A method for determining the tension control stress limit of cold rolled thread prestressed steel

Abstract

The present application relates to a kind of cold roll thread prestressed steel wire tension control stress limit value determination method, comprising: obtaining the geometric dimension of cold roll thread prestressed steel wire;Determine the material constitutive relation and ultimate strength of the cold roll thread prestressed steel wire, establish corresponding material constitutive model;Based on the geometric dimension and the material constitutive model, the finite element simulation model of the cold roll thread prestressed steel wire is established;Determine elastic stress concentration coefficient using the finite element simulation model;According to the elastic stress concentration coefficient and the ultimate strength, the tension control stress limit value of the cold roll thread prestressed steel wire is determined.The present application realizes the accurate, scientific determination of the tension control stress limit value of the cold roll thread prestressed steel wire by finite element simulation combined with stress concentration coefficient calculation, significantly improves the rationality and reliability of prestress application, avoids the risk of steel damage caused by stress concentration in the tensioning process, and ensures construction safety.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to the application technology of high-strength prestressed steel bars in prestressed structures, specifically to a method for determining the tension control stress limit of cold-rolled threaded prestressed steel bars. Background Technology

[0002] With the rapid development of large bridges, high-rise buildings, and special engineering structures, the demand for large-diameter, high-strength prestressed steel bars in the engineering field continues to increase. Cold-rolled threaded prestressed steel bars, with their excellent comprehensive mechanical properties and convenient connection construction advantages, have been widely used in modern prestressed concrete structures.

[0003] In the design and construction of prestressed concrete structures, the tension control stress is a core technical indicator that determines the structure's load-bearing capacity, long-term durability, and overall safety. Traditionally, the tension control stress is determined based on the material's nominal strength and empirical coefficients, without fully considering the significant stress concentration effect at the thread root caused by geometric abrupt changes in the threaded section of the reinforcing bar. This problem is particularly prominent for large-diameter, high-strength cold-rolled threaded prestressed reinforcing bars: excessively high tension stress can cause the thread root to enter the plastic stage prematurely, even leading to brittle fracture risk, which in turn can cause prestressing failure and jeopardize structural safety.

[0004] Current design specifications do not provide a precise method for determining the stress concentration factor of this type of steel reinforcement, which leads to the problem that the setting of the tension control stress limit is generally conservative or has insufficient safety reserve, making it difficult to fully utilize the material properties of high-strength steel reinforcement and restricting the level of precision in the design and construction of prestressed structures.

[0005] Therefore, there is an urgent need for a scientific and precise method for determining the tension control stress limit of cold-rolled threaded prestressed steel bars, so as to achieve a reasonable value for the tension control stress and ensure the reliability of prestressing application and the overall structural safety. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the main objective of this invention is to provide a method for determining the tension control stress limit of cold rolled threaded prestressed steel bars, so as to solve the technical problem that the prior art is unable to accurately quantify the stress concentration effect caused by geometric discontinuity at the root of the thread of cold rolled threaded prestressed steel bars under axial tensile force, which leads to the inability to scientifically and reliably determine the reasonable upper limit of the tension control stress.

[0007] The technical solution of the present invention is as follows:

[0008] This invention proposes a method for determining the tension control stress limit of cold-rolled threaded prestressed steel bars, characterized by comprising:

[0009] Obtain the geometric dimensions of cold-rolled threaded prestressed steel bars;

[0010] The material constitutive relation and ultimate strength of the cold-rolled threaded prestressed steel bars were determined, and the corresponding material constitutive model was established.

[0011] Based on the geometric dimensions and the material constitutive model, a finite element simulation model of the cold-rolled threaded prestressed steel bar is established.

[0012] The elastic stress concentration factor is determined using the aforementioned finite element simulation model;

[0013] Based on the elastic stress concentration factor and the ultimate strength, the tension control stress limit of the cold-rolled threaded prestressed steel bar is determined.

[0014] Optionally, obtaining the geometric dimensions of the cold-rolled threaded prestressed steel bar includes: determining the geometric dimensions of the cold-rolled threaded prestressed steel bar according to the design documents; and / or, measuring the full-size solid of the cold-rolled threaded prestressed steel bar and measuring the thread details by cutting a longitudinal section of the steel bar to determine the geometric dimensions of the cold-rolled threaded prestressed steel bar.

