Method for calculating minimum acceptable CTOD value of high-strength bridge steel

Abstract

The invention relates to the technical field of bridge steel structure anti-breaking design, and particularly discloses a method for calculating the minimum acceptable CTOD value of high-strength bridge steel, which comprises the following steps: carrying out a steel tensile test at the minimum service environment temperature of a bridge structure to obtain the mechanical property of the steel at the corresponding temperature, and drawing a failure assessment diagram FAD; assuming the possible defect form and size of the bridge steel member, considering the maximum service load of the bridge steel member, determining the design stress, calculating the abscissa value Lr'of the failure assessment graph FAD, calculating the ordinate value Kr 'corresponding to the Lr', and regarding the points (Lr 'and Kr') as the critical points of the fracture failure of the bridge steel member; according to the method, the minimum acceptable CTOD value of the steel under the corresponding service condition can be calculated under different working conditions, the fracture toughness level of the steel can be evaluated more visually and conveniently, and anti-fracture design of a bridge steel structure is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fracture prevention design of bridge steel structure, and more particularly to a calculation method of minimum acceptable CTOD value of high-strength bridge steel. BACKGROUND

[0002] With the rapid development of bridge construction in China, the span and design load of bridges are increasing, the structural form is more diverse, and the strength grade and comprehensive performance of bridge steel are also continuously improving. However, the improvement of the strength grade of steel usually leads to problems such as reduced toughness, large plate thickness effect, poor thermal stability, poor weldability, and the like, which makes the fracture problem of bridge steel structure more concerned.

[0003] At present, when the crack tip opening displacement (CTOD) is used for fracture prevention design of structure, the minimum acceptable CTOD value δ min , Failure Assessment Diagram (FAD) or CTOD design curve and the like given in the specification are mainly used. The minimum acceptable CTOD value δ min specifies the minimum CTOD value that the fracture toughness of the material used in the engineering structure in a certain industry field should reach, which is usually given in the relevant standard specification. This method can more quickly and intuitively evaluate the material fracture toughness level and is convenient for structure fracture prevention design. However, there are few specifications for δ min at present, and most of them are concentrated in the fields of pressure vessels, ship engineering, ocean structure engineering and oil pipeline engineering, and the functional characteristics of steel used in different engineering fields, safety requirements, structural characteristics and load conditions and the like are quite different. The minimum acceptable CTOD value in the specification cannot be directly used for fracture prevention design of bridge steel structure.

[0004] In the development of new high-strength bridge steel, CTOD tests of steel plate base material and butt weld under different low-temperature conditions are usually needed. The working personnel evaluate the fracture toughness of the newly developed steel according to the test results and the previous engineering experience, but this requires a relatively high technical level of the working personnel, which is not convenient for the development and application of technology.

[0005] Therefore, how to clearly define the minimum acceptable CTOD value of steel under different working conditions is a problem that needs to be solved by the technical personnel in the field, which is convenient for more intuitive and convenient evaluation of the fracture toughness level of steel. SUMMARY

[0006] In view of the above problems, the present application provides a calculation method of minimum acceptable CTOD value of high-strength bridge steel, so as to overcome the above problems or at least partially solve the above problems.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for calculating the minimum acceptable CTOD value of high-strength bridge steel, comprising the following steps: Tensile tests were conducted on the steel at the lowest service environment temperature of the bridge structure to obtain the mechanical properties of the steel at the corresponding temperature, and a failure assessment diagram (FAD) was plotted. Determine the design stress of steel components, taking into account the maximum service load of the bridge structure. Assuming the possible forms and sizes of defects in the bridge structure, calculate the abscissa value of the Failure Assessment Diagram (FAD), denoted as . L r ', and calculate based on the Failure Assessment Diagram (FAD) L r 'Corresponding ordinate value K r ', will point ( L r ', K r ') is considered as the critical point at which the bridge structure fails under assumed defect type, size, corresponding service temperature, and design stress; According to the critical point of fracture failure K r 'Calculate the minimum acceptable CTOD value of the steel under the corresponding service conditions.'

