Corrosion deterioration analysis method for cracked reinforced concrete beam in carbonization environment

Abstract

The invention discloses a corrosion degradation analysis method for a cracked reinforced concrete beam in a carbonization environment, which comprises the following steps: dividing the service time of the reinforced concrete beam, and determining the sequence of calculation time points; establishing a reinforced concrete beam load field entity finite element model, calculating crack distribution and width of a beam body at the time point ti under the load effect, and calculating a crack width field variable; establishing a concrete beam carbon dioxide diffusion field analysis model, importing a crack width field variable at a ti time point, and calculating and outputting a carbonization field variable of the concrete beam at the end of ti + dt time; establishing a reinforced concrete beam oxygen diffusion field analysis model, importing a crack width field variable and a carbonization field variable, and calculating and outputting a steel bar corrosion field variable at the end of the ti + dt time; judging whether the calculation time point reaches the total service time t or not; updating a calculation time point ti + 1 = ti + dt, and taking a model calculation result of a previous time point as an initial state; and extracting deformation and crack results of each time point in the service time of the reinforced concrete beam to obtain a deformation and crack degradation rule.

Description

Technical Field

[0001] The invention relates to the field of bridge degradation analysis, and in particular to a method for analyzing corrosion degradation of cracked reinforced concrete beams under a carbonization environment. Background Art

[0002] Reinforced concrete beams are widely used in railways, highways and civil buildings. The corrosion and deterioration of reinforced concrete beams in a carbonized environment is one of the most common durability diseases, which has an important impact on the service performance and service life of the structure.

[0003] In a carbonized environment, the acidic gas carbon dioxide in the atmosphere will continuously penetrate into the interior of the beam through the pores of the concrete, react with the alkaline substances inside the concrete to reduce the alkalinity inside the beam, and cause the passivation film on the surface of the steel bar to be destroyed, and then electrochemical corrosion occurs. In the design of reinforced concrete beams, a certain thickness of concrete protective layer is generally set around the steel bar to ensure that the carbonization depth during the service life does not exceed the thickness of the concrete protective layer to protect the steel bar from corrosion. However, since reinforced concrete beams are usually in a cracked working state during normal use, the cracks provide accelerated corrosion pathways for substances such as carbon dioxide, oxygen and moisture, resulting in carbonization of concrete at the cracks and early corrosion of steel bars. The reduction in effective area, bond degradation and rust expansion caused by steel bar corrosion will cause further development of beam cracks, and the development of cracks will accelerate environmental erosion and steel bar corrosion. There is a significant coupling effect between carbonization environmental erosion and crack development.

[0004] At present, the empirical formula method is generally used to directly evaluate the carbonization depth and steel corrosion rate of reinforced concrete beams, without considering the influence of crack state on concrete carbonization and steel corrosion, and the corrosion degradation assessment of cracked concrete beams is inaccurate. In terms of simulation analysis models, a two-dimensional local model with "preset cracks" is generally used to analyze the influence of cracking on the carbonization depth of concrete. There are two main deficiencies: 1) Only the unidirectional effect of cracks on environmental erosion is considered, and the coupling effect between environmental erosion and crack development is not considered; 2) It can only be used for local analysis of concrete beam sections, and cannot analyze the corrosion degradation of the overall beam structure. The existing simulation analysis methods are difficult to reflect the coupling relationship between crack development and environmental erosion of reinforced concrete beams under carbonization environments, and the evaluation results are different from the actual situation.

[0005] A corrosion degradation analysis method for cracked reinforced concrete beams in a carbonized environment is needed to solve the above problems. Summary of the invention

[0006] The present invention aims to solve the problem that the conventional method generally adopts the empirical formula method to directly evaluate the carbonization depth and steel corrosion rate of reinforced concrete beams, but does not consider the influence of crack state on concrete carbonization and steel corrosion, and the corrosion degradation evaluation of cracked concrete beams is inaccurate; in terms of simulation analysis models, a two-dimensional local model with "preset cracks" is generally used to analyze the influence of cracking on the carbonization depth of concrete, which has two main deficiencies: only the unidirectional influence of cracks on environmental erosion is considered, and the coupling effect between environmental erosion and crack development is not considered; it can only be used for local analysis of concrete beam cross-sections, and the corrosion degradation of the overall beam structure cannot be analyzed. The existing simulation analysis method is difficult to reflect the coupling relationship between the crack development and environmental erosion of reinforced concrete beams under carbonization environment, and the evaluation results are different from the actual situation. A corrosion degradation analysis method for cracked reinforced concrete beams under carbonization environment is provided to solve the above problems.

