Method for evaluating bearing capacity of wood structure building node

Abstract

The invention relates to a method for evaluating the bearing capacity of a wood structure building node, the node comprises a wood component and a bolt and a connecting piece used for connecting the wood component, and the method for evaluating the bearing capacity comprises the following steps: S1, carrying out refined description on the node; s2, establishing a node refinement model by utilizing finite element software based on the refinement description of the node; s3, simulating the stress conditions of the nodes under different load combinations by using a node refining model, and respectively calculating the stress and strain distribution of a node region to determine the most unfavorable stress working condition of the nodes; s4, analyzing the bolt connection mechanical characteristics at the joints, and calculating the bearing capacity of bolt connection; s5, optimizing the bolt layout of the nodes, the size of the connecting piece and the material configuration by adopting a topological optimization algorithm; and S6, based on the results of the steps S3-S5, comprehensive bearing capacity evaluation is conducted on the node. According to the evaluation method, the material characteristics and complex load conditions of the wood structure are fully considered, and the accuracy and reliability of node design can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of wood structure engineering, and particularly relates to a method for evaluating the bearing capacity of wood structure building joints. Background Art

[0002] Due to its aesthetics, environmental friendliness, and the renewability of materials, wood structure buildings are becoming increasingly important in the modern construction industry. Among many wood structure projects, the design and application of the joints between horizontal and vertical beams and columns are particularly common in many wood structure projects and are the core to ensure the stability and reliability of the overall structure. The design of these joints not only needs to consider the unique mechanical properties of wood materials but also needs to cope with variable load conditions. However, the existing methods for evaluating joint bearing capacity are basically designed for metal material structures. There are essential differences in mechanical properties between wood structure materials and metal materials. The existing methods for evaluating joint bearing capacity relying on empirical formulas or simplified models fail to fully consider the material characteristics of wood structures and complex load conditions, making it difficult to accurately evaluate the performance of joints under actual stress conditions, resulting in a deviation between the evaluation results and the actual situation and unable to ensure the accuracy and reliability of joint design. Summary of the Invention

[0003] To solve the above problems, the present invention provides a method for evaluating the bearing capacity of wood structure building joints, which fully considers the material characteristics of wood structures and complex load conditions, can significantly improve the accuracy and reliability of the design of wood structure building joints, and ensure the safety and stability of wood structures.

[0004] The present invention is realized through the following scheme. A method for evaluating the bearing capacity of wood structure building joints, the joints include wood components and bolts and connectors for connecting the wood components, and the bearing capacity evaluation method includes the steps:

[0005] S1. Make a refined description of the joint, including the geometric dimensions, material properties, bolt arrangement, and detailed conditions of the connection interface of the joint;

[0006] S2. Based on the refined description of the joint, use finite element software to establish a refined model of the joint;

[0007] S3. Use the refined model of the joint to simulate the stress conditions of the joint under different load combinations, and calculate the stress and strain distributions in the joint area respectively to determine the most unfavorable stress condition of the joint;

[0008] S4. Analyze the mechanical properties of the bolt connection at the joint and calculate the bearing capacity of the bolt connection;

[0009] S5. Use a topology optimization algorithm to optimize the bolt layout, connector size, and material configuration of the joint;

[0010] S6. Based on the results of steps S3 to S5, comprehensively evaluate the bearing capacity of the node.

[0011] A further improvement of the present invention lies in that: the material properties in step S1 include micro-scale material properties and macro-scale material properties;

[0012] The refined node model in step S2 includes a micro-model for simulating wood fibers and a macro-model for simulating the entire node;

[0013] When performing step S3:

[0014] S31. Use the micro-model to simulate the mechanical behavior at the micro-scale, calculate the stress and strain of the wood micro-units, and then map the calculation results to the macro-scale through homogenization technology;

[0015] S32. In the macro-model, use the micro-scale material properties as inputs, and use the method of continuum mechanics to calculate the stress and strain distributions in the node region considering the interaction between bolts and wooden members.

[0016] A further improvement of the present invention is that when establishing the micro-model and the macro-model: generate finite element meshes. For the micro-scale, use high-resolution meshes to capture the local stress and strain of wood fibers. For the macro-scale, use structured meshes to simulate the entire node, ensuring that the mesh density of bolts and connection areas is sufficient to capture stress concentrations.

