Concrete bridge deflection monitoring method based on distributed fiber bragg grating

Abstract

The invention relates to a concrete bridge deflection monitoring method based on a distributed fiber bragg grating in the field of optical fiber sensing. The problems that in an existing bridge deflection monitoring method, instruments are inconvenient to install and prone to being affected by the environment, and networking is difficult are solved. The invention provides a distributed fiber Bragg grating-based concrete bridge deflection monitoring method, which comprises the following steps of: determining a monitoring total length, and dividing units and end points; distributed fiber bragg grating sensors are arranged at the bottom and the upper portion of a bridge in a parallel topology mode, and monitoring intervals are divided; wavelength data are collected, and strain values of the bottom and the upper portion of the bridge in each monitoring interval under the load condition are obtained; calculating the curvature of each end point by using a parallel topology principle; and calculating the deflection value of each end point by using a finite integral method and a Lagrange interpolation method. The method is simple in thought, the deflection values of multiple points of the bridge are obtained through the wavelength-strain-curvature-deflection data processing flow, and the method has certain engineering use value.

Description

(I) Technical field

[0001] The invention relates to the field of bridge deflection monitoring, in particular to a concrete bridge deflection monitoring method based on distributed fiber Bragg gratings. (II) Background technology

[0002] After a concrete bridge is put into use for a long time, it is inevitable that damage will gradually accumulate over time. When faced with heavy loads, the bridge will show significant deflection changes. If this change exceeds the critical threshold that the bridge can withstand, it is very likely to lead to serious consequences. Therefore, continuous monitoring of the deflection changes of concrete bridges can effectively reduce the risk factor of the structure and avoid unfortunate accidents.

[0003] At present, traditional deflection monitoring equipment, such as dial indicators, extensometers and mechanical distance meters, face many challenges in monitoring bridge structure performance, exposing problems such as limited local deflection capture capability, time-consuming operation, and unsuitability for long-term monitoring. Therefore, emerging deflection monitoring technologies, such as differential GPS, drones and laser rangefinders, are gradually being introduced into long-term deflection monitoring of large concrete bridges. However, the measurement accuracy of differential GPS is low and is easily affected by weather and high-rise building obstruction; drones are greatly affected by weather conditions such as wind, and it is difficult to form a monitoring network; laser rangefinders are greatly restricted by light beams, and changes in beam tilt will directly affect monitoring accuracy, and it is inconvenient to fix and calibrate the instrument.

[0004] Since the end of the last century, fiber optic sensing technology has developed rapidly due to its simplicity, reliability, high sensitivity, and ease of forming a sensor network. It has become the mainstream direction of sensor technology development and is widely used in various sensing fields. In recent years, with the continuous advancement of distributed fiber optic sensing technology, some researchers have used Brillouin optical time domain analysis, Brillouin optical frequency domain analysis technology and other methods to monitor bridge deflection, but they are all greatly affected by environmental factors. (III) Summary of the invention

[0005] In order to solve the shortcomings of the existing bridge deflection monitoring method, the present invention studies a concrete bridge deflection monitoring method based on distributed fiber Bragg grating, which can reliably, real-time, quickly and effectively monitor the deflection change of the bridge. The specific technical scheme is as follows:

[0006] The method for monitoring the deflection of a concrete bridge based on a distributed fiber Bragg grating comprises the following steps:

[0007] Step 1. Determine the total monitoring length L, and divide the total monitoring length L into i segments (i is an even number) of length l along the length direction of the bridge, and number them into units 1 to i. The beginning and end of each unit are set as endpoints. The bridge has a total of (i+1) endpoints;

[0008] Step 2. The (i-1) endpoints of the 2nd to (i-1)th units divided in step 1 are set as the center points of the (i-1) Bragg gratings of the distributed fiber Bragg grating sensor, and the (i-1) endpoint is the midpoint of the (i-1) monitoring interval with a length of l. Within the total length of the (i-1) monitoring interval, the distributed fiber Bragg grating sensors distributed in a parallel topology are arranged at the bottom and the top of the bridge respectively;

