Evaluation method for stability of inner steel pipe of round hollow interlayer steel pipe concrete member

Abstract

The invention provides a method for evaluating the stability of an inner steel pipe of a round hollow interlayer steel pipe concrete member, and relates to the technical field of constructional engineering. An inner steel pipe buckling model of the concrete member is established through mechanical analysis of the concrete member; sandwich concrete can be regarded as an elastic foundation, an inner steel pipe is a thin-wall structure on the foundation for mechanical analysis, and compression resistance and tensile elastic foundation bed coefficients of the interlayer concrete regarded as the elastic foundation are deduced and simplified; introducing a bending wavelength calculation formula of the werkel elastic foundation long beam to calculate the bending wavelength of the inner steel pipe; and based on the thin-shell theory, a critical stress expression of the inner steel pipe is solved by utilizing an energy method. Therefore, the critical stress value of local buckling instability of the inner steel pipe in the circular hollow interlayer steel pipe concrete member can be determined, the stability of the inner steel pipe is evaluated, local instability of the inner steel pipe is prevented, the good mechanical property of the whole member is guaranteed, and design guidance is provided for engineering practice.

Description

Technical Field

[0001] This application relates to the technical field of construction engineering, and particularly to an evaluation method for the stability of the inner steel pipe of a circular hollow sandwich steel tube concrete member. Background Art

[0002] The circular hollow sandwich steel tube concrete member is a new type of member innovated and improved from the traditional solid steel tube concrete member, and is a new type of composite structure formed by pouring concrete between two concentric circular steel tubes. At present, circular hollow sandwich steel tube concrete members have been widely used in construction in China. The thin-walled steel tube in the steel tube concrete is not prone to buckling due to the presence of concrete, and the thin-walled steel tube also helps the brittle concrete increase its plasticity, so that the steel tube concrete structure has better characteristics than the traditional concrete structure.

[0003] However, there are still many defects in the mechanical properties of this kind of member that need to be solved and improved. For example, the local instability problem of the inner steel pipe of the circular hollow sandwich steel tube concrete member. Usually, the inner surface of the concrete layer of the circular sandwich steel tube concrete column member inevitably has initial defects, so that under axial compression, the inner steel pipe is prone to local instability deformation, which in turn affects the overall mechanical properties of the member. However, the current research on the local instability of the inner steel pipe of the circular hollow sandwich steel tube concrete member is still blank, resulting in potential safety hazards due to the easy occurrence of local instability deformation of the inner steel pipe in engineering practice. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide an evaluation method for the stability of the inner steel pipe of a circular hollow sandwich steel tube concrete member. By constructing a buckling model of the inner steel pipe, deriving the compressive elastic bedding coefficient and the tensile elastic bedding coefficient through mechanical analysis, introducing the bending wavelength calculation formula of the Winkler elastic foundation long beam to calculate the buckling wavelength of the inner steel pipe, and then using the energy method to solve the critical stress expression of the inner steel pipe. In this way, the critical stress value of local buckling instability of the inner steel pipe in the circular hollow sandwich steel tube concrete member can be determined, and then the stability of the inner steel pipe can be evaluated, the local instability of the inner steel pipe can be prevented, the good mechanical properties of the overall member can be ensured, and design guidance can be provided for engineering practice.

[0005] The embodiment of this application provides an evaluation method for the stability of the inner steel pipe of a circular hollow sandwich steel tube concrete member, and the evaluation method includes: Through mechanical analysis of the interaction between the inner steel pipe and the sandwich concrete in the concrete member, constructing deformation coordination relations, steel pipe circumferential stress expressions, sandwich concrete radial stress expressions, and inner steel pipe force balance equations in each direction between the inner steel pipe and the sandwich concrete; Axial buckling wavelength and circumferential buckling wavelength are respectively taken along the axial direction and the circumferential direction on the surface of the inner steel pipe to form a wave band surface, and a buckling model of the inner steel pipe in the concrete member is constructed on the wave band surface; wherein, the buckling model is used to characterize the functional relationship between the buckling displacement on the surface of the inner steel pipe and the parameters of the sandwich concrete; During the deformation process of the inner steel pipe, according to the deformation coordination relation formula, the circumferential stress expression of the steel pipe, the radial stress expression of the sandwich concrete, and the force balance equation of the inner steel pipe, the compressive elastic bedding coefficient of the inner steel pipe is determined; and the tensile elastic bedding coefficient of the inner steel pipe is determined according to the circumferential stress expression of the steel pipe; wherein, the deformation process includes a first deformation stage in which the inner steel pipe changes from a stress-free zero state to a first state of coordinated deformation with the sandwich concrete, and a second deformation stage from the first state to a second state of local buckling instability deformation; Combining the bending wavelength calculation formula of the Winkler elastic foundation and the compressive elastic bedding coefficient, the axial buckling wavelength and the circumferential buckling wavelength of the inner steel pipe are determined; On the wave band surface, according to the compressive elastic bedding coefficient, the tensile elastic bedding coefficient, the axial buckling wavelength, the circumferential buckling wavelength and the buckling model of the inner steel pipe, the total potential energy equation at the time of local buckling instability of the inner steel pipe is determined; According to the total potential energy equation at the time of local buckling instability of the inner steel pipe, the critical stress expression of the inner steel pipe is determined, and the mechanical parameter values of the concrete member are substituted into the critical stress expression to obtain the critical stress value of local buckling instability of the inner steel pipe in the concrete member; Compare the critical stress value with the engineering design index value to determine the stability of the inner steel pipe of the concrete member.

[0006] The embodiment of the present application also provides an evaluation device for the stability of the inner steel pipe of a circular hollow sandwich steel pipe concrete member, and the evaluation device includes: An analysis module, configured to construct deformation coordination relation formulas, circumferential stress expressions of the steel pipe, radial stress expressions of the sandwich concrete, and force balance equations of the inner steel pipe in each direction by performing mechanical analysis on the interaction between the inner steel pipe and the sandwich concrete in the concrete member; A construction module, configured to respectively take an axial buckling wavelength and a circumferential buckling wavelength along the axial direction and the circumferential direction on the surface of the inner steel pipe to form a wave band surface, and construct a buckling model of the inner steel pipe in the concrete member on the wave band surface; wherein, the buckling model is used to characterize the functional relationship between the buckling displacement on the surface of the inner steel pipe and the parameters of the sandwich concrete; The first determination module is used to determine the compressive elastic bedding coefficient of the inner steel pipe during the deformation process of the inner steel pipe according to the deformation coordination relation formula, the circumferential stress expression of the steel pipe, the radial stress expression of the sandwich concrete, and the force balance equation of the inner steel pipe; and determine the tensile elastic bedding coefficient of the inner steel pipe according to the circumferential stress expression of the steel pipe; wherein, the deformation process includes a first deformation stage in which the inner steel pipe changes from a stress-free zero state to a first state of coordinated deformation with the sandwich concrete, and a second deformation stage from the first state to a second state of local buckling instability deformation; The second determination module is used to determine the axial buckling wavelength and the circumferential buckling wavelength of the inner steel pipe by combining the bending wavelength calculation formula of the Winkler elastic foundation and the compressive elastic bedding coefficient; The third determination module is used to determine the total potential energy equation when the inner steel pipe undergoes local buckling instability on the wave band surface according to the compressive elastic bedding coefficient, the tensile elastic bedding coefficient, the axial buckling wavelength, the circumferential buckling wavelength, and the buckling model of the inner steel pipe; The calculation module is used to determine the critical stress expression of the inner steel pipe according to the total potential energy equation when the inner steel pipe undergoes local buckling instability, and substitute the mechanical parameter values of the concrete component into the critical stress expression to obtain the critical stress value of the inner steel pipe in the concrete component when local buckling instability occurs; The comparison module is used to compare the critical stress value with the engineering design index value to determine the stability of the inner steel pipe of the concrete component.

