A method for analyzing corrosion deterioration of a reinforced concrete beam cracking in a carbonization environment

Abstract

The application discloses a kind of carbonization environment under cracking reinforced concrete beam corrosion deterioration analysis method, comprising the following steps: reinforced concrete beam service time division, determine the sequence of calculation time point;Establish the load field entity finite element model of reinforced concrete beam, calculate the crack distribution and width of beam body under the action of load at ti time point, calculate crack width field variable;Establish the analysis model of carbon dioxide diffusion field of concrete beam, import crack width field variable at ti time point, calculate and output carbonization field variable of concrete beam at t i +dt time end;Establish the analysis model of oxygen diffusion field of reinforced concrete beam, import crack width field variable and carbonization field variable, calculate and output reinforced corrosion field variable at t i+1 +dt time end;Whether the total service time is t is judged to the calculation time point;Update the calculation time point t i =t +dt, the model calculation result of previous time point is initial state;Extract the deformation and crack result of reinforced concrete beam at each time point during service time, obtain deformation and crack deterioration law.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of bridge deterioration analysis, in particular to a method for analyzing the corrosion deterioration of a cracked reinforced concrete beam in a carbonation environment. BACKGROUND

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

[0003] In a carbonation environment, the acidic gas carbon dioxide in the atmosphere will continuously invade the inside of the beam through the pores of the concrete, and the carbonation reaction with the internal alkaline substances will reduce the alkalinity inside the beam, causing the passivation film on the surface of the steel to be damaged, and then electrochemical corrosion occurs. In the design of reinforced concrete beams, a certain thickness of concrete protective layer is generally provided around the steel to ensure that the carbonation depth does not exceed the thickness of the concrete protective layer during the service life, so as to protect the steel from corrosion. However, since the reinforced concrete beam is usually in a cracked working state during the normal use stage, the cracks provide an accelerated erosion path for carbon dioxide, oxygen and moisture, causing the carbonation of the concrete and the corrosion of the steel at the cracks to be accelerated. The reduction of effective area, the degradation of adhesion and the rust expansion caused by steel corrosion will cause the further development of the beam cracks, and the development of the cracks will accelerate the environmental erosion and the corrosion process of the steel, and there is a significant coupling effect between the carbonation environment erosion and the crack development.

[0004] At present, the carbonation depth and the steel corrosion rate of the reinforced concrete beam are generally directly evaluated by using the empirical formula method, without considering the influence of the crack state on the carbonation of the concrete and the corrosion of the steel, and the corrosion deterioration evaluation of the cracked concrete beam is not accurate. In terms of simulation analysis models, the current two-dimensional local model with "preset cracks" is generally used to analyze the influence of cracking on the carbonation depth of concrete, which has two main shortcomings: 1) only the one-way influence 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 the cross section of the concrete beam, and cannot be used for analysis of the corrosion deterioration of the overall beam structure. The existing simulation analysis method cannot reflect the coupling relationship between the crack development and the environmental erosion of the reinforced concrete beam in a carbonation environment, and the evaluation results are different from the actual situation.

[0005] There is a need for a method for analyzing the corrosion deterioration of a cracked reinforced concrete beam in a carbonation environment to solve the above problems. SUMMARY

[0006] The present application provides a kind of carbonization environment under cracking reinforced concrete beam corrosion degradation analysis method, comprising the following steps:

[0007] The present application provides a kind of carbonization environment under cracking reinforced concrete beam corrosion degradation analysis method, comprising the following steps:

[0008] S1, the total service time of reinforced concrete beam is t years, the total service time t is divided into n sections with dt years as time interval, and the calculation time point sequence t is obtained i (i=0~n), satisfy t i+1 =t i +dt;

[0009] S2, the load field entity finite element model of reinforced concrete beam is established, and the crack distribution and width of beam body under load at t i Time point are calculated, and crack width field variable Field_Crack is calculated.

