A method for evaluating the residual mechanical properties of grouting sleeve connectors after corrosion

Abstract

The present invention discloses a method for evaluating the residual mechanical properties of a grouting sleeve connector after corrosion. The method is simple and easy to master, and has strong operability. It fills the gap in the method for studying the residual mechanical properties of a grouting sleeve connector after corrosion in a prefabricated bridge, and has important practical application value for the formulation of disaster prevention plans and repair and reinforcement decisions for prefabricated bridges throughout their life cycle.

Description

Technical Field

[0001] The invention relates to a method for evaluating the full-life mechanical properties of a grouting sleeve in an assembled structure, and in particular to a method for evaluating the residual mechanical properties of a grouting sleeve connector after corrosion. Background Art

[0002] Prefabricated bridges are mainly made of reinforced concrete and face the risk of corrosion during their service life. As the key force-transmitting components of prefabricated bridges, the degradation of the mechanical properties of sleeve grouting connectors after corrosion will directly threaten the service safety of prefabricated bridge structures.

[0003] Existing research mainly focuses on the initial mechanical properties of grouting sleeve connectors, and very few scholars have conducted preliminary research on the mechanical properties of connectors after corrosion. However, there are few studies reporting on the precise description of the non-uniformity of sleeve surface corrosion, and there is also a lack of a force transmission model for connectors under the dual attenuation of the mechanical properties of the corroded sleeve and the interfacial bonding properties of the steel bar and grouting material, which leads to a unclear understanding of the evolution mechanism of the force transmission performance of connectors after corrosion. Therefore, on the basis of establishing a method for characterizing the sleeve corrosion morphology, the dual degradation effects of the sleeve mechanical properties and the interfacial bonding properties of the steel bar and grouting material are comprehensively considered, and it is necessary to establish a method for evaluating the residual mechanical properties of grouting sleeve connectors after corrosion, so as to provide a theoretical basis and scientific basis for the evaluation of the mechanical properties of prefabricated bridge structures throughout their life cycle. Summary of the invention

[0004] In view of the above-mentioned technical deficiencies, the purpose of the present invention is to provide a method for evaluating the residual mechanical properties of grouting sleeve connectors after corrosion, thereby laying a theoretical foundation for further full-life safety assessment of grouting sleeve connected prefabricated bridge structures.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for evaluating the residual mechanical properties of a grouting sleeve connector after corrosion, which at least comprises the following steps:

[0007] S1. Prepare multiple grouting sleeve connectors, use insulating tape and epoxy resin to perform rust-proof treatment on the exposed steel bars at both ends of the sleeve, and perform electrochemical accelerated corrosion on the outer surface of the sleeve;

[0008] S2. Use a 3D profile scanner to perform multiple segmented scans on the sleeve connector, establish a 3D geometric model of the sleeve through the template matching method and the scanner's own software, reconstruct the sleeve surface corrosion morphology, and establish a binary function of sleeve wall thickness corrosion degradation;

[0009] S3. Taking the sleeve wall thickness corrosion degradation binary function as the input variable, the sleeve is subjected to segmented equal cross-sectional area corrosion equivalence, the lateral constraint force degradation factor of the corroded sleeve is introduced, and the sleeve connection force transmission model based on nonlinear spring unit is established using thick-walled cylinder theory;

[0010] S4. Conduct a uniaxial pull-out test on the corroded sleeve connector, establish a relationship curve between the tension and end displacement of the connector, and obtain a distribution curve of the sleeve outer surface strain along the radial direction;

[0011] S5. The force transmission model of the sleeve connector is calibrated using the uniaxial pull-out test data, and the expression of the bond stress-slip constitutive parameter of the nonlinear spring unit with respect to the sleeve lateral constraint force degradation factor is fitted. Combined with the binary function of sleeve wall thickness corrosion degradation, it can be used to predict the degree of degradation of the residual mechanical properties of the sleeve connector under any corrosion conditions.