[0007] An embodiment of the present application also provides an electronic device, including: a processor, a memory, and a bus. The memory stores machine-readable instructions executable by the processor. When the electronic device runs, the processor communicates with the memory through the bus. When the machine-readable instructions are executed by the processor, the steps of the evaluation method as described above are executed.

[0008] An embodiment of the present application also provides a computer-readable storage medium. A computer program is stored on the computer-readable storage medium. When the computer program is run by a processor, the steps of the evaluation method as described above are executed.

[0009] To make the above objects, features, and advantages of the present application more obvious and understandable, the following specifically enumerates preferred embodiments and, in conjunction with the accompanying drawings, makes the following detailed description. Description of the Drawings

[0010] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0011] Figure 1 Shows the overall structural schematic diagram of a circular hollow sandwich steel tube concrete member provided by an embodiment of the present application; Figure 2 Shows the flowchart of an evaluation method for the stability of the inner steel tube of a circular hollow sandwich steel tube concrete member provided by an embodiment of the present application; Figure 3 Shows the schematic diagram of the cross-sectional deformation of a concrete unit provided by an embodiment of the present application; Figure 4 Shows the schematic diagram of the force on the inner steel tube provided by an embodiment of the present application; Figure 5(a) shows the schematic diagram of the dimensions of an inner steel tube provided by an embodiment of the present application; Figure 5(b) shows the schematic diagram of the compression curved section of an inner steel tube provided by an embodiment of the present application; Figure 6 Shows the coordinate schematic diagram of a local wave section of the inner steel tube provided by an embodiment of the present application; Figure 7(a) shows the diagram of the cross-sectional deformation state of an inner steel tube provided by an embodiment of the present application; Figure 7(b) shows the schematic diagram of the circumferential local buckling deformation of an inner steel tube provided by an embodiment of the present application; Figure 8 Shows the structural schematic diagram of an evaluation device for the stability of the inner steel tube of a circular hollow sandwich steel tube concrete member provided by an embodiment of the present application; Figure 9 Shows the structural schematic diagram of an electronic device provided by an embodiment of the present application. Detailed implementation manners

[0012] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Usually, the components of the embodiments of the present application described and shown in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application to be protected, but only represents the selected embodiments of the present application. Based on the embodiments of the present application, every other embodiment obtained by those skilled in the art without creative efforts belongs to the scope of protection of the present application.

[0013] It has been found through research that there are still many defects in the mechanical properties of circular concrete-filled double-skin steel tubular members that need to be solved and improved. For example, the local instability problem of the inner steel tube of circular concrete-filled double-skin steel tubular members. Usually, the inner surface of the concrete layer of circular concrete-filled double-skin steel tubular columns inevitably has initial defects, which makes the inner steel tube prone to local instability deformation under axial compression, thus affecting the overall mechanical properties of the members. However, the current research on the local instability of the inner steel tube of circular concrete-filled double-skin steel tubular members is still blank, resulting in potential safety hazards due to the easy occurrence of local instability deformation of the inner steel tube in engineering practice.

[0014] For the convenience of description, first, the mechanical background knowledge of circular concrete-filled double-skin steel tubular members in the embodiments of the present application will be introduced. A circular concrete-filled double-skin steel tubular member is a new type of composite structure formed by pouring concrete between two concentric circular steel tubes (inner steel tube and outer steel tube). Please refer to Figure 1 , Figure 1 which is the overall structural schematic diagram of a circular concrete-filled double-skin steel tubular member provided by the embodiment of the present application. As shown in Figure 1 , the thicknesses of the inner and outer steel tubes of the circular concrete-filled double-skin steel tubular short column are the same, denoted as , the outer steel tube radius is , the inner steel tube radius is , and the vertical length is . In the embodiments of the present application, the inner and outer layer radii of the sandwich concrete correspond to the radius values of the inner and outer steel tubes respectively.

[0015] I. Alphabet symbol table used in the embodiments of the present application: is the wall thickness of the inner steel tube; is the radius of the inner steel tube; is the length of the steel tube; is the flexural rigidity of the inner steel tube; is the axial compressive stress on the bending section of the inner steel tube; is the circumferential stress of the steel tube; is the radial compressive stress generated by the sandwich concrete; is the circumferential buckling wavelength of the steel tube, and the curved section can be regarded as a thin shell; is the axial buckling wavelength of the inner steel tube; B is the buckling displacement coefficient; is the axial contact length between the inner steel tube and the concrete; is its non-contact length; is the circumferential instability contact length; is the circumferential non-contact length; is the defect rate of the sandwich concrete; is the buckling displacement function; is the function at The value at, i.e., the buckling displacement at the concave-convex demarcation point on the inner steel pipe surface; Is the radial deformation corresponding to the circumferential stress magnitude of the inner steel pipe; Is the lateral compression displacement jointly caused by the coordinated deformation of the sandwich concrete and the inner steel pipe; Is the radial stress increment of the sandwich concrete; Is the circumferential strain increment of the inner steel pipe under compression; Is the circumferential stress increment of the inner steel pipe under compression; Is the radial stress increment of the inner steel pipe under compression; Is the non-simplified compressive elastic bedding coefficient of the inner steel pipe; Is the simplified compressive elastic bedding coefficient of the inner steel pipe; Is the circumferential stress increment of the inner steel pipe under tension; Is the circumferential strain increment of the inner steel pipe under tension; Is the radial stress increment of the inner steel pipe under tension; Is the tensile elastic bedding coefficient with concrete as the elastic foundation; Is the volume when the inner steel pipe just detaches from the sandwich concrete and bulges inward, and the volume of the sunken part is ; Is the axial strain increment of the sandwich concrete; Is the radial strain increment of the sandwich concrete; Is the axial stress increment of the sandwich concrete; Is the radial stress increment of the sandwich concrete; Is the elastic modulus of the sandwich concrete; Is the Poisson's ratio of the sandwich concrete; Is the circumferential strain of the steel pipe; Is the axial strain of the steel pipe; Is the circumferential stress of the steel pipe; Is the axial stress of the steel pipe; Is the elastic modulus of the steel pipe; Is the Poisson's ratio of the steel pipe; Is the compressive bedding coefficient in the Winkler elastic foundation cylindrical shell model; Is the elastic modulus of the shell; Is the flexural rigidity of the shell; Is the radius of the cylindrical shell; Is the external work; Is the total potential energy.

[0016] II. The constitutive calculation model of the sandwich concrete used in the embodiments of the present application.