[0007] The present invention provides a method for analyzing corrosion degradation of cracked reinforced concrete beams under a carbonization environment, comprising the following steps:

[0008] S1. Assume that the total service time of reinforced concrete beam is t years, and divide the total service time t into n segments with time intervals of dt years to obtain the calculation time point sequence t i (i=0~n), satisfying t i+1 =t i +dt;

[0009] S2. Establish a solid finite element model of the reinforced concrete beam load field and calculate t i The crack distribution and width of the beam under load at a certain time point, and the calculation of the crack width field variable Field_Crack;

[0010] S3. Establish a carbon dioxide diffusion field analysis model for concrete beams and import t i The crack width field variable Field_Crack at the time point is calculated and output t i +dt Carbonization field variable Field_Carbon of the concrete beam at the end of time;

[0011] S4. Establish the oxygen diffusion field analysis model for reinforced concrete beams, import the crack width field variable Field_Crack and the carbonization field variable Field_Carbon, and calculate the output t i +Rebar corrosion field variable Field_Corr at the end of time dt;

[0012] S5, determine whether the calculated time point reaches the total service time t, if so, proceed to step S7, otherwise proceed to step S6;

[0013] S6. Update calculation time point t i+1 =ti +dt, the model calculation result at the previous time point is taken as the initial state, and step S2 is performed;

[0014] S7. Extract the deformation and crack results of the reinforced concrete beam at each calculation time point within the service time 0 to t, and obtain the deformation and crack degradation law of the beam body.

[0015] The present invention provides a method for analyzing corrosion degradation of cracked reinforced concrete beams under carbonization environment. As a preferred embodiment, step S2 specifically includes:

[0016] Constructing a crack analysis model, which includes concrete entity units, steel bar units and steel bar rust expansion layer units;

[0017] The concrete solid unit adopts three-dimensional eight-node solid unit simulation to calculate the tensile constitutive equation of concrete. The formula is as follows:

[0018]

[0019] Calculate the crack width using the following formula:

[0020] w cr =(ε c -ε e )·L e ;

[0021] Among them, E c is the elastic modulus of concrete, ε c is the tensile strain of concrete, ε cr is the peak tensile strain of concrete, ε e is the elastic tensile strain of concrete, σ c is the tensile stress of concrete, f t is the tensile strength of concrete, w cr is the concrete crack width, L e is the characteristic length of the concrete unit in the cracking direction;

[0022] The reinforcement bar element is simulated by a two-node bar element, and the unit section properties are assigned according to the actual cross-sectional area of ​​the reinforcement;

[0023] Define the field variable subroutine at the unit integration point, calculate and apply the effective area reduction factor according to the steel bar corrosion rate;

[0024] The steel bar expansion layer unit is modeled using Cohesive units according to the actual position and size of the steel bars.

[0025] The steel bar section is divided into 4 units, with a common node at the center of the section circle; the length direction of the steel bar is taken as the axial direction, the normal direction of the outer surface of the steel bar is taken as the normal direction, the unit axial stiffness is taken as 0, and the normal and tangential stiffness are taken according to the steel bar elastic modulus;

[0026] Define the expansion subroutine in the element normal direction, calculate and apply the expansion strain according to the steel corrosion rate; define the field variable subroutine in the element tangential direction, calculate and apply the shear modulus reduction factor according to the steel corrosion rate;

[0027] An embedded connection is set between the internal nodes of the steel bar unit and the steel bar expansion layer unit, and an embedded connection is set between the external nodes of the steel bar expansion layer unit and the concrete entity unit;

[0028] Set the static analysis step, apply load on the reinforced concrete beam entity unit model, solve the unit tensile strain, calculate the crack width of the concrete beam entity unit through the concrete entity unit, and output the crack width result w of the concrete beam entity unit cr to the crack width field variable, denoted as Field_Crack;

[0029] The crack width field variable data include: unit number, integration point number, integration point coordinates, and crack width.

