Prediction method for bond strength of prestressed steel strand

Abstract

The invention relates to the technical field of advanced steel and iron materials, and provides a prestressed steel strand bond strength prediction method which comprises the following steps: acquiring design parameters of target ground anchor cement paste and a steel strand, and sequentially constructing a compressive strength model, a limit stress model, a stress attenuation model, an interface contact model, a single-branch limit load model, a branch reduction model and a total limit load model. The predicted bond strength is obtained by combining the total limit load and the interface contact area; according to the method, the nonlinear reduction effect of the number of the prestressed steel strands on the bond strength is quantified, the correlation between the number of the prestressed steel strands in the anchor group system and the reduction of the bond strength of a single support is defined, and the problem that in the prior art, the single anchor stress field rule is directly migrated to the anchor group system, and the multi-support interference influence cannot be accurately evaluated is solved.

Description

Technical Field

[0001] This invention relates to the field of advanced steel materials technology, specifically a method for predicting the bond strength of prestressed steel strands. Background Technology

[0002] Ground anchors are structural components that ensure the safety of engineering structures such as slope stability, deep foundation pit excavation, and highway tunnel support. Their load-bearing capacity and failure resistance directly depend on the interfacial bond between the prestressed steel strands and the cement grout. The prestressed steel strands need to transfer anchoring force through the bond effect with the cement grout to resist the risk of structural instability under external forces, which is the key to the ground anchor's anchoring function. Therefore, predicting the bond strength between the prestressed steel strands and the cement grout during the engineering design phase is a prerequisite for balancing engineering safety and economy: it is necessary to avoid structural safety hazards caused by bond failure, and also to prevent waste of materials and costs due to overly conservative design.

[0003] Existing technologies focus on the bonding mechanism of a single anchor, assuming that the independent stress field law of a single anchor can be directly transferred to a group anchor system. However, the interfacial shear stress fields of multiple steel strands in a group anchor will superimpose each other. The stress penetration of cement grout around adjacent steel strands will lead to a reduction in the effective bonding area of ​​a single steel strand and uneven stress distribution, thereby changing the transmission law of bonding strength. Calculating the group anchor strength based solely on the linear superposition logic of a single anchor cannot quantify the correlation between the number of steel strands and the reduction in bonding strength of a single strand, resulting in low prediction accuracy.

[0004] In summary, this invention provides a method for predicting the bond strength of prestressed steel strands to solve the above-mentioned problems. Summary of the Invention

[0005] This invention provides a method for predicting the bond strength of prestressed steel strands, which solves the problem of low prediction accuracy in the prior art by comprehensively analyzing the prestressed steel strands.

[0006] The specific technical solution of this invention is as follows:

[0007] A method for predicting the bond strength of prestressed steel strands includes the following steps:

[0008] S1. Based on the design parameters of the target anchor, obtain the cement grout water-cement ratio, curing age, and the number, diameter, and effective bond length of the prestressed steel strands of the target anchor.

[0009] In this invention, the water-cement ratio of cement slurry refers to the ratio of the mass of water to the mass of cement during the preparation of cement slurry; the curing age refers to the time the cement slurry is placed under standard curing conditions of 20±2℃ and relative humidity ≥95% after mixing and forming, directly reflecting the degree of cement hydration completion; the number of prestressed steel strands refers to the total number of prestressed steel strands configured in the target anchor; the helical parameters of the prestressed steel strands refer to the characteristic parameters of the helical structure on the surface of the steel strands, including the helical rib height and the pitch. The helical rib height is the height of the helical protrusion on the surface of the steel strand, and the pitch is the axial distance of a single steel wire rotating around the central axis of the steel strand. Both of these parameters jointly determine the strength of the mechanical interlocking effect; the diameter of the prestressed steel strands refers to the nominal outer diameter of the steel strands; the effective bond length refers to the length of the steel strands that are completely covered by the cement slurry and can effectively transmit the bond shear stress; the protective layer thickness of the prestressed steel strands refers to the radial distance from the surface of the steel strands to the outer side of the cement slurry; and the spacing of the prestressed steel strands refers to the center distance between multiple steel strands.