[0017] In concrete-filled double-skin steel tubular columns, the outer steel tube and the inner steel tube enclose the sandwich concrete. When the axial compression starts and reaches a certain stage, the three components begin to act together, causing changes in the working performance of the sandwich concrete. In the embodiments of this application, the constitutive model of the sandwich concrete adopts the fiber model of circular concrete-filled double-skin steel tubular members in the latest specification "T / CCES7—2020". The relationship between the monotonic compressive stress ( ) and strain ( ) of the sandwich concrete is calculated according to the following formula: (1) Wherein, and are the longitudinal stress and longitudinal strain of the concrete inside the steel tube respectively; The parameters , , , , , are taken as follows:

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024] In the formula: is the nominal steel ratio; is the nominal confinement effect coefficient; is the axial compressive strength of the concrete cylinder.

[0025] When the lateral deformation coefficient of the concrete gradually becomes larger than that of the inner and outer steel tubes, the inner and outer steel tubes and the sandwich concrete begin to deform together and follow the deformation coordination law. The interaction force between the steel tubes and the sandwich concrete changes with the vertical external load in the lateral direction. The sandwich concrete becomes a state of triaxial compressive stress and is no longer in a completely elastic state. The confinement effect of the steel tubes causes plastic deformation of the sandwich concrete. Therefore, the stress strain relationship of the sandwich concrete in the embodiments of this application can adopt the incremental equation: (2) In the formula, is the increment of the axial strain of the sandwich concrete; is the incremental radial strain of the sandwich concrete; is the incremental axial stress of the sandwich concrete; is the incremental radial stress of the sandwich concrete; is the elastic modulus of the sandwich concrete; is the Poisson's ratio of the sandwich concrete, and this value refers to the equivalent formula proposed by Han Linhai, that is = , (3).

[0026] III. The constitutive calculation model of the thin-walled steel pipe used in the embodiments of the present application.

[0027] For the low-carbon mild steel commonly used in actual construction projects, the elastic and plastic performance is very obvious. The steel pipe used in the embodiments of the present application is an isotropic material. Therefore, the stress-strain relationship constitutive model of the steel pipe proposed by Han Linhai is adopted, and the mathematical expression of this constitutive model is shown in Equation (4): (4) In the formula, , , , , , , .

[0028] The inner and outer steel pipe walls are relatively thin and can be regarded as cylindrical shells. The axial stress and circumferential stress are much larger than the radial stress. Therefore, the steel pipe is in a two-dimensional stress state, and the two dimensions are the axial direction and the circumferential direction. Regarding the stress state of the steel pipe as a plane stress state, according to Hooke's law, the stress-strain relationship of the thin-walled steel pipe is as follows: (5) In the formula, is the circumferential strain of the steel pipe; is the axial strain of the steel pipe; is the circumferential stress of the steel pipe; is the axial stress of the steel pipe; is the elastic modulus of the steel pipe, which can be obtained by referring to the literature; is the Poisson's ratio of the steel pipe. Generally, in actual situations, the steel pipe follows the Von Mises yield condition. Therefore, in the elastic stage of the steel, its Poisson's ratio changes very little and can be considered a constant. Generally takes 0.283.

[0029] Next, the implementation process of the technical solution of the present application will be specifically introduced.

[0030] Please refer to Figure 2 , Figure 2The flowchart of a method for evaluating the stability of the inner steel pipe of a circular hollow sandwich concrete-filled steel tubular member provided by an embodiment of the present application. As Figure 2 shown in S201. By performing a mechanical analysis on the interaction between the inner steel pipe and the sandwich concrete in the concrete member, establish the deformation coordination relationship, the steel pipe circumferential stress expression, the sandwich concrete radial stress expression, and the inner steel pipe force balance equation in each direction.

[0031] S202. Along the axial and circumferential directions on the surface of the inner steel pipe, respectively take the axial buckling wavelength and the circumferential buckling wavelength to form a wave band surface, and construct the buckling model of the inner steel pipe in the concrete member on this wave band surface.

[0032] Among them, the buckling model is used to characterize the functional relationship between the buckling displacement on the surface of the inner steel pipe and the parameters of the sandwich concrete.

[0033] S203. During the deformation process of the inner steel pipe, according to the deformation coordination relationship, the steel pipe circumferential stress expression, the sandwich concrete radial stress expression, and the inner steel pipe force balance equation, determine the compressive elastic bedding coefficient of the inner steel pipe; and determine the tensile elastic bedding coefficient of the inner steel pipe according to the steel pipe circumferential stress expression.

[0034] Among them, the deformation process includes a first deformation stage in which the inner steel pipe changes from a stress-free zero state to a first state of coordinated deformation with the sandwich concrete, and a second deformation stage from the first state to a second state of local buckling instability deformation.

[0035] S204. Combine the bending wavelength calculation formula of the Winkler elastic foundation and the compressive elastic bedding coefficient to determine the axial buckling wavelength and the circumferential buckling wavelength of the inner steel pipe.

[0036] S205. On this wave band surface, according to the compressive elastic bedding coefficient, the tensile elastic bedding coefficient, the axial buckling wavelength, the circumferential buckling wavelength, and the buckling model of the inner steel pipe, determine the total potential energy equation when the inner steel pipe undergoes local buckling instability.

[0037] S206. Determine the critical stress expression of the inner steel pipe according to the total potential energy equation when the inner steel pipe undergoes local buckling instability, and substitute the mechanical parameter values of the concrete member into the critical stress expression to obtain the critical stress value when the inner steel pipe in the concrete member undergoes local buckling instability.

[0038] S207. Compare the critical stress value with the engineering design index value to determine the stability of the inner steel pipe of the concrete member.

[0039] Here, if the critical stress value of the concrete member is greater than the engineering design index value, it indicates that the stability of the inner steel pipe of the concrete member meets the engineering requirements at this time, and local buckling deformation is not likely to occur. Alternatively, the engineering index of the critical stress can also be designed based on the calculated critical stress value of the concrete member, which helps to ensure engineering safety.

[0040] An evaluation method for the stability of the inner steel pipe of a circular hollow sandwich steel tube concrete member provided by an embodiment of the present application constructs a buckling model of the inner steel pipe, derives the compressive elastic bedding coefficient and the tensile elastic bedding coefficient through mechanical analysis, introduces the bending wavelength calculation formula of a Winkler elastic foundation long beam to calculate the buckling wavelength of the inner steel pipe, and then uses the energy method to solve the critical stress expression of the inner steel pipe. In this way, the critical stress value at which local buckling instability occurs in the inner steel pipe of the circular hollow sandwich steel tube concrete member can be determined, thereby evaluating the stability of the inner steel pipe, preventing local instability of the inner steel pipe, ensuring the good mechanical properties of the overall member, and providing design guidance for engineering practice.

[0041] The implementation manners of each step in the technical solution of the present application will be specifically introduced below.

[0042] Regarding step S201, first, it can be known from the concrete constitutive relationship in formula (1) that in the initial stage, the stress-strain relationship of concrete is a linear elastic relationship. When entering the plastic stage, the stress and strain show a non-linear relationship. Therefore, an integration method is used to calculate the stress and strain of the sandwich concrete, and the formula is as follows: (6) Among them, is the axial strain of the sandwich concrete; is the radial strain of the sandwich concrete; is the axial stress of the sandwich concrete; is the radial stress of the sandwich concrete.