[0010] S3, the carbon dioxide diffusion field analysis model of concrete beam is established, and the crack width field variable Field_Crack at t i Time point is introduced, and the carbonization field variable Field_Carbon of concrete beam at t i +dt Time end is calculated and exported.

[0011] S4, the oxygen diffusion field analysis model of reinforced concrete beam is established, and crack width field variable Field_Crack and carbonization field variable Field_Carbon are introduced, and the steel corrosion field variable Field_Corr at t i +dt Time end is calculated and exported.

[0012] S5, whether the calculation time point reaches total service time t is judged, if yes, step S7 is carried out, otherwise step S6 is carried out.

[0013] S6, the calculation time point t i+1 =ti +dt, the previous time point model calculation result is the initial state, step S2 is carried out;

[0014] S7, the deformation and crack results of the reinforced concrete beam in the service time 0-t are extracted, and the deformation and crack deterioration law of the beam body is obtained.

[0015] The reinforced concrete beam cracking corrosion deterioration analysis method in the carbonization environment, as an preferred mode, step S2 specifically includes:

[0016] The crack analysis model is constructed, and the crack analysis model includes concrete solid element, steel bar element and steel bar rust expansion layer element;

[0017] The concrete solid element is simulated by three-dimensional eight-node solid element, and the tensile constitutive relationship equation of concrete is calculated, and the formula is as follows:

[0018]

[0019] The crack width is calculated, and the formula is as follows:

[0020] w cr =(ε c -ε e )·L e ;

[0021] Wherein, 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 crack width of concrete, L e is the characteristic length of concrete element in the cracking direction;

[0022] The steel bar element is simulated by two-node bar element, and the element section attribute is valued according to the actual steel cross section area;

[0023] The field variable subroutine is defined at the element integration point, and the effective area reduction coefficient is calculated and applied according to the steel corrosion rate;

[0024] The steel rust expansion layer element is modeled according to the position and size of the actual steel bar, and the cohesive element is used;

[0025] The steel section is divided into four elements, and the nodes are shared at the center of the section circle; the steel length direction is taken as the axial direction, and the steel outer surface normal direction is taken as the normal direction, the axial stiffness of the element is taken as 0, and the normal and tangential stiffness is taken according to the steel elastic modulus;

[0026] In the unit normal definition expansion subroutine, expansion strain is calculated and applied according to the steel corrosion rate; in the unit tangential definition field variable subroutine, the shear modulus reduction coefficient is calculated and applied according to the steel corrosion rate;

[0027] The internal nodes of the steel bar element and the steel rust expansion layer element are embeddedly connected, and the external nodes of the steel rust expansion layer element are embeddedly connected with the concrete entity element;

[0028] A static analysis step is set, loads are applied on the reinforced concrete beam entity element model, element tensile strain is solved, crack width of the concrete beam entity element is calculated through the concrete entity element, and crack width result w of the concrete beam entity element is output cr to the crack width field variable, which is Field_Crack.

[0029] The crack width field variable data includes: element number, integral point number, integral point coordinates, crack width.

[0030] The reinforced concrete beam corrosion deterioration analysis method under carbonization cracking environment, as an preferred mode, step S3 specifically comprises the following steps:

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

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

[0033]

[0034] Where, L e is the characteristic length of the element, and κ is the ratio of the crack diffusion coefficient to the internal diffusion coefficient of concrete, and κ=1000 is taken;

[0035] According to the concrete material mix parameter, the diffusion coefficient material attribute is given to the element, and the concrete porosity ε p is calculated, and the formula is as follows:

[0036]

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

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

[0039]

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

[0041] The carbon dioxide concentration boundary C CO2 is applied to the contact surface of the concrete beam and the atmosphere, 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] The cumulative diffusion flux J CO2 (t c ) of each integral point of the unit within the time dt is extracted, the carbonation degree index I c is calculated, and the formula is as follows:

[0043]

[0044] If I c >1, then the complete carbonation time t c is stored as the carbonation field variable Field_Carbon; otherwise, the complete carbonation time t c is not stored as the carbonation field variable Field_Carbon.

