A calculation method for the composite slope of bridge longitudinal section based on train axle load

Abstract

The present application relates to a method for calculating the composite slope of a bridge longitudinal section based on train axle load, comprising: step S1, obtaining the total number of time steps for a train to cross a bridge and the position of the wheelset of the train at each time step; step S2, fitting the bridge linear function within the length of the train crossing the bridge at a certain time step; step S3, determining the slope corresponding to the axle load borne by the wheelset at the position of the wheelset on the bridge based on the position of the wheelset of the train crossing the bridge at that time step and the bridge linear function; step S4, calculating the composite slope of the train crossing the bridge at that time step based on the axle load borne by the locomotive wheelset and the axle load borne by the truck wheelset, and the slope corresponding to the axle load borne by the wheelset at the position of the wheelset on the bridge at that time step; repeating steps S2 to S4 to obtain the dynamic composite slope within the time history of the train crossing the bridge. The calculation method provided in the present application considers the influence of different slope sections and the axle load borne by the train wheelset on the slope, and the calculation results are more consistent with the actual situation and the accuracy is correspondingly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of bridge longitudinal section design, and in particular to a method for calculating the composite slope of a bridge longitudinal section based on train axle load. Background Art

[0002] During operation and maintenance, railway bridges inevitably deform due to temperature, train loads, and wind loads. For example, suspension bridges, due to their high overall flexibility, are significantly affected by temperature loads. When the temperature drops significantly, the bridge's overall alignment will exhibit a certain upward arch, posing a challenge for heavily loaded trains climbing grades. Therefore, under the influence of natural loads, limited by project investment and terrain, the question of how to accurately identify the slope of railway bridges while ensuring economic efficiency and enabling heavy-load trains to negotiate steeper slopes has become a pressing issue.

[0003] In related technologies, for example, the locomotive algorithm is based on a heavy-load train with a traction locomotive. It only calculates the corresponding slope of the locomotive at the front position during the continuous uphill phase. The slope result calculated by the locomotive algorithm is too conservative, and the slope limit is too large, which cannot be used as a representative value for bridge slope calculation. Alternatively, the slope of the line connecting the coordinate points at both ends of the bridge is used as the slope. However, when a train crosses a bridge, the longitudinal section of the bridge does not have a long longitudinal section like a railway line. Generally, a herringbone slope is considered. Therefore, when a train crosses a bridge, within the total length of the train, the train may be in a stage of crossing multiple slopes and cannot be completely in the train climbing stage. In addition, the longitudinal section of the bridge line section contains a relatively short restricted slope, even shorter than the length of the train. If other slope sections in the middle section are not considered, the calculation results will not match the actual situation and the accuracy will be low. Summary of the Invention

[0004] The present application provides a method for calculating the composite slope of the longitudinal section of a bridge based on train axle weight, which solves the technical problems in related technologies that the calculation results of the slope calculated by the locomotive algorithm are too conservative, inconsistent with the actual situation when the intermediate slope sections are not considered, and have low accuracy.

[0005] The present application provides a method for calculating the composite slope of a bridge longitudinal section based on train axle load, which includes the following steps:

[0006] Step S1, obtaining the total number of time steps for a train to cross a bridge and the wheel position of the train at each time step;

[0007] Step S2, fitting the bridge linear function within the length range of the train on the bridge at a certain time step;

[0008] Step S3, determining the slope corresponding to the axle load borne by the wheelset at the wheelset position on the bridge according to the wheelset position of the train on the bridge at the time step and the bridge linear function;

[0009] Step S4, calculating the composite slope of the train when crossing the bridge at the time step based on the axle load borne by the locomotive wheelsets and the axle load borne by the freight car wheelsets in the train and the slope corresponding to the axle load borne by the wheelsets at the wheelset positions on the bridge at the time step;

[0010] Repeat steps S2 to S4 to obtain the dynamic composite slope during the time history of the train crossing the bridge.

[0011] In one embodiment, the step S4 calculates the composite slope of the train when crossing the bridge at the time step based on the axle load borne by the locomotive wheelset and the axle load borne by the freight car wheelset in the train and the slope corresponding to the axle load borne by the wheelset at the wheelset position on the bridge at the time step,

[0012] The calculation formula is: ;

[0013] in, is the composite slope; The axle load borne by the locomotive wheelset; The axle load borne by the truck wheelset; The slope corresponding to the axle load borne by the wheelset at the wheelset position; The total number of wheelsets in the train formation.

