Bridge structure monitoring device and method based on distributed optical fiber coupling

Abstract

The invention belongs to the technical field of bridge monitoring, and discloses a bridge structure monitoring device and method based on distributed optical fiber coupling, and the device comprises two supporting racks, a loading weight, a test optical fiber, a BOTDA optical fiber distributed demodulator, a supporting platform, and a dial indicator. The two supporting racks are respectively arranged on two sides of the bottom of the bridge concrete beam to form a simply supported structure, the loading weight is arranged above the midspan position of the bridge concrete beam, and the testing optical fiber is arranged in the center of the upper surface of the bridge concrete beam along the length direction of the bridge concrete beam; two ends of the test optical fiber are connected with the BOTDA optical fiber distributed demodulator; the supporting platform and the dial indicator are arranged below the midspan position of the bridge concrete beam, and the dial indicator is located between the bridge concrete beam and the supporting platform and used for measuring the midspan deflection of the bridge concrete beam. According to the method, the coupling performance of the optical fiber and the concrete can be remarkably improved, the monitoring error is reduced, and high-precision distributed monitoring of the deflection and strain of the bridge is realized by combining algorithm correction.

Description

Technical Field

[0001] This invention belongs to the field of bridge monitoring technology, specifically relating to a bridge structure monitoring device and method based on distributed optical fiber coupling. Background Technology

[0002] In existing bridge structural health monitoring systems, commonly used point sensors (such as resistance strain gauges and accelerometers) can only provide information from a limited number of measurement points, making it difficult to cover the entire span of the bridge. Furthermore, they are susceptible to environmental factors during long-term service, resulting in poor durability and high maintenance costs. These problems limit further improvements in monitoring accuracy and the full utilization of monitoring data. To overcome this limitation, researchers have proposed using distributed fiber optic sensing technology to acquire continuous strain or displacement distributions along the entire length of the fiber, thereby reducing the number of sensors and improving monitoring efficiency and spatial resolution.

[0003] Distributed fiber optic sensing enables full-length monitoring of bridge deformation, deflection, and crack development, representing a significant advancement in bridge health monitoring. Currently, there are two main types of distributed fiber optic monitoring methods: surface-mounted deployment, where the fiber is adhered to the bridge surface—simple in structure but prone to unstable coupling and long-term detachment; and embedded deployment, where the fiber is pre-buried within concrete or dedicated conduits—offering better coupling but complex construction and limited flexibility. Furthermore, in terms of data processing, existing methods often directly utilize strain data output by BOTDA (Bridge-to-the-Air) sensors, lacking effective error correction mechanisms, leading to discrepancies between measurement results and theoretical deflection or dial gauge readings.

[0004] In summary, the application of distributed fiber optic sensing in engineering is limited by insufficient coupling between optical fibers and concrete structures, significant differences in optical cable types, inconsistent deployment methods, and systematic deviations between BOTDA measurement results and actual values. Therefore, it is necessary to improve existing distributed fiber optic coupling structures to ensure the long-term stability and engineering practicality of bridge structure monitoring results. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in current bridge structure overall deformation monitoring technologies, such as poor fiber-structure coupling, low strain transfer efficiency, complex installation and construction, and deviations between monitoring results and actual values. The invention provides a bridge structure coupling monitoring device and method based on distributed optical fibers that is easy to operate, low in cost, and can achieve automated and intelligent monitoring of the overall deformation of bridge structures.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a bridge structure monitoring device based on distributed optical fiber coupling, comprising two support platforms, a loading weight, a test optical fiber, a BOTDA fiber distributed demodulator, a support platform, and a dial gauge; the two support platforms are respectively set on both sides of the bottom of the bridge concrete beam to form a simply supported structure, the loading weight is set above the mid-span position of the bridge concrete beam, and the test optical fiber is set at the center of its upper surface along the length direction of the bridge concrete beam; both ends of the test optical fiber are connected to the BOTDA fiber distributed demodulator; the support platform and the dial gauge are set below the mid-span position of the bridge concrete beam, and the dial gauge is located between the bridge concrete beam and the support platform, for measuring the mid-span deflection of the bridge concrete beam.

