Bridge damage assessment method based on acceleration spectrum analysis after axle impact event

Abstract

The invention discloses a bridge damage assessment method based on acceleration spectrum analysis after an axle impact event. According to the method, based on long-term vibration monitoring data of the bridge and real-time data during axle collision, the maximum impact force borne by the bridge during collision is calculated, the maximum impact force calculated through the two methods is compared, the fitting degree is analyzed, and therefore a bridge damage state evaluation model is constructed, and basic bridge damage evaluation indexes are established; and the damage degree of the impacted bridge can be quickly evaluated in real time. By establishing the bridge damage state evaluation model, the real-time damage condition of the prestressed concrete bridge can be evaluated, and the damage degree of the bridge after being impacted can be quickly judged.

Description

Technical Field

[0001] This invention relates to the field of real-time condition assessment technology for bridge structures, and specifically to a bridge damage assessment method based on acceleration spectrum analysis after a vehicle-bridge collision event. Background Technology

[0002] In recent years, with the vigorous development of transportation infrastructure, vehicle collisions with bridges have posed serious challenges to the safety and normal performance of bridge structures. Damage assessment of bridges under vehicle collision impact loads is a complex problem, and the results of the damage assessment determine subsequent maintenance and reinforcement strategies. When a bridge structure is damaged, various parameters within the structure generally exhibit characteristics different from those in its normal state (i.e., the initial state of a healthy structure). These differences contain rich damage information. Currently, research on methods for bridge structural damage identification and health status assessment has become a hot topic in academic and engineering circles both domestically and internationally, and significant theoretical research results have been achieved. However, whether based on dynamic or static information, and whether using neural network methods, mechanical parameter back analysis, or modal identification methods, all methods utilize deterministic structural analysis models under defined load and boundary conditions. Theoretical calculation models cannot fully reflect actual conditions. In the field of engineering structural collision resistance design and safety assessment, establishing scientific methods for quantitative analysis of impact damage has significant theoretical value and promising engineering applications. Summary of the Invention

[0003] In bridge collisions involving vehicles, the maximum impact force is a crucial parameter for assessing localized impact damage to the structure. Addressing the issue that theoretical calculation models in the aforementioned background technologies cannot fully reflect actual damage, this invention provides a bridge damage assessment method based on post-vehicle-bridge collision acceleration spectrum analysis. Through long-term vibration monitoring of the bridge, this method focuses on analyzing the changes in the vibration acceleration spectrum of the main bridge beam after a vehicle collision to estimate the maximum impact force. This allows for the construction of a relevant bridge damage state assessment model to evaluate the real-time damage status of prestressed concrete bridges.

[0004] This invention analyzes the changes in the ultimate bearing capacity of a bridge after a collision by examining key monitoring indicators such as vertical displacement of the main girder, vertical vibration, and strain at key sections. The ultimate bearing capacity primarily reflects the bridge's strength and resistance to damage after the collision, while residual stiffness reflects its stiffness and resistance to deformation. The ultimate bearing capacity can be estimated using the vertical displacement monitoring data of the main girder, and the residual stiffness can be estimated using the vibration acceleration data of the main girder after the collision. Vehicle speed and mass have a significant impact on the ultimate bearing capacity; therefore, the maximum impact force is a crucial evaluation indicator for quickly and effectively assessing the impact damage to bridges under collision loads. The maximum impact force can be calculated based on data such as vehicle speed, weight, and maximum deformation at the time of impact.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A bridge damage assessment method based on acceleration spectrum analysis after a vehicle-bridge collision event is proposed. Based on long-term vibration monitoring data of the bridge and real-time data at the time of vehicle-bridge collision, the maximum impact force that the bridge bears at the time of the collision is calculated respectively. The fitting degree of the maximum impact force calculated by the two methods is compared and analyzed, thereby constructing a bridge damage state assessment model and establishing basic bridge damage evaluation indicators to quickly assess the degree of bridge damage after the impact.

