Bridge crack monitoring and early warning system and method

Abstract

The application provides a bridge crack monitoring and early warning system and method, which comprises a grid covering and fixed on a vertical surface to be measured of a bridge, a sensing optical fiber is sequentially wired on each horizontal grid line and then sequentially wired on each vertical grid line, for each grid line, when a crack occurs at a corresponding position of the grid line on the surface to be measured, the corresponding grid line segment and the optical fiber segment at the position both stretch perpendicularly to the extending direction of the crack; and when the bridge vibrates in the vertical direction, the corresponding grid line segment and the optical fiber segment at the position move in the vertical direction under the action of gravity, so that the strain curve of the sensing optical fiber fluctuates, when the wiring direction of the optical fiber segment is different from the extending direction of the crack, the characteristics of the fluctuation of the strain curve are different; and the extending direction and the width of the crack at the corresponding position on the surface to be measured are determined according to the fluctuation characteristics of the fluctuation regions in the strain curve of the sensing optical fiber at corresponding time and the spatial positional relationship between the fluctuation regions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical fiber sensing, and particularly relates to a bridge crack monitoring and early warning system and method. BACKGROUND

[0002] The existing bridge crack nondestructive detection methods mainly include ultrasonic detection, elastic wave detection, acoustic emission detection, image detection and sensor detection, in the sensor detection, using optical fiber sensors for detection is a common means, but in the traditional detection means, since the position of the crack is relatively random, in order to determine the detection point, the bridge to be detected surface needs to be completely covered. However, the existing crack monitoring and early warning system based on sensing optical fiber can only monitor the crack width, and cannot determine the extension direction of the crack, so that the construction accuracy of the crack along the line is low. SUMMARY

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

[0004] According to a first aspect of the embodiment of the present application, a bridge crack monitoring and early warning system is provided, which comprises a grid covering and fixed on a vertical to-be-detected surface of a bridge, a sensing optical fiber is sequentially wired on each horizontal grid line, and then sequentially wired on each vertical grid line. For each grid line, when a crack occurs at the corresponding position of the grid line on the to-be-detected surface, the corresponding grid line segment and the optical fiber segment at the position both occur stretching perpendicular to the extension direction of the crack; and when the bridge occurs vibration in the vertical direction, the corresponding grid line segment and the optical fiber segment at the position occur movement in the vertical direction under the action of gravity, so that the strain curve of the sensing optical fiber occurs fluctuation, wherein when the wiring direction of the optical fiber segment and the extension direction of the crack 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 with the sensing optical fiber, the strain of each measurement point on the sensing optical fiber is determined according to the backscattered signals transmitted back by the sensing optical fiber, the strain curve of the sensing optical fiber at the corresponding time is determined according to the measured strain of each measurement point on the sensing optical fiber at the corresponding time, and the strain curve is associated with the spatial position of the sensing optical fiber; the extension direction and the width of the crack at the corresponding position of the sensing optical fiber on the to-be-detected surface are determined according to the fluctuation characteristics of the fluctuation region in the strain curve and the spatial position relationship between the fluctuation regions.

[0006] In an alternative implementation, the longitudinal direction is vertical, the sensing optical fiber is arranged in a serpentine manner on each of the lateral grid lines, and then arranged in a serpentine manner on each of the longitudinal grid lines, wherein when arranged on each of the longitudinal grid lines, if the lateral grid line is encountered, the sensing optical fiber is arranged to cross over the lateral grid line and then continue to be arranged.

[0007] In another alternative implementation, each of the grid lines has the same elasticity.

[0008] According to a second aspect of the embodiments of the present application, 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 measurement point on the sensing optical fiber according to the scattering signals transmitted back by the sensing optical fiber;

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

[0011] 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 regions in the strain curve and the spatial position relationship between the fluctuation regions.

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

[0013] Step S310, for each fluctuation region in the strain curve at the corresponding time, determining whether the fluctuation region is arc-shaped, if yes, indicating that the fluctuation region is in a first case that the corresponding fiber segment is arranged in a lateral direction and the crack at the corresponding fiber segment extends in a longitudinal direction, determining the corresponding distance between the two ends of the arc-shaped region as the width of the crack, obtaining the corresponding vibration size according to the determined width of the crack based on a first relationship between the width of the crack and the vibration size in the first case, and performing step S320; otherwise, returning to perform step S310 for the next undetermined fluctuation region.