[0030] The present invention discloses a method for analyzing corrosion degradation of a cracked reinforced concrete beam under a carbonization environment. As a preferred embodiment, step S3 specifically includes the following steps:

[0031] According to the actual geometric dimensions of the concrete beam, the solid unit is used to model the carbon dioxide diffusion field analysis model, and the unit type is a three-dimensional 8-node transfer unit;

[0032] In the USDFLD field variable subroutine at the unit integration point, the crack width field variable Field_Crack is read to calculate the magnification factor f(w) of the diffusion effect at each integration point of the unit. cr ), the formula is as follows:

[0033]

[0034] Among them, L e is the unit characteristic length, κ is the ratio of the crack diffusion coefficient to the diffusion coefficient in concrete, and κ is taken as 1000;

[0035] According to the concrete material mix parameters, the diffusion coefficient material property is assigned to the unit to calculate the concrete porosity ε p , the formula is as follows:

[0036]

[0037] Where w is the water content of concrete per unit volume (kg / m 3 ),ρ w is the water density (kg / m 3 ), c is the cement content per unit volume of concrete (kg / m 3 ),ρ cis the cement density (kg / m 3 );

[0038] According to the concrete porosity ε p Calculate the diffusion coefficient D of carbon dioxide at the unit integration point CO2 , the formula is as follows:

[0039]

[0040] Wherein, RH is the relative humidity of the environment (%);

[0041] Apply a carbon dioxide concentration boundary C on the interface between the concrete beam and the atmosphere CO2 , the mass diffusion module is used for analysis, the total diffusion time is set as dt, and the carbon dioxide diffusion flux and concentration distribution in the concrete beam body within the diffusion time dt are calculated;

[0042] Extract the cumulative diffusion flux J at each unit integration point within the time dt CO2 (t c ), calculate the carbonization degree index I c , the formula is as follows:

[0043]

[0044] If I c >1, the complete carbonization time t c Stored as the carbonization field variable Field_Carbon; otherwise, the complete carbonization time t c Stored as carbonization field variable Field_Carbon;

[0045] The data of the carbonization field variable Field_Carbon include: unit number, integration point number, integration point coordinates, complete carbonization time t c .

[0046] The present invention provides a method for analyzing corrosion degradation of cracked reinforced concrete beams under carbonization environment. As a preferred embodiment, step S4 specifically includes:

[0047] An oxygen diffusion field analysis model is established. The oxygen diffusion field analysis model includes concrete units and steel bar units. Concrete beams and steel bars are modeled using solid units according to actual geometric dimensions, and the steel bar units are built into concrete units.

[0048] At the unit integration point, the USDFLD field variable subroutine reads the crack width field variable Field_Crack and assigns it to the concrete unit, and calculates the magnification factor f(w) of the diffusion effect at each integration point of the unit. cr ); read the carbonization field variable Field_Carbon and assign it to the steel bar unit using the nearest coordinate mapping method;

[0049] According to the concrete material mix parameters, the diffusion coefficient material property is assigned to the concrete unit, and the diffusion coefficient D of oxygen at the unit integration point is calculated. O2 , the formula is as follows:

[0050]

[0051] Apply an oxygen concentration boundary C on the interface between the concrete beam and the atmosphere. O2,s , use the mass diffusion module for analysis, set the total diffusion time as dt, and calculate t i ~t i The oxygen concentration C at the integration point in the steel bar unit during +dt time O2 (t);

[0052] At the steel unit integration point, the concrete resistivity r is calculated using the following formula:

[0053] r=100(1-RH) 2 +40;

[0054] The corrosion current intensity i(t) is calculated based on the concrete resistivity r, and the formula is as follows:

[0055]

[0056] At the steel bar unit integration point, the steel bar volume corrosion rate γ is calculated using the following formula:

[0057]

[0058] Where A is the atomic weight of Fe element, A=56 g / mol, z is the valence of the corrosion electrode iron (z=2), F is the Faraday constant, F=96500 C / mol, ρ is the steel density, ρ=7.86×10 -3 g / mm 3 , R is the radius of the steel bar section (mm);

[0059] At the reinforcement unit integration point, calculate the reinforcement effective area reduction factor κ r , the formula is as follows:

[0060] κ r =1-αγ;

[0061] Calculation of the bond degradation coefficient κ between steel bars and concrete p , the formula is as follows:

[0062]

[0063] Calculation of steel bar expansion strain ε f , the formula is as follows:

[0064]

[0065] Wherein, α is the volume expansion coefficient of the corrosion product, and the value range is α=2~4;

[0066] Store the steel bar corrosion field variable, recorded as Field_Corr. The steel bar corrosion field variable data includes: unit number, integration point number, integration point coordinates, effective area reduction coefficient κ r , Adhesion degradation coefficient κ p 、Rebar expansion strain ε f .