[0012] Preferably, the specific method of step S1 is:

[0013] 1) Taking the steel bar diameter as a parameter, a plurality of steel bar grouting sleeve connectors are prepared, and the geometric parameters and initial mechanical properties of the connectors are consistent;

[0014] 2) Wrap insulating tape around the exposed steel bars at both ends of the prepared sleeve connector, and then apply epoxy resin to ensure that the steel bars are well sealed and will not be affected by chloride corrosion in the later stage;

[0015] 3) preparing a container for holding a chloride solution and injecting a chloride solution having a concentration of 3.5% into the container;

[0016] 4) The sleeve connector is immersed in a chloride salt solution to carry out electrochemical accelerated corrosion: the sleeve connector is divided into 8 groups, 3 in each group, and the sleeve corrosion rates are set to 0%, 5%, 10%, 15%, 20%, 25%, 30%, and 35% respectively;

[0017] 5) Select the corrosion current density i = 100 μA / cm 2 , combined with the outer surface area A of the sleeve, calculate the constant current I = i * A, and conduct power-on for different durations. The power-on duration is determined by Faraday's law, specifically:

[0018]

[0019] Where, T cor is the power-on time, m los is the mass loss of the rusted sleeve, Z Fe is the valence of iron, F is the Faraday constant, M Fe is the molar mass of steel bar.

[0020] Preferably, the specific method of step S2 is:

[0021] 1) Use a 3D profile scanner for non-contact three-dimensional scanning. Considering that the sleeve length exceeds the scanner's measurement range, the sleeve needs to be scanned in sections, and the number of section scans should be greater than the ratio of the sleeve length to the scanning range;

[0022] 2) The three-dimensional coordinate point cloud of the sleeve surface is established through the template matching method and the scanner's own software, and the rust morphology reconstruction data is statistically analyzed to determine the rust pit distribution map;

[0023] 3) Based on the rust pit distribution diagram and the inner wall geometric dimensions, a binary function t(l,θ) of sleeve wall thickness corrosion degradation with radial length l and annular rotation angle θ as independent variables is established;

[0024] Preferably, the specific method of step S3 is:

[0025] 1) According to the sleeve wall thickness corrosion degradation binary function t(l,θ) established in step S2, the sleeve is divided into multiple sections along the radial direction, and each section of the sleeve is subjected to uniform corrosion of the same area. For the i-th section of the sleeve, the average remaining wall thickness t is calculated. ave,i , and obtain the average mass loss rate η of the sleeve ave,i , specifically

[0026]

[0027]

[0028] In the formula, r1 is the inner radius of the sleeve, r2 is the outer radius of the sleeve, and t(l i ,θ) is the binary function of wall thickness corrosion degradation of the i-th section sleeve.

[0029] 2) The thick-walled cylinder theory is used to calculate the lateral restraint stress of each sleeve with the same area and uniform corrosion on the grouting material. The degradation factor λ(η) of the lateral restraint force of each sleeve is introduced, which is defined as the ratio of the lateral restraint stress of the corroded sleeve to the restraint stress of the uncorroded sleeve, specifically:

[0030]

[0031] Where η is the mass loss rate of the corroded sleeve, f n (0) is the lateral restraint stress of the uncorroded sleeve, f n (η) is the lateral restraint stress of the uncorroded sleeve.

[0032] 3) The lateral constraint force degradation factor is taken as the core variable affecting the constitutive parameters of the bonded sliding spring, and the sleeve is equivalent to a multi-segment nonlinear truss unit to form a force transmission model of the corroded sleeve connector that takes into account the coupling effects of the reduction of the sleeve mechanical properties and the weakening of the lateral constraint effect;

[0033] Preferably, the specific method of step S4 is:

[0034] 1) Performing a uniaxial tensile test on the corroded sleeve connector in step S2, recording the pull-out force by a tensile machine, measuring the end displacement by an LVDT, and establishing a pull-out force-displacement relationship curve of the connector corresponding to the binary function t(l,θ) of corrosion degradation of different sleeve wall thicknesses;

[0035] 2) Seven strain gauges are pasted at equal intervals along the radial direction of the sleeve to measure the strain, and the radial distribution curve of the sleeve strain corresponding to the binary function t(l,θ) of corrosion degradation with different wall thicknesses is established.

