Method for evaluating fracture damage of steel truss type cantilever crane

Abstract

The invention discloses a steel truss type cantilever crane fracture damage assessment method. The method comprises the steps that cantilever crane parameters and rated load parameters are initialized; building fracture damage indexes of a stress ratio, a flexural span ratio and a bearing capacity loss rate; calculating an envelope stress ratio, and carrying out stress ratio threshold division on the boom rod piece; carrying out rod piece position partitioning on the whole cantilever crane structure; dividing fracture damage evaluation grades, and quantifying to form a damage grade evaluation standard; and according to the fracture damage index and the rod piece position partition, the cantilever crane fracture degree evaluation and repair suggestion can be obtained according to the fracture damage evaluation distribution diagram. According to the method, the fracture damage degree of the cantilever crane structure is effectively considered through the simple damage index and the judgment method, and the fracture damage condition of the cantilever crane can be rapidly and comprehensively evaluated.

Description

Technical Field

[0001] The invention relates to the technical field of lifting machinery damage assessment, and in particular to a method for assessing the breaking damage of a steel truss boom. Background Art

[0002] Steel truss boom cranes are the main mechanical equipment for offshore lifting operations and lifting cargoes, and are widely used in ship fields such as container ships, barge carriers, and offshore wind power installation ships. As an important support for the lifting travel rails on platform cranes, the steel truss boom structure is usually welded from rods such as the upper chord, lower chord, crossbeam, and diagonal brace, and has the characteristics of high load, large span, and high frequency of operation. When the steel truss boom of the crane is carrying out lifting operations at sea, it is often inevitably subjected to fatigue, vibration, collision, and impact, and is prone to fatigue cracking, external load cracking, and other rod cracking and fracture phenomena. As a large-scale offshore lifting equipment, the rapid assessment of the breakage of the steel truss boom is crucial to ensure the safety of personnel and projects.

[0003] However, the complex combination of rods and stress states make it difficult to assess the fracture of steel truss booms. At present, the damage analysis of steel truss booms is mainly focused on the early design, including structural strength verification, weld strength verification, fatigue life verification, etc. However, the assessment method of the residual strength and operating capacity of steel truss booms after fracture is relatively lacking, especially the fracture damage assessment method of steel truss booms suitable for crane operation mode has not yet been established.

[0004] In view of the above, it is necessary to construct a steel truss boom breakage damage assessment method based on the broken position and damage degree of the crane steel truss boom, form a unified steel truss boom damage evaluation level, and provide an evaluation method for the residual strength and operating capacity of the steel truss boom crane after breakage damage. Summary of the invention

[0005] The purpose of the present invention is to solve the problem of evaluating the remaining operating capacity of a crane steel truss boom after the rod is broken, and to propose a steel truss boom breakage damage evaluation method. Through the breakage evaluation indicators of stress ratio, deflection-span ratio and bearing capacity loss rate, the damage assessment level and standard are quantified according to the breakage situation of the steel truss boom, and a steel truss boom breakage damage assessment diagram is drawn to give corresponding breakage damage evaluation and remaining operating capacity evaluation, thereby determining the degree of breakage damage according to the positional relationship of the steel truss boom damage indicator combination in the damage assessment diagram.

[0006] To achieve the above object, the technical solution of the present invention is as follows: a method for assessing the fracture damage of a steel truss boom, comprising obtaining the structural type and load condition parameters of a crane steel truss boom; Obtaining the yield strength of steel truss boom members f y, establish the stress of the truss boom in the working condition s and the yield strength of the member f y The dimensionless stress ratio index of the parameter R ; On the basis of the member stress ratio, considering the specific structure of the boom and the force characteristics under the load, the steel truss boom structure is subdivided into a number of different position partitions. The component level of the steel truss boom structure at least includes the upper chord, the lower chord, the crossbeam and the diagonal brace. The fracture damage evaluation distribution diagram is formed with the different location zones and component parts as the horizontal coordinates and the dimensionless stress ratio index R as the vertical coordinate; The cells in the fracture damage evaluation distribution diagram are formed according to the critical values ​​of the member deflection-span ratio η and the bearing capacity failure rate γ between various damage levels to form the damage level standard of the steel truss boom; The damage grade of the damaged part of the steel truss boom is calculated and compared with the damage grade standard in the fracture damage evaluation distribution diagram, and the fracture damage degree is evaluated based on the comparison result.

[0007] Furthermore, the dimensionless stress ratio index R The calculation formula is: ; In the formula, R is the stress ratio, s is the stress on the truss member, f y is the yield strength of the member.

[0008] Furthermore, the deflection-span ratio of the rod is or The calculation formula is: ; In the formula, or is the deflection-span ratio, n is the change in arm deflection, L is the length of the boom.