[0067] The present invention provides a method for analyzing corrosion degradation of cracked reinforced concrete beams under carbonization environment. As a preferred embodiment, step S6 specifically includes:

[0068] For the load field crack analysis model, t i The result of the load field crack analysis model at the time point is the initial state, and the restart analysis is set; read the steel bar corrosion field variable Field_Corr, and set κ r Given the effective area reduction of the steel bar element due to corrosion, κ p Assign the rust expansion layer unit to consider the interface adhesion degradation caused by corrosion, and change ε f Assign the rust-expansion layer unit to consider the expansion deformation caused by corrosion; update the crack width field variable Field_Crack after considering the steel bar corrosion effect;

[0069] The carbon dioxide diffusion field analysis model is based on t i The carbon dioxide concentration distribution result at the end of +dt time is the initial state, and the analysis is restarted; the updated crack width field variable Field_Crack is read, and the concrete carbonization field variable Field_Carbon after the output dt time increment is updated;

[0070] The oxygen diffusion field analysis model is based on t i The oxygen concentration and steel corrosion rate results at the end of +dt time are the initial state, and the restart analysis is set; read the updated crack width field variable Field_Crack and concrete carbonization field variable Field_Carbon, and update the steel corrosion field variable Field_Corr after the output dt time increment.

[0071] The beneficial effects of the present invention are as follows:

[0072] 1) The analysis method of the present invention can realize the comprehensive consideration of the strong coupling effect between the carbonization environment and the beam body cracks and the time-dependent dynamic changes, the accelerated diffusion effect of the beam body cracks on carbon dioxide and oxygen, and the development of beam body cracks caused by steel corrosion, which is more consistent with the actual deterioration of reinforced concrete beams;

[0073] 2) Compared with the existing local cross-section analysis method, the present invention can better consider the overall stress characteristics of the beam structure, and can directly obtain macroscopic performance indicators such as overall structural deformation and cracks, which is more accurate and convenient for evaluating the overall performance degradation of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 A flow chart of the corrosion degradation analysis method for cracked reinforced concrete beams in a carbonized environment. DETAILED DESCRIPTION

[0075] 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.

[0076] Example 1

[0077] like Figure 1 As shown, a corrosion degradation analysis method for cracked reinforced concrete beams under carbonization environment includes the following main steps:

[0078] The service time of reinforced concrete beams is divided to determine the calculation time point sequence. Assuming that the total service time of reinforced concrete beams is t = 10 years, the total service time t is divided into n segments with a time interval of dt = 1 year, and the calculation time point sequence t is obtained. i (i=0~n), satisfying t i+1 =t i +dt.

[0079] Establish a solid finite element model of the reinforced concrete beam load field and calculate t i The crack distribution and width of the beam under load at a certain time point are calculated and output as the crack width field variable, recorded as Field_Crack.

[0080] 1) The crack analysis model consists of three types of units: concrete solid unit, steel bar unit and rust expansion layer unit.

[0081] 2) The concrete beam is simulated by a three-dimensional eight-node solid element, and the damage plasticity constitutive model is used to analyze the cracking and post-crack nonlinear behavior of the beam. The tensile constitutive relationship equation of concrete and the crack width calculation formula are as follows.

[0082]

[0083] wcr =(ε c -ε e )·L e

[0084] In the formula, E c is the elastic modulus of concrete, ε c is the tensile strain of concrete, ε cr is the peak tensile strain of concrete, ε e is the elastic tensile strain of concrete, σ c is the tensile stress of concrete, f t is the tensile strength of concrete, w cr is the concrete crack width, L e is the characteristic length of the concrete element in the cracking direction.

[0085] 3) The steel bars are simulated by two-node bar elements, and the ideal elastic-plastic constitutive relation is adopted. The unit section properties are assigned according to the cross-sectional area of ​​the steel bars. The field variable subroutines are defined at the unit integration points, and the effective area reduction coefficient is calculated and applied according to the steel bar corrosion rate.