[0010] S2. Analyze the historical engineering data of the target ground anchor, and construct a correlation model between the water-cement ratio, curing age and compressive strength of the cement grout, denoted as the compressive strength model.

[0011] In this invention, the historical engineering data of the target anchor refers to historical engineering data that is consistent with the cement type and preparation process used in the target anchor. It is mainly used to analyze the measured compressive strength data. When constructing the compressive strength model, tools such as Python and MATLAB can be used to perform linear regression on the data. Finally, after inputting the water-cement ratio and curing age, the compressive strength can be automatically calculated and output.

[0012] S3. Analyze the supporting effect of cement paste on steel strands, and construct an analytical correlation model between the compressive strength model and the ultimate bond stress, denoted as the ultimate stress model.

[0013] In this invention, the mechanical interlocking effect between the prestressed steel strand and the cement grout refers to the anti-slip effect generated by the spiral concave surface of the steel strand and the interlocking structure formed after the cement grout hardens, which utilizes the structural characteristics of the multi-strand steel wire spiral winding. This is the core source of the bond strength and is related to the spiral parameters of the prestressed steel strand. The supporting effect of the cement grout on the steel strand refers to the auxiliary role of the cement grout in providing lateral constraints for the mechanical interlocking effect of the steel strand through its own compressive strength, preventing mechanical interlocking failure due to compression damage. This is a prerequisite for the full realization of the mechanical interlocking effect and is related to the compressive strength of the cement grout. When constructing the ultimate stress model, tools such as Python and MATLAB can be used to linearly superimpose the contributions of the mechanical interlocking effect and the supporting effect of the cement grout, ultimately realizing the automatic calculation and output of the ultimate bond stress after inputting the spiral parameters and compressive strength.

[0014] S4. Based on the attenuation characteristics of the bond stress, a functional relationship model between the effective bond length of the prestressed steel strand and the stress attenuation coefficient is constructed, denoted as the stress attenuation model.

[0015] In this invention, the attenuation characteristic of the bond stress refers to the bond stress at the interface between the prestressed steel strand and the cement paste, especially the ultimate bond stress. This stress exhibits a non-linear decrease with increasing effective bond length, and the attenuation rate gradually slows down. Furthermore, the degree of attenuation is controlled by the helical parameters of the steel strand, which directly reflects the uneven distribution of interfacial shear stress during stress transmission. When constructing the stress attenuation model, tools such as Python and MATLAB can be used to fit the law using an exponential function. Ultimately, after inputting the helical parameters and the effective bond length, the stress attenuation coefficient can be automatically calculated and output.

[0016] S5. Based on the interface contact morphology between the prestressed steel strand and the cement grout, construct a correlation model between the diameter of the prestressed steel strand, the effective bond length, and the interface contact area, denoted as the interface contact model.

[0017] In this invention, the interface contact morphology between the prestressed steel strand and the cement grout refers to the physical morphology in which the prestressed steel strand is uniformly covered by the cement grout, and the two are directly bonded and in close contact only through the cylindrical side of the steel strand. This is the physical basis for calculating the interface contact area. When constructing the interface contact model, tools such as Python and MATLAB can be used to perform calculations using geometric formulas. Ultimately, after inputting the diameter and effective bond length of the prestressed steel strand, the interface contact area can be automatically calculated and output.

[0018] S6. Based on the ultimate bond stress output by the ultimate stress model, the interface contact area output by the interface contact model, and the stress attenuation coefficient output by the stress attenuation model, a prediction model for the ultimate load of a single prestressed steel strand is constructed, denoted as the single-strand prediction model.

[0019] In this invention, when constructing a single-strand prediction model, tools such as Python and MATLAB can be used. Based on the basic principles of mechanics of materials, namely that shear force is the product of shear stress and contact area, mathematical calculations are performed to finally realize the automatic calculation and output of the ultimate load of a single prestressed steel strand after inputting the ultimate grip stress, stress attenuation coefficient, and interface contact area.

[0020] S7. Based on the stress interference effect when prestressed steel strands are wrapped in parallel, a correction coefficient correlation model between the number of prestressed steel strands and the number of strands reduction coefficient is constructed, which is denoted as the number of strands reduction model.

