Method and system for analyzing dynamic response of simply supported girder bridge in different traffic flow states

Abstract

The invention discloses a method for analyzing dynamic response of a simply supported girder bridge in different traffic flow states, relates to the technical field of bridges, and aims to understand the influence of the traffic flow states on the dynamic response of the bridge, select a vehicle head distance and a vehicle speed as traffic flow state evaluation indexes according to the road service level, select a two-axis plane whole vehicle model and analyze the dynamic response of the simply supported girder bridge based on a modal synthesis method. And establishing a multi-vehicle axle coupling vibration analysis model, and analyzing the dynamic response of the simply supported girder bridge in different traffic flow states. The result shows that when the number of vehicles reaches 3, the maximum vertical displacement in the bridge span is maximum, and when the number of vehicles is increased to 5, the maximum vertical displacement in the bridge span tends to be stable; when the distance between the vehicles is increased, the superposed dynamic effect between the vehicles is weakened, and the maximum vertical displacement in the bridge span is gradually reduced and is close to the numerical value of a single vehicle; in different traffic flow states, the stable flow has the weakest influence on the dynamic response of the bridge, and the limited flow has the strongest influence on the dynamic response of the bridge.

Description

Technical Field

[0001] The present invention relates to the technical field of bridges, and in particular to a dynamic response analysis method system for a simply supported beam bridge under different traffic flow conditions. Background Art

[0002] With the rapid development of highway bridge construction in my country, the vehicle speed is constantly increasing, the traffic density is increasing, and the vibration problem of bridges under vehicle loads is attracting more and more attention. In the early research on vehicle-bridge coupling, the uniform moving constant force model, uniform moving simple harmonic force model, uniform rolling mass model, and uniform spring-mass model were generally used for simplified analysis and calculation to obtain approximate solutions.

[0003] With the development of electronic computer technology and the application of finite element method, people can build more realistic vehicle models and bridge models for numerical calculation. In the study of vehicle-bridge coupled vibration of simply supported beams, most of them use multi-degree-of-freedom single-vehicle models to calculate the vibration problem when vehicles pass through bridges. Tan Guojin et al. established a spatial vehicle-bridge coupled vibration model based on the modal synthesis method to analyze the influence of vehicle, bridge and other parameters on the bridge impact coefficient. Jiang Peiwen et al. will use ANSYS to build vehicle and bridge models respectively, use APDL programming language to achieve coupling, and analyze the dynamic response of the bridge.

[0004] In actual bridge operation, multiple vehicles often travel on the bridge at the same time. Although the dynamic response of the bridge under a single vehicle load can reflect the vibration law of the bridge, the error is relatively large compared to the actual situation. Summary of the invention

[0005] In order to overcome the shortcoming that the dynamic response of the bridge under a single vehicle load in the above-mentioned prior art cannot reflect the dynamic response of the bridge under an actual multi-vehicle load, the main purpose of the present invention is to provide a method and system for analyzing the dynamic response of a simply supported beam bridge under different traffic flow conditions, which can obtain the dynamic response results of a simply supported beam bridge under multiple vehicles in different traffic flow conditions.

[0006] To achieve the above object, the present invention adopts the following technical solution, a method for analyzing the dynamic response of a simply supported beam bridge under different traffic flow conditions, comprising the following steps:

[0007] Select the vehicle type and simplify it into a plane model, obtain the physical property parameters of the vehicle components, combine the dynamic characteristics of the vehicle, and establish the multi-vehicle vehicle motion equation based on the d'Alembert principle;

[0008] Obtain the physical technical parameters of the simply supported beam bridge, establish a simply supported beam bridge model through Midas, and use modal analysis to obtain the natural frequency ω and vibration mode of the simply supported beam bridge As well as the bridge vibration equation, the vehicle motion equation and the bridge vibration equation are combined to obtain a multi-vehicle bridge coupling vibration analysis model;

[0009] The traffic flow state evaluation index is input into the multi-vehicle-bridge coupled vibration analysis model to obtain the dynamic response analysis results of the simply supported beam bridge under different traffic flow states.

