ef is the elastic modulus of the distributed fiber; rf is the radius of the distributed fiber; rp is the radius of the fiber composite reinforcement; Gt is the shear modulus of the bonding layer; Gp is ​​the shear modulus of the fiber composite reinforcement; and t0 is the thickness of the bonding layer.

[0018] S300: Establish the slippage S(x) between the fiber composite bar and concrete, and the shear stress τ on the surface of the fiber composite bar, respectively.ps (x) and ε px The functional relationship between them is calculated by replacing continuous functions with dense discrete data to compute S(x) and τ. ps (x);

[0019]

[0020] In the formula, τ px (x)——Surface shear stress of the fiber composite reinforcement at coordinate x;

[0021] m — resolution of the distributed fiber optic sensor;

[0022] ε px (x)——Axial strain of the fiber composite reinforcement at coordinate x;

[0023] E p —The elastic modulus of fiber-reinforced composite reinforcement;

[0024]

[0025]

[0026] In the formula, S(x) represents the amount of slippage between the fiber composite reinforcement and the concrete at coordinate x.

[0027] L – Half the length of the distributed optical fiber bonding.

[0028] S400: The surface shear stress τ of the fiber composite reinforcement is obtained by calculating the axial strain of the distributed optical fiber. ps (x) and the slippage between the fiber composite bar and concrete, S(x).

[0029] A method for monitoring the internal health of concrete structures based on an online bond-slip monitoring system for fiber composite reinforcement with built-in OFDR distributed optical fibers is disclosed. When health problems such as non-uniform deformation and local fracture occur inside the concrete, a force is generated on the fiber composite reinforcement assembly. After the force is transmitted to the distributed optical fibers inside, a constant strain anomaly peak will appear at the corresponding position of the distributed optical fibers. By reading the coordinate position corresponding to the strain anomaly peak and performing coordinate conversion, the specific location of the health problem point inside the structure can be obtained.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention places distributed optical fibers inside the fiber composite reinforcement to provide a safe measurement environment for distributed optical fibers inside the concrete structure, thereby obtaining a concrete internal monitoring system with high spatial resolution (up to mm level).

[0032] (2) The present invention can monitor the bonding-slipping of the fiber composite reinforcement inside the concrete in real time, and obtain the bonding-slipping status and internal health status of the structure at any point along the monitoring system.

[0033] (3) The optical fiber used in this invention can be a common single-mode optical fiber, which is inexpensive and suitable for large-scale use in concrete structures.

[0034] (4) The fiber composite reinforcement used in this invention is not limited to the type of fiber and is applicable to a variety of fiber fields. Attached Figure Description

[0035] Figure 1 A schematic diagram of the overall structure of the fiber composite bar bonding-slip online monitoring system based on built-in OFDR distributed optical fiber provided in an embodiment of the present invention;

[0036] Figure 2 A schematic diagram of the overall structure of the built-in OFDR distributed optical fiber-fiber composite reinforcement provided in an embodiment of the present invention;

[0037] Figure 3 This is a schematic diagram of the cross-section of the distributed monitoring optical fiber in this invention;

[0038] Figure 4 This is a schematic diagram of the cross-section of the distributed temperature compensation optical fiber in this invention;

[0039] Figure 5 This is a schematic diagram of the OFDR distributed optical fiber-fiber composite reinforcement micro-segment in this invention;

[0040] Figure 6 This is a schematic diagram of the mechanical state of the OFDR distributed optical fiber micro-segment in this invention.

[0041] Figure 7 This is a schematic diagram of the mechanical state of the epoxy resin layer micro-segments in this invention;

[0042] Figure 8 This is a schematic diagram of a concrete-fiber composite reinforcement micro-segment in this invention;

[0043] Figure 9 This is a schematic diagram of the mechanical state of the fiber composite reinforcement micro-segment in this invention;

[0044] Explanation of reference numerals in the attached figures: 1-Data acquisition instrument, 2-OFDR sensing and measurement system and light source emitting device, 3-Fiber composite reinforcement assembly, 4-Adapter cable, 5-End canceller, 31-Distributed monitoring fiber, 32-Distributed temperature compensation fiber, 33-Epoxy resin, 6-Fiber composite reinforcement, 7-Fiber core, 8-Coating layer, 9-Clad layer, 10-Tight sheath, 11-Loose sheath. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] like Figure 1 As shown, this embodiment of the invention provides an online monitoring system for bond-slip of fiber composite reinforcement based on built-in OFDR distributed optical fiber, including a data acquisition instrument 1, an OFDR sensing and measurement system and a light source emitting device 2, a fiber composite reinforcement assembly 3, an adapter cable 4, and a tail end eliminator 5, connected in sequence.

