Simulation Method for Impact Performance of Concrete-Filled Steel Tube Structures with Randomly Distributed Void Defects

Abstract

The present invention relates to a simulation method for the impact performance of a concrete-filled steel tubular structure with randomly distributed void defects, including: establishing a concrete-filled steel tubular solid model with randomly distributed void defects; performing a static non-linear history calculation on the axial force loading stage of the concrete-filled steel tubular solid model by using a static calculation method to obtain a static calculation result; performing a dynamic non-linear history calculation on the impact load loading stage of the concrete-filled steel tubular solid model by using a dynamic calculation method to obtain an impact force history calculation result and an animation of the model deformation state during the entire process of the impact load action; comparing the measured impact force history result of the concrete-filled steel tubular with the impact force history calculation result obtained by the non-linear history calculation method to evaluate the simulation result. This method is beneficial to accurately simulate the stress process of a concrete-filled steel tubular structure with randomly distributed void defects under the coupled action of axial force and impact load, and further refine the evaluation of the impact resistance performance of the actual defective structure.

Description

Technical Field

[0001] The invention belongs to the field of structural safety, and particularly relates to a method for simulating the impact performance of a concrete-filled steel tubular structure with randomly distributed void defects. Background Art

[0002] Affected by factors such as concrete pouring technology, shrinkage and cold shrinkage of concrete during curing, solar radiation and seasonal temperature differences during operation, and late shrinkage of concrete, the concrete-filled steel tubular structures in actual projects often have void defects, posing potential safety hazards to the structures. Under conditions such as dynamic loads, corrosion, and high temperatures, the internal void defects of the concrete-filled steel tubular structures may cause structural damage. Under extreme impact loads caused by vehicle or ship impacts, etc., it may even lead to structural collapse, resulting in serious casualties and significant economic losses. Accurately simulating the impact performance of a concrete-filled steel tubular structure with void defects is an important means to evaluate the structural safety under extreme loads.

[0003] However, the current simulation methods for concrete-filled steel tubular structures with void defects all adopt the assumption of idealized uniform distribution of void defects or the form of presetting several local defects at certain positions of the structure, which is difficult to reflect the true situation of randomly distributed void defects in actual projects and may lead to inaccurate evaluation of the impact resistance of actual concrete-filled steel tubular structures, thus causing safety accidents. Specifically, there are the following two problems in using the uniform void model to simulate a concrete-filled steel tubular structure with void defects: (1) The uniform void model uses uniformly distributed void defects to equivalent the randomly distributed void defects in the actual structure, idealizing the distribution of void defects and unable to reflect the influence of the void defect distribution on the mechanical properties of the concrete-filled steel tubular structure; (2) The change in the void defect distribution means the change in the contact relationship between the concrete and the steel pipe in the finite element model, resulting in the inability to accurately evaluate the bearing capacity of the structure by the calculation results. Therefore, providing a method and device for simulating the impact performance of a concrete-filled steel tubular structure with randomly distributed void defects has become an urgent problem to be solved in this field. Summary of the Invention

[0004] The purpose of the invention is to provide a method for simulating the impact performance of a concrete-filled steel tubular structure with randomly distributed void defects, which is beneficial to accurately simulate the stress process of a concrete-filled steel tubular structure with randomly distributed void defects under the coupling action of axial force and impact load, and further refine the evaluation of the impact resistance of the actual defective structure.

[0005] To achieve the above purpose, the technical solution adopted by the invention is: A method for simulating the impact performance of a concrete-filled steel tubular structure with randomly distributed void defects, comprising the following steps:

[0006] Step S1: Establish a concrete-filled steel tube solid model with randomly distributed void defects, including a concrete-filled steel tube model with axially randomly distributed void defects and a concrete-filled steel tube model with radially randomly distributed void defects;

[0007] Step S2: Use the static calculation method to perform a static non-linear history calculation on the axial force loading stage of the concrete-filled steel tube solid model with randomly distributed void defects. The contact between the steel tube and the concrete is determined by the relative displacement of the unit nodes to obtain the static calculation results;

[0008] Step S3: Use the dynamic calculation method to perform a dynamic non-linear history calculation on the impact load loading stage of the concrete-filled steel tube solid model with randomly distributed void defects. The contact between the steel tube and the concrete is determined by the dynamic pressure of the unit nodes to obtain the calculation results of the impact force history and the history animation of the deformation state of the model during the whole process of the impact load action;

[0009] Step S4: Compare the measured impact force history results of the concrete-filled steel tube with the calculated impact force history results obtained by the non-linear history calculation method to evaluate the simulation results.

[0010] Furthermore, the concrete-filled steel tube model with axially randomly distributed void defects is constructed by the random sketch edge method, and the concrete-filled steel tube model with radially randomly distributed void defects is constructed by the random offset concrete solid method.

[0011] Furthermore, in step S1, the specific method for establishing the concrete-filled steel tube model with axially randomly distributed void defects is as follows:

[0012] Step S111: According to the designed pipe diameter, with the sketch origin as the center, use the planar sketch to draw the cross-sectional shape of the steel tube; and use the method of stretching the planar sketch of the steel tube to form a steel tube solid model;

[0013] Step S112: According to the designed concrete size, with the sketch origin as the center, use the polyline to draw the longitudinal cross-sectional planar sketch of the concrete; and use the method of rotating the planar sketch of the concrete cross-section to form a concrete solid model, where the distribution of each node (X i , Y i ) on the axial edge of the concrete sketch is as shown in the following formula:

[0014]

[0015] Among them, X i is the abscissa of each node on the axial edge of the concrete; R is the inner radius of the steel tube; d c is the maximum void distance of the concrete, taking the maximum distance from the concrete surface to the inner wall of the steel tube; Y iis the ordinate of each node on the axial side of the concrete; L is the length of the concrete-filled steel tube;

[0016] Step S113: Assemble the concrete solid model and the steel tube solid model to form a concrete-filled steel tube model with axially randomly distributed void defects.