[0036] Preferably, the specific method of step S5 is:

[0037] 1) The force transmission model of the sleeve connector is established using the Opensees finite element platform. Based on the test data of the tension-displacement curve and sleeve strain distribution obtained from the tensile test, the force transmission model of the sleeve connector is calibrated, and the expression of the bond stress-slip constitutive parameter of the nonlinear spring unit with respect to the degradation factor of the sleeve lateral constraint force is fitted, which is specifically:

[0038]

[0039] S1(η)=ψ1(λ(η))·S1(0) (6)

[0040] S2(η)=ψ2(λ(η))·S2(0) (7)

[0041] In the formula, τ m (η) is the interfacial bond strength between the steel bar and the grouting material, f g is the compressive strength of the grouting material, A(η) and B(η) are expressions obtained by calibration and fitting of the test data, S1(0) is the maximum slip value corresponding to the rising section of the bond-slip curve in the uncorroded case, S2(0) is the maximum slip value corresponding to the platform section of the bond-slip curve in the uncorroded case, S1(η) is the maximum slip value corresponding to the rising section of the bond-slip curve under the influence of corrosion, S2(η) is the maximum slip value corresponding to the platform section of the bond-slip curve under the influence of corrosion, ψ1(λ(η)) and ψ2(λ(η)) are expressions for the degradation factor λ(η) of the sleeve lateral constraint force obtained by calibration and fitting of the test data.

[0042] 2) Based on the binary function of sleeve wall thickness corrosion degradation and the bond stress-slip constitutive parameters of the nonlinear spring unit, they are used in the force transmission model of the connector. The model outputs the tension-displacement curve of the connector and calculates the average mass loss rate η of the sleeve. ave , calculate the relative value of the yield strength of the connector α y (η ave ), relative value of yield strain βy (η ave ), peak intensity relative value α y (η ave ), relative value of peak strain β m (η ave ) and the relative value of the ultimate strain β u (η ave ), these five indicators are used to comprehensively evaluate the degree of degradation of the residual mechanical properties of the sleeve connector under any corrosion conditions, specifically:

[0043]

[0044]

[0045]

[0046]

[0047]

[0048] In the formula, F y (0) and F y (η ave ) are the yield strengths of the uncorroded and corroded sleeve connectors, respectively, F m (0) and F m (η ave ) are the peak strengths of the uncorroded and corroded sleeve connectors, ε y (0) and ε y (η ave ) are the yield strains of the uncorroded and corroded sleeve connectors, ε m (0) and ε m (η ave ) are the peak strains of the uncorroded and corroded sleeve connectors, ε u (0) and ε u (η ave ) are the ultimate strains of the non-corroded and corroded sleeve connectors, respectively.

[0049] The beneficial effects of the present invention are:

[0050] 1. The present invention adopts non-contact 3D scanning technology to establish a binary function of sleeve wall thickness corrosion degradation, realizes the precise quantitative characterization of the corrosion morphology of the sleeve connector, and makes up for the defect that the sleeve corrosion morphology is still unclear in existing research.

[0051] 2. The present invention establishes a quantitative relationship between the degree of sleeve corrosion and the degree of mechanical property degradation, providing a theoretical basis and scientific basis for the full-life seismic design and evaluation of grouting sleeve-connected prefabricated bridge structures in my country.

[0052] 3. The method proposed in the present invention provides experimental verification data for the refined three-dimensional mechanical model of the corroded sleeve connector, and has practical value for the numerical simulation of the mechanical properties of the sleeve connector and the prefabricated bridge.

[0053] 4. The method of the present invention has a wide range of practical applications and can be applied to the simulation of the average corrosion degree and corrosion randomness of the sleeve in the bridge pier.

[0054] 5. The method of the present invention more realistically reflects the corrosion of the outer wall of the sleeve connector, which is closer to the actual situation than the existing research that considers the corrosion of the inner wall of the sleeve.

[0055] 6. The force transmission model of the corroded sleeve connection established in the method of the present invention takes into account both the degradation of the mechanical properties of the sleeve and the degradation of the interfacial bonding properties between the steel bar and the grouting material, and is an accurate numerical model. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0057] Figure 1 A flow chart of a method for evaluating the residual mechanical properties of a grouting sleeve connector after corrosion provided by an embodiment of the present invention;

[0058] Figure 2 A schematic diagram of a sleeve connector used in an embodiment of the present invention;

[0059] Figure 3 Schematic diagram of electrochemical accelerated corrosion test of sleeve connector in an embodiment of the present invention;

[0060] Figure 4 Schematic diagram of a 3D scanning method for the corrosion morphology of a sleeve connector in an embodiment of the present invention;

[0061] Figure 5 Schematic diagram of a uniaxial tensile test of a sleeve connector in an embodiment of the present invention;