[0007] The specific steps include the following:

[0008] (1) Real-time monitoring of long-term bridge vibration and vehicle-bridge impact: Long-term bridge vibration data is monitored by deploying sensors on the bridge, and monitoring data before and after the impact time period is extracted after a vehicle-bridge impact event to analyze the ultimate bearing capacity (strength) and stiffness of the bridge after the impact.

[0009] The long-term vibration monitoring data of the bridge includes the vertical displacement of the main girder, the vibration and strain of the main girder, and the vehicle mass. The vertical displacement of the main girder is collected by a photoelectric deflectometer, the vibration of the main girder is collected by an accelerometer, the strain is collected by a strain gauge, the vehicle mass is collected by a dynamic weighing system, and the vehicle speed is calculated by the vehicle mass and the vibration of the main girder.

[0010] The monitoring data before and after the vehicle-bridge impact period includes the vertical displacement of the main beam, the strain (strength) of the key section, and the vibration (stiffness) of the main beam. The vertical displacement increment of the bridge main beam is monitored in real time by photoelectric deflectometer, the vibration signal of the main beam is collected by accelerometer, and the strain change of the key section is monitored by strain gauge.

[0011] Among them, the vertical displacement increment of the bridge main beam is monitored in real time by photoelectric deflectometer. The maximum vertical displacement change during the impact is monitored. The vehicle-bridge impact may cause a decrease in the local stiffness of the main beam or failure of the support. The vertical displacement (deflection) of the main beam will increase under the same load. If the impact causes the main beam to break or crack severely, the displacement may show a nonlinear sudden increase.

[0012] Vibration signals of the main beam (including acceleration amplitude, decay time, etc.) are collected by accelerometers. Natural frequencies and damping parameters are extracted by modal analysis (such as FFT transformation). The changes in the acceleration spectrum after impact are analyzed, and the amplitude and decay are extracted. The vertical vibration characteristics of the main beam are characterized by the natural frequency. The reduction of structural stiffness will lead to a decrease in the natural frequency of the bridge, especially the low-order frequency (the lowest natural frequency) (such as the first-order bending frequency).

[0013] By monitoring the strain changes at the key section (mid-span of the bridge) using strain gauges, and analyzing the local strain in the impact area, it was found that the concrete near the impact point may be crushed or cracked, the strain of the steel bars may exceed the yield limit, resulting in permanent plastic deformation, and the strain gradient near the damaged area increases significantly.

[0014] (2) Theoretical calculation method of maximum impact force: Based on the damage mechanism of concrete bridge under vehicle-bridge impact load and the energy conservation theory, a prediction model of maximum impact force was constructed. The calculation model of maximum impact force can provide theoretical basis and practical analysis method for impact damage assessment of prestressed concrete (PC) beam members.

[0015] In impact dynamic response analysis, the application of the energy conservation principle requires the following basic assumptions: First, the total mechanical energy (including kinetic energy and deformation energy) of the impact system remains conserved under the premise of neglecting secondary energy dissipation factors (such as heat energy, sound energy, etc.); Second, the impact process satisfies the quasi-static analysis assumption, that is, when the structure reaches the maximum displacement response, the velocity of the impactor drops to zero, and its initial kinetic energy is completely converted into the plastic deformation energy of the structure.

[0016] The impact force prediction formula established based on the above principles, by considering key factors such as structural stiffness characteristics and impactor mass parameters, achieves a theoretical solution for the maximum impact force. This model overcomes the spatiotemporal limitations of traditional experimental methods, providing an efficient analytical tool for damage assessment of prestressed concrete beams under impact loads such as vehicle collisions. It is particularly suitable for the preliminary design and rapid assessment of structural impact resistance. The energy conservation equation can be expressed by equation (4.1).

[0017]

[0018] In the formula: m is the mass of the vehicle, v is the speed of the vehicle, and Eb, Es, and Ec represent the bending deformation energy, shear deformation energy, and energy of the impact zone of the main beam, respectively.