[0014] In one embodiment, the step S1 of obtaining the total number of time steps for the train to cross the bridge and the wheel position of the train at each time step includes:

[0015] Step S11: Obtain the train speed and bridge length to obtain the total time steps for the train to cross the bridge;

[0016] Step S12: Determine the train length and the total number of wheelsets according to the train formation, so as to obtain the bridge position corresponding to each wheelset of the train at each time step as the wheelset position.

[0017] In one embodiment, the step S2 of fitting the bridge linear function within the length range of the train on the bridge at a certain time step includes:

[0018] Step S21, determining the train length of the train on the bridge and the number of bridge nodes within the train length based on the positions of different wheel sets at a certain time step;

[0019] Step S22: extracting the bridge node coordinates and node displacement values ​​within the train length range according to the positions of the corresponding wheelsets on the bridge to obtain the longitudinal section alignment of the bridge;

[0020] Step S24: curve fitting is performed on the longitudinal section line of the bridge to obtain a bridge line function within the length range of the train on the bridge at this time step.

[0021] In one embodiment, the bridge node coordinates and node displacement values ​​are obtained through a bridge finite element model.

[0022] In one embodiment, the step S2 of fitting the bridge linear function within the length range of the train on the bridge at a certain time step further includes: step S23 of encrypting the longitudinal section linear shape of the bridge.

[0023] In one embodiment, the step S23 of encrypting the longitudinal section of the bridge comprises any one of a cubic spline interpolation method, a least squares method, a Lagrange polynomial interpolation method, and a Hermite polynomial interpolation method.

[0024] In one embodiment, dynamic fitting is used when performing curve fitting on the longitudinal section line shape of the bridge.

[0025] In one embodiment, the dynamic fitting includes:

[0026] Select the fitting objective function as n-order polynomial;

[0027] The optimal polynomial degree is evaluated according to the longitudinal section line shape of the bridge and fitted.

[0028] In one embodiment, the step S3 of determining the slope corresponding to the axle load borne by the wheelset at the wheelset position on the bridge according to the wheelset position of the train on the bridge at the time step and the bridge linear function includes:

[0029] Step S31: performing a derivative of the bridge linear function to obtain a slope expression;

[0030] Step S32: Calculate the bridge linear slope value corresponding to each wheelset according to the wheelset position of the train on the bridge at this time step and the slope expression, as the slope corresponding to the axle load borne by the wheelset at the wheelset position on the bridge.

[0031] The beneficial effects of the technical solutions provided in the embodiments of the present application include:

[0032] The present application provides a method for calculating the composite slope of the longitudinal section of a bridge based on the train axle weight, taking into account the influence of different slope sections, fitting the train bridge crossing line shape in segments based on the time steps of the train crossing the bridge, accurately fitting the bridge line shape function, and the calculation result is more in line with the actual situation; at the same time, considering the influence of the axle weight borne by different wheelsets of the train on the slope, the train calculation mass and traction mass are shared on the wheelsets of the locomotive and freight car, and the average slope of the train when crossing the bridge is calculated as the composite slope through the conversion relationship between the axle weight borne by the wheelset and the slope. The calculation result is further in line with the actual situation, will not be conservative, and the accuracy is correspondingly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0034] Figure 1 Schematic diagram of the geometric structure of a train in one embodiment of the present invention.

[0035] Figure 2 Schematic diagram of a finite element model of a bridge in one embodiment of the present invention.

[0036] Figure 3 This is a result curve diagram based on the locomotive algorithm in one embodiment of the present invention.

[0037] Figure 4 This is a curve diagram showing the results of a method for calculating the composite slope of a bridge longitudinal section based on train axle load in one embodiment of the present invention. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0039] An embodiment of the present application provides a method for calculating the composite slope of the longitudinal section of a bridge based on train axle weight, which can solve the technical problems in related technologies in which the locomotive algorithm calculates the slope in an overly conservative manner, does not conform to reality when not considering the intermediate slope section, and has low accuracy.

[0040] This embodiment provides a method for calculating the composite slope of a bridge longitudinal section based on train axle load, which includes the following steps:

[0041] Step S1, obtaining the total number of time steps for the train to cross the bridge and the wheel position of the train at each time step;

[0042] Step S2, fitting the bridge linear function within the length range of the train that gets on the bridge at a certain time step;

[0043] Step S3, determining the slope corresponding to the axle load borne by the wheelset at the wheelset position on the bridge according to the wheelset position of the train on the bridge at the time step and the bridge linear function;

[0044] Step S4, calculating the composite slope of the train when crossing the bridge at the time step based on the axle load borne by the locomotive wheelsets and the axle load borne by the freight car wheelsets in the train and the slope corresponding to the axle load borne by the wheelsets at the wheelset positions on the bridge at the time step;

[0045] Repeat steps S2 to S4 to obtain the dynamic composite slope during the time history of the train crossing the bridge.