[0009] Step 3. Collect the central wavelength data of the Bragg grating at the top and bottom of the bridge in the (i-1)th monitoring interval divided in step 2, and obtain the strain values ​​of the bottom and top of the bridge in the (i-1)th monitoring interval under any load condition;

[0010] Step 4. Use the parallel topology principle to establish the relationship between the strain value and the curvature of each monitoring interval in step 3, calculate the average curvature of the (i-1)th monitoring interval, and the average curvature of the (i-1)th monitoring interval is regarded as the curvature value at the i-th endpoint;

[0011] Step 5. Use the finite integration method and Lagrange interpolation method to establish the relationship function between the curvature value and the deflection value of each endpoint in step 4, and derive the deflection value at the 2nd to i-th endpoints of the bridge.

[0012] Furthermore, the total monitoring length L described in step 1 is defined as the support spacing on both sides of a span of the bridge, and the curvature value at the first endpoint and the (i+1)th endpoint is set to 0 and the deflection value is set to 0 by default.

[0013] Furthermore, the optical fiber of the distributed fiber Bragg grating sensor in step 2 is pre-forced, is in a straightened state within the monitoring interval, and is fixed at both ends of the (i-1) monitoring intervals.

[0014] Furthermore, the relationship between the Bragg grating center wavelength data and the strain value at the bottom of the bridge in the (i-1)th monitoring interval described in step 3 is:

[0015] ε l(i-1) =(λ l ' (i-1) -λ l(i-1) ) / λ l(i-1) / (1-ρe)

[0016] Where: ε l(i-1) represents the strain value at the bottom of the bridge in the (i-1)th monitoring interval; λ' l(i-1) represents the central wavelength data of the Bragg grating at the bottom of the bridge in the (i-1)th monitoring interval under the load condition; l(i-1) represents the initial central wavelength data of the Bragg grating at the bottom of the bridge in the (i-1)th monitoring interval; ρe is the effective elastic-optical coefficient of the optical fiber.

[0017] Furthermore, the relationship between the Bragg grating center wavelength data and the strain value on the upper part of the bridge in the (i-1)th monitoring interval described in step 3 is:

[0018] ε u(i-1) =(λ' u(i-1) -λ u(i-1) ) / λ u(i-1) / (1-ρe)

[0019] Where: ε u(i-1) represents the strain value of the upper part of the bridge in the (i-1)th monitoring interval; λ' u(i-1) represents the central wavelength data of the Bragg grating on the upper part of the bridge under the load condition in the (i-1)th monitoring interval; u(i-1) Represents the initial central wavelength data of the Bragg grating on the upper part of the bridge in the (i-1)th monitoring interval.

[0020] Furthermore, the relationship between the average curvature in the (i-1)th monitoring interval, the curvature value at the i-th endpoint and the strain value in step 4 is:

[0021]

[0022] Where: represents the average curvature in the (i-1)th monitoring interval; K i represents the curvature value at the i-th endpoint; h represents the distance between the distributed fiber Bragg grating sensors arranged on the upper and lower parts of the bridge at the (i-1)-th monitoring interval.

[0023] Furthermore, the calculation formula for the deflection at the i-th endpoint of the bridge in step 5 is:

[0024]

[0025] Where: F i represents the deflection value at the i-th endpoint; [A(i)] represents a 1×(i+1) screening matrix that can screen out the i-th element of the (i+1)×1 matrix; [x] represents an (i+1)×1 matrix composed of the distances of the (i+1) endpoints relative to the origin; x (i+1) It is represented by the (i+1)th element in [x]; [D] represents the (i+1)×(i+1)th order curvature-deflection conversion matrix; [K] represents the (i+1)×1th order matrix composed of the curvature values ​​at the (i+1)th endpoint; [D (i+1) ] represents the (i+1)th row in the curvature-deflection conversion matrix [D].

