Method for analyzing temperature field of concrete box girder structure under fire high-temperature action

Abstract

The invention provides a method for analyzing a temperature field of a concrete box girder structure under the action of fire high temperature. The method comprises the following steps: determining a heat transfer constitutive relationship of a concrete material in the concrete box girder structure; determining thermal parameters of a concrete material in the concrete box girder structure, wherein the thermal parameters comprise the heat conductivity coefficient, the specific heat capacity, the density and the elastic modulus of the concrete material; establishing a space finite element model of the concrete box girder, and assigning values to concrete materials in different areas in the finite element model according to the thermal parameters and the heat transfer constitutive relation; dividing grid units in the finite element model; fire parameters are determined, the fire parameters are applied to the finite element model, and temperature field analysis of the concrete box girder is carried out. According to the method for analyzing the temperature field of the concrete box girder structure under the fire high-temperature action, the thermal response condition of concrete in a fire high-temperature scene can be simulated more accurately, and a reliable basis is provided for structural safety assessment.

Description

Technical Field

[0001] The present application relates to a concrete box girder detection technology, and in particular to a temperature field analysis method for a concrete box girder structure under high temperature in a fire. Background Art

[0002] Under the action of high temperature in fire, the performance of concrete materials, steel bars and steel strands in concrete box girders will be seriously degraded. The resistance of the concrete box girder structure will drop sharply under high temperature, and its structural bearing capacity will be reduced, thereby reducing the safety factor, which may eventually cause a collapse accident. Therefore, it is of great significance to carry out performance analysis of concrete box girder structures under high temperature in fire.

[0003] Under the action of high temperature of fire, the high temperature generated by the burning materials is transferred from the surrounding environment to the surface of the structure through convection and radiation, and then transferred from the surface of the beam to the inside of the beam through heat conduction. The superposition of multiple effects leads to a very complex temperature field distribution of the concrete box beam structure. Fire is an accidental and sudden disaster, and it is difficult to obtain the true temperature field of the structure under the action of high temperature of fire, which makes the temperature field analysis process of the concrete box beam difficult and it is not easy to simulate the real fire situation. Summary of the invention

[0004] The present application provides a method for analyzing the temperature field of a concrete box girder structure under high temperature in a fire, so as to solve the technical problem that the temperature field analysis process of a concrete box girder in the related art is not realistic and accurate enough.

[0005] The present application provides a method for analyzing the temperature field of a concrete box girder structure under high temperature in a fire, comprising:

[0006] Determine the constitutive relationship of heat transfer of concrete materials in concrete box girder structures;

[0007] Determining thermal parameters of the concrete material in the concrete box girder structure, wherein the thermal parameters include thermal conductivity, specific heat capacity, density and elastic modulus of the concrete material;

[0008] Establishing a spatial finite element model of the concrete box girder, and assigning values ​​to concrete materials in different regions of the finite element model with reference to the thermal parameters and the heat transfer constitutive relationship;

[0009] Dividing mesh elements in the finite element model;

[0010] Fire parameters are determined, applied to the finite element model, and temperature field analysis of the concrete box girder is performed.

[0011] In a possible implementation, the heat transfer constitutive relation of the concrete material includes the surface heat conduction relation of the concrete material, and the surface heat conduction relation of the concrete material is calculated by the following formula:

[0012]

[0013] Where Q is the heat transferred from the outside; k is the thermal conductivity; T is the temperature; n is the external normal of the hot surface; Г is the heat transfer surface; h c is the convection coefficient; ε is the radiation coefficient; σ=5.67×10 -8 W / (m 2 ·K 4 );T f is the ambient temperature; T is the surface temperature of the concrete box girder.

[0014] In a possible implementation, the heat transfer constitutive relation of the concrete material includes the internal heat conduction relation of the concrete material, and the internal heat conduction relation of the concrete material is calculated by the following formula:

[0015]

[0016] Among them, ρ is density, c is specific heat capacity, t is time; q is the heat generated inside the material.

[0017] In a possible implementation manner, establishing the spatial finite element model of the concrete box girder includes:

[0018] Defining the geometric structure, and creating a geometric model of the concrete box girder according to the dimensions in finite element software;

[0019] Set up the analysis steps and define the interaction of the concrete box beam.

[0020] In a possible implementation, in the analysis step, the duration is set to 7200 seconds; in the interaction, the bottom surface of the concrete box girder is on fire.

