Prestressed tendon relaxation loss constitutive model construction method and system

Abstract

The invention discloses a method and a system for constructing a constitutive model of prestressed tendon relaxation loss, relates to the technical field of material constitutive model construction, and solves the technical problems that factors considered in prestressed relaxation calculation are not comprehensive and long-term deformation of a large-span PC box bridge cannot be accurately evaluated in the prior art. The method comprises the following steps: 1, constructing a rate expression of the total strain of the prestressed tendon based on a small strain and strain additive splitting principle; 2, considering variable strain and variable temperature conditions in the rate expression of the total strain of the prestressed tendons, and exporting a stress rate expression of the prestressed tendons; and 3, by using the prestressed tendon rate expression, considering the influence of fatigue damage on the stress relaxation of the prestressed tendon, introducing a damage variable, and completing the construction of the prestressed tendon relaxation loss constitutive model considering fatigue damage, the method considers the influence of multiple factors, and has the advantages of high evaluation accuracy and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of material constitutive model construction, and particularly relates to a method and system for constructing a constitutive model of prestressed tendon relaxation loss. Background Art

[0002] Research on the long-term deformation of long-span PC box girder bridges shows that for the design of creep-sensitive structures, it is necessary to more accurately predict the long-term prestress loss of prestressed tendons. On the other hand, for creep-sensitive structures such as long-span segmental box girders, the influence of concrete strain changes on the prestress relaxation of prestressed tendons cannot be ignored, and the influence of the temperature rise of concrete slabs exposed to sunlight on prestress relaxation is also important.

[0003] During the entire service life of a bridge structure, it will be subjected to the repeated action of vehicle loads and the periodic action of temperature loads caused by solar radiation temperature differences. With the increase in the service life requirements of bridges and the rapid growth of traffic volume, the fatigue damage of concrete bridges caused by vehicle cyclic loads will be more prominent, especially for bridges with heavy truck traffic. At present, the existing calculation models for prestress relaxation loss are single models, which are only applicable to constant strain and constant temperature and do not consider the fatigue damage caused by cyclic load actions; although some scholars have proposed some more advanced prestress relaxation calculation methods, the factors considered are not comprehensive enough and need to be further improved.

[0004] Due to the shrinkage, creep of concrete and stress relaxation characteristics of prestressed tendons, the prestress in prestressed concrete structures will continuously decrease over time, that is, there is a phenomenon of long-term prestress loss in prestressed concrete structures. Long-term prestress loss is the main reason for the excessive long-term deformation of long-span PC box girder bridges; therefore, the estimation of prestress loss related to time is an important issue. At present, the calculation methods of long-term prestress loss can basically be classified into three categories: one is the comprehensive estimation method, that is, directly selecting the total loss value of long-term prestress according to relevant calculation codes; the second is the sub-item superposition method, that is, calculating the prestress losses caused by concrete shrinkage, creep and relaxation of prestressed tendons respectively, and then summing them to obtain the total long-term prestress loss value, which is the most commonly used method in existing codes; the third is the step-by-step calculation method, which is mainly applicable to numerical calculations, considering the mutual influence of concrete creep, shrinkage and relaxation of prestressed tendons, and the calculated value is relatively accurate. With the progress of computer software and hardware calculations, the step-by-step calculation method is booming, and more accurate calculation of long-term prestress loss can be achieved through the fusion of multiple models. In actual structures, the strain of prestressed tendons is affected by concrete shrinkage and creep and changes over time. Therefore, it is only necessary to establish a stress relaxation calculation model of prestressed tendons under variable strain conditions to simultaneously consider the influence of concrete shrinkage and creep. In addition, considering the influence of fatigue damage and temperature change on prestress relaxation, it is necessary to consider these two factors simultaneously in the prestress relaxation loss calculation model of prestressed tendons. For this, model fusion can be carried out to comprehensively consider the influence of variable strain, variable temperature and material fatigue damage on prestress relaxation loss to solve the problems existing in the prior art. Summary of the Invention

[0005] In view of this, the present invention discloses a method and system for constructing a constitutive model of prestress relaxation loss of prestressed tendons, aiming to solve the technical problems that the existing technology for prestress relaxation calculation does not comprehensively consider factors and cannot accurately evaluate the long-term deformation of long-span PC box girder bridges.

