A method for assessing stiffness and bearing capacity of crack-damaged tenon joints

Abstract

The invention discloses a method for evaluating the stiffness and bearing capacity of a cracked and damaged tenon-through joint, and relates to the technical field of node stiffness and bearing capacity evaluation, and comprises the following steps: arranging measuring points for the tenon-through joint; obtaining each impact point in the process of wood fracture; classifying the impact point of each measuring point; meshing the tenon-through joint, locating each impact point in the tenon-through joint grid, and determining the failed grid in the tenon-through joint grid; establishing an extended finite element model, wherein the grid in the extended finite element model is consistent with the grid of the tenon-through joint, the failed grid in the extended finite element model is deleted, and loading simulation of the extended finite element model is performed to simulate and observe the change of the fracture position; determining the fracture parameters of the tenon-through joint, including the wood cracking load and the crack extension coefficient; inputting the fracture parameters of the tenon-through joint into the extended finite element model, outputting a bending moment-rotation curve, and calculating the bearing capacity damage and stiffness damage of the tenon-through joint.

Description

Technical Field

[0001] The invention relates to the technical field of node stiffness and bearing capacity evaluation, and in particular to a method for evaluating the stiffness and bearing capacity of a cracked and damaged tenon-through joint. Background Art

[0002] The tenon and mortise joints of ancient wooden structures are key stress-bearing locations, and damage to the tenon and mortise joints will cause the collapse of the structure. However, the tenons are hidden in the mortises, and there are no obvious signs when they break, making it impossible to visually observe the damage and conduct bearing capacity assessment.

[0003] The current method of detecting through-tenon joints only evaluates the deformation and strength of the nodes, but cannot clearly determine the location and extent of material damage in the through-tenon joints themselves, nor can it qualitatively and quantitatively evaluate the remaining bearing capacity and stiffness of the through-tenon joints. The extent and location of damage cannot be determined in the early stage of damage to the through-tenon joints.

[0004] Acoustic emission is a technology that is sensitive to wood fracture and damage. It can monitor damage to components during normal service and identify the extent and location of damage in the early stages of component damage. This provides a better understanding of component damage. However, further research is needed to assess the stiffness and bearing capacity of tenon joints and to provide safety warnings. Summary of the invention

[0005] In view of the problems in the background technology, the present invention provides a method for evaluating the stiffness and bearing capacity of a cracked and damaged tenon-tenon joint, comprising the following steps:

[0006] Arrange measurement points for tenon joints.

[0007] Carry out mechanical property tests of wood of corresponding grade on the tenon joints, use acoustic emission equipment to monitor the mechanical property tests, and obtain the impact points during the wood fracture process.

[0008] The characteristic parameter range of acoustic emission of fracture is statistically analyzed, and the impact points of each measuring point are classified according to energy based on the parameter range.

[0009] The tenon-through node is meshed, each impact point is located in the tenon-through node mesh, and the failed mesh in the tenon-through node mesh is determined.

[0010] An extended finite element model is established. The mesh in the extended finite element model is consistent with the mesh of the tenon node. The failed mesh in the extended finite element model is deleted. The extended finite element model is loaded and simulated to observe the changes in the fracture position.

[0011] Determine the fracture parameters of through-tenon joints, including wood cracking load and crack growth coefficient.

[0012] The fracture parameters of the tenon-tenon joint are input into the extended finite element model, the moment-rotation curve is output, and the bearing capacity damage and stiffness damage of the tenon-tenon joint are calculated.

[0013] Furthermore, the measuring point is arranged at the junction of the tenon and the column.

[0014] Furthermore, the mechanical property test includes: a wood longitudinal tensile test, a wood longitudinal compression test, a wood transverse tensile test, a wood transverse compression test, and a wood three-point bending test.

[0015] Furthermore, the impact points of each measuring point are classified into two types according to energy according to the parameter range, including the following steps:

[0016] Define the energy centroid of each impact point.

[0017] The impact points are initially classified and each impact point is associated with the nearest energy centroid.

[0018] Re-determine the energy center of mass position and repeat the calculation Until J is minimized, where J is the objective function, ||x j -μ i || is the impact point x j To cluster center μ i A specific length between.