[0017] A further improvement of the present invention is that when performing step S5:

[0018] S51. Use the macro-model to perform modal analysis to determine the natural frequencies and vibration modes:

[0019]

[0020] where, W n represents the natural frequency; k represents the stiffness; m represents the mass;

[0021] S52. Define the contact surface between the bolt and the wooden member, and use the penalty function method or the Lagrange multiplier method to simulate the contact behavior:

[0022] P = K contact ×u

[0023] where, P represents the reaction force on the contact surface, K contact represents the contact stiffness matrix, and u represents the displacement of the contact surface;

[0024] S53. Define the topology optimization design variable as the material density ρ(x), where 0 ≤ ρ(x) ≤ 1;

[0025] S54. Establish the objective function and constraint conditions. The objective function J is to minimize the structural mass:

[0026]

[0027] where Ω represents the entire structural domain;

[0028] The constraint condition is that the von Mises stress of the nodes does not exceed the material yield strength;

[0029] S55. Use the SIMP method to map the design variables to the elastic modulus E(x) of the wood structure material:

[0030]

[0031] where E 0 represents the original elastic modulus of the material, that is, the elastic property of the material before topology optimization; ρmin represents the minimum value of the material density; p represents the SIMP parameter, usually taking 3 or 4;

[0032] S56. Iteratively solve, and use the Newton - Raphson iteration method to solve the macroscopic model until the convergence condition is met. In each iteration, update the material properties in the macroscopic model according to the design variables. The convergence condition is:

[0033] ΔU < ∈ tol

[0034]

[0035] where ΔU represents the increment of displacement; ∈ tol represents the preset convergence tolerance; α represents the learning rate, represents the partial derivative of the objective function J with respect to ρ. ρ k+1 and ρ k respectively represent the material density distributions in the (k + 1)-th and k-th iterations;

[0036] S57. Optimize the bolt layout, connector size, and material configuration of the nodes based on the elastic modulus E(x) of the wood structure material after iterative solution.

[0037] A further improvement of the present invention is that the content of the comprehensive bearing capacity assessment includes multi-scale coupling, modal analysis, fatigue analysis, stress concentration analysis, and multi-physics field coupling analysis.

[0038] A further improvement of the present invention is to optimize the design of the nodes according to the comprehensive bearing capacity assessment results and verify whether the bearing capacity of the optimized nodes meets the requirements.

[0039] A further improvement of the present invention lies in that the steps of verifying whether the bearing capacity of the optimized node meets the requirements include:

[0040] Calculating the maximum bending moment and axial force of each wooden member of the node under the most unfavorable stress state;

[0041] Describing the design parameters of the node in detail and introducing a humidity adjustment coefficient to adjust the bearing capacity of the wood;

[0042] Calculating the longitudinal bearing capacity and cross-grain bearing capacity of a single bolt under different yield modes for each wooden member respectively and taking the minimum value;

[0043] Judging whether the von Mises stress of the node exceeds the material yield strength. Taking each wooden member as a unit, respectively judging whether the maximum axial force of the wooden member is less than the minimum longitudinal bearing capacity of the corresponding single bolt and whether the maximum bending moment is less than the cross-grain bearing capacity of the corresponding single bolt. Only when all the judgment results of all wooden members are less, can it be concluded that the bearing capacity of the node meets the requirements.

[0044] A further improvement of the present invention lies in that the method for calculating the maximum bending moment and axial force of each wooden member of the node under the most unfavorable stress state is:

[0045] According to the axial force balance, the axial force balance formula of the node is obtained:

[0046]

[0047] wherein, N represents the axial force of the node, f t,b represents the tensile or compressive strength of the wood, A t represents the cross-sectional area of the wooden member, α t represents the adjustment coefficient considering factors such as the swelling and shrinkage of the wood due to moisture, and respectively represent the axial forces acting on both sides of the node;

[0048] According to the moment balance, the moment balance formula of the node is obtained:

[0049]

[0050] wherein, M represents the maximum bending moment of the node, l 1 and l 2 are the lever arm lengths on both sides of the node, is the height of the node, x is the effective stress length of the node, M pl is the allowable plastic moment value of the wood.