[0006] To solve the above-mentioned existing technical problems, the technical solutions adopted by the present invention are as follows:

[0007] A method for constructing a constitutive model of prestress relaxation loss of prestressed tendons, comprising the following steps:

[0008] Step 1: Based on the small strain and strain additive splitting principle, construct a rate expression of the total strain of prestressed tendons;

[0009] Step 2: Consider the variable strain and variable temperature conditions in the rate expression of the total strain of prestressed tendons, and derive the stress rate expression of prestressed tendons;

[0010] Step 3: Use the rate expression of prestressed tendons, consider the influence of fatigue damage on the stress relaxation of prestressed steel bars, introduce a damage variable, and complete the construction of the constitutive model of prestress relaxation loss considering fatigue damage.

[0011] Furthermore, the rate expression of the total strain of the prestressing tendon in Step 1 is as follows:

[0012]

[0013] In the formula, ε is the total normal (axial) strain of the prestressing tendon, ε se is the instantaneous elastic strain, ε sv is the viscoplastic strain, is the absolute temperature, α s is the coefficient of thermal expansion of the prestressing tendon, E t is the tangential modulus of the prestressing tendon, σ p is the stress of the prestressing tendon, A T is the temperature influence factor. At the temperature T0 = 293K (20°C), A T = 1.

[0014] Furthermore, Step 2 includes the following steps:

[0015] Step 201: Based on the rate process theory, obtain the specific expression of A T :

[0016]

[0017] In the formula, Q p is the flow activation energy of the prestressing tendon, k B = 1.38×10 -23 J / K, (at the temperature T0 = 293K, A T = 1);

[0018] Step 202: Under constant strain and constant temperature, the change of the prestress in the prestressing tendon with time is calculated by the following formula:

[0019]

[0020] In the formula, λ1 = 1000h; k, c, ρ0 and γ are empirical fitting constants of the given prestressing tendon (k≈0.08, c≈2, ρ0 = 0.32, γ = 0.45); is the average yield strength of the prestressing tendon; is the lowest threshold that can cause prestress relaxation; 〈〉 is the Macaulay bracket, which is defined here as 〈x〉 = max(x, 0); furthermore, F p is a function describing the stress-strain law of short-term loading of the prestressing tendon, σ p = F p (ε); under constant strain, F p (ε) = σ p0 = the initial prestress.

[0021] Furthermore, step 202 further includes the following steps:

[0022] Under variable strain conditions, the function f is expressed as follows:

[0023]

[0024] where λ1 = 1000h, k, c, ρ0, and γ are empirical fitting constants for the given prestressing tendon, k ≈ 0.08, c ≈ 2, ρ0 = 0.32, γ = 0.45; ε m is the maximum strain experienced by the prestressing tendon. During loading, and ε ≥ ε m , E t = F′ p (ε) = dF(ε) / d ε = the tangent modulus of the prestressing tendon; during unloading or reloading, or ε < ε m , E t = E = the initial Young's elastic modulus of the prestressing tendon = 198.5 GPa.

[0025] Furthermore, step 2 also includes the following steps:

[0026] Step 203: Under variable temperature conditions, the strain that enters the viscous law as the first parameter of the function f is the mechanical strain, which is obtained by subtracting the thermal strain from the total strain, i.e.:

[0027] ε* = ε - α T (T - T init )

[0028] where T init represents the initial temperature; α T is the thermal expansion coefficient of the prestressing tendon.

[0029] Step 204: According to the function f and step 203, the stress rate expression of the prestressing tendon is obtained:

[0030]

[0031] Furthermore, the specific content of step 3 is as follows:

[0032] When a metallic material is under cyclic loading, certain fatigue damage will occur inside it. For a prestressing tendon, under fatigue loading, the pores inside it will increase and become uneven. Fatigue has an accelerating and amplifying effect on the stress relaxation of the steel wire, and the fatigue-relaxation stress shows a development characteristic of rapid growth in the early stage and gradual flattening in the later stage. Considering the above nonlinear characteristics of the damage evolution of the prestressing tendon, a non-linear evolution damage variable is used to describe it. A non-linear evolution damage variable is used to describe it:

[0033]

[0034] In the formula, k is a material parameter related to fatigue damage, and N f is the fatigue life. When k = 0, the damage variable is a linear model, i.e., D = N / N f ;

[0035] Considering that fatigue-creep gradually flattens out over time, it can be assumed that k is a function proportional to the relative number of loading cycles N / N f , that is, k can be expressed as:

[0036] k = αN / N f

[0037] In the formula, α is the material micro-damage parameter.

