Bridge crack monitoring and early warning system and method

Abstract

The invention provides a bridge crack monitoring and early warning system and method, and the system comprises a grid which covers and is fixed on a vertical to-be-detected surface of a bridge, a sensing optical fiber is sequentially arranged on each transverse grid line and then is sequentially arranged on each longitudinal grid line, and for each grid line, a sensing optical fiber is arranged on each longitudinal grid line. When a crack appears in the corresponding position, covered with the grid lines, of the to-be-detected surface, stretching perpendicular to the extension direction of the crack occurs in the grid line segment and the optical fiber segment corresponding to the position; when the bridge vibrates in the vertical direction, the grid line segments and the optical fiber segments corresponding to the positions move in the vertical direction under the action of gravity, so that the strain curve of the sensing optical fiber fluctuates, and when the wiring direction of the optical fiber segments and the extension direction of the crack are different, the fluctuation characteristics of the strain curve are different; and determining the extension direction and width of the crack at the corresponding position on the to-be-measured surface according to the fluctuation characteristics of the fluctuation areas in the strain curve of the sensing optical fiber at the corresponding moment and the spatial position relationship among the fluctuation areas.

Description

Technical Field

[0001] The invention belongs to the field of optical fiber sensing, and in particular relates to a bridge crack monitoring and early warning system and method. Background Art

[0002] The existing non-destructive detection methods for bridge cracks mainly include ultrasonic detection, elastic wave detection, acoustic emission detection, image detection and sensor detection. In sensor detection, the use of optical fiber sensors for detection is a common method. However, in traditional detection methods, since the location of cracks is relatively random, in order to determine the detection points, the bridge surface to be tested needs to be completely covered. However, the existing crack monitoring and early warning system based on sensor optical fiber can only monitor the width of the crack, but cannot determine the extension direction of the crack, which makes the accuracy of the construction along the crack line low. Summary of the invention

[0003] The present invention provides a bridge crack monitoring and early warning system and method, so as to solve the problem that the extension direction of the crack cannot be determined at present, thus resulting in low accuracy of construction along the crack line.

[0004] According to a first aspect of an embodiment of the present invention, a bridge crack monitoring and early warning system is provided, comprising a grid covering and fixed on a vertical test surface of the bridge, a sensing optical fiber is sequentially routed on each horizontal grid line, and then sequentially routed on each longitudinal grid line, for each grid line, when a crack appears at a corresponding position on the test surface covered by the grid line, the grid line segment and the optical fiber segment corresponding to the position are stretched perpendicular to the extension direction of the crack; and when the bridge vibrates in the vertical direction, the grid line segment and the optical fiber segment corresponding to the position move in the vertical direction under the action of gravity, so that the strain curve of the sensing optical fiber fluctuates, wherein when the routing direction of the optical fiber segment and the crack extension direction are different, the characteristics of the fluctuation of the strain curve of the sensing optical fiber are different;

[0005] A stress measurement and analysis system is connected to the sensing optical fiber, and the strain of each measuring point on the sensing optical fiber is determined according to the scattered signal transmitted back by the sensing optical fiber; the strain curve of the sensing optical fiber at the corresponding moment is determined according to the strain magnitude of each measuring point on the sensing optical fiber at the corresponding moment, and the strain curve is associated with the spatial position of the sensing optical fiber; the extension direction and width of the crack at the corresponding position of the sensing optical fiber on the surface to be measured are determined according to the fluctuation characteristics of the fluctuation area in the strain curve and the spatial position relationship between each fluctuation area.

[0006] In an optional implementation, the longitudinal direction is the vertical direction, and the sensing optical fiber is arranged on each transverse grid line in a serpentine manner, and then arranged on each longitudinal grid line in a serpentine manner. When arranged on each longitudinal grid line, if the transverse grid line is encountered, the wiring continues after crossing the transverse grid line.

[0007] In another optional implementation, each grid line has the same elasticity.

[0008] According to a second aspect of an embodiment of the present invention, a warning method of the bridge crack monitoring and warning system is provided, and the stress measurement and analysis system performs the following steps:

[0009] Step S100, determining the strain of each measuring point on the sensing optical fiber according to the scattered signal transmitted back by the sensing optical fiber;

[0010] Step S200, determining the strain curve of the sensing optical fiber at the corresponding moment according to the strain magnitude of each measuring point on the sensing optical fiber at the corresponding moment, and associating the strain curve with the spatial position of the sensing optical fiber;

[0011] Step S300: Determine the extension direction and width of the crack at the corresponding position of the sensing optical fiber on the measured surface of the bridge according to the fluctuation characteristics of the fluctuation area in the strain curve and the spatial position relationship between each fluctuation area.