[0046] This embodiment provides a method for calculating the composite slope of the longitudinal section of a bridge based on the train axle weight, taking into account the influence of different slope sections, and fitting the train bridge crossing line shape in segments based on the time steps of the train crossing the bridge, accurately fitting the bridge line shape function, and the calculation result is more in line with the actual situation; at the same time, the influence of the axle weight borne by different wheelsets of the train on the slope is taken into account, and the train calculation mass and traction mass are shared by the wheelsets of the locomotive and freight car. The average slope of the train when crossing the bridge is calculated as the composite slope through the conversion relationship between the axle weight borne by the wheelset and the slope. The calculation result is further in line with the actual situation, will not be conservative, and the accuracy is correspondingly improved.

[0047] Each step is described and explained in detail below.

[0048] In one embodiment, step S1, obtaining the total number of time steps for a train to cross a bridge and the wheel position of the train at each time step, includes:

[0049] Step S11: Obtain the train speed and bridge length to obtain the total time steps for the train to cross the bridge.

[0050] Step S12: Determine the train length and the total number of wheelsets according to the train formation to obtain the bridge position corresponding to each wheelset of the train at each time step as the wheelset position.

[0051] Specifically, the train length and the total number of wheelsets of the train can be determined through the train formation, and then the bridge position corresponding to each wheelset of the train at each time step within the total time step can be calculated based on the geometric structure of the train. This can be used as the wheelset position or the wheelset coordinates; the wheelset position can be in matrix form.

[0052] Through the above scheme, the wheelset position of the train at each time step is determined, which serves as the basis for the subsequent segmented fitting of the bridge linear function to obtain the slope of each wheelset position.

[0053] like Figure 1 As shown, Figure 1 Schematic diagram of the geometric structure of a train in one embodiment of the present invention.

[0054] in, m c is the mass of the train body; m b is the mass of the train bogie;m t is the mass of the wheelset; the axle load is the weight of the train acting on the rails through each wheelset, so the axle load mass borne by the wheelset = ( m c +2* m b +4* m t ) / 4; l 1 and l 2 is the distance between the primary and secondary suspensions, used to determine the coordinates of the wheelset within a time step. The primary suspension, also known as the main suspension, is installed between the locomotive bogie frame and the axlebox, primarily transmitting forces between the axlebox and wheelset and providing positioning. The secondary suspension, also known as the secondary suspension, is installed between the carbody underframe and the bogie frame, primarily connecting the underframe and the carbody, limiting lateral rotation.

[0055] In one embodiment, step S2, fitting the bridge linear function within the length range of the train on the bridge at a certain time step, includes:

[0056] Step S21: Determine the train length of the train on the bridge and the number of bridge nodes within the train length based on the positions of different wheel sets at a certain time step.

[0057] Specifically, the length of the train on the bridge is determined based on the position of different wheelsets at a given time step. If a wheelset is on the bridge, that portion of the train is also on the bridge. The bridge alignment for this portion of the train is then selected. It should be noted that only the length of the train on the bridge is considered in the calculation; the portion of the train not on or off the bridge is not included in the calculation.

[0058] Step S22: extract the bridge node coordinates and node displacement values ​​within the train length range according to the position of the corresponding wheelset on the bridge to obtain the longitudinal section line shape of the bridge.

[0059] In one embodiment, the bridge node coordinates and node displacement values ​​are obtained from the bridge finite element model. The bridge node coordinates are used as the abscissa, and the node displacement values, i.e., the vertical deformation values ​​of the bridge nodes, are used as the ordinate, thereby extracting the bridge longitudinal section line shape.

[0060] Step S24: curve fitting is performed on the longitudinal section line of the bridge to obtain the bridge line shape function within the length range of the train on the bridge at this time step.

[0061] Since the bridge alignment within the train range is different in different time steps, the above scheme is used to fit the bridge alignment function within the train length range under the segmented fitting time step, which is closer to the actual situation and ensures the smoothness and stability of the alignment.

[0062] In one embodiment, step S2, fitting the bridge linear function within the length range of the train on the bridge at a certain time step, further includes: step S23, encrypting the longitudinal section linear shape of the bridge.