[0043] Figure 3 This is a schematic diagram of the cross-sectional deformation of a concrete unit provided by an embodiment of the present application. As Figure 3 shown in, when the concrete deforms and elongates from L1 to L2 in the radial direction, at the same time, it deforms from S1 to S2 in the circumferential direction. At this time, the concrete radial strain and the circumferential strain have the following relationship: (7) In the formula, is the angle corresponding to the arcs S1 and S2.

[0044] When the entire component of the circular hollow sandwich steel tube concrete begins to undergo plastic deformation and has not yet failed, the radial, circumferential, and axial deformations of the steel tube and the concrete meet the deformation compatibility conditions and are consistent. Therefore, according to Equation (6), the deformation compatibility relationship between the inner steel tube and the sandwich concrete in each direction can be obtained: (8).

[0045] Secondly, by combining Equations (2), (5), and (6), the expression of the circumferential stress of the steel tube and the expression of the incremental radial stress of the sandwich concrete can be obtained: (9) (10).

[0046] Finally, Figure 4 is a schematic diagram of the force on the inner steel tube provided by the embodiment of the present application. As shown in Figure 4 , considering that the inner steel tube mainly plays a supporting role in the circular hollow sandwich steel tube concrete column, the concrete generates a uniform compressive stress in the inward radial direction on the inner steel tube, which is not equal to the compressive stress of the outer steel tube, while the circumferential compressive stress is generated in the inner steel tube, which is opposite to the circumferential stress direction of the outer steel tube. Therefore, the force balance equation of the inner steel tube can be established: (11).

[0047] Regarding step S202, Figure 5(a) is a schematic diagram of the dimensions of the inner steel tube provided by the embodiment of the present application; Figure 5(b) is a schematic diagram of the compressed curved section of the inner steel tube provided by the embodiment of the present application. As shown in Figure 5(a) and Figure 5(b), under the axial compression of the circular hollow sandwich steel tube concrete component, the sandwich concrete expands under force and squeezes the inner steel tube, and the inner steel tube will undergo axial and circumferential buckling. Therefore, it is necessary to establish a buckling mechanical model for the inner steel tube to lose stability in two directions.

[0048] Please refer to Figure 6 , Figure 6 is a coordinate schematic diagram of a local wave section of the inner steel tube provided by the embodiment of the present application. In specific implementation, step S202 may include: S2021. Taking the deepest part of the defect in the sandwich concrete as the origin, a coordinate system is constructed.

[0049] S2022. Starting from the origin of the coordinate system, a section with a length equal to the axial buckling wavelength is taken along the axial direction on the surface of the inner steel tube, and a section with a length equal to the circumferential buckling wavelength is taken along the circumferential direction to form a wave section.

[0050] For the above steps S2021 and S2022, as Figure 6 shown, taking the center of the deepest part of the concrete defect as the origin , the axial direction is the axis, the circumferential direction is the axis, and the radial direction is the axis, to construct a coordinate system. On the inner steel pipe, along the axis and the axis, a section with a length equal to the axial buckling wavelength and the circumferential buckling wavelength is taken respectively to form a wave band surface. Among them, the inner steel pipe forms a cosine deformation curve on this wave band surface.

[0051] S2023. According to the axial buckling wavelength and the circumferential buckling wavelength, construct the first buckling model (12) of the inner steel pipe.

[0052] According to the plate and shell theory, the first buckling displacement model of the inner steel pipe element can be constructed as: (12) wherein, the first buckling model is used to characterize the functional relationship between the buckling displacement on the surface of the inner steel pipe and the axial buckling wavelength and the circumferential buckling wavelength.

[0053] S2024. Divide the axial buckling wavelength into an axial convex length and an axial concave length, and divide the circumferential buckling wavelength into a circumferential convex length and a circumferential concave length.

[0054] If the sandwich concrete in the circular hollow sandwich steel tube concrete column member is regarded as an elastic foundation, then at the concave part, the inner steel pipe is pressed in; at the non-concave part, the inner steel pipe is tensioned and bulges. Let the contact length between the inner steel pipe and the concrete in the axial direction, that is, the axial convex length be ; the non-contact length, that is, the axial concave length be ; the circumferential contact length, that is, the circumferential convex length be ; the non-contact length, that is, the circumferential concave length be ; then there is , .

[0055] S2025. Considering the sandwich concrete as an isotropic material, determine the defect rate expression according to the axial convex length and the axial concave length, and according to the circumferential convex length and the circumferential concave length.

[0056] Considering that the sandwich concrete is an isotropic material, then whether in the axial direction or the circumferential direction, the elastic bedding coefficient generated by the sandwich concrete as an elastic foundation is the same. Therefore, in the axial and circumferential directions, the proportion of the convex part should be the same, so there is , is the axial deformation, It is the circumferential deformation, and the expression of the defect rate is defined as: (13).

[0057] S2026. Substitute the defect rate expression into the first buckling model (12) to obtain the second buckling model (14) of the inner steel pipe.

[0058] First buckling model At The value at can be set to , then the second buckling model is used to characterize the functional relationship between the buckling displacement and the defect rate at the concave-convex demarcation point on the surface of the inner steel pipe.

[0059] As Figure 6 shown in, let be point (the concave-convex demarcation point on the surface of the inner steel pipe). Starting from point, extend along the radial axis and the circumferential , distance respectively to form a curved surface . Let the curved surface be the concrete surface. The entire first buckling displacement model above the curved surface is approximately set as the protruding part of the inner steel pipe, and the rest of the surrounding part is approximately regarded as the part sinking into the concrete. The defect rate expression (13) can be substituted into the first buckling model (12) to obtain the second buckling model of the inner steel pipe : (14).

[0060] Regarding step S203, in order to obtain the compressive elastic bedding coefficient and the tensile elastic bedding coefficient of the inner steel pipe, the embodiments of the present application first analyze the deformation process of the inner steel pipe. Please refer to FIGS. 7(a) and 7(b). FIG. 7(a) is a diagram of the deformation state of a cross-section of the inner steel pipe provided by the embodiments of the present application; FIG. 7(b) is a schematic diagram of the circumferential local buckling deformation of the inner steel pipe provided by the embodiments of the present application.

[0061] In the embodiments of the present application, the state of the inner steel pipe during the axial compression of the circular hollow sandwich steel tube concrete member is divided into 3 states. First is the initial stress-free state, that is, state 0. In the first deformation stage, the sandwich concrete and the inner steel pipe undergo coordinated deformation and jointly compress transversely inward from state 0 to state 1. At this time, the circumferential deformation of the inner steel pipe is as shown by A1D1 in FIG. 7(b).

[0062] Subsequently, local buckling deformation of the inner steel pipe begins, entering the second deformation stage. In the second deformation stage, the inner steel pipe changes from state 1 to state 2. At this time, the steel pipe is in a small deformation state, the axial strain is 0, forming a sine-cosine deformation curve, and the circumferential deformation of the inner steel pipe is shown as OD2 in Fig. 7(b).

[0063] Based on the above analysis, it can be known that for the compressive elastic bedding coefficient of the inner steel pipe, it can be divided into two parts: one part is the compressive stress effect generated by the inner steel pipe being pressed into the concrete and the concrete being pressed in a certain displacement; the other part is the compressive stress effect of the inner steel pipe being laterally compressed and deformed by the concrete.

