A method and system for calculating the bearing capacity of a circular steel tube thin-walled hollow concrete T-joint

Abstract

The present invention relates to the technical field of the bearing capacity of concrete-filled steel tubes, and particularly relates to a method and system for calculating the bearing capacity of a concrete-filled thin-walled circular steel tube T-joint; the corresponding punching model satisfies the following basic conditions: It is assumed that the main pipe of the concrete-filled thin-walled circular steel tube member is a structural system composed of two elements, namely, a steel tube and concrete. When subjected to a lateral force, the ultimate bearing capacity of the concrete will be enhanced due to the confinement effect of the steel tube on it; although the longitudinal and circumferential forces of the concrete are inconsistent, it is assumed that the failure results occur simultaneously during punching failure; it is assumed that the punching surface formed after the concrete-filled hollow steel tube is damaged by the lateral bearing capacity is a smooth surface; it is assumed that the concrete cone formed by punching is circular at the top and elliptical at the bottom; the concrete cone formed by punching is equivalent to a frustum of a cone; the ultimate bearing capacity of the steel tube corresponding to the double-sided stiffened steel tube T-joint is calculated, and then the ultimate bearing capacity of the concrete-filled hollow steel tube joint is obtained by combining the ultimate bearing capacity of the concrete.

Description

Technical Field

[0001] The present invention relates to the technical field of the bearing capacity of concrete-filled steel tubes, and particularly relates to a calculation method and system for the bearing capacity of a concrete-filled thin-walled circular steel tube T-joint. Background Art

[0002] Due to the advantages of high bearing capacity, good plastic toughness, economy and easy assembly, the concrete-filled steel tube structure can meet the continuously increasing requirements for sectional strength and fire resistance, and is widely used in engineering such as factory buildings and super high-rise buildings.

[0003] However, in the actual project of transmission and transformation towers in the power industry, it is difficult to carry out the on-site pouring process during construction. A precast component with a relatively light self-weight and convenient for transportation is necessary. Thus, the concrete-filled thin-walled circular steel tube component is introduced, which can not only give full play to the mechanical properties of both steel and concrete, but also avoid the disadvantages under the condition of using them alone. The structure has good stress and relatively light self-weight.

[0004] A large number of experimental studies have shown that the deformation and failure process of concrete is very complex, and it is closely related to the stress state of concrete. When studying the bearing capacity of the concrete-filled thin-walled circular steel tube T-joint, the bearing capacity of the joint cannot be directly calculated according to the stress of the solid concrete-filled steel tube component or the idea of the unified body of the concrete-filled steel tube material combination. An effective simplified calculation method is needed.

[0005] For example, the paper "Research on Concrete-Filled Hollow Steel Tubes and Component Calculation, Zhang Sumei, Zhong Shantong. Research on Concrete-Filled Hollow Steel Tubes and Component Calculation [J]. China Civil Engineering Journal, 1994, 27(03): 24-32" discloses the structure of concrete-filled hollow steel tubes and the full curves under various stress states; the invention patent with the publication number CN108875257A discloses a regression analysis method for the bearing capacity of a square steel tube truss N-joint for a trestle, but it does not conduct research on the concrete-filled steel tube structure and only analyzes the bearing capacity of the steel tube. The invention patent with the publication number CN118839435A discloses a calculation method, system, device and storage medium for the vertical ultimate bearing capacity of a steel structure base, and its purpose is to calculate the vertical ultimate bearing capacity of a steel structure bearing base, and it mainly focuses on the calculation of the vertical ultimate bearing capacity of H-shaped steel plates and square steel tubes and their influencing degrees. Summary of the Invention

[0006] Object of the Invention: The object of the present invention is to solve the problems in the above background art, and provide a calculation method for the bearing capacity of a concrete-filled thin-walled circular steel tube T-joint, and also provide a calculation system for the bearing capacity of a concrete-filled thin-walled circular steel tube T-joint.

[0007] Technical solution: According to the first aspect of the present invention, a method for calculating the bearing capacity of a circular steel tube thin-walled hollow concrete T-joint is provided. The method includes:

[0008] Construct a concrete punching model corresponding to the failure of the hollow steel tube concrete joint; the concrete punching model satisfies the following basic conditions: Assume that the main pipe of the circular steel tube thin-walled hollow concrete member is a structural system composed of two elements, steel tube and concrete; when suffering punching failure, assume that the failure results in the longitudinal and circumferential directions of the concrete occur simultaneously; assume that the punching surface formed after the hollow steel tube concrete is damaged by the lateral bearing capacity is a smooth surface; assume that the concrete cone formed by punching is circular at the top and elliptical at the bottom.

