Bridge bearing service state evaluation method based on non-contact measurement

Abstract

The application provides a bridge support service state evaluation method based on non-contact measurement. The method comprises the following steps: collecting the vertical dynamic deflection signal of the bridge support and the beam span of the railway bridge to be detected when the operating train passes through the bridge to be detected by using a non-contact visual measurement method; calculating the damage index of the railway bridge to be detected based on the support-beam span displacement ratio according to the vertical dynamic deflection signal; calculating the damage index limit value according to the design parameters of the railway bridge to be detected; comparing the measured value of the damage index with the limit value, and determining the service state of the bridge support of the railway bridge to be detected according to the comparison result. The damage index based on the support-beam stiffness ratio can accurately locate the damaged support and quantitatively evaluate the vertical stiffness of the support, solves the problem that the existing method can only identify the weak end of the bridge but cannot locate the damaged support, does not need to establish a finite element model or an agent model, and is not sensitive to track irregularities, beam body and diaphragm damage and environmental noise, and has strong anti-interference ability and robustness.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bridge support damage assessment, and particularly relates to a bridge support service state assessment method based on non-contact measurement. BACKGROUND

[0002] The support is a key component connecting the upper structure and the lower structure of the bridge, and plays an important role in transmitting loads and ensuring the proper deformation of the beam. However, under the action of external environment such as temperature and humidity changes, vehicle dynamic action and uneven foundation settlement, the bridge support is prone to a series of diseases such as rubber aging cracking, deformation exceeding limit and voiding, and its performance degradation will change the boundary conditions and stress performance of the bridge, and even endanger the safety of driving on the bridge. Therefore, timely detection and assessment of the damage condition of the support is of great significance to ensure the safety of bridge operation.

[0003] At present, the support damage assessment methods mainly include visual detection method, force sensor monitoring method and vibration test based method. The visual detection method can be divided into manual visual inspection and image processing detection method based on intelligent algorithm. Manual visual inspection is usually time-consuming and labor-intensive, and to some extent, it depends on the professional experience of the inspector. The image processing detection method based on intelligent algorithm still faces challenges in distinguishing different types of damage and quantitatively evaluating the damage degree of the support, because it is difficult to obtain specific and extensive database in practice. The force sensor monitoring method needs to install force sensors in the support during the construction of the bridge, which is not suitable for the general inspection of the support of a large number of small and medium span bridges due to high cost and is mainly applied to large span bridges.

[0004] In recent years, the vibration test based method has gradually become a research hotspot due to its advantages of non-destructive testing, low cost, flexible sensor deployment and strong real-time online monitoring capability. However, the existing vibration test based support assessment method still has some problems to be solved:

[0005] 1) The analysis model used in the existing research is mostly a two-dimensional model, which simplifies the bridge as an elastic supported beam with spring constraints at both ends, and can only determine the weak end of the bridge and cannot realize accurate positioning of the damaged support;

[0006] 2) The relationship between the existing damage index and the support stiffness is not clear, and the damage index limit value is often set based on probability and statistical methods, which lacks clear physical meaning. The method based on finite element model correction can accurately identify the support stiffness, but it needs to know the bridge design parameter information and establish a finite element model, which is not conducive to the rapid detection of the bridge;

[0007] 3) The existing dynamic test mainly relies on contact sensors to collect the dynamic response of the bridge, and the arrangement of the sensors may be restricted by the site environment, and the arrangement efficiency is low. SUMMARY

[0008] The application provides a bridge support service state evaluation method based on non-contact measurement, to realize rapid and effective evaluation of the service state of a railway bridge support.

[0009] To achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0010] A bridge support service state evaluation method based on non-contact measurement, comprising:

[0011] The non-contact visual measurement method is used to collect the vertical dynamic deflection signals of the support and the mid-span of the bridge when an operating train passes through the railway bridge to be detected; and the damage index of the railway bridge to be detected based on the support-mid-span displacement ratio is calculated according to the vertical dynamic deflection signals.

[0012] The damage index limit value is calculated according to the design parameters of the railway bridge to be detected.

[0013] The measured value of the damage index is compared with the damage index limit value, and the service state of the support of the railway bridge to be detected is determined according to the comparison result.