[0047] The light source emitting device is used to emit laser light into the distributed optical fibers in the fiber composite reinforcement assembly and to receive the scattered light transmitted back by the distributed optical fibers.

[0048] The OFDR sensing and measurement system is used to collect the optical fiber monitoring signals transmitted back by the distributed optical fiber, convert the optical signals into electrical signals, and transmit them to the data acquisition instrument 1. The data acquisition instrument 1 includes a terminal computer and supporting data processing software, which is used to analyze the received distributed optical fiber monitoring values ​​and obtain the bond-slip parameters of the fiber composite reinforcement.

[0049] The fiber composite reinforcement assembly 3 includes multiple built-in OFDR distributed optical fiber-fiber composite reinforcements disposed inside the concrete matrix, each including a distributed monitoring optical fiber and a distributed temperature compensation optical fiber.

[0050] The distributed monitoring optical fiber in this invention serves as both a signal sensing device and a signal transmission device, enabling distributed online monitoring of the bond-slip of fiber composite reinforcement. This monitoring system boasts high spatial resolution (up to the millimeter level). For any point along the monitoring path, the surface shear stress τps(x) of the fiber composite reinforcement, the slippage S(x) between the fiber composite reinforcement and concrete, and the health status of the concrete matrix containing the fiber composite reinforcement can be obtained in real time through the spectral shift of the optical fiber. This invention offers high monitoring accuracy, a wide monitoring range, uses optical signal transmission along the path, resulting in low signal loss and strong resistance to electromagnetic interference.

[0051] like Figure 2 As shown, in one embodiment, the built-in OFDR distributed fiber-fiber composite reinforcement includes one distributed monitoring fiber and one distributed temperature compensation fiber. The distributed monitoring fiber and the distributed temperature compensation fiber are symmetrically arranged inside the fiber reinforcement and along the fiber reinforcement axis. The distance between the outer wall of the fiber and the outer wall of the fiber reinforcement is d0. The distributed monitoring fiber and the distributed temperature compensation fiber are fixed inside the fiber composite reinforcement with epoxy resin.

[0052] like Figure 3 As shown, as one embodiment, the distributed monitoring optical fiber includes an optical fiber core 7, a coating layer 8, a cladding layer 9, and a sheath 10 arranged sequentially from the inside out.

[0053] In a preferred embodiment, the fiber composite reinforcement assembly further includes a distributed temperature compensation optical fiber. This distributed temperature compensation optical fiber and the distributed monitoring optical fiber are symmetrically arranged inside the fiber composite reinforcement to monitor the fiber strain caused by temperature changes in the concrete matrix, thereby compensating for the monitored values ​​of the distributed monitoring optical fiber. Each fiber composite reinforcement has a corresponding distributed temperature compensation optical fiber, and both are located within the same fiber composite reinforcement, close to each other, resulting in a small temperature gradient and providing the most accurate and realistic temperature compensation value for the monitored values. Figure 4 As shown, the distributed temperature compensation optical fiber includes, from the inside out, an optical fiber core 7, a coating layer 8, a cladding layer 9, a tight sheath 10, and a loose sheath 11. A gap exists between the tight sheath and the loose sheath to ensure that the optical fiber and the tight sheath can move freely within the loose sheath and undergo free deformation. By setting a rigid sheath, stress caused by external interference cannot directly act on the distributed temperature compensation optical fiber; that is, the strain measured in the distributed temperature compensation optical fiber is only related to changes in the external temperature.

[0054] Furthermore, the distributed fiber-optic composite reinforcement is integrally arranged within the concrete as a reinforcing bar, using the reinforcement as the monitoring range to obtain bond-slip data between the fiber-optic composite reinforcement and the concrete. One end of the distributed monitoring fiber and the distributed temperature compensation fiber needs to be fused with adapter cable 4, which is then connected to the distributed fiber optic sensing and measurement system. This system is connected to a computer to collect and record data. The other end of the distributed monitoring fiber and the distributed temperature compensation fiber needs to be fused with adapter cable, which is then connected to a tail-end eliminator, thus forming a complete monitoring system.