[0015] Optionally, the geometric dimensions include at least the total length of the reinforcing bar, its diameter, the thread pitch, the thread profile angle, and the radius of the transition fillet at the thread root.

[0016] Optionally, the determination of the material constitutive relation and ultimate strength of the cold-rolled threaded prestressed steel bar, and the establishment of the corresponding material constitutive model, includes:

[0017] Standard uniaxial tensile test specimens were cut from the cold-rolled threaded prestressed steel bars of the same batch or furnace number;

[0018] A quasi-static uniaxial tensile test was conducted on the test specimen using a constant strain rate, and the load-displacement curve of the test specimen was recorded.

[0019] Based on the load-displacement curve, the original cross-sectional area of ​​the specimen and the gauge length, the engineering stress-strain curve is calculated and plotted, and the engineering stress-strain curve is converted into the real stress-strain curve.

[0020] Based on the actual stress-strain curve, the ultimate strength of the material is determined, and a constitutive model of the material is constructed based on the actual stress-strain curve.

[0021] Optionally, establishing the finite element simulation model of the cold-rolled threaded prestressed steel bar includes:

[0022] Based on the geometric dimensions of the cold-rolled threaded prestressed steel bar, a three-dimensional solid geometric model of the cold-rolled threaded prestressed steel bar is established using a three-dimensional modeling tool;

[0023] The material constitutive model is assigned to the three-dimensional solid geometric model;

[0024] The three-dimensional solid geometry model is meshed, and the mesh is refined at least in the stress concentration areas of the three-dimensional solid geometry model, including the thread root and the tooth root.

[0025] Optionally, the establishment of the finite element simulation model of the cold-rolled threaded prestressed steel bar further includes:

[0026] A fixed constraint is applied to one end face of the three-dimensional solid geometric model to constrain translational and rotational degrees of freedom, and an axial displacement load or a uniformly distributed axial surface force is applied to the other end face to generate the average axial cross-sectional stress σ0.

[0027] Optionally, determining the elastic stress concentration factor using the finite element simulation model includes:

[0028] An axial cross-sectional mean stress σ0 is applied to the finite element simulation model.

[0029] The maximum axial stress σ1 at the root of the thread was calculated using the finite element method.

[0030] The elastic stress concentration factor K is calculated using the formula K=σ1 / σ0.

[0031] Optionally, the value of the axial cross-sectional average stress σ0 is determined to ensure that the finite element simulation model as a whole is within the linear elastic range, and the value of the axial cross-sectional average stress σ0 is lower than the yield strength of the cold rolled threaded prestressed steel bar material.

[0032] Optionally, determining the tension control stress limit for the cold-rolled threaded prestressed steel bar includes:

[0033] Establish a safety criterion based on the allowable stress method;

[0034] The tension control stress limit is derived based on the safety criterion.

[0035] Optionally, the safety criterion is: at the tension control stress σ con Under the action of the force, the maximum axial stress σ1 at the root of the thread satisfies the following relationship:

[0036] σ1=K×σ con ≤f pt

[0037] Where K is the elastic stress concentration factor, f pt The ultimate strength of the cold-rolled threaded prestressed steel bar; and

[0038] The tension control stress limit derived from the safety criterion satisfies:

[0039] σ con ≤f pt / K

[0040] Among them, f pt / K represents the tension control stress limit of the cold-rolled threaded prestressed steel bar.

[0041] The advantages of this invention over the prior art are:

[0042] Scientifically precise and theoretically rigorous: This invention abandons the traditional empirical coefficient estimation method, obtains the real stress-strain relationship through material tensile tests and constructs an accurate material constitutive model, and establishes a refined finite element simulation model based on the actual geometric dimensions of the steel bars. Based on elasticity mechanics, it directly numerically solves the stress concentration factor at the root of the thread, realizing the accurate calculation of the stress concentration effect. This provides a solid mechanical and experimental foundation for determining the tension control stress limit, significantly improving the scientificity and accuracy of the calculation results.

[0043] A balance between safety and economy: This invention, by precisely quantifying the stress concentration effect, avoids setting excessively high tension control stresses due to underestimating the stress concentration effect, thereby completely eliminating potential safety accidents caused by premature failure at the thread root. Simultaneously, it avoids setting overly conservative tension control stresses due to overestimating the stress concentration effect, allowing the performance of high-strength materials to be fully utilized. This reduces material redundancy while ensuring safety, achieving the optimal balance between structural safety and construction economy.