[0014] Preferably, the non-contact visual measurement method is used to collect the vertical dynamic deflection signals of the support and the mid-span of the bridge when an operating train passes through the railway bridge to be detected, comprising:

[0015] Each measurement point in the bridge to be detected is selected, a tripod is erected, the instrument is leveled, the lens is installed and the aperture and focal length are adjusted, it is ensured that the measurement points are located within the field of view of the lens, the camera parameters are set, the sampling frequency and exposure setting are selected, the range-finding telescope is used to add and calibrate the measurement points to determine the coefficient of each measurement point, at least 5 groups of vertical dynamic deflection signals of each measurement point under the action of operating trains are collected, and the low-pass filter is used for noise reduction pretreatment of the vertical dynamic deflection signals.

[0016] Preferably, the damage index of the railway bridge to be detected based on the support-mid-span displacement ratio is calculated according to the vertical dynamic deflection signals, comprising:

[0017] The maximum value of the vertical dynamic deflection response at the support is obtained according to the collected vertical dynamic deflection signals at the support, and the maximum value of the vertical dynamic deflection response at the mid-span of the bridge is obtained according to the collected vertical dynamic deflection signals at the mid-span of the bridge.

[0018] The damage index η based on the support-mid-span displacement ratio is defined as follows: i The calculation method of the damage index η based on the support-mid-span displacement ratio is as follows:

[0019]

[0020] In the formula, N tTo test the number of train passes through the bridge section, U bi represents the maximum value of the vertical dynamic deflection response at the i-th support, U mid represents the maximum value of the vertical dynamic deflection response at the beam span;

[0021] Based on the measured dynamic deflection data at the beam span, the dynamic coefficients of the prestressed concrete simply supported beam bridge under each group of working conditions are calculated:

[0022]

[0023] In the formula: δ dmax is the measured maximum deflection value, δ smax Take the vertex value of the amplitude center trajectory line of this waveform or the maximum deflection value of low speed.

[0024] Preferably, the damage index limit value is calculated according to the design parameters of the railway bridge to be detected, comprising:

[0025] According to the actual arrangement form of the railway T-beam bridge support, the bridge is regarded as a spatial elastic support beam supported by four springs with stiffness K1, K2, K3 and K4, and the train load is regarded as a moving load train with axle load P and spacing d j , j=1, 2, 3, passing through the bridge at a uniform speed v;

[0026] The vibration mode of the spatial elastic support beam is approximately the superposition of the first-order bending vibration mode of the corresponding simply supported beam and the rigid body displacement vibration mode of the rigid beam:

[0027]

[0028] In the formula: κ A = EIπ 3 / ((K1+K2)L 3 ) and κ B = EIπ 3 / ((K3+K4)L 3 ) represent the beam-support stiffness ratio of the A end and the B end of the beam; L is the beam length;

[0029] Introduce the support damage coefficients α1=K1 / K, α2=K2 / K, α3=K3 / K, α4=K4 / K, wherein K is the support stiffness limit value;

[0030] The maximum displacement of the spatial elastic support beam support under the action of the moving load train is:

[0031]

[0032] In the formula: and respectively represent the distance of the k-th axle of the moving load train from the A end and the B end of the beam;

[0033] The maximum displacement of the spatial elastic support beam at the mid-span under the action of the moving load column is approximately:

[0034]

[0035] When all bearings are in the undamaged state, i.e. α1=α2=α3=α4=1, based on the above derivation, a mathematical relationship between the theoretical value of the damage index and the bearing stiffness when the bearing is in the undamaged state can be established as:

[0036]

[0037] In the formula, EI is the bending stiffness of the beam; K is the bearing vertical stiffness limit value specified in the specification; and L is the beam span. represents the distance from the kth axis of the moving load column to the A end of the beam.

[0038] The bending stiffness EI of the beam is calculated according to the design elastic modulus E of the beam body and the cross-sectional bending inertia moment I, and the bearing vertical stiffness limit value K is calculated according to the design bearing capacity and the design height, and the relationship between the damage index and the bearing stiffness is substituted into the above relationship to calculate the bearing damage index limit value η under different vehicle types. theo The minimum value of all η theo is taken as the bearing damage index limit value.

[0039] Preferably, the measured value of the damage index is compared with the damage index limit value, and the service state of the bearing of the railway bridge to be detected is determined according to the comparison result, which comprises:

[0040] When η i ≤η theo , when the bearing vertical stiffness identification value is greater than or equal to the bearing stiffness limit value specified in the specification, it is judged that the bearing is in good service state.

[0041] When η i >η theo , when the bearing vertical stiffness identification value is less than the bearing stiffness limit value specified in the specification, it is judged that the bearing has a disease, and the disease degree is determined according to the corresponding stiffness of the damage index.