[0055] As a preferred embodiment, considering the fragility of the optical fiber and the adapter cable itself and the roughness of concrete construction, in order to obtain accurate and complete monitoring information, the distributed monitoring optical fiber, distributed temperature compensation optical fiber and adapter cable outside the fiber composite reinforcement are laid out in the form of an outer stainless steel sleeve to avoid them from being severely impacted and damaged by the subsequent concrete pouring process and other external damage, and the optical fiber and adapter cable can move freely inside the stainless steel sleeve.

[0056] Each optical fiber in the fiber composite reinforcement assembly can be a common single-mode optical fiber, which is inexpensive and suitable for large-scale use in concrete structures.

[0057] The fiber composite reinforcement used in this invention is not limited to the type of fiber and is applicable to a variety of fiber fields.

[0058] This invention also provides a monitoring method for the above-mentioned online bond-slip monitoring system for fiber composite reinforcement based on built-in OFDR distributed optical fiber. This monitoring method can be executed in the data acquisition instrument and is used to analyze the received distributed optical fiber monitoring values ​​to obtain the bond-slip parameters between the fiber composite reinforcement and concrete. The monitoring method includes:

[0059] 1) Based on the interlaminar strain transfer theory between embedded optical fibers and resin layers and fiber composite reinforcement, the axial strain ε on the surface of the fiber composite reinforcement is established. px (x) and the axial strain ε of the internally distributed optical fiber f The second-order linear nonhomogeneous differential equation (x) is solved by combining the boundary conditions to obtain the particular solution at coordinate x. f With ε px 1) Calculate the relationship between the fiber-reinforced composite bar and the concrete; 2) Based on the basic mechanical equilibrium relationship of bond-slip and the geometric deformation compatibility relationship, establish the slip amount S(x) between the fiber-reinforced composite bar and the shear stress τ on the surface of the fiber-reinforced composite bar. ps (x) and ε px Based on the high-resolution characteristics of the distributed optical fiber in this invention, the functional relationship between S(x) and τ is calculated using dense discrete data instead of continuous functions. ps (x). Based on the above solution method, and considering the proportional relationship between the spectral shift of the distributed monitoring fiber and its axial strain, the surface shear stress τ of the fiber composite reinforcement can be calculated by directly acquiring the internal fiber spectral shift. ps (x) and the slippage between the fiber composite bar and concrete, S(x).

[0060] By observing whether there are constant abnormal strain peaks in the distributed monitoring optical fibers, it can be determined whether the fiber composite reinforcement has been subjected to abnormal impact or significant deformation, in order to obtain the health status of the internal structure.

[0061] The above monitoring method can also compensate for the interference of temperature changes in the concrete matrix by using the monitoring values ​​of distributed temperature-compensated optical fibers, including:

[0062] By subtracting the monitoring value from the monitoring value of the distributed temperature compensation fiber, the error caused by the temperature change of the concrete matrix can be eliminated.

[0063] By implementing the temperature error compensation measures described above, more accurate monitoring data can be obtained.

[0064] The following section explains the principles and detailed methods for obtaining various bond-slip parameters and compensating for temperature disturbances in the concrete matrix using the above monitoring methods.

[0065] The above monitoring methods can obtain two main categories of monitoring results: fiber composite bar-concrete bond-slip monitoring along the fiber bar length direction and internal structural health monitoring.

[0066] (1) Bond-slip monitoring between fiber composite reinforcement and concrete

[0067] For distributed optical fibers undergoing strain, the strain value can be obtained based on the principle of optical heterodyne detection. This involves emitting reference and signal light into the fiber, collecting and analyzing the backscattered spectrum in Rayleigh scattering, and then using the proportional relationship between the spectral shift and the fiber strain. The distributed optical fiber and fiber composite reinforcement are bonded together with an elastic resin material, and the fiber reinforcement is in turn bonded to the concrete matrix. External loads on the concrete matrix are transmitted sequentially to the fiber composite reinforcement, elastic resin, and distributed optical fiber according to certain mechanical relationships, ultimately causing strain in the distributed optical fiber. Furthermore, due to their significant differences in properties, the deformation of the concrete matrix and fiber composite reinforcement under external forces differs significantly, leading to slippage between the concrete and fiber composite reinforcement. All of these phenomena satisfy certain mechanical equilibrium and deformation compatibility relationships. Therefore, the bonding force and slippage between the concrete and fiber composite reinforcement can be deduced from the monitored fiber strain value through the following derivation process.