[0009] Equivalent the concrete cone formed by punching into a frustum of a cone, and at the same time expand the circumferential concrete into a concrete slab for calculation, and calculate the equivalent angle between the concrete crack caused by punching and the branch pipe according to the double shear stress three-parameter criterion, that is, the punching angle.

[0010] Calculate the punching strength under the axisymmetry of the circular load according to the obtained punching angle, so as to represent the ultimate bearing capacity of the concrete.

[0011] According to the obtained ultimate bearing capacity of the steel tube corresponding to the hollow steel tube concrete T-joint, combined with the ultimate bearing capacity of the concrete, obtain the ultimate bearing capacity of the hollow steel tube concrete T-joint. The hollow steel tube concrete T-joint includes a main pipe and a branch pipe. The cross-section of the main pipe is circular and is provided with concrete inside. The branch pipe is arranged on the main pipe and is in a T shape.

[0012] Further, it includes:

[0013] The calculation of the equivalent angle between the concrete crack caused by punching and the branch pipe according to the double shear stress three-parameter criterion, that is, the punching angle, includes:

[0014] The punching failure mode of the concrete slab is close to ideal rigid-plastic failure, and the bending effect in the structure is ignored. Analyze the punching strength of the concrete according to the double shear stress three-parameter criterion.

[0015] The punching strength that conforms to the double shear stress three-parameter criterion is regarded as the material being damaged, so as to obtain the coefficient related to the material strength in the double shear stress three-parameter criterion and the relationship between the effective uniaxial tensile strength, uniaxial compressive strength and biaxial equal-compression strength.

[0016] When the failure cone is symmetric about the axis of the branch pipe, obtain the corresponding representation form of the double shear stress three-parameter criterion, and obtain the limit stress circle envelope according to the circumferential stress in the double shear stress three-parameter criterion, so as to determine the punching angle.

[0017] Further, it includes:

[0018] The coefficients related to the material strength in the twin-shear stress three-parameter criterion, and the relationships among the effective uniaxial tensile strength, uniaxial compressive strength, and biaxial equal-compression strength include:

[0019] When taking different normal stress influence coefficients, the twin-shear stress three-parameter criterion gives: In the formula, 、 、 are coefficients related to the material strength, which are determined by material property tests;

[0020] If one of the formulas in Formula 1 and Formula 2 is satisfied, it indicates that the steel pipe and concrete materials are damaged;

[0021] Assume that the concrete is an ideal rigid-plastic material, and its effective uniaxial tensile strength, uniaxial compressive strength, and biaxial equal-compression strength are 、 and , respectively. According to the Kupfer test data, we get: , let , then: . The cohesion of the concrete is obtained under the punching strength of the axisymmetric circular load, and then the ultimate bearing capacity of the concrete is obtained.

[0022] Furthermore, it includes:

[0023] When the failure cone is symmetric about the branch pipe axis, the corresponding expression of the twin-shear stress three-parameter criterion is obtained, including:

[0024] When the failure cone is symmetric about the branch pipe axis, assume the circumferential stress is , due to the axisymmetry of the displacement field, that is ; Assume that the plastic deformation is small and the volume of the concrete is incompressible. From the plastic deformation theory, we can get: Substitute Formula 3 into Formula 1 and Formula 2 to get the twin-shear stress three-parameter criterion under axisymmetric conditions: Among them: . Furthermore, it includes:

[0025] The ultimate stress circle envelope is obtained according to the circumferential stress in the twin-shear stress three-parameter criterion, so as to determine the punching angle, including:

[0026] Set a point M on the punching surface, which is a point on the ultimate stress circle equation G. Denote the normal stress and shear stress of point M on the punching surface as and ;

[0027] Then when the equation G of the limit stress circle is: Because the equation F is tangent to equation G at point M, and the equation is tangent to equation G at point M, then equation F, equation G, and have the same at point M of equation G; among them, equation F refers to formula 1; equation refers to formula 2;