[0063] Through the above scheme, encryption processing can improve the integrity and continuity of the data and supplement the values ​​between known bridge data points, making the data smoother and the trends more obvious.

[0064] In one embodiment, step S23, encrypting the bridge longitudinal section line shape includes any one of the cubic spline interpolation method, the least squares method, the Lagrange polynomial interpolation method, and the Hermite polynomial interpolation method.

[0065] Specifically, the data points on the bridge longitudinal section are preferably encrypted using a cubic spline interpolation method. The interpolation curve generated by the cubic spline interpolation method gradually approaches the actual curve as the interval between interpolation points decreases. In addition, the interpolation curve has the characteristics of good shape preservation and smoothness.

[0066] In one embodiment, in step S24, dynamic fitting is used when performing curve fitting on the longitudinal section of the bridge.

[0067] In one embodiment, dynamic fitting includes:

[0068] Select the fitting objective function as n polynomials;

[0069] The optimal polynomial degree is evaluated according to the longitudinal section line shape of the bridge and fitted.

[0070] Specifically, the fitting objective function of the bridge line shape is generally n Polynomial of degree: If the order of the objective function is n If the value is set too small, underfitting may occur, that is, the fitted function cannot capture the complexity and characteristics of the bridge line shape, which is manifested as the fitting curve cannot accurately track the trend of the data points, resulting in a large prediction error. n Setting it too large may lead to overfitting.

[0071] Through the above scheme, the optimal polynomial degree is evaluated according to the longitudinal section line shape of the bridge, and dynamic fitting is performed to obtain the appropriate order of the objective function.

[0072] In one embodiment, step S3, determining the slope corresponding to the axle load borne by the wheelset at the wheelset position on the bridge according to the wheelset position of the train on the bridge at the time step and the bridge linear function, includes:

[0073] Step S31: Derivative the bridge linear function to obtain a slope expression;

[0074] Step S32: Calculate the bridge linear slope value corresponding to each wheelset based on the wheelset position and slope expression of the train going up the bridge at this time step, as the slope corresponding to the axle load borne by the wheelset at the wheelset position going up the bridge.

[0075] In one embodiment, step S4, the composite slope of the train when crossing the bridge at the time step is calculated based on the axle load borne by the locomotive wheelset in the train and the axle load borne by the freight car wheelset, and the slope corresponding to the axle load borne by the wheelset at the wheelset position on the bridge at the time step.

[0076] The calculation formula is: ;

[0077] in, is the composite slope; The axle load borne by the locomotive wheelset; The axle load borne by the truck wheelset; The slope corresponding to the axle load borne by the wheelset at the wheelset position; The total number of wheelsets in the train formation.

[0078] In related technologies, a locomotive algorithm is used to calculate the slope. Specifically, according to the Railway Line Design Specifications (GB50090-2006), the maximum slope of a single-locomotive heavy-haul railway line is the slope at which a locomotive pulling a heavy-haul train, on a continuous upward slope, eventually runs at a constant speed at the locomotive's calculated speed. The calculation formula is:

[0079] ;

[0080] Where: Calculate the mass for the locomotive; The traction quality standards proposed for the design; is the locomotive traction coefficient, which is taken as 0.9; is the maximum traction mass of the train; 、 is the unit basic resistance of the locomotive and freight car; this formula is adapted to the environment where a single locomotive is pulling a heavy-load train on a continuous uphill slope.

[0081] This application discovered that slope is a dimensionless constant of the train's traction mass, derived by converting between wheelset masses. Therefore, by considering the impact of the axle loads borne by different wheelsets on the slope, the calculated train mass and traction mass are distributed among the locomotive and freight car wheelsets. The average slope of the train crossing the bridge is calculated using the axle loads borne by the wheelsets as the composite slope. This calculation results in a more realistic and less conservative result, resulting in improved accuracy.

[0082] Through the above scheme, the composite slope at a certain time step is obtained. According to different loop solutions of the train's forward position, steps S2-S4 are repeated to obtain the dynamic composite slope of the train's time history when crossing the bridge.

[0083] A specific embodiment is provided below for illustration.

[0084] like Figure 2 As shown, Figure 2 Schematic diagram of a finite element model of a bridge in one embodiment of the present invention.

[0085] The project is based on a large-span suspension bridge scheme, which is a double-cable-plane railway bridge with a span arrangement of 168m+1092m+168m, and three continuous spans.