[0007] An optical fiber groove is provided along the length direction at the center of the upper surface of the bridge concrete beam, and the test optical fiber is fixed in the optical fiber groove by epoxy resin.

[0008] The width of the fiber optic slot is 1.2-1.5 times the diameter of the test fiber, and the depth of the slot is 1.1-1.3 times the diameter of the test fiber.

[0009] The test optical fiber is a bare fiber with a diameter of approximately 250 μm or a high-transmission tight-packed sheathed optical cable with a diameter of 2.0 mm.

[0010] The test optical fiber is subjected to a controllable pre-stretch of 1-10 mm through a servo guide rail pre-stretching platform before being fixedly laid on the upper surface of the bridge concrete beam; when the test optical fiber is a bare fiber, the stretching amount is set to 5 mm, and when the test optical fiber is a tightly sheathed optical cable, the stretching amount is set to 3 mm.

[0011] Furthermore, this invention also provides a bridge structure monitoring method based on distributed optical fiber coupling, implemented using the aforementioned bridge structure monitoring device based on distributed optical fiber coupling, comprising the following steps: Step 1: Apply pre-stretching to the test fiber using a servo guide rail pre-stretching platform; Step 2: Process fiber optic grooves along the length of the concrete beam surface of the bridge, then embed the test fiber into the fiber optic grooves and apply epoxy resin evenly for fixation; at the same time, connect the test fiber to the BOTDA demodulator. Step 3: Apply an experimental load at the mid-span of the bridge concrete beam and measure the mid-span deflection under the applied experimental load using a dial gauge; simultaneously, collect the strain distribution along the applied experimental load using a BOTDA demodulator; then calculate the experimental deflection function based on the strain distribution along the applied experimental load and calculate the correction coefficient. Step 4: Set the pre-stretched measuring fiber inside the concrete beam of the actual bridge, obtain the strain distribution along the bridge in the concrete beam using a BOTDA demodulator, and calculate the deflection function. Step 5: Correct the deflection function using a correction factor to obtain the corrected deflection distribution.

[0012] In step 1, the servo guide rail pre-stretching platform includes a platform guide rail, a sliding platform, an optical fiber clamp, and an adjustable column. Both ends of the test optical fiber are fixed by one of the optical fiber clamps, and the optical fiber clamp is set on the platform guide rail by a sliding platform. The adjustable column is set on the platform guide rail and located between the two optical fiber clamps. The middle part of the test optical fiber is set on the adjustable column. The adjustable column is used to adjust the height of the test optical fiber so that the force direction is parallel to the movement direction of the sliding platform. The sliding platform is used to drive the optical fiber clamp to move along both ends of the platform guide rail to realize the pre-stretching of the test optical fiber.

[0013] In step 3, the formula for calculating the correction coefficient is: ; Where n represents the correction factor. This indicates the mid-span deflection under applied load conditions measured by dial gauge (5). This represents the mid-span deflection measured by the BOTDA demodulator; In step 5, the formula for correcting the deflection function is: ; in, Represents the deflection function. This represents the corrected deflection distribution, where x represents the location.

[0014] In step 4, the curvature distribution along the bridge concrete beam (4) is first calculated. The formula for calculating the curvature distribution is: ; in, This represents the equivalent distance from the neutral axis to the fiber's position. Represents the curvature distribution. This represents the strain distribution, where x represents the location; Then, the curvature distribution is integrated twice to obtain the deflection function, which is calculated using the following formula: ; in, Represents the deflection function. Indicates position The curvature at point s, where s represents the curvature. The integral constant is obtained through boundary conditions, which are: =0, =0; Where L represents the length of the concrete beam of the bridge.