[0044] With a wide range of applications and significant engineering guidance value, this method is applicable to cold-rolled threaded prestressed steel bars of different diameters, thread parameters, and strength grades, demonstrating strong versatility. Through coupled calculation of the elastic stress concentration factor and the material's ultimate strength, a clear limit value for tension control stress is derived. This limit can be directly used as the allowable value in design specifications, the control target value during construction tensioning, or the evaluation basis for quality acceptance, providing direct guidance for engineering design, construction, and acceptance.

[0045] The implementation path is clear and the operability is good: This invention combines advanced finite element simulation technology with conventional material mechanics testing. The steps are clear, and the required equipment, such as testing machines, measuring instruments, computers and finite element software, are all common in the engineering field. It is easy to implement and promote in R&D institutions, large production enterprises or professional testing centers, and has good engineering application prospects.

[0046] In summary, this invention, through a systematic technical solution of "precise acquisition of geometric dimensions—construction of material constitutive model—finite element simulation modeling—calculation of stress concentration factor—scientific determination of tension limit," effectively solves the technical problem of inaccurate and unreasonable determination of tension control stress values ​​for cold-rolled threaded prestressed steel bars, and provides efficient and feasible technical support for improving the safety, reliability, and design economy of prestressed concrete structures.

[0047] It should be understood that the description in the Summary of the Invention is not intended to limit the key or essential features of the embodiments of the present invention, nor is it intended to restrict the scope of the invention. Other features of the invention will become readily apparent from the following description. Furthermore, implementation of any embodiment of the present invention does not imply the simultaneous possession or achievement of multiple or all of the aforementioned beneficial effects. Attached Figure Description

[0048] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0049] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0050] Figure 1 This is a flowchart illustrating a method for determining the tension control stress limit of cold-rolled threaded prestressed steel bars according to an embodiment of the present invention.

[0051] Figure 2 This is a schematic diagram of a cold-rolled threaded prestressed steel bar model disclosed in an embodiment of the present invention;

[0052] Figure 3 This is a schematic diagram of the detailed dimensions of the thread disclosed in an embodiment of the present invention;

[0053] Figure 4 This is a schematic diagram of mesh generation for a three-dimensional solid geometric model as disclosed in an embodiment of the present invention;

[0054] Figure 5 This is a schematic diagram of the numerical simulation results of stress calculation for cold-rolled threaded prestressed steel bars disclosed in an embodiment of the present invention. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0056] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0057] It should be understood that the terms "comprising / including," "consisting of," or any other variations are intended to cover non-exclusive inclusion, such that a product, apparatus, process, or method that comprises a list of elements includes not only those elements but may also include, where necessary, other elements not expressly listed, or elements inherent to such a product, apparatus, process, or method. Without further limitation, an element defined by the phrases "comprising / including," "consisting of," does not exclude the presence of additional identical elements in the product, apparatus, process, or method that includes said element.

[0058] It should also be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device, component or structure referred to must have a specific orientation, be constructed or operated in a specific orientation, and should not be construed as a limitation of the present invention.

[0059] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0060] The implementation of the present invention will be described in detail below with reference to preferred embodiments.

[0061] like Figures 1 to 5As shown, this invention proposes a method for determining the tension control stress limit of cold-rolled threaded prestressed steel bars. This method is mainly for large-diameter, high-strength cold-rolled threaded prestressed steel bars: these steel bars bear higher tension loads, and the cold rolling process leads to a more significant stress concentration effect at the root of the thread. The traditional empirical coefficient method is difficult to accurately match their mechanical properties, which can easily lead to safety hazards or waste of material properties. Therefore, this invention provides a precise solution to their engineering pain points.

[0062] This method mainly includes:

[0063] S1: Obtain the geometric dimensions of cold-rolled threaded prestressed steel bars;

[0064] S2: Determine the material constitutive relation and ultimate strength of cold-rolled threaded prestressed steel bars, and establish the corresponding material constitutive model;

[0065] S3: Based on geometric dimensions and material constitutive models, a finite element simulation model of cold-rolled threaded prestressed steel bars is established;

[0066] S4: Determine the elastic stress concentration factor using a finite element simulation model;

[0067] S5: Determine the tension control stress limit for cold-rolled threaded prestressed steel bars based on the elastic stress concentration factor and ultimate strength.