[0026] Advantages of the present invention

[0027] Compared with the prior art, the advantages of the present invention are:

[0028] (1) The bridge deflection monitoring method of the present invention is applicable to static loads and moving loads. Distributed fiber Bragg grating sensors are fixed at the bottom and top of the bridge, which can obtain multiple wavelength data at high frequency, facilitating the formation of a monitoring network.

[0029] (2) The bridge deflection monitoring method of the present invention uses a distributed fiber Bragg grating sensor pasted on the outside of the beam, which does not need to be buried in the concrete of the bridge structure, reducing the difficulty of on-site construction. At the same time, temperature compensation technology is used to eliminate the influence of temperature and improve the accuracy of the monitoring results.

[0030] (3) The bridge deflection monitoring method of the present invention is concise and clear in concept. The wavelength data of each monitoring interval at the bottom and top of the bridge is measured by a distributed fiber Bragg grating sensor, and the wavelength data is sent to a monitoring host using a fiber Bragg grating demodulator. The wavelength-strain-curvature-deflection data processing flow is performed in the monitoring host, and the deflection value of each end point of the bridge can be calculated, thereby obtaining the overall deformation of the bridge. (IV) Description of the drawings

[0031] Figure 1 Flow chart of the bridge deflection monitoring method.

[0032] Figure 2 Schematic diagram of the distribution of distributed fiber Bragg grating sensors on the beam.

[0033] Figure 3 Schematic diagram of the beam discretization process.

[0034] Figure 4 The schematic diagram of the deflection monitoring system is shown in FIG. 1 , which indicates a distributed fiber Bragg grating sensor, 2 indicates a fiber Bragg grating demodulator, and 3 indicates a monitoring host. (V) Specific implementation methods

[0035] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The concrete bridge deflection monitoring method based on distributed fiber Bragg grating provided in this specific embodiment is as follows: Figures 1 to 3 As shown, the following steps are included:

[0037] Step 1. Determine the required total monitoring length L, and divide the total monitoring length L into i segments of length l (i is an even number) along the length direction of the bridge. Number them into units 1 to i, and set the beginning and end of each unit as endpoints. The bridge has a total of (i+1) endpoints.

[0038] In this embodiment, the distance between the supports on both sides of a span of the bridge is defined as the required monitoring total length L. The first endpoint and the (i+1)th endpoint are at the inner edge of the supports at both ends. The supports provide vertical reaction forces to offset the vertical displacement caused by the load, so that the bridge cannot be deformed vertically at this position. At the supports at both ends of each span of the bridge, the rotation of the bridge is restricted, the bending moment approaches zero, and no bending or torsion occurs because the supports provide rigid constraints. Therefore, the curvature value and deflection value at the first endpoint and the (i+1)th endpoint are 0.

[0039] Step 2. The (i-1) endpoints of the 2nd to (i-1)th units divided in step 1 are set as the center points of the (i-1) Bragg gratings of the distributed fiber Bragg grating sensor, and the (i-1) endpoint is the midpoint of the (i-1) monitoring interval with a length of l. Within the total length of the (i-1) monitoring interval, distributed fiber Bragg grating sensors distributed in a parallel topology are arranged at the bottom and the top of the bridge respectively.

[0040] The optical fiber of the distributed fiber Bragg grating sensor is pre-loaded with force and is in a straightened state within the monitoring interval and fixed at both ends of (i-1) monitoring intervals. The bottom of the bridge is the tension zone, and the upper part of the bridge is the compression zone. The gauge length of the sensors in the tension zone and the compression zone in each monitoring interval is the length of the monitoring interval and is parallel to the neutral axis. The parallel topology distribution principle is applied to analyze the unidirectional bending state of the bridge under load conditions. Using the parallel topology distribution principle, the average curvature within the gauge length range is obtained:

[0041]

[0042] In formula (1), represents the average curvature within the gauge length, ρ represents the radius of curvature, Indicates the tensile strain value measured by the sensor at the bottom of the bridge. It represents the compressive strain value measured by the sensor located on the upper part of the bridge, and d represents the distance between the sensors arranged at the bottom of the bridge and the upper part of the bridge.