[0062] Figure 6 Schematic diagram of the force transmission model of the sleeve connector in an embodiment of the present invention. DETAILED DESCRIPTION

[0063] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0064] like Figures 1 to 4 As shown, a method for evaluating the residual mechanical properties of a grouting sleeve connector after corrosion specifically comprises the following steps:

[0065] Step S1, preparing a plurality of grouting sleeve connectors, using insulating tape and epoxy resin to perform rust-proof treatment on the exposed steel bars at both ends of the sleeves, and performing electrochemical accelerated corrosion on the outer surface of the sleeves, specifically:

[0066] 1)Reference Figure 2 , prepare multiple grouting sleeve connectors, the geometric parameters of each connector are consistent with the initial mechanics. In this embodiment, 24 sleeve connectors with the same geometric dimensions and mechanical properties are designed, the steel bar diameter is 14mm, and the sleeve is selected from Beijing Star Jianmao GTL series full grouting sleeve, the corresponding model is GT14L, and the variable parameter of the test is the duration of rusting after power on;

[0067] 2) Wrap insulating tape around the steel bars at both ends of the prepared sleeve connector, and then apply epoxy resin to ensure that the steel bars are well sealed and will not be affected by chloride corrosion in the later stage;

[0068] 3) preparing a container for the chloride salt solution, and injecting a chloride salt solution with a concentration of 3.5% into the container;

[0069] 4) Place the sleeve connector in a chloride salt solution and conduct electrochemical accelerated corrosion: divide the sleeve connector into 8 groups, 3 in each group, and set the sleeve corrosion rates to 0%, 5%, 10%, 15%, 20%, 25%, 30%, and 35% respectively;

[0070] 5) Select the corrosion current density i = 100 μA / cm 2 , combined with the outer surface area of ​​the sleeve, the constant current is calculated; the negative electrode 2 of the DC power supply 1 is connected to the stainless steel mesh, and the positive electrode 3 of the DC power supply 1 is connected to the surface of the sleeve, and power is applied for different durations. The power-on duration is determined by Faraday's law, and the 8 groups of sleeve connectors are accelerated according to the corrosion time; specifically:

[0071]

[0072] Where, T cor is the power-on time, m los is the mass loss of the rusted sleeve, Z Feis the valence of iron, F is the Faraday constant, M Fe is the molar mass of steel bar.

[0073] Step S2: Use a 3D profile scanner to perform multiple segmented scans on the sleeve connector, establish a three-dimensional geometric model of the sleeve through a template matching method and the scanner's own software, reconstruct the sleeve surface corrosion morphology, and establish a binary function of sleeve wall thickness corrosion degradation, specifically:

[0074] 1) Select a 3D profile scanner of model VR5200 to perform three-dimensional scanning on the 8 groups of corroded sleeve connectors in step S2. Considering that the sleeve length exceeds the measurement range of the scanner, the sleeve needs to be scanned in sections, and the number of section scans should be greater than the ratio of the sleeve length to the scanning range;

[0075] 2) The template matching method is used to identify the image overlap area of ​​adjacent scanning segments, that is, the homologous two-dimensional image. Subsequently, based on the guidance of the homologous two-dimensional image, the mapping relationship between the image and the three-dimensional coordinate points established by the scanner's own software is used to achieve complete splicing of the three-dimensional data point cloud and complete the three-dimensional reconstruction of the overall appearance of the sleeve corrosion; the overall reconstruction data of the corrosion of 8 groups of sleeve connectors are statistically analyzed to analyze the number and spacing of rust pits, the length, width and depth of a single rust pit, and determine the distribution map of rust pits;

[0076] 3) Based on the rust pit distribution diagram and the three-dimensional geometric dimensions of the inner wall, the rusted sleeve wall thickness distribution function t(l,θ) with respect to the radial length l and the annular rotation angle θ is established;

[0077] Step S3, taking the sleeve wall thickness corrosion degradation binary function as the input variable, performing segmented equal cross-sectional area corrosion equivalence on the sleeve, introducing the lateral constraint force degradation factor of the corroded sleeve, and using the thick-walled cylinder theory to establish a sleeve connector force transmission model based on nonlinear spring units, specifically:

[0078] 1) According to the sleeve wall thickness corrosion degradation binary function t(l,θ) established in step S2, the sleeve is divided into multiple sections along the radial direction, and each section of the sleeve is subjected to uniform corrosion of the same area. For the i-th section of the sleeve, the average remaining wall thickness t is calculated. ave,i , and obtain the average mass loss rate η of the sleeve ave,i , specifically

[0079]

[0080]

[0081] In the formula, r1 is the inner radius of the sleeve, r2 is the outer radius of the sleeve, and t(l i ,θ) is the binary function of wall thickness corrosion degradation of the i-th section sleeve.

