Method for monitoring migration process of ancient building based on ultra-weak fiber grating array

Abstract

The invention discloses an ancient building migration process monitoring method based on an ultra-weak fiber grating array, and the method comprises the steps: building a mechanical model of a tray, burying a strain optical cable, determining the position of a grating array, monitoring a lifting process, monitoring a moving process, monitoring a placing process, and the like, and is characterized in that the static strain distribution of the tray is measured, and the lifting process is measured. In the moving process and the placing process, strain changes and deflection are monitored in real time, and whether stress and differential settlement exceed threshold values or not is judged. According to the historic building migration monitoring method based on the ultra-weak fiber grating array, the maximum strain and differential settlement of the building in the lifting, moving and placing processes can be monitored in real time, the influence of the migration action on the building is quantified in combination with simulation analysis, and an effective evaluation and optimization approach is provided for building migration.

Description

Technical Field

[0001] The invention belongs to the technical field of strain and deformation monitoring of pallet beams, and in particular relates to a monitoring method for the migration process of ancient buildings based on an ultra-weak fiber grating array. Background Art

[0002] After long-term service, the strength of the ancient building structure will gradually deteriorate due to factors such as material aging and environmental influences. The structure itself becomes relatively fragile and very sensitive to external influences. The overall translation technology of the building is complicated, and it is very easy to cause man-made damage to the ancient building during the displacement process, causing safety accidents. During the displacement process, the pallet beam bears the load of the upper ancient building, and is subjected to traction or thrust during the displacement process. Its strain field distribution and uneven settlement are related to the smooth completion of the displacement project. Therefore, real-time online monitoring of the strain field distribution and uneven settlement of the pallet beam has become a necessary choice for the smooth completion of the displacement project! At present, the main means of monitoring the strain field distribution of pallet beams are vibrating-wire strain gauges, resistive strain gauges, and fiber Bragg Gratings (FBGs), and the main means of monitoring uneven settlement are static levels, high-precision level rulers, etc. In 2020, Zhang Rui et al. used 4 vibrating-wire strain gauges to monitor the strain of the replacement steel frame during the translation of the Buddha statue, and used a static level to monitor the uneven settlement of the pallet beam during the translation of the main hall. The strain monitoring accuracy was about 0.5 mm, and the uneven settlement monitoring accuracy was about 0.5 mm. In 2022, Xie Liyu et al. used 13 FBGs to monitor the strain of the pallet beam during the station shift, and used a static level to observe the uneven settlement. The strain monitoring accuracy was about 0.5 mm, and the uneven settlement monitoring accuracy was about 1 mm. However, these monitoring methods are generally single-point static monitoring, and cannot achieve distributed dynamic measurement of pallet beam strain and uneven settlement. Summary of the invention

[0003] The purpose of the present invention is to address the deficiencies of the prior art and the practical problems of strain field distribution and uneven settlement monitoring of existing pallet beams. The present invention introduces uwFBG into the strain and uneven settlement monitoring of pallet beams, and proposes a monitoring method for the migration process of ancient buildings based on ultra-weak fiber grating arrays. The monitoring method can monitor the maximum strain and uneven settlement during the lifting, movement and placement of the building in real time, and quantifies the impact of the relocation action on the building in combination with simulation analysis, providing an effective evaluation and optimization approach for building relocation.

[0004] The technical purpose of the present invention is achieved through the following technical solutions: A method for monitoring the migration process of ancient buildings based on ultra-weak fiber grating arrays, comprising: (1) Mechanical model construction: The pallet beam adopts a double-wall-beam pallet. A rectangular concrete beam is built on both sides of the load-bearing wall of the ground building. The load-bearing wall is modeled according to the actual size, thereby establishing the actual model of the pallet beam. The model of the building above the pallet beam is simplified. After the model is established, the changes in the mechanical properties of the pallet are simulated and analyzed according to the structure of the ground building and the gravity distribution, and the layout route of the ultra-weak fiber Bragg grating strain cable is determined, as well as the position of the support point of the pallet beam of the mechanical model is constructed; (2) Strain optical cable burial: Ultra-weak fiber Bragg grating strain optical cables are symmetrically laid on the upper and lower sides of the steel cage of the building tray; (3) Determine the position of the grating array: After the optical cable is laid, connect the ultra-weak fiber Bragg grating strain demodulator and use a hot air gun to heat the grating to cause a significant drift in the wavelength, thereby determining the position of the sensor on the tray. (4) Monitoring of the lifting process: Before lifting, measure the static strain distribution of the pallet; during the lifting process, monitor the strain changes of the pallet in real time; combine the mechanical model of the pallet to invert the strain of the pallet to obtain the corresponding deflection; extract the maximum strain value and uneven settlement to determine whether the force and uneven settlement of the pallet exceed the limit; (5) Monitoring of the movement process: According to step (4), adjust the sampling frequency, extract the maximum strain value and deflection, and determine whether the maximum strain and uneven settlement during the movement process exceed the limit; (6) Monitoring the placement process: According to step (4), extract the maximum strain value and deflection during the placement process to determine whether the maximum strain and uneven settlement during the placement process exceed the limit.

