Method for analyzing transient stress field of concrete box girder under action of sunlight

Abstract

The invention discloses a method for analyzing a transient stress field of a concrete box girder under the action of sunlight, which comprises the following steps of: S1, establishing a finite element model of the concrete box girder, and dividing grid units; s2, acquiring meteorological parameters such as wind speed, daily maximum temperature, daily minimum temperature, atmospheric transparency coefficient and the like; s3, applying materials and meteorological parameters to the finite element model, and calculating a sunlight temperature field of the box girder; s4, the transient temperature field obtained through calculation in the S3 serves as a load to be imported into the box girder structure finite element model; and S5, calculating to obtain stress field changes of the box girder in one day, wherein the stress field changes comprise transverse temperature stress, longitudinal temperature stress, vertical temperature stress and the like of the box girder. The invention provides a method for calculating the sunlight temperature field of the concrete box girder according to weather conditions, and the method can be used for calculating daily periodic deformation of the box girder.

Description

Technical Field

[0001] The invention relates to the field of temperature field, and in particular to a method for analyzing transient stress field of a concrete box beam under sunlight. Background Art

[0002] With the development of economy, bridge construction has advanced by leaps and bounds. Various types of bridges span rivers, valleys and obstacles. Among them, concrete box girder bridges are popular because of their light structure and easy assembly. As the service life of bridges increases, concrete box girder bridges will suffer different degrees of bridge damage. After a lot of tracking and analysis, it is found that complex and changeable climate is the key factor causing concrete box girder bridge damage.

[0003] The reason why complex and changeable climates can cause damage to concrete box girder bridges is mainly because complex and changeable climates can cause uneven temperature distribution in the structure of concrete box girder bridges. In order to ensure the strength and stability of concrete box girder bridges and improve their service life, it is of great significance to conduct in-depth research on the temperature field and temperature effect of concrete box girder bridges. However, the temperature effect of concrete box girder bridges is relatively complex, and there are many factors that affect the temperature field. How to conduct long-term and effective real-time monitoring of the temperature field of concrete box girder bridges is a technical problem that technicians in this field need to solve urgently.

[0004] In the natural environment, concrete box girders are affected by direct solar radiation, scattered radiation, atmospheric back radiation and surface environmental radiation. The superposition of multiple effects makes the temperature field distribution of concrete box girders very complex. For a long time, the temperature field has been mainly obtained by actual measurement, which requires a large number of buried sensors and is costly.

[0005] A transient stress field analysis method for concrete box girders under sunlight is needed to solve the above problems. Summary of the invention

[0006] The present invention aims to solve the problem in the prior art that concrete box girders in natural environments are affected by direct solar radiation, scattered radiation, atmospheric back radiation and surface environmental radiation. The superposition of multiple effects makes the temperature field distribution of concrete box girders very complicated. For a long time, the temperature field has been mainly obtained by actual measurement, which requires a large number of buried sensors and is costly. A method for analyzing the transient stress field of concrete box girders under sunlight is provided to solve the above problems.

[0007] The present invention provides a method for analyzing the transient stress field of a concrete box beam under sunlight, comprising the following steps:

[0008] S1. Establish a finite element model of the concrete box girder in the finite element software;

[0009] S2, dividing the finite element model into mesh units;

[0010] S3, obtaining environmental parameters according to the actual environmental conditions of the concrete box girder;

[0011] S4, substituting the material parameters and environmental parameters of the concrete box girder into the finite element model to calculate the sunshine temperature field of the box girder;

[0012] S5. Import the transient solar temperature field as a load into the finite element model of the box girder structure;

[0013] S6. According to the time sequence, calculate the stress field variation parameters of the box girder during the day.

[0014] The method for analyzing the transient stress field of a concrete box girder under sunlight described in the present invention is, as a preferred embodiment, the specific steps of calculating the sunlight temperature field of the box girder in step S4 include:

[0015] Calculate the thermal load, thermal conduction differential equation and thermal boundary conditions of the box girder respectively;

[0016] Among them, the thermal load calculation formula of the box girder is as follows:

[0017] I s =I d +I h ;

[0018] I d =I0P 1 / sinh ;

[0019]

[0020] Where Is is the solar radiation reaching the concrete surface, Id is the normal direct radiation, Ih is the horizontal scattered radiation, and P is the atmospheric composite transparency coefficient; q a is the radiation absorption coefficient of water vapor, ozone, oxygen and hydrosol, h is the solar altitude angle, and I0 is the solar constant;

[0021] The calculation formula of the thermal conduction differential equation of the box girder is as follows:

[0022]

[0023] Where T is the temperature function at a certain position of the structure; τ, x, y, z are the independent variables of T, representing time and coordinate values ​​respectively; ρ is the structure density; c is the structure specific heat capacity; λ is the thermal conductivity;

[0024] The thermal boundary condition formula of the box girder is as follows:

[0025]

[0026] Where Γ represents the boundary of the object; n represents the direction of the outer normal of the boundary Γ; h represents the surface heat transfer coefficient of the heat exchange between the boundary of the object and the surrounding fluid; Ta represents the temperature of the fluid; q(x, y, τ) represents the heat flux density flowing from the outside into the object through the boundary;

[0027] In the mesh of the finite element model of the box girder, the thermal load is applied by applying heat flux density on the concrete surface. The thermal load is transferred inside the concrete according to the heat conduction differential equation. The thermal boundary condition is applied to the concrete surface of the beam body. The equations are solved simultaneously. The formula is as follows:

[0028] I s =I d +I h ;

[0029]

[0030] The temperature field of the concrete box girder that changes with time is obtained.