[0019] The paper "Abrate S. Impact on composite structures [M]. Cambridge: Cambridge University Press 2005" proposes a method for calculating the energy balance equation, as shown in equation (4.2) below:

[0020]

[0021] Where: K bs To consider the stiffness against bending and shear, i.e., bending-shear stiffness; ω max This represents the maximum deformation at the point of impact.

[0022] The relationship between impact force and maximum deformation during impact is given in the literature “Abrate S. Modeling of impacts on composite structures[J]. Composite Structures,2001,51(2):129-138”, as shown in Equation (4.3).

[0023]

[0024] Where k is the stiffness of the impact contact area, and α is the impact indentation at the impact point.

[0025] The literature “Pham TM, Hao H. Prediction of the impact force on reinforced concrete beams from a drop weight[J]. Advances in Structural Engineering,2016,19(11):1710-1722” gives an expression for the energy stored in the impact contact region, that is, Ec in equation (4.1) can be expressed by the following formula:

[0026]

[0027] The literature provides the impact indentation α and the maximum deformation ω at the impact point. max The relationship is:

[0028]

[0029] Substituting equation (4.5) into equation (4.4), we get:

[0030]

[0031] Similarly, substituting equation (4.5) into equation (4.3) yields:

[0032]

[0033] Substituting equations (4.2) and (4.6) into equation (4.1), the energy conservation equation can be transformed into:

[0034]

[0035] Based on equation (4.7), k in equation (4.6) bs ω max After substitution and rearrangement, we can obtain the maximum impact force p. max The expression, whose value is a theoretically calculated value:

[0036]

[0037] For reinforced concrete box girders, due to their high bending and torsional stiffness, the cross-section hardly deforms, and the influence of shear effects is ignored. Therefore, bending stiffness is used instead of linear stiffness of the reinforced concrete main beam for calculation. Bridge vibration signals are collected by accelerometers, and the fundamental frequency is extracted using Fourier transform (FFT) or random subspace method (SSI) (Farrar & Worden, 2012).

[0038]

[0039] Where EI is the bending stiffness, ρA is the linear density, and L is the bridge span.

[0040] By transforming the above formula, the bending stiffness of the bridge can be calculated:

[0041]

[0042] Substituting equation (4.11) into equation (4.9), we get:

[0043]

[0044] The impact contact stiffness k can be calculated using the following formula:

[0045]

[0046] In the formula: E is the elastic modulus, and R is the radius of curvature. The calculation methods are shown in equations (4.14) and (4.15) respectively:

[0047]

[0048] Where E1 and V1 are the elastic modulus and Poisson's ratio of the vehicle body, and E2 and V2 are the elastic modulus and Poisson's ratio of the main beam.

[0049]

[0050] R1 and R2 are the radii of curvature of the vehicle and the main beam, respectively. In the calculation, since the bridge impact surface is a plane, R2 tends to ∞, and R = R1.

[0051] (3) Calculate the maximum impact force using the response spectrum: that is, calculate the maximum impact force using long-term real-time monitoring data of the bridge. Assuming the structure is a single-degree-of-freedom system, the maximum impact force can be calculated through the following steps:

[0052] The accelerometer outputs the acceleration response spectrum, and the maximum response value is read, i.e., the maximum acceleration a is obtained from the acceleration response spectrum Sa(fn). max ;

[0053] Calculate the maximum impact force: F max =m·a max ;

[0054] The software was used to perform a correlation analysis between the maximum impact force calculated from the acceleration response spectrum and the maximum impact force calculated in equation (4.12). Multiple sets of theoretical and measured impact data were used for fitting, and the correlation coefficient between the two was calculated to determine whether the formula for the maximum impact force calculated from the response spectrum can be used to provide a reference for the damage assessment of concrete main beams under collision impact load.