[0014] Step S320, determining other fluctuation regions within a corresponding set spatial range centered on the corresponding fiber segment of the fluctuation region, taking the obtained vibration size as the vibration size of the other fluctuation regions within the set spatial range, and performing step S330 for the other fluctuation regions; and returning to perform step S310 for other fluctuation regions outside the set spatial range.

[0015] Step S330, judging whether the fluctuation region is a square, if yes, indicating that the second case that the fluctuation region corresponds to the fiber segment arranged transversely and the crack at the corresponding fiber segment extends transversely, based on a second relationship between the longitudinal height of the square and the crack width under different vibration sizes in the second case, determining the width of the crack at the corresponding fiber segment according to the obtained vibration size and the longitudinal height of the square; otherwise, executing step S340.

[0016] Step S340, judging whether the fluctuation region is a bending line, the bending line including an intermediate segment with the same strain size and bending segments respectively located on both sides of the intermediate segment, the slopes of the two bending segments being unique and increasing or decreasing in the same direction, if yes, taking the distance corresponding to the intermediate segment as the crack width to be detected, and executing step S350; otherwise, when there are other fluctuation regions not judged in the set space range, returning to execute step S330 for the next other fluctuation region not judged in the set space range, and when there is no other fluctuation region not judged in the set space range, returning to execute step S310 for other fluctuation regions outside the set space range.

[0017] Step S350, based on a third relationship between the slope of the bending segment and the crack width under different vibration sizes in the third case that the fluctuation region corresponds to the fiber segment arranged longitudinally and the crack at the corresponding fiber segment extends transversely, determining the slope of the bending segment according to the obtained vibration size and the crack width to be detected.

[0018] Step S360, judging whether the slope of the bending segment in the bending line is greater than the determined slope of the bending segment, if yes, indicating the fourth case that the fluctuation region corresponds to the fiber segment arranged longitudinally and the crack at the corresponding fiber segment extends longitudinally, and the crack width to be detected is the length of the crack at the corresponding fiber segment, and thereafter based on a fourth relationship between the slope of the bending segment and the crack width under different vibration sizes in the fourth case, determining the width of the crack at the corresponding fiber segment according to the obtained vibration size and the slope of the bending segment in the bending line; otherwise, indicating the third case, and taking the crack width to be detected as the width of the crack at the corresponding fiber segment.

[0019] In another optional implementation, after the step S300, the method further includes: determining a strain curve of the sensing fiber at the time according to the measured strain sizes of the measuring points on the sensing fiber at the next time, and executing the step S300.

[0020] The present application has the following advantages:

[0021] The present application fixes the grid with elasticity on the vertical surface to be detected of the bridge, and then lays the sensing optical fiber segment on the grid, utilizes the vibration in the vertical direction of the bridge to make the grid line segment and the optical fiber segment in the corresponding position of the crack move in the vertical direction under the action of gravity, so that the strain curve of the sensing optical fiber fluctuates, because the fluctuation characteristics of 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 the width of the crack on the surface to be detected can be determined according to the fluctuation characteristics of the strain curve; in addition, the grid can also make the fluctuation characteristics in the strain curve more obvious; because the extension direction of the crack can be determined, the crack along the line can be constructed more accurately; based on the extension direction of the crack, the cross crack composition section can be distinguished. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is an embodiment structure schematic diagram of the bridge crack monitoring and early warning system of the present application;

[0023] Figure 2 is a schematic diagram of four position relationships between the crack and the optical fiber segment of the present application;

[0024] Figure 3 is an embodiment structure flow chart of the bridge crack monitoring and early warning method of the present application. DETAILED DESCRIPTION

[0025] In order to make the person in the art better understand the technical solutions in the embodiments of the present application, and make the above-mentioned purposes, characteristics and advantages of the embodiments of the present application more obvious and easy to understand, the technical solutions in the embodiments of the present application will be further described in detail below with reference to the drawings.

[0026] In the description of the present application, unless otherwise specified and limited, it is necessary to explain that the term “connection” should be understood broadly, for example, it can be mechanical connection or electrical connection, or the internal communication of two elements, it can be directly connected, or indirectly connected through intermediate medium, for those skilled in the art, the specific meaning of the above-mentioned term can be understood according to the specific circumstances.