[0045] The data of the carbonation field variable Field_Carbon includes: the unit number, the integral point number, the integral point coordinates, the complete carbonation time t c .

[0046] The cracking reinforced concrete beam corrosion deterioration analysis method in the carbonation environment, as an preferred mode, step S4 specifically includes:

[0047] An oxygen diffusion field analysis model is established, the oxygen diffusion field analysis model includes concrete units and steel units, the concrete beam and the steel are modeled by using solid units according to actual geometric sizes, and the steel unit is embedded in the concrete unit;

[0048] In the USDFLD field variable subroutine, the crack width field variable Field_Crack is read and given to the concrete unit, the amplification factor f(w cr ) of the diffusion effect at each integral point of the unit is calculated; the carbonation field variable Field_Carbon is read and given to the steel unit by using a near neighbor coordinate mapping method;

[0049] According to the concrete material mix parameter, the diffusion coefficient material attribute is given to the concrete unit, and the diffusion coefficient D of oxygen at the integral point of the unit is calculated O2 , and the formula is as follows:

[0050]

[0051] The oxygen concentration boundary C is applied on the contact surface of the concrete beam body and the atmosphere O2,s , the mass diffusion module is used for analysis, the total diffusion time is set as dt, and the oxygen concentration C i (t) at the integral point in the steel unit within t i ~t O2 +dt time is calculated.

[0052] The concrete resistivity r at the integral point of the steel unit is calculated, and the formula is as follows:

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

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

[0055]

[0056] The steel volume corrosion rate γ at the integral point of the steel unit is calculated, and the formula is as follows:

[0057]

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

[0059] The steel effective area reduction coefficient κ r at the integral point of the steel unit is calculated, and the formula is as follows:

[0060] κ r =1-αγ;

[0061] The bond degradation coefficient κ p between the steel and the concrete is calculated, and the formula is as follows:

[0062]

[0063] The steel rust expansion strain ε f is calculated, and the formula is as follows:

[0064]

[0065] wherein, alpha is the volume expansion coefficient of rusting product, and alpha is equal to 2-4;

[0066] The steel bar rusting field variable is stored and is denoted as Field_Corr, and the steel bar rusting field variable data includes: unit number, integral point number, integral point coordinate, effective area reduction coefficient Kappa r , bond degradation coefficient Kappa p , steel bar rust expansion strain Epsilon f .

[0067] The method for analyzing the rusting deterioration of the cracking reinforced concrete beam in the carbonization environment, as a preferred mode, the step S6 specifically includes:

[0068] The load field crack analysis model is analyzed, and the load field crack analysis model at the t i time point is taken as the initial state, and the restart analysis is set; the steel bar rusting field variable Field_Corr is read, and Kappa r is given to the steel bar unit to consider the effective area reduction caused by rusting, Kappa p is given to the rust expansion layer unit to consider the interface bond degradation caused by rusting, and Epsilon f is given to the rust expansion layer unit to consider the expansion deformation caused by rusting; the crack width field variable Field_Crack considering the steel bar rusting effect is updated and output.

[0069] The carbon dioxide diffusion field analysis model is analyzed, and the carbon dioxide concentration distribution result at the t i +dt time end is taken as the initial state, and the restart analysis is set; the updated crack width field variable Field_Crack is read, and the concrete carbonization field variable Field_Carbon after the dt time increment is updated and output.

[0070] The oxygen diffusion field analysis model is analyzed, and the oxygen concentration and steel bar rusting rate result at the t i +dt time end is taken as the initial state, and the restart analysis is set; the updated crack width field variable Field_Crack and the concrete carbonization field variable Field_Carbon are read, and the steel bar rusting field variable Field_Corr after the dt time increment is updated and output.

[0071] The method has the following beneficial effects:

[0072] 1) The analysis method of the present application can realize comprehensive consideration of the strong coupling effect and dynamic change over time between the carbonation environment and the opening crack of the beam body, and the accelerated diffusion effect of carbon dioxide and oxygen by the opening crack of the beam body, the development of the beam crack caused by reinforcement corrosion, and the actual deterioration of the reinforced concrete beam.