[0031] The method for analyzing the transient stress field of a concrete box girder under sunlight described in the present invention is, as an optimal mode, the stress field variation parameters include the transverse temperature stress of the box girder, the longitudinal temperature stress of the box girder and the vertical temperature stress of the box girder.

[0032] The method for analyzing the transient stress field of a concrete box girder under sunlight described in the present invention is, as a preferred embodiment, the environmental parameters include wind speed, daily maximum temperature, daily minimum temperature, and atmospheric transparency coefficient.

[0033] The method for analyzing the transient stress field of a concrete box beam under sunlight described in the present invention is, as a preferred embodiment, a specific method for changing the stress field parameters in step S6 is:

[0034] The box girder temperature field is calculated and recorded in chronological order for 24 hours a day.

[0035] The transverse temperature stress of the top plate at the center line of the box girder is obtained through finite element calculation, and the temperature field is imported into the structural calculation module to calculate the stress field of the box girder;

[0036] Among them, the calculation method of the transverse temperature stress of the top plate at the center line of the box girder is as follows:

[0037] σ y = k(σ y0 +σ y1 ), k = 2.134;

[0038]

[0039] The beneficial effects of the present invention are as follows:

[0040] This method provides a method for calculating the sunlight temperature field of concrete box girders based on weather conditions, which can be used to calculate the daily periodic deformation of box girders. It can effectively reflect the actual conditions of the temperature field of more complex concrete box girders caused by the superposition of multiple effects, reduce the need for actual measurement, reduce the need for pre-embedded sensors, improve the integrity of the box girder, and reduce maintenance and monitoring costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a flow chart of a method for analyzing transient stress field of concrete box beams under sunlight;

[0042] Figure 2 A method for analyzing the transient stress field of a concrete box girder under sunlight is shown in the schematic diagram of the geometric dimensions of the cross section of the concrete box girder;

[0043] Figure 3 A schematic diagram of the relationship between top plate temperature difference and strain in a method for analyzing transient stress field of concrete box beams under sunlight.

[0044] Figure 4 This is a schematic diagram of the basic structure of the framework of a method for analyzing the transient stress field of concrete box beams under sunlight. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0046] Example 1

[0047] like Figure 1 As shown, a method for analyzing the transient stress field of a concrete box beam under sunlight includes the following steps:

[0048] S1. Establish a finite element model of the concrete box girder in the finite element software;

[0049] S2, dividing the finite element model into mesh units;

[0050] S3, obtaining environmental parameters according to the actual environmental conditions of the concrete box girder;

[0051] S4, substituting the material parameters and environmental parameters of the concrete box girder into the finite element model to calculate the sunshine temperature field of the box girder;

[0052] S5, importing the transient solar temperature field as a load into the finite element model of the box girder structure;

[0053] S6. According to the time sequence, calculate the stress field variation parameters of the box girder during the day.

[0054] The calculation of the box girder solar temperature field includes the following aspects:

[0055] 1. Thermal load

[0056] The heat load, i.e. the solar radiation Is reaching the concrete surface, and the normal direct radiation Id are calculated using formula (2), and the horizontal scattered radiation Ih is calculated as follows:

[0057] I s =I d +I h

[0058] I d =I0P 1 / sinh

[0059]

[0060] Where: P is the atmospheric composite transparency coefficient; q a is the radiation absorption coefficient of water vapor, ozone, oxygen and hydrosol, h is the solar altitude angle, and I0 is the solar constant.

[0061] 2. Thermal differential equation

[0062] The temperature field formed under the influence of various environmental factors is actually a three-dimensional non-steady-state temperature field. The three-dimensional transient heat conduction differential equation is:

[0063]

[0064] Where: T is the temperature function at a certain position of the structure; τ, x, y, z are the independent variables of T, representing time and coordinate values ​​respectively; ρ is the structural density; c is the structural specific heat capacity; λ is the thermal conductivity.

[0065] 3. Thermal boundary conditions

[0066] Under the action of sunlight, the heat exchange between the concrete beam structure and the outside world includes not only the heat flow from solar radiation, but also the convection and radiation heat exchange with the surrounding environment, which is expressed by the following formula.

[0067]

[0068] Where: Γ represents the boundary of the object; n represents the direction of the outer normal of the boundary Γ; h represents the surface heat transfer coefficient of heat exchange between the boundary of the object and the surrounding fluid; Ta represents the temperature of the fluid; q(x, y, τ) represents the heat flux density flowing from the outside into the object through the boundary.