[0038] For the fatigue life of prestressing tendons, the following formula is used for evaluation:

[0039] log N f = 13.84 - 3.5logΔσ

[0040] In the formula, N f is the fatigue life and Δσ is the fatigue stress amplitude;

[0041] Under variable stress amplitude, for the convenience of engineering application, similar to the fatigue damage of concrete, the fatigue damage of prestressing tendons can also be calculated using the linear cumulative damage criterion. As the number of load cycles increases, the damage accumulates continuously, and the degree of material damage will increase continuously. For prestressing tendons, the growth of damage will inevitably cause the attenuation of the internal prestress. Therefore, for prestressed concrete structures affected by cyclic loads such as vehicles, it is necessary to consider the influence of fatigue damage on the stress relaxation of prestressing tendons, that is, to consider the dynamic relaxation of prestressing tendons. In this regard, after introducing the damage variable Ds to consider the fatigue damage of prestressing tendons, the stress of prestressing tendons can be expressed as follows:

[0042] σ D (t) = (1 - D s )σ P (t)

[0043] In the formula, D s is the damage variable, and σ P (t) is the prestress without considering fatigue damage.

[0044] Currently, the prestressing tendons widely used in prestressed concrete bridge structures are low-relaxation 1860-grade 7-wire steel strands with a nominal diameter of 15.2 mm. For such prestressing tendons, the typical stress-strain curve is shown in the attached drawings of the specification as Figure 2 shown.

[0045] To make the calculation of prestress relaxation loss more applicable, a multi-stage linear stress-strain relationship can be adopted. In prestressed concrete bridges, the stress level of the steel strand is usually in the elastic-plastic section. Therefore, only considering the mechanical behavior of the steel strand in the elastic stage and the elastic-plastic stage, its stress-strain relationship is as follows:

[0046]

[0047] In the formula, Es = the initial Young's elastic modulus of the prestressing tendon; ε p , ε pt are the proportional limit strain and the ultimate strain respectively, ε 0.2 represents the strain corresponding to a residual strain of 0.2%, E s = 198.5 GPa, ε p = 0.00413, ε 0.2 = 0.0109, ε u = 0.0460, σ 0.2 = 1772 MPa, σ u = 1944 MPa.

[0048] A system for constructing a constitutive model of prestressing tendon relaxation includes:

[0049] A total strain rate construction module of the prestressing tendon: used to construct the rate expression of the total strain of the prestressing tendon based on the small strain and the principle of strain additive splitting;

[0050] A stress rate construction module of the prestressing tendon: used to consider the variable strain and temperature conditions in the rate expression of the total variation of the prestressing tendon to obtain the stress rate expression of the prestressing tendon;

[0051] A constitutive model construction module of prestressing tendon relaxation loss: used to utilize the rate expression of the prestressing tendon, consider the influence of fatigue damage on the stress relaxation of the prestressed steel bar, introduce the damage variable, and complete the construction of the constitutive model of prestressing tendon relaxation loss considering fatigue damage.

[0052] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows: By introducing the damage variable Ds to describe the fatigue damage degree of the prestressing tendon, the long-term prestress loss can be effectively estimated through the above formula, so as to accurately evaluate the long-term deformation of long-span PC box girder bridges. By comprehensively considering the influence of variable strain, variable temperature and material fatigue damage on prestress relaxation loss, model fusion is carried out, which makes up for the limitations of the existing calculation model of prestress relaxation loss, and has important promoting significance for accurately evaluating the long-term deformation of long-span PC box girder bridges. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The present invention will be described by way of examples and with reference to the accompanying drawings, wherein:

[0054] Figure 1 This is the overall flowchart of the present invention;

[0055] Figure 2 This is a schematic diagram of the typical strain-strain relationship of prestressed steel strands. Detailed implementation manners

[0056] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application and the accompanying drawings. Obviously, the described embodiments are only a part rather than all of the embodiments of the present application. Generally, the components of the embodiments of the present application described and marked in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application claimed, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts fall within the scope of protection of the present application.