[0068] 1) Strain transfer relationship between OFDR distributed fiber-fiber composite reinforcement

[0069] like Figure 5 As shown, a mechanical analysis was performed on a micro-segment of the OFDR distributed fiber-fiber composite reinforcement.

[0070] like Figure 6 As shown, a mechanical equilibrium analysis is performed on a distributed optical fiber micro-segment, and the following results are obtained:

[0071] (1-1)

[0072] (1-2)

[0073] like Figure 7 As shown, mechanical equilibrium analysis is performed on a small segment of the resin layer, and the results are as follows:

[0074] (1-3)

[0075] (1-4)

[0076] Substituting equation (1-2) into equation (1-4), we get:

[0077] (1-5)

[0078] In the formula, r fThe radius of the fiber composite reinforcement;

[0079] σ fx The normal stress along the x-direction of the fiber-reinforced composite reinforcement;

[0080] Assuming all materials remain in a linear elastic state, then according to Hooke's Law, we have:

[0081] (1-6)

[0082] (1-7)

[0083] In the formula, E is the elastic modulus;

[0084] ε is the axial strain;

[0085] τ is the shear stress;

[0086] G is the shear modulus;

[0087] γ is the shear strain.

[0088] Substituting equations (1-6) and (1-7) into equation (1-5), we get:

[0089] (1-8)

[0090] Express the shear strain γ using the small displacement assumption:

[0091] (1-9)

[0092] Among them, the radial displacement w can be ignored compared with the axial displacement u.

[0093] Let equation (1-8) equal equation (1-9), we get:

[0094] (1-10)

[0095] For equation (1-10) from r f to r f Integrating at +t0, we get:

[0096] (1-11)

[0097] In the formula, u rf+t0 and u f These represent the axial displacements of the resin layer and the distributed optical fiber, respectively.

[0098] By performing the above calculations on the fiber composite reinforcement layer, the relationship between the surface of the fiber composite reinforcement and the axial displacement of the distributed optical fiber can be obtained:

[0099] (1-12)

[0100] To simplify the representation, let .

[0101] and Differentiating both sides of equation (1-12), we get:

[0102] (1-13)

[0103] Solving for the given information, we get: .

[0104] Determine the boundary conditions: (1-14)

[0105] Where, ε px This represents the axial strain of the fiber-reinforced composite reinforcement.

[0106] L is half the length of the distributed fiber bonding.

[0107] p represents the proportion of residual strain inside the distributed optical fiber.

[0108] We can obtain the results from equations (1-13) and (1-14). .

[0109] Therefore, the strain transfer relationship between OFDR distributed fiber-fiber composite reinforcements is as follows:

[0110] (1-15)

[0111] 2) The bond strength τ of the concrete-fiber composite reinforcement was inferred from the strain data. ps (x) and slip S(x)

[0112] like Figure 8 As shown, a mechanical analysis was performed on a concrete-fiber composite reinforcement micro-element segment:

[0113] like Figure 9 As shown, a mechanical equilibrium analysis was performed on a micro-segment of the fiber composite reinforcement, and the results are as follows:

[0114] (2-1)

[0115] (2-2)

[0116] Equation (1-15) can be used to calculate the surface axial strain data of fiber composite reinforcement based on the distributed fiber axial strain data at a specific resolution. When the distance between data points is small enough, equation (2-2) can be replaced by equation (2-3), thereby obtaining the surface shear stress data of fiber composite reinforcement.

[0117] (2-3)

[0118] In the formula, τ px (x)——Surface shear stress of the fiber composite reinforcement at coordinate x.

[0119] m — resolution of the distributed fiber optic sensor

[0120] E p — Elastic modulus of fiber-reinforced composite reinforcement.