[0055] (4) Construction of bridge damage assessment model: Based on the review of existing literature, the damage assessment criteria for concrete bridges after vehicle impact can be divided into static indicators (such as deflection) and dynamic indicators (such as acceleration change). Combining the effects of instantaneous vibration and deflection, a health status assessment system based on multiple parameters can be established. The following is a comprehensive assessment framework and a bridge damage assessment model derived from the formula:

[0056]

[0057] Each parameter represents:

[0058] Δ max This represents the maximum deflection measured after the impact. This represents the average normal deflection of the bridge under long-term observation conditions.

[0059] a peak The peak instantaneous acceleration upon impact. This represents the average vibration of the bridge under long-term observation conditions.

[0060] f0、f post These are the fundamental frequencies of the structure before and after the impact;

[0061] p max F u These are the maximum impact force and the ultimate lateral bearing capacity of the bridge, respectively.

[0062] C1, C2, C3, and C4 are weighting coefficients. The weighting coefficients are calibrated based on existing monitoring data of the bridges used to establish health monitoring systems, or by combining machine learning (such as neural networks) for big data calibration. The accuracy of the model is verified after the model coefficients are calibrated using existing data.

[0063] (5) Preliminary establishment of bridge damage evaluation indicators to assess bridge damage status:

[0064] γ≤0.3: Healthy (no significant damage, can be used normally);

[0065] 0.3 < γ ≤ 0.6: Mild damage (requires local repair);

[0066] 0.6 < γ ≤ 1.0: Moderate damage (reinforcement and load limiting required);

[0067] γ>1.0: Severe damage (requires discontinuation or reconstruction);

[0068] (6) Verify the bridge damage status in step (5) based on the actual bridge measurement data and determine the final evaluation index.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] Based on long-term monitoring data of the bridge and real-time data at the time of impact, the maximum impact force that the bridge will bear at the time of the impact event is estimated, and basic bridge damage evaluation indicators are established to quickly assess the degree of damage to the bridge after an impact, for reference by the maintenance team. Attached Figure Description

[0071] Figure 1 This is a flowchart of the bridge damage assessment method of the present invention.

[0072] Figure 2 This refers to the real-time deflection monitoring value of the bridge impact event described in the embodiments of the present invention.

[0073] Figure 3 The values ​​are real-time vibration acceleration monitoring values ​​for the bridge impact event described in this embodiment of the invention.

[0074] Figure 4 The fundamental frequency of the structure before the impact event described in the embodiment of the present invention is the fundamental frequency of the structure.

[0075] Figure 5 The fundamental frequency of the structure after the impact event described in the embodiment of the present invention is the fundamental frequency of the structure. Detailed Implementation

[0076] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0077] A bridge damage assessment method based on post-vehicle-bridge impact acceleration spectrum analysis includes the following steps:

[0078] (1) Real-time monitoring of long-term bridge vibration and vehicle-bridge impact: Long-term bridge vibration data is monitored by deploying sensors on the bridge, and monitoring data before and after the impact time period is extracted after a vehicle-bridge impact event to analyze the ultimate bearing capacity (strength) and stiffness of the bridge after the impact.

[0079] The long-term vibration monitoring data of the bridge includes the vertical displacement of the main girder, the vibration and strain of the main girder, and the vehicle mass. The vertical displacement of the main girder is collected by a photoelectric deflectometer, the vibration of the main girder is collected by an accelerometer, the strain is collected by a strain gauge, the vehicle mass is collected by a dynamic weighing system, and the vehicle speed is calculated by the vehicle mass and the vibration of the main girder.

[0080] The monitoring data before and after the vehicle-bridge impact period includes the vertical displacement of the main beam, the strain (strength) of the key section, and the vibration (stiffness) of the main beam. The vertical displacement increment of the bridge main beam is monitored in real time by photoelectric deflectometer, the vibration signal of the main beam is collected by accelerometer, and the strain change of the key section is monitored by strain gauge.

[0081] Among them, the vertical displacement increment of the bridge main beam is monitored in real time by photoelectric deflectometer. The maximum vertical displacement change during the impact is monitored. The vehicle-bridge impact may cause a decrease in the local stiffness of the main beam or failure of the support. The vertical displacement (deflection) of the main beam will increase under the same load. If the impact causes the main beam to break or crack severely, the displacement may show a nonlinear sudden increase.