[0027] Reference Figure 1This is a schematic diagram 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. The grid may include horizontal grid lines 2 and vertical grid lines 3. A sensing optical fiber 4 is sequentially routed along each horizontal grid line 2 and then sequentially routed along each vertical grid line 3. For each grid line, when a crack appears at the corresponding position on the test surface covered by the grid line, both the corresponding grid line segment and the optical fiber segment undergo stretching perpendicular to the crack extension direction. Furthermore, when the bridge experiences vertical vibration, the corresponding grid line segment and optical fiber segment move vertically under gravity, causing fluctuations in the strain curve of the sensing optical fiber. The characteristics of the fluctuations in the strain curve of the sensing optical fiber differ depending on the routing direction of the optical fiber segment and the crack extension direction.

[0028] The stress measurement and analysis system is connected to the sensing fiber. Based on the scattered signal transmitted back from the sensing fiber, the strain at each measurement point on the sensing fiber is determined. Based on the strain magnitude at each measurement point on the sensing fiber at the corresponding time, the strain curve of the sensing fiber at that time is determined, and the strain curve is correlated with the spatial position of the sensing fiber. Based on the fluctuation characteristics of the fluctuation region in the strain curve and the spatial relationship between the fluctuation regions, the extension direction and width of the crack at the corresponding position of the sensing fiber on the surface to be tested are determined.

[0029] In this embodiment, the longitudinal direction can be vertical. The sensing optical fiber can be laid out in a serpentine pattern on each horizontal grid line, and then similarly in a serpentine pattern on each longitudinal grid line. When laying out a longitudinal grid line, if it encounters a horizontal grid line, it crosses that horizontal grid line before continuing the laying. Each grid line has the same elasticity. The grid line can be made of an elastic material such as plastic.

[0030] Combination Figure 2 As shown, there are four possible directions for fiber optic cable routing and crack propagation. Figure 2 (a) is the first case: the wave region corresponds to the transverse setting of the optical fiber segment, and the crack at the corresponding optical fiber segment extends longitudinally. As can be seen from the figure, when the bridge vibrates in the vertical direction, the optical fiber segment between the crack edges will experience arc-shaped wavering. Figure 2 (b) is the second case: the wave region corresponds to the transverse setting of the optical fiber segment, and the crack at the corresponding optical fiber segment extends transversely. As can be seen from the figure, when the bridge vibrates in the vertical direction, the optical fiber segment between the crack edges will experience square wave. Figure 2(c) is the third case: the fluctuation region corresponds to the longitudinal arrangement of the fiber segment, and the crack at the corresponding fiber segment extends transversely. As can be seen from the figure, when the bridge appears vertical vibration, the fiber segment between the crack edges will occur bending line fluctuation; Figure 2 (d) is the fourth case: the fluctuation region corresponds to the longitudinal arrangement of the fiber segment, and the crack at the corresponding fiber segment extends longitudinally. As can be seen from the figure, when the bridge appears vertical vibration, the fiber segment between the crack edges will occur bending line fluctuation. For the third case and the fourth case, due to the stretching of the grid line segment between the crack edges, the corresponding fiber segment moves a corresponding distance towards the measured surface, so that the fiber segment is misaligned with the fiber segments located on both sides of the crack edge, and the fiber segment between the crack edges will occur bending line fluctuation. In addition, in the third case, not only the grid line segment between the crack edges is stretched, but also the fiber segment between the crack edges is stretched, so compared with the fourth case, the misalignment between the fiber segment and the fiber segments located on both sides of the crack edge is greater, and correspondingly the slope of the bending segment in the bending line fluctuation in the fourth case is greater than that in the third case.

[0031] As can be seen from the above embodiments, the grid with elasticity is fixed on the vertical measured surface of the bridge, and the sensing fiber segment is laid on the grid. The vertical vibration of the bridge causes the grid line segment and the fiber segment at the corresponding position of the crack to move vertically under the action of gravity, so that the strain curve of the sensing fiber fluctuates. Since the wiring direction of the fiber segment is different from the extension direction of the crack, the characteristics of the fluctuation of the strain curve of the sensing fiber are different, so the extension direction and the width of the crack on the measured surface can be determined according to the fluctuation characteristics of the strain curve. In addition, the grid can make the fluctuation characteristics in the strain curve more obvious. Since the extension direction of the crack can be determined, the crack along the line can be constructed more accurately, and based on the extension direction of the crack, the cross crack composition segment can be distinguished.