[0012] In an optional implementation, step S300 specifically includes:

[0013] Step S310: for each fluctuation region in the strain curve at the corresponding moment, determine whether the fluctuation region is an arc. If so, it indicates that it is in the first case: the fluctuation region corresponds to the optical fiber segment arranged horizontally, and the crack at the corresponding optical fiber segment extends longitudinally. The corresponding distance between the two ends of the arc is determined as the width of the crack. Based on the first relationship between the crack width and the vibration magnitude in the first case, the corresponding vibration magnitude is obtained according to the determined crack width, and step S320 is executed; otherwise, for the next undetermined fluctuation region, return to step S310;

[0014] Step S320, determining other fluctuation areas within the set spatial range corresponding to the optical fiber segment corresponding to the fluctuation area as the center, using the obtained vibration magnitude as the vibration magnitude of other fluctuation areas within the set spatial range, and executing step S330 for the other fluctuation areas; for other fluctuation areas outside the set spatial range, returning to execute step S310;

[0015] Step S330, determining whether the fluctuation area is a square, if so, it indicates that it is in the second situation: the fluctuation area is arranged horizontally corresponding to the optical fiber segment, and the crack at the corresponding optical fiber segment extends horizontally, based on the second relationship between the longitudinal height of the square and the crack width under different vibration magnitudes in the second situation, according to the obtained vibration magnitude and the longitudinal height of the square, the width of the crack at the corresponding optical fiber segment is determined; otherwise, executing step S340;

[0016] Step S340, determine whether the fluctuation area is a bending line, the bending line includes a middle section with the same strain size and bending sections located on both sides of the middle section, the slopes of the two bending sections are unique and increase or decrease in the same direction. If so, take the corresponding distance of the middle section as the crack width to be tested, and execute step S350; otherwise, when there are other fluctuation areas that have not been determined within the set space range, for the next other fluctuation area that has not been determined within the set space range, return to execute step S330; when there are no other fluctuation areas that have not been determined within the set space range, for other fluctuation areas outside the set space range, return to execute step S310;

[0017] Step S350, based on the third relationship between the bending section slope and the crack width under different vibration magnitudes in the third case, the third case is that the fluctuation area is longitudinally arranged corresponding to the optical fiber segment, and the crack at the corresponding optical fiber segment extends transversely, and the bending section slope is determined according to the obtained vibration magnitude and the crack width to be inspected;

[0018] Step S350, determine whether the slope of the bending section in the bending line is greater than the determined slope of the bending section, if so, it indicates that it is in the fourth situation: the fluctuation area is longitudinally arranged at the corresponding optical fiber segment, and the crack at the corresponding optical fiber segment extends longitudinally, and the width of the crack to be tested is the length of the crack at the corresponding optical fiber segment, and then based on the fourth relationship between the slope of the bending section and the crack width under different vibration magnitudes in the fourth situation, the width of the crack at the corresponding optical fiber segment is determined according to the obtained vibration magnitude and the slope of the bending section in the bending line; otherwise, it indicates that it is in the third situation, and the width of the crack to be tested is taken as the width of the crack at the corresponding optical fiber segment.

[0019] In another optional implementation, after step S300, the method further includes: determining the strain curve of the sensing optical fiber at the moment according to the strain magnitude of each measuring point on the sensing optical fiber at the next moment measured, and executing step S300.

[0020] The beneficial effects of the present invention are:

[0021] The present invention fixes an elastic grid on the vertical test surface of the bridge, and then lays a sensing optical fiber segment on the grid. By utilizing the vertical vibration of the bridge, the grid line segments and optical fiber segments at the corresponding positions where cracks appear move in the vertical direction under the action of gravity, thereby causing the strain curve of the sensing optical fiber to fluctuate. Since the characteristics of the fluctuations in the strain curve of the sensing optical fiber are different when the wiring direction of the optical fiber segment and the extension direction of the crack are different, the extension direction and width of the crack on the test surface can be determined according to the fluctuation characteristics of the strain curve; in addition, setting the grid can also make the fluctuation characteristics in the strain curve more obvious; since the present invention can determine the extension direction of the crack, the crack can be constructed more accurately along the line; based on the extension direction of the crack, the intersecting crack component segments can be distinguished. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of an embodiment of the bridge crack monitoring and early warning system of the present invention;