[0086] 4) The rust-expansion layer unit is modeled using Cohesive units according to the actual position and size of the steel bars. The steel bar section is divided into four units, and a common node is set at the center of the section. The length direction of the steel bar is taken as the axial direction, the normal direction of the outer surface of the steel bar is taken as the normal direction, the unit axial stiffness is taken as 0, and the normal and tangential stiffness are taken according to the steel bar elastic modulus. An expansion subroutine is defined in the unit normal direction, and the expansion strain is calculated and applied according to the steel bar corrosion rate. A field variable subroutine is defined in the unit tangential direction, and the shear modulus reduction factor is calculated and applied according to the steel bar corrosion rate.

[0087] 5) Embedded connections are set between the internal nodes of the reinforcement bar unit and the rust expansion layer unit, and embedded connections are set between the external nodes of the rust expansion layer unit and the concrete entity unit.

[0088] 6) Set up a static analysis step, apply loads to the reinforced concrete beam entity unit model, solve for the unit tensile strain, calculate the crack width of the concrete beam entity unit, and output the crack width result w of the concrete beam entity unit. cr To the crack width field variable, recorded as Field_Crack, the data includes: unit number, integration point number, integration point coordinates, crack width.

[0089] Establish a carbon dioxide diffusion field analysis model for concrete beams and import t i The crack width field variable Field_Crack at the time point is calculated and output t i The carbonization field variable of the concrete beam at time point +dt is denoted as Field_CarbonTime.

[0090] 1) The carbon dioxide diffusion field analysis model is modeled using solid elements according to the actual geometric dimensions of the concrete beam, and the element type is a three-dimensional 8-node transfer element.

[0091] 2) Define the USDFLD field variable subroutine at the unit integration point, read the crack width field variable Field_Crack, and calculate the magnification of the diffusion effect at the unit integration point.

[0092]

[0093] Among them, f(w cr ) is the magnification of the diffusion effect at the crack, L e is the unit characteristic length, κ is the ratio of the crack diffusion coefficient to the diffusion coefficient in concrete, and κ is taken as 1000.

[0094] 3) According to the concrete material mix parameters, the diffusion coefficient material property is assigned to the unit. The diffusion coefficient of carbon dioxide at the unit integration point is D CO2 The calculation formula is as follows,

[0095]

[0096] Where RH is the relative humidity of the environment (%); ε p is the porosity of concrete, calculated according to the following formula:

[0097]

[0098] Where w is the water content of concrete per unit volume (kg / m 3 ),ρ w is the water density (kg / m 3 ), c is the cement content per unit volume of concrete (kg / m 3 ),ρ c is the cement density (kg / m 3 ).

[0099] 4) Apply a carbon dioxide concentration boundary C on the contact surface between the concrete beam and the atmosphere CO2 =0.03%, the mass diffusion module is used for analysis, the total diffusion time is set to dt = 1 year, and the carbon dioxide diffusion flux and concentration distribution in the concrete beam within the diffusion time of dt = 1 year are calculated.

[0100] 5) Extract the cumulative diffusion flux J at each unit integration point within dt = 1 year CO2 (t c ), calculate the carbonization degree index I c ; when I c >1, output complete carbonization time t cStored as a carbonization field variable, recorded as Field_Carbon, the data includes: unit number, integration point number, integration point coordinates, complete carbonization time t c .

[0101]

[0102] Establish the oxygen diffusion field analysis model of reinforced concrete beams, import the crack width field variable Field_Crack and the carbonization field variable Field_Carbon, and calculate the output t i The steel bar corrosion field variable at the end of time +dt is denoted as Field_Corr.

[0103] 1) The oxygen diffusion field analysis model consists of concrete units and steel units. Concrete beams and steel bars are modeled using solid units according to their actual geometric dimensions, and the steel bar units are built into the concrete units.

[0104] 2) Define the USDFLD field variable subroutine at the unit integration point, read the crack width field variable Field_Crack and assign it to the concrete unit, and calculate the magnification factor f(w) of the diffusion effect at each integration point of the unit. cr ); read the carbonization field variable Field_Carbon and assign it to the steel bar unit using the nearest coordinate mapping method.