[0015] Step 3 further includes the step of calculating the correction coefficient by applying experimental loads multiple times and averaging the results to obtain the average correction coefficient. In step 5, the deflection function is corrected using the average correction coefficient.

[0016] Compared with the prior art, the present invention has the following advantages: This invention proposes a bridge structure coupling monitoring device and method based on distributed optical fiber. The "pre-stretching + groove embedding + epoxy fixing" deployment process significantly improves the coupling effect between the optical fiber and the structure interface, increasing strain transfer efficiency by approximately 25% and reducing monitoring error from 15% with traditional surface bonding to less than 5%. Furthermore, this invention effectively suppresses integral drift and system cumulative error through a correction algorithm based on "boundary condition constraints + mid-span calibration," achieving high-precision monitoring of bridge deflection and strain, reducing monitoring errors, and ensuring the long-term stability and engineering applicability of monitoring results. Utilizing BOTDA distributed demodulation technology combined with a data processing module and host computer software, distributed real-time demodulation, automatic correction, and remote transmission are achieved. The device has a simple structure, standardized deployment process, convenient construction, and low cost. This method is not only applicable to full-span monitoring of bridge main beams and decks but can also be extended to long-term health monitoring of various engineering structures such as tunnel linings, bridge bearings and piers, and slope retaining structures, demonstrating significant social and economic benefits. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a bridge structure monitoring device based on distributed optical fiber coupling provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of a bridge concrete beam in an embodiment of the present invention; Figure 3 This is a schematic diagram of the servo guide rail pre-stretching platform in an embodiment of the present invention; Figure 4 This is a schematic diagram of the adjustable column in an embodiment of the present invention; Figure 5 A flowchart illustrating a bridge structure monitoring method based on distributed optical fiber coupling provided in Embodiment 2 of the present invention; In the diagram: 1 is the support platform, 2 is the test fiber, 3 is the fiber optic slot, 4 is the bridge concrete beam, 5 is the dial indicator, 6 is the loading weight, 7 is the fiber optic disk, 8 is the BOTDA fiber optic distributed demodulator, 9 is the fiber optic clamp, 10 is the platform guide rail, 11 is the adjustable column, 12 is the sliding platform, 13 is the metal column, 14 is the fiber optic slot, 15 is the bracket, 16 is the adjustment knob, 17 is the column guide rail, and 18 is the support frame. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but 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.

[0019] Example 1 like Figure 1-2 As shown, this embodiment of the invention provides a bridge structure monitoring device based on distributed optical fiber coupling, including two support frames 18, a loading weight 6, a test optical fiber 2, a BOTDA fiber distributed demodulator 8, a support platform 1, and a dial gauge 5. The two support frames 18 are respectively set on both sides of the bottom of the bridge concrete beam 4 to form a simply supported structure. The loading weight 6 is set above the mid-span position of the bridge concrete beam 4. The test optical fiber 2 is set at the center of its upper surface along the length direction of the bridge concrete beam 4. The two ends of the test optical fiber 2 are connected to the BOTDA fiber distributed demodulator 8. The support platform 1 and the dial gauge 5 are set below the mid-span position of the bridge concrete beam 4, and the dial gauge 5 is located between the bridge concrete beam 4 and the support platform 1, for measuring the mid-span deflection of the bridge concrete beam 4.

[0020] Specifically, such as Figure 2 As shown, in this embodiment, an optical fiber groove 3 is provided along the length direction at the center of the upper surface of the bridge concrete beam 4, and the test optical fiber 2 is fixed in the optical fiber groove 3 with epoxy resin. Specifically, the bridge concrete beam 4 is a rectangular cross-section beam, with a length of 1.5 m and a cross-section of 0.1 m × 0.1 m in this embodiment. Both ends are supported on a support platform 18 1.2 m apart, forming a simply supported beam structure. The support platform 18 adopts a steel support, and a 2 mm thick rubber gasket is pasted on the support surface to reduce local stress concentration.