[0064] First, according to the radial stress expression (10) of the sandwich concrete, the increment of the radial stress of the sandwich concrete caused by being pressed by the inner steel pipe is determined in stages, that is, the following formula (17).

[0065] The stress-strain relationships of the concrete and the inner steel pipe satisfy formulas (9) and (10), and the inner steel pipe is pressed into the inner layer of the sandwich concrete along the radial direction, and the pressing depth is When (formula 3), the stress and strain of the sandwich concrete are determined by formula (10): (15) (16) In the formula, is the strain increment corresponding to the sandwich concrete from state 0 to state 1; is the increment of the radial stress of the sandwich concrete.

[0066] When transitioning from state 1 to state 2, elastic buckling instability of the inner steel pipe occurs, obeying the small deformation principle, so the axial strain of the sandwich concrete. Therefore, from formula (16), the formula can be obtained: (17).

[0067] Secondly, according to the deformation coordination relations (7), (8), the circumferential stress expression (9) of the steel pipe and the force balance equation (11) of the inner steel pipe, the increment of the radial stress in the compressed state of the inner steel pipe caused by being laterally compressed and deformed by the sandwich concrete is determined in stages (20).

[0068] The inner steel pipe is radially compressed by from state 0 to state 1, and from state 1 to state 2, it is compressed by again at the defect. According to the deformation coordination relation (8), it can be known that when the inner steel pipe reaches the critical state of instability conversion, that is, the axial strain when transitioning from state 1 to state 2 is 0, that is . Considering formulas (8) and (9) and based on formulas (18) and (19) are obtained: (18) (19) In the formula, is the incremental circumferential strain when the inner steel pipe is in the compressive state; is the incremental circumferential stress when the inner steel pipe is in the compressive state.

[0069] Also, according to equations (11), (18), (19), etc., formula (20) is obtained (20) In the formula, is the incremental radial stress when the inner steel pipe is in the compressive state.

[0070] Finally, the sum of the incremental radial stress of the sandwich concrete (17) and the incremental radial stress when the inner steel pipe is in the compressive state (20) is calculated, and based on the summation result and Hooke's law, the compressive elastic bedding coefficient of the inner steel pipe (24) is determined.

[0071] Let be the compressive elastic bedding coefficient of the concrete. Summing up the incremental radial stress of the sandwich concrete (17) and the incremental radial stress when the inner steel pipe is in the compressive state (20), and by analogy with Hooke's law it can be obtained that: (21).

[0072] Combining equations (17)-(21), the compressive elastic bedding coefficient is obtained: (22).

[0073] Combined with engineering practice, even if the radius of the inner steel pipe is small, it is still two orders of magnitude larger than the thickness of the thin-walled steel pipe. Therefore, the thickness-to-diameter ratio of the inner steel pipe is much less than 1, that is . Therefore, the above formula (22) can be simplified.

[0074] The formula (22) is disassembled: (23) According to the actual mechanical parameters of the two materials, , while . Therefore, the second term in the square brackets of the above formula is much less than 1 and can be ignored. Therefore, the simplified compressive elastic bedding coefficient of the inner steel pipe is taken as: (24).

[0075] For the tensile elastic bedding coefficient of the inner steel pipe, it can be seen from Figure 7(b) that when the inner steel pipe buckles to state 2, it is in a small deformation state. From to In the interval section, the inner steel pipe just breaks away from the sandwich concrete and bulges inward. At this time, the inner steel pipe is in the circumferential tension state, and the maximum value of its radial bulge is . During the buckling process of the inner steel pipe in the bulging part from state 1 to state 2, it always shows a tensile state. When reaching the critical state 2, the radial deformation corresponding to the stress of the inner steel pipe is . First, according to the circumferential stress expression (9) of the steel pipe and ignoring the vertical strain increment in the critical buckling state, it can be obtained that: (25) (26) And the formula (27) for the radial stress increment of the inner steel pipe in the tensile state is obtained: (27) In the formula, is the circumferential stress increment of the inner steel pipe in the tensile state; is the circumferential strain increment of the inner steel pipe in the tensile state; is the radial stress increment of the inner steel pipe in the tensile state.

[0076] Secondly, according to the formula (27) of the radial stress increment of the inner steel pipe in the tensile state and Hooke's law, the tensile elastic bedding coefficient of the inner steel pipe is determined, that is, the following formula (28).

[0077] When determining the tensile elastic bedding coefficient of concrete as an elastic foundation, the radial displacement of the inner steel pipe bulging inward relative to the concrete is , and the radial stress increment is . By analogy with Hooke's law , and combining formulas (25)-(27), the formula (28) for the tensile elastic bedding coefficient can be obtained: (28) In the formula, is the tensile elastic bedding coefficient.

[0078] Furthermore, according to the above analysis of compression and tension, the tensile and compressive forces between the concrete and the steel pipe should be equal to maintain the balance of the concrete component, and the balance condition can be set accordingly.

[0079] Therefore, the evaluation method further includes: Step 1, on this wave band surface, according to the axial buckling wavelength (36), circumferential buckling wavelength (34) of the inner steel pipe and the buckling models (12), (14), solve the volume of the bulging part and the volume of the sunken part of the inner steel pipe through geometric integration.

[0080] On the inner steel pipe in one wave band, let the volume of the bulging part be , the volume of the sunken part is , and it can be approximately obtained that: (29) (30).

[0081] Step 2: Based on the equilibrium condition that the tensile force and the compressive force between the sandwich concrete and the inner steel pipe are equal, according to the volume of the protruding part, the volume of the sunken part, and the compressive elastic bedding coefficient (24) and the tensile elastic bedding coefficient (28), solve the defect rate equation of the sandwich concrete.

[0082] First, list the equilibrium condition that the tensile force and the compressive force are equal: (31).

[0083] After that, substitute and , that is, formulas (24) and (28) into formula (31), and then combined with formulas (12) - (15), (29) and (30), the defect rate equation of the sandwich concrete can be solved as follows: (32) In the formula, is the radius of the inner steel pipe; is the elastic modulus of the steel pipe; is the elastic modulus of the sandwich concrete; is the Poisson's ratio of the sandwich concrete; is the Poisson's ratio of the steel pipe; is the wall thickness.

[0084] Step 3: Substitute the mechanical parameter values of the concrete member into the defect rate equation of the sandwich concrete to obtain the defect rate parameter value of the concrete member.

[0085] Specifically, given the mechanical parameter values of the concrete member: the elastic modulus of the steel pipe, the elastic modulus of the sandwich concrete, the Poisson's ratio of the sandwich concrete, the Poisson's ratio of the steel pipe, the wall thickness of the inner steel pipe, the outer radius of the steel pipe, and substitute them into the above formula (32) respectively, then the defect rate parameter value can be obtained.

[0086] As mentioned above, it is found that there is a correlation between the concrete surface defect and the local instability phenomenon of the inner steel pipe. Therefore, the evaluation method in the embodiments of the present application can also determine the stability of the inner steel pipe of the concrete member by comparing the defect rate parameter value and the engineering design index value.