[0105] 3) According to the concrete material mix parameters, the diffusion coefficient material property is assigned to the concrete unit. The diffusion coefficient of oxygen at the unit integration point is D O2 The calculation formula is as follows,

[0106]

[0107] 4) Apply oxygen concentration boundary C on the contact surface between the concrete beam and the atmosphere O2,s = 21%, use the mass diffusion module for analysis, set the total diffusion time as dt, and calculate t i ~t i The oxygen concentration C at the integration point in the steel bar unit during +dt time O2 (t).

[0108] 5) Calculate the corrosion current intensity at the steel bar unit integration point.

[0109]

[0110] Where r is the resistivity of concrete (Ω·m), and the calculation formula is as follows:

[0111] r=100(1-RH) 2 +40

[0112] 6) At the steel bar unit integration point, calculate the steel bar volume corrosion rate using the following formula.

[0113]

[0114] Where A is the atomic weight of Fe element, taking A = 56 g / mol, z is the valence of the corrosion electrode iron, taking z = 2, F is the Faraday constant, taking F = 96500 C / mol, ρ is the steel density, taking ρ = 7.86 × 10 -3 g / mm 3 , R is the cross-sectional radius of the steel bar, R=25mm.

[0115] 7) At the steel bar unit integration point, calculate the steel bar effective area reduction factor κ r , the bond degradation coefficient between steel bar and concrete κ p 、Rebar expansion strain ε f .

[0116] κ r =1-αγ

[0117]

[0118] Where α is the volume expansion coefficient of the rust product, and its value range is α=2~4.

[0119] 8) Store the steel bar corrosion field variable, recorded as Field_Corr, the data includes: unit number, integration point number, integration point coordinates, effective area reduction coefficient κ r , Adhesion degradation coefficient κ p 、Rebar expansion strain ε f .

[0120] Update calculation time point t i+1 =t i +dt, take the model calculation result at the previous time point as the initial state, set the restart analysis, and repeat steps 2 to 4 until the calculation time point reaches the total service time t.

[0121] 1) For the load field crack analysis model, t i The result of the load field crack analysis model at the time point is the initial state, and the restart analysis is set; read the steel bar corrosion field variable Field_Corr, and set κ r Given the effective area reduction of the steel bar element due to corrosion, κ p Assign the rust expansion layer unit to consider the interface adhesion degradation caused by corrosion, and change ε f Assign the rust-expansion layer unit to consider the expansion deformation caused by corrosion; update and output the crack width field variable Field_Crack after considering the steel bar corrosion effect.

[0122] 2) Analyze the carbon dioxide diffusion field model with t i The carbon dioxide concentration distribution result at the end of +dt time is the initial state, and the analysis is restarted; the updated crack width field variable Field_Crack is read, and the concrete carbonization field variable Field_Carbon after the output dt time increment is updated.

[0123] 3) Analysis model of oxygen diffusion field, with t i The oxygen concentration and steel corrosion rate results at the end of +dt time are the initial state, and the restart analysis is set; read the updated crack width field variable Field_Crack and concrete carbonization field variable Field_Carbon, and update the steel corrosion field variable Field_Corr after the output dt time increment.

[0124] 4) Repeat steps 2 to 4, with dt = 1 year as the time increment, and gradually perform sequential coupling analysis of the load field, carbon dioxide diffusion field, and oxygen diffusion field until the calculation time point reaches the total service time t.

[0125] The deformation and crack results of reinforced concrete beams at each calculation time point within the service time of 0 to t are extracted to obtain the deformation and crack deterioration law of the beam.

[0126] 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 corrosion degradation of cracked reinforced concrete beams in a carbonized environment, characterized by: The following steps are involved: S1. Assume that the total service time of reinforced concrete beam is t years, and divide the total service time t into n segments with time intervals of dt years to obtain the calculation time point sequence t i (i=0~n), satisfying t i+1 =t i +dt; S2. Establish a solid finite element model of the reinforced concrete beam load field and calculate t i The crack distribution and width of the beam under load at a certain time point, and the calculation of the crack width field variable Field_Crack; S3. Establish a carbon dioxide diffusion field analysis model for concrete beams and import t i The crack width field variable Field_Crack at the time point is calculated and outputted as t i +dt Carbonization field variable Field_Carbon of the concrete beam at the end of time; S4, establish the oxygen diffusion field analysis model of reinforced concrete beam, import the crack width field variable Field_Crack and the carbonization field variable Field_Carbon, calculate and output t i +Rebar corrosion field variable Field_Corr at the end of time dt; S5, determine whether the calculated time point reaches the total service time t, if so, proceed to step S7, otherwise proceed to step S6; S6. Update calculation time point t i+1 =t i +dt, the model calculation result at the previous time point is taken as the initial state, and step S2 is performed; S7. Extract the deformation and crack results of the reinforced concrete beam at each calculation time point within the service time 0 to t, and obtain the deformation and crack degradation law of the beam body.