[0010] The traffic flow state evaluation index includes the headway and vehicle speed, and the traffic flow state is divided into free flow, stable flow, and restricted flow. Among them, the stable flow has the weakest impact on the dynamic response of the bridge, and the restricted flow has the strongest impact on the dynamic response of the bridge.

[0011] The dynamic response analysis results of the simply supported beam bridge under different traffic flow conditions are as follows:

[0012] Under different traffic flow conditions, the maximum vertical displacement of the bridge mid-span increases as the traffic flow condition worsens;

[0013] In the free flow state, the distance between vehicles is large, exceeding the length of the bridge. At the same time, the number of vehicles on the bridge increases, and the vertical displacement of the bridge mid-span shows periodic changes, and the maximum displacement is close to the value under a single vehicle;

[0014] Under the steady flow and restricted flow conditions, the vehicle speed is reduced, the distance between vehicles is reduced, the vehicle superposition dynamic effect is enhanced, and the bridge dynamic response is enhanced;

[0015] Among different traffic flow states, the stable flow state has the least impact on the dynamic response of the bridge, while the restricted flow state has the greatest impact on the dynamic response of the bridge.

[0016] The selected vehicle type is a two-axle flat vehicle model.

[0017] The physical technical parameters of the simply supported beam bridge are obtained by Midas, and a simply supported beam bridge model is established. The natural frequency ω and vibration mode of the simply supported beam bridge are obtained by modal analysis. As well as the bridge vibration equation, the vehicle motion equation and the bridge vibration equation are combined to obtain a multi-vehicle bridge coupling vibration analysis model, which includes the following steps:

[0018] The actual size and structural characteristics of the simply supported beam bridge are obtained through Midas.

[0019] Establish a geometric model based on the actual size and structural characteristics of the simply supported beam bridge;

[0020] According to the actual support conditions of the simply supported beam bridge, boundary conditions are set, modal analysis is performed, and the natural frequency ω and vibration mode of the simply supported beam bridge are extracted.

[0021] According to the modal analysis results, the mode that contributes most to the vibration response is selected as the main mode;

[0022] The modal synthesis method is used to reduce the degrees of freedom of the bridge model and retain the degrees of freedom corresponding to the main modes; the interaction force between the vehicle and the bridge, including the contact force between the tire and the bridge deck, is determined, and the bridge vibration equation is obtained;

[0023] Combining the vehicle motion equations and bridge vibration equations, the vehicle-bridge coupled vibration equations are constructed, and then the multi-vehicle-bridge coupled vibration analysis model is obtained.

[0024] The modal analysis is used to obtain the natural frequency ω and vibration mode of the simply supported beam bridge. The following steps are included:

[0025] Define the properties of the bridge material in Midas, including elastic modulus, density, Poisson's ratio, and assign corresponding cross-sectional properties to different parts of the bridge;

[0026] Set boundary conditions according to the actual support conditions of the bridge, select the modal analysis type in Midas, and set the analysis parameters, such as the number of extracted modes and frequency range, run the modal analysis calculation, and solve the natural frequency ω and vibration mode of the bridge

[0027] The method of obtaining the physical properties of the vehicle and the material properties of its related components according to the dynamic characteristics of the vehicle and establishing the multi-vehicle motion equation according to the d'Alembert principle includes the following steps:

[0028] According to the dynamic characteristics of the vehicle, the two-axle vehicle is simplified into a four-degree-of-freedom plane vehicle, including the sinking and nodding of the vehicle body and the floating and sinking of the front and rear wheels;

[0029] According to the d'Alembert principle, the motion equation of a multi-vehicle two-axle plane vehicle is established and expressed in matrix form as follows:

[0030]

[0031] In the formula [M v ]、[C v ]、[K v ] are the mass matrix, damping matrix and stiffness matrix of the multi-vehicle vehicle respectively; {F v} is the vehicle's overall external force vector; {Z v} is the displacement matrix of each degree of freedom of the vehicle.