[0073] 2) Compared with the existing sectional analysis method, the present application can better consider the overall stress characteristics of the beam structure, and can directly obtain macro performance indicators such as overall deformation and crack of the structure, and is more accurate and convenient for overall performance deterioration evaluation of the structure. BRIEF DESCRIPTION OF DRAWINGS

[0074] Figure 1 A flowchart of a corrosion deterioration analysis method for a cracked reinforced concrete beam in a carbonation environment. DETAILED DESCRIPTION

[0075] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all.

[0076] Embodiment 1

[0077] As shown in the figure, a corrosion deterioration analysis method for a cracked reinforced concrete beam in a carbonation environment includes the following main steps: Figure 1

[0078] Divide the service time of the reinforced concrete beam to determine the calculation time point sequence. Let the total service time of the reinforced concrete beam be t = 10 years, divide the total service time t into n sections with dt = 1 year as the time interval to obtain the calculation time point sequence t i (i = 0 ~ n), which satisfies t i+1 = t i + dt.

[0079] Establish a load field entity finite element model of the reinforced concrete beam, calculate the crack distribution and width of the beam body under the action of the load at the t i time point, calculate and output the crack width field variable, denoted as Field_Crack.

[0080] 1) The crack analysis model is composed of three types of elements: concrete entity elements, steel bar elements and rust expansion layer elements.

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

[0082]

[0083] w​cr = (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 crack width of concrete, and 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 an ideal elastic-plastic constitutive relationship is used. The element cross-section properties are assigned according to the cross-sectional area of the steel bars. Field variable subroutines are defined at the integration points of the elements, and the effective area reduction coefficient is calculated and applied according to the corrosion rate of the steel bars.

[0086] 4) The rust expansion layer element is modeled by using a cohesive element according to the actual position and size of the steel bars. The steel bar cross-section is divided into four elements, and a common node is set at the center of the cross-section. The axial stiffness of the element is taken as 0, and the normal and shear stiffnesses are valued according to the elastic modulus of the steel bars. An expansion subroutine is defined in the normal direction of the element, and the expansion strain is calculated and applied according to the corrosion rate of the steel bars. Field variable subroutines are defined in the shear direction of the element, and the shear modulus reduction coefficient is calculated and applied according to the corrosion rate of the steel bars.

[0087] 5) The internal nodes of the steel bar element and the rust expansion layer element are set to be embeddedly connected, and the external nodes of the rust expansion layer element are set to be embeddedly connected with the concrete solid element.

[0088] 6) A static analysis step is set, and loads are applied to the steel reinforced concrete beam solid element model to obtain the tensile strain of the element and calculate the crack width of the concrete beam solid element. The crack width results of the concrete beam solid element are output as w cr , and the crack width field variable is recorded as Field_Crack, which includes the element number, integration point number, integration point coordinates, and crack width.

[0089] A carbon dioxide diffusion field analysis model of the concrete beam is established, and the t i time point crack width field variable Field_Crack is imported to calculate and output the carbonation field variable of the concrete beam at the t i + dt time point, which is recorded as Field_CarbonTime.

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

[0091] 2) The USDFLD field variable subroutine is defined at the element integration point, the crack width field variable Field_Crack is read, and the magnification of the diffusion effect at the element integration point is calculated according to the calculation,

[0092]

[0093] where f(w cr ) is the magnification of the diffusion effect at the crack, L e is the characteristic length of the element, and κ is the ratio of the crack diffusion coefficient to the internal diffusion coefficient of concrete, κ = 1000.

[0094] 3) According to the mix proportion parameters of concrete material, the diffusion coefficient material attribute is given to the element, and the diffusion coefficient D CO2 of carbon dioxide at the element integration point is calculated as follows,

[0095]

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

[0097]

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

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

[0100] 5) The cumulative diffusion flux J CO2 (t c ) at each element integration point within dt = 1 year is extracted, the carbonation degree index I c is calculated; when I c > 1, the complete carbonation time t cField_Carbon, data include: element number, integration point number, integration point coordinate, complete carbonation time t c .