[0017] Furthermore, in the said Step S1, the specific method for establishing a concrete-filled steel tube model with radially randomly distributed void defects is as follows:

[0018] Step S121: According to the designed pipe diameter, with the origin of the sketch as the center, use the planar sketch to draw the cross-sectional shape of the steel tube, and use the method of stretching the planar sketch of the steel tube to stretch the planar sketch of the steel tube to form a steel tube solid model;

[0019] Step S122: According to the designed concrete size, with the origin of the sketch as the center, use the planar sketch to draw the cross-sectional shape of the concrete, and use the method of stretching the planar sketch of the concrete to stretch the planar sketch of the concrete to form a concrete solid model, where the concrete radius R n takes the value as shown in the following formula:

[0020] R n = R - d c

[0021] wherein, R n is the concrete solid radius of the concrete-filled steel tube model with radially randomly distributed void defects; R is the inner radius of the steel tube; d c is the maximum void distance of the concrete, taking the maximum distance from the concrete surface to the inner wall of the steel tube;

[0022] Step S123: Assemble the steel tube solid model and the concrete solid model, and copy multiple concrete solid models. Then, taking the center of the bottom surface of the model (X0, Y0) as the reference point, translate the copied concrete solid models so that the distribution of the reference points (X i , Y i ) after translation is as shown in the following formula:

[0023]

[0024] wherein, X0 is the abscissa of the translation reference point; Y0 is the abscissa of the translation reference point; X i is the abscissa of the reference point after translation; Y i is the abscissa of the reference point after translation;

[0025] Step S124: Use Boolean operation to intersect and merge all the concrete solid models, thereby forming a concrete-filled steel tube model with radially randomly distributed void defects.

[0026] Further, in step S2, when performing static nonlinear history calculation, a static material constitutive model and a static calculation method are used to calculate the process of applying axial pressure to the concrete-filled steel tube specimen, and the calculation results are stored as a restart result file.

[0027] In step S3, when performing dynamic nonlinear history calculation, a dynamic material constitutive model and a dynamic calculation method are used to calculate the impact process of the concrete-filled steel tube specimen. Then, the restart result file is introduced to endow the model with the initial axial compression state. Meanwhile, a spring element is used to apply axial force to ensure the existence of axial force during the action of the impact load.

[0028] Further, in step S2, with the state of no initial stress and static boundary conditions as the first initial state, a static nonlinear history calculation is performed on the axial force loading stage of the concrete-filled steel tube solid model with randomly distributed void defects by using a static calculation method. The specific steps are as follows:

[0029] Step S21: Establish an implicit analysis step; generate a restart result file during the static calculation process, and write the final state of the calculated model and the load-displacement relationship into the restart result file.

[0030] Step S22: Assign static material properties, axial force loads, and C3D8R mesh elements to the steel tube and concrete solid models respectively.

[0031] In step S23, the static contact relationship adopts the contact relationship between the concrete surface and the steel tube surface that depends on the relative distance of the element nodes, including normal contact and tangential contact. The normal contact is a hard contact, as shown in the following formula:

[0032]

[0033] where S is the relative distance of the element nodes; F N is the element contact force; σ is the element contact compressive stress; A is the normal area of the element compressive stress. According to the above formula, the contact compressive stress is 0 when the steel tube and the core concrete are not in contact, and the normal contact compressive stress can be transmitted after they are in contact.

[0034] The tangential contact adopts a penalty friction contact that depends on the contact compressive stress, as shown in the following formula:

[0035]

[0036] where S is the relative distance of the element nodes; F N is the element contact force; τ is the interfacial shear stress; μ is the interfacial friction coefficient, N uis the compressive stress perpendicular to the element; according to the above formula, when the node of the steel pipe and the core concrete element is greater than zero, the initial bond stress is set to 0, and when the node of the steel pipe and the core concrete element is equal to zero, the interface bond stress is determined according to the contact compressive stress;

[0037] Step S24: Establish the model boundary conditions and loads. One end of the concrete-filled steel tube solid model is completely fixed, and the other end only has the translational degree of freedom in the z-axis direction;

[0038] Step S25: Submit the model file, calculate and obtain the static calculation results, and then store the calculation results as a restart result file.