[0032] A system for analyzing the dynamic response of a simply supported beam bridge under different traffic flow conditions, comprising:

[0033] The vehicle motion analysis module is used to select the vehicle type and simplify it into a plane model, obtain the physical property parameters of the vehicle components, combine the dynamic characteristics of the vehicle, and establish the multi-vehicle vehicle motion equation based on the d'Alembert principle;

[0034] The analysis model building module is used to obtain the physical technical parameters of the simply supported beam bridge, establish the simply supported beam bridge model through Midas, and use modal analysis to obtain the natural frequency ω and vibration mode of the simply supported beam bridge As well as the bridge vibration equation, the vehicle motion equation and the bridge vibration equation are combined to obtain a multi-vehicle bridge coupling vibration analysis model;

[0035] The dynamic response analysis module is used to input the traffic flow state evaluation index into the multi-vehicle bridge coupling vibration analysis model to obtain the dynamic response analysis results of the simply supported beam bridge under different traffic flow states.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] 1. In view of the large number of degrees of freedom under multi-vehicle bridge coupling, the modal synthesis method can select a small number of modes and obtain higher vehicle and bridge dynamic responses at a lower computational cost, which has a wide range of application value;

[0038] 2. In actual bridge operation, vehicles mostly pass through bridges in the form of traffic flow. The study of the dynamic response of bridges under single-vehicle loads often ignores the impact between vehicles and has limitations. However, traffic flow involves many complex parameters. Directly simulating the state of traffic flow, although the accuracy is improved, greatly increases the difficulty and scale of calculation. Through the close connection between the microscopic parameter headway and the three parameters of macroscopic traffic flow, combined with the road service level, headway and speed are used as important parameters to simplify the simulation of different traffic flow states, which can improve the calculation efficiency while ensuring a certain accuracy.

[0039] 3. It can analyze the impact of different arrangements of vehicles on the bridge on the dynamic response of the bridge from the perspective of vehicle head spacing, providing a reference for the development of unmanned driving and smart highways. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0041] Figure 1 The vertical displacement response of the bridge mid-span under different vehicle types;

[0042] Figure 2 It is a two-axle flat vehicle model in the embodiment of the present invention;

[0043] Figure 3 is the vertical displacement of the mid-span of the bridge under different numbers of vehicles in the embodiment of the present invention;

[0044] Figure 4 is the vertical displacement of the bridge mid-span under different headway distances in the embodiment of the present invention;

[0045] Figure 5 is the vertical displacement of the bridge mid-span under different traffic flow conditions in the embodiment of the present invention;

[0046] Figure 6 It is a schematic diagram of the process structure of the present invention. DETAILED DESCRIPTION

[0047] The present invention will be further described below in conjunction with the accompanying drawings and implementation modes.

[0048] With the rapid development of highway bridge construction in my country, vehicle speeds are constantly increasing, and traffic density is increasing. The vibration problem of bridges under vehicle loads has attracted more and more attention. In the early research on vehicle-bridge coupling, the uniform moving constant force model, uniform moving simple harmonic force model, uniform rolling mass model, and uniform spring-mass model were generally used to simplify analysis and calculation to obtain approximate solutions. With the development of electronic computer technology and the application of finite element method, people can establish relatively realistic vehicle models and bridge models for numerical calculations. In the research on vehicle-bridge coupling vibration of simply supported beams, most of them use multi-degree-of-freedom single-vehicle models to calculate the vibration problem when vehicles pass through bridges. Tan Guojin et al. established a spatial vehicle-bridge coupling vibration model based on the modal synthesis method to analyze the influence of vehicle, bridge and other parameters on the bridge impact coefficient. Jiang Peiwen et al. will use ANSYS to establish vehicle and bridge models respectively, use APDL programming language to achieve coupling, and analyze the dynamic response of the bridge. In actual bridge operation, at the same time, multiple vehicles often travel on the bridge at the same time. Although the dynamic response of the bridge under a single vehicle load can reflect the vibration law of the bridge, it has a large error with the actual situation.