[0069] 4. Temperature field calculation

[0070] A finite element model of a simply supported box girder for high-speed railway is established and meshed. The solar radiation heat load is applied by applying heat flux density on the concrete surface. The heat transfer inside the concrete is calculated according to the thermal conduction differential equation. The thermal boundary conditions are applied to the concrete surface of the beam. By solving the equations simultaneously, the temperature field of the concrete box girder that changes with time can be obtained.

[0071] The specific calculation of stress field variation parameters is as follows:

[0072] 1. Temperature stress calculation

[0073] First, the temperature field of the box girder for 24 hours a day is calculated by finite element thermal analysis, and then the temperature field is imported into the structural calculation module to calculate the stress field of the box girder. The transverse temperature stress of the top plate at the center line of the box girder is obtained by finite element calculation. Compared with the stress calculation method in the specification, the transverse stress distribution of the top plate obtained by this fine finite element simulation method is the same, and the stress value is larger. The stress calculation method in the specification is as follows:

[0074]

[0075] Since the deformation of the top plate does not completely conform to the flat section assumption, and the superposition of temperature effects along the beam width is considered in the finite element calculation, the finite element calculation result is greater than the result of the theoretical formula calculation. Considering the correction of the above influencing factors, a nonlinear correction coefficient k is introduced into the stress calculation method in the specification, and the k value is 2.134. The formula is as follows:

[0076] σ y = k(σ y0 +σ y1 );

[0077] In the above formula, c y =5, E is the elastic modulus of concrete, other parameters refer to Figures 2 to 4 As shown, the coefficients are calculated as follows:

[0078]

[0079] b' = b - δ3; A1=δ1;A2=δ2

[0080]

[0081] It can be seen that the finite element calculation results are in good agreement with the corrected calculation results.

[0082] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for analyzing transient stress field of concrete box beams under sunlight, characterized by: The following steps are involved: S1. Establish a finite element model of the concrete box girder in the finite element software; S2, dividing the finite element model into mesh units; S3, obtaining environmental parameters according to the actual environmental conditions of the concrete box girder; S4, substituting the material parameters and environmental parameters of the concrete box girder into the finite element model to calculate the sunshine temperature field of the box girder; S5, importing the transient solar temperature field as a load into the finite element model of the box girder structure; S6. According to the time sequence, calculate the stress field variation parameters of the box girder during the day.

2. The method for analyzing transient stress field of concrete box beams under sunlight according to claim 1 is characterized in that: The specific steps of calculating the box girder solar temperature field described in step S4 include: Calculate the thermal load, thermal conduction differential equation and thermal boundary conditions of the box girder respectively; Among them, the thermal load calculation formula of the box girder is as follows: I s =I d +I h ; I d =I0P 1 / sinh ; Where Is is the solar radiation reaching the concrete surface, Id is the normal direct radiation, Ih is the horizontal scattered radiation, and P is the atmospheric composite transparency coefficient; q a is the radiation absorption coefficient of water vapor, ozone, oxygen and hydrosol, h is the solar altitude angle, and I0 is the solar constant; The calculation formula of the thermal conduction differential equation of the box girder is as follows: Where T is the temperature function at a certain position of the structure; τ, x, y, z are the independent variables of T, representing time and coordinate values ​​respectively; ρ is the structure density; c is the structure specific heat capacity; λ is the thermal conductivity; The thermal boundary condition formula of the box girder is as follows: Where Γ represents the boundary of the object; n represents the direction of the outer normal of the boundary Γ; h represents the surface heat transfer coefficient of the heat exchange between the boundary of the object and the surrounding fluid; Ta represents the temperature of the fluid; q(x, y, τ) represents the heat flux density flowing from the outside into the object through the boundary; In the mesh of the finite element model of the box beam, the thermal load is applied by applying heat flux density on the concrete surface. The thermal load is transferred inside the concrete according to the heat conduction differential equation. The thermal boundary condition is applied on the concrete surface of the beam body. The equations are solved simultaneously. The formula is as follows: I s =I d +I h ; The temperature field of the concrete box girder that changes with time is obtained.

3. The method for analyzing transient stress field of concrete box beam under sunlight according to claim 1 is characterized by: The stress field variation parameters include the box girder transverse temperature stress, the box girder longitudinal temperature stress and the box girder vertical temperature stress.

4. The method for analyzing transient stress field of concrete box beam under sunlight according to claim 1 is characterized by: The environmental parameters include wind speed, daily maximum temperature, daily minimum temperature, and atmospheric transparency coefficient.

5. The method for analyzing transient stress field of concrete box beam under sunlight according to claim 3 is characterized by: The specific method of changing the stress field parameters in step S6 is: The box girder temperature field is calculated and recorded in chronological order for 24 hours a day. The transverse temperature stress of the top plate at the center line of the box girder is obtained through finite element calculation, and the temperature field is imported into the structural calculation module to calculate the stress field of the box girder; Among them, the calculation method of the transverse temperature stress of the top plate at the center line of the box girder is as follows: s y =k(σ y0 +s y1 ), k=2.134;

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