[0051] This method combines multi-scale finite element analysis and topology optimization algorithm to achieve accurate assessment of the bearing capacity of wooden structure joints under variable working conditions. By finely simulating the mechanical behavior of bolt connections and the bearing characteristics of wooden components, it significantly improves the accuracy and reliability of the design of wooden structure building joints. Compared with the existing methods for assessing the bearing capacity of joints based on metal material structures, the present invention can optimize the material use and structural layout while comprehensively capturing the response of the structure under complex loads to ensure structural safety. Specifically:

[0052] (1)Enhance structural safety: This method fully considers the non-homogeneity, anisotropy and swelling / shrinkage effects of wood in mechanical properties, and finely simulates the mechanical behavior from micro to macro scales through multi-scale finite element analysis technology. This method can accurately predict the structural response of wooden structure joints under complex load conditions and combinations of environmental factors, ensure that defects can be identified at the design stage, and thus effectively prevent structural failure.

[0053] (2)Improve structural durability: This method introduces the topology optimization algorithm into the design of wooden structure joints, optimizes the bolt layout and design of the joints through finite element analysis, accurately adjusts the mechanical distribution of the structure, minimizes the risk of stress concentration, and reduces the probability of fatigue failure of the joints.

[0054] (3)Reduce construction and maintenance costs: Through accurate assessment of the bearing capacity, the structural design can be optimized, over-design and material waste can be avoided, and the purpose of economical use of materials can be achieved. In addition, the optimized structural design reduces the need for later maintenance, thus reducing the maintenance costs over the entire life cycle.

[0055] (4)Enhance the flexibility of structural design: Allow rapid iteration and design adjustment to adapt to changing engineering requirements and environmental conditions.

[0056] (5)Improve design efficiency: It can comprehensively evaluate the mechanical properties of joints and significantly improve the conversion efficiency from conceptual design to detailed design. Description of the Drawings

[0057] Figure 1 Shows the flow chart of the evaluation method of the present invention.

[0058] Figure 2 Shows the detail drawing of the cross beam-column joint evaluated by the evaluation method of the present invention.

[0059] Figure 3 Shows the plan view of the cross beam-column joint evaluated by the evaluation method of the present invention.

[0060] Figure 4 Shows the front elevation view of the cross beam-column joint evaluated by the evaluation method of the present invention.

[0061] Figure 5 The side elevation view of the crossbeam-column joint evaluated by using the evaluation method of the present invention is shown. Detailed implementation manners

[0062] In order to solve the problems that the existing evaluation methods for the bearing capacity of building joints deviate from the actual situation due to the failure to fully consider the characteristics of wooden structure buildings, the present invention provides an evaluation method for the bearing capacity of wooden structure building joints, which fully considers the material properties of wooden structures and complex load conditions, significantly improves the accuracy and reliability of the design of wooden structure building joints, and ensures the safety and stability of wooden structures. The following further illustrates the evaluation method for the bearing capacity of wooden structure building joints with specific embodiments in conjunction with the drawings.

[0063] Refer to Figure 1 As shown, an evaluation method for the bearing capacity of wooden structure building joints, the joint includes wooden components and bolts and connectors for connecting the wooden components, and the bearing capacity evaluation method includes the steps:

[0064] Step S1: Make a refined description of the joint, including the geometric dimensions, material properties, bolt arrangement and detailed conditions of the connection interface of the joint.

[0065] Step S2: Based on the refined description of the joint, establish a refined model of the joint by using finite element software. Specifically taking glued laminated wood components as an example, the steps for establishing the refined model of the joint include:

[0066] 1) Define the material properties. According to the mechanical test data of wood, define the elastic modulus E micro = 12 GPa of the wood fibers at the microscopic scale, the Poisson's ratio V micro = 0.3, as well as the tensile and compressive strengths in the longitudinal and transverse directions. At the same time, the elastic modulus E macro of the macroscopic-scale glued laminated wood is also defined and determined by the homogenization method.

[0067] 2) At the microscopic scale, establish a microscopic model of the wood fibers to simulate the mechanical behavior of the wood fibers and their influence on the macroscopic material properties. The length × width × thickness dimensions of the simulated wood layer are L micro × W micro × T micro , where the thickness T micro of the wood layer is set to 0.01 m.

[0068] 3) Construct the macroscopic model of the entire wooden structure joint, including the geometric layout of bolts, connectors and wooden components. Taking the beam element simulating the combination of longitudinal and transverse beams as an example, the length × width × thickness dimensions are L macro × W macro × T macro , where Lmacro and W macro are the dimensions of the longitudinal beam and the cross beam respectively, while T macro is the thickness of the glued laminated timber, which is set to 0.1 m.

[0069] 4) Generate a finite element mesh. For the microscale, a high-resolution mesh is adopted to capture the local stresses and strains of the wood fibers; for the macroscale, a structured mesh is used to simulate the entire joint, ensuring that the mesh density in the bolt and connection areas is sufficient to capture the stress concentration.