[0021] In this invention, the stress interference effect when prestressed steel strands are bonded in parallel refers to the phenomenon where, when multiple steel strands are simultaneously embedded in cement grout, the shear stress fields around adjacent steel strands permeate and superimpose, leading to a reduction in the effective bonding area of ​​a single steel strand and uneven distribution of interfacial shear stress. Ultimately, this results in the actual bonding strength of a single steel strand being lower than its independent bonding strength, which is the reason for the reduction in bonding strength of the group anchor system. Essentially, the overlapping stress fields cause the cement grout between the steel strands to bear multi-directional shear stress, making it prone to premature micro-cracks or even splitting failure. This leads to a simultaneous decrease in the effective bonding area and shear stress transfer efficiency of a single steel strand, forming a nonlinear law where the more strands there are, the more significant the reduction in bonding strength of a single strand. The thickness of the protective layer directly determines the ability of the cement grout to resist splitting failure caused by stress superposition. The spacing between steel strands determines the degree of overlap of the stress fields of adjacent steel strands. When constructing the strand number reduction model, tools such as Python and MATLAB can be used to fit the nonlinear reduction of the strand number using an exponential function. Finally, after inputting the number of steel strands, the thickness of the protective layer, and the spacing, the model can automatically calculate and output the strand number reduction coefficient.

[0022] S8. Based on the single-strand prestressed steel strand ultimate load, the number of prestressed steel strands, and the number of strands reduction coefficient output by the single-strand prediction model, construct a prediction model for the total ultimate load.

[0023] In this invention, when constructing the prediction model for the total ultimate load, tools such as Python and MATLAB can be used to perform calculations based on mechanical logic. Ultimately, after inputting the ultimate load of a single prestressed steel strand, the number of prestressed steel strands, and the reduction factor for the number of strands, the model automatically calculates and outputs the total ultimate load, which is the overall ultimate load.

[0024] S9. Based on the interface contact area and total ultimate load of the target anchor, calculate the ultimate load per unit area of ​​the target anchor, which is the predicted grip strength of the target anchor.

[0025] In this invention, the formula for predicting grip strength is as follows:

[0026]

[0027] In the formula, This represents the predicted grip strength of the target anchor, which is the predicted maximum grip shear stress that the target anchor can withstand per unit area of ​​interface.

[0028] In a preferred embodiment, the compressive strength model in step S2 includes the following formula:

[0029]

[0030] In the formula, t represents the compressive strength of cement slurry, that is, the ultimate compressive bearing capacity of cement slurry under a specific curing age; t represents the curing age of cement slurry, that is, the time that cement slurry has been placed under standard curing conditions after mixing and forming, reflecting the degree of completion of cement hydration reaction. It represents the intercept constant, which is related to the initial hydration rate of cement paste and reflects the strength growth characteristics of cement paste at a very short age. This represents the slope constant, which is related to the rate of increase in strength during the later stages of cement paste hydration and reflects the degree to which the strength of cement paste slows down with age.

[0031] In a preferred embodiment, the ultimate stress model in step S3 includes the following formula:

[0032]

[0033] In the formula, The value represents the ultimate bond stress, which is the maximum shear stress that the interface can withstand; h represents the height of the spiral rib of the prestressed steel strand. The greater the rib height, the deeper the interlocking depth between the steel strand and the cement paste, and the stronger the interlocking force; P represents the pitch of the prestressed steel strand, which reflects the interlocking frequency of the spiral rib. The smaller the pitch, the more spiral ribs per unit length, the more frequent the mechanical interlocking, and the more uniform the bond force. The coefficient represents the contribution of the mechanical interlocking effect. It is used to quantify the contribution of the steel strand helix parameters to the ultimate grip stress. The larger the coefficient, the stronger the grip force provided by the mechanical interlocking under the same helix parameters. The coefficient represents the contribution of cement paste to the supporting effect. It is used to quantify the degree of support of the compressive strength of cement paste to the ultimate bond stress. The larger the coefficient, the stronger the lateral constraint of cement paste on the helical ribs under the same compressive strength, and the higher the shear stress that the interface can withstand.