[0049] The present invention uses a simply supported beam bridge as the bridge type, selects the headway and vehicle speed as traffic flow state evaluation indicators, adopts the modal comprehensive analysis method, establishes the multi-vehicle bridge coupling vibration equation, uses Matlab programming to solve and obtain the bridge dynamic response, and compares and analyzes the influence of multiple vehicles crossing the bridge on the bridge dynamic response under different traffic flow states. Figure 6 , specifically including the following steps:

[0050] Select the vehicle type and simplify it into a plane model, obtain the physical property parameters of the vehicle components, combine the dynamic characteristics of the vehicle, and establish the multi-vehicle vehicle motion equation based on the d'Alembert principle;

[0051] Obtain the physical technical parameters of the simply supported beam bridge, establish a simply supported beam bridge model through Midas, and use modal analysis to obtain the natural frequency ω and vibration mode of the simply supported beam bridge As well as the bridge vibration equation, the vehicle motion equation and the bridge vibration equation are combined to obtain a multi-vehicle bridge coupling vibration analysis model;

[0052] The traffic flow state evaluation index is input into the multi-vehicle-bridge coupled vibration analysis model to obtain the dynamic response analysis results of the simply supported beam bridge under different traffic flow states.

[0053] Example:

[0054] See also Figure 1-Figure 6 In the actual analysis, by comparing the influence of the two-axle plane vehicle model and the space vehicle model on the dynamic response of the bridge, it is found that without considering the effect of the lateral force, the bridge vibration caused by the two-axle plane vehicle model and the two-axle space vehicle model is similar in form, and the difference in the calculation results is small. The maximum vertical displacement error of the bridge is within 1%. Since the parameters required for the simulation of the space vehicle model are complex and have more degrees of freedom than the plane vehicle model, it will increase the calculation time and reduce the calculation efficiency. Under the premise of ensuring a certain calculation accuracy and efficiency, the two-axle plane vehicle model is selected as the subsequent research model.

[0055] According to the dynamic characteristics of the vehicle, the two-axle vehicle is simplified into a 4-DOF plane vehicle, including the rise and fall of the vehicle body and the rise and fall of the front and rear wheels. nvr and J nvr represents the body mass and pitch moment of inertia of the nth vehicle, and represents the sum of the mass of the suspension and wheelset, and Represents the front and rear suspension spring damping and stiffness, and Represents the damping and stiffness of the front and rear wheels, Z vr and θ vr Represents the vertical displacement and pitch displacement of the vehicle body, Z vaL and Z cL Represents the wheel displacement and the bridge deck displacement at the wheel-bridge contact point. The vehicle model and technical parameters are shown in the figure and table.

[0056] According to the d'Alembert principle, the equation of motion of a multi-vehicle two-axle plane vehicle is established:

[0057]

[0058] The equation group (1) can be written in matrix form as:

[0059]

[0060] Where [M], [C], and [K] are the mass matrix, damping matrix, and stiffness matrix of the multi-vehicle vehicle, respectively; {F v} is the vehicle's overall external force vector; {Z v} is the displacement matrix of each degree of freedom of the vehicle.

[0061] Table 1 Vehicle technical parameters

[0062]

[0063] According to the technical parameters of the bridge shown in Table 2, the bridge model was established by Midas, and the natural frequency ω and vibration mode of the bridge were obtained by modal analysis. The modal equation of the structure is constructed by the vibration mode superposition method, and the structural geometric coordinates are converted into modal coordinates. The equation is as follows:

[0064] [M B ]{U..}+[C B ]{U.}+[K B ]{U}={F B} (3)

[0065] Where: The modal mass matrix of the bridge structure; [M], the mass matrix of the bridge structure.

[0066] Modal damping matrix of the bridge structure; [C], damping matrix of the bridge structure.

[0067] The modal stiffness matrix of the bridge structure; [K], the stiffness matrix of the bridge structure.

[0068] The modal force vector of the bridge structure; {F} is the load vector of the bridge acting on the vehicle. The modal equation obtained by equation (3) is further simplified by regularization, and equation (3) can be transformed into:

[0069] [M b ]{U..}+[C b ]{U.}+[K b ]{U}={F b} (4)

[0070]

[0071] Among them, ω i is the i-th order natural circular frequency of the bridge; ξ i is the damping ratio corresponding to the i-th order frequency of the bridge.

[0072] Table 2 Bridge technical parameters

[0073]

[0074] Regarding the selection of traffic flow status evaluation indicators, the road service level can reflect the quality of the service provided to users under the influence of various factors. It is usually related to indicators such as traffic volume, traffic density, and vehicle speed, and can describe the status of vehicles running on the road from multiple angles. According to the actual situation, the highway service level is divided into four levels. The driving state of vehicles on the bridge is regarded as a continuous flow, and Table 3 is selected as the reference standard for the service level.