[0019] The impact points of each measuring point are classified according to energy, and the energy is 25-1200mv 2 The impact point of the fracture acoustic emission signal of / s is defined as the impact point of the category 1 signal, and the energy is 0-25mv 2 The impact point of the fracture acoustic emission signal of / s is defined as the category 2 signal impact point.

[0020] Further, the determining of the failed mesh in the tenon-through node mesh specifically includes:

[0021] The tenon-through node mesh appearing at the signal impact point of category 1 is determined as the failed mesh, and the tenon-through node mesh forming a through fracture surface at the signal impact point of category 2 is determined as the failed mesh.

[0022] Further, the determination of the fracture parameters of the tenon-through node specifically includes:

[0023] Using the maximum normal stress criterion in the traction-separation law Define the timber cracking load, where is the normal stress intensity of the crack direction surface, t n is the corresponding normal stress, and the other two terms are the tangential stresses on the crack surface.

[0024] When 1<f<1.0+f tolWhen , wood cracks appear, and the process of crack generation satisfies the traction-separation law, that is, when the cohesive strength of the unit is 0, the unit separates and forms cracks.

[0025] Furthermore, the determination of the fracture parameters of the tenon-through node also includes:

[0026] Using the Griffith Criteria Define the crack growth coefficient, where G I , G II , G III is the strain energy release rate at the crack tip of the three fracture modes, G IC , G IIC , G IIIC is the critical strain energy release rate, a m , a n , a0 is the corresponding index.

[0027] Furthermore, the establishment of the extended finite element model specifically includes:

[0028] ABAQUS was used to model the structure using solid elements. Wood was an anisotropic material and its mechanical properties were set according to the actual mechanical properties of wood. The elastic stage was represented by engineering constants in ABAQUS, the plastic stage was represented by potential functions, hard contact was used for normal contact, and penalty function was used for tangential contact.

[0029] The loading method adopts displacement loading, and the loading point is the inflection point of the beam. The loading is carried out until the bending moment of the tenon-tenon node drops to 85% of the ultimate bending moment.

[0030] Furthermore, the calculation of the bearing capacity damage and stiffness damage of the tenon-tenon joint specifically includes:

[0031] The damage of the bearing capacity of the tenon joint is calculated by D M =(M2-M1) / M2, where D M is the residual bearing capacity of the tenon-tenon joint, M1 is the ultimate bending moment of the tenon-tenon joint after damage, and M2 is the ultimate bending moment of the intact tenon-tenon joint.

[0032] The stiffness damage of the tenon joint is calculated by D K =(K2-K1) / K2, K1=M1 / θ1, K2=M2 / θ2, where D K is the residual stiffness of the tenon-through node, K1 is the rotational stiffness of the tenon-through node after damage, M1 is the ultimate bending moment after damage, K2 is the rotational stiffness of the intact node, M2 is the ultimate bending moment of the intact node, θ1 is the angle between the straight line formed by the ultimate load point of the tenon-through node after damage and the origin and the X-axis, θ2 is the angle between the straight line formed by the ultimate load point of the intact tenon-through node and the origin and the X-axis.

[0033] Compared with the prior art, the present invention provides a method for evaluating the stiffness and bearing capacity of cracked and damaged tenon-tenon joints, which has the following beneficial effects:

[0034] The present invention provides a method for evaluating the stiffness and bearing capacity of cracked and damaged tenon-tenon joints. The method locates the internal damage position of a component by an acoustic emission monitoring instrument, and simulates the tenon-tenon joints before and after damage based on ABAQUS. In the early stage of microscopic cracking and damage of the material, the damage and destruction degree of the node can be evaluated without disassembling the node. The method is simple to operate and the result is clear. The method can effectively evaluate the damage degree of the tenon-tenon joints of the wooden structure of an ancient building both qualitatively and quantitatively, and provide a theoretical basis and technical support for the real-time evaluation and collapse warning of the tenon-tenon joints of the wooden structure of an ancient building, so that the repair and reinforcement of the nodes are more targeted. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A flow chart of a method for evaluating the stiffness and bearing capacity of a cracked and damaged tenon-tenon joint provided by the present invention;

[0036] Figure 2 Schematic diagram of monitoring position of tenon-through nodes in an embodiment of the present invention;

[0037] Figure 3 Schematic diagram of the installation position of acoustic emission measurement points of tenon-through nodes in an embodiment of the present invention;

[0038] Figure 4 This is a schematic diagram of the impact point of category 1 in an embodiment of the present invention;