[0101]

[0102] Establish the oxygen diffusion field analysis model of reinforced concrete beam, import crack width field variable Field_Crack and carbonation field variable Field_Carbon, calculate and output the steel corrosion field variable at t i +dt, recorded as Field_Corr.

[0103] 1) The oxygen diffusion field analysis model is composed of concrete elements and steel elements. The concrete beam and the steel are modeled by solid elements according to the actual geometric size, and the steel element is embedded in the concrete element.

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

[0105] 3) According to the mix proportion parameters of concrete material, the diffusion coefficient material attribute is given to the concrete element, and the diffusion coefficient D O2 of oxygen at the element integration point is calculated as follows,

[0106]

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

[0108] 5) Calculate the corrosion current intensity at the integration point of the steel element.

[0109]

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

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

[0112] 6) Calculate the steel volume corrosion rate at the integration point of the steel element, the formula is as follows.

[0113]

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

[0115] 7) Calculate the effective area reduction coefficient κ r of steel, the bond degradation coefficient κ p between steel and concrete, and the steel rust expansion strain ε f at the integration point of the steel element.

[0116] κ r = 1-αγ

[0117]

[0118] Wherein, α is the volume expansion coefficient of corrosion product, α = 2 ~ 4.

[0119] 8) Store the steel corrosion field variables, denoted as Field_Corr, including: element number, integration point number, integration point coordinates, effective area reduction coefficient κ r , bond degradation coefficient κ p , and steel rust expansion strain ε f .

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

[0121] 1) For the load field crack analysis model, take the results of the load field crack analysis model at t i time point as the initial state, set the restart analysis; read the steel corrosion field variables Field_Corr, assign κ r to the steel bar element to consider the effective area reduction caused by corrosion, assign κ p to the rust expansion layer element to consider the interface bond degradation caused by corrosion, and assign ε f to the rust expansion layer element to consider the expansion deformation caused by corrosion; update the output crack width field variable Field_Crack considering the effect of steel corrosion.

[0122] 2) Analysis model of carbon dioxide diffusion field, with t i +dt time end carbon dioxide concentration distribution results for the initial state, set restart analysis; read the updated crack width field variable Field_Crack, update the output of concrete carbonation field variable Field_Carbon after dt time increment.

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

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

[0125] Extract the deformation and crack results of the reinforced concrete beam at each calculation time point within the service time 0-t, and obtain the deformation and crack deterioration law of the beam body.

[0126] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art in the technical range disclosed by the present application, according to the technical scheme and the inventive concept of the present application, equivalent replacement or change, should be covered in the protection scope of the present application.