[0009] Furthermore, the bearing capacity failure rate c The calculation formula is: ; In the formula, c is the bearing capacity failure rate, Δ C is the reduction in component strength, f y is the yield strength of the member, C 0 is the initial bearing capacity of the component, C 1 is the bearing capacity of the component after damage.

[0010] Furthermore, considering the specific structure of the boom and the stress characteristics under load, the steel truss boom structure is subdivided into three position zones, numbered as zone A, zone B and zone C respectively; among them, zone A is usually the boom installation section, zone B is the boom transition section, and zone C is the boom lifting section.

[0011] Furthermore, the evaluation of the degree of breaking damage includes the remaining working strength and treatment suggestions of the steel truss boom structure at each damage assessment level according to the breaking damage classification of the steel truss boom: For structures with damage assessment level I, no reinforcement will be carried out; For structures with damage assessment level II, immediate reinforcement is not required; For structures with damage assessment level III, the safety level can be increased by one level after reinforcement; For structures with damage assessment level IV, they need to be reinforced immediately, and after reinforcement, they can be upgraded by one level; For structures with a damage assessment level of V, the structure has been severely damaged and cannot continue to bear load through reinforcement.

[0012] The advantages and beneficial effects of the present invention are as follows: the present invention establishes a fracture damage evaluation distribution diagram with partitions and component parts as the horizontal coordinates and dimensionless stress ratio index as the vertical coordinates, avoiding the complexity of selecting a large number of index systems in the traditional analysis method. The present invention comprehensively considers the degree of fracture damage under the specific boom structure through simple damage indicators and evaluation methods, and can more accurately, universally and quickly evaluate the fracture damage of the boom. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic flow chart of a method for assessing the breaking damage of a steel truss boom according to the present invention; Figure 2 is a classification diagram of stress ratios of steel truss boom members in the present invention; Figure 3 It is a position partition diagram of the steel truss boom in the present invention; Figure 4 is a distribution diagram of fracture damage evaluation in the present invention; DETAILED DESCRIPTION

[0014] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0015] S10, parameter initialization Obtain the structural type and load conditions of the crane steel truss boom, such as Figure 1 shown.

[0016] S11. The structural type includes the component level and the structural level. The component level includes the specifications and arrangements of the upper chord, lower chord, crossbeam and diagonal brace, and the structural level includes the arm size and boundary conditions.

[0017] S12. Load conditions include two basic operating conditions: lifting and boom lengthening, which should cover the most unfavorable load combination of the steel truss boom under basic conditions.

[0018] S20. Establish and calculate damage indicators S21. Through finite element numerical simulation calculation, the stress ratio of each member of the steel truss boom under each working condition is obtained. ; In the formula, s is the stress on the truss member, f y is the yield strength of the member.

[0019] S22. Calculate the deflection value of the steel truss boom at different breaking positions and numbers, and then calculate the deflection ratio of the rod breaking. ; In the formula, or is the deflection-span ratio, n is the change in arm deflection, L is the length of the boom; that is, the ratio of the change in boom deflection to the length of the boom.

[0020] S23. Calculate the strength of the rod after breaking through finite element numerical simulation and calculate the local bearing capacity loss rate. The calculation formula of the bearing capacity failure rate γ is: ; In the formula, c is the bearing capacity failure rate, Δ C is the reduction in component strength, f y is the yield strength of the member, C 0 is the initial bearing capacity of the component, C 1 is the bearing capacity of the component after damage; that is, the ratio of the reduction in component strength to the yield strength of the material.

[0021] S30, arm and rod partition S31. Based on the envelope stress ratio, classify all rods according to the stress ratio range. Figure 2 As shown, Figure 2 The different patterns in the figure represent the range of the envelope stress ratio of the rod under various working conditions.

[0022] S32. Based on the stress ratio of the rod, the specific structure of the boom and the force characteristics under load are considered, and the steel truss boom structure is divided into three types of position zones, which are numbered as zone A, zone B and zone C respectively. Figure 3As shown in the figure, area A is usually the boom installation section, area B is the boom transition section, and area C is the boom lifting section.

[0023] S40, Damage Level Standard S41. Considering the location of the broken rod and the structural damage characteristics, the damage level of the steel truss boom after breaking is qualitatively divided as shown in the following table: Table 1 Fracture damage assessment level

[0024] S42. In the classification of breaking damage levels, based on the apparent damage phenomenon of the structure, the critical values ​​of the member deflection-span ratio and the bearing capacity failure rate between the damage levels are determined to form the damage level standard of the steel truss boom, as shown in the following table: Table 2 Damage level assessment criteria

[0025] Note: The bearing capacity loss rate of the broken section is approximately estimated by the damaged area of ​​the damaged section member.