2. The method for analyzing corrosion degradation of cracked reinforced concrete beams in a carbonized environment according to claim 1, characterized in that: The step S2 specifically includes: Constructing a crack analysis model, wherein the crack analysis model includes a concrete entity unit, a steel bar unit, and a steel bar rust expansion layer unit; The concrete entity unit adopts a three-dimensional eight-node entity unit simulation to calculate the tensile constitutive equation of concrete, and the formula is as follows: Calculate the crack width using the following formula: w cr =(e c -e e )·L e ; Among them, E c is the elastic modulus of concrete, ε c is the tensile strain of concrete, ε cr is the peak tensile strain of concrete, ε e is the elastic tensile strain of concrete, σ c is the tensile stress of concrete, f t is the tensile strength of concrete, w cr is the concrete crack width, L e is the characteristic length of the concrete unit in the cracking direction; The steel bar unit is simulated by a two-node bar unit, and the unit section attribute is assigned according to the actual steel bar cross-sectional area; Define the field variable subroutine at the unit integration point, calculate and apply the effective area reduction factor according to the steel bar corrosion rate; The steel bar rust expansion layer unit is modeled using a cohesive unit according to the actual position and size of the steel bar; The steel bar section is divided into 4 units, with a common node at the center of the section circle; the length direction of the steel bar is taken as the axial direction, the normal direction of the outer surface of the steel bar is taken as the normal direction, the unit axial stiffness is taken as 0, and the normal and tangential stiffness are taken according to the steel bar elastic modulus; Define the expansion subroutine in the element normal direction, calculate and apply the expansion strain according to the steel corrosion rate; define the field variable subroutine in the element tangential direction, calculate and apply the shear modulus reduction factor according to the steel corrosion rate; The inner nodes of the steel bar unit and the steel bar expansion layer unit are provided with an embedded connection, and the outer nodes of the steel bar expansion layer unit and the concrete entity unit are provided with an embedded connection; Set the static analysis step, apply load on the reinforced concrete beam entity unit model, solve the unit tensile strain, calculate the crack width of the concrete beam entity unit through the concrete entity unit, and output the crack width result w of the concrete beam entity unit cr to the crack width field variable, denoted as Field_Crack; The crack width field variable data includes: unit number, integration point number, integration point coordinates, and crack width.

3. The method for analyzing corrosion degradation of cracked reinforced concrete beams under carbonization environment according to claim 2 is characterized in that: The step S3 specifically comprises the following steps: According to the actual geometric dimensions of the concrete beam, the solid unit is used to model the carbon dioxide diffusion field analysis model, and the unit type is a three-dimensional 8-node transfer unit; In the USDFLD field variable subroutine at the unit integration point, the crack width field variable Field_Crack is read to calculate the magnification factor f(w) of the diffusion effect at each integration point of the unit. cr ), the formula is as follows: Among them, L e is the unit characteristic length, κ is the ratio of the crack diffusion coefficient to the diffusion coefficient in concrete, and κ is taken as 1000; According to the concrete material mix parameters, the diffusion coefficient material property is assigned to the unit. Calculation of concrete porosity ε p , the formula is as follows: Where w is the water content of concrete per unit volume (kg / m 3 ),ρ w is the water density (kg / m 3 ), c is the cement content per unit volume of concrete (kg / m 3 ),ρ c is the cement density (kg / m 3 ); According to the concrete porosity ε p Calculate the diffusion coefficient D of carbon dioxide at the unit integration point CO2 , the formula is as follows: Wherein, RH is the relative humidity of the environment (%); Apply a carbon dioxide concentration boundary C on the interface between the concrete beam and the atmosphere CO2 , the mass diffusion module is used for analysis, the total diffusion time is set as dt, and the carbon dioxide diffusion flux and concentration distribution in the concrete beam body within the diffusion time dt are calculated; Extract the cumulative diffusion flux J at each unit integration point within the time dt CO2 (t c ), calculate the carbonization degree index I c , the formula is as follows: If I c >1, the complete carbonization time t c Stored as the carbonization field variable Field_Carbon; otherwise, the complete carbonization time t c Stored as carbonization field variable Field_Carbon; The data of the carbonization field variable Field_Carbon include: unit number, integration point number, integration point coordinates, complete carbonization time t c .