Claims

1. A method for analyzing the corrosion deterioration of a cracked reinforced concrete beam in a carbonation environment, comprising the following steps: S5, judging whether the calculation time point reaches the total service time t, if yes, proceeding to step S7, otherwise, proceeding to step S6; S7, extracting the deformation and crack results of the reinforced concrete beam at each calculation time point within the service time 0-t, and obtaining the deformation and crack deterioration law of the beam body. 2.The method for analyzing the corrosion deterioration of a cracked reinforced concrete beam in a carbonation environment according to claim 1, wherein the step S2 specifically comprises: constructing a crack analysis model, wherein the crack analysis model comprises a concrete solid element, a steel bar element and a steel bar rust expansion layer element; the concrete solid element is simulated by a three-dimensional eight-node solid element, and a concrete tensile constitutive relationship equation is calculated, and the equation is as follows: the crack width is calculated, and the equation is as follows: the steel bar element is simulated by a two-node bar element, and the element cross-section attribute is valued according to the actual steel cross-sectional area; a field variable subroutine is defined at the element integration point, and an effective area reduction coefficient is calculated and applied according to the steel corrosion rate; the steel bar rust expansion layer element is modeled according to the position and size of the actual steel bar, and a cohesive element is used; the steel cross-section is divided into four elements, and the nodes are shared at the center of the cross-section; the element axial stiffness is taken as 0, and the normal and tangential stiffnesses are valued according to the steel elastic modulus; an expansion subroutine is defined in the element normal direction, and the expansion strain is calculated and applied according to the steel corrosion rate; a field variable subroutine is defined in the element tangential direction, and a shear modulus reduction coefficient is calculated and applied according to the steel corrosion rate; the internal nodes of the steel bar element and the steel bar rust expansion layer element are set to be embeddedly connected, and the external nodes of the steel bar rust expansion layer element are set to be embeddedly connected with the concrete solid element; the crack width field variable data comprises: element number, integration point number, integration point coordinates and crack width. S1, total service time of the reinforced concrete beam is t years, total service time t is divided into n sections with dt years as the time interval, to obtain the calculation time point sequence t i (i = 0~n), satisfy t i+1 = t i + dt; S2, establish the reinforced concrete beam load field entity finite element model, calculate t i The crack distribution and width of the beam body under the action of the load at the time point, and the crack width field variable Field_Crack is calculated. S3, establish a carbon dioxide diffusion field analysis model of the concrete beam, import t i the crack width field variable Field_Crack at the time point, calculate and output the carbonation field variable Field_Carbon of the concrete beam at the end of t i +dt S4, establishing an oxygen diffusion field analysis model of the reinforced concrete beam, importing the crack width field variable Field_Crack and the carbonation field variable Field_Carbon, and calculating and outputting t i +dt time-end steel bar corrosion field variable Field_Corr; 3.The method for analyzing the corrosion deterioration of a cracked reinforced concrete beam in a carbonation environment according to claim 2, wherein the step S3 specifically comprises the following steps: a carbon dioxide diffusion field analysis model is modeled according to the geometric size of the actual concrete beam, and the element type is a three-dimensional eight-node transfer element; the diffusion coefficient material attribute is given to the element according to the concrete material mix proportion parameters, and the equation is as follows: wherein, RH is the relative humidity of the environment (%). S6, update the calculation time point t i+1 = t i + dt, using the model calculation result at the previous time point as the initial state, proceed to step S2; 4.The method for analyzing the corrosion deterioration of a cracked reinforced concrete beam in a carbonation environment according to claim 3, wherein the step S4 specifically comprises: an oxygen diffusion field analysis model is established, wherein the oxygen diffusion field analysis model comprises a concrete element and a steel element, the concrete beam and the steel are modeled by solid elements according to the actual geometric size, and the steel element is embedded in the concrete element; the concrete resistivity r is calculated at the integration point of the steel element, and the equation is as follows: the corrosion current intensity i(t) is calculated according to the concrete resistivity r, and the equation is as follows: the steel volume corrosion rate γ is calculated at the integration point of the steel element, and the equation is as follows: ​ ​ ​ ​ ​ w cr = (ε c - ε e ) · L e ; where E c is the concrete elastic modulus, ε c is the concrete tensile strain, ε cr is the concrete peak tensile strain, ε e is the concrete elastic tensile strain, σ c is the concrete tensile stress, f t is the concrete tensile strength, w cr is the concrete crack width, L e is the characteristic length of the concrete element in the cracking direction; ​ ​ ​ ​ ​ ​ A static