[0057] In the description of the embodiments of the present application, it should be noted that the orientation or positional relationships indicated by the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationships in which the invention is customarily placed during use. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the present application. In addition, the terms "first", "second", "third", etc. are only used for descriptive distinction and cannot be construed as indicating or implying relative importance.

[0058] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0059] Embodiment 1

[0060] A method for constructing a constitutive model of the relaxation loss of prestressed tendons, as Figure 1 shown, includes the following steps:

[0061] Step 1: Based on the small strain and strain additive splitting principle, construct the rate expression of the total strain of the prestressed tendon;

[0062] Step 2: Consider the variable strain and variable temperature conditions in the rate expression of the total strain of the prestressed tendon, and derive the stress rate expression of the prestressed tendon;

[0063] Step 3: Using the rate expression of prestressing tendon, considering the influence of fatigue damage on the stress relaxation of prestressing steel bars, introducing the damage variable, and completing the construction of the constitutive model for the relaxation loss of prestressing tendon considering fatigue damage.

[0064] The rate expression of the total strain of the prestressing tendon in Step 1 is as follows:

[0065]

[0066] In the formula, ε is the total normal (axial) strain of the prestressing tendon, ε se is the instantaneous elastic strain, ε sv is the viscoplastic strain, is the absolute temperature, α s is the coefficient of thermal expansion of the prestressing tendon, E t is the tangential modulus of the prestressing tendon, σ p is the stress of the prestressing tendon, A T is the temperature influence factor. At the temperature T0 = 293K (20°C), A T = 1.

[0067] Step 2 includes the following steps:

[0068] Step 201: Based on the rate process theory, obtain the specific expression of A T :

[0069]

[0070] In the formula, Q p is the flow activation energy of the prestressing tendon, k B = 1.38×10 -23 J / K, (at the temperature T0 = 293K, A T = 1);

[0071] Step 202: Under constant strain and constant temperature, the change of the prestress in the prestressing tendon with time is calculated by the following formula:

[0072]

[0073] In the formula, λ1 = 1000h; k, c, ρ0, and γ are empirical fitting constants for the given prestressing tendon, k≈0.08, c≈2, ρ0 = 0.32, γ = 0.45; is the average yield strength of the prestressing tendon; is the lowest threshold that can cause prestress relaxation; 〈〉 is the Macaulay bracket, defined here as 〈x〉 = max(x, 0); in addition, F p is a function describing the stress-strain law of short-term loading of the prestressing tendon, σ p = F p(ε); under constant strain, F p (ε) = σ p0 = initial prestress.

[0074] Step 202 further includes the following steps:

[0075] Under variable strain conditions, the function f is expressed as follows:

[0076]

[0077]

[0078] where λ1 = 1000h, k, c, ρ0 and γ are empirical fitting constants for the given prestressing tendon, k ≈ 0.08, c ≈ 2, ρ0 = 0.32, γ = 0.45; ε m is the maximum strain experienced by the prestressing tendon. During loading, and ε ≥ ε m , E t = F′ p (ε) = dF(ε) / d ε = the tangent modulus of the prestressing tendon; during unloading or reloading, or ε < ε m , E t = E = the initial Young's elastic modulus of the prestressing tendon = 198.5 GPa.

[0079] Step 2 also includes the following steps:

[0080] Step 203: Under variable temperature conditions, the strain that enters the viscosity law as the first parameter of the function f is the mechanical strain (obtained by subtracting the thermal strain from the total strain), i.e.:

[0081] ε* = ε - αT(T - Ti n i t )

[0082] where T init represents the initial temperature; α T is the thermal expansion coefficient of the prestressing tendon.

[0083] Step 204: According to the function f and the strain, obtain the stress rate expression of the prestressing tendon:

[0084]

[0085] Step 3 is specifically:

[0086] Under cyclic loading, certain fatigue damage will occur inside metal materials. For prestressing tendons, under fatigue loading, the pores inside will increase and become uneven. Fatigue has an accelerating and amplifying effect on the stress relaxation of steel wires. The fatigue-relaxation stress shows a development characteristic of rapid growth in the early stage and gradual flattening in the later stage. Considering the above nonlinear characteristics of the damage evolution of prestressing tendons, a damage variable with nonlinear evolution is used to describe it:

[0087]

[0088] In the formula, k is a material parameter related to fatigue damage, and N f is the fatigue life. When k = 0, the damage variable is a linear model, that is, D = N / N f .