[0082] Vibration signals of the main beam (including acceleration amplitude, decay time, etc.) are collected by accelerometers. Natural frequencies and damping parameters are extracted by modal analysis (such as FFT transformation). The changes in the acceleration spectrum after impact are analyzed, and the amplitude and decay are extracted. The vertical vibration characteristics of the main beam are characterized by the natural frequency. The reduction of structural stiffness will lead to a decrease in the natural frequency of the bridge, especially the low-order frequency (the lowest natural frequency) (such as the first-order bending frequency).

[0083] (2) Theoretical calculation method for maximum impact force: Based on the damage mechanism of concrete bridges under vehicle-bridge impact load and the energy conservation theory, a prediction model for maximum impact force was constructed. The energy conservation equation can be expressed by equation (4.1).

[0084]

[0085] In the formula: m is the mass of the vehicle, v is the speed of the vehicle, and Eb, Es, and Ec represent the bending deformation energy, shear deformation energy, and energy of the impact zone of the main beam, respectively.

[0086] The paper "Abrate S. Impact on composite structures [M]. Cambridge: Cambridge University Press 2005" proposes a method for calculating the energy balance equation, as shown in equation (4.2) below:

[0087]

[0088] Where: K bs To consider the stiffness against bending and shear, i.e., bending-shear stiffness; ω max This represents the maximum deformation at the point of impact.

[0089] The relationship between impact force and maximum deformation during impact is given in the literature “Abrate S. Modeling of impacts on composite structures[J]. Composite Structures,2001,51(2):129-138”, as shown in Equation (4.3).

[0090]

[0091] Where k is the stiffness of the impact contact area, and α is the impact indentation at the impact point.

[0092] The literature “Pham TM, Hao H. Prediction of the impact force on reinforced concrete beams from a drop weight[J]. Advances in Structural Engineering,2016,19(11):1710-1722” gives an expression for the energy stored in the impact contact region, that is, Ec in equation (4.1) can be expressed by the following formula:

[0093]

[0094] The literature provides the impact indentation α and the maximum deformation ω at the impact point. max The relationship is:

[0095]

[0096] Substituting equation (4.5) into equation (4.4), we get:

[0097]

[0098] Similarly, substituting equation (4.5) into equation (4.3) yields:

[0099]

[0100] Substituting equations (4.2) and (4.6) into equation (4.1), the energy conservation equation can be transformed into:

[0101]

[0102] Based on equation (4.7), k in equation (4.6) bs ω max After substitution and rearrangement, we can obtain the maximum impact force p. max The expression, whose value is a theoretically calculated value:

[0103]

[0104] For reinforced concrete box girders, due to their high bending and torsional stiffness, the cross-section hardly deforms, and the influence of shear effects is ignored. Therefore, bending stiffness is used instead of linear stiffness of the reinforced concrete main beam for calculation. Bridge vibration signals are collected by accelerometers, and the fundamental frequency is extracted using Fourier transform (FFT) or random subspace method (SSI) (Farrar & Worden, 2012).

[0105]

[0106] Where EI is the bending stiffness, ρ is the material density, A is the cross-sectional area, and L is the bridge span.

[0107] For a beam with fixed supports at both ends, the bending stiffness can be calculated using the following formula:

[0108]

[0109] Substituting equation (4.11) into equation (4.9), we get:

[0110]

[0111] The impact contact stiffness k can be calculated using the following formula:

[0112]

[0113] In the formula: E is the elastic modulus, and R is the radius of curvature. The calculation methods are shown in equations (4.14) and (4.15) respectively:

[0114]

[0115] Where E1 and V1 are the elastic modulus and Poisson's ratio of the vehicle body, and E2 and V2 are the elastic modulus and Poisson's ratio of the main beam.