[0082] 2) The thick-walled cylinder theory is used to calculate the lateral restraint stress of each sleeve with the same area and uniform corrosion on the grouting material. The degradation factor λ(η) of the lateral restraint force of each sleeve is introduced, which is defined as the ratio of the lateral restraint stress of the corroded sleeve to the restraint stress of the uncorroded sleeve, specifically:

[0083]

[0084] Where η is the mass loss rate of the corroded sleeve, f n (0) is the lateral restraint stress of the uncorroded sleeve, f n (η) is the lateral restraint stress of the uncorroded sleeve.

[0085] 3) The lateral constraint force degradation factor is taken as the core variable affecting the constitutive parameters of the bond-slip spring, and the sleeve is equivalent to a multi-segment nonlinear truss unit, forming a force transmission model of the rusted sleeve connector that takes into account the coupling effects of the reduction in the mechanical properties of the sleeve and the weakening of the lateral constraint effect.

[0086] Step S4, carry out a uniaxial pull-out test on the corroded sleeve connector, establish a relationship curve between the tension and end displacement of the connector, and obtain a distribution curve of the sleeve outer surface strain along the radial direction, specifically:

[0087] 1) Uniaxial tensile tests were carried out on 8 groups of corroded sleeve connectors. The pull-out force F was recorded by a tensile machine, and the end displacement S was measured by LVDT. The FS relationship curve of the sleeve connector corresponding to the binary function t(l,θ) of corrosion degradation with different sleeve wall thickness was established.

[0088] 2) Based on the measurement data of 7 strain gauges pasted at equal intervals along the radial direction of the sleeve, the radial distribution curve of the sleeve strain corresponding to the binary function t(l,θ) of corrosion degradation with different wall thicknesses is established.

[0089] Step S5: calibrate the force transmission model of the sleeve connector using the uniaxial pull-out test data, and fit the expression of the bond stress-slip constitutive parameter of the nonlinear spring unit with respect to the sleeve lateral constraint force degradation factor. Combined with the sleeve wall thickness corrosion degradation binary function, it can be used to predict the degree of degradation of the residual mechanical properties of the sleeve connector under any corrosion condition, specifically:

[0090] 1) The Opensees finite element platform was used to establish the force transmission model of the sleeve connector. Based on the test data of the tension-displacement curve and the sleeve strain distribution obtained from the tensile test, 8 sets of sleeve connector force transmission models were calibrated, and the expression of the bond stress-slip constitutive parameters of the nonlinear spring unit with respect to the degradation factor of the sleeve lateral constraint force was fitted, which is specifically:

[0091]

[0092] S1(η)=ψ1(λ(η))·S1(0) (6)

[0093] S2(η)=ψ2(λ(η))·S2(0) (7)

[0094] In the formula, τ m (η) is the interfacial bond strength between the steel bar and the grouting material, f g is the compressive strength of the grouting material, A(η) and B(η) are expressions obtained by calibration fitting of the test data, S1(0) is the maximum slip value corresponding to the rising section of the bond-slip curve in the uncorroded case, S2(0) is the maximum slip value corresponding to the platform section of the bond-slip curve in the uncorroded case, S1(η) is the maximum slip value corresponding to the rising section of the bond-slip curve under the influence of corrosion, S2(η) is the maximum slip value corresponding to the platform section of the bond-slip curve under the influence of corrosion, ψ1(λ(η)) and ψ2(λ(η)) are expressions for the degradation factor λ(η) of the sleeve lateral constraint force obtained by calibration fitting of the test data.