[0121] This method treats the concrete matrix as an infinitely large whole and does not consider its own deformation. Therefore, the deformation of the fiber composite reinforcement is the slip.

[0122] Based on the geometric deformation compatibility relationship, at a certain point x on the fiber composite reinforcement... i The slip at a point can be expressed by the following formula:

[0123] (2-4)

[0124] When the distance between data points is small enough, equation (2-4) can be replaced by equation (2-5) to obtain the surface slip data of the fiber composite reinforcement.

[0125] (2-5)

[0126] (2-6)

[0127] In the formula, S(x) represents the amount of slippage between the fiber composite reinforcement and the concrete at coordinate x.

[0128] (2) Internal health monitoring of concrete structures

[0129] When non-uniform deformation or localized fractures occur within the concrete, significant forces are exerted on the fiber-reinforced composite reinforcement. These forces are transmitted to the internal distributed optical fibers, resulting in constant strain anomaly peaks at corresponding locations on the fibers. By reading the coordinates of these strain anomaly peaks and performing coordinate conversion, the specific location of the structural health problem can be determined. It should be noted that when the fiber-reinforced composite reinforcement becomes disjointed or fractured, the internal distributed optical fibers may also break. In such cases, Rayleigh scattering can still be used to locate and repair the fault.

[0130] The OFDR distributed optical fiber-fiber composite reinforcement described in this invention is embedded in the interior of large-volume concrete structures. In the early stages of concrete pouring, the intense heat release during cement hydration, coupled with the relatively enclosed and poorly cooled environment of the large-volume concrete, causes drastic changes in the internal temperature field of the concrete, lasting for 5-14 days. Furthermore, reinforced concrete structures are mostly used outdoors for extended periods, and seasonal temperature variations also cause significant and prolonged fluctuations in the internal temperature field. These factors all contribute to significant changes in the internal refractive index of the distributed optical fiber, leading to non-negligible errors in the fiber optic monitoring results. Therefore, this invention configures a distributed temperature compensation fiber within each reinforcing rib for the distributed monitoring fiber. The outermost and second-to-last layers of this fiber are a tight sheath and a loose sheath, respectively, with a certain space between them. This allows the distributed temperature compensation fiber and its flexible cladding to be protected from external forces, expanding and contracting freely only due to temperature. In other words, the strain monitored by the distributed temperature compensation fiber is only related to changes in external temperature. Subtracting the monitoring value of the distributed monitoring fiber from the monitoring value of the distributed temperature compensation fiber eliminates the error caused by external temperature changes in the fiber optic monitoring results.