[0005] Preferably, step (6) further includes (7): optimizing the relocation plan, combining the simulation model, analyzing and comparing the maximum strain and uneven settlement during lifting, moving and placement, and formulating an optimization plan for the relocation process.

[0006] Preferably, the strain optical cable is symmetrically laid on the upper and lower sides of the steel cage of the building tray and connected to the ultra-weak fiber grating demodulator after the cable is laid to test the wavelength change of the optical cable, and then the wavelength-strain coefficient calibrated in advance is used to calculate the strain optical cable. Calculate the strain at different positions of the pallet .

[0007] Preferably, according to the calculated strains at different positions of the pallet, combined with the mechanical model of the pallet, the deformation of the pallet is inverted using a curve reconstruction algorithm to obtain the uneven settlement information of the pallet; the calculation process is as follows: Assume that there is a micro-element structure that is not bent for a period of , width is , after bending, the upper side is stretched , lower side compression , the central axis remains unchanged, and the radius of curvature is , the central angle of the bend is , from the definition we know that the strain According to the geometric relationship: ; According to the calculated strain distribution at each position on the pallet, the curvature k corresponding to each sensor is calculated. It can be seen that the relationship between curvature and strain is as follows: ; Thus, the arc length-curvature data pair of the sensing point is obtained, and the curvature data of the curvature curve continuity is obtained by using the interpolation algorithm. For the reconstructed curve, the distance between two adjacent points is close enough, and the curve between the two points is approximately considered to be a micro-arc. The uneven settlement of the pallet beam can be obtained by using the curve reconstruction algorithm. According to the recursive principle of cutting angle, it can be known that: ; Among them, by plotting the x and y data, the uneven settlement information of the pallet beam can be obtained.

[0008] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a monitoring method for the migration process of ancient buildings based on an ultra-weak fiber grating array. The method utilizes the large-capacity multiplexing characteristics of ultra-weak fiber gratings and multi-point sensing, thereby overcoming the problem of a small number of traditional monitoring points and avoiding the complex series connection of multiple sensor elements. There is no need to weld additional sensor elements, thus avoiding problems such as sensor element breakage and failure. The method can dynamically and distributedly monitor the strain field and uneven settlement of the ancient building tray.

[0009] The invention discloses a monitoring method for the migration process of ancient buildings based on ultra-weak fiber grating array, which has high sensitivity, good cost performance and is easy to monitor automatically. The strain monitoring sensitivity reaches a high level of fiber optic sensing engineering monitoring. The ultra-weak fiber grating demodulator is 1 / 4 to 1 / 5 of the price of the same BOTDA, and is easy to operate. It can monitor the strain field distribution and uneven settlement of the pallet beam in real time online, reducing the potential safety hazards of the project. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a schematic diagram of the arrangement of the strain optical cable in the present invention.

[0011] Figure 2 The strain changes of the pallet during the concrete curing process and after complete curing.

[0012] Figure 3 Schematic diagram of the strain-curvature conversion relationship.

[0013] Figure 4 Schematic diagram of the principle of the angle cutting recursive algorithm.

[0014] Figure 5 Schematic diagram of the double-ended fixed beam model.