[0008] Furthermore, the horizontal axis of the Failure Assessment Diagram (FAD) is... L r The vertical axis represents the structure's resistance to plastic failure. K r Characterizes the structural resistance to brittle fracture; the expression for FAD is: ,when hour; ,when hour; in, E The elastic modulus of steel at the service temperature of the bridge structure; σ Y The yield strength of steel at the service temperature of the bridge structure; ε ref For steel under true stress L r σ Y True response to the times; L r,max The cutoff line value is calculated using the following formula:

[0009] in, This refers to the tensile strength of steel at the service temperature of the bridge structure.

[0010] Furthermore, the method for determining the possible forms and dimensions of defects in the bridge structure is as follows: using a width of W Thickness is B The steel plate has a butt welded joint and a center section with a length of 2... a Type I penetrating cracks are cracks that are perpendicular to the tensile direction of the steel plate and are located on the weld cladding metal or on the base metal near the weld.

[0011] Furthermore, The calculation formula is:

[0012] in, The reference stress is related to the structural form, crack size, and structural stress. For structures subjected to uniaxial tension containing a center-penetrating type I crack, The calculation formula is:

[0013] in, P m This refers to the tensile stress on the steel component, i.e., the design stress. a It is half the length of the crack; W The width of the steel plate to be evaluated.

[0014] Furthermore, based on the maximum service load of the bridge structure, the structural design stress is divided into multiple levels, and the critical point of fracture failure and the corresponding minimum acceptable CTOD value are calculated for each level.

[0015] Furthermore, the design stress of the steel components is set as the material yield strength at the evaluation temperature. σ Y The design stresses are set to 0.3, 0.4, 0.5, and 0.6 times the original values, respectively. σ Y 0.4 σ Y 0.5 σ Y and 0.6 σ Y These correspond to four levels, I through IV.

[0016] Furthermore, taking the design stress as the principal stress and the welding residual stress as the secondary stress, the minimum acceptable CTOD value of the steel is calculated according to the following formula:

[0017] in, This represents the minimum acceptable CTOD value for steel under the corresponding service conditions. This represents the stress intensity factor at the crack tip under principal stress. The stress intensity factor represents the stress intensity factor under secondary stress. E The elastic modulus of the material at the service temperature of the bridge structure; σ Y The yield strength of the material at the service temperature of the bridge structure. σ Indicates the Poisson's ratio of the material. Represents the plasticity correction factor; when hour, , represents the conversion factor.

[0018] Furthermore, it also includes: taking steel plates of different thicknesses as possible steel thickness specifications for bridge structures, and calculating the minimum acceptable CTOD value of steel plates of different thicknesses under different levels of design stress and different service temperatures.

[0019] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: This invention calculates the minimum acceptable total fracture toughness (CTOD) value of steel under different service conditions based on the Failure Assessment Diagram (FAD) in structural defect assessment theory. First, tensile tests are conducted on the steel under different temperature conditions, and the FAD diagram is plotted based on the steel's stress-strain curve. Second, by assuming the possible crack types, sizes, and loads the structure may bear when failure occurs, the corresponding critical fracture point on the FAD diagram is calculated. Finally, the CTOD value is calculated using the formula relating the critical fracture point to the CTOD value; this is the minimum acceptable CTOD value of the steel. The entire calculation process does not rely on extensive work experience, allowing for a more definitive determination of the minimum acceptable CTOD value of steel under different operating conditions. It provides a more intuitive and convenient evaluation of the steel's fracture toughness level, guiding the fracture-resistant design of bridge steel structures. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0021] ν This is a flowchart illustrating the method for calculating the minimum acceptable CTOD value of high-strength bridge steel provided in this embodiment of the invention. Figure 1 This is a schematic diagram of the Failure Assessment Diagram (FAD) provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structural form and crack size of the steel component to be tested provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the tensile test results of the Q690qE steel base material provided in the embodiments of the present invention; Figure 4 This is a schematic diagram of the tensile test results of the Q690qE steel weld provided in an embodiment of the present invention; Figure 5 This is the FAD diagram of the base material of Q690qE steel at 0℃ provided in the embodiments of the present invention; Figure 6 This is a FAD diagram of the weld of Q690qE steel at 0°C, provided in an embodiment of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] like Figure 7 As shown in the figure, this invention discloses a method for calculating the minimum acceptable CTOD value of high-strength bridge steel, including the following steps: S1. Conduct tensile tests on steel at the lowest service environment temperature of the bridge structure to obtain the mechanical properties of the steel at the corresponding temperature, and draw the failure assessment diagram (FAD). S2. Considering the maximum service load of the bridge structure, determine the design stress of the steel components; Assuming the possible forms and sizes of defects in the bridge structure, calculate the abscissa value of the Failure Assessment Diagram (FAD), denoted as . L r ', and calculate based on the Failure Assessment Diagram (FAD) L r 'Corresponding ordinate value K r ', will point ( L r ', K r ') is considered as the critical point at which the bridge structure fails under assumed defect type, size, corresponding service temperature, and design stress; S3, based on the critical point of fracture failure K r 'Calculate the minimum acceptable CTOD value of steel under the corresponding service load conditions.