[0075] Table 3 Service level classification table for basic sections of expressways

[0076]

[0077] When vehicles are traveling on a bridge, the headway between vehicles is rarely equidistant. According to relevant research, under different traffic conditions, the distance between vehicles will show different distribution characteristics within a certain range, that is, the distribution of headway is closely related to the operation status of the entire fleet. According to the road service level evaluation index, the relationship between traffic density and headway is used to convert traffic density under different service levels into average headway, and headway and vehicle speed are selected as traffic flow state evaluation indicators. The relationship between traffic density and headway is shown in formula (5).

[0078]

[0079] In practice, vehicles often pass through bridges in the form of convoys, and there may be complex situations such as driving side by side and overtaking. Although the study of the dynamic response of the bridge under a single vehicle should be able to reflect the changes and laws of bridge vibration, there is a large error with the actual situation. While keeping the working conditions unchanged, by increasing the number of vehicles in the convoy, the dynamic response of the bridge under different numbers of vehicles is analyzed.

[0080] according to Figure 3 The analysis shows that under the same working conditions, as the number of vehicles in the convoy increases, the bridge vibrates significantly, and the maximum vertical displacement in the mid-span first increases and then decreases and remains stable; when the number of vehicles in the convoy reaches 5, the maximum vertical displacement in the mid-span of the bridge will no longer increase significantly with the increase in the number of vehicles, and gradually remain stable; compared with a single vehicle, the maximum vertical displacement in the mid-span of the bridge increases by 26% for two vehicles, and by 10% for three vehicles compared with two vehicles, and by 3% for five vehicles compared with three vehicles. The influence of multiple vehicles on the vibration response of the bridge is significantly greater than that of a single vehicle, and as the number of vehicles in the convoy increases, the influence of the convoy on the vibration amplitude of the bridge gradually weakens.

[0081] To ensure safety, vehicles should maintain a certain distance from the vehicle in front when driving, especially when driving on highways, the minimum distance should not be less than 50 meters. However, in actual driving, due to the influence of various factors and the complex driving environment, the distance between the two vehicles is often less than 50 meters. Two vehicles are selected to drive at a constant speed of 80km / h, and the dynamic response of the bridge is studied when the head spacing is 4m, 8m, 16m, and 32m. p is the ratio of the head spacing to the bridge, that is, p = 1 / 8, p = 1 / 4, p = 1 / 2, and p = 1.

[0082] according to Figure 4 The analysis found that as the head spacing increases, the distance between the two vehicles increases, and the maximum vertical displacement of the bridge mid-span decreases; when the head spacing is 4m and 8m, the maximum vertical displacement of the bridge mid-span increases significantly, and when the head spacing is 16m and 32m, it is close to the maximum vertical displacement of the bridge mid-span under a single vehicle load; the head spacing can affect the dynamic response of the bridge to a certain extent, and the larger the spacing, the weaker the impact.

[0083] According to the characteristic that the dynamic response of the bridge tends to be stable when the number of vehicles in the convoy reaches a certain value under the action of multiple vehicles load, 6 vehicles are selected to form a convoy. According to Table 4, the corresponding vehicle speed and average headway are selected. The weighted method is used to process the dynamic response of the bridge under 50 groups of random headway, and the influence of different traffic flow states on the dynamic response of the bridge is analyzed.

[0084] Table 4 Multi-vehicle bridge coupling service level classification table

[0085]

[0086] according to Figure 5 The analysis of Table 5 shows that under different traffic flow conditions, the maximum vertical displacement of the bridge mid-span increases with the deterioration of traffic flow conditions. Under free flow conditions, the distance between vehicles is large, exceeding the length of the bridge. At the same time, there is usually only one vehicle on the bridge, and the superimposed dynamic effect of the vehicles is weak. The vertical displacement of the bridge mid-span shows periodic changes, and the maximum displacement is close to the value under a single vehicle. Under stable flow and restricted flow conditions, the speed is further reduced, the distance between vehicles is reduced, the superimposed dynamic effect of vehicles is enhanced, and the dynamic response of the bridge changes significantly. Among the different traffic flow conditions, the stable flow state has the least effect on the dynamic response of the bridge, and the restricted flow state has the greatest effect on the dynamic response of the bridge.