[0021] In a possible implementation manner, assigning values ​​to concrete materials in different regions of the finite element model with reference to the thermal parameters and the heat transfer constitutive relationship includes:

[0022] According to the thermal parameters and the heat transfer constitutive relationship, section properties of the concrete material in different regions are created in the finite element model.

[0023] In a possible implementation, dividing the mesh units in the finite element model includes:

[0024] The grid units include key area refinement units and gradual grid units. The key area refinement units are located in stress concentration areas and / or expected temperature change areas of the concrete box girder structure. The gradual grid units gradually increase grid density from the edge to the core of the concrete box girder structure.

[0025] In a possible implementation manner, the stress concentration area includes a connection and joint area of ​​the concrete box beam and a peripheral area of ​​the diaphragm.

[0026] In a possible implementation manner, the fire parameters include burning material, burning location and burning time.

[0027] In a possible implementation manner, applying the fire parameter to the finite element model to perform temperature field analysis on the concrete box girder includes:

[0028] Defining combustion materials, wherein different combustion materials correspond to different maximum heat release rates and heat source growth times;

[0029] Define a combustion position, determine the longitudinal distance, transverse distance and vertical distance of the combustion material from the concrete box beam according to the corresponding combustion position in the concrete box beam, and input the longitudinal distance, transverse distance and vertical distance of the combustion material from the concrete box beam to the finite element model;

[0030] A burn time is defined and input into the finite element model.

[0031] The temperature field analysis method of the concrete box girder structure under the high temperature of fire provided in the present application can more accurately simulate the thermal response of concrete at different temperatures by determining the heat transfer constitutive relationship and thermal parameters in detail, thereby ensuring the accuracy of the analysis results; in addition, by establishing a finite element model and dividing the grid units, the material properties of different regions can be considered, such as the difference in heat conduction in different parts, thereby providing more personalized and more accurate analysis results. Therefore, the present application can scientifically evaluate the impact of fire on the concrete box girder structure, including temperature distribution, thermal stress and deformation, provide a reliable basis for structural safety assessment, and help design more fire-resistant bridge structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0033] Figure 1 It is a flow chart of the temperature field analysis method of the concrete box girder structure in the embodiment of the present application;

[0034] Figure 2 It is a schematic curve diagram of the thermal conductivity and specific heat capacity of the concrete material at different temperatures in the embodiment of the present application;

[0035] Figure 3 It is a schematic curve diagram of the density and elastic modulus of the concrete material at different temperatures in the embodiment of the present application;

[0036] Figure 4 This is a schematic diagram of the structure of the spatial finite element model of the fire temperature field in the embodiment of the present application;

[0037] Figure 5 A schematic diagram of mesh division units of a structural finite element model of a concrete box girder in an embodiment of the present application;

[0038] Figure 6 This is a schematic diagram of heat conduction of a concrete box girder in an embodiment of the present application;

[0039] Figure 7 A cloud diagram of the temperature field of the concrete box girder in the embodiment of the present application;

[0040] Figure 8 This is a schematic diagram of the temperature region distribution of Section I at different fire exposure times in the embodiment of the present application;

[0041] Fig. 9 This is a schematic diagram of the temperature region distribution of the cross section II at different fire exposure times in the embodiment of the present application;

[0042] Fig.10 This is a schematic diagram of the temperature region distribution of the cross section III at different fire exposure times in the embodiment of the present application;

[0043] Fig.11 This is a schematic diagram of the temperature region distribution of the cross section IV at different fire exposure times in the embodiment of the present application;

[0044] Fig.12 Schematic diagram of temperature zone distribution of different cross sections at different fire exposure times in the embodiment of the present application.

[0045] The above drawings have shown clear embodiments of the present application, which will be described in more detail later. These drawings and text descriptions are not intended to limit the scope of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiment of the present application will be described in more detail below in conjunction with the drawings in the preferred embodiments of the present application. In the drawings, the same or similar reference numerals throughout represent the same or similar parts or parts with the same or similar functions. The described embodiments are part of the embodiments of the present application, not all of the embodiments. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limitations on the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application. The embodiments of the present application are described in detail below in conjunction with the drawings.

[0047] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, or it can be an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0048] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present application.

[0049] The terms "first", "second", "third", "fourth", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in an order other than those illustrated or described herein.