[0068] Step S1, obtaining the geometric dimensions of the cold-rolled threaded prestressed steel bar includes: determining the geometric dimensions of the cold-rolled threaded prestressed steel bar based on the design documents; and measuring the full-size solid cold-rolled threaded prestressed steel bar, and measuring the detailed thread dimensions by cutting a longitudinal section of the steel bar to determine the geometric dimensions of the cold-rolled threaded prestressed steel bar.

[0069] In this step, obtaining the geometric dimensions is the physical foundation for subsequent simulation analysis, and the accuracy of its measurement directly determines the accuracy of the finite element modeling and the reliability of the stress calculation results. Therefore, in a specific embodiment, a combination of design file values ​​and precise physical measurement is used, as follows:

[0070] Based on the design documents, the nominal diameter and thread specifications, such as thread pitch, thread height, and thread root curvature, are directly obtained from the product design drawings and technical specifications of the cold-rolled threaded prestressed steel bars.

[0071] Verification and refinement through full-scale physical measurement: High-precision measurement of actual reinforcing bars. First, macroscopic dimensions such as overall length and straightness are measured. The key step lies in obtaining the detailed dimensions of the thread profile, such as... Figure 3As shown: A sample containing a complete threaded section needs to be cut from the reinforcing bar. This is done by precision wire cutting or similar methods to obtain a clear longitudinal section of the thread. Then, using a tool microscope, optical profilometer, or high-precision coordinate measuring machine, the thread pitch, crest and root widths, and especially the root fillet radius, are precisely measured and recorded. This radius is the most sensitive geometric parameter affecting stress concentration and must be obtained accurately. Finally, by integrating the design documents and measured data, a complete and accurate dataset of the reinforcing bar's three-dimensional geometric dimensions is formed.

[0072] The nominal diameter is the standard nominal outer diameter of cold-rolled threaded prestressed steel bars, providing a basic dimensional basis for structural design, reinforcement calculation and accessory matching.

[0073] Thread specifications refer to the set of geometric parameters of the external threads of cold-rolled prestressed steel bars, which are continuously rolled and spirally distributed around the circumference of the bar. These parameters comprehensively characterize the shape and dimensional features of the threaded portion of the steel bar surface. Key parameters include: pitch (axial distance between adjacent threads, directly determining thread density); thread height (radial height from the crest to the root); crest width and root width (width of the straight section at the thread crest and root); and root fillet radius (radius between the root and flank), which is the most critical geometric parameter affecting stress concentration. Smaller fillets result in more severe stress concentration, making root cracking or brittle fracture more likely during tensioning.

[0074] In step S2, the material constitutive relation and ultimate strength of cold-rolled threaded prestressed steel bars are determined, and the corresponding material constitutive model is established, including:

[0075] Test specimens were cut from the bare rod section of cold-rolled threaded prestressed steel bars from the same batch or furnace number;

[0076] Quasi-static uniaxial tensile tests were conducted on the test specimens using a constant strain rate, and the load-displacement curves of the test specimens were recorded.

[0077] Based on the load-displacement curve, the original cross-sectional area of ​​the specimen, and the gauge length (i.e., the length of the standard working section on the specimen used for deformation measurement), the engineering stress-strain curve is calculated and plotted, and then converted into a true stress-strain curve; the specific conversion formula is as follows:

[0078]

[0079] In the formula, To respond realistically, For actual stress, For engineering contingency, For engineering stress;

[0080] Based on the actual stress-strain curves, the ultimate strength of the material is determined, and a constitutive model of the material is constructed based on the actual stress-strain curves.

[0081] In this step, the ultimate strength of the material is the strength value corresponding to the peak stress point on the actual stress-strain curve.

[0082] In this step, the material constitutive model is a mathematical model used in the finite element simulation process to quantitatively analyze the mechanical behavior of cold-rolled threaded prestressed steel bars. Its core function is to transform the macroscopic mechanical response of the material (such as elastic deformation and plastic yielding) into mathematical expressions that can be recognized and calculated by the finite element software. The accuracy of its parameters directly determines the reliability and accuracy of the calculation results of the stress concentration effect at the root of the thread in the subsequent finite element simulation.