[0032] Referring to Figure 3 The application also provides a warning method of the bridge crack monitoring and warning system, and the stress measurement and analysis system can perform the following steps:

[0033] Step S100, determining the strain of each measurement point on the sensing fiber according to the scattering signal transmitted back by the sensing fiber in reverse;

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

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

[0036] Step S310, for each fluctuation region in the strain curve at the corresponding time, it is judged whether the fluctuation region is arc-shaped, if yes, it indicates that the first case is in that the corresponding fiber segment is transversely arranged and the crack at the corresponding fiber segment extends longitudinally, the corresponding distance between the two ends of the arc-shaped is determined as the width of the crack, according to the first relationship between the crack width and the vibration size in the first case, the corresponding vibration size is obtained according to the determined crack width, and step S320 is executed; otherwise, for the next undetermined fluctuation region, step S310 is returned to be executed;

[0037] Step S320, other fluctuation regions in a corresponding set spatial range (which can be a set square space region) centered on the fluctuation region corresponding fiber segment are determined, the obtained vibration size is taken as the vibration size of the other fluctuation regions in the set spatial range, and step S330 is executed for the other fluctuation regions; for the other fluctuation regions outside the set spatial range, step S310 is returned to be executed;

[0038] Step S330, it is judged whether the fluctuation region is square-shaped, if yes, it indicates that the second case is in that the corresponding fiber segment is transversely arranged and the crack at the corresponding fiber segment extends transversely, according to the second relationship between the longitudinal height of the square-shaped and the crack width under different vibration sizes in the second case, the width of the crack at the corresponding fiber segment is determined according to the obtained vibration size and the longitudinal height of the square-shaped; otherwise, step S340 is executed;

[0039] Step S340, it is judged whether the fluctuation region is a bending line, the bending line includes an intermediate segment with the same strain size and bending segments located on both sides of the intermediate segment respectively, the slopes of the two bending segments are unique and increase or decrease in the same direction, if yes, the corresponding distance of the intermediate segment is taken as the crack width to be detected, and step S350 is executed; otherwise, when there are other undetermined fluctuation regions in the set spatial range, for the next undetermined other fluctuation region in the set spatial range, step S330 is returned to be executed, and when there is no undetermined other fluctuation region in the set spatial range, for the other fluctuation regions outside the set spatial range, step S310 is returned to be executed;

[0040] Step S350, based on a third relationship between the bending segment slope and the crack width under different vibration sizes, the third situation being that the fluctuation region corresponds to the longitudinal arrangement of the fiber segment, and the crack at the corresponding fiber segment extends transversely, according to the obtained vibration size and the crack width to be inspected, the bending segment slope is determined;

[0041] Step S360, judging whether the slope of the bending segment in the bending line is greater than the determined bending segment slope, if yes, indicating that the fourth situation is that the fluctuation region corresponds to the longitudinal arrangement of the fiber segment, and the crack at the corresponding fiber segment extends longitudinally, the crack width to be inspected is the length of the crack at the corresponding fiber segment, and thereafter, based on the fourth relationship between the bending segment slope and the crack width under different vibration sizes, according to the obtained vibration size and the slope of the bending segment in the bending line, the width of the crack at the corresponding fiber segment is determined; otherwise, indicating that the third situation is that the crack width to be inspected is taken as the width of the crack at the corresponding fiber segment.

[0042] In addition, after the step S300, the method can further include: determining the strain curve of the sensing optical fiber at the time according to the strain sizes of the measuring points on the sensing optical fiber at the next time, and executing the step S300, so that the determination accuracy of the crack extension direction and width can be improved. The stress measurement and analysis system can include an optical frequency domain reflectometer (OFDR) system to determine the strain at each measuring point on the sensing optical fiber. In addition to the above-mentioned corresponding fluctuation of the sensing optical fiber under the bridge vibration, the fiber segment between the crack edges will also be bent under the influence of the force (such as wind) perpendicular to the bridge surface to be measured (at this time, the fluctuation driving of all cracks is in an arc shape), so that the strain curve of the sensing optical fiber at different times can be determined. After the arc-shaped fluctuation region is determined in the step S310, it is judged whether all the other fluctuation regions in the set spatial range of the fluctuation region are arc-shaped, if yes, the set spatial range is marked as pending, and the waveforms of all the fluctuation regions in the set spatial range are monitored, and the step S360 is executed; otherwise, the step S320 is executed.