[0023] Figure 2 Schematic diagrams of four positional relationships between cracks and optical fiber segments of the present invention;

[0024] Figure 3 It is a structural flow chart of an embodiment of the bridge crack monitoring and early warning method of the present invention. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0026] In the description of the present invention, unless otherwise specified and limited, it should be noted that the term "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two elements. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0027] See also Figure 1, is a schematic diagram of the structure of an embodiment of the bridge crack monitoring and early warning system of the present invention. The bridge crack monitoring and early warning system may include a grid covering and fixed on the vertical test surface 1 of the bridge, and the grid may include transverse grid lines 2 and longitudinal grid lines 3. A sensing optical fiber 4 is sequentially wired on each transverse grid line 2 and then sequentially wired on each longitudinal grid line 3. For each grid line, when a crack appears at the corresponding position on the test surface covered by the grid line, the grid line segment and the optical fiber segment corresponding to the position are stretched perpendicular to the extension direction of the crack; and when the bridge vibrates in the vertical direction, the grid line segment and the optical fiber segment corresponding to the position move in the vertical direction under the action of gravity, so that the strain curve of the sensing optical fiber fluctuates, wherein when the wiring direction of the optical fiber segment and the crack extension direction are different, the characteristics of the fluctuation of the strain curve of the sensing optical fiber are different;

[0028] A stress measurement and analysis system is connected to the sensing optical fiber, and the strain of each measuring point on the sensing optical fiber is determined according to the scattered signal transmitted back by the sensing optical fiber; the strain curve of the sensing optical fiber at the corresponding moment is determined according to the strain magnitude of each measuring point on the sensing optical fiber at the corresponding moment, and the strain curve is associated with the spatial position of the sensing optical fiber; the extension direction and width of the crack at the corresponding position of the sensing optical fiber on the surface to be measured are determined according to the fluctuation characteristics of the fluctuation area in the strain curve and the spatial position relationship between each fluctuation area.

[0029] In this embodiment, the longitudinal direction may be a vertical direction, and the sensing optical fiber may be arranged on each transverse grid line in a serpentine manner, and then arranged on each longitudinal grid line in a serpentine manner, wherein when arranged on each longitudinal grid line, if the transverse grid line is encountered, the wiring is continued after crossing the transverse grid line. Each grid line has the same elasticity. The grid line may be made of elastic materials such as plastic.

[0030] Combination Figure 2 As shown in the figure, there are four situations for the fiber segment wiring direction and the crack extension direction: Figure 2 (a) is the first case: the fluctuation area corresponds to the horizontal arrangement of the optical fiber segment, and the crack at the corresponding optical fiber segment extends longitudinally. It can be seen from the figure that when the bridge vibrates in the vertical direction, the optical fiber segment between the crack edges will fluctuate in an arc shape; Figure 2 (b) is the second case: the fluctuation area corresponds to the horizontal arrangement of the optical fiber segment, and the crack at the corresponding optical fiber segment extends horizontally. It can be seen from the figure that when the bridge vibrates in the vertical direction, the optical fiber segment between the crack edges will experience square fluctuations; Figure 2(c) is the third case: the fluctuation area corresponds to the longitudinal arrangement of the optical fiber segment, and the crack at the corresponding optical fiber segment extends horizontally. It can be seen from the figure that when the bridge vibrates in the vertical direction, the optical fiber segment between the crack edges will experience bending line fluctuations; Figure 2 (d) is the fourth case: the fluctuation area corresponds to the longitudinal arrangement of the optical fiber segment, and the crack at the corresponding optical fiber segment extends longitudinally. It can be seen from the figure that when the bridge vibrates in the vertical direction, the optical fiber segment between the crack edges will experience bending line fluctuations. For the third and fourth cases, since the grid line segments between the crack edges are stretched, the corresponding optical fiber segment moves toward the surface to be measured by a corresponding distance, so that the optical fiber segment and the optical fiber segments on both sides of the crack edge are misaligned, and the optical fiber segment between the crack edges will experience bending line fluctuations. In addition, since in the third case, not only the grid line segments between the crack edges are stretched, but also the optical fiber segments between the crack edges are stretched, the degree of misalignment between the optical fiber segment and the optical fiber segments on both sides of the crack edge is greater than that in the fourth case, and correspondingly, the slope of the bending segment in the bending line fluctuation in the fourth case is greater than the slope of the bending segment in the bending line fluctuation in the third case.