[0089] Considering that fatigue-relaxation gradually flattens out over time, therefore, it can be assumed that k is a function proportional to the relative number of loading cycles N / N f , that is, k can be expressed as:

[0090] k = αN / N f

[0091] In the formula, α is the material micro-damage parameter.

[0092] For the fatigue life of prestressing tendons, the following formula is used for evaluation:

[0093] log N f = 13.84 - 3.5logΔσ

[0094] In the formula, N f is the fatigue life, and Δσ is the fatigue stress amplitude;

[0095] Under variable stress amplitude, for the convenience of engineering application, similar to the fatigue damage of concrete, the fatigue damage of prestressing tendons can also be calculated using the linear cumulative damage criterion. As the number of load cycles increases, the damage accumulates continuously, and the degree of material damage will increase continuously. For prestressing tendons, the increase in damage will inevitably cause the attenuation of the internal prestress. Therefore, for prestressed concrete structures affected by cyclic loads such as vehicles, it is necessary to consider the influence of fatigue damage on the stress relaxation of prestressing tendons, that is, to consider the dynamic relaxation of prestressing tendons. In this regard, after introducing the damage variable Ds to consider the fatigue damage of prestressing tendons, the stress of prestressing tendons can be expressed as follows:

[0096] σ D (t) = (1 - D s )σ P (t)

[0097] In the formula, Ds is the damage variable, and σ P (t) is the prestress without considering fatigue damage.

[0098] As Figure 2 shown, at present, the prestressing tendons widely used in prestressed concrete bridge structures are low-relaxation 1860-grade 7-wire steel strands with a nominal diameter of 15.2 mm. For such prestressing tendons, the typical stress-strain curve in the specification drawings is as Figure 2 shown.

[0099] To make the calculation of prestress relaxation loss more applicable, a multi-stage linear stress-strain relationship can be adopted. In prestressed concrete bridges, the stress level of the steel strand is usually in the elastic-plastic section. Therefore, only considering the mechanical behavior of the steel strand in the elastic stage and the elastic-plastic stage, the stress-strain relationship is specifically as follows:

[0100]

[0101] In the formula, Es = the initial Young's elastic modulus of the prestressing tendon; ε p , ε pt are the proportional limit strain and the ultimate strain respectively, ε 0.2 represents the strain corresponding to a residual strain of 0.2%, E s = 198.5 GPa, ε p = 0.00413, ε 0.2 = 0.0109, ε u = 0.0460, σ 0.2 = 1772 MPa, σ u = 1944 MPa.

[0102] Example 2

[0103] This example proposes a prestressing tendon relaxation constitutive model construction system, including:

[0104] Total strain rate construction module of prestressing tendon: used to construct the rate expression of the total strain of the prestressing tendon based on the small strain and strain additive splitting principle;

[0105] Stress rate construction module of prestressing tendon: used to consider the variable strain and temperature conditions in the rate expression of the total change of the prestressing tendon to obtain the stress rate expression of the prestressing tendon;

[0106] Prestressing tendon relaxation loss constitutive model construction module: used to utilize the rate expression of the prestressing tendon, consider the influence of fatigue damage on the stress relaxation of the prestressed steel bar, introduce the damage variable, and complete the construction of the prestressing tendon relaxation loss constitutive model considering fatigue damage.

[0107] The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for constructing a constitutive model of relaxation loss of prestressed tendons, characterized in that, It includes the following steps: Step 1: Based on the small strain and strain additive splitting principle, construct the rate expression of the total strain of the prestressed tendon; Step 2: Consider the variable strain and variable temperature conditions in the rate expression of the total strain of the prestressed tendon, and derive the stress rate expression of the prestressed tendon; Step 3: Use the rate expression of the prestressed tendon, introduce the damage variable, and complete the construction of the constitutive model of the relaxation loss of the prestressed tendon considering fatigue damage.