[0039] Furthermore, in the step S3, taking the axial force holding state as the second initial state, the dynamic nonlinear history calculation is carried out on the impact load stage of the concrete-filled steel tube solid model with randomly distributed void defects by using the dynamic calculation method, which specifically includes the following steps:

[0040] Step S31: The dynamic contact relationship adopts to establish a dynamic explicit analysis step, import the restart result file obtained from the static calculation, and assign the initial state of axial force loading to the dynamic model;

[0041] Step S32: Use the dynamic calculation method, establish a drop hammer entity by using an analytical rigid body, and assign dynamic properties to the entity model; replace the static material constitutive of the steel tube and the concrete entity model with the dynamic material constitutive considering the strain rate effect, including the dynamic material constitutive of steel and the dynamic material constitutive of concrete;

[0042] Step S33: Replace the static contact relationship between the concrete surface and the steel tube surface with a dynamic contact relationship, where the contact judgment depends on the dynamic compressive stress between unit nodes, including normal hard contact and tangential frictional contact. The normal contact is hard contact, as shown in the following formula:

[0043]

[0044] where, F N is the unit contact force; σ is the unit contact compressive stress; A is the normal unit area of the unit compressive stress;

[0045] The tangential contact adopts a penalty friction contact depending on the contact compressive stress, as shown in the following formula:

[0046]

[0047] where, F N is the unit contact force; τ is the shear stress between interfaces; μ is the interface friction coefficient, N uis the compressive stress perpendicular to the element; before the steel pipe and the core concrete come into contact, the initial bonding stress is set to 0, and after the steel pipe and the core concrete come into contact, the interfacial bonding stress is determined according to the contact compressive stress;

[0048] Define the contact relationship between the drop hammer and the model surface as hard contact. When the two surfaces come into contact, the pressure perpendicular to the contact surface can be fully transmitted. When the two surfaces separate, the contact pressure drops to zero;

[0049] Step S34: Adjust the model boundary conditions. To prevent the axial pressure in the dynamic model from disappearing instantaneously during impact, the axial force load is applied using a linear spring. By controlling the spring compression, the load at the end of the specimen is made consistent with the axial force load in the static calculation;

[0050] Step S35: Divide the mesh elements. Both the steel pipe and concrete elements use C3D8R eight-node linear hexahedral elements, and an enhanced hourglass stiffness control method is used to control the hourglass effect generated in the explicit analysis;

[0051] Step S36: Submit the model file to calculate the impact force history calculation result of the concrete-filled steel tube solid model with randomly distributed void defects, and the history animation of the deformation state of the model during the impact load action process.

[0052] Compared with the prior art, the present invention has the following beneficial effects: It provides a method for simulating the impact performance of a concrete-filled steel tube structure with randomly distributed void defects. By establishing a concrete-filled steel tube solid model with randomly distributed void defects, static non-linear history calculation and dynamic non-linear history calculation are carried out on this basis to obtain the impact force history calculation result for comparison with the actual measured impact force history result of the concrete-filled steel tube. This method can effectively improve the calculation accuracy of the concrete-filled steel tube model with void defects, accurately simulate the stress process of the concrete-filled steel tube structure with randomly distributed void defects under the coupled action of axial force and impact load, make the calculation result closer to the real situation, and thus more precisely evaluate the impact resistance of the actual defective structure. Description of the Drawings

[0053] Figure 1 is the overall implementation flowchart of the method for simulating the impact performance of a concrete-filled steel tube structure with randomly distributed void defects in the embodiment of the present invention;

[0054] Figure 2 is the schematic diagram of the history analysis steps of the concrete-filled steel tube structure with randomly distributed void defects in the embodiment of the present invention;

[0055] Figure 3 is the schematic diagram of the concrete-filled steel tube model with randomly distributed void defects in the embodiment of the present invention;

[0056] Figure 4It is the flowchart for modeling the axial randomly distributed concrete-filled steel tube void defects in the embodiments of the present invention;

[0057] Figure 5 It is the flowchart for modeling the radial randomly distributed concrete-filled steel tube void defects in the embodiments of the present invention;

[0058] Figure 6 It is the schematic diagram of the axial randomly distributed concrete-filled steel tube void defects in the embodiments of the present invention;

[0059] Figure 7 It is the schematic diagram of the radial randomly distributed concrete-filled steel tube void defects in the embodiments of the present invention;

[0060] Figure 8 It is the schematic diagram of the static calculation method device and loading in the embodiments of the present invention;

[0061] Figure 9 It is the schematic diagram of the dynamic calculation method device and loading in the embodiments of the present invention;

[0062] Figure 10 It is the visualized stress nephogram in the embodiments of the present invention;

[0063] Figure 11 It is the comparison chart of impact force-time history curves in the embodiments of the present invention.

[0064] In the figure: 1 - envelope line of the inner wall of the steel tube; 2 - axial non-uniform concrete side line; 3 - axial non-uniform concrete node; 4 - radial non-uniform void offset range; 5 - steel tube entity; 6 - radial non-uniform void concrete entity; 7 - radius of the radial non-uniform void concrete entity; 8 - steel tube; 9 - uniform void defect; 10 - concrete; 11 - non-uniform void defect; 12 - rigid body drop hammer; 13 - end plate; 14 - axial force; 15 - spring element; 16 - impact force. Detailed implementation manners

[0065] The following further describes the present invention in conjunction with the accompanying drawings and embodiments.

[0066] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0067] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0068] As Figure 1 , 2 shown, this embodiment provides a method for simulating the impact performance of a concrete-filled steel tubular structure with randomly distributed void defects, including the following steps:

[0069] Step S1: Establish a concrete-filled steel tubular solid model with randomly distributed void defects, including a concrete-filled steel tubular model with axially randomly distributed void defects and a concrete-filled steel tubular model with radially randomly distributed void defects;

[0070] Step S2: Use the static calculation method to perform a static non-linear history calculation on the axial force loading stage of the concrete-filled steel tubular solid model with randomly distributed void defects. The contact between the steel pipe and the concrete is determined by the relative displacement of the unit nodes to obtain the static calculation results;

[0071] Step S3: Use the dynamic calculation method to perform a dynamic non-linear history calculation on the impact load loading stage of the concrete-filled steel tubular solid model with randomly distributed void defects. The contact between the steel pipe and the concrete is determined by the dynamic pressure of the unit nodes to obtain the impact force history calculation results and the history animation of the deformation state of the model during the entire process of the impact load action;

[0072] Step S4: Compare the actual measured impact force history results of the concrete-filled steel tube with the impact force history calculation results obtained by the non-linear history calculation method to evaluate the simulation results.