[0039] Figure 5 This is a schematic diagram of a category 2 impact point in an embodiment of the present invention;

[0040] Figure 6 Schematic diagram of the mesh division and classification of tenon-through nodes 1 and collision points in an embodiment of the present invention;

[0041] Figure 7 Schematic diagram of mesh division and classification 2 of tenon-through nodes and collision points in an embodiment of the present invention;

[0042] Figure 8 Schematic diagram of a damaged tenon-through model in an embodiment of the present invention;

[0043] Fig. 9 Schematic diagram of a complete tenon-through model in an embodiment of the present invention;

[0044] Fig.10 This is a diagram showing the analysis results of the damaged tenon-through model in an embodiment of the present invention;

[0045] Fig.11 This is a diagram showing the analysis results of a complete tenon-through model in an embodiment of the present invention;

[0046] Fig.12It is a loading moment-rotation curve diagram of the tenon-tenon node in an embodiment of the present invention. DETAILED DESCRIPTION

[0047] The following is combined with Figures 1 to 12 The following examples 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.

[0048] Embodiment 1: A method for evaluating the stiffness and bearing capacity of a cracked and damaged tenon-tenon joint provided by the present invention comprises the following steps:

[0049] Step 1: Conduct an acoustic emission test on the mechanical properties of Pinus sylvestris, a wood commonly used in tenon joints, and classify the impact points based on the K-means clustering algorithm:

[0050] (1) First, define the energy centroids, where the number of energy centroids depends on the number of assumed clusters. The relative positions of the energy centroids must be as far as possible to improve the accuracy of the analysis.

[0051] (2) Associate each point to the nearest energy centroid. When all points are classified, the initial classification is completed.

[0052] (3) Recalculate the new position of the energy center of mass until the objective function J is minimized.

[0053]

[0054] Where J is the objective function, ||x j -μ i || is point x j To cluster center μ i A specific length between.

[0055] The fracture acoustic emission signals were statistically analyzed to divide the range of larger fracture acoustic emission signals and smaller fracture acoustic emission signals, and the energy of 25-1200mv 2 The impact point of the fracture acoustic emission signal of / s is defined as the impact point of the category 1 signal, and the energy is 0-25mv 2 The impact point of the fracture acoustic emission signal of / s is defined as the impact point of the category 2 signal, such as Figure 4 and Figure 5 shown.

[0056] Step 2: Define the key stress-bearing parts of the tenon-tenon joint. For the tenon-tenon joint, the main load is the bending load, and the key stress-bearing part is the intersection of the tenon and the column, such as Figure 2 Arrange acoustic emission measuring points on the tenon joint, open four 5mm holes on both sides of the mortise, and install acoustic emission measuring points, as shown in the figure below. Figure 3 shown.

[0057] Step 3: When the material of the tenon joint is damaged, the impact point location will be transmitted to the computer. Take the grid with a side length of 1 cm as the standard, such as Figure 6 and Figure 7 When the impact point of the category 1 signal appears within the grid, the grid can be considered to be invalid, such as Figure 6 When the impact point of the Class 2 signal forms a through fracture surface, the grid can be considered to be failed, such as Figure 7 shown.

[0058] Step 4: Establish an extended finite element model in ABAQUS, using solid unit modeling. Wood is an anisotropic material, and the mechanical properties are set according to the actual mechanical properties of wood. The elastic stage is represented by the engineering constants in ABAQUS, and the plastic stage is represented by the potential function. The normal contact uses hard contact, the tangential contact uses a penalty function, and the friction coefficient is 0.3. The loading method uses displacement loading. The loading point is the beam inflection point, and the loading is until the bending moment of the tenon node drops to 85% of the limit bending moment.

[0059] The grid division is consistent with the actual grid division, and the grid side length is 1cm. Figure 8 and Fig. 9 shown.

[0060] Step 5: Define the fracture parameters in ABAQUS and use the maximum normal stress criterion in the traction separation law to define the wood cracking load. The maximum normal stress criterion is as follows:

[0061]

[0062] In the formula, is the normal stress intensity of the crack direction surface, t n is the corresponding normal stress, and the other two terms are the tangential stresses of the crack surface. When 1<f<1.0+f tol When the unit cohesion strength is 0, the unit separates and cracks are formed.