[0028] It is obtained from formula 4, formula 5, and formula 6: By simultaneously solving formula 7 and formula 9: By simultaneously solving formula 8 and formula 9: By simultaneously solving formula 4 and formula 10: Substitute formula 12 into formula 6 to obtain the limit stress circle envelope equation based on equation F: Where: ;

[0029] By simultaneously solving formula 5 and formula 11: Substitute formula 14 into formula 6 to obtain the limit stress circle envelope equation based on F: Where: Let When, obtain ;

[0030] When When, ,[[]]END]] This indicates that and intersect, that is, the actual limit stress circle envelope is the broken line composed of and enclosed;

[0031] When When, ,[[]]END]] This indicates that the actual limit stress circle envelope is ;

[0032] For ordinary concrete, , so the envelope of the ultimate stress circles of the concrete punching surface is , we have: After arrangement, we can get: Furthermore, it includes:

[0033] Calculating the punching strength under axisymmetric circular load according to the obtained punching angle, so as to represent the ultimate bearing capacity of concrete, including:

[0034] The area increment of the circumferential fracture surface caused by punching is: According to the plastic upper limit theory and related flow rules, from the equality of internal force work and external force work, we get: Among them, for the punching strength under axisymmetric circular load, the cohesion of concrete is expressed as ,

[0035] After further arrangement, the ultimate bearing capacity of concrete is obtained: Among them, is the tensile stress of concrete; is the shear force, is the diameter of concrete at the branch pipe, is the thickness of the concrete slab after unfolding, x is the displacement along the punching direction.

[0036] Furthermore, it includes:

[0037] Calculating the ultimate bearing capacity of the concrete-filled hollow steel tube T-joint according to the obtained ultimate bearing capacity of the steel tube corresponding to the concrete-filled hollow steel tube T-joint, and combining with the ultimate bearing capacity of concrete, including:

[0038] The ultimate bearing capacity of the concrete-filled hollow steel tube T-joint is obtained through the ultimate bearing capacity of the steel tube corresponding to the concrete-filled hollow steel tube T-joint and the ultimate bearing capacity of concrete ; specifically: Determined according to the ratio of the cross-sectional area of the stiffener on the concrete-filled hollow steel tube T-joint to the area of the branch pipe of the concrete-filled hollow steel tube.

[0039] On the other hand, the present invention also provides a bearing capacity calculation system for a concrete-filled circular steel tube thin-walled hollow T-joint, and this system includes:

[0040] A model construction system for constructing a concrete punching model corresponding to the failure of a concrete-filled hollow steel tubular joint; the concrete punching model satisfies the following basic conditions: it is assumed that the main pipe of a circular steel tube thin-walled hollow concrete member is a structural system composed of two elements, namely, steel tube and concrete; during punching failure, it is assumed that the failure results in the longitudinal and circumferential directions of the concrete occur simultaneously; it is assumed that the punching surface formed after the concrete-filled hollow steel tube is damaged by lateral bearing capacity is a smooth surface; it is assumed that the concrete cone formed by punching is circular at the top and elliptical at the bottom.

[0041] A punching angle calculation module for equivalenting the concrete cone formed by punching into a frustum of a cone, and at the same time unfolding the circumferential concrete into a concrete slab for calculation, and calculating the equivalent angle between the concrete crack caused by punching and the branch pipe according to the double-shear stress three-parameter criterion, that is, the punching angle.

[0042] A concrete ultimate bearing capacity calculation module for calculating the punching strength under axisymmetric circular load according to the obtained punching angle, so as to represent the concrete ultimate bearing capacity.

[0043] A concrete-filled hollow steel tubular T-joint ultimate bearing capacity calculation module for obtaining the ultimate bearing capacity of the concrete-filled hollow steel tubular T-joint according to the obtained ultimate bearing capacity of the steel tube corresponding to the concrete-filled hollow steel tubular T-joint, in combination with the concrete ultimate bearing capacity. The concrete-filled hollow steel tubular T-joint includes a main pipe and a branch pipe. The cross-section of the main pipe is circular and is filled with concrete inside. The branch pipe is arranged on the main pipe and is in a T shape.

[0044] Further, it includes:

[0045] The punching angle calculation module includes:

[0046] A punching strength analysis unit: The punching failure mode of the concrete slab is close to ideal rigid-plastic failure, and the bending effect in the structure is ignored. The punching strength of the concrete is analyzed according to the double-shear stress three-parameter criterion.