[0073] In this embodiment, step S1 specifically includes the following steps:

[0074] Step S11: Establish a concrete-filled steel tubular model with axially randomly distributed void defects.

[0075] Step S12: Establish a concrete-filled steel tubular model with radially randomly distributed void defects.

[0076] The established concrete-filled steel tubular models with axially and radially randomly distributed void defects are as Figure 3 shown.

[0077] Step S11 specifically includes:

[0078] Step S111: According to the designed pipe diameter, draw the cross-sectional shape of the steel pipe using a planar sketch, and further stretch the planar sketch to form a steel pipe entity;

[0079] Step S112: Establish a concrete entity by rotating the planar sketch. The axial side line of the concrete sketch is drawn using a polyline, and the abscissa X of each node of the polyline i satisfies a random distribution within the void range, as shown in Equation (1).

[0080] X i ~U[R - d c , R](1)

[0081] where X i ~U is the random distribution function, and X i is the abscissa of each node on the axial side line of the concrete; R is the inner radius of the steel pipe; d c is the maximum void distance of the concrete (d c takes the maximum distance from the concrete surface to the inner wall of the steel pipe).

[0082] The ordinate Y of each node of the polyline i is randomly distributed within the length range of the specimen, as shown in Equation (2).

[0083] Y i ~U[-L / 2, L / 2](2)

[0084] where Y i ~U is the random distribution function, and Y i is the ordinate of each node on the axial side line of the concrete; L is the length of the concrete-filled steel pipe.

[0085] Further, assign coordinates to the multi-segment line and rotate the planar sketch along the center line to form a concrete entity;

[0086] Step S113: Assemble the steel pipe and the concrete entity to form a concrete-filled steel pipe entity model with axially randomly distributed void defects.

[0087] The specific steps of Step S12 are as follows:

[0088] Step S121: According to the designed pipe diameter, draw the cross-sectional shape of the steel pipe using a planar sketch, and further stretch the planar sketch to form a steel pipe entity;

[0089] Step S122: Determine the concrete radius according to the maximum void value, draw the cross-sectional shape of the concrete with uniform void defects using a planar sketch, and further stretch the planar sketch to form a concrete entity;

[0090] Step S123: Assemble the steel pipe and the concrete entity, and use array replication to randomly offset multiple concrete entities. The offset reference point is the centroid of the bottom surface of the steel pipe, and the offset coordinates are within the range shown in Equation (3).

[0091]

[0092] Wherein, X i ~U is a random distribution function, X i is the abscissa of each node on the axial edge of the concrete; Y i is the ordinate of each node on the axial edge of the concrete; X0 is the abscissa of the reference point; Y0 is the ordinate of the reference point; d c is the maximum concrete debonding distance.

[0093] Step S124: Further use Boolean operation to merge all concrete entities, and delete the boundaries of the merged entities to obtain a concrete entity with a randomly distributed cross-sectional radius, as shown in Equation (4).

[0094]

[0095] Wherein, X i is the abscissa of each node on the axial edge of the concrete; Y i is the ordinate of each node on the axial edge of the concrete; R is the inner radius of the steel pipe; d c is the maximum concrete debonding distance.

[0096] In this embodiment, Step S2: Based on the concrete-filled steel tube model with axially randomly distributed debonding defects and the concrete-filled steel tube model with radially randomly distributed debonding defects, with the stress-free state and static boundary conditions as the first initial state, use the static implicit finite element calculation method to perform a non-linear history calculation on the axial force loading process of the concrete-filled steel tube model with randomly distributed debonding defects, and obtain the history calculation results.

[0097] The specific steps of Step S2 are as follows:

[0098] Step S21: Establish an implicit analysis step. Generate a restart result file during the static calculation process, and write the calculated load-displacement relationship into the *Restart file;

[0099] Step S22: Assign static material constitutions, loads, and mesh attributes to the steel pipe and concrete entity models respectively;

[0100] Step S23: Consider the random distribution characteristics of debonding defects in the static contact simulation. The contact simulation in the model is divided into the contact relationship before the contact between the steel pipe and the concrete and the contact relationship after the contact between the steel pipe and the concrete.

[0101] Furthermore, the contact between the steel pipe and the concrete is judged by the distance between the unit nodes. When the distance between the unit nodes of the steel pipe and the core concrete unit is greater than 0, the two are in a non-contact compressive stress state. When the distance between the unit nodes of the steel pipe and the core concrete unit is equal to 0, the normal contact compressive stress can be transmitted between the two.

[0102] Furthermore, the tangential contact adopts penalty friction contact depending on the relative displacement. When the distance between the unit nodes of the steel pipe and the core concrete unit is greater than 0, the two are in an initial separated state without cohesion, and the contact state between the two is automatically judged according to the relative position of the unit nodes during the loading process. Once the distance between the unit nodes of the steel pipe and the core concrete unit is equal to 0, the interfacial bonding stress is determined according to the contact compressive stress. After the steel pipe and the core concrete unit are in contact, the concrete and the steel pipe always remain in contact, and there is cohesion between the two.