[0015] Figure 6 is the deformation of the object under test obtained by the curve reconstruction algorithm. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] As a preferred embodiment of the present invention, this embodiment provides a monitoring method for the migration process of ancient buildings based on ultra-weak fiber grating array, comprising: (1) Mechanical model construction: The pallet beam adopts a double-wall-beam pallet. A rectangular concrete beam is built on both sides of the load-bearing wall of the ground building. The load-bearing wall is modeled according to the actual size, thereby establishing the actual model of the pallet beam. The model of the building above the pallet beam is simplified. After the model is established, the changes in the mechanical properties of the pallet are simulated and analyzed according to the structure of the ground building and the gravity distribution, and the layout route of the ultra-weak fiber Bragg grating strain cable is determined, as well as the position of the support point of the pallet beam of the mechanical model is constructed; (2) Strain optical cable burial: Ultra-weak fiber Bragg grating strain optical cables are symmetrically laid on the upper and lower sides of the steel cage of the building tray. After determining the cable laying route, select a main reinforcement on each side of the steel cage of the ancient building tray to lay the ultra-weak fiber Bragg grating strain optical cable. The laying method is as follows: Figure 1 As shown, when laying the optical cable, one person arranges and feeds the stacked optical cables at the cable entry end to prevent the optical cables from being severely twisted or bent. One person pulls the optical cables into the steel cage for a certain distance and then pulls out all the optical cables and reserves a 2m sensing optical cable at the entry end. After pulling out, two people straighten the optical cables that have entered the steel cage at both ends, fix the two ends with metal clamps, and then tie the optical cables and the steel cage together with nylon tie; (3) Determine the position of the grating array: After the optical cable is laid, connect the ultra-weak fiber Bragg grating strain demodulator, use a hot air gun to heat the grating wavelength to cause a significant drift, and determine the position of the sensor on the pallet. After the position of the sensor on the pallet is determined, pour concrete and connect the ultra-weak fiber Bragg grating demodulator to detect the survival of the optical cable; after the concrete pouring is completed, connect the ultra-weak fiber Bragg grating demodulator and collect data. Based on the wavelength data before and after the concrete pouring, the wavelength change of the pallet sensor can be obtained. , and the strain at each position on the tray is calculated based on the pre-calibrated wavelength-gauge coefficient During the concrete curing process, data was collected multiple times and compared and analyzed, such as Figure 2 Shown are the concrete curing process and data after full curing; (4) Monitoring of the lifting process: Before lifting, measure the static strain distribution of the pallet; during the lifting process, monitor the strain changes of the pallet in real time; combine the mechanical model of the pallet to invert the strain of the pallet to obtain the corresponding deflection; extract the maximum strain value and uneven settlement to determine whether the force and uneven settlement of the pallet exceed the limit; (5) Monitoring of the movement process: According to step (4), adjust the sampling frequency, extract the maximum strain value and deflection, and determine whether the maximum strain and uneven settlement during the movement process exceed the limit; (6) Monitoring the placement process: According to step (4), extract the maximum strain value and deflection during the placement process to determine whether the maximum strain and uneven settlement during the placement process exceed the limit.

[0018] Ultra weak fiber Bragg Grating (uwFBG) is a general term for fiber Bragg Grating with a reflectivity lower than 0.1%. Thousands of ultra weak fiber Bragg Gratings can be multiplexed on a single optical fiber, and industrial production has been achieved.

[0019] In some embodiments, based on the calculated strains at different positions of the pallet, combined with the mechanical model of the pallet, a curve reconstruction algorithm is used to invert the deformation of the pallet to obtain the uneven settlement information of the pallet; the calculation process is as follows: Figure 3 As shown, it is assumed that there is a micro-element structure that is not bent for a period of , width is , after bending, the upper side is stretched , lower side compression , the central axis remains unchanged, and the radius of curvature is , the central angle of the bend is , from the definition we know that the strain According to the geometric relationship: ; According to the calculated strain distribution at each position on the pallet, the curvature k corresponding to each sensor is calculated. It can be seen that the relationship between curvature and strain is as follows: ; Thus, the arc length-curvature data pair of the sensing point is obtained, and the curvature data of the curvature curve continuity is obtained by interpolation algorithm. For the reconstructed curve, Figure 4 As shown in the figure, the distance between two adjacent points is close enough, and the curve between the two points is approximately considered to be a micro-arc. The uneven settlement of the pallet beam can be obtained by using the curve reconstruction algorithm. According to the recursive principle of cutting angle, it can be known that: ; Among them, the uneven settlement information of the pallet beam can be obtained by plotting the x and y data. From this, the maximum strain value and uneven settlement of the building pallet during the lifting process can be extracted, and it can be judged whether the force and uneven settlement of the pallet during the lifting process exceed the limit.

[0020] Before the building is moved, data is collected once and used as the initial data of the lifting process to analyze the strain changes of the building during the lifting process. During the movement, the sampling frequency is adjusted to monitor the strain changes of the tray in real time. Combined with the constructed mechanical model, the strain is inverted to obtain the corresponding deflection, extract the maximum strain value and deflection, and determine whether the stress and uneven settlement of the tray during the movement exceed the limit.

[0021] Data collection is performed before placement in the building; during the placement process, the strain changes of the pallet are monitored in real time, and combined with the constructed mechanical model, the strain is inverted to obtain the corresponding deflection, extract the maximum strain value and deflection, and determine whether the stress and uneven settlement of the pallet during the placement process exceed the limit.