[0034] In a preferred embodiment, the stress attenuation model in step S4 includes the following formula:

[0035]

[0036] In the formula, It represents the stress attenuation coefficient, which characterizes the degree of attenuation of the bond stress at the interface between the prestressed steel strand and the cement paste with the effective bond length. The value ranges from 0 to 1. The closer it is to 1, the weaker the attenuation and the more uniform the bond stress distribution. The smaller the value, the stronger the attenuation and the lower the effective bond stress at a longer bond length. It represents the effective bond length of the prestressed steel strand, which is the length that can be completely covered by cement paste and can transmit bond stress. The longer the length, the more the bond stress is lost when it is transmitted along the interface, and the smaller the attenuation coefficient. The value represents the contribution coefficient of the helical parameter, used to quantify the influence of the helical characteristic value of the steel strand on the attenuation suppression capability. The larger the value, the stronger the mechanical chain effect, the more uniform the stress transmission of the gripping, the larger the attenuation coefficient, and the weaker the attenuation, all under the same helical parameter. The value represents the attenuation rate coefficient, used to quantify the influence of the effective gripping length on the degree of attenuation. The larger the value, the smaller the exponential attenuation term, the smaller the attenuation coefficient, and the stronger the attenuation, all under the same gripping length. The smaller the value, the weaker the attenuation and the more uniform the distribution of the gripping stress.

[0037] In a preferred embodiment, in step S5, the interface contact model includes the following formula:

[0038]

[0039] In the formula, A represents the interfacial contact area between the prestressed steel strand and the cement grout, that is, the area on the surface of the steel strand that is directly bonded to the cement grout and can transfer the bond shear stress. This indicates the diameter of the prestressed steel strand. The larger the diameter, the larger the cross-sectional perimeter, the larger the contact area per unit grip length, and the stronger the grip force that can be transmitted.

[0040] In a preferred embodiment, in step S6, the single-branch prediction model includes the following formula:

[0041]

[0042] In the formula, It represents the ultimate load of a single prestressed steel strand, that is, the maximum pull-out force that a single steel strand can withstand under the actual bracing length, reflecting the bracing bearing capacity of a single steel strand.

[0043] In a preferred embodiment, step S7 includes the following formula for the branch number reduction model:

[0044]

[0045] In the formula, The number of strands represents the reduction factor, which describes the overall reduction in the ultimate load of a single prestressed steel strand when multiple prestressed steel strands run in parallel, due to factors such as the number of strands, the thickness of the protective layer, and the spacing. The value ranges from 0 to 1, with smaller values ​​indicating stronger reduction. n represents the number of prestressed steel strands. The attenuation rate coefficient related to the number of strands is used to quantify how quickly the number of strands reduction coefficient decreases when one more strand is added. The larger the value, the stronger the attenuation effect of the number of strands on the number of strands reduction coefficient. g represents the thickness of the protective layer of the prestressed steel strand, which can be regarded as the distance from the surface of the prestressed steel strand to the outside of the cement slurry. This represents the critical value for the thickness of the protective layer of prestressed steel strands. When the thickness of the protective layer is equal to the critical value, the protective layer has no additional effect on the reduction of the number of strands. The fitting parameter representing the protective layer thickness is used to quantify the influence of the number of strands reduction factor when the protective layer thickness deviates from the critical value. The trend is influenced by the positive and negative values ​​of the parameter. z represents the spacing of the prestressed steel strands, which can be regarded as the center-to-center spacing between multiple steel strands and affects the degree of mutual interference of the bond stress. This represents the critical value of the spacing between prestressed steel strands. When the spacing of the prestressed steel strands is equal to the critical value, the spacing has no additional effect on the reduction of the number of strands. The fitting parameter representing the spacing of prestressed steel strands is used to quantify the influence of the strand spacing deviation from the critical value on the number of strands reduction factor. The trend is influenced by the positive or negative value of the parameter.

[0046] In a preferred embodiment, the prediction model for the total ultimate load in step S8 includes the following formula:

[0047]

[0048] In the formula, It represents the ultimate load of all prestressed steel strands, that is, the maximum grip load that all prestressed steel strands can withstand as a whole.

[0049] In a preferred embodiment, step S1 further involves obtaining the protective layer thickness and spacing of the prestressed steel strands; and step S7 further incorporates the protective layer thickness and spacing of the prestressed steel strands as co-variables.