[0043] Step 3. Collect the Bragg grating center wavelength data of the distributed fiber Bragg grating sensors deployed at the top and bottom of the bridge in the (i-1) monitoring intervals in step 2, process the initial wavelength and the wavelength data under the load condition, and use the sensing principle that the Bragg center wavelength is sensitive to the change of strain to obtain the strain values ​​at the bottom and top of the bridge in the same monitoring interval under any load condition.

[0044] Specifically, based on the fiber Bragg grating sensing principle, the center wavelength of the fiber Bragg grating will drift due to changes in temperature and strain. In this embodiment, the distributed fiber Bragg grating sensor used uses temperature compensation technology to eliminate the influence of temperature, so that the drift of the center wavelength of the Bragg grating monitored in the experiment is all derived from the strain value of the axial tension and compression of the optical fiber under load conditions. The relationship between the drift of the center wavelength of the Bragg grating and the strain change is as follows:

[0045] Δλ Bε =λ B (1-ρe)Δε (2)

[0046] In formula (2), Δλ Bε The central wavelength drift of the Bragg grating caused by strain, λ B represents the central wavelength of the Bragg grating, ρe represents the effective elastic-optical coefficient of the optical fiber, Δε represents the axial strain, and the strains of the optical fiber at the bottom and top of the bridge distributed in the (i-1) monitoring intervals are the axial tension and axial pressure respectively.

[0047] The relationship between the central wavelength data of the Bragg grating at the bottom of the bridge in the (i-1)th monitoring interval and the strain value is:

[0048] ε l(i-1) =(λ′ l(i-1) -λ l(i-1) ) / λ l(i-1) / (1-ρe) (3)

[0049] In formula (3), ε l(i-1) represents the strain value at the bottom of the bridge in the (i-1)th monitoring interval, λ' l(i-1) represents the central wavelength data of the Bragg grating at the bottom of the bridge in the (i-1)th monitoring interval under the load condition, λ l(i-1) Represents the initial central wavelength data of the Bragg grating at the bottom of the bridge in the (i-1)th monitoring interval.

[0050] The relationship between the central wavelength data of the Bragg grating arranged on the upper part of the bridge in the (i-1)th monitoring interval and the strain value is:

[0051] ε u(i-1) =(λ′u(i-1) -λ u(i-1) ) / λ u(i-1) / (1-ρe) (4)

[0052] In formula (4), ε u(i-1) represents the strain value of the upper part of the bridge in the (i-1)th monitoring interval, λ' u(i-1) represents the central wavelength data of the Bragg grating on the bridge under the load condition in the (i-1)th monitoring interval, λ u(i-1) Represents the initial central wavelength data of the Bragg grating on the upper part of the bridge in the (i-1)th monitoring interval.

[0053] Step 4. Use the parallel topology principle to process the strain values ​​monitored by the sensors at the bottom and top of the bridge in each monitoring interval in step 3, establish the relationship between the strain value and the curvature, and calculate the average curvature of the (i-1)th monitoring interval. The average curvature of the (i-1)th monitoring interval is regarded as the curvature value at the i-th endpoint;

[0054] In this embodiment, the i-th endpoint is located at the center of the (i-1)th monitoring interval. It can be considered that the curvature at the endpoint can reflect the overall situation in the monitoring interval and can more accurately reflect the overall geometric characteristics of the interval. The curvature at the i-th endpoint is considered to be equal to the average curvature in the (i-1)th monitoring interval, so that all curvature information in the interval is effectively simplified to an average value.