[0042] 1. The damage index based on the bearing-beam stiffness ratio of the present application can accurately locate the damaged bearing, solve the problem that the existing method can only identify the weak end of the bridge but cannot locate the damaged bearing, and is not sensitive to track irregularities, beam and diaphragm damage and environmental noise, and has strong anti-interference ability and robustness.

[0043] 2. This invention belongs to the data-driven method. By utilizing the mathematical relationship between damage index and bearing stiffness, the bearing stiffness can be quantitatively evaluated without establishing a finite element model or surrogate model, which helps to realize the rapid assessment and online monitoring of bridge bearing condition.

[0044] 3. This invention uses operational traffic load as an incentive, and the non-contact measurement scheme is low-cost and easy to operate. It eliminates the need to deploy sensors on the bridge and conduct online operations, greatly improving detection efficiency.

[0045] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and will become apparent from the description or may be learned by practice of the invention. Attached Figure Description

[0046] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 A flowchart illustrating a method for evaluating the service status of bridge bearings based on non-contact measurement of the bearing-beam displacement ratio, provided in an embodiment of the present invention.

[0048] Figure 2 This is a schematic diagram of a dynamic test based on non-contact measurement provided in an embodiment of the present invention;

[0049] Figure 3 This is a schematic diagram of a spatial elastic support beam under the action of a moving load column, provided in an embodiment of the present invention.

[0050] Figure 4 A schematic diagram of a single-track 32m heavy-haul railway double-piece simply supported T-beam bridge model provided in this embodiment of the invention;

[0051] Figure 5 This invention provides a diagram showing the damage identification results of various supports under different damage conditions, as provided in an embodiment of the invention.

[0052] Figure 6 This is an image showing the damage identification results of various supports under different track irregularities, provided by an embodiment of the present invention.

[0053] Figure 7 This is a diagram showing the damage identification results of each support under damage to a transverse diaphragm at different locations, provided as an embodiment of the present invention. Detailed Implementation

[0054] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0055] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we say an element is “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or there may be intermediate elements. Furthermore, “connected” or “coupled” as used herein can include wireless connections or couplings. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0056] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0057] To facilitate understanding of the embodiments of the present invention, the following will provide further explanation and description with reference to the accompanying drawings and several specific embodiments. These embodiments do not constitute a limitation on the embodiments of the present invention.

[0058] This invention addresses the shortcomings of existing bridge bearing assessment methods, such as difficulty in accurately locating damaged bearings, the need to establish a bridge finite element model, and the deployment of sensors on the bridge. This invention provides a bridge bearing stiffness assessment method based on the bearing-beam displacement ratio under non-contact measurement, aiming to achieve quantitative assessment of the bridge bearing condition without a model by utilizing the vibration response of operating vehicles and non-contact measurement.

[0059] Figure 1 The flowchart below shows a method for evaluating bridge bearing stiffness based on non-contact measurement of the bearing-beam displacement ratio, according to an embodiment of the present invention. The method includes the following processing steps:

[0060] Step S1: Select the railway bridge bearing to be tested and conduct dynamic response testing.

[0061] The bridge to be tested was selected, and the dynamic response test of the bridge was carried out using the load of an operating train as an excitation. Figure 2 This is a schematic diagram of a dynamic test based on non-contact measurement provided in an embodiment of the present invention, as shown below. Figure 2 As shown, non-contact visual measurement technology is used to collect vertical dynamic deflection signals at each support and the mid-span of the beam when an operating train crosses the bridge. A tripod is set up at a suitable location with a good field of view, and the instrument is leveled. Then, the lens is installed, and the aperture and focal length are adjusted appropriately to ensure that the measurement points are clearly within the lens's field of view. Camera parameters are set, and the sampling frequency and exposure settings are selected. Measurement points are added and calibrated using a rangefinder telescope to determine the coefficients for each measurement point. Preferably, at least five sets of vertical dynamic deflection signals at each measurement point under train action are collected, and low-pass filtering is used to preprocess the vertical dynamic deflection signals for noise reduction.

[0062] Step S2: Calculate the damage index of each support according to the support-beam displacement ratio damage index formula, and calculate the average value of the impact coefficient under all data acquisition conditions.

[0063] The maximum value of the vertical dynamic deflection response at the support is obtained based on the collected vertical dynamic deflection signal at the support, and the maximum value of the vertical dynamic deflection response at the mid-span of the beam is obtained based on the collected vertical dynamic deflection signal at the mid-span of the beam.