[0050] In a preferred embodiment, in step S1, the helical parameters of the prestressed steel strand are further obtained; in step S3, the mechanical interlocking effect between the prestressed steel strand and the cement paste is further analyzed, and the helical parameters of the prestressed steel strand are included as variables in the ultimate stress model; in step S4, the helical parameters of the prestressed steel strand are also included as variables in the stress attenuation model.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] 1. This invention clarifies the relationship between the number of strands and the reduction in bond strength of a single strand in a group anchor system by quantifying the nonlinear reduction effect of the number of strands in the prestressed steel strands. This solves the problem in existing technologies that directly transfer the stress field law of a single anchor to a group anchor system and cannot accurately assess the interference effect of multiple strands.

[0053] 2. This invention corrects the actual effective stress under long grip length by quantifying the influence of effective grip length on grip stress distribution, thus solving the problem in the prior art that ignores the attenuation characteristics of grip stress, resulting in a large deviation in the prediction of grip strength of ground anchors with long grip length. Attached Figure Description

[0054] Figure 1This is a schematic diagram of the overall process of the present invention.

[0055] Figure 2 This is a schematic diagram showing the relationship between the curing period and compressive strength of the present invention.

[0056] Figure 3 This is a schematic diagram showing the relationship between the ultimate load, effective grip length, and compressive strength of the present invention. Detailed Implementation

[0057] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0058] Example 1: As Figure 1-3 As shown in the figure, this embodiment takes the ground anchor installed in a foundation pit support project as an example.

[0059] In this embodiment, silicate cement is selected as the cement, and a pure cement slurry without aggregate is prepared by mixing water and cement at a mass ratio of 0.45. The curing environment temperature is controlled at 20±2℃, the relative humidity is not less than 95%, and the curing period is set at 28 days.

[0060] The prestressed steel strands are selected with a 1×7 structure (seven strands twisted together), a nominal diameter of 12.7mm, and spiral parameters of 0.5mm spiral rib height, 312.5mm pitch, nominal cross-sectional area of ​​98.71mm², and tensile strength of 18700kgf. The effective grip length is determined to be 30cm, the protective layer thickness is 3.66cm, the steel strand spacing is about 2cm, and the total number of steel strands is 3.

[0061] Meanwhile, the compressive strength data of the same cement type and water-cement ratio in the historical projects of the target anchor were compiled, as shown in the table below:

[0062]

[0063] Then, by performing linear regression on the historical engineering data, it can be concluded that under the condition of a water-cement ratio of 0.45, , Substituting the curing age t=28 into the compressive strength model, the compressive strength of the cement grout can be obtained. .

[0064] Furthermore, historical engineering data indicates that, under the same helical parameters and compressive strength, the ultimate load of a single prestressed steel strand varies with the effective bond length, as shown in the table below:

[0065]

[0066] Therefore, based on historical engineering data, the ultimate load of a single prestressed steel strand at an effective bond length of 30cm and an age of 28 days is approximately 31.934kN. Furthermore, the number of prestressed steel strands can be compared with the ultimate load of a single prestressed steel strand in historical engineering data, as shown in the table below:

[0067]

[0068] By analyzing the influence of helical parameters and compressive strength on ultimate bond stress in historical engineering data using the controlled variable method, the contribution coefficient of the mechanical chain effect can be determined. Contribution coefficient of cement paste support Substituting into the ultimate stress model, we can obtain the ultimate grip stress when the effective grip length is 30cm. .

[0069] Furthermore, by analyzing the influence of effective grip length on ultimate grip stress in historical engineering data using the controlled variable method, the contribution coefficient of the helical parameters can be determined. The attenuation rate coefficient c = 1.68. Substituting this into the stress attenuation model, we can obtain the stress attenuation coefficient when the effective grip length is 30cm. .

[0070] Then, substituting the diameter and effective bond length of the prestressed steel strand into the interface contact model, we can obtain the interface contact area A≈11938mm². 2 .

[0071] By further substituting the ultimate bond stress, stress attenuation coefficient, and interfacial contact area into the single-strand prediction model, the ultimate load of a single prestressed steel strand can be obtained. Compared with historical engineering data, the error is less than 10%, which is within the acceptable range for engineering.