[0103] Step S24: Establish the model boundary conditions. One end of the concrete-filled steel tube model is completely fixed, and the other end only releases the translational degree of freedom in the z-axis direction.

[0104] Step S25: Submit the model file, calculate the static calculation results, and store the calculation results as a restart result file.

[0105] In this embodiment, in step S3: taking the axial force holding state as the second initial state, replacing the static implicit finite element calculation method with the dynamic explicit finite element calculation method, performing a non-linear history calculation on the axial force loading process of the concrete-filled steel tube model with randomly distributed void defects, and obtaining the impact force history calculation results.

[0106] The specific steps of step S3 include: Step S31: Establish a display analysis step, import the restart file calculated by the static model, and assign the initial state of axial force loading to the dynamic model.

[0107] Step S32: Use an analytical rigid body to establish a drop hammer entity and replace the model attributes based on the dynamic calculation method.

[0108] In the dynamic contact simulation, replace the static contact relationship between the concrete surface and the steel pipe surface with a display contact relationship based on the dynamic algorithm. Use the instantaneous dynamic pressure stress value to judge the contact relationship between the steel pipe unit and the concrete unit. The normal contact adopts hard contact, and the tangential contact adopts penalty friction contact depending on the instantaneous dynamic pressure stress value. If the value is equal to zero, there is no contact; if it is greater than zero, penalty friction contact occurs. Define the contact relationship between the drop hammer and the model surface as hard contact. When the two surfaces are in contact, the pressure perpendicular to the contact surface can be completely transmitted. When the two surfaces are separated, the contact pressure drops to zero.

[0109] Step S34: Establish the model boundary conditions. To prevent the axial pressure from disappearing instantaneously during impact, two-point spring elements are established at one end of the concrete-filled steel tube model where the z-axis degree of freedom is released, and the end load of the specimen is made consistent with the axial force load in the static calculation by controlling the spring compression amount.

[0110] Step S35: Divide the mesh elements. Both the steel tube and concrete elements adopt C3D8R eight-node linear hexahedron elements, and the enhanced hourglass stiffness control method is used.

[0111] Step S36: Submit the model file to calculate the impact force history calculation results of the concrete-filled steel tube solid model with randomly distributed void defects.

[0112] In this embodiment, in step S4, the actual measured impact history curve of the concrete-filled steel tube is compared with the history result obtained according to the non-linear history calculation method, and an animation of the model deformation state during the impact load action process is generated.

[0113] In an embodiment of the present invention, first, the model construction module is used to materialize the concrete-filled steel tube model, which specifically includes: constructing the model, storing the model parameters and discriminating the ranges of each parameter, and outputting the model parameters.

[0114] The model construction process is as Figure 4 、 5 shown.

[0115] In this embodiment, step S1 of using the model construction module to establish a concrete-filled steel tube solid model with randomly distributed void defects specifically includes:

[0116] Step S11: Establish a concrete-filled steel tube model with axially randomly distributed void defects; step S12: Establish a concrete-filled steel tube model with radially randomly distributed void defects.

[0117] In an embodiment of the present invention, step S11 specifically includes:

[0118] Step S111: According to the designed pipe diameter, with the origin of the sketch as the center, use the planar sketch to draw the cross-sectional shape of the steel tube, and use the method of stretching the planar sketch of the steel tube to form a steel tube solid model.

[0119] Step S112: According to the designed concrete size, with the origin of the sketch as the center, use the polyline to draw the longitudinal cross-sectional planar sketch of the concrete. And use the method of rotating the planar sketch of the concrete cross-section to form a concrete solid model, where the distribution of each node (X i , Y i ) on the axial side line of the concrete sketch is as shown in formula (5):

[0120]

[0121] Among them, X i is the abscissa of each node on the axial side line of the concrete; R is the inner radius of the steel pipe; d c is the maximum concrete debonding distance (d c takes the maximum distance from the concrete surface to the inner wall of the steel pipe); Y i is the ordinate of each node on the axial side line of the concrete; L is the length of the concrete-filled steel tube.

[0122] Step S113: Assemble the concrete and steel pipe solid models to form a concrete-filled steel tube model with axially randomly distributed debonding defects, as Figure 6 shown.

[0123] In an embodiment of the present invention, the step S12 specifically includes:

[0124] Step S121: According to the designed pipe diameter, with the origin of the sketch as the center, draw the cross-sectional shape of the steel pipe using a planar sketch, and stretch the steel pipe planar sketch using the method of stretching the planar sketch to form a steel pipe solid model;

[0125] Step S122: With the origin of the sketch as the center, draw the cross-sectional shape of the concrete using a planar sketch, and stretch the concrete planar sketch using the method of stretching the planar sketch to form a concrete solid model, where the concrete radius R n is obtained as shown in Equation 6:

[0126] R n = R - d c (6)

[0127] Among them, R n is the concrete solid radius of the concrete-filled steel tube model with radially randomly distributed debonding defects; R is the inner radius of the steel pipe; d c is the maximum debonding distance (d c takes the maximum distance from the concrete surface to the inner wall of the steel pipe).