[0083] Based on the experimental data and simulation requirements of this invention, the material constitutive model includes at least the elastic modulus and true stress-strain data. The elastic modulus is taken from the elastic stage of the true stress-strain curve and is used to characterize the elastic deformation characteristics of the material. The true stress-strain data is directly derived from the engineering stress-strain curve obtained from the experiment and is used to accurately describe the plastic deformation behavior of the material after the stress exceeds the yield strength, providing a reliable basis for the simulation of the plastic response in the stress concentration region at the root of the thread.

[0084] In one specific embodiment, establishing the corresponding material constitutive model specifically includes:

[0085] Specimen preparation and testing: Uniaxial tensile test specimens conforming to the national standard (GB / T228.1) are cut from cold-rolled threaded prestressed steel bars of the same batch or furnace number. Specimens should be taken from the smooth section, avoiding the threaded area, to ensure that the test results reflect the true properties of the material matrix.

[0086] Uniaxial tensile test: A quasi-static uniaxial tensile test is performed at room temperature on a universal testing machine. To accurately obtain the plastic behavior of the material, a low, constant strain rate (recommended range 0.00025~0.0025 mm / s) should be used for loading. During the test, the strain of the specimen should be continuously measured with high precision using an extensometer.

[0087] Data processing and model building: Based on the load-displacement curves recorded in the experiments, combined with the original cross-sectional area and gauge length of the specimen, the engineering stress-strain curve was calculated and plotted. Further, through formula transformation, considering the uniform deformation stage before necking, the true stress-strain curve of the material was obtained. From this curve, key parameters such as the material's yield strength and tensile strength can be determined.

[0088] The strength value corresponding to the peak stress point is the ultimate strength f of the material. ptBased on the obtained real stress-strain data, a suitable material constitutive model can be selected and established, and then input into the subsequent finite element software.

[0089] Step S3, establishing the finite element simulation model of cold-rolled threaded prestressed steel bars includes:

[0090] Based on the geometric dimensions of the cold-rolled threaded prestressed steel bars, a three-dimensional solid geometric model of the cold-rolled threaded prestressed steel bars was established using a three-dimensional modeling tool;

[0091] Assigning the material constitutive model to the three-dimensional solid geometric model;

[0092] Mesh the three-dimensional solid geometry model, and refine the mesh at least in the stress concentration areas of the three-dimensional solid geometry model, including the thread root and the tooth root.

[0093] Furthermore, the finite element simulation model for cold-rolled threaded prestressed steel bars also includes:

[0094] A fixed constraint is applied to one end face of the three-dimensional solid geometric model to constrain translational and rotational degrees of freedom, while an axial displacement load or a uniformly distributed axial surface force is applied to the other end face to generate the average axial cross-sectional stress σ0.

[0095] Furthermore, during the meshing process of the three-dimensional solid geometric model, mesh sensitivity analysis is required to ensure that the stress results in the key areas do not change significantly as the mesh is further refined, thereby ensuring the convergence of the results.

[0096] This step is the core and crucial step in transforming the physical problem of tensioning cold-rolled threaded prestressed steel bars into a mathematical model that can be solved numerically. Its core value lies in accurately converting the actual geometry, material mechanical properties, and actual tensioning state of the steel bars into a simulation model that can be recognized and calculated by finite element software through a high-precision modeling process. This provides a high-precision simulation model for the subsequent accurate calculation of stress concentration factors.

[0097] Specifically, a precise 3D solid model describing the geometric dimensions of the reinforcing bars ensures the accuracy of the morphology of key stress concentration areas such as the root and base of the threads; by defining a material constitutive model, the simulation model possesses elastoplastic mechanical response characteristics consistent with real reinforcing bars; the model is meshed to balance the calculation accuracy of stress concentration areas with the overall computational efficiency of the model, avoiding stress calculation deviations caused by unreasonable mesh division; scientific time boundary constraints and loads accurately simulate the stress state of the reinforcing bars during actual tensioning, ensuring a high degree of consistency between the simulation process and actual engineering conditions.

[0098] The accuracy, completeness, and rationality of the modeling in this step directly determine the reliability and accuracy of the subsequent finite element calculation results. It is the core prerequisite and technical guarantee for the scientific and precise determination of the tension control stress limit.