[0063] The crack growth coefficient is defined using the Griffith criterion, which is as follows:

[0064]

[0065] Among them G I , G II , G III is the strain energy release rate at the crack tip of the three fracture modes, G IC , G IIC , G IIIC is the critical strain energy release rate, a m , an , a0 is the corresponding index

[0066] Step 6: Delete the failed mesh in Part in ABAQUS, perform loading simulation on the damaged model and the undamaged model respectively, and observe the changes of the main force cloud diagram, such as Fig.10 , Fig.11 As shown. The stiffness damage is obtained:

[0067] D K =(K2-K1) / K2

[0068] Among them, K1 is the elastic stage rotation stiffness of the tenon-tenon joint after damage, and K2 is the elastic stage rotation stiffness of the intact node.

[0069] K1=M1 / θ1

[0070] Where M1 is the ultimate bending moment of the node after damage, and θ1 is the angle between the straight line formed by the ultimate load point of the tenon-tenon node after damage and the origin and the X-axis.

[0071] K2 is the rotational stiffness of the intact node.

[0072] K2=M2 / θ2

[0073] Where M2 is the ultimate bending moment of the intact node, and θ2 is the angle between the straight line formed by the ultimate load point of the intact tenon joint and the origin and the X-axis.

[0074] Bearing capacity damage:

[0075] D M =(M2-M1) / M2

[0076] Among them, M1 is the ultimate bending moment of the damaged tenon-tenon joint, and M2 is the ultimate bending moment of the intact joint, such as Fig.12 shown.

[0077] Step 7: According to D K The residual stiffness of the node is evaluated using the value. K The damage is 10.5%, and the bearing capacity and stiffness of the tenon joint are still relatively sufficient, so it is not necessary to reinforce it for the time being. M The residual bearing capacity of the node is evaluated based on the value. M The damage is 10.5%, and the bearing capacity and stiffness of the tenon-tenon joint are still sufficient, so there is no need to reinforce it for the time being.

[0078] Compared with the prior art, the present invention provides a method for assessing the stiffness and bearing capacity of cracked and damaged tenon-tenon joints. The method locates the damage position of the internal bearing capacity and rotational stiffness of the component by using an acoustic emission monitoring instrument, and simulates the tenon-tenon joints before and after damage based on ABAQUS. In the early stage of microscopic cracking and damage of the material, the damage and degree of destruction of the node can be assessed without disassembling the node. The method is simple to operate and the results are clear. The method can effectively assess the degree of damage of the tenon-tenon joints of the wooden structure of ancient buildings both qualitatively and quantitatively, and provide a theoretical basis and technical support for the real-time assessment and collapse warning of the tenon-tenon joints of the wooden structure of ancient buildings, so that the repair and reinforcement of the nodes are more targeted.

[0079] The embodiments described above are only preferred specific implementation modes of the present invention, and the protection scope of the present invention is not limited thereto. Any simple changes or equivalent replacements of the technical solutions that can be obviously obtained by any technician familiar with the field within the technical scope disclosed in the present invention belong to the protection scope of the present invention.

Claims

1. A method for evaluating the stiffness and bearing capacity of cracked and damaged tenon joints, characterized in that: The following steps are involved: Arrange measurement points for tenon joints; Conduct mechanical property tests on wood of corresponding grades at tenon joints, use acoustic emission equipment to monitor the mechanical property tests, and obtain the impact points during the wood fracture process; The acoustic emission characteristic parameter range of the fracture is statistically classified, and the impact points of each measuring point are classified according to the energy based on the parameter range; Meshing the tenon-through node, locating each impact point in the tenon-through node mesh, and determining the failed mesh in the tenon-through node mesh; An extended finite element model is established. The mesh in the extended finite element model is consistent with the mesh of the tenon-tenon node. The failed mesh in the extended finite element model is deleted. The extended finite element loading simulation is performed to simulate and observe the changes in the fracture position. Determine the fracture parameters of through-tenon joints, including wood cracking load and crack growth coefficient; The fracture parameters of the tenon-tenon joint are input into the extended finite element model, the moment-rotation curve is output, and the bearing capacity damage and stiffness damage of the tenon-tenon joint are calculated.

2. A method for evaluating stiffness and bearing capacity of cracked and damaged tenon joints according to claim 1, characterized in that: The measuring point is arranged at the junction of the tenon and the column.