[0022] like Figure 5 The figure shows a schematic diagram of a double-ended fixed beam model. The two ends are fixed devices. The optical cable is laid in the object to be measured between the two fixed devices. The thickness of the object to be measured that is deformed is , the distance between two grating points is the arc length The solid line indicates the position without deformation, and the dotted line indicates the position after deformation. The optical cable deforms along with the deformation of the measured object. According to the change of the grating wavelength Calculate the strain change of the measured object According to the conversion relationship between strain and curvature, the curvature information at the grid point can be obtained. , from which the corresponding arc length-curvature data pair can be obtained, and then a suitable interpolation algorithm is used to obtain a more precise arc length-curvature data pair to reduce the error of curve reconstruction. Then, one end fixed point is used as the starting point, the initial cutting angle is zero, and the deformed curve is derived by substituting it into the cutting angle recursive algorithm. Figure 6 The figure shows the deformation of the object under test obtained by the curve reconstruction algorithm. From this, the uneven settlement of the building tray during the lifting process can be inverted.

[0023] Based on the real-time strain changes and uneven settlement of the pallet obtained through monitoring and the simulation results, the maximum strain values ​​and uneven settlement during the lifting, moving and placement processes are analyzed and compared. When the strain changes are large, the relocation plan is optimized to ensure the safety of the locations where the strain of the pallet is concentrated and the uneven settlement is large.

[0024] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A monitoring method for the migration process of ancient buildings based on ultra-weak fiber grating array, characterized in that: include: (1) Mechanical model construction: The pallet beam adopts a double-wall-beam pallet. A rectangular concrete beam is built on both sides of the load-bearing wall of the ground building. The load-bearing wall is modeled according to the actual size, thereby establishing the actual model of the pallet beam. The model of the building above the pallet beam is simplified. After the model is established, the changes in the mechanical properties of the pallet are simulated and analyzed according to the structure of the ground building and the gravity distribution, and the layout route of the ultra-weak fiber Bragg grating strain cable is determined, as well as the position of the support point of the pallet beam of the mechanical model is constructed; (2) Strain optical cable burial: Ultra-weak fiber Bragg grating strain optical cables are symmetrically laid on the upper and lower sides of the steel cage of the building tray; (3) Determine the position of the grating array: After the optical cable is laid, connect the ultra-weak fiber Bragg grating strain demodulator and use a hot air gun to heat the grating to cause a significant drift in the wavelength, thereby determining the position of the sensor on the tray. (4) Monitoring of the lifting process: Before lifting, measure the static strain distribution of the pallet; during the lifting process, monitor the strain changes of the pallet in real time; combine the mechanical model of the pallet to invert the strain of the pallet to obtain the corresponding deflection; extract the maximum strain value and uneven settlement to determine whether the force and uneven settlement of the pallet exceed the limit; (5) Monitoring of the movement process: According to step (4), adjust the sampling frequency, extract the maximum strain value and deflection, and determine whether the maximum strain and uneven settlement during the movement process exceed the limit; (6) Monitoring the placement process: According to step (4), extract the maximum strain value and deflection during the placement process to determine whether the maximum strain and uneven settlement during the placement process exceed the limit.

2. The method for monitoring the migration process of ancient buildings based on ultra-weak fiber grating array according to claim 1 is characterized in that: Step (6) also includes (7): optimization of the relocation plan, combining the simulation model, analyzing and comparing the maximum strain and uneven settlement during lifting, moving and placement, and formulating an optimization plan for the relocation process.

3. The method for monitoring the migration process of ancient buildings based on ultra-weak fiber grating array according to claim 1 is characterized in that: The strain optical cable is symmetrically laid on the upper and lower sides of the steel cage of the building tray and connected to the ultra-weak fiber grating demodulator after the cable is laid. The wavelength change of the optical cable is tested and then the wavelength-strain coefficient calibrated in advance is used. Calculate the strain at different positions of the pallet .

4. The method for monitoring the migration process of ancient buildings based on ultra-weak fiber grating array according to claim 1 is characterized in that: According to the calculated strains at different positions of the pallet, combined with the mechanical model of the pallet, the curve reconstruction algorithm is used to invert the deformation of the pallet to obtain the uneven settlement information of the pallet; the calculation process is as follows: Assume that there is a micro-element structure that is not bent for a period of , width is , after bending, the upper side is stretched , lower side compression , the central axis remains unchanged, and the radius of curvature is , the central angle of the bend is , from the definition we know that the strain According to the geometric relationship: ； According to the calculated strain distribution at each position on the pallet, the curvature k corresponding to each sensor is calculated. It can be seen that the relationship between curvature and strain is as follows: ； Thus, the arc length-curvature data pair of the sensing point is obtained, and the curvature data of the curvature curve continuity is obtained by using the interpolation algorithm. For the reconstructed curve, the distance between two adjacent points is close enough, and the curve between the two points is approximately considered to be a micro-arc. The uneven settlement of the pallet beam can be obtained by using the curve reconstruction algorithm. According to the recursive principle of cutting angle, it can be known that: ； Among them, by plotting the x and y data, the uneven settlement information of the pallet beam can be obtained.

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