[0043] Step S370, after the strain curve at each time completes the steps S310 to S360, it is judged whether the waveforms of at least one fluctuation region in the set spatial range have changed according to the strain curve at the next time, if yes, the extension direction and width of the crack at the corresponding fiber segment of each fluctuation range determined when all the fluctuation regions in the set spatial range at the time are arc-shaped are deleted, the steps S310 to S360 are executed based on the strain curve at the next time to determine the extension direction and width of the crack at the corresponding fiber segment of each fluctuation region in the set spatial range, and the pending mark of the set spatial range is removed.

[0044] From the above embodiment, it can be seen that the grid with elasticity is fixed on the vertical testing surface of the bridge, and the sensing optical fiber section is laid on the grid, the grid line section and the optical fiber section at the corresponding position of the crack are moved in the vertical direction under the action of gravity due to the vibration of the bridge in the vertical direction, so that the strain curve of the sensing optical fiber is fluctuated, the characteristics of the fluctuation of the strain curve of the sensing optical fiber are different when the wiring direction of the optical fiber section and the extension direction of the crack are different, so the extension direction and the width of the crack on the testing surface can be determined according to the fluctuation characteristics of the strain curve; in addition, the grid can also make the fluctuation characteristics in the strain curve more obvious; since the extension direction of the crack can be determined, the crack along the line can be constructed more accurately, and based on the extension direction of the crack, the cross crack composition section can be distinguished.

[0045] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the application being indicated by the following claims.

[0046] It is to be understood that the application is not limited to the precise construction here described and as shown in the drawings, and that various modifications and changes can be made by those skilled in the art without departing from the scope of the application. The scope of the application is to be determined only by the appended claims.

Claims

1. A bridge crack monitoring and early warning system, characterized by, The grid is covered and fixed on the vertical surface to be measured of the bridge, a sensing optical fiber is sequentially wired on each horizontal grid line and then sequentially wired on each vertical grid line, for each grid line, when a crack occurs at the corresponding position of the grid line on the surface to be measured, the corresponding grid line segment and the optical fiber segment at the position both stretch perpendicularly to the extension direction of the crack; and when the bridge vibrates in the vertical direction, the corresponding grid line segment and the optical fiber segment at 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 extension direction of the crack are different, the characteristics of the fluctuation of the strain curve of the sensing optical fiber are different; The stress measurement and analysis system is connected with the sensing optical fiber, the strain of each measurement point on the sensing optical fiber is determined according to the back transmission scattering signal of the sensing optical fiber, the strain curve of the sensing optical fiber at the corresponding time is determined according to the strain of each measurement point on the sensing optical fiber at the corresponding time, and the strain curve is associated with the spatial position of the sensing optical fiber; the extension direction and the 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 region in the strain curve and the spatial position relationship between the fluctuation regions. Each grid line has the same elasticity. The wiring direction of the optical fiber segment and the extension direction of the crack have the following four cases, the first case: the corresponding optical fiber segment of the fluctuation region is horizontally arranged, and the crack at the corresponding optical fiber segment extends vertically, when the bridge vibrates in the vertical direction, the optical fiber segment between the edges of the crack will fluctuate in an arc shape; The second case: the corresponding optical fiber segment of the fluctuation region is horizontally arranged, and the crack at the corresponding optical fiber segment extends horizontally, when the bridge vibrates in the vertical direction, the optical fiber segment between the edges of the crack will fluctuate in a square shape; The third case: the corresponding optical fiber segment of the fluctuation region is vertically arranged, and the crack at the corresponding optical fiber segment extends horizontally, when the bridge vibrates in the vertical direction, the optical fiber segment between the edges of the crack will fluctuate in a bending line shape; The fourth case: the corresponding optical fiber segment of the fluctuation region is vertically arranged, and the crack at the corresponding optical fiber segment extends vertically, when the bridge vibrates in the vertical direction, the optical fiber segment between the edges of the crack will fluctuate in a bending line shape; the slope of the bending segment in the fourth case is greater than the slope of the bending segment in the third case.