[0116]

[0117] R1 and R2 are the radii of curvature of the vehicle and the main beam, respectively. In the calculation, since the bridge impact surface is a plane, R2 tends to ∞, and R = R1.

[0118] (3) Calculate the maximum impact force using the response spectrum: that is, calculate the maximum impact force using long-term real-time monitoring data of the bridge. Assuming the structure is a single-degree-of-freedom system, the maximum impact force can be calculated through the following steps:

[0119] The accelerometer outputs the acceleration response spectrum, and the maximum response value is read, i.e., the maximum acceleration a is obtained from the acceleration response spectrum Sa(fn). max ;

[0120] Calculate the maximum impact force: F max =m·a max ;

[0121] The software was used to perform a correlation analysis between the maximum impact force calculated from the acceleration response spectrum and the maximum impact force calculated in equation (4.12). Multiple sets of theoretical and measured impact data were used for fitting, and the correlation coefficient between the two was calculated to determine whether the formula for the maximum impact force calculated from the response spectrum can be used to provide a reference for the damage assessment of concrete main beams under collision impact load.

[0122] (4) Construction of bridge damage assessment model: Based on the review of existing literature, the damage assessment criteria for concrete bridges after vehicle impact can be divided into static indicators (such as deflection) and dynamic indicators (such as acceleration change). Combining the effects of instantaneous vibration and deflection, a health status assessment system based on multiple parameters can be established. The following is a comprehensive assessment framework and a bridge damage assessment model derived from the formula:

[0123]

[0124] Each parameter represents:

[0125] Δ max This represents the maximum deflection measured after the impact. This represents the average normal deflection of the bridge under long-term observation conditions.

[0126] a peak The peak instantaneous acceleration upon impact. This represents the average vibration of the bridge under long-term observation conditions.

[0127] f0、fpost These are the fundamental frequencies of the structure before and after the impact;

[0128] p max F u These are the maximum impact force and the ultimate lateral bearing capacity of the bridge, respectively.

[0129] C1, C2, C3, and C4 are weighting coefficients. The weighting coefficients are calibrated based on existing monitoring data of the bridges used to establish health monitoring systems, or by combining machine learning (such as neural networks) for big data calibration. The accuracy of the model is verified after the model coefficients are calibrated using existing data.

[0130] (5) Preliminary establishment of bridge damage evaluation indicators to assess bridge damage status:

[0131] γ≤1: Healthy (no significant damage, can be used normally);

[0132] 1 < γ ≤ 2: Mild damage (requires local repair);

[0133] 2 < γ ≤ 3: Moderate damage (reinforcement and load limiting required);

[0134] γ>3: Severe damage (requires discontinuation or reconstruction);

[0135] (6) Verify the bridge damage status in step (5) based on the actual bridge measurement data and determine the final evaluation index.

[0136] The weighting coefficients, based on long-term monitoring data, are: C1 = 0.01, C2 = 0.001, C3 = 0.1, C4 = 1.

[0137] Substituting into the evaluation model, we get:

[0138]

[0139] Example

[0140] Based on the measured data of the bridge, the main beam of a bridge in Nanjing was affected by a vehicle collision. After calculation, the vehicle weight m = 10000 kg and the vehicle speed v = 40 km / h were obtained. The bridge damage status was assessed using the bridge damage assessment method based on vehicle-bridge collision event described in this invention.

[0141] First, based on real-time data from the bridge's deployed sensors: the average normal deflection of the bridge was 0.23 mm, and the maximum measured deflection after impact was 1.217 mm; the average bridge vibration was 0.0014 m / s². 2 The peak instantaneous acceleration upon impact was 1.598 m / s². 2 ;

[0142] Secondly, by performing Fourier transform on the vibration data 10 minutes before and after the impact event, the fundamental frequencies f0 and f2 of the structure before and after the impact can be obtained. post f0 = 3.066 Hz, f post =3.125Hz

[0143] Then, the maximum impact force was calculated using equation (4.9): The impacted bridge structure is a continuous box girder with a span of 50m, and the bending stiffness is:

[0144] For the impact contact stiffness k reference value, the impact stiffness k of a heavy vehicle on the web of a box girder is: 10. 6 ~10 7 kN / m;

[0145] Given that the vehicle weight m = 10000 kg and the vehicle speed v = 40 km / h, substituting these values ​​into equation (4.9) yields:

[0146]

[0147] Get p max ≈6.03×10 3 kN

[0148] The existing formula for calculating the shear capacity of the main beam (Article 5.2.7 of JTG 3362) is as follows:

[0149]

[0150] α1: Prestress enhancement factor, taken as 1.25;

[0151] α2: Cross-section height influence coefficient (taken as 1.0 when h0 < 2m);

[0152] α3: Axial pressure coefficient (taken as 1 + 0.07σ) pc / f cu,k );

[0153] b: Web thickness;

[0154] h0: Effective height of the cross section;

[0155] f cu,k Standard value of compressive strength of concrete cube;

[0156] f sd Design value of tensile strength of stirrups;

[0157] Stirrup reinforcement ratio;

[0158]

[0159] Substituting all the above data into the evaluation model yields:

[0160]

[0161]

[0162] Based on damage assessment status 1

Claims

1. A bridge damage assessment method based on acceleration spectrum analysis after a vehicle-bridge collision event, characterized in that, Based on long-term vibration monitoring data of the bridge and real-time data during vehicle-bridge collisions, the maximum impact force that the bridge will bear during the collision is calculated. The fitting degree of the maximum impact force calculated by the two methods is compared and analyzed. In this way, a bridge damage state assessment model is constructed and basic bridge damage evaluation indicators are established to quickly assess the degree of bridge damage after an impact.