4. The method for analyzing corrosion degradation of cracked reinforced concrete beams in a carbonized environment according to claim 3 is characterized in that: The step S4 specifically includes: Establishing an oxygen diffusion field analysis model, the oxygen diffusion field analysis model includes a concrete unit and a steel unit, the concrete beam and the steel bar are both modeled using solid units according to actual geometric dimensions, and the steel bar unit is built into the concrete unit; In the USDFLD field variable subroutine at the unit integration point, the crack width field variable Field_Crack is read to calculate the magnification factor f(w) of the diffusion effect at each integration point of the unit. cr ); read the carbonization field variable Field_Carbon, and assign it to the steel bar unit using the nearest neighbor coordinate mapping method; According to the concrete material mix parameters, the diffusion coefficient material property is assigned to the concrete unit, and the diffusion coefficient D of oxygen at the unit integration point is calculated. O2 , the formula is as follows: Apply an oxygen concentration boundary C on the interface between the concrete beam and the atmosphere. O2,s , use the mass diffusion module for analysis, set the total diffusion time as dt, and calculate t i ~t i The oxygen concentration C at the integration point in the steel bar unit during +dt time O2 (t); At the steel unit integration point, the concrete resistivity r is calculated using the following formula: r=100(1-RH) 2 +40; The corrosion current intensity i(t) is calculated according to the concrete resistivity r, and the formula is as follows: At the steel bar unit integration point, the steel bar volume corrosion rate γ is calculated using the following formula: Where A is the atomic weight of Fe element, A=56 g / mol, z is the valence of the corrosion electrode iron (z=2), F is the Faraday constant, F=96500 C / mol, ρ is the steel density, ρ=7.86×10 -3 g / mm 3 , R is the radius of the steel bar section (mm); At the reinforcement unit integration point, calculate the reinforcement effective area reduction factor κ r , the formula is as follows: k r =1-ag; Calculation of the bond degradation coefficient κ between steel bars and concrete p , the formula is as follows: Calculation of steel bar expansion strain ε f , the formula is as follows: Wherein, α is the volume expansion coefficient of the corrosion product, and the value range is α=2~4; Store the steel bar corrosion field variable, denoted as Field_Corr, the steel bar corrosion field variable data includes: unit number, integration point number, integration point coordinates, effective area reduction coefficient κ r , Adhesion degradation coefficient κ p 、Rebar expansion strain ε f .

5. The method for analyzing corrosion degradation of cracked reinforced concrete beams in a carbonized environment according to claim 4, characterized in that: The step S6 specifically includes: For the load field crack analysis model, t i The result of the load field crack analysis model at the time point is the initial state, and the restart analysis is set; read the steel bar corrosion field variable Field_Corr, and set κ r Given the effective area reduction of the steel bar element due to corrosion, κ p Assign the rust expansion layer unit to consider the interface adhesion degradation caused by corrosion, and change ε f Assign the rust expansion layer unit to consider the expansion deformation caused by corrosion; update and output the crack width field variable Field_Crack after considering the steel bar corrosion effect; The carbon dioxide diffusion field analysis model is based on t i +dt time end carbon dioxide concentration distribution result is the initial state, set restart analysis; read the updated crack width field variable Field_Crack, update the output dt time increment of the concrete carbonization field variable Field_Carbon; The oxygen diffusion field analysis model is based on t i The oxygen concentration and steel corrosion rate results at the end of +dt time are the initial state, and the restart analysis is set; the updated crack width field variable Field_Crack and concrete carbonization field variable Field_Carbon are read, and the steel corrosion field variable Field_Corr after the output dt time increment is updated.

Images