3. A method for evaluating stiffness and bearing capacity of cracked and damaged tenon joints according to claim 1, characterized in that: The mechanical property tests include: wood tensile test along the grain, wood compression test along the grain, wood transverse tensile test, wood transverse compression test, and wood three-point bending test.

4. A method for evaluating stiffness and bearing capacity of cracked and damaged tenon joints according to claim 1, characterized in that: The method of classifying the impact points of each measuring point into two types according to energy based on the parameter range includes the following steps: Define the energy center of mass of each impact point; Perform an initial classification of the impact points and associate each impact point to the nearest energy centroid; Re-determine the energy center of mass position and repeat the calculation Until J is minimized, where J is the objective function, ||x j -μ i || is the impact point x j To cluster center μ i A specific length between The impact points of each measuring point are classified according to energy, and the energy is 25-1200mv 2 The impact point of the fracture acoustic emission signal of / s is defined as the impact point of the category 1 signal, and the energy is 0-25mv 2 The impact point of the fracture acoustic emission signal of / s is defined as the category 2 signal impact point.

5. A method for evaluating the stiffness and bearing capacity of a cracked and damaged tenon-tenon joint as claimed in claim 4, characterized in that: The determining of the failed mesh in the tenon-through node mesh specifically includes: The tenon-through node mesh appearing at the signal impact point of category 1 is determined as the failed mesh, and the tenon-through node mesh forming a through fracture surface at the signal impact point of category 2 is determined as the failed mesh.

6. A method for evaluating the stiffness and bearing capacity of a cracked and damaged tenon-tenon joint as claimed in claim 1, characterized in that: Determining the fracture parameters of the tenon-through node specifically includes: Using the maximum normal stress criterion in the traction-separation law Define the timber cracking load, where is the normal stress intensity of the crack direction surface, t n is the corresponding normal stress, and the other two terms are the tangential stresses on the crack surface; When 1<f<1.0+f tol When , wood cracks appear, and the process of crack generation satisfies the traction-separation law, that is, when the cohesive strength of the unit is 0, the unit separates and forms cracks.

7. A method for evaluating the stiffness and bearing capacity of a cracked and damaged tenon-tenon joint as claimed in claim 6, characterized in that: The determining of the fracture parameters of the tenon-through node also includes: Using the Griffith Criteria Define the crack growth coefficient, where G I , G II , G III is the strain energy release rate at the crack tip of the three fracture modes, G IC , G IIC , G IIIC is the critical strain energy release rate, a m , a n , a0 is the corresponding index.

8. A method for evaluating stiffness and bearing capacity of cracked and damaged tenon joints according to claim 1, characterized in that: The establishing of the extended finite element model specifically includes: ABAQUS was used to model the structure using solid elements. Wood was an anisotropic material and its mechanical properties were set according to the actual mechanical properties of wood. The elastic stage was represented by engineering constants in ABAQUS, the plastic stage was represented by potential functions, hard contact was used for normal contact, and penalty function was used for tangential contact. The loading method adopts displacement loading, and the loading point is the inflection point of the beam. The loading is carried out until the bending moment of the tenon-tenon node drops to 85% of the ultimate bending moment.

9. A method for evaluating stiffness and bearing capacity of cracked and damaged tenon joints according to claim 1, characterized in that: The calculation of the bearing capacity damage and stiffness damage of the tenon-tenon joint specifically includes: The damage of the bearing capacity of the tenon joint is calculated by D M =(M2-M1) / M2, where D M is the residual bearing capacity of the tenon-tenon joint, M1 is the ultimate bending moment of the tenon-tenon joint after damage, and M2 is the ultimate bending moment of the intact tenon-tenon joint; The stiffness damage of the tenon joint is calculated by D K =(K2-K1) / K2, K1=M1 / θ1, K2=M2 / θ2, where D K is the residual stiffness of the tenon-through node, K1 is the rotational stiffness of the tenon-through node after damage, M1 is the ultimate bending moment after damage, K2 is the rotational stiffness of the intact node, M2 is the ultimate bending moment of the intact node, θ1 is the angle between the straight line formed by the ultimate load point of the tenon-through node after damage and the origin and the X-axis, θ2 is the angle between the straight line formed by the ultimate load point of the intact tenon-through node and the origin and the X-axis.

Images