2. The bridge damage assessment method based on post-vehicle-bridge impact acceleration spectrum analysis according to claim 1, characterized in that, The specific steps include the following: (1) Real-time monitoring of long-term bridge vibration and vehicle-bridge impact: Long-term vibration data of the bridge is monitored by deploying sensors on the bridge, and monitoring data before and after the impact time period is extracted after a vehicle-bridge impact event to analyze the ultimate bearing capacity and stiffness of the bridge after the impact. The long-term vibration monitoring data of the bridge includes the vertical displacement of the main beam, the vibration and strain of the main beam, and the vehicle mass. The monitoring data before and after the vehicle-bridge impact period includes the vertical displacement of the main beam, the strain of key sections, and the vibration of the main beam. (2) Theoretical calculation method for maximum impact force: Based on the damage mechanism of concrete bridges under vehicle-bridge impact load and the energy conservation theory, a prediction model for maximum impact force was constructed. The energy conservation equation can be expressed by equation (4.1). In the formula: m is the mass of the vehicle, v is the speed of the vehicle, and Eb, Es, and Ec represent the bending deformation energy, shear deformation energy, and energy of the impact zone of the main beam, respectively. The method for the energy balance equation is shown in equation (4.2) below: in, Where: K bs To consider the stiffness against bending and shear, i.e., bending-shear stiffness; ω max This represents the maximum deformation at the point of impact. The relationship between impact force and maximum deformation during the impact process is shown in equation (4.3). Where k is the stiffness of the impact contact area, and α is the impact indentation at the impact point. The expression for the energy stored in the impact contact region, i.e., Ec in equation (4.1), can be represented by the following equation: Impact indentation α and maximum deformation ω at the impact point max The relationship is: Substituting equation (4.5) into equation (4.4), we get: Similarly, substituting equation (4.5) into equation (4.3) yields: Substituting equations (4.2) and (4.6) into equation (4.1), the energy conservation equation can be transformed into: Based on equation (4.7), k in equation (4.6) bs ω max After substitution and rearrangement, we can obtain the maximum impact force p. max The expression, whose value is a theoretically calculated value: Vibration signals from the bridge were collected using accelerometers, and the fundamental frequency was extracted using Fourier transform or the random subspace method. Where EI is the bending stiffness, ρA is the linear density, and L is the bridge span. By transforming the above formula, the bending stiffness of the bridge can be calculated: Substituting equation (4.11) into equation (4.9), we get: The impact contact stiffness k can be calculated using the following formula: In the formula: E is the elastic modulus, and R is the radius of curvature. The calculation methods are shown in equations (4.14) and (4.15) respectively: Where E1 and V1 are the elastic modulus and Poisson's ratio of the vehicle body, and E2 and V2 are the elastic modulus and Poisson's ratio of the main beam. R1 and R2 are the radii of curvature of the vehicle and the main beam, respectively. R2 tends to ∞, and R = R1. (3) Calculate the maximum impact force using the response spectrum: Output the acceleration response spectrum from the accelerometer and read the maximum response value, that is, obtain the maximum acceleration a from the acceleration response spectrum Sa(fn). max ; Calculate the maximum impact force: F max =m·a max ; The software was used to perform a correlation analysis between the maximum impact force calculated from the acceleration response spectrum and the maximum impact force calculated in equation (4.12). Multiple sets of theoretical and measured impact data were used for fitting, and the correlation coefficient between the two was calculated to determine whether the formula for the maximum impact force calculated from the response spectrum can be used to provide a reference for the damage assessment of concrete main beams under collision impact load. (4) Construction of bridge damage assessment model: After a vehicle impact, a multi-parameter health status assessment system is established for concrete bridges based on instantaneous vibration and deflection. The following is a comprehensive assessment framework and a bridge damage assessment model derived from the formulas: Each parameter represents: Δ max This represents the maximum deflection measured after the impact. This represents the average normal deflection of the bridge under long-term observation conditions. a peak The peak instantaneous acceleration upon impact. This represents the average vibration of the bridge under long-term observation conditions. f0、f post These are the fundamental frequencies of the structure before and after the impact; p max F i These are the maximum impact force and the ultimate lateral bearing capacity of the bridge, respectively. C1, C2, C3, and C4 are weighting coefficients. The weighting coefficients are calibrated based on existing monitoring data of the bridges used to establish health monitoring systems, or by combining machine learning with big data calibration. The accuracy of the model is verified after the model coefficients are calibrated using existing data. (5) Preliminary establishment of bridge damage evaluation indicators to assess bridge damage status: γ≤0.3: Healthy; 0.3 < γ ≤ 0.6: Mild damage; 0.6 < γ ≤ 1.0: Moderate injury; γ>1.0: Severe damage; (6) Verify the bridge damage status in step (5) based on the actual bridge measurement data and determine the final evaluation index.

3. The bridge damage assessment method based on post-vehicle-bridge impact acceleration spectrum analysis according to claim 2, characterized in that, In step (1), the long-term vibration monitoring data of the bridge is collected by using a photoelectric deflectometer to collect the vertical displacement of the main beam, by using an accelerometer to collect the vibration of the main beam, by using a strain gauge to collect the strain, by using a dynamic weighing system to collect the vehicle mass, and by using the vehicle mass and the vibration of the main beam to calculate the vehicle speed.

4. The bridge damage assessment method based on post-vehicle-bridge impact acceleration spectrum analysis according to claim 2, characterized in that, In step (1), the vertical displacement increment of the main beam of the bridge is monitored in real time using a photoelectric deflectometer in the monitoring data before and after the vehicle-bridge impact time period. Vibration signals of the main beam were collected by accelerometers, and natural frequencies and damping parameters were extracted by modal analysis to analyze the changes in the acceleration spectrum after impact. The strain changes at key sections are monitored using strain gauges, and the local strain in the impact area is analyzed.

5. The bridge damage assessment method based on post-vehicle-bridge impact acceleration spectrum analysis according to claim 2, characterized in that, In step (5), when the bridge is in a healthy state, it can be used normally; when the bridge is slightly damaged, it needs to be repaired locally; when the bridge is moderately damaged, it needs to be reinforced and its load limited; when the bridge is severely damaged, it needs to be taken out of service or rebuilt.

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