[0064] Define the damage index η based on the support-to-mid-span displacement ratio of the beam. i The calculation method is as follows:

[0065]

[0066] Where: N t To test the number of train trips at the bridge cross-section, U bi U represents the maximum vertical dynamic deflection response at the i-th support. mid This represents the maximum value of the vertical dynamic deflection response at the mid-span of the beam;

[0067] Based on the measured dynamic deflection data at the mid-span of the beam, the dynamic coefficients of the prestressed concrete simply supported beam bridge under each working condition were calculated:

[0068]

[0069] Where: δ dmax δ represents the measured maximum deflection value. smax Take the vertex value of the center trajectory line of the amplitude of this waveform or the maximum deflection value at low speed (quasi-static).

[0070] Step S3: Determine the beam stiffness, beam length, and support stiffness limits based on the beam and support design parameters and the "Railway Pot Rubber Bearing" (TB / T 2331-2013). Calculate the support damage index limits for different vehicle types based on the relationship between damage index and support stiffness, and take the minimum value as the final limit.

[0071] Based on the actual arrangement of the supports of the railway T-beam bridge, the bridge is regarded as a spatial elastic support beam with four spring supports of stiffness K1, K2, K3 and K4. Figure 3 This is a schematic diagram of a spatial elastic support beam under the action of a moving load column, as provided in an embodiment of the present invention. Figure 3 As shown. The train load is considered to be axle load of P and spacing of d. j A moving load train (j = 1, 2, 3) passes over the bridge at a constant speed v.

[0072] The mode shape of a spatially elastically supported beam is approximately the superposition of the first-order bending mode shape of a corresponding simply supported beam and the rigid body displacement mode shape of a rigid beam.

[0073]

[0074] In the formula: κ A =EIπ 3 / ((K1+K2)L 3 ) and κ B =EIπ 3 / ((K3+K4)L 3 ) represents the beam-support stiffness ratio at ends A and B of the beam; L is the beam length.

[0075] To facilitate the quantitative representation of the damage degree of the support, we introduce support damage coefficients α1 = K1 / K, α2 = K2 / K, α3 = K3 / K, and α4 = K4 / K, where K is the support stiffness limit.

[0076] The maximum displacement at the support of the spatial elastically supported beam under the action of a moving load column is:

[0077]

[0078] In the formula: and These represent the distances from the k-th axis of the moving load column to ends A and B of the beam, respectively.

[0079] The maximum mid-span displacement of a spatially elastically supported beam under the action of a moving load column can be approximated as:

[0080]

[0081] When all supports are in an undamaged state, i.e., α1=α2=α3=α4=1, based on the above derivation, the mathematical relationship between the theoretical value of the damage index and the support stiffness when the supports are in an undamaged state can be established as follows:

[0082]

[0083] In the formula: EI is the flexural stiffness of the beam; K is the vertical stiffness limit of the support specified in the code; L is the beam span; x k A This represents the distance from the k-th axis of the moving load column to end A of the beam.

[0084] The flexural stiffness of the beam is calculated based on the beam's design elastic modulus E and the flexural moment of inertia I of the cross section. According to the provisions of "Railway Pot Bearings" (TB / T 2331-2013), the vertical compressive deformation of the bearing under design load should not exceed 2% of the total height of the bearing. The vertical stiffness limit K of the bearing can be calculated based on the bearing's design bearing capacity and design height. Substituting the above relationship between damage indicators and bearing stiffness, the damage indicator limit η of the bearing under different vehicle models is calculated. theo And take the minimum value as the limit.

[0085] Step S4: Establish bridge bearing stiffness assessment criteria based on bearing damage indices, and quantitatively assess the bearing service status based on the identification results.

[0086] The following is established based on the support damage index η i Bridge bearing stiffness evaluation criteria:

[0087] When η i ≤η theo When the vertical stiffness identification value of the support is greater than or equal to the support stiffness limit specified in the standard, the service condition is good;

[0088] When η i >η theo If the vertical stiffness identification value of the support is less than the support stiffness limit specified in the code, it indicates that the support may have defects. The degree of defects can be determined based on the stiffness corresponding to the damage index.