analysis step is set to apply a load on the reinforced concrete beam solid element model, to solve the element tensile strain, to calculate the crack width of the concrete beam solid element through the concrete solid element, and to output the crack width result w of the concrete beam solid element cr to a crack width field variable, denoted as Field_Crack; ​ ​ ​ ​ At the integration points of the element, the USDFLD field variable subroutine reads the crack width field variable Field_Crack to calculate the amplification factor f(w cr ) of the diffusion effect at each integration point of the element, which is given by the formula: Among them, L e κ is the characteristic length of the element, and κ is the ratio of the crack diffusion coefficient to the internal diffusion coefficient of the concrete. κ = 1000. ​ Calculating the concrete porosity ε p The formula is as follows: where w is the water content of the concrete per unit volume (kg / m 3 ), ρ w is the density of water (kg / m 3 ), c is the cement content of the concrete per unit volume (kg / m 3 ), ρ c is the density of cement (kg / m 3 ). According to the concrete porosity ε p The carbon dioxide diffusion coefficient D at the integration point of the calculation unit is calculated CO2 The formula is as follows: ​ A carbon dioxide concentration boundary C is applied to the concrete beam's interface with the atmosphere CO2 The mass diffusion module is used to analyze, set the total diffusion time as dt, and calculate the carbon dioxide diffusion flux and concentration distribution in the concrete beam body within the dt diffusion time. Extracting the cumulative diffusion flux J at each unit integration point within the dt time CO2 (t c ), calculating the carbonization degree index I c , the formula is as follows: If I c >1, then the full carbonization time t c is stored as the carbonization field variable Field_Carbon; otherwise, the full carbonization time t c is not stored as the carbonization field variable Field_Carbon. The data of the carbonization field variable Field_Carbon includes: unit number, integral point number, integral point coordinate, complete carbonization time t c . ​ ​ ​ At the integration points of the element, the USDFLD field variable subroutine reads the crack width field variable Field_Crack to calculate the magnification factor f(w cr ) of the diffusion effect at the integration points of the element; and reads the carbonation field variable Field_Carbon to assign the reinforcement element using the near-node coordinate mapping method. According to the concrete material mix parameter, the concrete unit is endowed with the diffusion coefficient material attribute, and the diffusion coefficient D of oxygen at the integral point of the unit is calculated O2 , and the formula is as follows: Applying an oxygen concentration boundary C on the contact surface of the concrete beam body with the atmosphere O2,s , using a mass diffusion module to analyze, setting the total diffusion time as dt, calculating the oxygen concentration C i (t) at the integral point in the steel unit within t i ~t O2 +dt time; ​ r = 100 (1 - RH) 2 + 40; ​ ​ Wherein, 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, p is the density of steel bar, p = 7.86 x 10 -3 g / mm 3 , R is the cross-sectional radius of the steel bar (mm). In the formula, 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, p is the density of steel bar, p = 7.86 x 10 -3 g / mm <000 At the integration point of the steel unit, the effective area reduction coefficient κ of the steel is calculated r , as follows: Kappa r = 1 - a y; calculating the deterioration coefficient κ of the bond between the reinforcement and the concrete p The formula is as follows: The steel bar rust expansion strain ε is calculated f The formula is as follows: Wherein, alpha is the volume expansion coefficient of the corrosion product, and alpha=2~4; stores a steel bar corrosion field variable, denoted as Field_Corr, which includes: a unit number, an integral point number, integral point coordinates, an effective area reduction coefficient κ r , a bond deterioration coefficient κ p , a steel bar corrosion expansion strain ε f .

5. The method according to claim 4, characterized in that: The step S6 specifically comprises: The load field crack analysis model is analyzed to t i The result of the load field crack analysis model at the time point is the initial state, and a restart analysis is set. The steel bar corrosion field variable Field_Corr is read, κ r The steel bar rod unit is given to consider the effective area reduction caused by corrosion, κ p The rust expansion layer unit is given to consider the interface bond degeneration caused by corrosion, ε f The rust expansion layer unit is given to consider the expansion deformation caused by corrosion; the crack width field variable Field_Crack after considering the steel bar corrosion effect is updated and output. The carbon dioxide diffusion field analysis model is analyzed with t i The carbon dioxide concentration distribution result at the end of the time t is the initial state, and the restart analysis is set. The updated crack width field variable Field_Crack is read, and the concrete carbonation field variable Field_Carbon after the output dt time increment is updated. The oxygen diffusion field analysis model is analyzed for t i +dt time oxygen concentration and steel corrosion rate results for the initial state, set the restart analysis; read the updated crack width field variable Field_Crack and concrete carbonization field variable Field_Carbon, update the output dt time increment after the steel corrosion field variable Field_Corr.

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