[0128] Step S123: Assemble the steel pipe solid model and the concrete solid model, and copy multiple concrete solid models. Further, with the center of the bottom surface of the model (X0, Y0) as the reference point, translate the copied concrete solids so that the distribution of the reference point (X i , Y i ) after translation is according to Equation (7) shown

[0129]

[0130] Among them, X0 is the abscissa of the translation reference point; Y0 is the abscissa of the translation reference point; X i is the abscissa of the reference point after translation; Y iis the abscissa of the reference point after translation;

[0131] Step S124: Use Boolean operations to intersect and merge all concrete entities to form a concrete-filled steel tube model with radially randomly distributed void defects, as Figure 7 shown.

[0132] In this embodiment, a calculation module is used to calculate the parametric model and output the results of the structural dynamic response.

[0133] The specific calculation process includes: Step S2: Based on the model construction module, a combination of static calculation methods and dynamic calculation methods is used to calculate and analyze the embodiments of the present invention, including: Step S21: Static nonlinear history calculation; Step S22: Dynamic nonlinear history calculation.

[0134] In this embodiment, the state without initial stress and the static boundary conditions are used as the first initial state, and the nonlinear history calculation is carried out for the axial force loading stage of the concrete-filled steel tube solid model with randomly distributed void defects by using the static model method, as Figure 8 shown. Step S2 specifically includes:

[0135] Step S21: Establish an implicit analysis step. During the static calculation process, a restart result file is generated, and the final state of the calculated model and the load-displacement relationship are written into the *Restart result file;

[0136] Step S22: Assign static material properties, axial force loads, and C3D8R mesh elements to the steel tube and concrete solid models respectively;

[0137] In Step S23, the static contact relationship adopts the contact relationship between the concrete surface and the steel tube surface that depends on the relative distance of the unit nodes, including normal contact and tangential contact. The normal contact is a hard contact. According to Equation (8), when the steel tube and the core concrete are not in contact, the contact compressive stress is 0, and when they are in contact, the normal contact compressive stress can be transmitted.

[0138]

[0139] Among them, S is the relative distance of the unit nodes; F N is the unit contact force; σ is the unit contact compressive stress; A is the normal unit area of the unit compressive stress.

[0140] The tangential contact adopts the penalty friction contact that depends on the contact compressive stress. According to Equation (9), when the unit nodes of the steel tube and the core concrete are greater than zero, the initial bonding stress is set to 0, and when the unit nodes of the steel tube and the core concrete are equal to zero, the interface bonding stress is determined according to the contact compressive stress.

[0141]

[0142] Among them, S is the relative distance of unit nodes; F N is the unit contact force; τ is the shear stress between interfaces; μ is the interface friction coefficient, and N u is the compressive stress perpendicular to the unit.

[0143] Step S24: Establish the model boundary conditions and loads. One end of the concrete-filled steel tube model is completely fixed, and the other end only has translational freedom in the z-axis direction.

[0144] Step S25: Submit the model file and calculate the static calculation results. Further, store the calculation results as a restart result file.

[0145] In this embodiment, taking the axial force holding state as the second initial state, the non-linear history calculation of the impact force action stage of the concrete-filled steel tube solid model with randomly distributed void defects is carried out by using the dynamic calculation method, as Figure 9 shown. Step S3 specifically includes:

[0146] Step S31: The dynamic contact relationship adopts to establish a dynamic explicit analysis step, import the restart file calculated from the static model, and assign the initial state of axial force loading to the dynamic model;

[0147] Step S32: Use the dynamic calculation method, establish a drop hammer entity by using an analytical rigid body, and assign dynamic attributes to the entity model. Replace the static material constitutions of the steel tube and the concrete solid model with the dynamic material constitutions considering the strain rate effect, including the dynamic material constitutions of steel and concrete.

[0148] Step S33: Replace the static contact relationship between the concrete surface and the steel tube surface with a dynamic contact relationship, where the contact judgment depends on the dynamic compressive stress between unit nodes, including normal hard contact and tangential frictional contact. The normal contact is hard contact as shown in Equation (10).

[0149]

[0150] Among them, F N is the unit contact force; σ is the unit contact compressive stress; A is the normal unit area of the unit compressive stress.

[0151] The tangential contact adopts penalty friction contact depending on the contact compressive stress. Before the steel tube and the core concrete come into contact, the initial bonding stress is set to 0. After the steel tube and the core concrete come into contact, the interface bonding stress is determined according to the contact compressive stress, as shown in Equation (11).

[0152]

[0153] Among them, F N is the unit contact force; τ is the shear stress between interfaces; μ is the interface friction coefficient, and N u is the compressive stress perpendicular to the unit.

[0154] Furthermore, the contact relationship between the drop hammer and the model surface is defined as hard contact. When the two surfaces come into contact, the pressure perpendicular to the contact surface can be fully transmitted. When the two surfaces separate, the contact pressure drops to zero;

[0155] Step S34: Adjust the model boundary conditions. To prevent the axial pressure in the dynamic model from disappearing instantaneously during impact, the axial force load is applied using a linear spring. By controlling the spring compression, the load at the end of the specimen is made consistent with the axial force load in the static calculation.

[0156] Step S35: Divide the mesh elements. Both the steel pipe and concrete elements use C3D8R eight-node linear hexahedral elements, and the enhanced hourglass stiffness control method is used to control the hourglass effect generated in the explicit analysis.

[0157] Step S36: Submit the model file to calculate the impact force history calculation results of the concrete-filled steel tube solid model with randomly distributed void defects, and the history animation of the deformation state of the model during the impact load action process.