[0055] Specifically, the relationship between the average curvature in the (i-1)th monitoring interval, the curvature value at the i-th endpoint and the strain value obtained based on formula (1) is:

[0056]

[0057] In formula (5), represents the average curvature in the (i-1)th monitoring interval, K i represents the curvature value at the i-th endpoint, and h represents the distance between the distributed fiber Bragg grating sensors arranged on the upper part and the lower part of the bridge at the (i-1)-th monitoring interval.

[0058] Step 5. Use the finite integration method and Lagrange interpolation method to establish the relationship function between the curvature value and the deflection value of each endpoint in step 4, and derive the deflection value at the 2nd to i-th endpoints of the bridge.

[0059] Specifically, the function F=F(x) on the domain [0,L] is defined as the deflection function. According to the mathematical relationship between curvature and deflection, we know that:

[0060]

[0061] In formula (6), φ(x) represents the curvature, F′(x) represents the first-order derivative of the deflection, and F″(x) represents the second-order derivative of the deflection. Most concrete bridge structures are small deformation structures. According to the general practice of material mechanics, formula (6) can be converted into:

[0062] φ(x)=-F″(x)(7)

[0063] The beam is discretized, and the beam with a total length of L is divided into i segments (i is an even number). The length of each segment is denoted as l, and the position of the first endpoint is the origin. The discretized data at the (i+1) endpoints on the beam are numbered: [x] represents the (i+1)×1-order matrix composed of the distances of the (i+1) endpoints relative to the origin, [F] represents the (i+1)×1-order matrix composed of the deflection values ​​at the (i+1) endpoints, [F′] represents the (i+1)×1-order matrix composed of the first-order derivatives of the deflection values ​​at the (i+1) endpoints, and [F″] represents the (i+1)×1-order matrix composed of the second-order derivatives of the deflection values ​​at the (i+1) endpoints.

[0064] Combining formula (5) with formula (7), we can obtain the relationship between the curvature value and the second-order derivative of the deflection value at the (i+1) endpoint:

[0065] [K]=-[F″](8)

[0066] In formula (8), [K] represents the (i+1)×1 matrix composed of the curvature values ​​at the (i+1) endpoints. Using [x] and [F″], the Lagrange interpolation method is used to obtain a polynomial function F″=F″(x) that just passes through the (i+1) points on the two-dimensional plane. The core formula of the Lagrange interpolation method is:

[0067]

[0068] In formula (9), F k ″ represents the kth element in [F″], x k With x j They represent the kth and jth elements in [x] respectively. Using the finite integral formula, we integrate F″(x) and get the integral expression of the (i+1)th element in [F′]:

[0069]

[0070] In formula (10), F′ (i+1) represents the (i+1)th element in [F′], and F′(0) represents the value of the function F′=F′(x) at x=0. Further calculation of formula (10) yields F′ (i+1) The relationship with [F″] is:

[0071] F′(i+1) = l·[M (i+1) ]·[F″]+F′(0) (11)

[0072] [M k ](k=1,2,...i+1) is defined as the integral transformation matrix. In formula (11), [M (i+1) ] is the same as F′ (i+1) The corresponding 1×(i+1)-order integral transformation matrix. k (k=1,2,...i+1) respectively corresponding to the (i+1) 1×(i+1) order integral transformation matrices are combined to obtain:

[0073]

[0074] In formula (12), [M] is a (i+1)×(i+1)-order matrix composed of (i+1) integral transformation matrices. Combining formula (11) with formula (12), the relationship between [F′] and [F″] is obtained as follows:

[0075] [F′]=l·[M]·[F″]+F′(0)·[1](13)

[0076] In formula (13), [1] is a (i+1)×1-order all-one matrix. Combined with formula (12), the curvature-deflection conversion matrix [D] is defined as:

[0077] [D]=[M]·[M](14)

[0078] Using the finite integration method, the integral relationship expression between F(x) and F″(x) is obtained as follows:

[0079]