[0095] 2) Based on the binary function of sleeve wall thickness corrosion degradation and the bond stress-slip constitutive parameters of the nonlinear spring unit, they are used in the force transmission model of the connector. The model outputs the tension-displacement curve of the connector and calculates the average mass loss rate η of the sleeve. ave , calculate the relative value of the yield strength of the connector α y (η ave ), relative value of yield strain β y (η ave ), peak intensity relative value α y (η ave ), relative value of peak strain β m (η ave ) and the relative value of the ultimate strain β u (η ave ), these five indicators are used to comprehensively evaluate the degradation degree of the residual mechanical properties of the sleeve connector under any corrosion condition, and their variation law is analyzed and fitted to obtain their expressions, which are specifically:

[0096]

[0097]

[0098]

[0099]

[0100]

[0101] In the formula, F y (0) and F y (η ave) are the yield strengths of the uncorroded and corroded sleeve connectors, respectively, F m (0) and F m (η ave ) are the peak strengths of the uncorroded and corroded sleeve connectors, ε y (0) and ε y (η ave ) are the yield strains of the uncorroded and corroded sleeve connectors, ε m (0) and ε m (η ave ) are the peak strains of the uncorroded and corroded sleeve connectors, ε u (0) and ε u (η ave ) are the ultimate strains of the non-corroded and corroded sleeve connectors, respectively.

[0102] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for evaluating the residual mechanical properties of a grouting sleeve connector after corrosion, characterized in that: The specific steps include: S1. Prepare multiple grouted sleeve connectors, perform anti-rust treatment on the exposed steel bars at both ends of the sleeves, and perform electrochemical accelerated corrosion on the outer surface of the sleeves; S2. Use a scanner to scan the sleeve connector in sections for multiple times, establish a three-dimensional geometric model of the sleeve, reconstruct the rust morphology of the sleeve surface, and establish a binary function of sleeve wall thickness rust degradation; S3. Taking the sleeve wall thickness corrosion degradation binary function as the input variable, the sleeve is subjected to segmented equal cross-sectional area corrosion equivalence, the lateral constraint force degradation factor of the corroded sleeve is introduced, and the sleeve connection force transmission model based on nonlinear spring unit is established using thick-walled cylinder theory; S4. Conduct a uniaxial pull-out test on the corroded sleeve connector, establish a relationship curve between the tension and end displacement of the connector, and obtain a distribution curve of the sleeve outer surface strain along the radial direction; S5. The force transmission model of the sleeve connector is calibrated using the uniaxial pull-out test data, and the expression of the bond stress-slip constitutive parameter of the nonlinear spring unit with respect to the degradation factor of the sleeve lateral constraint force is fitted. Combined with the binary function of sleeve wall thickness corrosion degradation, it is used to predict the degree of degradation of the residual mechanical properties of the sleeve connector under any corrosion conditions; The specific method of step S5 is: 1) The force transmission model of the sleeve connector is established using the Opensees finite element platform. Based on the test data of the tension-displacement curve and sleeve strain distribution obtained from the tensile test, the force transmission model of the sleeve connector is calibrated, and the expression of the bond stress-slip constitutive parameter of the nonlinear spring unit with respect to the degradation factor of the sleeve lateral constraint force is fitted, which is specifically: S1(η)=ψ1(λ(η))·S1(0) (6) S2(η)=ψ2(λ(η))·S2(0) (7) In the formula, τ m (η) is the interfacial bond strength between the steel bar and the grouting material, f g is the compressive strength of the grouting material, λ(η) is the degradation factor of the lateral restraint force of each sleeve section, η is the mass loss rate of the corroded sleeve, and f n (0) is the lateral constraint stress of the uncorroded sleeve, A(η) and B(η) are expressions obtained by calibration fitting of test data, S1(0) is the maximum slip value corresponding to the rising section of the bond-slip curve in the uncorroded case, S2(0) is the maximum slip value corresponding to the platform section of the bond-slip curve in the uncorroded case, S1(η) is the maximum slip value corresponding to the rising section of the bond-slip curve under the influence of corrosion, S2(η) is the maximum slip value corresponding to the platform section of the bond-slip curve under the influence of corrosion, ψ1(λ(η)) and ψ2(λ(η)) are expressions for the degradation factor λ(η) of the sleeve lateral constraint force obtained by calibration fitting of test data; 2) According to the binary function of sleeve wall thickness corrosion degradation and the bond stress-slip constitutive parameters of the nonlinear spring unit, they are used in the force transmission model of the connector, the tension-displacement curve of the connector is output, and the average mass loss rate η of the sleeve is calculated. ave , calculate the relative value of the yield strength of the connector α y (η ave ), relative value of yield strain β y (η ave ), peak intensity relative value α y (η ave ), relative value of peak strain β m (η ave ) and the relative value of the ultimate strain β u (η ave ), specifically In the formula, F y (0) and F y (η ave ) are the yield strengths of the uncorroded and corroded sleeve connectors, respectively, F m (0) and F m (η ave ) are the peak strengths of the uncorroded and corroded sleeve connectors, ε y (0) and ε y (η ave ) are the yield strains of the uncorroded and corroded sleeve connectors, ε m (0) and ε m (η ave ) are the peak strains of the uncorroded and corroded sleeve connectors, ε u (0) and ε u (η ave ) are the ultimate strains of the non-corroded and corroded sleeve connectors, respectively.