[0089] The following section describes the location and quantitative assessment of bridge bearing damage based on actual conditions. A single-track, 32m heavy-haul railway double-panel simply supported T-beam bridge was constructed as follows: Figure 4 As shown, the beam is modeled using beam elements and divided into 64 equal-length elements. The elastic modulus of the concrete is 3.45 × 10⁻⁶. 4 MPa, with a density of 4665 kg / m³ after considering the second-phase dead load. 3 With a Poisson's ratio of 0.3 and a vertical stiffness of 1×10⁻⁶, the support is... 9 The bridge system damping ratio is 0.02, with a resistance of N / m. The following damage simulation conditions are considered for different damage combinations:

[0090] Condition 1: No damage occurred to any of the supports, i.e., α1 = 1, α2 = 1, α3 = 1, α4 = 1;

[0091] Condition 2: The stiffness of support 1 decreases by 50%, while other supports remain undamaged, i.e., α1 = 0.5, α2 = 1, α3 = 1, α4 = 1;

[0092] Condition 3: The stiffness of support 1 decreases by 50%, the stiffness of support 2 increases by 50%, the stiffness of support 3 increases by 50%, and the stiffness of support 4 decreases by 80%, i.e., α1 = 0.5, α2 = 1.5, α3 = 1.5, and α4 = 0.2.

[0093] Eight-car C80 open wagons were selected as the vehicle model. A five-level spectrum was used to generate track irregularity samples. Considering the randomness of train speeds operating on the bridge during actual testing and the differences in axle loads (23t–30t) between different open wagon models, train speed and car body mass coefficients were randomly generated within the ranges of [60, 80] km / h and [0.9, 1.2], respectively, during the bearing damage identification process. The dynamic responses of five train sets crossing the bridge were collected for each damage condition, and 10% Gaussian white noise was added to the responses to account for the influence of environmental noise. The bearing damage identification results under different conditions are as follows: Figure 5 As shown, Figure 5 The figure shows the mean value and error bar (±1σ) of the damage index identification under various working conditions. The red dashed line represents the theoretical value of the damage index under different support stiffnesses, calculated based on the mathematical relationship between the theoretical value of the damage index and the support stiffness under the undamaged state. The identification results show that the identified damage index values ​​of supports with different damage degrees under single-damage and multi-damage conditions are in good agreement with the theoretical values, indicating that the established damage index can effectively identify and quantify the vertical stiffness of the support under random operating loads.

[0094] Taking working condition 2 as an example, further parameter analysis was carried out. The train speed and axle load were still randomly generated, and 10% Gaussian white noise was added to the calculated bridge dynamic response to account for the noise effect. Figure 6 The identification results of support damage indices under different levels of US spectrum generated by orbital irregularities are presented. From Figure 6 It can be seen that different track irregularity levels have little impact on the proposed support damage assessment method, and the damage index based on the support-beam displacement ratio has good robustness to changes in track irregularity. Figure 7 The results of bearing damage identification were analyzed when the stiffness of the diaphragm decreased by 50% at different locations. The identification results show that the damage of the diaphragm at different locations has little impact on the proposed bearing damage index. Even in the presence of diaphragm damage, the proposed bearing-beam displacement ratio index can still effectively achieve the location and quantitative assessment of bearing damage.

[0095] In summary, the bridge bearing stiffness assessment method based on non-contact measurement of the bearing-beam displacement ratio of this invention is a data-driven method. Using operational traffic loads as excitation, it leverages the mathematical relationship between damage indicators and bearing stiffness to achieve damaged bearing location and quantitative assessment of bearing stiffness without the need for finite element models or surrogate models. Furthermore, it is insensitive to environmental noise and other influencing parameters, exhibiting strong anti-interference capabilities and robustness. The non-contact measurement scheme is low-cost and easy to operate, eliminating the need for sensor deployment on the bridge and online operations, significantly improving detection efficiency and facilitating rapid assessment and online monitoring of bridge bearing conditions.

[0096] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of one embodiment, and the modules or processes shown in the drawings are not necessarily essential for implementing the present invention.

[0097] As can be seen from the above description of the embodiments, those skilled in the art can clearly understand that the present invention can be implemented by means of software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in various embodiments or some parts of the embodiments of the present invention.