2. The bridge crack monitoring and warning system of claim 1, wherein The vertical direction is the vertical direction, the sensing optical fiber is arranged in a serpentine manner on each horizontal grid line, and then is also arranged in a serpentine manner on each vertical grid line, wherein when arranged on each vertical grid line, if the horizontal grid line is encountered, the wiring is continued after crossing the horizontal grid line.

3. A method of warning in the bridge crack monitoring and warning system according to claim 1 or 2, characterized by, The stress measurement and analysis system performs the following steps: Step S100, determining the strain of each measurement point on the sensing optical fiber according to the back transmission scattering signal of the sensing optical fiber; Step S200, determining the strain curve of the sensing optical fiber at the corresponding time according to the strain of each measurement point on the sensing optical fiber at the corresponding time, and associating the strain curve with the spatial position of the sensing optical fiber; Step S300, according to the fluctuation characteristics of the fluctuation regions in the strain curve and the spatial position relationship between the fluctuation regions, the extension direction and the width of the crack at the corresponding position of the sensing optical fiber on the measured surface of the bridge are determined.

4. The early warning method of claim 3, wherein, The step S300 specifically includes: Step S310, for each fluctuation region in the strain curve at the corresponding time, it is judged whether the fluctuation region is arc-shaped, if yes, it indicates that the fluctuation region corresponds to the transversely arranged optical fiber segment, and the crack at the corresponding optical fiber segment extends longitudinally, the corresponding distance between the two ends of the arc-shaped is determined as the width of the crack, according to the first relationship between the crack width and the vibration size under the first condition, the corresponding vibration size is obtained according to the determined crack width, and step S320 is executed; otherwise, for the next undetermined fluctuation region, step S310 is executed again. Step S320, other fluctuation regions in a set spatial range centered on the fluctuation region corresponding to the optical fiber segment are determined, the obtained vibration size is taken as the vibration size of the other fluctuation regions in the set spatial range, and step S330 is executed for the other fluctuation regions; for the other fluctuation regions outside the set spatial range, step S310 is executed again. Step S330, it is judged whether the fluctuation region is square-shaped, if yes, it indicates that the fluctuation region corresponds to the transversely arranged optical fiber segment, and the crack at the corresponding optical fiber segment extends transversely, according to the second relationship between the longitudinal height of the square-shaped and the crack width under the second condition, the width of the crack at the corresponding optical fiber segment is determined according to the obtained vibration size and the longitudinal height of the square-shaped; otherwise, step S340 is executed. Step S340, it is judged whether the fluctuation region is a bending line, the bending line includes an intermediate segment with the same strain size and bending segments located on both sides of the intermediate segment, the slopes of the two bending segments are unique and increase or decrease in the same direction, if yes, the corresponding distance of the intermediate segment is taken as the crack width to be detected, and step S350 is executed; otherwise, when there are other undetermined fluctuation regions in the set spatial range, for the next undetermined other fluctuation region in the set spatial range, step S330 is executed again, and when there is no undetermined other fluctuation region in the set spatial range, for the other fluctuation regions outside the set spatial range, step S310 is executed again. Step S350, according to the third relationship between the slope of the bending segment and the crack width under the third condition, the third condition is that the fluctuation region corresponds to the longitudinally arranged optical fiber segment, and the crack at the corresponding optical fiber segment extends transversely, the slope of the bending segment is determined according to the obtained vibration size and the crack width to be detected. In step S360, it is judged whether the slope of the bending section in the bending line is greater than the determined slope of the bending section. If yes, it indicates that the fourth case is present, i.e. the fluctuation region corresponds to the longitudinally arranged optical fiber section, and the crack at the corresponding optical fiber section extends longitudinally, and the width of the crack to be detected is the length of the crack at the corresponding optical fiber section. Then, based on the fourth relationship between the slope of the bending section and the width of the crack at different vibration amplitudes in the fourth case, the width of the crack at the corresponding optical fiber section is determined according to the obtained vibration amplitude and the slope of the bending section in the bending line. Otherwise, it indicates that the third case is present, and the width of the crack to be detected is taken as the width of the crack at the corresponding optical fiber section.

5. The early warning method of claim 3, wherein, After step S300, it further includes determining the strain curve of the sensing optical fiber at the time according to the measured strain of each measuring point on the sensing optical fiber at the next time, and executing step S300.

Images