[0070] 5) Set the loads and boundary conditions, define appropriate boundary conditions to simulate the actual supports and constraints, and apply nodal loads on the macro model, including the maximum bending moment M max and the axial force N max , which are determined according to the actual building design requirements.

[0071] Step S3: Use this refined joint model to simulate the mechanical behavior of the joint under different load combinations, including self-weight, live load, wind load, and seismic action, etc., and calculate the stress and strain distributions in the joint area respectively to determine the most unfavorable mechanical working condition of the joint. The maximum bending moment and axial force of the joint under this most unfavorable mechanical working condition can be further calculated, providing key data for the subsequent verification steps. Among them, when calculating the stress and strain distributions in the joint area, the microscale analysis needs to be coupled to the macroscale. Specifically:

[0072] Step S31: At the microscale, in addition to the micro model used to simulate the wood fibers, the glued layer also needs to be modeled, and the Hill criterion (a yield criterion) is used to describe the yield behavior of the material:

[0073]

[0074] where σ yield represents the material yield strength, σ 1 and σ 2 represent the principal stresses respectively, and f t and f s represent the yield strengths of the wood in different directions respectively.

[0075] Apply the mechanical behavior at the microscale, use the orthotropic material model to calculate the stresses and strains of the wood micro-elements, and apply Hooke's law: σ micro = E micro × ∈ micro , and use the bottom-up method (i.e., the method of gradually building from the bottom layer) to map the calculation results at the microscale to the macroscale through the homogenization technique.

[0076] where σ microrepresents the stress of wood fibers at the microscale, E micro represents the elastic modulus at the microscale, that is, represents the stiffness of the wood micro-unit, ∈ micro represents the strain of wood fibers at the microscale.

[0077] Step S32, Macroscale analysis. In this macro model, the microscale material properties are used as inputs to reflect the inhomogeneity of wood. Using the method of continuum mechanics, considering the interaction between bolts and wood members, structural analysis is carried out through finite element software to calculate the stress and strain distributions in the joint area.

[0078] Step S4, Analyze the mechanical properties of the bolt connection at this joint and calculate the bearing capacity of the bolt connection. Specifically, comprehensively considering the diameter, material, grade and connection method of the bolt, the bearing capacity of the bolt connection is calculated using mechanical principles and formulas of mechanics of materials.

[0079] Step S5, Adopt a topology optimization algorithm. Based on the geometric and mechanical properties of the joint obtained from the previous steps, optimize the bolt layout, connector size and material configuration of this joint. Specifically, it includes the steps:

[0080] Step S51, Use this macro model for modal analysis to determine the natural frequency and vibration mode:

[0081]

[0082] where, W n represents the natural frequency; k represents the stiffness; m represents the mass.

[0083] Step S52, Contact problem analysis. Define the contact surface between the bolt and the wood member, and use the penalty function method or the Lagrange multiplier method to simulate the contact behavior:

[0084] P = K contact ×u

[0085] where, P represents the reaction force on the contact surface, K contact represents the contact stiffness matrix, and u represents the displacement of the contact surface.

[0086] Step S53, Define the topology optimization design variable as the material density ρ(x), where, 0 ≤ ρ(x) ≤ 1.

[0087] Step S54, Establish the objective function and constraint conditions. The objective function J is to minimize the structural mass:

[0088]

[0089] where, Ω represents the entire structural domain.

[0090] The constraint condition is that the von Mises stress σ of the node vm does not exceed the material yield strength f y , where the von Mises stress is a criterion for measuring material yield and is used to ensure that the structural design does not exceed the yield point of the material.

[0091] Step S55: Use the SIMP method to map the design variable to the elastic modulus E(x) of the wood structure material:

[0092]

[0093] where E 0 represents the original elastic modulus of the material, that is, the elastic properties of the material before topology optimization; ρmin represents the minimum value of the material density; p represents the SIMP parameter, usually taking 3 or 4.

[0094] Step S56: Iteratively solve and use the Newton-Raphson iteration method to solve the macroscopic model until the convergence condition is satisfied. In each iteration, update the material properties in the macroscopic model according to the design variable. The convergence condition is:

[0095] ΔU < ∈ tol

[0096]

[0097] where ΔU represents the increment of displacement; ∈ tol represents the preset convergence tolerance; α represents the learning rate, represents the partial derivative of the objective function J with respect to ρ. ρ k+1 and ρ k represent the material density distributions of the (k + 1)-th and k-th iterations respectively.