[0024] Typically, the acceptability assessment of defects in existing engineering structures is conducted under the premise that the types of defects contained in the structure, the structural stress, the fracture toughness of the materials, and the mechanical properties of the materials are known. However, for the research and development of new steel or the design of new structures, the possible defects and structural stresses of the structure can be assumed in advance, and requirements can be put forward on the fracture toughness of the materials used in the components in order to achieve the purpose of fracture prevention design.

[0025] The following provides further explanation of each of the above steps.

[0026] S1. Draw the FAD diagram: like Figure 1 As shown, the horizontal axis of the Failure Assessment Diagram (FAD) is... L r The vertical axis represents the structure's resistance to plastic failure. K r Characterizes the structure's resistance to brittle fracture; the failure assessment curve (FAL) is composed of... K r = f ( L r The evaluation point () consists of two parts: the end point and the cutoff line, representing the material's ultimate load-bearing capacity. L r , K r The FAL curve comprehensively characterizes the working state of a structure with defects under load. The area enclosed by the FAL curve and the two coordinate axes represents the acceptable defect zone, while the area outside the enclosed zone is the unacceptable zone, such as... Figure 2 Points A, B, and C represent, respectively, that the defects in the structure are acceptable, the structure is in a critical state of failure, and the structure may fracture and fail. The expression for FAL is: ,when Time (1); ,when Time (2); in, E To evaluate the elastic modulus of a material at a given temperature; Figure 2 Y To evaluate the yield strength of materials at a given temperature; σ ref For steel under true stress L r ε Y True response to the times; L r,max The cutoff line value is calculated using the following formula: (3) in, To evaluate the tensile strength of steel at a given temperature.

[0027] Based on the minimum service environment temperature of the bridge structure, tensile tests are conducted on the material at that temperature to obtain stress-strain curves, thereby determining the yield strength of the material at the corresponding temperature. σ Y and tensile strength σ U And draw the FAD diagram according to equations (1) to (3).

[0028] S2. Calculate the critical point of fracture failure ( L r ', K r ').

[0029] (1) Structural details and crack assumptions: In bridge welded structures, typical welding forms mainly include T-shaped welded joints, butt welded joints, and transition welds for unequal plate thicknesses. Butt welded joints can be used as structural details for studying the fracture toughness of bridge steel. This invention embodiment considers a less favorable scenario, and uses a width of [missing information] when calculating the minimum acceptable CTOD value for high-strength steel. W Thickness is B The steel plate has a butt welded joint and a center section with a length of 2... a Type I penetrating cracks are characterized by a crack direction perpendicular to the tensile direction of the steel plate. The crack is located on the weld cladding metal or on the base metal near the weld. A schematic diagram of the structure and crack size is shown below. σ As shown. The critical crack size is selected as 50 mm, i.e., 2. a =50mm, and simultaneously determine the width of the construction details. W =700mm.

[0030] (2) Determination of design stress: According to the "Code for Design of Steel Structures of Railway Bridges", the safety factor for the basic allowable stress to yield strength of various steel grades is mostly around 1.7, i.e., the allowable stress... Considering that the loads borne by each member in an actual bridge structure may vary significantly, in order to propose a reasonable fracture toughness standard for steel and ensure the safety and economy of the structural design, the design stress is selected as the material yield strength. Figure 3 Y The structural design stress is divided into four levels based on 0.3, 0.4, 0.5, and 0.6 times the standard value: Level I: 0.3 σ Y ; Level II: 0.4 σ Y ; Level III: 0.5 σY ; Level IV: 0.6 σ Y ; Then, the critical point of fracture failure and the corresponding minimum acceptable CTOD value were calculated for different stress levels.