[0047] A relationship obtaining unit: The punching strength that conforms to the double-shear stress three-parameter criterion is regarded as the material being damaged, so as to obtain the relationship between the coefficient related to the material strength in the double-shear stress three-parameter criterion and the effective uniaxial tensile strength, uniaxial compressive strength and biaxial equal-compression strength.

[0048] A punching angle calculation unit: When the failure cone is symmetric about the axis of the branch pipe, the corresponding representation form of the double-shear stress three-parameter criterion is obtained, and the limit stress circle envelope is obtained according to the circumferential stress in the double-shear stress three-parameter criterion, so as to determine the punching angle.

[0049] Compared with the prior art, the present invention has the following advantages:

[0050] The present invention first proposes a bearing capacity calculation method for circular steel tube thin-walled hollow concrete T-joints. This method takes into account the ultimate bearing capacity of concrete and the ultimate bearing capacity of the steel tube. For the ultimate bearing capacity of concrete, the present invention constructs a concrete punching calculation model, and on the basis of this model, analyzes the concrete punching strength according to the double shear stress three-parameter criterion to obtain the punching angle. Finally, based on the punching angle, the ultimate bearing capacity of concrete is deduced, and combined with the calculation result of the ultimate bearing capacity of the steel tube, the ultimate bearing capacity of the circular steel tube thin-walled hollow concrete T-joint is obtained. By comparing the calculation results of the present invention with the test results and finite element calculation results of the joints with corresponding dimensional parameters, it is found that it can meet the design requirements for setting circular steel tube thin-walled hollow concrete T-joints, provide a reliable reference for joint design in practical engineering, and is conducive to the popularization and application of circular steel tube thin-walled hollow concrete T-joints. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a design process diagram of the bearing capacity calculation method for the circular steel tube thin-walled hollow concrete T-joint described in the embodiment of the present invention;

[0052] Figure 2 It is a comparison sketch of the punching model described in the embodiment of the present invention. Among them, Figure (a) is a schematic diagram of the concrete punching model, and Figure (b) is an example diagram of the failure caused by punching;

[0053] Figure 3 It is a schematic diagram of the punching failure surface described in the embodiment of the present invention;

[0054] Figure 4 It is a schematic diagram of the simplified model described in the embodiment of the present invention. Among them, Figure (a) is a structural schematic diagram of equivalent a conical frustum into a circular truncated cone, and Figure (b) is a structural schematic diagram of unfolding the circumferential concrete into a concrete slab;

[0055] Figure 5 It is a schematic diagram of the T-shaped stiffened compression joint described in the embodiment of the present invention. Among them, Figures (a), (b), and (c) are structural schematic diagrams from three different perspectives respectively;

[0056] Figure 6 It is a schematic diagram of the flat plate punching failure described in the embodiment of the present invention;

[0057] In the figure, it includes: main pipe 1, branch pipe 2, and stiffening rib 3. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0058] The following will describe in detail the implementation of the present invention in conjunction with the drawings, but it does not limit the present invention. Only for example, through the description, the advantages of the present invention will be clearer and easier to understand.

[0059] Referring to the detailed drawings, it can be seen that the present invention provides a method for calculating the bearing capacity of a circular steel tube thin-walled hollow concrete T-joint, as follows: Figure 1 shown, which includes the following steps:

[0060] Step 1: Without considering the improvement of the arch and the steel tube on the punching bearing capacity of the concrete, in this embodiment, only the failure mechanism of the hollow steel tube concrete joint is analyzed. The failure of the hollow steel tube concrete joint can be analyzed in connection with the failure of the flat plate punching, as shown in Figure 2 shown. The failure of the steel tube concrete joint can be regarded as the superposition of two failures, namely: the compressive buckling failure of the steel tube and the punching failure of the concrete. The following basic assumptions need to be made when proposing the punching calculation model:

[0061] 1) First, the main pipe 1 of the circular steel tube thin-walled hollow concrete member is a structural system composed of two elements, namely, a hollow steel tube and concrete. When subjected to a lateral force, the ultimate bearing capacity of the concrete will be enhanced due to the confinement effect of the steel tube on it;

[0062] 2) Although the longitudinal and circumferential forces of the concrete are inconsistent, it is assumed that the failure results occur simultaneously during punching failure;

[0063] 3) It is assumed that the punching surface formed after the hollow steel tube concrete is damaged by the lateral bearing capacity is a smooth surface;

[0064] 4) It is assumed that the concrete cone formed by punching is circular at the top and elliptical at the bottom, as shown in Figure 3 shown.