[0072] Subsequently, by analyzing the influence of the number of prestressed steel strands on the ultimate load in historical engineering data using the controlled variable method, the attenuation rate coefficient related to the number of strands was determined. Based on mechanical mechanisms and historical engineering data, it is known that when the protective layer thickness of a single steel strand reaches approximately 6.865 cm, the ultimate load no longer increases with further thickness. Therefore, the critical value for the protective layer thickness of prestressed steel strands is... Furthermore, existing technologies generally consider that when the spacing between steel strands reaches 10 times or more of their nominal diameter, the spacing effect of the anchor group can be ignored. Therefore, the critical value of the prestressed steel strand spacing is... Further analysis of the effects of changes in protective layer thickness on the ultimate load, and the effects of changes in strand spacing on the protective layer thickness, reveals the fitting parameters for the protective layer thickness. Fitting parameters for prestressed steel strand spacing After substituting into the number of branches reduction model, it was found that the number of branches reduction coefficient under the comprehensive conditions was... The error compared to historical engineering data is relatively large. After analysis, it is considered that the thickness and spacing of the protective layer in this embodiment do not significantly deviate from the critical value, and its additional reduction in load is negligible. Therefore, the number of supports reduction model can be simplified, considering only the reduction dominated by the number of supports. , , Substituting the data into the simplified branch reduction model, we can obtain the branch reduction coefficient. The error compared to historical engineering data is approximately 0.8%, indicating that in this embodiment, the number of supports is the dominant factor in load reduction.

[0073] Finally, by substituting the reduction factor for the number of strands, the ultimate load of a single prestressed steel strand, and the number of prestressed steel strands into the prediction model for the total ultimate load, the ultimate load of all prestressed steel strands can be obtained. The final calculated predicted grip strength Compared with historical engineering data, the error is less than 10%, which is within the acceptable range for engineering, verifying the predictive effect of this embodiment on the bond strength of prestressed steel strands.

[0074] Example 2: This example is basically the same as Example 1, except that the aggregate-free pure cement slurry is prepared according to a water-to-cement mass ratio of 0.55.

[0075] In this embodiment, linear regression is performed on historical engineering data to determine the optimal water-cement ratio of 0.55. , Substituting the curing age t=28 into the compressive strength model, the compressive strength of the cement grout can be obtained. .

[0076] Substituting further into the ultimate stress model, we can obtain the ultimate grip stress. .

[0077] Then, substituting this into the stress attenuation model, we can obtain the stress attenuation coefficient. .

[0078] The interfacial contact area is independent of the water-cement ratio; therefore, the interfacial contact area A≈11938mm². 2 constant.

[0079] Substituting this into the single-strand prediction model, the ultimate load of a single prestressed steel strand can be obtained. Obviously, the decrease in the compressive strength of the cement slurry leads to a reduction in the ultimate bond stress compared to Example 1.

[0080] Substituting this into the thread count reduction model, we can obtain the thread count reduction coefficient. Obviously, the higher the water-cement ratio, the lower the tensile strength of the cement grout, and the more likely it is to split and fail under the superposition of group anchor stress. The effective bonding area of ​​a single steel strand decreases, and the reduction factor decreases.

[0081] Finally, by substituting the values ​​into the prediction model for the total ultimate load, the ultimate load of all prestressed steel strands can be obtained. This demonstrates the principle that the more steel strands there are and the lower the slurry strength, the greater the decrease in the total ultimate load. The predicted bond strength was ultimately calculated. .