[0087] Specifically, if the defect rate parameter value of the concrete member is less than the engineering design index value, it indicates that the internal steel pipe stability of the concrete member meets the engineering requirements at this time and is not prone to local buckling deformation. Alternatively, the engineering index of the defect rate can also be designed based on the calculated defect rate parameter value of the concrete member, which helps to ensure engineering safety.

[0088] Furthermore, when considering the defect rate, this evaluation method may further include: if the critical stress value is greater than the engineering design index value of the critical stress and the defect rate parameter value is less than the engineering design index value of the defect rate, it is determined that the internal steel pipe stability of the concrete member meets the engineering requirements.

[0089] In this way, the internal steel pipe stability of the concrete member can be more comprehensively evaluated from two aspects: critical stress and defect rate.

[0090] Regarding step S204, for the circumferential buckling wavelength of the internal steel pipe, the internal steel pipe undergoes bending deformation in the circumferential direction. Therefore, the wavelength formula for the circumferential bending instability can refer to the bending wavelength formula of a circular cylindrical shell on a Winkler elastic foundation, as follows: (33) In the formula, is the compressive bedding coefficient in the circular cylindrical shell model on a Winkler elastic foundation; is the thickness of the circular cylindrical shell; is the elastic modulus of the shell; is the flexural rigidity of the shell; is the radius of the circular cylindrical shell.

[0091] The internal steel pipe is equivalent to a circular cylindrical shell, the sandwich concrete is equivalent to a Winkler elastic foundation, the internal steel pipe radius is equivalent to the thickness of the compressible layer, and the compressive elastic bedding coefficient (24) and the dimensional parameters 、 and the mechanical parameters 、 are substituted into the bending wavelength formula (33) of the circular cylindrical shell on a Winkler elastic foundation to solve for the circumferential buckling wavelength (34) of the internal steel pipe: (34)。

[0092] For the axial buckling wavelength of the internal steel pipe, the axial instability of the internal steel pipe can be regarded as the instability of a long beam on an elastic foundation. Therefore, the following formula of the Winkler elastic foundation beam model is adopted: (35) In the formula, is the compressive bedding coefficient in the Winkler elastic foundation beam model; is the width of the long beam; is the elastic modulus of the long beam; is the moment of inertia of the cross-section of the long beam.

[0093] The axial instability of the inner steel pipe is equivalent to the instability of a long beam on an elastic foundation. Substitute the elastic compressive bedding coefficient (24) and the mechanical parameters of the strip steel pipe element 、 and the geometric parameters 、 into the bending wavelength formula of the beam on the Winkler elastic foundation to solve the axial buckling wavelength (36) of the inner steel pipe: (36).

[0094] Regarding step S205, it may include: S2051. On this wave band surface, according to the thin shell theory and substitute the buckling model (12), the axial buckling wavelength (36), and the circumferential buckling wavelength (34) to determine the bending strain energy (37) of the inner steel pipe: (37) Substitute formula (12) and into formula (37) to obtain the bending strain energy of the inner steel pipe, that is, the following formula (38): (38).

[0095] S2052. According to the compressive elastic bedding coefficient (Equation 24), the tensile elastic bedding coefficient (Equation 28), the buckling model (Equations 12 and 14), the axial buckling wavelength (Equation 36), and the circumferential buckling wavelength (Equation 34), determine the elastic foundation strain energy (39) of the inner steel pipe: (39).

[0096] Substitute the first buckling model (Equation 12) and the second buckling model (Equation 14) into the elastic foundation strain energy (39) formula to calculate two of the integrals: Let the first item be , (40).

[0097] Let the second item be , (41).

[0098] It can be seen from formula (32) that let the parameter ,then: (42).

[0099] Substitute formulas (28), (41)~(42) into (39) to obtain the elastic foundation strain energy : (43).

[0100] S2053. Determine the axial external force work equation (44) of the inner steel pipe according to the buckling model (Equation 12), the axial buckling wavelength (Equation 36), and the circumferential buckling wavelength (Equation 34): (44).

[0101] Substituting the formula (12) of the first buckling model into (44) gives: (45).

[0102] S2054. Determine the total potential energy equation for the local buckling instability of the inner steel pipe according to the bending strain energy of the inner steel pipe (Equation 38), the elastic foundation strain energy (Equation 39), and the axial external force work equation (Equation 45): .

[0103] In specific implementation, step S206 may include: According to the principle of stationary potential energy, take the first-order partial derivative of the total potential energy equation with respect to the buckling displacement coefficient; set the first-order partial derivative equation to 0 and solve for the critical stress expression of the inner steel pipe, that is, the following equation (49).

[0104] According to the principle of stationary potential energy, when the inner steel pipe is in the critical instability equilibrium state, its potential energy of the first variation is equal to zero. Take the first-order partial derivative of the parameters in namely: (46).

[0105] Substitute formulas (38), (43), and (45) into the partial derivative equation (46) and simplify to get: (47) The parameters in the formula are as follows: .

[0106] According to the principle of basic inequality, it can be obtained that: (48).

[0107] When , then approaches 0 infinitely. At this time, the critical stress expression for the local instability of the inner steel pipe in the concrete wall is: (49).

[0108] After that, substitute the mechanical parameter values of the concrete component into the critical stress expression (49) to obtain the critical stress value of the local buckling instability of the inner steel pipe in the concrete component 。

[0109] The evaluation method for the stability of the inner steel pipe of the circular hollow sandwich steel tube concrete member provided by the embodiments of the present application establishes a buckling model of the inner steel pipe of the concrete member through the mechanical analysis of the concrete member; regarding the sandwich concrete as an elastic foundation and the inner steel pipe as a thin-walled structure on the foundation for mechanical analysis, the compressive and tensile elastic bedding coefficients of regarding the sandwich concrete as an elastic foundation are deduced and simplified; the bending wavelength calculation formula of the Winkler elastic foundation long beam is introduced to calculate the buckling wavelength of the inner steel pipe; based on the thin shell theory, the critical stress expression of the inner steel pipe is obtained by using the energy method.

[0110] In this way, the critical stress value of local buckling instability of the inner steel pipe in the circular hollow sandwich steel tube concrete member can be determined, and then the stability of the inner steel pipe can be evaluated, preventing the inner steel pipe from local instability, ensuring the good mechanical properties of the overall member, and providing design guidance for engineering practice.