[0050] In addition, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus that includes a series of steps or elements is not necessarily limited to those steps or elements explicitly listed, but may include other steps or elements not explicitly listed or inherent to such process, method, product, or apparatus.

[0051] At present, the total number of concrete simply supported beams has increased significantly with the expansion of railway scope. The "eight vertical and eight horizontal" high-speed rail network is about to take shape, passenger and freight lines and heavy-load railways are gradually becoming denser. Railway bridge operations face a complex environment, and various types of major disasters have had a significant impact, and fire is an important one among them.

[0052] Railway transportation is characterized by strong continuity. The collapse and damage of the concrete box girder structure after a fire is difficult to repair and lasts for a long time, which has a significant impact on railway network transportation and society.

[0053] Under the action of high temperature of fire, the high temperature generated by the combustion of materials is transferred from the surrounding environment to the surface of the structure through convection and radiation, and then transferred from the surface of the beam to the inside of the beam through heat conduction. The superposition of multiple effects leads to a very complex temperature field distribution of the concrete box beam structure. Fire is an accidental and sudden disaster, and it is difficult to obtain the true temperature field of the structure under the action of high temperature of fire. Based on this, the present invention discloses a temperature field analysis method for concrete box beams based on the characteristics and positions of combustion materials, which makes up for the problem of insufficient temperature field data in existing research. The temperature field obtained based on this method can be used for structural damage analysis of concrete box beams under the action of high temperature of fire.

[0054] The following is a description of the temperature field analysis method of the concrete box girder structure under the high temperature of a fire according to an embodiment of the present application in conjunction with the accompanying drawings.

[0055] like Figure 1 As shown, the temperature field analysis method of the concrete box girder structure under the high temperature of fire provided in the embodiment of the present application includes the following steps:

[0056] Step 100, determining the heat transfer constitutive relation of the concrete material in the concrete box girder structure;

[0057] Step 200, determining thermal parameters of the concrete material in the concrete box girder structure, wherein the thermal parameters include thermal conductivity, specific heat capacity, density and elastic modulus of the concrete material;

[0058] Step 300, establishing a spatial finite element model of the concrete box girder, and assigning values ​​to concrete materials in different regions of the finite element model with reference to the thermal parameters and the heat transfer constitutive relationship;

[0059] Step 400, dividing grid units in the finite element model;

[0060] Step 500: determine fire parameters, apply the fire parameters to the finite element model, and perform temperature field analysis on the concrete box girder.

[0061] From the above description, it can be seen that the temperature field analysis method of the concrete box girder structure under the high temperature of the fire provided in the embodiment of the present application can more accurately simulate the thermal response of concrete at different temperatures by determining the heat transfer constitutive relationship and thermal parameters in detail, thereby ensuring the accuracy of the analysis results; in addition, by establishing a finite element model and dividing the grid units, the material properties of different regions can be considered, such as the difference in heat conduction in different parts, thereby providing more personalized and more accurate analysis results. Therefore, the present application can scientifically evaluate the impact of fire on the concrete box girder structure, including temperature distribution, thermal stress and deformation, provide a reliable basis for structural safety assessment, and help design more fire-resistant bridge structures.

[0062] Here, it should be noted that in the embodiments of the present application, the concrete box girder can be set with reference to the box girder structure form in the bridge engineering related technology. The cross section of the concrete box girder is box-shaped and the interior is a hollow structure. This design not only enhances the bending and torsion resistance of the beam, but also improves the overall stability of the structure. The box girder can be a prestressed concrete structure or a non-prestressed one, and is divided into a cast-in-place box girder and a prefabricated box girder according to the construction method. In this regard, no absolute limitation is made in the embodiments of the present application.

[0063] In some embodiments, in step 100, the heat transfer constitutive relation of the concrete material includes the surface heat conduction relation of the concrete material, and the surface heat conduction relation of the concrete material is calculated by the following formula:

[0064]

[0065] Where Q is the heat transferred from the outside; k is the thermal conductivity; T is the temperature; n is the external normal of the hot surface; Г is the heat transfer surface; h c is the convection coefficient; ε is the radiation coefficient; σ=5.67×10 -8 W / (m 2 ·K 4 );T f is the ambient temperature; T is the surface temperature of the concrete box girder.