[0131] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for monitoring the internal health of concrete structures based on an online bond-slip monitoring system for fiber composite reinforcement with built-in OFDR distributed optical fiber, characterized in that, The systems used include: The fiber composite reinforcement assembly (3) includes multiple built-in OFDR distributed optical fiber-fiber composite reinforcements disposed inside the concrete matrix. The built-in OFDR distributed optical fiber-fiber composite reinforcements are provided with distributed monitoring optical fiber (31) and distributed temperature compensation optical fiber (32). A light source emitting device is used to emit laser light into the distributed monitoring fiber (31) and distributed temperature compensation fiber (32) in the fiber composite rib assembly (3) and to receive the returned scattered light. The OFDR sensing and measurement system is used to acquire the fiber monitoring signals transmitted back from the distributed monitoring fiber (31) and the distributed temperature compensation fiber (32). Data acquisition instrument (1) is used to process the signals acquired by the OFDR sensing and measurement system; The monitoring method includes the following steps: S100: The light source emitting device emits laser light into the distributed monitoring fiber (31) and the distributed temperature compensation fiber (32). The OFDR sensing and measurement system collects the optical signals transmitted back from the distributed monitoring fiber (31) and the distributed temperature compensation fiber (32), converts the optical signals into electrical signals, and transmits them to the data acquisition instrument (1); the measured axial strain value ε of the distributed monitoring fiber is then transferred to the instrument. fx1 Subtract the measured axial strain value ε of the distributed temperature-compensated fiber optic cable fx2 To eliminate errors caused by external temperature changes in fiber optic monitoring results, the axial strain ε of the distributed monitoring fiber optic cable due to substrate deformation is obtained. fx This is referred to as distributed fiber optic axial strain. S200: Establish the axial strain ε on the surface of the fiber composite reinforcement px With the axial strain ε of the internally distributed optical fiber fx The second-order linear nonhomogeneous differential equation (x) is solved by combining the boundary conditions to obtain the particular solution at coordinate x. fx With ε px The calculation relationship; In the formula, denoted as x, where x represents the axial strain of the internal distributed fiber; p represents the proportion of the residual strain inside the distributed fiber; L represents half the bonding length of the distributed fiber; E represents the axial strain of the internal distributed fiber. f The elastic modulus of the distributed optical fiber; r f r is the radius of the distributed optical fiber. p G is the radius of the fiber composite reinforcement; t G is the shear modulus of the adhesive layer. p t0 represents the shear modulus of the fiber-reinforced composite reinforcement; t0 represents the thickness of the bonding layer. S300: Establish the slippage S(x) between the fiber composite bar and concrete, and the shear stress τ on the surface of the fiber composite bar, respectively. ps (x) and ε px The functional relationship between them is calculated by replacing continuous functions with dense discrete data to compute S(x) and τ. ps (x); In the formula, τ px (x)——Surface shear stress of the fiber composite reinforcement at coordinate x; m — resolution of the distributed fiber optic sensor; ε px —Axial strain of the fiber composite reinforcement at coordinate x; E p —The elastic modulus of fiber-reinforced composite reinforcement; In the formula, S(x) represents the amount of slippage between the fiber composite reinforcement and the concrete at coordinate x. L – Half the length of the distributed optical fiber bonding; S400: The surface shear stress τ of the fiber composite reinforcement is obtained by calculating the axial strain of the distributed optical fiber. ps (x) and the slippage between the fiber composite bar and concrete, S(x).

2. The method for monitoring the internal health of concrete structures based on the fiber composite reinforcement bond-slip online monitoring system with built-in OFDR distributed optical fiber as described in claim 1, characterized in that, The two ends of the fiber composite rib assembly (3) are connected to the adapter cable (4) respectively. The adapter cable (4) at the input end is connected to the OFDR sensing and measurement system and the light source emitting device (2), and the adapter cable (4) at the output end is connected to the tail end eliminator (5).

3. The method for monitoring the internal health of concrete structures using an online monitoring system for bond-slip of fiber composite reinforcement based on built-in OFDR distributed optical fiber as described in claim 1, characterized in that, The fiber composite reinforcement assembly (3) includes a distributed monitoring fiber (31), a distributed temperature compensation fiber (32), an epoxy resin (33), and a fiber composite reinforcement (6). The epoxy resin (33) is wrapped around the outside of the distributed monitoring fiber (31) and the distributed temperature compensation fiber (32), and the fiber composite reinforcement (6) is wrapped around the outside of the epoxy resin (33).

4. The method for monitoring the internal health of concrete structures based on the online bond-slip monitoring system for fiber composite reinforcement with built-in OFDR distributed optical fiber as described in claim 1 or 3, characterized in that, The distributed monitoring optical fiber (31) includes an optical fiber core (7), a coating layer (8), a cladding layer (9), and a sheath (10) arranged sequentially from the inside out.

5. The method for monitoring the internal health of concrete structures based on the online bond-slip monitoring system for fiber composite reinforcement with built-in OFDR distributed optical fiber as described in claim 1 or 3, characterized in that, The distributed temperature compensation optical fiber (32) includes an optical fiber core (7), a coating layer (8), a cladding layer (9), a tight sheath (10), and a loose sheath (11) arranged sequentially from the inside out, with a gap between the tight sheath (10) and the loose sheath (11).

6. The method for monitoring the internal health of concrete structures using an online monitoring system for bond-slip of fiber composite reinforcement based on built-in OFDR distributed optical fiber as described in claim 1, characterized in that: When non-uniform deformation or localized fracture occurs inside the concrete, it exerts a force on the fiber composite reinforcement assembly. This force is transmitted to the distributed optical fibers inside, and a constant strain anomaly peak will appear at the corresponding position of the distributed optical fibers. By reading the coordinate position corresponding to the strain anomaly peak and performing coordinate conversion, the specific location of the health problem point inside the structure can be obtained.

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