[0158] In this embodiment, the display module is used to perform visual conversion on the calculation results and output the visual results of the structural dynamic response.

[0159] The visual conversion results are as Figure 10 shown. Step S4 specifically includes: comparing the measured impact resistance performance of the concrete-filled steel tube with the results obtained according to the non-linear history calculation method.

[0160] In the display module, the calculation results of the structural response of the concrete-filled steel tube structure with randomly distributed void defects under impact loads are visually displayed through a display, Figure 11 which presents a comparison of the impact test results of the concrete-filled steel tube specimens with void defects, the finite element calculation results of the concrete-filled steel tube with randomly distributed void defects, and the finite element calculation results of the concrete-filled steel tube with uniform void defects. It can be seen that the finite element calculation results fit well with the test results. All the finite element calculation results of the concrete-filled steel tube with randomly distributed void defects are consistent with the test results in trend and can be divided into an impact force oscillation section, a plateau section, and a descending section. Among them, the peak and plateau values of the impact force calculated by the concrete-filled steel tube model with randomly distributed void defects are closer to the test values, while there is a certain error between the calculation results of the uniform void model and the test values. This shows that using the randomly distributed void defect modeling method can more effectively simulate the void defects in the actual structure, and the calculation results are more accurate than the uniform void defect modeling method.

[0161] In summary, the present invention provides a dynamic finite element modeling method for concrete-filled steel tubular structures with randomly distributed void defects. The calculation results show that this method is more in line with the actual void defect distribution, effectively improving the accuracy, generality and reliability of finite element software, providing a basic method for studying the impact resistance of other structures with void defects, and expanding the application scope.

[0162] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in other forms. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A simulation method for the impact performance of a concrete-filled steel tubular structure with randomly distributed void defects, characterized in that, It includes the following steps: Step S1: Establish a concrete-filled steel tube solid model with randomly distributed void defects, including a concrete-filled steel tube model with axially randomly distributed void defects and a concrete-filled steel tube model with radially randomly distributed void defects; Step S2: Use the static calculation method to perform a static non-linear history calculation on the axial force loading stage of the concrete-filled steel tube solid model with randomly distributed void defects. The contact between the steel tube and the concrete is determined by the relative displacement of the unit nodes to obtain the static calculation results; Step S3: Use the dynamic calculation method to perform a dynamic non-linear history calculation on the impact load loading stage of the concrete-filled steel tube solid model with randomly distributed void defects. The contact between the steel tube and the concrete is determined by the dynamic pressure of the unit nodes to obtain the calculation results of the impact force history and the history animation of the deformation state of the model during the entire process of the impact load action; Step S4: Compare the measured impact force history results of the concrete-filled steel tube with the calculated impact force history results obtained by the non-linear history calculation method to evaluate the simulation results; In step S2, when performing the static non-linear history calculation, use the static material constitutive and static calculation methods to calculate the process of applying axial pressure to the concrete-filled steel tube specimen, and store the calculation results as a restart result file; In step S3, when performing the dynamic non-linear history calculation, use the dynamic material constitutive and dynamic calculation methods to calculate the process of the concrete-filled steel tube specimen under impact, then introduce the restart result file, assign the initial axial compression state to the model, and at the same time use spring elements to apply axial force to ensure that the axial force still exists during the impact load action.

2. The impact performance simulation method of a concrete-filled steel tube structure with randomly distributed void defects according to claim 1, wherein, The concrete-filled steel tube model with axially randomly distributed void defects is constructed by the random sketch edge method, and the concrete-filled steel tube model with radially randomly distributed void defects is constructed by the random offset concrete solid method.

3. The impact performance simulation method of a concrete-filled steel tubular structure with randomly distributed void defects according to claim 2, characterized in that, In step S1, the specific method for establishing a concrete-filled steel tube model with axially randomly distributed void defects is as follows: Step S111: According to the designed pipe diameter, draw the cross-sectional shape of the steel tube with the sketch origin as the center using a planar sketch; and use the method of stretching the planar sketch to stretch the steel tube planar sketch to form a steel tube solid model; Step S112: According to the designed concrete dimensions, draw a plane sketch of the concrete longitudinal section with the origin of the sketch as the center using a polyline; and rotate the plane sketch of the concrete section to form a concrete solid model by rotating the plane sketch of the concrete section, where the nodes (X i , Y i ) on the axial side line of the concrete sketch are distributed as shown in the following formula: Among them, X i is the abscissa of each node on the axial edge of the concrete; R is the inner radius of the steel pipe; d c is the maximum concrete debonding distance, taking the maximum distance from the concrete surface to the inner wall of the steel pipe; Y i is the ordinate of each node on the axial edge of the concrete; L is the length of the concrete-filled steel pipe; Step S113: Assemble the concrete solid model and the steel tube solid model to form a concrete-filled steel tube model with axially randomly distributed void defects.