[0099] In one specific embodiment, establishing a finite element simulation model for cold-rolled threaded prestressed steel bars specifically includes:

[0100] Geometric modeling: SolidWorks was used to model the cold-rolled threaded prestressed steel bars, specifically as follows: Figure 2 As shown, strictly following the precise geometric dimensions obtained in step S1, a three-dimensional solid geometric model is established, containing a complete thread segment (usually containing 3-5 complete pitches) and its adjacent smooth rod segment. The modeling of the threaded portion must be smooth and continuous, especially the root fillet must be accurately reproduced.

[0101] Material property assignment: The material constitutive model determined in step S2, including elastic modulus, Poisson's ratio, and plastic stress-strain data, is assigned to the entire geometric model.

[0102] Mesh generation: Structured or high-precision free mesh generation techniques are used for... Figure 3 The model shown is discretized. Meshing strategy is crucial: in critical regions where stress gradients are expected to be large, such as the thread root and tooth base, highly refined meshes must be used, employing extremely small, regularly shaped hexahedral or higher-order tetrahedral elements to ensure the capture of peak stresses. In areas far from stress concentration zones, a gradually coarser mesh can be used to balance computational accuracy and efficiency. Specific meshing details are as follows... Figure 4 As shown.

[0103] Furthermore, while meshing the three-dimensional solid geometric model, mesh sensitivity analysis is carried out. By gradually refining the mesh and comparing the stress calculation results in key areas, it is ensured that when the mesh is further refined, the stress calculation values ​​of key parts such as the thread root no longer change significantly, so that the finite element calculation results meet the convergence criteria, thereby ensuring the accuracy of stress solution and the reliability of results.

[0104] Boundary conditions and load application: To simulate the actual stress state of the reinforcing bars in the tensioning device, a fixed constraint is applied to one end face of the model, restricting all translational and rotational degrees of freedom. At the other end face of the model, an axial displacement load or a uniformly distributed axial surface force is applied. The target value of the applied load is to generate a specific average stress σ0 (axial cross-sectional average stress) on the model's cross-section.

[0105] The value of σ0 should ensure that the model as a whole is within the linear elastic range, and can usually be taken as a value lower than the material's yield strength, such as 0.5 times the yield strength. The specific value of this load itself is not the final result; its function is to generate a known, uniform far-field stress field.

[0106] In step S4, determining the elastic stress concentration factor using the finite element simulation model includes:

[0107] The axial cross-sectional mean stress σ0 is applied to the finite element simulation model;

[0108] The maximum axial stress σ1 at the root of the thread was calculated using the finite element method.

[0109] The elastic stress concentration factor K is calculated using the formula K=σ1 / σ0.

[0110] This step accurately extracts the true peak stress at the root of the thread through finite element simulation and calculates the stress concentration factor K based on linear elasticity theory. This objectively and quantitatively reflects the stress amplification effect caused by the geometrical abrupt change in the rebar thread, thus achieving precise quantification of the stress concentration degree. Determining this factor eliminates the subjectivity and uncertainty of traditional empirical values, providing a true and reliable mechanical parameter for the subsequent derivation of the tension control stress limit. It is a core step in achieving the scientific setting of the tension stress for cold-rolled threaded rebar and ensuring the rigorous and reliable calculation results.

[0111] In one specific embodiment, determining the elastic stress concentration factor using a finite element simulation model specifically includes:

[0112] Finite Element Solution: Submit your established finite element model for calculation. The finite element solver will calculate the stress field of the model under given boundaries and loads based on the theory of elasticity.

[0113] As is easy to understand, the finite element solver is the core calculation module in finite element analysis software that uses numerical analysis methods to solve mechanical equations. It is used to perform overall numerical solutions on the model based on the given material constitutive relations, boundary conditions and load conditions, and the basic theory of linear elasticity, and output the displacement, stress and strain of each element of the model.

[0114] Result Extraction: After the calculation is completed, the axial stress distribution cloud map of the entire model under the applied load σ0 is extracted in the post-processing module, as shown in the following figure. Figure 5 As shown. The focus is on the stress distribution in the thread root region, identifying and reading the axial stress σ in all thread root elements. z The maximum value is denoted as σ1. Due to the fine mesh, this maximum value can be located very precisely at the minimum radius of curvature of the root fillet.

[0115] Coefficient Calculation: Based on the definition of elastic stress concentration factor, calculate the elastic stress concentration factor K of the reinforcing bar under the current geometric configuration. The calculation formula is: K = σ1 / σ0.