[0080] In formula (15), F(0) represents the value of function F=F(x) at x=0. Combining formula (13), formula (14) and formula (15), the relationship expression between [F] and [F″] is obtained:

[0081] [F] = l 2 ·[D]·[F″]+F′(0)·[x]+F(0)·[1] (16)

[0082] Using formula (8), further analysis is performed on formula (16) to obtain the relationship between deflection and curvature:

[0083] [F]=F′(0)·[x]+F(0)·[1]-l 2 [D] · [K] (17)

[0084] In this embodiment, the deflection values ​​at the first endpoint located at the left origin and the (i+1)th endpoint located at the right boundary are both 0, so F(0) = 0. By eliminating F'(0) using the boundary condition of the deflection value being 0, the relationship between deflection and curvature is deduced as follows:

[0085]

[0086] In formula (18), x (i+1) represents the (i+1)th element in [x], [D (i+1) ] represents the (i+1)th row in the curvature-deflection conversion matrix [D]. After screening [F], the deflection calculation formula at the i-th endpoint of the bridge is obtained as follows:

[0087]

[0088] In formula (19), F i represents the deflection value at the i-th endpoint, and [A(i)] represents a 1×(i+1)-order screening matrix that can screen out the i-th element in [F].

[0089] Based on the above steps, the deflection values ​​of each end point between the supports of a certain span of the concrete bridge can be obtained. Figure 4 The invention shows a deflection monitoring system designed based on the distributed fiber Bragg grating concrete bridge deflection monitoring method. The distributed fiber Bragg grating sensor 1 arranged at the bottom and the top of the bridge is connected to the fiber Bragg grating demodulator 2, and the fiber Bragg grating demodulator 2 is connected to the monitoring host 3. When the distributed fiber Bragg grating sensor 1 measures the real-time wavelength data of each monitoring interval under any load, it is sent to the monitoring host 3 through the fiber Bragg grating demodulator 2. In the data processing software in the monitoring host 3, the fiber Bragg grating sensing principle, parallel topology principle, Lagrange interpolation method and finite integration method are used to calculate the deflection value of each end position of the bridge at any time.

[0090] This embodiment utilizes distributed fiber Bragg grating sensors attached to the bottom and top of the bridge to obtain multiple wavelength data at a high frequency, and utilizes the wavelength-strain-curvature-deflection data processing flow to achieve real-time monitoring of the deflection values ​​at each end point of the bridge. It has the advantages of being less affected by environmental factors, simple sensor installation, and easy to form a monitoring network.

[0091] Although the present invention is described herein with reference to specific embodiments, it should be understood that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Any technician familiar with the technical field can make equivalent replacements or changes based on the concept of the present invention without departing from the spirit and scope of the present invention, which should be within the protection scope of the present invention. It should be understood that the scope of protection required by the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for monitoring the deflection of a concrete bridge based on distributed fiber Bragg gratings, characterized in that: The following steps are involved: Step 1. Determine the total monitoring length L, and divide the total monitoring length L into i segments (i is an even number) of length l along the length direction of the bridge, and number them into units 1 to i. The beginning and end of each unit are set as endpoints. The bridge has a total of (i+1) endpoints; Step 2. The (i-1) endpoints of the 2nd to (i-1)th units divided in step 1 are set as the center points of the (i-1) Bragg gratings of the distributed fiber Bragg grating sensor, and the (i-1) endpoint is the midpoint of the (i-1) monitoring interval with a length of l. Within the total length of the (i-1) monitoring interval, the distributed fiber Bragg grating sensors distributed in a parallel topology are arranged at the bottom and the top of the bridge respectively; Step 3. Collect the central wavelength data of the Bragg grating at the top and bottom of the bridge in the (i-1)th monitoring interval divided in step 2, and obtain the strain values ​​of the bottom and top of the bridge in the (i-1)th monitoring interval under any load condition; Step 4. Use the parallel topology principle to establish the relationship between the strain value and the curvature of each monitoring interval in step 3, calculate the average curvature of the (i-1)th monitoring interval, and the average curvature of the (i-1)th monitoring interval is regarded as the curvature value at the i-th endpoint; Step 5. Use the finite integration method and Lagrange interpolation method to establish the relationship function between the curvature value and the deflection value of each endpoint in step 4, and derive the deflection value at the 2nd to i-th endpoints of the bridge.