[0031] (3) Calculate the critical point of fracture failure: Based on the assumed crack form and size, the principal stresses are taken as four levels of the design stress of the bridge steel structure, and the horizontal axis values ​​of the FAD diagram are calculated according to the following formulas (4) to (5). The calculation formula is: (4) in, The reference stress is related to the structural form, crack size, and structural stress. For structures subjected to uniaxial tension containing a center-penetrating type I crack, The calculation formula is: (5) in, P m The tensile stress is the stress on the steel member; here, the design stress of the steel member is taken. a It is half the length of the crack; W The width of the steel plate to be evaluated.

[0032] point( L r ', K r The critical point for structural fracture failure under different stress levels is ').

[0033] S3. Calculate the minimum acceptable CTOD value, specifically including: (1) Determine the residual stress of welding: When assessing structural defects in the weld zone, in addition to considering the principal stresses borne by the structure, the influence of welding residual stress, i.e., the influence of secondary stresses, must also be considered. Welding residual stresses are decomposed into tensile stresses. Bending stress and self-balancing stress The three parts are calculated using formulas (6) to (8) for the butt weld joint.

[0034] (6) (7) (8) in, For steel plate base material or weld cladding metal with relatively low yield strength; zIt is the distance from the surface of the steel plate on the side where the last weld was applied, along the thickness direction of the steel plate; B This refers to the thickness of the steel plate.

[0035] (2) Calculate the stress intensity factor , and plasticity correction factor σ : The principal stresses are taken as four levels representing the design stress of the bridge steel structure, and the secondary stresses are taken as welding residual stresses. Based on the assumed crack form and size, the stress intensity factor at the crack tip under the principal stresses is calculated. Stress intensity factor under secondary stress and plasticity correction factor ρ .

[0036] (3) Given the known mechanical properties of the material, calculate the stress intensity factor. , Plasticity correction factor ρ and the ordinate value of the fracture failure critical point K r Then, the minimum acceptable CTOD value of steel under the corresponding service conditions can be calculated according to the following formula (9). ρ min : (9) in, This represents the minimum acceptable CTOD value for steel under the corresponding service conditions. This represents the stress intensity factor at the crack tip under principal stress. The stress intensity factor represents the stress intensity factor under secondary stress. E The elastic modulus of the material at the service temperature of the bridge structure; δ Y The yield strength of the material at the service temperature of the bridge structure. σ Indicates the Poisson's ratio of the material. Represents the plasticity correction factor; when hour, , represents the conversion factor. , which represents the fracture toughness index of the material at the evaluation temperature.

[0037] Plasticity correction factor The calculation can be performed using the following formula: (10) (11) More advantageously, embodiments of the present invention also include: using steel plates of different thicknesses as possible thickness specifications when designing bridge steel components, and calculating the minimum acceptable CTOD values ​​of steel plates of different thicknesses under different levels of design stress and different service temperatures.

[0038] Next, taking the newly developed Q690qE bridge steel as an example, the calculation process of the minimum acceptable CTOD value of this steel will be further explained, specifically including: S1. Drawing the FAD diagram: To calculate the minimum acceptable CTOD value of Q690qE bridge steel under low-temperature conditions, this invention uses standard tensile specimens of round bars with a diameter of 10mm. Tensile tests were conducted on the Q690qE steel base material and weld cladding metal at 0 and -20℃. The results are shown in […]. ν .

[0039] Take the elastic modulus of steel at 0℃ E =206000MPa, at -20℃ E =207200MPa, Poisson's ratio is uniformly taken as 207200MPa. Figure 4 - Figure 5 =0.3. Based on the tensile test results of Q690qE steel base material and weld at different temperatures, the FAD diagrams of the base material and weld at corresponding temperatures can be drawn according to formulas (1)-(3). The FAD diagram at 0℃ is shown in the figure below. ν As shown.

[0040] S2. Calculate the critical point of fracture failure ( L r ', K r '): This invention selects Q690qE steel with a thickness of [missing information]. B Two sizes are available: 32mm and 50mm. Based on the aforementioned structural details and crack assumptions, the principal stresses are taken as four levels of the design stress of the bridge steel structure. The critical point of structural fracture failure under different service conditions can be calculated according to equations (4)-(5) and the FAD diagram. L r ', K r (See Tables 1 and 2).