[0086] This embodiment provides a method for calculating the composite slope of a bridge longitudinal section based on train axle load, which includes the following steps:

[0087] Step S1: Obtain the total number of time steps for a train to cross a bridge and the wheel position of the train at each time step.

[0088] Specifically, the bridge length is 1428 meters, the train speed is set to 30m / s, and the distance the train moves forward per time step is 3 meters. The total number of time steps for the train to cross the bridge is approximately t_num=476 time steps. Assume that the train has 8 marshalings and a total of 32 wheel sets. Figure 1 As shown, l 1=1.25 meters, l 2 = 8.75 meters. Calculate the bridge position xx of each wheelset in 476 time steps. The xx matrix dimension is (476, 32).

[0089] Step S2: Fitting the bridge linear function within the length range of the train that gets on the bridge at a certain time step.

[0090] Based on the positions of different wheelsets at a given time step, the train length L_nihe and the number of bridge nodes within that train length, n_fenduan, are determined. Bridge node coordinates and node displacements are obtained from the bridge finite element model. Based on the positions of the corresponding wheelsets on the bridge, the bridge node coordinates and node displacements within the train length are extracted, using the bridge node coordinates as the abscissa and the node displacements as the ordinate, to extract the bridge longitudinal profile. The extracted longitudinal profile is encrypted using cubic spline interpolation. A dynamic fitting function is then performed to determine the bridge profile function within the train length of the bridge at that time step.

[0091] Step S3: Determine the slope corresponding to the axle load borne by the wheelset at the wheelset position on the bridge according to the wheelset position of the train on the bridge at the time step and the bridge linear function.

[0092] Specifically, the bridge linear function is differentiated once to obtain the slope expression; the slope expression is substituted into the position of the wheelset where the train enters the bridge at that time step to calculate the bridge linear slope value corresponding to each wheelset, which is used as the slope corresponding to the axle load borne by the wheelset at the position of the wheelset on the bridge.

[0093] Step S4, calculate the composite slope of the train when crossing the bridge at this time step based on the axle load borne by the locomotive wheelset and the axle load borne by the freight car wheelset in the train and the slope corresponding to the axle load borne by the wheelset at the wheelset position on the bridge at this time step.

[0094] The calculation formula is: .

[0095] Repeat steps S2 to S4 to obtain the dynamic composite slope during the time history of the train crossing the bridge.

[0096] Under the same conditions, the locomotive algorithm is used to calculate the slope.

[0097] The calculation formula is: .

[0098] like Figure 3 and Figure 4 As shown, Figure 3 This is a result curve diagram based on the locomotive algorithm in one embodiment of the present invention. Figure 4 This is a curve diagram showing the results of a method for calculating the composite slope of a bridge longitudinal section based on train axle load in one embodiment of the present invention.

[0099] pass Figure 3 、 Figure 4 It can be seen that the maximum slope calculated using the existing locomotive algorithm is 3.052‰. Using the composite slope calculation method provided in the embodiments of this application, the maximum composite slope calculated based on a single-track operation of one locomotive and eight freight cars with an axle load of 8.4 tons per linear meter is 2.888‰, a 5.4% decrease compared to the slope calculated using the locomotive algorithm. The maximum composite slope calculated for a single-track operation of one locomotive and sixteen freight cars is 2.488‰, an 18.48% decrease compared to the slope calculated using the locomotive algorithm.

[0100] The above results show that the existing locomotive algorithm is more conservative than the calculation method provided in the embodiment of this application, which will have an adverse impact on bridge design and railway operation investment. The calculation method provided in the embodiment of this application has positive significance for saving construction costs and improving the operating capacity of heavy-load trains.

[0101] It should be noted that the above-mentioned serial numbers of the embodiments of the present application are only for description and do not represent the advantages and disadvantages of the embodiments. The terms "including" and "having" in the specification and claims of this application and the above-mentioned drawings, as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device comprising a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or units inherent to these processes, methods, products or devices. The terms "first", "second" and "third" are used to distinguish different objects, etc., and do not represent a sequential order, nor do they limit "first", "second" and "third" to being different types.

[0102] In the description of the embodiments of this application, the words "exemplary," "for example," or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary," "for example," or "for example" in the embodiments of this application should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary," "for example," or "for example" is intended to present the relevant concepts in a concrete manner.

[0103] In the description of the embodiments of the present application, unless otherwise specified, “ / ” means or, for example, A / B can mean A or B; “and / or” in the text is merely a description of the association relationship of associated objects, indicating that three relationships may exist, for example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the embodiments of the present application, “multiple” refers to two or more than two.