[0026] S50, Fracture damage classification According to the stress ratio before breaking damage, the partition of the damaged rod, the deflection-span ratio and the bearing capacity damage rate, the breaking damage grade evaluation of the steel truss boom is shown in the following table, and the resulting breaking damage evaluation distribution diagram is shown in Figure 4 shown.

[0027] Table 3 Fracture damage evaluation table

[0028] S60, fracture damage evaluation According to the fracture damage classification of steel truss boom, the residual working strength and application recommendations of steel truss boom structures at each damage assessment level are as follows: For structures with damage assessment level I, no reinforcement will be carried out; For structures with damage assessment level II, immediate reinforcement is not required; For structures with damage assessment level III, the safety level can be increased by one level after reinforcement; For structures with damage assessment level IV, they need to be reinforced immediately, and after reinforcement, they can be upgraded by one level; For structures with a damage assessment level of V, the structure has been severely damaged and cannot continue to bear load through reinforcement.

[0029] The reinforcement recommendations for each damage assessment level are shown in the following table.

[0030] Table 4 Reinforcement recommendations for each damage assessment level

[0031] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for assessing the fracture damage of a steel truss boom, characterized in that: It includes initializing the boom parameters and load condition parameters of the crane steel truss boom, establishing and calculating the breaking damage index, partitioning the rod position based on the boom structure and load action, constructing a breaking damage evaluation distribution map, and forming the breaking damage classification and standard of the steel truss boom.

2. A steel truss boom fracture damage assessment method according to claim 1, characterized in that: The boom parameters are the stress σ of the boom members and the yield strength f of the members. y , and establish the dimensionless stress ratio index R.

3. A method for assessing the fracture damage of a steel truss boom according to claim 1, characterized in that: The rod position partition is based on the stress ratio index R, taking into account the specific structure of the boom and the force characteristics under the load, and subdividing the steel truss boom structure into positions or functional distributions.

4. A steel truss boom fracture damage assessment method according to claim 1, characterized in that: The fracture damage evaluation distribution diagram is constructed by taking the position partition and the component part as the horizontal coordinate and taking the dimensionless stress ratio index R as the vertical coordinate.

5. A steel truss boom fracture damage assessment method according to claim 1, characterized in that: The cells in the fracture damage evaluation distribution diagram form the damage grade standard of the steel truss boom according to the critical values ​​of the member deflection-span ratio η and the bearing capacity failure rate γ between various damage grades.

6. A steel truss boom fracture damage assessment method according to claim 1, characterized in that: The damage grade of the damaged part of the steel truss boom is calculated and compared with the damage grade standard in the fracture damage evaluation distribution diagram, and the fracture damage degree is evaluated based on the comparison result.

7. A method for assessing the fracture damage of a steel truss boom according to claim 2, characterized in that: The calculation formula of the dimensionless stress ratio index R is: ； In the formula, R is the stress ratio, σ is the stress of the truss rod, and f y is the yield strength of the member.

8. A method for assessing the fracture damage of a steel truss boom according to claim 2, characterized in that: The calculation formula of the deflection-span ratio η of the rod is: ； Where η is the deflection-span ratio, ν is the change in boom deflection, and L is the length of the boom.

9. A steel truss boom fracture damage assessment method according to claim 2, characterized in that: The calculation formula of the bearing capacity failure rate γ is: 、 ； In the formula, γ is the bearing capacity failure rate, ΔC is the reduction in component strength, and f y is the yield strength of the member, C0 is the initial bearing capacity of the member, and C1 is the bearing capacity of the member after damage.

10. A steel truss boom fracture damage assessment method according to claim 3, characterized in that: Taking into account the specific structure of the boom and the stress characteristics under load, the steel truss boom structure is subdivided into three position zones, numbered as zone A, zone B and zone C respectively; among them, zone A is usually the boom installation section, zone B is the boom transition section, and zone C is the boom lifting section.

11. A steel truss boom fracture damage assessment method according to claim 5, characterized in that: The evaluation of the degree of breaking damage includes the residual strength and repair suggestions of the steel truss boom structure at each damage assessment level according to the breaking damage classification of the steel truss boom: For structures with damage assessment level I, no reinforcement will be carried out; For structures with damage assessment level II, immediate reinforcement is not required; For structures with damage assessment level III, the safety level can be increased by one level after reinforcement; For structures with damage assessment level IV, they need to be reinforced immediately, and after reinforcement, they can be upgraded by one level; For structures with a damage assessment level of V, the structure has been severely damaged and cannot continue to bear load through reinforcement.

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