[0066] In the above formula, σ is the Stefan-Boltzmann constant. The external normal of the thermal surface of a concrete box girder is a vector perpendicular to the surface and pointing to the external space. In heat conduction analysis, the direction of the external normal is crucial for defining boundary conditions. For example, in temperature field analysis, the direction of the external normal determines the direction of heat flow.

[0067] In addition, in step 100, the heat transfer constitutive relation of the concrete material also includes the internal heat conduction relation of the concrete material, and the internal heat conduction relation of the concrete material is calculated by the following formula:

[0068]

[0069] Among them, ρ is density, c is specific heat capacity, t is time; q is the heat generated inside the material.

[0070] In the above formula, since the embodiment of the present application is used to simulate the scenario of a fire in a concrete box girder structure, the fire cannot be generated inside the concrete box girder structure, and therefore, the above q (heat generated inside the material) is determined to be 0.

[0071] In some embodiments, in the box beam structure, the thermal parameters (thermal conductivity, specific heat capacity and density) of the concrete material are calculated according to Figure 2 and Figure 3 Here, the curve in the embodiment of the present application is used as an example for explanation. The curve is obtained through experimental data testing. Since the thermal parameters of concrete corresponding to different temperature nodes are different, the thermal characteristics of the material can be accurately located according to the curve.

[0072] In the embodiment of the present application, in step 300, a spatial finite element model of the concrete box girder is established, including:

[0073] Step 301, defining the geometric structure, and creating a geometric model of the concrete box girder according to the size in finite element software;

[0074] Step 302, setting analysis steps and defining the interaction of the concrete box beam.

[0075] In the above step 300, in the finite element model, since the volume of the steel bars accounts for a small proportion, their influence on heat transfer is ignored, and it is assumed that the temperature of the steel bars is the same as the temperature of the concrete at the same position.

[0076] The modeling process mainly includes several aspects such as geometric modeling, material property assignment, meshing, and boundary condition setting.

[0077] The specific steps include:

[0078] (1) Import the cross-sectional view of the component's outer surface into the sketch module, and then import the sketch into the component module to create a concrete component.

[0079] (2) Create materials: Input the heat transfer constitutive relationship of concrete materials and relevant data such as the thermal parameters of concrete materials, and create section properties. The created section properties are: the concrete material is solid and homogeneous.

[0080] (3) Define assemblies and put them together.

[0081] (4) Set the analysis step and set the duration to 7200 seconds, which means 120 minutes of analysis time.

[0082] (5) Define the interaction. In a fire, usually only the bottom surface of a beam in an engineering structure is directly affected by the fire. Therefore, when performing heat transfer analysis on the box beam here, it is assumed that the bottom surface is affected by the fire.

[0083] like Figure 6 As shown in the figure, in the temperature field analysis, the ground fire source conducts heat upward, causing the interior of the concrete box girder to transfer heat with the air from bottom to top.

[0084] Here, the above-mentioned spatial finite element model is established using three-dimensional modeling software, such as Figure 4 As shown, a three-dimensional model is established using modeling software such as ANSYS, ABAQUS or Midas Civil, which will not be described in detail in the embodiments of this application.

[0085] In the above embodiment, in step 400, if Figure 5 As shown, mesh units are divided in the finite element model, and the mesh units include key area refinement units and gradient mesh units. The key area refinement units are located in the stress concentration area and / or expected temperature change area of ​​the concrete box girder structure, and the gradient mesh units gradually increase the mesh density from the edge to the core of the concrete box girder structure.

[0086] Specifically, stress concentration areas include support points, connections, opening edges, or any areas expected to be subjected to high stress. These areas are all key area refinement elements and should use finer meshes. Mesh refinement in these areas helps to more accurately capture the details of stress distribution, reduce local errors, and ensure the reliability of calculation results.

[0087] The expected temperature change areas are specifically, in concrete box girders, temperature changes may occur on the surface (such as temperature differences caused by fire), especially in prestressed concrete structures, there may also be temperature gradients inside due to temperature changes. These areas require fine meshes to simulate accurate changes in the temperature field.

[0088] In addition, the mesh density gradually increases from the boundary to the center of the box girder. This method can balance the calculation accuracy and resource consumption. The mesh at the boundary is coarser to reduce the total number of calculation units, while the mesh is gradually denser when approaching the critical area or the interior of the structure to ensure accurate simulation of important areas. As an alternative implementation, in areas with large geometric changes, such as the transition area from the beam body to the wing plate, a gradient mesh should also be used to adapt to the changes in geometry while maintaining sufficient resolution.