[0111] Please refer to Figure 8 , Figure 8 which is a schematic structural diagram of an evaluation device for the stability of the inner steel pipe of a circular hollow sandwich steel tube concrete member provided by the embodiments of the present application. As shown in Figure 8 , the evaluation device 800 includes: An analysis module 810, configured to construct a deformation coordination relation formula, a steel pipe circumferential stress expression, a sandwich concrete radial stress expression, and an inner steel pipe force balance equation in each direction between the inner steel pipe and the sandwich concrete in the concrete member through mechanical analysis of the interaction between the inner steel pipe and the sandwich concrete in the concrete member; A construction module 820, configured to respectively take an axial buckling wavelength and a circumferential buckling wavelength along the axial and circumferential directions on the surface of the inner steel pipe to form a wave band surface, and construct a buckling model of the inner steel pipe in the concrete member on the wave band surface; wherein, the buckling model is used to characterize the functional relationship between the buckling displacement on the surface of the inner steel pipe and the parameters of the sandwich concrete; A first determination module 830, configured to determine the compressive elastic bedding coefficient of the inner steel pipe according to the deformation coordination relation formula, the steel pipe circumferential stress expression, the sandwich concrete radial stress expression, and the inner steel pipe force balance equation during the deformation process of the inner steel pipe; and determine the tensile elastic bedding coefficient of the inner steel pipe according to the steel pipe circumferential stress expression; wherein, the deformation process includes a first deformation stage in which the inner steel pipe changes from a stress-free zero state to a first state of coordinated deformation with the sandwich concrete, and a second deformation stage from the first state to a second state of local buckling instability deformation; A second determination module 840, configured to determine the axial buckling wavelength and the circumferential buckling wavelength of the inner steel pipe by combining the bending wavelength calculation formula of the Winkler elastic foundation and the compressive elastic bedding coefficient; A third determination module 850, configured to determine a total potential energy equation when the inner steel pipe undergoes local buckling instability on the wave band surface according to the compressive elastic bedding coefficient, tensile elastic bedding coefficient, axial buckling wavelength, circumferential buckling wavelength, and buckling model of the inner steel pipe; A calculation module 860, configured to determine a critical stress expression of the inner steel pipe according to the total potential energy equation when the inner steel pipe undergoes local buckling instability, and substitute the mechanical parameter values of the concrete member into the critical stress expression to obtain a critical stress value at which the inner steel pipe in the concrete member undergoes local buckling instability; A comparison module 870, configured to compare the critical stress value with an engineering design index value to determine the stability of the inner steel pipe of the concrete member.

[0112] Please refer to Figure 9 , Figure 9 which is a schematic structural diagram of an electronic device provided by an embodiment of the present application. As Figure 9 shown in

[0113] FIG. 1, the electronic device 900 includes a processor 910, a memory 920, and a bus 930. Figure 2 The memory 920 stores machine-readable instructions executable by the processor 910. When the electronic device 900 runs, the processor 910 communicates with the memory 920 through the bus 930. When the machine-readable instructions are executed by the processor 910, the steps of the evaluation method in the method embodiment as shown in

[0114] FIG. 1 can be executed. The specific implementation manner can refer to the method embodiment and will not be described in detail here. Figure 2 The embodiment of the present application further provides a computer-readable storage medium. A computer program is stored on the computer-readable storage medium. When the computer program is run by a processor, the steps of the evaluation method in the method embodiment as shown in

[0115] FIG. 1 can be executed. The specific implementation manner can refer to the method embodiment and will not be described in detail here.

[0116] In several embodiments provided by the present application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of the units is only a logical functional division, and there may be other division methods in actual implementation. For another example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some communication interfaces, and the indirect couplings or communication connections of the devices or units can be in electrical, mechanical, or other forms.

[0117] The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they can be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0118] In addition, the functional units in various embodiments of the present application can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit.

[0119] If the function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a non-volatile computer-readable storage medium executable by a processor. Based on such an understanding, the technical solution of the present application, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present application. The foregoing storage medium includes: USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs, etc., which can store program codes.

[0120] Finally, it should be noted that the above-described embodiments are only specific embodiments of the present application, which are used to illustrate the technical solutions of the present application, rather than limiting it. The protection scope of the present application is not limited thereto. Although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that any person skilled in the technical field of the present application can still modify the technical solutions described in the foregoing embodiments, or can easily conceive of changes, or perform equivalent replacements on some of the technical features; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be covered by the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. An evaluation method for the stability of the inner steel pipe of a circular hollow sandwich concrete-filled steel tubular member, characterized in that, The evaluation method includes: By performing a mechanical analysis of the interaction between the inner steel pipe and the sandwich concrete in the concrete member, establishing deformation coordination relationships, steel pipe circumferential stress expressions, sandwich concrete radial stress expressions, and inner steel pipe force balance equations in each direction; Axial buckling wavelengths and circumferential buckling wavelengths are respectively taken along the axial and circumferential directions on the surface of the inner steel pipe to form a wave band surface, and a buckling model of the inner steel pipe in the concrete member is established on this wave band surface; wherein, the buckling model is used to characterize the functional relationship between the buckling displacement on the surface of the inner steel pipe and the parameters of the sandwich concrete; During the deformation process of the inner steel pipe, according to the deformation coordination relationship, steel pipe circumferential stress expression, sandwich concrete radial stress expression, and inner steel pipe force balance equation, determine the compressive elastic bedding coefficient of the inner steel pipe; and determine the tensile elastic bedding coefficient of the inner steel pipe according to the steel pipe circumferential stress expression; wherein, the deformation process includes a first deformation stage in which the inner steel pipe changes from a stress-free zero state to a first state of coordinated deformation with the sandwich concrete, and a second deformation stage from the first state to a second state of local buckling instability deformation; Combined with the bending wavelength calculation formula of the Winkler elastic foundation and the compressive elastic bedding coefficient, determine the axial buckling wavelength and circumferential buckling wavelength of the inner steel pipe; On this wave band surface, according to the compressive elastic bedding coefficient, tensile elastic bedding coefficient, axial buckling wavelength, circumferential buckling wavelength, and buckling model of the inner steel pipe, determine the total potential energy equation when the inner steel pipe undergoes local buckling instability; Determine the critical stress expression of the inner steel pipe according to the total potential energy equation when the inner steel pipe undergoes local buckling instability, and substitute the mechanical parameter values of the concrete member into the critical stress expression to obtain the critical stress value of the inner steel pipe in the concrete member when local buckling instability occurs; Compare the critical stress value with the engineering design index value to determine the stability of the inner steel pipe of the concrete member.

2. The evaluation method according to claim 1, wherein The evaluation method further includes: On this wave band surface, according to the axial buckling wavelength, circumferential buckling wavelength, and buckling model of the inner steel pipe, geometrically integrate to solve the volume of the convex part and the volume of the concave part of the inner steel pipe; Based on the equilibrium condition that the tensile force and compressive force between the sandwich concrete and the inner steel pipe are equal, according to the volume of the convex part, the volume of the concave part, the compressive elastic bedding coefficient, and the tensile elastic bedding coefficient, solve the sandwich concrete defect rate equation; Substitute the mechanical parameter values of the concrete member into the sandwich concrete defect rate equation to obtain the defect rate parameter value of the concrete member; Compare the defect rate parameter value with the engineering design index value to determine the stability of the inner steel pipe of the concrete member.

3. The evaluation method according to claim 2, wherein Comparing the defect rate parameter value with the engineering design index value to determine the stability of the inner steel pipe of the concrete member includes: If the critical stress value is greater than the engineering design index value of the critical stress, and the defect rate parameter value is less than the engineering design index value of the defect rate, it is determined that the stability of the inner steel pipe of the concrete member meets the engineering requirements.