[0021] Furthermore, in this embodiment, the width of the fiber optic slot 3 is 1.2-1.5 times the diameter of the test fiber 2, and the depth of the slot is 1.1-1.3 times the diameter of the test fiber 2.

[0022] Furthermore, in this embodiment, the test optical fiber 2 is a bare fiber with a diameter of approximately 250 μm or a high-transmission tight-buffered optical cable with a diameter of 2.0 mm. The bare fiber is characterized by high sensitivity and is suitable for laboratory monitoring with small deflections; the high-transmission tight-buffered optical cable weighs approximately 2 kg / km, has high mechanical strength and good tensile properties, and is suitable for long-term service monitoring.

[0023] Furthermore, in this embodiment, the test optical fiber 2 is subjected to a controllable pre-tension of 1 to 10 mm by a servo guide rail pre-tensioning platform before being fixedly laid on the upper surface of the bridge concrete beam 4; when the test optical fiber 2 is a bare fiber, the tension is set to 5 mm, and when the test optical fiber 2 is a tightly sheathed optical cable, the tension is set to 3 mm.

[0024] Specifically, in this embodiment, as Figure 3 As shown, the servo guide rail pre-stretching platform includes a platform guide rail 10, a sliding platform 12, fiber optic clamps 9, and an adjustable column 11. The two ends of the test fiber 2 are respectively fixed by one of the fiber optic clamps 9, and one of the fiber optic clamps 9 is mounted on the platform guide rail 10 via a sliding platform 12. The adjustable column 11 is mounted on the platform guide rail 10 and located between the two fiber optic clamps 9. The middle part of the test fiber 2 is mounted on the adjustable column 11. The adjustable column 11 is used to adjust the height of the test fiber 2 so that its force direction is parallel to the moving direction of the sliding platform 12. The sliding platform 12 is used to drive the fiber optic clamps 9 to move along both ends of the platform guide rail 10, thereby achieving the pre-stretching of the test fiber 2.

[0025] Furthermore, such as Figure 4 As shown, in this embodiment, the adjustable column 11 includes a bracket 15, a metal column 13, an adjustment knob 16, and a column guide rail 17. The bracket 15 is fixed on the platform guide rail 10, and the column guide rail 17 is set on the bracket 15 and perpendicular to the direction of the platform guide rail 10. The metal column 13 is set on the column guide rail 17 through the adjustment knob 16. The metal column 13 is provided with an optical fiber slot 14 for placing the test optical fiber 2. By rotating the adjustment knob 16, the metal column 13 can be adjusted to move to the right along the column guide rail 17, thereby applying strain to the test optical fiber 2. The actual movement distance of the test optical fiber 2 can be determined by the scale on the adjustment knob 16, and compared with the displacement value obtained by the BOTDA optical fiber distributed demodulator 8, thereby determining the optimal pre-stretch length.

[0026] Example 2 like Figure 5 As shown, Embodiment 2 of the present invention provides a bridge structure monitoring method based on distributed optical fiber coupling, which is implemented based on the bridge structure monitoring device based on distributed optical fiber coupling described in Embodiment 1, and includes the following steps: Step 1: Apply pre-stretching to the test fiber 2 using a servo guide rail pre-stretching platform.

[0027] Specifically, in this embodiment, the pre-stretching range of the test fiber 2 is set to 1 to 10 mm, and the displacement sensor monitors the platform displacement in real time with an accuracy of ±0.1 mm.

[0028] In this embodiment, the optimal pre-stretching amount was determined by minimizing the error between the displacement data obtained from multiple experiments and the actual displacement data under different pre-stretching amounts for the test fiber 2. Experimental results show that the strain transfer efficiency of the bare fiber is best when pre-stretched by 5 mm (per 2 m), while the performance of the tightly sheathed optical cable is best when pre-stretched by 3 mm. If the pre-stretching is insufficient, a slack section exists between the optical fiber and the structure, resulting in a lag in strain response; if the pre-stretching is too large, residual stress may be introduced or the optical fiber may break.