[0087] Table 5 Maximum vertical displacement values ​​of bridge mid-span under different traffic flow conditions

[0088]

[0089] (1) Based on the road service level, traffic flow theory is introduced and headway and speed are selected as traffic flow state evaluation indicators, which can reduce the difficulty of calculating the dynamic response of bridges under different traffic flow states and improve the calculation efficiency.

[0090] (2) As the number of vehicles in the traffic flow increases, the dynamic response of the bridge first increases and then decreases and remains stable, and is greater than the value in the single-vehicle case. When the number of vehicles is 3, the maximum vertical displacement of the bridge mid-span reaches its maximum value. When the number of vehicles is 5, the maximum vertical displacement of the bridge mid-span will no longer increase significantly with the increase in the number of vehicles and gradually remain stable.

[0091] (3) As the distance between vehicles in the traffic flow increases, the maximum vertical displacement at the mid-span of the bridge gradually decreases. When the distance between vehicles is half the length of the bridge, the direct superimposed dynamic response of the vehicles weakens, and the maximum vertical displacement at the mid-span of the bridge approaches the value under a single vehicle.

[0092] (4) As the traffic flow changes from free flow to restricted flow, the dynamic response of the bridge shows an increasing trend. In the free flow state, the superimposed dynamic effect of vehicles is the weakest, close to the value under a single vehicle. In the stable flow state, the superimposed dynamic effect of vehicles is obvious, the vertical displacement value fluctuates weakly, and the impact on the dynamic response of the bridge is minimal. In the restricted flow state, the distance between vehicles is further reduced, the vehicle speed slows down, and the impact on the dynamic response of the bridge is the greatest.

[0093] It should be noted that, in the present invention, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0094] The above embodiments are merely examples of the present invention and do not limit the protection scope of the present invention. All designs that are the same or similar to the present invention fall within the protection scope of the present invention.

Claims

1. A method for analyzing the dynamic response of a simply supported beam bridge under different traffic flow conditions, characterized in that: The following steps are involved: Select the vehicle type and simplify it into a plane model, obtain the physical property parameters of the vehicle components, combine the dynamic characteristics of the vehicle, and establish the multi-vehicle vehicle motion equation based on the d'Alembert principle; Obtain the physical technical parameters of the simply supported beam bridge, establish a simply supported beam bridge model through Midas, and use modal analysis to obtain the natural frequency ω and vibration mode of the simply supported beam bridge , and the bridge vibration equation, combined with the vehicle motion equation and the bridge vibration equation, obtain the multi-vehicle bridge coupling vibration analysis model; The traffic flow state evaluation index is input into the multi-vehicle-bridge coupled vibration analysis model to obtain the dynamic response analysis results of the simply supported beam bridge under different traffic flow states.

2. The dynamic response analysis method of a simply supported beam bridge under different traffic flow conditions as claimed in claim 1, characterized in that: The traffic flow state evaluation index includes the headway and vehicle speed, and the traffic flow state is divided into free flow, stable flow and restricted flow.

3. The dynamic response analysis method of a simply supported beam bridge under different traffic flow conditions as claimed in claim 1, characterized in that: The dynamic response analysis results of the simply supported beam bridge under different traffic flow conditions are as follows: Under different traffic flow conditions, the maximum vertical displacement of the bridge mid-span increases as the traffic flow condition worsens; Among them, in the free flow state, the distance between vehicles is large, exceeding the length of the bridge. At the same time, the number of vehicles on the bridge increases, and the vertical displacement of the bridge mid-span shows periodic changes, and the maximum displacement is close to the value under a single vehicle; Under the steady flow and restricted flow conditions, the vehicle speed is reduced, the distance between vehicles is reduced, the vehicle superposition dynamic effect is enhanced, and the bridge dynamic response is enhanced; Among different traffic flow states, the stable flow state has the least impact on the dynamic response of the bridge, while the restricted flow state has the greatest impact on the dynamic response of the bridge.