[0098] Apply filtering technology to avoid numerical oscillations and repeat the iteration until convergence.

[0099] Step S57: Optimize the bolt layout, connector size, and material configuration of the node based on the elastic modulus E(x) of the wood structure material after iterative solution.

[0100] Step S6: Based on the results of steps S3 to S5 (including bolt bearing capacity, weld quality, maximum bending moment and axial force of the node under the most unfavorable stress state, and the calculation results of the bearing strength of the corresponding wood members), conduct a comprehensive bearing capacity assessment of the node to ensure that the node design meets the relevant safety factor requirements of the "Wood Structure Design Standard Requirements". Specifically, the content of this comprehensive bearing capacity assessment also includes:

[0101] (1) Multi-scale coupling, by coupling the results of the micro-scale and macro-scale, update the material properties of the macro-model to reflect the damage and deformation at the micro-level.

[0102] (2) Modal analysis, perform modal analysis on the structure to determine the natural frequencies and vibration modes of the structure, providing a basis for dynamic response analysis.

[0103] (3) Fatigue analysis, conduct fatigue analysis according to the S-N curve (i.e., stress-life curve) and Miner's Rule (i.e., fatigue damage criterion) to evaluate the life of the structure under cyclic loads.

[0104] (4) Stress concentration analysis, using the von Mises criterion, calculate the stress concentration factor K t around the bolt hole, and apply the failure criterion to evaluate the failure risk of the structure:

[0105]

[0106] where, K t is the stress concentration factor, used to describe the degree of stress concentration in the area around the bolt hole, σ max is the maximum stress around the bolt hole, σ nom is the nominal stress, that is, the uniformly distributed stress without considering the stress concentration effect.

[0107] (5) Multi-physics field coupling analysis, considering the influence of environmental factors such as temperature and humidity on material properties, conduct multi-physics field coupling analysis.

[0108] According to the above comprehensive bearing capacity evaluation results, the design of this node can be optimized, and it can be verified whether the bearing capacity of the optimized node meets the requirements. The results can also be post-processed first, including the visualization of stress and strain distributions, and the analysis of damage and failure modes, etc. According to the calculation and analysis results, convert the optimization result ρ(x) into a bolt layout, put forward suggestions for the optimized design of the node, and then optimize the design of the node based on the suggestions.

[0109] The following details the steps to verify whether the bearing capacity of the optimized node meets the requirements in combination with a specific implementation.

[0110] Specific cooperation Figures 2 to 5As shown, the node of this embodiment is the longitudinal beam - column node in the long - span wooden structure. The wooden components in this node include longitudinal beam 11, two cross - beams 12, and column 13. The connecting components include cruciform connecting plate 21, two first connecting plates 22, two pairs of second connecting plates 23, and two third connecting plates 24. The bolts include first bolt 31, second bolt 32, and third bolt 33. Among them, the two cross - beams 12 are arranged along the same axis and horizontally intersect at the opposite sides of the longitudinal beam 11. The column 13 supports at the bottom of the intersection of the longitudinal beam 11 and the two cross - beams 12. The two first connecting plates 22 are clamped on the opposite sides of the longitudinal beam 11 and are respectively opposite to the two cross - beams 12. The two first connecting plates 22 extend along the longitudinal beam 11 towards both ends and extend out of the opposite sides of the corresponding cross - beams 12. The two first connecting plates 22 respectively penetrate through the first bolt 31 at the two extended parts to be fixed on the opposite sides of the longitudinal beam 11. The two pairs of second connecting plates 23 are respectively arranged on the two cross - beams 12 and near the connection points. Each pair of second connecting plates 23 is respectively arranged on the opposite sides of the corresponding cross - beam 12 and is welded and fixed on the two extended parts of the corresponding first connecting plate 22. Each second connecting plate 23 and the extended part of the corresponding first connecting plate 22 together form a right - angled plate group that is attached to the connecting internal corner of the longitudinal beam 11 and the cross - beam 12. The number of the second bolts 32 is two, and they are arranged in one - to - one correspondence at the two pairs of second connecting plates 23, and are used to penetrate through the paired second connecting plates 23 to fixedly connect the two second connecting plates 23 of each pair on the opposite sides of the corresponding cross - beam 12. The lateral displacement of the corresponding longitudinal beam 11 or cross - beam 12 is restricted by the first bolt 31 and the second bolt 32. Similarly, the two third connecting plates 24 are respectively located on the opposite sides of the column 13 and are fixedly penetrated by the third bolt 33. The cruciform connecting plate 21 is padded on the top of the column 13. The two first connecting plates 22 and the two pairs of second connecting plates 23 are all fixed on the top surface of the cruciform connecting plate 21, while the two third connecting plates 24 are all fixed on the bottom surface of the cruciform connecting plate 21. In this embodiment, the number of the third bolts 33 is two. The two third bolts 33 are arranged side by side and fixedly penetrated on the two third connecting plates 24. The first bolt 31 and the second bolt are arranged in parallel. All the bolts are 8.8 - grade M16 bolts, and the welding consumables for the welds use E50 materials, where the minimum fillet weld size is 6mm.