[0104] In some processes described in the embodiments of this application, multiple operations or steps are included that appear in a specific order. However, it should be understood that these operations or steps may not be executed in the order in which they appear in the embodiments of this application or may be executed in parallel. The sequence numbers of the operations are only used to distinguish different operations, and the sequence numbers themselves do not represent any execution order. In addition, these processes may include more or fewer operations, and these operations or steps may be executed in sequence or in parallel, and these operations or steps may be combined.

[0105] The above are only preferred embodiments of the present application and do not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for calculating the composite slope of a bridge longitudinal section based on train axle load, characterized in that: It includes the following steps: Step S1, obtaining the total number of time steps for a train to cross a bridge and the wheel position of the train at each time step; Step S2, fitting the bridge linear function within the length range of the train on the bridge at a certain time step; Step S3, determining the slope corresponding to the axle load borne by the wheelset at the wheelset position on the bridge according to the wheelset position of the train on the bridge at the time step and the bridge linear function; Step S4, calculating the composite slope of the train when crossing the bridge at the time step based on the axle load borne by the locomotive wheelsets and the axle load borne by the freight car wheelsets in the train and the slope corresponding to the axle load borne by the wheelsets at the wheelset positions on the bridge at the time step; The calculation formula is: ; in, is the composite slope; The axle load borne by the locomotive wheelset; The axle load borne by the truck wheelset; The slope corresponding to the axle load borne by the wheelset at the wheelset position; is the total number of wheelsets in the train formation; Repeat steps S2 to S4 to obtain a dynamic composite slope during the time history of the train crossing the bridge; The step S2 of fitting the bridge linear function within the length range of the train on the bridge at a certain time step includes: Step S21, determining the train length of the train on the bridge and the number of bridge nodes within the train length based on the positions of different wheel sets at a certain time step; Step S22: extracting the bridge node coordinates and node displacement values ​​within the train length range according to the positions of the corresponding wheelsets on the bridge to obtain the longitudinal section alignment of the bridge; Step S24: curve fitting is performed on the longitudinal section line of the bridge to obtain a bridge line function within the length range of the train on the bridge at this time step.

2. The method for calculating the composite slope of a bridge longitudinal section based on train axle load according to claim 1, characterized in that: The step S1 of obtaining the total number of time steps for the train to cross the bridge and the wheel position of the train at each time step includes: Step S11: Obtain the train speed and bridge length to obtain the total time steps for the train to cross the bridge; Step S12: Determine the train length and the total number of wheelsets according to the train formation, so as to obtain the bridge position corresponding to each wheelset of the train at each time step as the wheelset position.

3. The method for calculating the composite slope of a bridge longitudinal section based on train axle load according to claim 1, characterized in that: The bridge node coordinates and node displacement values ​​are obtained through a bridge finite element model.

4. The method for calculating the composite slope of a bridge longitudinal section based on train axle load according to claim 1, wherein: The step S2 of fitting the bridge linear function within the length range of the train on the bridge at a certain time step also includes: step S23 of encrypting the longitudinal section linear shape of the bridge.

5. The method for calculating the composite slope of a bridge longitudinal section based on train axle load according to claim 4, characterized in that: The step S23, encrypting the longitudinal section of the bridge, includes any one of the cubic spline interpolation method, the least squares method, the Lagrange polynomial interpolation method, and the Hermite polynomial interpolation method.

6. The method for calculating the composite slope of a bridge longitudinal section based on train axle load according to claim 1, wherein: Dynamic fitting is adopted when performing curve fitting on the longitudinal section line shape of the bridge.

7. The method for calculating the composite slope of a bridge longitudinal section based on train axle load according to claim 6, characterized in that: The dynamic fitting includes: Select the fitting objective function as n-order polynomial; The optimal polynomial degree is evaluated according to the longitudinal section line shape of the bridge and fitted.

8. The method for calculating the composite slope of a bridge longitudinal section based on train axle load according to claim 1, wherein: The step S3 of determining the slope corresponding to the axle load borne by the wheelset at the wheelset position on the bridge according to the wheelset position of the train on the bridge at the time step and the bridge linear function includes: Step S31: performing a derivative of the bridge linear function to obtain a slope expression; Step S32: Calculate the bridge linear slope value corresponding to each wheelset according to the wheelset position of the train on the bridge at this time step and the slope expression, as the slope corresponding to the axle load borne by the wheelset at the wheelset position on the bridge.

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