[0098] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for apparatus or system embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. The apparatus and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0099] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for assessing the service status of bridge bearings based on non-contact measurement, characterized in that, include: A non-contact visual measurement method was used to collect vertical dynamic deflection signals at the supports and mid-span of the bridge under inspection when an operating train passed over the bridge under inspection. The damage index of the railway bridge under inspection is calculated based on the support-beam mid-span displacement ratio according to the vertical dynamic deflection signal. Calculate the damage index limit based on the design parameters of the railway bridge to be inspected; The measured value of the damage index is compared with the limit value of the damage index, and the service status of the railway bridge bearing to be inspected is determined based on the comparison result. The method of acquiring vertical dynamic deflection signals at the supports and mid-span of the bridge under inspection using a non-contact visual measurement method when an operating train passes over the bridge under inspection includes: Select various measurement points on the bridge to be measured, set up the tripod, level the instrument, install the lens and adjust the aperture and focal length to ensure that the measurement points are within the field of view of the lens, set the camera parameters, select the sampling frequency and exposure settings, add and calibrate measurement points using a rangefinder telescope to determine the coefficient of each measurement point, collect at least 5 sets of vertical dynamic deflection signals of each measurement point under the action of operating trains, and use low-pass filtering to perform noise reduction preprocessing on the vertical dynamic deflection signals; The calculation of the damage index of the railway bridge under inspection based on the support-beam mid-span displacement ratio according to the vertical dynamic deflection signal includes: The maximum value of the vertical dynamic deflection response at the support is obtained based on the collected vertical dynamic deflection signal at the support, and the maximum value of the vertical dynamic deflection response at the mid-span of the beam is obtained based on the collected vertical dynamic deflection signal at the mid-span of the beam. Define the damage index η based on the support-to-mid-span displacement ratio of the beam. i The calculation method is as follows: Where: N t To test the number of train trips at the bridge cross-section, U bi U represents the maximum vertical dynamic deflection response at the i-th support. mid This represents the maximum value of the vertical dynamic deflection response at the mid-span of the beam; Based on the measured dynamic deflection data at the mid-span of the beam, the dynamic coefficients of the prestressed concrete simply supported beam bridge under each working condition were calculated: Where: δ dmax δ represents the measured maximum deflection value. smax Take the peak value of the amplitude center trajectory line of this waveform or the maximum deflection value at low speed, where μ is δ. dmax With δ smax The ratio; The calculation of damage index limits based on the design parameters of the railway bridge to be inspected includes: Based on the actual arrangement of the supports of the railway T-beam bridge, the bridge is considered as a spatially elastic supported beam with four spring supports of stiffness K1, K2, K3, and K4. The train load is considered as axle load P and spacing d. j A moving load train, j=1, 2, 3, passes over the bridge at a constant speed v; The mode shape of a spatially elastically supported beam is approximately the superposition of the first-order bending mode shape of a corresponding simply supported beam and the rigid body displacement mode shape of a rigid beam. In the formula: =EI / ((K1+K2)L 3 )and =EI / ((K3+K4)L 3 The number ) represents the beam-support stiffness ratio at ends A and B of the beam; L is the beam length. Introduce support damage coefficients α1=K1 / K, α2=K2 / K, α3=K3 / K, α4=K4 / K, where K is the support stiffness limit; The maximum displacement at the support of the spatial elastically supported beam under the action of a moving load column is: ， ， In the formula: and These represent the distances from the k-th axis of the moving load column to ends A and B of the beam, respectively. The maximum mid-span displacement of a spatially elastically supported beam under the action of a moving load column is approximately: P is the axle load of the moving load column. When all supports are in an undamaged state, i.e., α1=α2=α3=α4=1, based on the above derivation, the mathematical relationship between the theoretical value of the damage index and the support stiffness when the supports are in an undamaged state can be established as follows: In the formula: EI is the bending stiffness of the beam; K is the vertical stiffness limit of the support specified in the code; L is the beam span; φ represents the distance from the k-th axis of the moving load column to end A of the beam; φ is the approximate mode shape function of the spatially elastically supported beam. The flexural stiffness EI of the beam is calculated based on the beam's design elastic modulus E and the flexural moment of inertia I of the cross section. The vertical stiffness limit K of the support is calculated based on the design bearing capacity and design height of the support. Substituting these values ​​into the relationship between the damage index and the support stiffness, the support damage index limit η for different vehicle models is calculated. theo Take all η theo The minimum value in the range is used as the limit value for bearing damage index.

2. The method according to claim 1, characterized in that, The step of comparing the measured value of the damage index with the limit value of the damage index and determining the service status of the railway bridge bearing to be inspected based on the comparison result includes: When η i ≤η theo When the vertical stiffness identification value of the support is greater than or equal to the support stiffness limit specified in the standard, the support is judged to be in good service condition. When η i >η theo When the vertical stiffness identification value of the support is less than the support stiffness limit specified in the standard, it is determined that the support has defects, and the degree of defects is determined according to the stiffness corresponding to the damage index.

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