[0111] For the above - mentioned embodiment, referring to Articles 6.2.5 - 6.2.8 of the "Code for Design of Timber Structures Requirements", the bearing capacity of the node is checked according to the empirical formula:

[0112] (1) Calculate the maximum bending moment and axial force of each wooden component in the node under the most unfavorable stress state according to the following formula:

[0113] According to the axial force balance, the axial force balance formula of the node is obtained:

[0114]

[0115] Among them, N represents the axial force of the node, and f t,b represents the tensile or compressive strength of the wood, and A t represents the cross-sectional area of the wooden member, and α t represents the adjustment coefficient considering factors such as the swelling and shrinkage of the wood due to moisture changes. and respectively represent the axial forces acting on both sides of the node.

[0116] According to the moment balance, the node moment balance formula is obtained:

[0117]

[0118] Among them, M represents the maximum moment of the node, l 1 and l 2 are the lever arm lengths on both sides of the node, is the height of the node, x is the effective stress-bearing length of the node, and M pl is the allowable value of the plastic moment of the wood.

[0119] (2) Describe the design parameters of the node in detail. The thickness t s of the wooden member in the middle of the bolt of the column part of the design is 200 mm, and the cross-grain bearing strength f e,0 of the pin slot is 38.50 kN / m 2 , and the cross-grain bearing strength f e,90 of the pin slot is 19.40 kN / m 2 . Calculate the effective length coefficients of the pin slot bearing under three yield modes respectively.

[0120] (3) Consider the influence of the swelling and shrinkage of the wood due to moisture changes. Introduce the humidity adjustment coefficient δ h to adjust the bearing capacity of the wood:

[0121] f s，adjusted = f s ×(1 + δ h )

[0122] Among them, f s represents the shear strength of the wood, and f s，adjusted considers the influence of humidity changes on the strength of the wood and represents the adjusted shear strength of the wood.

[0123] (4) The effective length coefficient of the pin slot bearing under the yield mode:

[0124] Under the action of the longitudinal load, when the node fails in the yield mode Ⅳ, the effective length coefficient of the pin slot bearing takes the minimum value k min = 0.100.

[0125] Under the action of transverse load, when the joint failure is in yield mode Ⅳ, the effective length coefficient of pin-slot bearing pressure takes the minimum value k min = 0.166

[0126] (5) Calculation of the design value of the longitudinal bearing capacity:

[0127] Then the design value of the longitudinal bearing capacity of each shear plane of a single bolt:

[0128] Z 1 = k min ×t s ×d×f e,0 = 18.48 kN

[0129] Among them, k min represents the effective length coefficient of pin-slot bearing pressure, t s represents the thickness of the middle wood member, d is the bolt diameter, and f e,0 refers to the maximum stress that the bolt can withstand under the action of shear force

[0130] The design value of the longitudinal bearing capacity of a single bolt for the side member:

[0131] Z d,1 = 2×C m C n C t k g Z 1 = 36.96 kN

[0132] Including C m is the material coefficient, C n is the nut coefficient, C t , k g are different fastening coefficients, which are used to ensure the safety of the connection

[0133] Take the maximum axial force of the column in all working conditions:

[0134] N max = 24.43 kN < 1×Z d,1

[0135] (6) Calculation of the design value of the transverse bearing capacity:

[0136] Then the design value of the transverse bearing capacity of each shear plane of a single bolt:

[0137] Z 2 = k min ×t s ×d×f e,90 = 15.46 kN

[0138] The design value of the transverse bearing capacity of a single bolt for the side member:

[0139] Zd,2 = 2 × C m C n C t k g Z 2 = 30.92 kN

[0140] Take the maximum column top shear force in all working conditions:

[0141] V max = 13.76 kN < 1 × Z d,2

[0142] (7) Design value of bolt bearing capacity for the cross and longitudinal beams:

[0143] Thickness t of the wooden member in the middle of the bolts for the cross and longitudinal beams s = 200 mm, cross grain bearing strength f e,0 = 38.50 kN / m 2 , cross grain bearing strength f e,90 = 19.40 kN / m 2 . Calculate the effective length coefficients of cross grain bearing for the three yield modes respectively. Under the action of longitudinal load, when the joint failure is in yield mode Ⅳ, the effective length coefficient of cross grain bearing takes the minimum value k min = 0.100. Under the action of cross grain load, when the joint failure is in yield mode Ⅳ, the effective length coefficient of cross grain bearing takes the minimum value k min = 0.166.

[0144] Then the design value of longitudinal bearing capacity for each shear plane of a single bolt:

[0145] Z 1 = k min × t s × d × f e,0 = 18.48 kN

[0146] Design value of longitudinal bearing capacity for a single bolt of the side member:

[0147] Z d,1 = 2 × C m C n C t k g Z 1 = 36.96 kN

[0148] Take the maximum axial force of the cross beam in all working conditions:

[0149] N max = 24.43 kN < 1 × Z d,1

[0150] Take the maximum axial force of the longitudinal beam in all working conditions:

[0151] Nmax = 13.76 kN < 1 × Z d,1

[0152] Then the design value of the cross-grain bearing capacity of each shear plane of a single bolt:

[0153] Z 2 = k min × t s × d × f e,90 = 15.46 kN

[0154] The design value of the cross-grain bearing capacity of a single bolt in the side member:

[0155] Z d,2 = 2 × C m C n C t k g Z 2 = 30.92 kN

[0156] Take the maximum shear force of the cross beam in all working conditions:

[0157] V max = 24.43 kN < 1 × Z d,1

[0158] Take the maximum shear force of the longitudinal beam in all working conditions:

[0159] V max = 24.43 kN < 1 × Z d,1

[0160] After verification, the bearing capacity of this pin joint meets the requirements.

[0161] This method integrates multi-scale finite element analysis and topology optimization algorithm, and realizes the accurate evaluation of the bearing capacity of wooden structure joints under variable working conditions. By finely simulating the mechanical behavior of bolt connections and the bearing characteristics of wooden components, while improving the reliability and safety of structural design, it optimizes the use of materials and reduces the maintenance cost. The present invention is not only applicable to the field of long-span wooden structure buildings, but its technical principles and methods can also be extended to multiple fields such as other building engineering, bridge design, mechanical structure design, and metal material building joints, etc., and has broad application prospects and significant economic benefits.

[0162] The present invention has been described in detail above in combination with the embodiments with the accompanying drawings. Those of ordinary skill in the art can make various variations of the present invention according to the above description. Therefore, certain details in the embodiments should not constitute a limitation to the present invention, and the present invention will take the scope defined by the appended claims as the protection scope of the present invention.

Claims

1. A method for evaluating the bearing capacity of a timber structure node, wherein the node comprises a timber member and bolts and connectors for connecting the timber members, characterized in that: The bearing capacity assessment method comprises the steps of: S1. Provide a detailed description of the node, including the geometry, material properties, bolt arrangement and connection interface details of the node; S2. Based on the refined description of the node, a refined node model is established using finite element software; S3, using the node refined model to simulate the stress conditions of the node under different load combinations, and respectively calculating the stress and strain distribution of the node area to determine the most unfavorable stress condition of the node; S4, analyzing the mechanical characteristics of the bolt connection at the node, and calculating the bearing capacity of the bolt connection; S5. Optimizing the bolt layout, connector size and material configuration of the node using a topology optimization algorithm; S6. Based on the results of steps S3 to S5, a comprehensive bearing capacity assessment is performed on the node.

2. The method for evaluating the bearing capacity of a timber structure node according to claim 1, characterized in that: The material properties in step S1 include micro-scale material properties and macro-scale material properties; The node refinement model in step S2 includes a microscopic model for simulating wood fibers and a macroscopic model for simulating the entire node; When executing step S3: S31, using the microscopic model to simulate microscopic mechanical behavior, and calculating the stress and strain of the wood microscopic unit, and then mapping the calculation results to the macroscopic scale through homogenization technology; S32. In the macro model, the micro-scale material properties are used as input, and the continuum mechanics method is used to consider the interaction between bolts and wooden components to calculate the stress and strain distribution in the node area.