[0031] As can be seen from the above embodiments, the present invention fixes an elastic grid on the vertical test surface of the bridge, and then lays a sensing optical fiber segment on the grid, and utilizes the vertical vibration of the bridge to make the grid line segments and optical fiber segments at the corresponding positions where cracks appear move in the vertical direction under the action of gravity, so that the strain curve of the sensing optical fiber fluctuates. Since the characteristics of the fluctuations in the strain curve of the sensing optical fiber are different when the wiring direction of the optical fiber segment and the extension direction of the crack are different, the extension direction and width of the crack on the test surface can be determined according to the fluctuation characteristics of the strain curve; in addition, setting the grid can also make the fluctuation characteristics in the strain curve more obvious; since the present invention can determine the extension direction of the crack, it can more accurately construct the crack along the line, and based on the extension direction of the crack, the intersecting crack component segments can be distinguished.

[0032] See also Figure 3 The present invention also provides an early warning method of the above bridge crack monitoring and early warning system, wherein the stress measurement and analysis system can perform the following steps:

[0033] Step S100, determining the strain of each measuring point on the sensing optical fiber according to the scattered signal transmitted back by the sensing optical fiber;

[0034] Step S200, determining the strain curve of the sensing optical fiber at the corresponding moment according to the strain magnitude of each measuring point on the sensing optical fiber at the corresponding moment, and associating the strain curve with the spatial position of the sensing optical fiber;

[0035] Step S300, determining the extension direction and width of the crack at the corresponding position of the sensing optical fiber on the bridge surface to be measured according to the fluctuation characteristics of the fluctuation area in the strain curve and the spatial position relationship between each fluctuation area. The step S300 may specifically include:

[0036] Step S310: for each fluctuation region in the strain curve at the corresponding moment, determine whether the fluctuation region is an arc. If so, it indicates that it is in the first case: the fluctuation region corresponds to the optical fiber segment arranged horizontally, and the crack at the corresponding optical fiber segment extends longitudinally. The corresponding distance between the two ends of the arc is determined as the width of the crack. Based on the first relationship between the crack width and the vibration magnitude in the first case, the corresponding vibration magnitude is obtained according to the determined crack width, and step S320 is executed; otherwise, for the next undetermined fluctuation region, return to step S310;

[0037] Step S320, determining other fluctuation areas within a corresponding set spatial range (which may be a set square spatial range) centered on the corresponding optical fiber segment of the fluctuation area, using the obtained vibration magnitude as the vibration magnitude of other fluctuation areas within the set spatial range, and executing step S330 for the other fluctuation areas; for other fluctuation areas outside the set spatial range, returning to execute step S310;

[0038] Step S330, determining whether the fluctuation area is a square, if so, it indicates that it is in the second situation: the fluctuation area is arranged horizontally corresponding to the optical fiber segment, and the crack at the corresponding optical fiber segment extends horizontally, based on the second relationship between the longitudinal height of the square and the crack width under different vibration magnitudes in the second situation, according to the obtained vibration magnitude and the longitudinal height of the square, the width of the crack at the corresponding optical fiber segment is determined; otherwise, executing step S340;

[0039] Step S340, determine whether the fluctuation area is a bending line, the bending line includes a middle section with the same strain size and bending sections located on both sides of the middle section, the slopes of the two bending sections are unique and increase or decrease in the same direction. If so, take the corresponding distance of the middle section as the crack width to be tested, and execute step S350; otherwise, when there are other fluctuation areas that have not been determined within the set space range, for the next other fluctuation area that has not been determined within the set space range, return to execute step S330; when there are no other fluctuation areas that have not been determined within the set space range, for other fluctuation areas outside the set space range, return to execute step S310;

[0040] Step S350, based on the third relationship between the bending section slope and the crack width under different vibration magnitudes in the third case, the third case is that the fluctuation area is longitudinally arranged corresponding to the optical fiber segment, and the crack at the corresponding optical fiber segment extends transversely, and the bending section slope is determined according to the obtained vibration magnitude and the crack width to be inspected;

[0041] Step S350, determine whether the slope of the bending section in the bending line is greater than the determined slope of the bending section, if so, it indicates that it is in the fourth situation: the fluctuation area is longitudinally arranged at the corresponding optical fiber segment, and the crack at the corresponding optical fiber segment extends longitudinally, and the width of the crack to be tested is the length of the crack at the corresponding optical fiber segment, and then based on the fourth relationship between the slope of the bending section and the crack width under different vibration magnitudes in the fourth situation, the width of the crack at the corresponding optical fiber segment is determined according to the obtained vibration magnitude and the slope of the bending section in the bending line; otherwise, it indicates that it is in the third situation, and the width of the crack to be tested is taken as the width of the crack at the corresponding optical fiber segment.