[0089] An exemplary step of dividing the grid units in the embodiment of the present application is as follows:

[0090] Step 401, applying a global grid to set a basic grid density for the entire model;

[0091] Step 402, according to the design and analysis requirements, clarify the key area refinement units such as the stress concentration area and the expected temperature change area;

[0092] Step 403, refine the cells in the key areas to manually or automatically set a finer mesh, and use the software's gradient mesh function in other areas to ensure a smooth transition of mesh density.

[0093] Step 404, by analyzing the preliminary results, the mesh is further calibrated and adjusted, especially in areas where stress or displacement results are found to be non-convergent.

[0094] In the embodiment of the present application, in step 500, the fire parameters include burning materials, burning positions and burning time. Applying the fire parameters to the finite element model to perform temperature field analysis on the concrete box girder includes:

[0095] Step 501, defining combustion materials, wherein different combustion materials correspond to different maximum heat release rates and heat source growth times;

[0096] Step 502, defining a combustion position, determining a longitudinal distance, a transverse distance, and a vertical distance from the combustion material to the concrete box beam according to the corresponding combustion position in the concrete box beam, and inputting the longitudinal distance, the transverse distance, and the vertical distance from the combustion material to the concrete box beam and the vertical distance from the bottom of the beam into a finite element model;

[0097] Step 503, defining the combustion time, and inputting the combustion time into the finite element model.

[0098] Table 1 is a growth data table of different fire combustion sources. It can be seen from Table 1 that the maximum heat release rate HRR corresponding to different combustion materials max Different from the heat source growth time, therefore, by setting fire parameters under different conditions, the combustion conditions of the concrete box girder structure under different fire scenarios can be flexibly simulated, thereby further improving the authenticity and accuracy of the simulation data.

[0099] Table 1 Fire source growth models used for different fires

[0100] Combustion <![CDATA[HRR max (KW)]]> Heat source growth time t(s) Gas 5000 163 wood 1600 185 coal 2000 207 Fuel vehicle 10000 231

[0101] Figure 7 It is a cloud map of the temperature field. For example, the fire exposure time is set to 30min, 60min, 90min, and 120min. The burning position is the bottom of the concrete box beam structure, and the burning material is wood. The cross-sectional diagrams of the four cross-sections in the construction design drawing of the concrete box beam structure are selected for data simulation, and the relevant data shown in Figure 1 to Figure 2 are obtained.

[0102] in, Figure 8 The temperature field simulation results of the cross section of Section I under different scenarios with fire exposure time of 30min, 60min, 90min and 120min. The dashed boxes of different colors in the figure represent the partial enlargement of different areas of the concrete box girder structure, and the color distribution in the dashed boxes corresponds to different temperature ranges.

[0103] Fig. 9 The temperature field simulation results of the cross section of section II under different scenarios of fire exposure time of 30min, 60min, 90min and 120min. The dashed boxes of different colors in the figure represent the partial enlargement of different areas of the concrete box girder structure, and the color distribution in the dashed boxes corresponds to different temperature ranges.

[0104] Fig.10 The temperature field simulation results of the cross section of section III under different scenarios with fire exposure time of 30min, 60min, 90min and 120min. The dashed boxes of different colors in the figure represent the partial enlargement of different areas of the concrete box girder structure, and the color distribution in the dashed boxes corresponds to different temperature ranges.

[0105] Fig.11 The temperature field simulation results of the cross section of section IV under different scenarios with fire exposure time of 30min, 60min, 90min and 120min. The dashed boxes of different colors in the figure represent the partial enlargement of different areas of the concrete box girder structure, and the color distribution in the dashed boxes corresponds to different temperature ranges.

[0106] Since the bottom fire situation of the concrete box beam structure is simulated in the embodiments of the present application, the top surface of the beam is not exposed to fire, and the bottom surface of the beam is directly exposed to fire, and heat transfer occurs in the concrete cross section. Fig.12 The four sections shown are used to check the temperature distribution on the concrete surface and inside the concrete.

[0107] in, Fig.12 The figure shows the temperature distribution of four corresponding sections in different scenarios with fire exposure time of 30min, 60min, 90min and 120min. It can be seen from the figure that the actual high temperature distribution condition of section III is the most severe.