2. The method for monitoring concrete bridge deflection based on distributed fiber Bragg grating according to claim 1 is characterized in that: The total monitoring length L described in step 1 is defined as the support spacing on both sides of a span of the bridge. By default, the curvature value at the first endpoint and the (i+1)th endpoint is 0 and the deflection value is 0.

3. The method for monitoring concrete bridge deflection based on distributed fiber Bragg grating according to claim 1, characterized in that: The optical fiber of the distributed fiber Bragg grating sensor in step 2 is pre-forced, is in a straightened state within the monitoring interval, and is fixed at both ends of the (i-1) monitoring intervals.

4. The method for monitoring concrete bridge deflection based on distributed fiber Bragg grating according to claim 1, characterized in that: The relationship between the Bragg grating center wavelength data and the strain value at the bottom of the bridge in the (i-1)th monitoring interval described in step 3 is: e l(i-1) =(λ l ′ (i-1) -l l(i-1) ) / min l(i-1) / (1-re) Where: ε l(i-1) represents the strain value at the bottom of the bridge in the (i-1)th monitoring interval; λ' l(i-1) represents the central wavelength data of the Bragg grating at the bottom of the bridge in the (i-1)th monitoring interval under the load condition; l(i-1) represents the initial central wavelength data of the Bragg grating at the bottom of the bridge in the (i-1)th monitoring interval; ρe is the effective elastic-optical coefficient of the optical fiber.

5. The method for monitoring concrete bridge deflection based on distributed fiber Bragg grating according to claim 1, characterized in that: The relationship between the Bragg grating center wavelength data and the strain value on the upper part of the bridge in the (i-1)th monitoring interval described in step 3 is: e u(i-1) =(λ' u(i-1) -l u(i-1) ) / min u(i-1) / (1-re) Where: ε u(i-1) represents the strain value of the upper part of the bridge in the (i-1)th monitoring interval; λ' u(i-1) represents the central wavelength data of the Bragg grating on the bridge under the load condition in the (i-1)th monitoring interval; u(i-1) Represents the initial central wavelength data of the Bragg grating on the upper part of the bridge in the (i-1)th monitoring interval.

6. The method for monitoring concrete bridge deflection based on distributed fiber Bragg grating according to claim 1, characterized in that: The relationship between the average curvature in the (i-1)th monitoring interval, the curvature value at the i-th endpoint and the strain value described in step 4 is: Where: represents the average curvature in the (i-1)th monitoring interval; K i represents the curvature value at the i-th endpoint; h represents the distance between the distributed fiber Bragg grating sensors arranged on the upper and lower parts of the bridge at the (i-1)-th monitoring interval.

7. The method for monitoring concrete bridge deflection based on distributed fiber Bragg grating according to claim 1, characterized in that: The calculation formula for the deflection at the i-th end point of the bridge described in step 5 is: Where: F i represents the deflection value at the i-th endpoint; [A(i)] represents a 1×(i+1) screening matrix that can screen out the i-th element of the (i+1)×1 matrix; [x] represents an (i+1)×1 matrix composed of the distances of the (i+1) endpoints relative to the origin; x (i+1) Represented as the (i+1)th element in [x]; [D] represents the (i+1)×(i+1)-order curvature-deflection conversion matrix; [K] represents the (i+1)×1-order matrix composed of the curvature values ​​at the (i+1) endpoints; [D (i+1) ] represents the (i+1)th row in the curvature-deflection conversion matrix [D].

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