[0116] In the formula, σ1 is the maximum axial stress at the root of the thread obtained by finite element calculation (i.e., the maximum axial stress of the thread root element); σ0 is the known average axial stress in the far field (a region far from the stress concentration area, with uniform stress state, and unaffected by local geometric abrupt changes) artificially applied in the finite element model, which is the specific average stress generated on the cross section of the model by applying the target load value mentioned above.

[0117] Since the material is in a linear elastic state, K is a constant that depends only on the geometry and is independent of the load magnitude. Therefore, the K value obtained through a single finite element analysis is applicable to the stress conditions of this steel bar in all elastic ranges.

[0118] In step S5, determining the tension control stress limit for cold-rolled threaded prestressed steel bars includes:

[0119] Establish a safety criterion based on the allowable stress method;

[0120] The tension control stress limit is derived based on the safety criteria.

[0121] In this step, the safety criterion is: at the tension control stress σ con Under the action of the force, the maximum axial stress σ1 at the root of the thread satisfies the following relationship:

[0122] σ1=K×σ con ≤f pt

[0123] Where K is the elastic stress concentration factor, f pt This represents the ultimate strength of the cold-rolled threaded prestressed steel bar.

[0124] In this step, the tension control stress limit is derived based on the safety criterion and satisfies the following:

[0125] σ con ≤f pt / K

[0126] Among them, f pt / K represents the tension control stress limit for cold-rolled threaded prestressed steel bars.

[0127] This step, as the final objective of the method of this invention, organically combines the true ultimate strength measured by material testing with the stress concentration effect of the thread geometry obtained by precise finite element calculation. Based on the allowable stress method, a rigorous mechanical safety criterion is established, and the tension control stress limit is directly determined through theoretical derivation. This derivation process is theoretically sound and logically rigorous, achieving accurate characterization of material properties and structural stress characteristics. It fully considers the impact of stress amplification at the thread root on the bearing capacity of the reinforcing steel, while avoiding the conservatism or dangers of traditional empirical values. This makes the final determined tension control stress limit more accurate, reasonable, and safe, providing direct, quantitative, and sufficiently safe technical basis for prestressed engineering design and tensioning construction.

[0128] In one specific embodiment, determining the tension control stress limit of cold-rolled threaded prestressed steel bars specifically includes:

[0129] Safety Criterion: Based on the fundamental principles of the allowable stress method, and considering the root of the thread as the most dangerous point, a safety criterion is established: at the tension control stress σ... con Under the action of the load, the maximum local calculated stress at the root of the thread should not exceed the ultimate strength f of the material. pt .Right now:

[0130] σ1=K×σ con ≤f pt

[0131] Limit Derivation: The tension control stress σ can be directly derived from the above inequality. con The following conditions must be met:

[0132] σ con ≤f pt / K

[0133] The "f" on the right side of the formula pt " / K" is defined as the tension control stress limit for large-diameter, high-strength, cold-rolled threaded prestressed steel bars of this specification. This limit is a quantitative indicator with clear physical meaning and mechanical basis: it represents the maximum value of the average tensile stress that can be safely applied to the cross-section of the steel bar while ensuring that the strength failure does not occur due to stress concentration at the root of the thread.

[0134] In this invention, the use of this limit value for tension control can ensure that the peak stress at the root of the thread does not exceed the ultimate strength of the material, avoid premature yielding or brittle fracture in local areas, and guarantee the structural safety of prestressed components during construction and use. It can also avoid the waste of material properties due to overly conservative values, so that the mechanical properties of high-strength steel bars can be fully and reasonably utilized.

[0135] Therefore, the tension control stress limit determined by this invention not only has a rigorous mechanical theoretical basis and clear physical meaning, but also provides a scientific, unified, and directly executable technical basis for engineering design, tension construction control, and quality acceptance. It has important engineering application value for improving the safety, reliability, and economy of prestressed structures.

[0136] It will be readily understood by those skilled in the art that, without conflict, the above-mentioned preferred solutions can be freely combined and superimposed.