4. The impact performance simulation method of a concrete-filled steel tubular structure with randomly distributed void defects according to claim 2, wherein, In step S1, the specific method for establishing a concrete-filled steel tube model with radially randomly distributed void defects is as follows: Step S121: According to the designed pipe diameter, draw the cross-sectional shape of the steel tube with the sketch origin as the center using a planar sketch, and use the method of stretching the planar sketch to stretch the steel tube planar sketch to form a steel tube solid model; Step S122: According to the designed concrete dimensions, with the origin of the sketch as the center, draw the concrete cross-sectional shape using a planar sketch, and use the method of stretching the planar sketch to stretch the concrete planar sketch to form a concrete solid model, where the concrete radius R n takes the value as shown in the following formula: R n = R - d c Among them, R n is the radius of the concrete entity of the concrete-filled steel tube model with randomly distributed radial void defects; R is the inner radius of the steel tube; d c is the maximum void distance of the concrete, which is taken as the maximum distance from the concrete surface to the inner wall of the steel tube; Step S123: Assemble the steel pipe solid model and the concrete solid model, and copy multiple concrete solid models. Then, taking the center of the bottom surface of the model (X0, Y0) as the reference point, translate the copied concrete solids so that the distribution of the reference points (X i , Y i ) is as shown in the following formula: Among them, X0 is the abscissa of the translation reference point; Y0 is the abscissa of the translation reference point; X i is the abscissa of the reference point after translation; Y i is the abscissa of the reference point after translation; Step S124: Use Boolean operations to intersect and merge all the concrete solid models to form a concrete-filled steel tube model with radially randomly distributed void defects.

5. The impact performance simulation method of a concrete-filled steel tubular structure with randomly distributed void defects according to claim 1, characterized in that, In step S2, with the state of no initial stress and static boundary conditions as the first initial state, use the static calculation method to perform a static non-linear history calculation on the axial force loading stage of the concrete-filled steel tube solid model with randomly distributed void defects, which specifically includes the following steps: Step S21: Establish an implicit analysis step; generate a restart result file during the static calculation process, and write the final state of the model after calculation and the load-displacement relationship into the restart result file; Step S22: Assign static material properties, axial force loads, and C3D8R mesh elements to the steel pipe and concrete solid models respectively; Step S23: The static contact relationship adopts the contact relationship between the concrete surface and the steel pipe surface that depends on the relative distance of the unit nodes, including normal contact and tangential contact. The normal contact is a hard contact, as shown in the following formula: where S is the relative distance between unit nodes; F N is the unit contact force; σ is the unit contact compressive stress; A is the normal unit area of the unit compressive stress; according to the above formula, the contact compressive stress is 0 when the steel pipe and the core concrete are not in contact, and the normal contact compressive stress can be transmitted after they are in contact; The tangential contact adopts a penalty friction contact that depends on the contact compressive stress, as shown in the following formula: Where S is the relative distance of unit nodes; τ is the shear stress between interfaces; μ is the interface friction coefficient, and N u is the compressive stress perpendicular to the unit. According to the above formula, when the unit nodes of the steel pipe and the core concrete are greater than zero, the initial bond stress is set to 0. When the unit nodes of the steel pipe and the core concrete are equal to zero, the interface bond stress is determined according to the contact compressive stress; Step S24: Establish the model boundary conditions and loads. One end of the concrete-filled steel tube solid model is completely fixed, and the other end only has the translational degree of freedom in the z-axis direction; Step S25: Submit the model file, calculate the static calculation results, and then store the calculation results as a restart result file.

6. The impact performance simulation method of a concrete-filled steel tubular structure with randomly distributed void defects according to claim 1, characterized in that In step S3, taking the axial force holding state as the second initial state, use the dynamic calculation method to perform the dynamic nonlinear time history calculation on the impact load stage of the concrete-filled steel tube solid model with randomly distributed void defects, specifically including the following steps: Step S31: The dynamic contact relationship adopts establishing a dynamic explicit analysis step, importing the restart result file obtained from the static calculation, and assigning the initial state of axial force loading to the dynamic model; Step S32: Use the dynamic calculation method, establish a drop hammer entity using an analytical rigid body, and assign dynamic attributes to the entity model; replace the static material constitutive relations of the steel pipe and concrete solid models with the dynamic material constitutive relations considering the strain rate effect, including the dynamic material constitutive relations of steel and concrete; Step S33: Replace the static contact relationship between the concrete surface and the steel pipe surface with a dynamic contact relationship, where the contact determination depends on the dynamic compressive stress between the unit nodes, including normal contact and tangential friction contact. The normal contact is a hard contact, as shown in the following formula: Among them, F N is the unit contact force; σ is the unit contact compressive stress; A is the normal unit area of the unit compressive stress; The tangential contact adopts a penalty friction contact that depends on the contact compressive stress, as shown in the following formula: Among them, F N is the unit contact force; τ is the shear stress between interfaces; μ is the interface friction coefficient, and N u is the compressive stress perpendicular to the element. Before the steel pipe and the core concrete come into contact, the initial bonding stress is set to 0. After the steel pipe and the core concrete come into contact, the interface bonding stress is determined according to the contact compressive stress; Define the contact relationship between the drop hammer and the model surface as a hard contact. When the two surfaces come into contact, the pressure perpendicular to the contact surface can be fully transmitted. When the two surfaces separate, the contact pressure drops to zero; Step S34: Adjust the model boundary conditions. To prevent the axial pressure in the dynamic model from disappearing instantaneously during impact, the axial force load is changed to be loaded by a linear spring, and the load at the end of the specimen is made consistent with the axial force load in the static calculation by controlling the spring compression amount; Step S35: Divide the mesh elements. Both the steel pipe and concrete elements adopt C3D8R eight-node linear hexahedron elements, and use the enhanced hourglass stiffness control method to control the hourglass effect generated in the explicit analysis; Step S36: Submit the model file, calculate the impact force history calculation results of the concrete-filled steel tube solid model with randomly distributed void defects, and the history animation of the model deformation state during the impact load action process.

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