[0082] The embodiments of the present invention are given for the purposes of illustration and description. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for predicting the bond strength of prestressed steel strands, characterized in that, Includes the following steps: S1. Based on the design parameters of the target anchor, obtain the cement grout water-cement ratio, curing age, and the number, diameter, and effective bond length of the prestressed steel strands of the target anchor. S2. Analyze the historical engineering data of the target ground anchor, and construct a correlation model between the water-cement ratio, curing age and compressive strength of the cement grout, denoted as the compressive strength model. S3. Analyze the supporting effect of cement paste on steel strands, and construct an analytical correlation model between the compressive strength model and the ultimate bond stress, denoted as the ultimate stress model. S4. Based on the attenuation characteristics of the bond stress, a functional relationship model between the effective bond length of the prestressed steel strand and the stress attenuation coefficient is constructed, denoted as the stress attenuation model. S5. Based on the interface contact morphology between the prestressed steel strand and the cement grout, construct a correlation model between the diameter of the prestressed steel strand, the effective bond length, and the interface contact area, denoted as the interface contact model. S6. Based on the ultimate bond stress output by the ultimate stress model, the interface contact area output by the interface contact model, and the stress attenuation coefficient output by the stress attenuation model, a prediction model for the ultimate load of a single prestressed steel strand is constructed, denoted as the single-strand prediction model. S7. Based on the stress interference effect when prestressed steel strands are wrapped in parallel, a correlation model between the number of prestressed steel strands and the number of strands reduction coefficient is constructed, which is denoted as the number of strands reduction model. S8. Based on the single-strand prestressed steel strand ultimate load, the number of prestressed steel strands, and the number of strands reduction coefficient output by the single-strand prediction model, construct a prediction model for the total ultimate load. S9. Based on the interface contact area and total ultimate load of the target anchor, calculate the ultimate load per unit area of ​​the target anchor, which is the predicted grip strength of the target anchor.

2. The method for predicting the bond strength of prestressed steel strands according to claim 1, characterized in that, In step S2, the compressive strength model includes the following formula: In the formula, t represents the compressive strength of the cement grout; t represents the curing age of the cement grout. Represents the intercept constant; This represents the slope constant.

3. The method for predicting the bond strength of prestressed steel strands according to claim 1, characterized in that, In step S5, the interface contact model includes the following formula: In the formula, A represents the interfacial contact area between the prestressed steel strand and the cement grout; This indicates the diameter of the prestressed steel strand.

4. The method for predicting the bond strength of prestressed steel strands according to claim 1, characterized in that, In step S6, the single-branch prediction model includes the following formula: In the formula, This indicates the ultimate load of a single prestressed steel strand. Indicates the ultimate grip stress. This represents the stress attenuation coefficient.

5. The method for predicting the bond strength of prestressed steel strands according to claim 1, characterized in that, In step S7, the branch reduction model includes the following formula: In the formula, This represents the reduction factor for the number of strands; n represents the number of strands in the prestressed steel strands. The attenuation rate coefficient is related to the number of strands; g represents the thickness of the protective layer of the prestressed steel strand. This indicates the critical value for the thickness of the protective layer of prestressed steel strands; The fitting parameter represents the thickness of the protective layer; z represents the spacing of the prestressed steel strands. This indicates the critical value for the spacing of prestressed steel strands; The fitting parameters represent the spacing of the prestressed steel strands.

6. The method for predicting the bond strength of prestressed steel strands according to claim 1, characterized in that, In step S8, the prediction model for the total ultimate load includes the following formula: In the formula, This indicates the ultimate load of all prestressed steel strands.

7. The method for predicting the bond strength of prestressed steel strands according to claim 1, characterized in that, In step S1, the protective layer thickness and spacing of the prestressed steel strands are also obtained; in step S7, the protective layer thickness and spacing of the prestressed steel strands are also included as variables in the strand reduction model.

8. The method for predicting the bond strength of prestressed steel strands according to claim 1, characterized in that, In step S1, the helical parameters of the prestressed steel strand are also obtained; in step S3, the mechanical interlocking effect between the prestressed steel strand and the cement paste is analyzed, and the helical parameters of the prestressed steel strand are included as variables in the ultimate stress model; in step S4, the helical parameters of the prestressed steel strand are included as variables in the stress attenuation model.

9. The method for predicting the bond strength of prestressed steel strands according to claim 8, characterized in that, In step S3, the ultimate stress model includes the following formula: In the formula, h represents the height of the helical rib of the prestressed steel strand; P represents the pitch of the prestressed steel strand. The contribution coefficient representing the mechanical chain effect; This represents the contribution coefficient of the cement paste's supporting effect.

10. The method for predicting the bond strength of prestressed steel strands according to claim 8, characterized in that, In step S4, the stress attenuation model includes the following formula: In the formula, Indicates the effective bond length of the prestressed steel strand; represents the contribution coefficient of the helical parameters; c represents the attenuation rate coefficient.

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