[0042] In addition, after the step S300, the method may further include: determining the strain curve of the sensing fiber at the next moment according to the strain magnitude of each measuring point on the sensing fiber, and executing step S300, thereby improving the accuracy of determining the extension direction and width of the crack. The stress measurement and analysis system may include an optical frequency domain reflectometer OFDR system to determine the strain at each measuring point on the sensing fiber. Since the sensing fiber will not only experience the above-mentioned corresponding fluctuations when it is subjected to bridge vibration, but also bend when it is affected by forces such as wind force perpendicular to the measured surface of the bridge (at this time, the fluctuation drive of all cracks is in an arc shape), the fiber segments between the crack edges will also bend, so the strain curve of the sensing fiber at different moments can be determined. After determining the arc-shaped fluctuation area in step S310, it is determined whether other fluctuation areas within the set spatial range of the fluctuation area are all arc-shaped. If so, the set spatial range is marked as pending, and the waveforms of all fluctuation areas within the set spatial range are monitored, and step S360 is executed; otherwise, step S320 is executed;

[0043] Step S360, after completing steps S310 to S350 for the strain curve at each moment, determine whether the waveform of at least one fluctuation area within the set spatial range has changed based on the strain curve at the next moment. If so, delete the extension direction and width of the cracks at the optical fiber segments corresponding to each fluctuation area within the set spatial range when all the fluctuation areas within the set spatial range at that moment are arc-shaped, and execute S310 to S350 based on the strain curve at the next moment to determine the extension direction and width of the cracks at the optical fiber segments corresponding to each fluctuation area within the set spatial range, and remove the pending mark of the set spatial range.

[0044] As can be seen from the above embodiments, the present invention fixes an elastic grid on the vertical test surface of the bridge, and then lays a sensing optical fiber segment on the grid, and utilizes the vertical vibration of the bridge to make the grid line segments and optical fiber segments at the corresponding positions where cracks appear move in the vertical direction under the action of gravity, so that the strain curve of the sensing optical fiber fluctuates. Since the characteristics of the fluctuations in the strain curve of the sensing optical fiber are different when the wiring direction of the optical fiber segment and the extension direction of the crack are different, the extension direction and width of the crack on the test surface can be determined according to the fluctuation characteristics of the strain curve; in addition, setting the grid can also make the fluctuation characteristics in the strain curve more obvious; since the present invention can determine the extension direction of the crack, it can more accurately construct the crack along the line, and based on the extension direction of the crack, the intersecting crack component segments can be distinguished.

[0045] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0046] It will be appreciated that the invention is not limited to the precise construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from its scope. The scope of the invention is governed solely by the appended claims.

Claims

1. A bridge crack monitoring and early warning system, characterized in that: It includes a grid covering and fixed on a vertical surface to be tested of a bridge, a sensing optical fiber is sequentially routed on each horizontal grid line, and then sequentially routed on each longitudinal grid line, for each grid line, when a crack appears at a corresponding position on the surface to be tested covered by the grid line, the grid line segment and the optical fiber segment corresponding to the position are stretched perpendicular to the extension direction of the crack; and when the bridge vibrates in the vertical direction, the grid line segment and the optical fiber segment corresponding to the position move in the vertical direction under the action of gravity, so that the strain curve of the sensing optical fiber fluctuates, wherein when the routing direction of the optical fiber segment and the crack extension direction are different, the characteristics of the fluctuation of the strain curve of the sensing optical fiber are different; A stress measurement and analysis system is connected to the sensing optical fiber, and the strain of each measuring point on the sensing optical fiber is determined according to the scattered signal transmitted back by the sensing optical fiber; the strain curve of the sensing optical fiber at the corresponding moment is determined according to the strain magnitude of each measuring point on the sensing optical fiber at the corresponding moment, and the strain curve is associated with the spatial position of the sensing optical fiber; the extension direction and width of the crack at the corresponding position of the sensing optical fiber on the surface to be measured are determined according to the fluctuation characteristics of the fluctuation area in the strain curve and the spatial position relationship between each fluctuation area.