[0108] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the invention disclosed herein. The present application is intended to cover any modification, use or adaptation of the present application, which follows the general principles of the present application and includes common knowledge or customary techniques in the art that are not disclosed in the present application. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present application are indicated by the following claims.

[0109] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A method for analyzing the temperature field of a concrete box girder structure under high temperature in a fire, characterized in that: include: Determine the constitutive relationship of heat transfer of concrete materials in concrete box girder structures; Determining thermal parameters of the concrete material in the concrete box girder structure, wherein the thermal parameters include thermal conductivity, specific heat capacity, density and elastic modulus of the concrete material; Establishing a spatial finite element model of the concrete box girder, and assigning values ​​to concrete materials in different regions of the finite element model with reference to the thermal parameters and the heat transfer constitutive relationship; Dividing mesh elements in the finite element model; Fire parameters are determined, applied to the finite element model, and temperature field analysis of the concrete box girder is performed.

2. The method for analyzing the temperature field of a concrete box girder structure under high temperature in a fire according to claim 1 is characterized in that: The heat transfer constitutive relation of the concrete material includes the surface heat conduction relation of the concrete material, and the surface heat conduction relation of the concrete material is calculated by the following formula: Where Q is the heat transferred from the outside; k is the thermal conductivity; T is the temperature; n is the external normal of the hot surface; Г is the heat transfer surface; h c is the convection coefficient; ε is the radiation coefficient; σ=5.67×10 -8 W / (m 2 ·K 4 );T f is the ambient temperature; T is the surface temperature of the concrete box girder.

3. The method for analyzing the temperature field of a concrete box girder structure under high temperature in a fire according to claim 2 is characterized in that: The heat transfer constitutive relation of the concrete material includes the internal heat conduction relation of the concrete material, and the internal heat conduction relation of the concrete material is calculated by the following formula: Among them, ρ is density, c is specific heat capacity, t is time; q is the heat generated inside the material.

4. The method for analyzing the temperature field of a concrete box girder structure under high temperature in a fire according to claim 1 is characterized in that: The step of establishing the spatial finite element model of the concrete box girder comprises: Defining the geometric structure, and creating a geometric model of the concrete box girder according to the dimensions in finite element software; Set up the analysis steps and define the interaction of the concrete box beam.

5. The method for analyzing the temperature field of a concrete box girder structure under high temperature in a fire according to claim 4 is characterized in that: In the analysis step, the duration is set to 7200 seconds; in the interaction, the bottom surface of the concrete box girder is on fire.

6. The method for analyzing the temperature field of a concrete box girder structure under high temperature in a fire according to claim 1 is characterized in that: The assigning of values ​​of concrete materials in different regions of the finite element model with reference to the thermal parameters and the heat transfer constitutive relationship includes: According to the thermal parameters and the heat transfer constitutive relationship, section properties of the concrete material in different regions are created in the finite element model.

7. The method for analyzing the temperature field of a concrete box girder structure under high temperature in a fire according to claim 1 is characterized in that: The dividing of mesh units in the finite element model comprises: The grid units include key area refinement units and gradual grid units. The key area refinement units are located in stress concentration areas and / or expected temperature change areas of the concrete box girder structure. The gradual grid units gradually increase grid density from the edge to the core of the concrete box girder structure.

8. The method for analyzing the temperature field of a concrete box girder structure under high temperature in a fire according to claim 7 is characterized in that: The stress concentration area includes the connection joint area of ​​the concrete box beam and the peripheral area of ​​the diaphragm.

9. The method for analyzing the temperature field of a concrete box girder structure under high temperature in a fire according to claim 1 is characterized in that: The fire parameters include burning material, burning location and burning time.

10. The method for analyzing the temperature field of a concrete box girder structure under high temperature in a fire according to claim 9, characterized in that: The step of applying the fire parameters to the finite element model to perform temperature field analysis on the concrete box girder includes: Defining combustion materials, wherein different combustion materials correspond to different maximum heat release rates and heat source growth times; Define a combustion position, determine the longitudinal distance, transverse distance and vertical distance of the combustion material from the concrete box beam according to the corresponding combustion position in the concrete box beam, and input the longitudinal distance, transverse distance and vertical distance of the combustion material from the concrete box beam to the finite element model; A burn time is defined and input into the finite element model.

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