4. The method for analyzing the dynamic response of a simply supported beam bridge under different traffic flow conditions as claimed in claim 1, characterized in that: The selected vehicle type is a two-axle flat vehicle model; the dynamic characteristics of the vehicle include the sinking and nodding of the vehicle body, and the sinking and floating of the front and rear wheels.

5. The method for analyzing the dynamic response of a simply supported beam bridge under different traffic flow conditions as claimed in claim 1, characterized in that: The physical technical parameters of the simply supported beam bridge are obtained, a simply supported beam bridge model is established through Midas, and the natural frequency ω and vibration mode of the simply supported beam bridge are obtained by modal analysis. As well as the bridge vibration equation, the vehicle motion equation and the bridge vibration equation are combined to obtain a multi-vehicle bridge coupling vibration analysis model, which includes the following steps: Obtain the actual dimensions and structural characteristics of simply supported beam bridges, Use Midas to build a geometric model based on the actual size and structural characteristics of the simply supported beam bridge; According to the actual support conditions of the simply supported beam bridge, boundary conditions are set, modal analysis is performed, and the natural frequency ω and vibration mode of the simply supported beam bridge are extracted. According to the modal analysis results, the mode that contributes most to the vibration response is selected as the main mode; The modal synthesis method is used to reduce the degrees of freedom of the bridge model and retain the degrees of freedom corresponding to the main modes; the interaction force between the vehicle and the simply supported beam bridge, including the contact force between the tire and the bridge deck, is determined, and the bridge vibration equation is obtained; Combining the vehicle motion equations and bridge vibration equations, the vehicle-bridge coupled vibration equations are constructed, and then the multi-vehicle-bridge coupled vibration analysis model is obtained.

6. The method for analyzing the dynamic response of a simply supported beam bridge under different traffic flow conditions as claimed in claim 5, characterized in that: The modal analysis is used to obtain the natural frequency ω and vibration mode of the simply supported beam bridge. , including the following steps: Define the material properties of the simply supported beam bridge, including elastic modulus, density, Poisson's ratio, and assign corresponding cross-sectional properties to different parts of the simply supported beam bridge; Set boundary conditions according to the actual support conditions of the simply supported beam bridge, select the modal analysis type in Midas, and set the analysis parameters, such as the number of extracted modes and frequency range, run the modal analysis calculation, and solve the natural frequency ω and vibration mode of the bridge 7. The method for analyzing the dynamic response of a simply supported beam bridge under different traffic flow conditions as claimed in claim 4, characterized in that: The method of selecting a vehicle type and simplifying it into a plane vehicle type, obtaining physical property parameters of vehicle components, combining the dynamic characteristics of the vehicle, and establishing a multi-vehicle vehicle motion equation based on the d'Alembert principle includes the following steps: According to the dynamic characteristics of the vehicle, the two-axle vehicle is simplified into a four-degree-of-freedom plane vehicle, including the sinking and nodding of the vehicle body and the floating and sinking of the front and rear wheels; According to the d'Alembert principle, the motion equation of a multi-vehicle two-axle plane vehicle is established and expressed in matrix form as follows: Among them, [Mv], [Cv], and [Kv] are the mass matrix, damping matrix, and stiffness matrix of the multi-vehicle vehicle respectively; {Fv} is the overall external force vector of the vehicle; and {Zv} is the displacement matrix of each degree of freedom of the vehicle.

8. A system for analyzing the dynamic response of a simply supported beam bridge under different traffic flow conditions, comprising: The vehicle motion analysis module is used to select the vehicle type and simplify it into a plane model, obtain the physical property parameters of the vehicle components, combine the dynamic characteristics of the vehicle, and establish the multi-vehicle vehicle motion equation based on the d'Alembert principle; The analysis model building module is used to obtain the physical technical parameters of the simply supported beam bridge, establish the simply supported beam bridge model through Midas, and use modal analysis to obtain the natural frequency ω and vibration mode of the simply supported beam bridge As well as the bridge vibration equation, the vehicle motion equation and the bridge vibration equation are combined to obtain a multi-vehicle bridge coupling vibration analysis model; The dynamic response analysis module is used to input the traffic flow state evaluation index into the multi-vehicle bridge coupling vibration analysis model to obtain the dynamic response analysis results of the simply supported beam bridge under different traffic flow states.

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