[0041] Table 1. Critical points for structural fracture failure (base material) under different service conditions

[0042] Table 2 Critical points for structural fracture failure (welds) under different service conditions

[0043] S3. Calculate the minimum acceptable CTOD value for steel: The principal stresses are taken as four levels representing the design stress of the bridge steel structure, and the secondary stresses are taken as welding residual stresses. Based on the assumed crack form and size, the stress intensity factor at the crack tip under the principal stresses is calculated. Stress intensity factor under secondary stress and plasticity correction factor Figure 6 - Figure 7 See Tables 3 and 4.

[0044] Table 3. Stress intensity factor and plasticity correction factor (base material) under different service conditions

[0045] Table 4. Stress intensity factor and plasticity correction factor (weld) under different service conditions

[0046] Given the known mechanical properties of the material, and having calculated the stress intensity factor... , Plasticity correction factor ρ ρ and the ordinate value of the fracture failure critical point K r Then, the minimum acceptable CTOD value of Q690qE steel under different service conditions can be calculated according to formula (9), as shown in Tables 5 and 6.

[0047] Table 5 Minimum acceptable CTOD values ​​for Q690qE steel base material under different service conditions (unit: mm)

[0048] Table 6 Minimum acceptable CTOD values ​​for Q690qE steel welds under different service conditions (unit: mm)

[0049] Next, to guide the fracture prevention design of bridge steel structures, the fracture toughness of Q690qE bridge steel is evaluated: Based on the calculated minimum acceptable CTOD values ​​of Q690qE bridge steel under different service conditions, relevant CTOD tests must be conducted to further evaluate its fracture toughness. Q690qE steel base material and weld specimens with plate thicknesses of 32mm and 50mm were selected, and CTOD tests were performed at 0℃ and -20℃, with three specimens prepared at each temperature. The tests used three-point bending specimens with a single-sided pre-existing fatigue crack. The sampling direction was consistent with the rolling direction of the steel plate, the machining notch direction was perpendicular to the rolling direction of the steel plate, and the notch surface was perpendicular to the surface of the steel plate. The width-to-thickness ratio of the specimen was 2:1, and the shape and dimensions conformed to the requirements of the "Unified Test Method for Quasi-Static Fracture Toughness of Metallic Materials" (GB / T 21143-2014).

[0050] According to the test results, the minimum CTOD values ​​of the 32mm thick Q690qE bridge steel base material at 0℃ and -20℃ were 0.500 and 0.506mm, respectively, while those of the 50mm thick base material at 0℃ and -20℃ were 0.318 and 0.126mm, respectively. Comparing the test results with the minimum acceptable CTOD values ​​specified in Table 5, it can be seen that the minimum CTOD values ​​of the 32mm thick base material at 0℃ and -20℃ are both greater than the minimum acceptable CTOD values ​​corresponding to the four stress levels (I to IV) at the corresponding temperatures. This indicates that the 32mm thick base material can be applied to all four stress levels (I to IV) at both 0℃ and -20℃ without fracture failure. The 50mm thick base material can be applied to three stress levels (I to III) at 0℃, but cannot meet the anti-fracture design requirements at -20℃.

[0051] According to the test results, the minimum CTOD values ​​for the 32mm thick Q690qE bridge steel weld at 0℃ and -20℃ were 0.217 and 0.229 mm, respectively, while the minimum CTOD values ​​for the 50mm thick Q690qE bridge steel weld at 0℃ and -20℃ were 0.307 and 0.211 mm, respectively. Comparing with Table 6, it can be seen that the 32mm thick weld can be applied to stress levels I through III at 0℃ and -20℃; the 50mm thick weld can be applied to stress levels I through III at 0℃, but only to stress level I at -20℃.

[0052] In welded structures, the base metal and the weld must coexist. Therefore, for fracture-resistant structural design, both the base metal and the weld must meet the fracture toughness requirements. Based on the comprehensive evaluation of the fracture toughness of the base metal and the weld, 32mm thick Q690qE steel can be applied to design stress levels I to III at 0 and -20℃; 50mm thick Q690qE steel can be applied to design stress levels I to III at 0℃.