2. The bridge crack monitoring and early warning system according to claim 1 is characterized in that: The longitudinal direction is the vertical direction. The sensing optical fiber is arranged on each transverse grid line in a serpentine manner, and then arranged on each longitudinal grid line in a serpentine manner. When arranged on each longitudinal grid line, if the transverse grid line is encountered, the wiring will continue after crossing the transverse grid line.

3. The bridge crack monitoring and early warning system according to claim 1 is characterized in that: Each grid line has the same elasticity.

4. An early warning method of a bridge crack monitoring and early warning system according to any one of claims 1 to 3, characterized in that: The stress measurement and analysis system performs the following steps: Step S100, determining the strain of each measuring point on the sensing optical fiber according to the scattered signal transmitted back by the sensing optical fiber; Step S200, determining the strain curve of the sensing optical fiber at the corresponding moment according to the strain magnitude of each measuring point on the sensing optical fiber at the corresponding moment, and associating the strain curve with the spatial position of the sensing optical fiber; Step S300: Determine the extension direction and width of the crack at the corresponding position of the sensing optical fiber on the measured surface of the bridge according to the fluctuation characteristics of the fluctuation area in the strain curve and the spatial position relationship between each fluctuation area.

5. The early warning method according to claim 4, characterized in that: The step S300 specifically includes: Step S310: for each fluctuation region in the strain curve at the corresponding moment, determine whether the fluctuation region is an arc. If so, it indicates that it is in the first case: the fluctuation region corresponds to the optical fiber segment arranged horizontally, and the crack at the corresponding optical fiber segment extends longitudinally. The corresponding distance between the two ends of the arc is determined as the width of the crack. Based on the first relationship between the crack width and the vibration magnitude in the first case, the corresponding vibration magnitude is obtained according to the determined crack width, and step S320 is executed; otherwise, for the next undetermined fluctuation region, return to step S310; Step S320, determining other fluctuation areas within the set spatial range corresponding to the optical fiber segment corresponding to the fluctuation area as the center, using the obtained vibration magnitude as the vibration magnitude of other fluctuation areas within the set spatial range, and executing step S330 for the other fluctuation areas; for other fluctuation areas outside the set spatial range, returning to execute step S310; Step S330, determining whether the fluctuation area is a square, if so, it indicates that it is in the second situation: the fluctuation area is arranged horizontally corresponding to the optical fiber segment, and the crack at the corresponding optical fiber segment extends horizontally, based on the second relationship between the longitudinal height of the square and the crack width under different vibration magnitudes in the second situation, according to the obtained vibration magnitude and the longitudinal height of the square, the width of the crack at the corresponding optical fiber segment is determined; otherwise, executing step S340; Step S340, determine whether the fluctuation area is a bending line, the bending line includes a middle section with the same strain size and bending sections located on both sides of the middle section, the slopes of the two bending sections are unique and increase or decrease in the same direction. If so, take the corresponding distance of the middle section as the crack width to be tested, and execute step S350; otherwise, when there are other fluctuation areas that have not been determined within the set space range, for the next other fluctuation area that has not been determined within the set space range, return to execute step S330; when there are no other fluctuation areas that have not been determined within the set space range, for other fluctuation areas outside the set space range, return to execute step S310; Step S350, based on the third relationship between the bending section slope and the crack width under different vibration magnitudes in the third case, the third case is that the fluctuation area is longitudinally arranged corresponding to the optical fiber segment, and the crack at the corresponding optical fiber segment extends transversely, and the bending section slope is determined according to the obtained vibration magnitude and the crack width to be inspected; Step S350, determine whether the slope of the bending section in the bending line is greater than the determined slope of the bending section, if so, it indicates that it is in the fourth situation: the fluctuation area is longitudinally arranged at the corresponding optical fiber segment, and the crack at the corresponding optical fiber segment extends longitudinally, and the width of the crack to be tested is the length of the crack at the corresponding optical fiber segment, and then based on the fourth relationship between the slope of the bending section and the crack width under different vibration magnitudes in the fourth situation, the width of the crack at the corresponding optical fiber segment is determined according to the obtained vibration magnitude and the slope of the bending section in the bending line; otherwise, it indicates that it is in the third situation, and the width of the crack to be tested is taken as the width of the crack at the corresponding optical fiber segment.

6. The early warning method according to claim 4, characterized in that: After step S300, the method further includes: determining the strain curve of the sensing optical fiber at the moment according to the strain magnitude of each measuring point on the sensing optical fiber at the next moment measured, and executing step S300.

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