[0029] Step 2: Process fiber groove 3 along the length direction on the surface of the bridge concrete beam 4, then embed the pre-stretched test fiber 2 into the fiber groove 3, and uniformly coat it with epoxy resin for fixation; at the same time, connect the test fiber (2) to the BOTDA demodulator.

[0030] In this embodiment, the epoxy resin adhesive is a two-component structural adhesive with a tensile strength ≥50 MPa, a shear strength ≥15 MPa, and an aging resistance life ≥10 years. After curing, it can form a stable coupling layer between the optical fiber and the concrete surface, ensuring efficient strain transfer. Redundant sections are wound up at both ends of the test optical fiber via fiber reel 7 and connected to the BOTDA fiber distributed demodulator 8 through FC / APC fiber connectors. Insertion loss is ≤0.3 dB, and return loss is ≥40 dB. A 20–30 cm relaxation section is reserved at the connection point to reduce the risk of breakage during loading.

[0031] Step 3: Apply the experimental load at the mid-span of the concrete beam 4 of the bridge, and measure the mid-span deflection under the applied experimental load using dial gauge 5; at the same time, collect the strain distribution along the applied experimental load using a BOTDA demodulator; then calculate the experimental deflection function based on the strain distribution along the applied experimental load, and calculate the correction coefficient.

[0032] In the loading test of this embodiment, a loading weight 6 was applied at the mid-span to simulate the deformation of the bridge under concentrated load. The loading amounts were 10 kg, 12 kg, and 14 kg. A dial gauge 5 was installed at the bottom of the mid-span, with its probe in contact with the bottom of the concrete beam 4 of the bridge, recording the mid-span deflection in real time with a measurement accuracy of 0.01 mm. The loading and unloading process was repeated multiple times to ensure that the beam deformed within the elastic range. The BOTDA fiber optic distributed demodulator 8 acquired the strain distribution ε(x) along the test fiber / cable 2 in real time and compared it with the measured data from the dial gauge 5 for subsequent correction.

[0033] In step 3, the formula for calculating the correction coefficient is: ; (1) Where n represents the correction factor. This represents the mid-span deflection under applied load conditions, measured by dial gauge 5. This indicates the mid-span deflection measured by the BOTDA demodulator.

[0034] Step 4: Lay out the pre-stretched test fiber 2 on the concrete beam 4 of the bridge in the actual application, and then connect it to the BOTDA demodulator to obtain the strain distribution along the concrete beam of the bridge, calculate the curvature distribution along the friction, and perform two integrations on the curvature distribution to obtain the deflection function.

[0035] The pre-stretching method and layout method of the test fiber 2 are the same as those in steps 1 and 2. The "pre-stretching + groove embedding + epoxy fixing" layout process significantly improves the coupling effect between the test fiber and the structural interface and reduces monitoring errors.

[0036] In step 4, the formula for calculating the curvature distribution is: (2) in, This represents the equivalent distance from the neutral axis to the fiber's position. Represents the curvature distribution. denoted by , x represents the strain distribution, and x represents the location.

[0037] Combining Euler-Bernoulli beam theory: (3) Therefore, the formula for calculating the deflection function is: ; (4) in, Represents the deflection function. Indicates position The curvature at point s, where s represents the curvature. The integral constant is obtained through boundary conditions, which are: =0, =0; (5) Where L represents the length of the concrete beam 4 of the bridge.

[0038] In step 3, the experimental deflection function of the bridge under different experimental loads can be calculated using the above formulas (3)-(5). The experimental deflection function is then used to... The value of is the experimental mid-span deflection measured by the BOTDA demodulator; then, substituting it into formula (1), the corresponding correction coefficients under each experimental load can be obtained. Experiments have shown that the correction coefficients are not significantly different under different experimental loads.