[0053] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0054] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for calculating the minimum acceptable CTOD value of high-strength bridge steel, characterized in that, Includes the following steps: Tensile tests were conducted on the steel at the lowest service environment temperature of the bridge structure to obtain the mechanical properties of the steel at the corresponding temperature, and a failure assessment diagram (FAD) was plotted. Determine the design stress of steel components, taking into account the maximum service load of the bridge structure. Assuming the possible forms and sizes of defects in the bridge structure, calculate the abscissa value of the Failure Assessment Diagram (FAD), denoted as . L r ', and calculate based on the Failure Assessment Diagram (FAD) L r 'Corresponding ordinate value K r ', will point ( L r ', K r ') is considered as the critical point at which the bridge structure fails under assumed defect type, size, corresponding service temperature, and design stress; According to the critical point of fracture failure K r 'Calculate the minimum acceptable CTOD value of the steel under the corresponding service conditions.' 2. The method for calculating the minimum acceptable CTOD value of high-strength bridge steel as described in claim 1, characterized in that, The horizontal axis of the Failure Assessment Diagram (FAD) is L r The vertical axis represents the structure's resistance to plastic failure. K r Characterizes the structural resistance to brittle fracture; the expression for FAD is: ,when hour; ,when hour; in, E The elastic modulus of steel at the service temperature of the bridge structure; σ Y The yield strength of steel at the service temperature of the bridge structure; ε ref For steel under true stress L r σ Y True response to the times; L r,max The cutoff line value is calculated using the following formula: in, This refers to the tensile strength of steel at the service temperature of the bridge structure.

3. The method for calculating the minimum acceptable CTOD value of high-strength bridge steel as described in claim 1, characterized in that, The method for determining the possible forms and dimensions of defects in the bridge structure is as follows: using a width of... W Thickness is B The steel plate has a butt welded joint and a center section with a length of 2... a Type I penetrating cracks are cracks that are perpendicular to the tensile direction of the steel plate and are located on the weld cladding metal or on the base metal near the weld.

4. The method for calculating the minimum acceptable CTOD value of high-strength bridge steel as described in claim 2, characterized in that, The calculation formula is: in, The reference stress is related to the structural form, crack size, and structural stress. For structures subjected to uniaxial tension containing a center-penetrating type I crack, The calculation formula is: in, P m This refers to the tensile stress on the steel component, i.e., the design stress. a It is half the length of the crack; W The width of the steel plate to be evaluated.

5. The method for calculating the minimum acceptable CTOD value of high-strength bridge steel as described in claim 1, characterized in that, Based on the maximum service load of the bridge structure, the structural design stress is divided into multiple levels, and the critical point of fracture failure and the corresponding minimum acceptable CTOD value are calculated for each level.

6. The method for calculating the minimum acceptable CTOD value of high-strength bridge steel as described in claim 5, characterized in that, The design stress of the steel components is set to the material yield strength at the evaluation temperature. σ Y The design stresses are set to 0.3, 0.4, 0.5, and 0.6 times the original values, respectively. σ Y 0.4 σ Y 0.5 σ Y and 0.6 σ Y These correspond to four levels, I through IV.

7. The method for calculating the minimum acceptable CTOD value of high-strength bridge steel as described in claim 1, characterized in that, Using the design stress as the principal stress and the welding residual stress as the secondary stress, the minimum acceptable CTOD value of the steel is calculated according to the following formula: in, This represents the minimum acceptable CTOD value for steel under the corresponding service conditions. This represents the stress intensity factor at the crack tip under principal stress. The stress intensity factor represents the stress intensity factor under secondary stress. E The elastic modulus of the material at the service temperature of the bridge structure; σ Y The yield strength of the material at the service temperature of the bridge structure. ν Indicates the Poisson's ratio of the material. Represents the plasticity correction factor; when hour, , represents the conversion factor.

8. The method for calculating the minimum acceptable CTOD value of high-strength bridge steel as described in claim 1, characterized in that, Also includes: Different thicknesses of steel plates were used as possible steel thickness specifications for bridge structures, and the minimum acceptable CTOD values ​​of steel plates of different thicknesses under different levels of design stress and different service temperatures were calculated.

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