[0137] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining the tension control stress limit of cold-rolled threaded prestressed steel bars, characterized in that, include: Obtain the geometric dimensions of cold-rolled threaded prestressed steel bars; The material constitutive relation and ultimate strength of the cold-rolled threaded prestressed steel bars were determined, and the corresponding material constitutive model was established. Based on the geometric dimensions and the material constitutive model, a finite element simulation model of the cold-rolled threaded prestressed steel bar is established. The elastic stress concentration factor is determined using the aforementioned finite element simulation model; Based on the elastic stress concentration factor and the ultimate strength, the tension control stress limit of the cold-rolled threaded prestressed steel bar is determined; wherein, The determination of the material constitutive relation and ultimate strength of the cold-rolled threaded prestressed steel bars, and the establishment of the corresponding material constitutive model, includes: Standard uniaxial tensile test specimens were cut from the cold-rolled threaded prestressed steel bars of the same batch or furnace number; A quasi-static uniaxial tensile test was conducted on the test specimen using a constant strain rate, and the load-displacement curve of the test specimen was recorded. Based on the load-displacement curve, the original cross-sectional area of ​​the specimen and the gauge length, the engineering stress-strain curve is calculated and plotted, and the engineering stress-strain curve is converted into the real stress-strain curve. Based on the actual stress-strain curve, the ultimate strength of the material is determined, and a constitutive model of the material is constructed based on the actual stress-strain curve; and, The determination of the tension control stress limit for the cold-rolled threaded prestressed steel bar includes: Establish a safety criterion based on the allowable stress method; The tension control stress limit is derived based on the aforementioned safety criterion; wherein... The safety criterion is: at the tension control stress σ con Under the action of the force, the maximum axial stress σ1 at the root of the thread satisfies the following relationship: σ1=K×σ con ≤f pt Where K is the elastic stress concentration factor, f pt The ultimate strength of the cold-rolled threaded prestressed steel bar; and The tension control stress limit derived from the safety criterion satisfies: s con ≤f pt / K Among them, f pt / K represents the tension control stress limit of the cold-rolled threaded prestressed steel bar.

2. The method for determining the tension control stress limit according to claim 1, characterized in that, Obtaining the geometric dimensions of the cold-rolled threaded prestressed steel bar includes: determining the geometric dimensions of the cold-rolled threaded prestressed steel bar based on the design documents.

3. The method for determining the tension control stress limit according to claim 1, characterized in that, The process of obtaining the geometric dimensions of the cold-rolled threaded prestressed steel bar includes: measuring the full-size solid cold-rolled threaded prestressed steel bar, and measuring the detailed dimensions of the thread by cutting a longitudinal section of the steel bar to determine the geometric dimensions of the cold-rolled threaded prestressed steel bar.

4. The method for determining the tension control stress limit according to claim 1, characterized in that, The geometric dimensions include at least the total length of the reinforcing bar, its diameter, thread pitch, thread angle, and the radius of the transition fillet at the thread root.

5. The method for determining the tension control stress limit according to claim 1, characterized in that, The establishment of the finite element simulation model for the cold-rolled threaded prestressed steel bar includes: Based on the geometric dimensions of the cold-rolled threaded prestressed steel bar, a three-dimensional solid geometric model of the cold-rolled threaded prestressed steel bar is established using a three-dimensional modeling tool; The material constitutive model is assigned to the three-dimensional solid geometric model; The three-dimensional solid geometry model is meshed, and the mesh is refined at least in the stress concentration areas of the three-dimensional solid geometry model, including the thread root and the tooth root.

6. The method for determining the tension control stress limit according to claim 5, characterized in that, The establishment of the finite element simulation model for the cold-rolled threaded prestressed steel bar also includes: A fixed constraint is applied to one end face of the three-dimensional solid geometric model to constrain translational and rotational degrees of freedom, and an axial displacement load or a uniformly distributed axial surface force is applied to the other end face to generate the average axial cross-sectional stress σ0.

7. The method for determining the tension control stress limit according to claim 1, characterized in that, The determination of the elastic stress concentration factor using the finite element simulation model includes: An axial cross-sectional mean stress σ0 is applied to the finite element simulation model. The maximum axial stress σ1 at the root of the thread was calculated using the finite element method. The elastic stress concentration factor K is calculated using the formula K=σ1 / σ0.

8. The method for determining the tension control stress limit according to claim 7, characterized in that, The value of the average stress σ0 of the axial cross section is determined by ensuring that the finite element simulation model as a whole is within the linear elastic range, and the value of the average stress σ0 of the axial cross section is lower than the yield strength of the cold rolled threaded prestressed steel bar material.

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