[0039] Step 5: Correct the deflection function using a correction factor to obtain the corrected deflection distribution.

[0040] In step 5, the formula for correcting the deflection function is: ; (6) in, Represents the deflection function. This represents the corrected deflection distribution, where x represents the location.

[0041] Furthermore, in step 3 of this embodiment, there is also a step of calculating the correction coefficient and averaging it by applying the experimental load multiple times to obtain the average correction coefficient. In step 5, the deflection function is corrected by the average correction coefficient.

[0042] Furthermore, in this embodiment, after obtaining the corrected deflection distribution, the method further includes the step of calculating the corrected strain distribution based on the corrected deflection distribution.

[0043] In this embodiment, the corrected deflection distribution is compared with the theoretical reference formula and error analysis is performed. The theoretical deflection of the simply supported beam under concentrated load is: (7) in, F For load, E The elastic modulus of concrete. I Let the moment of inertia of the beam section be , L Let be the beam length. The formula for calculating the percentage error is: (8) Experimental results show that under three load conditions, the uncorrected BOTDA integral deflection deviates from the dial gauge results by 15% to 20%; after applying the correction method of this invention, the deviation is reduced to less than 5%. Bare fiber responds sensitively under small deflection (<1 mm), while tightly sheathed optical cables maintain good stability after 50 load-unload cycles, with the corrected error fluctuation not exceeding ±0.5 mm. Compared with traditional surface bonding methods, the "pre-stretching + groove embedding + epoxy fixing" process proposed in this invention improves strain transfer efficiency by approximately 25%, reducing the monitoring error from 15% to less than 5%, significantly improving the accuracy and reliability of long-term health monitoring.

[0044] In summary, this invention provides a bridge structure monitoring device and method based on distributed optical fiber coupling. Through an integrated solution of "deployment process - loading monitoring - error correction", it successfully solves problems such as poor optical fiber coupling, integral drift and error accumulation in distributed optical fiber monitoring, and achieves high precision, long-term stability and engineering feasibility in bridge structure deflection monitoring, which has significant application and promotion value.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A bridge structure monitoring device based on distributed optical fiber coupling, characterized in that, It includes two support stands (18), a loading weight (6), a test optical fiber (2), a BOTDA fiber optic distributed demodulator (8), a support platform (1), and a dial gauge (5); the two support stands (18) are respectively set on both sides of the bottom of the bridge concrete beam (4) to form a simply supported structure, the loading weight (6) is set above the mid-span position of the bridge concrete beam (4), and the test optical fiber (2) is set at the center of its upper surface along the length direction of the bridge concrete beam (4); The two ends of the test optical fiber (2) are connected to the BOTDA fiber distributed demodulator (8); the support platform (1) and the dial gauge (5) are set below the mid-span of the bridge concrete beam (4), and the dial gauge (5) is located between the bridge concrete beam (4) and the support platform (1) to measure the mid-span deflection of the bridge concrete beam (4).

2. The bridge structure monitoring device based on distributed optical fiber coupling according to claim 1, characterized in that, The upper surface of the concrete beam (4) of the bridge is provided with an optical fiber groove (3) along the length direction, and the test optical fiber (2) is fixed in the optical fiber groove (3) by epoxy resin.

3. The bridge structure monitoring device based on distributed optical fiber coupling according to claim 2, characterized in that, The width of the fiber optic slot (3) is 1.2-1.5 times the diameter of the test fiber (2), and the depth of the slot is 1.1-1.3 times the diameter of the test fiber (2).

4. The bridge structure monitoring device based on distributed optical fiber coupling according to claim 1, characterized in that, The test optical fiber (2) is a bare fiber with a diameter of 250 μm or a high-transmission tight-packed sheathed optical cable with a diameter of 2.0 mm.