2. The method for constructing a constitutive model of relaxation loss of prestressed tendons according to claim 1, characterized in that, The rate expression of the total strain of the prestressed tendon in Step 1 is as follows: where ε is the total normal strain of the prestressing tendon, ε se is the instantaneous elastic strain, ε sv is the viscoplastic strain, T is the absolute temperature, α s is the coefficient of thermal expansion of the prestressing tendon, E t is the tangent modulus of the prestressing tendon, σ p is the stress of the prestressing tendon, A T is the temperature influence factor.

3. A method for constructing a constitutive model of relaxation loss of prestressed tendons according to claim 1, characterized in that: Step 2 includes the following steps: Step 201: Based on the rate process theory, obtain the specific expression of A T : Where Q p is the flow activation energy of the prestressing tendon, k B = 1.38×10 -23 J / K, (at temperature T0 = 293K, A T = 1); Step 202: Under constant strain and constant temperature, the change of the prestress in the prestressed tendon with time is calculated by the following formula: where λ1 = 1000h; k, c, ρ0 and γ are empirically fitted constants for the given prestressing tendon, k ≈ 0.08, c ≈ 2, ρ0 = 0.32, γ = 0.45; is the average yield strength of the prestressing tendon; is the lowest threshold that can cause prestress relaxation; 〈〉 is the Macaulay bracket, defined here as 〈x〉 = max(x, 0). In addition, F p is a function describing the stress-strain law of the prestressing tendon under short-term loading, σ p = F p (ε); under constant strain, F p (ε) = σ p0 = initial prestress.

4. A method for constructing a constitutive model of relaxation loss of prestressed tendons according to claim 3, characterized in that: Step 202 also includes the following steps: Under variable strain conditions, the function f expression is as follows: where λ1 = 1000h, k, c, ρ0 and γ are empirical fitting constants for the given prestressing tendon, k ≈ 0.08, c ≈ 2, ρ0 = 0.32, γ = 0.45; ε m is the maximum strain experienced by the prestressing tendon. During loading, and ε ≥ ε m , E t = F′ p (ε) = dF(ε) / d ε = the tangent modulus of the prestressing tendon; during unloading or reloading, or ε < ε m , E t = E = the initial Young's elastic modulus of the prestressing tendon = 198.5 GPa.

5. A method for constructing a constitutive model of relaxation loss of prestressed tendons according to claim 4, characterized in that: Step 2 also includes the following steps: Step 203: Under variable temperature conditions, the strain that enters the viscous law as the first parameter of the function f is the mechanical strain, which is obtained by subtracting the thermal strain from the total strain, that is: ε* = ε - α T (T - T init ) Where, T init represents the initial temperature; α T is the thermal expansion coefficient of the prestressed tendon, Step 204: According to the variable strain f function and Step 203, the stress rate expression of the prestressed tendon is obtained as follows:

6. A method for constructing a constitutive model of relaxation loss of prestressed tendons according to any one of claims 1-5, characterized in that, The specific content of Step 3 is: It is described by a non-linearly evolving damage variable: k = αN / N f where k is a material parameter related to fatigue damage, and N f is the fatigue life. When k = 0, the damage variable is a linear model, i.e., D = N / N f , and α is the material micro-damage parameter For the fatigue life of the prestressed tendon, the following formula is used for evaluation: logN f = 13.84 - 3.5 log Δσ Where N f is the fatigue life and Δσ is the fatigue stress amplitude; Finally, the constitutive model of the relaxation loss of the prestressed tendon considering fatigue damage is obtained: σ D (t) = (1 - D s )σ P (t) where D s is the damage variable, and σ P (t) is the prestress without considering fatigue damage.

7. A prestressed tendon relaxation constitutive model construction system for implementing the method for constructing a prestressed tendon relaxation loss constitutive model according to any one of claims 1-6, characterized in that, It includes: Total strain rate construction module of prestressed tendon: used to construct the rate expression of the total strain of the prestressed tendon based on the small strain and strain additive splitting principle; Stress rate construction module of prestressed tendon: used to consider the variable strain and temperature conditions in the rate expression of the total strain of the prestressed tendon and obtain the stress rate expression of the prestressed tendon; Constitutive model construction module of relaxation loss of prestressed tendon: used to use the rate expression of the prestressed tendon, consider the influence of fatigue damage on the stress relaxation of prestressed steel bars, introduce the damage variable, and complete the construction of the constitutive model of the relaxation loss of the prestressed tendon considering fatigue damage.

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