3. The method for evaluating the bearing capacity of a timber structure node according to claim 2, characterized in that: When establishing the micro model and the macro model: a finite element mesh is generated. For the micro scale, a high-resolution mesh is used to capture the local stress and strain of the wood fibers. For the macro scale, a structured mesh is used to simulate the entire node, ensuring that the mesh density of the bolt and connection area is sufficient to capture the stress concentration.

4. The method for evaluating the bearing capacity of a timber structure node according to claim 3, characterized in that: When executing step S5: S51. Perform modal analysis using the macro model to determine the natural frequency and vibration mode: Among them, W n represents the natural frequency; k represents the stiffness; m represents the mass; S52. Define the contact surface between the bolt and the wood member and simulate the contact behavior using the penalty function method or the Lagrange multiplier method: P=K contact ×u Where P represents the reaction force on the contact surface, K contact represents the contact stiffness matrix, and u represents the contact surface displacement; S53, define the topology optimization design variable as material density ρ(x), where 0≤ρ(x)≤1; S54, establish an objective function and constraint conditions, wherein the objective function J is to minimize the structural quality: Among them, Ω represents the entire domain; The constraint condition is that the von Mises stress of the node does not exceed the yield strength of the material; S55. Use the SIMP method to map the design variables to the elastic modulus E(x) of the wood structure material: Among them, E0 represents the original elastic modulus of the material, that is, the elastic properties of the material before topology optimization; ρmin represents the minimum value of the material density; p represents the SIMP parameter, which is usually 3 or 4; S56, iterative solution, using the Newton-Raphson iteration method to solve the macro model until a convergence condition is met, in each iteration, updating the material properties in the macro model according to the design variables, and the convergence condition is: ΔU<∈ tol Among them, ΔU represents the increment of displacement; ∈ tol represents the preset convergence tolerance; α represents the learning rate, Represents the partial derivative of the objective function J with respect to ρ. k+1 and ρ k denote the material density distributions of the k+1th and kth iterations respectively; S57. Optimize the bolt layout, connector size and material configuration of the node based on the elastic modulus E(x) of the wood structure material after iterative solution.

5. The method for evaluating the bearing capacity of a timber structure node according to claim 4, characterized in that: The contents of the comprehensive bearing capacity assessment include multi-scale coupling, modal analysis, fatigue analysis, stress concentration analysis, and multi-physical field coupling analysis.

6. The method for evaluating the bearing capacity of a timber structure node according to claim 1, characterized in that: The design of the node is optimized according to the comprehensive bearing capacity evaluation results, and it is verified whether the bearing capacity of the optimized node meets the requirements.

7. The method for evaluating the bearing capacity of a timber structure node according to claim 6, characterized in that: The steps to verify whether the optimized node carrying capacity meets the requirements include: Calculate the maximum bending moment and axial force of each wood member under the most unfavorable stress state of the node; The design parameters of the node are described in detail, and a humidity adjustment coefficient is introduced to adjust the bearing capacity of the wood; For each timber member, calculate the longitudinal and transverse bearing capacities of a single bolt under different yield modes and take the minimum value; Determine whether the von Mises stress of the node exceeds the yield strength of the material. Take each wood component as a unit and determine whether the maximum axial force of the wood component is less than the minimum longitudinal bearing capacity of the corresponding single bolt and whether the maximum bending moment is less than the transverse bearing capacity of the corresponding single bolt. Only when the judgment results of all wood components are less than, can it be concluded that the bearing capacity of the node meets the requirements.

8. The method for evaluating the bearing capacity of a timber structure node according to claim 7, characterized in that: The method for calculating the maximum bending moment and axial force of each wood member under the most unfavorable stress state of the node is: According to the axial force balance, the node axial force balance formula is obtained: Where N is the axial force at the node, f t,b Indicates the tensile or compressive strength of wood, A t represents the cross-sectional area of ​​the wood member, α t It represents the adjustment coefficient considering factors such as wood swelling and shrinkage. and They represent the axial forces acting on both sides of the node respectively; According to the moment balance, the node moment balance formula is obtained: Where M represents the maximum bending moment of the node, l1 and l2 are the lengths of the force arms on both sides of the node, is the height of the node, x is the effective force length of the node, M pl It is the allowable value of plastic bending moment of wood.

Images