5. A bridge structure monitoring device based on distributed optical fiber coupling according to claim 1, characterized in that, The test optical fiber (2) is pre-stretched to a controlled degree of 1-10 mm by a servo guide rail pre-stretching platform and then fixedly laid on the upper surface of the bridge concrete beam (4); when the test optical fiber (2) is a bare fiber, the stretching amount is set to 5 mm, and when the test optical fiber (2) is a tightly wrapped sheathed optical cable, the stretching amount is set to 3 mm.

6. A bridge structure monitoring method based on distributed optical fiber coupling, implemented based on the bridge structure monitoring device based on distributed optical fiber coupling as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Apply pre-stretching to the test fiber (2) using a servo guide rail pre-stretching platform; Step 2: Process fiber grooves (3) along the length direction on the surface of the bridge concrete beam (4), then embed the test fiber (2) into the fiber groove (3) and fix it by uniformly coating it with epoxy resin; at the same time, connect the test fiber (2) to the BOTDA demodulator. Step 3: Apply an experimental load at the mid-span of the concrete beam (4) of the bridge and measure the mid-span deflection under the applied experimental load using a dial gauge (5); at the same time, collect the strain distribution along the applied experimental load using a BOTDA demodulator; then calculate the experimental deflection function based on the strain distribution along the applied experimental load and calculate the correction coefficient. Step 4: Set the pre-stretched measuring fiber inside the concrete beam of the actual bridge, obtain the strain distribution along the bridge in the concrete beam using a BOTDA demodulator, and calculate the deflection function. Step 5: Correct the deflection function using a correction factor to obtain the corrected deflection distribution.

7. The bridge structure monitoring method based on distributed optical fiber coupling according to claim 6, characterized in that, In step 1, the servo guide rail pre-stretching platform includes a platform guide rail (10), a sliding platform (12), an optical fiber clamp (9), and an adjustable column (11). The two ends of the test optical fiber (2) are fixed by one of the optical fiber clamps (9), and the optical fiber clamp (9) is set on the platform guide rail (10) by the sliding platform (12). The adjustable column (11) is set on the platform guide rail (10) and located between the two optical fiber clamps (9). The middle part of the test optical fiber (2) is set on the adjustable column (11). The adjustable column (11) is used to adjust the height of the test optical fiber (2) so that the force direction is parallel to the moving direction of the sliding platform (12). The sliding platform (12) is used to drive the optical fiber clamp (9) to move along the two ends of the platform guide rail (10) to realize the pre-stretching of the test optical fiber (2).

8. A bridge structure monitoring method based on distributed optical fiber coupling according to claim 6, characterized in that, In step 3, the formula for calculating the correction coefficient is: ； Where n represents the correction factor. This indicates the mid-span deflection under applied load conditions measured by dial gauge (5). This represents the mid-span deflection measured by the BOTDA demodulator; In step 5, the formula for correcting the deflection function is: ； in, Represents the deflection function. This represents the corrected deflection distribution, where x represents the location.

9. A bridge structure monitoring method based on distributed optical fiber coupling according to claim 6, characterized in that, In step 4, the curvature distribution along the bridge concrete beam (4) is first calculated. The formula for calculating the curvature distribution is: ； in, This represents the equivalent distance from the neutral axis to the fiber's position. Represents the curvature distribution. This represents the strain distribution, where x represents the location; Then, the curvature distribution is integrated twice to obtain the deflection function, which is calculated using the following formula: ； in, Represents the deflection function. Indicates position The curvature at point s, where s represents the curvature. The integral constant is obtained through boundary conditions, which are: =0, =0； Where L represents the length of the concrete beam (4) of the bridge.

10. A bridge structure monitoring method based on distributed optical fiber coupling according to claim 6, characterized in that, Step 3 further includes the step of calculating the correction coefficient by applying experimental loads multiple times and averaging the results to obtain the average correction coefficient. In step 5, the deflection function is corrected using the average correction coefficient.

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