2. A method for evaluating the residual mechanical properties of a grouting sleeve connector after corrosion according to claim 1, characterized in that: The specific method of step S1 is: 1) Taking the steel bar diameter as a parameter, a plurality of steel bar grouting sleeve connectors are prepared, and the geometric parameters and initial mechanical properties of the sleeve connectors are consistent; 2) Wrap insulating tape around the steel bars at both ends of the prepared sleeve connector, and then apply epoxy resin to ensure that the steel bars are well sealed and will not be affected by chloride corrosion in the later stage; 3) preparing a container for holding a chloride solution and injecting a chloride solution having a concentration of 3.5% into the container; 4) Place the sleeve connector in a chloride salt solution and conduct electrochemical accelerated corrosion: divide the sleeve connector into 8 groups according to the corrosion rate; 5) Select the corrosion current density i = 100 μA / cm 2 , power on for different durations, and the duration of power on is determined by Faraday's law, specifically: Where, T cor is the power-on time, m los is the mass loss of the rusted sleeve, Z Fe is the valence of iron, F is the Faraday constant, M Fe is the molar mass of steel bar.

3. A method for evaluating the residual mechanical properties of a grouting sleeve connector after corrosion according to claim 1, characterized in that: The specific method of step S2 is: 1) Use a 3D profile scanner to perform multiple segmented three-dimensional scans on the outer surface of the sleeve. The number of segmented scans should be greater than the ratio of the sleeve length to the scanning range; 2) The three-dimensional coordinate point cloud of the sleeve surface is established through the template matching method and the scanner's own software, and the rust morphology reconstruction data is statistically analyzed to determine the rust pit distribution map; 3) Based on the rust pit distribution diagram and the inner wall geometric dimensions, a binary function t(l,θ) of sleeve wall thickness corrosion degradation is established with radial length l and annular rotation angle θ as independent variables.

4. A method for evaluating the residual mechanical properties of a grouting sleeve connector after corrosion according to claim 1, characterized in that: The specific method of step S3 is: 1) According to the sleeve wall thickness corrosion degradation binary function t(l,θ) established in step S2, the sleeve is divided into multiple sections along the radial direction, and each section of the sleeve is subjected to uniform corrosion of the same area. For the i-th section of the sleeve, the average remaining wall thickness t is calculated. ave,i , and obtain the average mass loss rate η of the sleeve ave,i , specifically In the formula, r1 is the inner radius of the sleeve, r2 is the outer radius of the sleeve, and t(l i ,θ) is the binary function of wall thickness corrosion degradation of the i-th sleeve; 2) Using the thick-walled cylinder theory, the lateral restraint stress of each sleeve with the same area and uniform corrosion on the grouting material is calculated, and the lateral restraint force degradation factor λ(η) of each sleeve is introduced, which is specifically: Where η is the mass loss rate of the corroded sleeve, f n (0) is the lateral restraint stress of the uncorroded sleeve, f n (η) is the lateral restraint stress of the uncorroded sleeve; 3) The lateral constraint force degradation factor is taken as the core variable affecting the constitutive parameters of the bond-slip spring, and the sleeve is equivalent to a multi-segment nonlinear truss unit to form a force transmission model of the corroded sleeve connector.

5. A method for evaluating the residual mechanical properties of a grouting sleeve connector after corrosion according to claim 1, characterized in that: The specific method of step S4 is: 1) Performing a uniaxial tensile test on the corroded sleeve connector in step S2 to obtain a pull-out force-displacement relationship curve of the connector corresponding to the binary function t(l,θ) of corrosion degradation of different sleeve wall thicknesses; 2) Using surface-bonded strain gauges, the strain distribution curves of sleeves with different degrees of corrosion along the radial direction are obtained.

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