4. The evaluation method according to claim 1, characterized in that Axially and circumferentially take the axial buckling wavelength and the circumferential buckling wavelength on the surface of the inner steel pipe respectively to form a wave band surface, and construct the buckling model of the inner steel pipe in the concrete member on this wave band surface, including: Taking the deepest defect in the sandwich concrete as the origin, construct a coordinate system; Starting from the origin of the coordinate system, take a section with a length of the axial buckling wavelength along the axial direction on the surface of the inner steel pipe and a section with a length of the circumferential buckling wavelength along the circumferential direction to form a wave band surface; wherein, the inner steel pipe forms a cosine deformation curve on this wave band surface; According to the axial buckling wavelength and the circumferential buckling wavelength, construct the first buckling model of the inner steel pipe; wherein, the first buckling model is used to characterize the functional relationship between the buckling displacement on the surface of the inner steel pipe and the axial buckling wavelength and the circumferential buckling wavelength; Divide the axial buckling wavelength into the axial bulge length and the axial depression length, and divide the circumferential buckling wavelength into the circumferential bulge length and the circumferential depression length; Considering the sandwich concrete as an isotropic material, determine the defect rate expression according to the axial bulge length and the axial depression length, and according to the circumferential bulge length and the circumferential depression length; Substitute the defect rate expression into the first buckling model to obtain the second buckling model of the inner steel pipe; wherein, the second buckling model is used to characterize the functional relationship between the buckling displacement at the concave-convex demarcation point on the surface of the inner steel pipe and the defect rate.

5. The evaluation method according to claim 1, characterized in that During the deformation process of the inner steel pipe, determine the compressive elastic bedding coefficient of the inner steel pipe according to the deformation coordination relation formula, the circumferential stress expression of the steel pipe, the radial stress expression of the sandwich concrete and the force balance equation of the inner steel pipe; And determine the tensile elastic bedding coefficient of the inner steel pipe according to the circumferential stress expression of the steel pipe, including: Determine the radial stress increment of the sandwich concrete generated by being pressed into the inner steel pipe in stages according to the radial stress expression of the sandwich concrete; Determine the radial stress increment in the compressed state of the inner steel pipe generated by the transverse compression deformation of the inner steel pipe by the sandwich concrete in stages according to the deformation coordination relation formula, the circumferential stress expression of the steel pipe and the force balance equation of the inner steel pipe; Sum the radial stress increment of the sandwich concrete and the radial stress increment in the compressed state of the inner steel pipe, and determine the compressive elastic bedding coefficient of the inner steel pipe according to the summation result and Hooke's law; Determine the radial stress increment in the tensile state of the inner steel pipe according to the circumferential stress expression of the steel pipe; Determine the tensile elastic bedding coefficient of the inner steel pipe according to the radial stress increment in the tensile state of the inner steel pipe and Hooke's law.

6. The evaluation method according to claim 1, characterized in that Combining the bending wavelength calculation formula of the Winkler elastic foundation and the compressive elastic bedding coefficient, determine the axial buckling wavelength and the circumferential buckling wavelength of the inner steel pipe, including: Equivalent the inner steel pipe to a cylindrical shell, equivalent the sandwich concrete to a Winkler elastic foundation, equivalent the radius of the inner steel pipe to the thickness of the compressible layer, substitute the compressive elastic bedding coefficient into the bending wavelength formula of the cylindrical shell of the Winkler elastic foundation, and solve the circumferential buckling wavelength of the inner steel pipe; Equivalent the axial instability of the inner steel pipe to the instability of a long beam on an elastic foundation, substitute the elastic compressive bedding coefficient into the bending wavelength formula of the beam of the Winkler elastic foundation, and solve the axial buckling wavelength of the inner steel pipe.

7. The evaluation method according to claim 1, characterized in that On this wave band surface, according to the compressive elastic subgrade coefficient, tensile elastic subgrade coefficient, axial buckling wavelength, circumferential buckling wavelength and buckling model of the inner steel pipe, the total potential energy equation at the time of local buckling instability of the inner steel pipe is determined, including: On this wave band surface, according to the thin shell theory and substituting the buckling model, axial buckling wavelength, and circumferential buckling wavelength, the bending strain energy of the inner steel pipe is determined; According to the compressive elastic subgrade coefficient, tensile elastic subgrade coefficient, buckling model, buckling model, axial buckling wavelength, and circumferential buckling wavelength, the elastic foundation strain energy of the inner steel pipe is determined; According to the buckling model, axial buckling wavelength, and circumferential buckling wavelength, the equation for the work done by the axial external force on the inner steel pipe is determined; According to the bending strain energy, elastic foundation strain energy of the inner steel pipe and the equation for the work done by the axial external force, the total potential energy equation at the time of local buckling instability of the inner steel pipe is determined.

8. The evaluation method according to claim 1, wherein According to the total potential energy equation at the time of local buckling instability of the inner steel pipe, the critical stress expression of the inner steel pipe is determined, including: According to the principle of stationary potential energy, the total potential energy equation is partially differentiated with respect to the buckling displacement coefficient for the first order; Let the first-order partial derivative equation be 0, and solve for the critical stress expression of the inner steel pipe.

9. An evaluation device for the stability of the inner steel pipe of a circular hollow sandwich concrete-filled steel tube member, characterized in that, The evaluation device includes: An analysis module, which is used to construct the deformation coordination relationship, steel pipe circumferential stress expression, sandwich concrete radial stress expression and inner steel pipe force balance equation in each direction between the inner steel pipe and the sandwich concrete in the concrete member through mechanical analysis of the interaction between the inner steel pipe and the sandwich concrete in the concrete member; A construction module, which is used to respectively take the axial buckling wavelength and the circumferential buckling wavelength along the axial and circumferential directions on the surface of the inner steel pipe to form a wave band surface, and construct the buckling model of the inner steel pipe in the concrete member on this wave band surface; wherein, the buckling model is used to characterize the functional relationship between the buckling displacement on the surface of the inner steel pipe and the parameters of the sandwich concrete; A first determination module, which is used to determine the compressive elastic subgrade coefficient of the inner steel pipe according to the deformation coordination relationship, steel pipe circumferential stress expression, sandwich concrete radial stress expression and inner steel pipe force balance equation during the deformation process of the inner steel pipe; and determine the tensile elastic subgrade coefficient of the inner steel pipe according to the steel pipe circumferential stress expression; wherein, the deformation process includes a first deformation stage from the stress-free zero state of the inner steel pipe to the first state of coordinated deformation with the sandwich concrete, and a second deformation stage from the first state to the second state of local buckling instability deformation; A second determination module, which is used to determine the axial buckling wavelength and the circumferential buckling wavelength of the inner steel pipe by combining the bending wavelength calculation formula of the Winkler elastic foundation and the compressive elastic subgrade coefficient; A third determination module, which is used to determine the total potential energy equation at the time of local buckling instability of the inner steel pipe on this wave band surface according to the compressive elastic subgrade coefficient, tensile elastic subgrade coefficient, axial buckling wavelength, circumferential buckling wavelength and buckling model of the inner steel pipe; A calculation module, which is used to determine the critical stress expression of the inner steel pipe according to the total potential energy equation at the time of local buckling instability of the inner steel pipe, and substitute the mechanical parameter values of the concrete member into the critical stress expression to obtain the critical stress value of local buckling instability of the inner steel pipe in the concrete member; A comparison module for comparing the critical stress value and the engineering design index value to determine the stability of the inner steel pipe of the concrete member.

10. An electronic device, characterized in that, Comprising: A processor, a memory, and a bus. The memory stores machine-readable instructions executable by the processor. When the electronic device runs, the processor communicates with the memory through the bus. When the machine-readable instructions are run by the processor, the steps of the evaluation method according to any one of claims 1 to 8 are executed.

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