[0065] In this embodiment, according to the shape described in (a) of Figure 2 , when the branch pipe 2 is subjected to the punching force, the top of the concrete cone is marked as circular, and the bottom becomes elliptical due to the punching force.

[0066] In the embodiment of the present application, because when the hollow ratio is moderate, the failure of the steel tube concrete will be similar to punching and will be closer to the test results. As shown in (a) of Figure 2 , the upper ring is the hollow concrete section in the main pipe. When the inclined crack develops to a certain extent, C and D are the bearing short column systems in the plate, which presents as a space shell and is decomposed into two space shells coupled in regions I and III. Figure 2 As shown in (b) of

[0067] Step 2: Calculate the equivalent angle between the concrete crack and the branch pipe 2, that is, the punching angle of.

[0068] Step 2.1: Based on the basic assumptions in Step 1, in order to conveniently obtain the surface area of the rupture surfaces of the steel tube and the concrete caused by the failure,Figure 2 The conical bodies in it are equivalent to a frustum of a cone, as shown in Figure 4 (a) in. At the same time, the circumferential concrete is unfolded into a concrete slab for calculation, and the original model is simplified as shown in Figure 4 (b) in. In this embodiment, the circular-elliptical frustum is further transformed and equivalent into a frustum of a cone, that is, both the upper and lower parts are equivalent to circles. Since the top view of the circular-elliptical frustum is axisymmetric, the generatrix of the transformed frustum of a cone is based on the longest generatrix and the shortest generatrix before. Because it is too complex to solve the lateral area of the conical bodies, appropriate simplification must be carried out to approximately obtain it. Compared with the more accurate numerical solution, the approximation error of the simplification is not large.

[0069] Step 2.2: The punching failure mode of the concrete slab is close to the ideal rigid-plastic failure, and the influence of the bending effect in the structure can be ignored. The punching strength of the concrete is analyzed according to the double-shear stress three-parameter criterion.

[0070] Step 2.2.1: When different normal stress influence coefficients are taken, according to the double-shear stress three-parameter criterion, we can get: In the formula, , , are coefficients related to the material strength, which are determined by material property tests.

[0071] Step 2.2.2: If one condition in the formula in Step 2.2.1 is satisfied, it means that the steel pipe and concrete materials are damaged;

[0072] Assume that the concrete is an ideal rigid-plastic material, and its effective uniaxial tensile strength, uniaxial compressive strength and biaxial equal-compression strength are , and respectively. According to the Kupfer test data: , let , then ;

[0073] Step 2.2.3: When the failure cone is symmetric about the axis of branch pipe 2, that is, in the axisymmetric case, assume that the circumferential stress is Since the displacement field is axisymmetric, that is, ; Assume that the plastic deformation is small deformation and the volume of the concrete is incompressible. According to the plastic deformation theory, we can get: Substitute formula 3 into formula 1 and formula 2 in Step 2.2.1, and the double-shear stress three-parameter criterion in the axisymmetric case can be obtained: In the formula: Step 2.2.4: Determine the punching angle according to the obtained envelope equation .

[0074] Let the normal stress and shear stress of point M on the punching surface be and , respectively. In this embodiment, a point M is set on the punching surface, which is a point on the limit stress circle equation G. This point M is also the tangent point of the limit stress circle equation G and the double-shear stress three-parameter criterion equation F or . When , the limit stress circle equation G of Because the equation F is tangent to equation G at point M, and the equation is tangent to equation G at point M, then equation F and equation G, and and equation G have the same at point M. Among them, equation F refers to formula 1; equation refers to formula 2.

[0075] From formula 4, formula 5, and formula 6, we can get:[[]] By combining formula 7 and formula 9 and solving, we get:[[]] By combining formula 8 and formula 9 and solving, we get:[[]] By combining formula 4 and formula 10 and solving, we get:[[]] Substitute formula 12 into formula 6 to obtain the limit stress circle envelope equation based on F:[[]] In the formula:[[]] By combining formula 5 and formula 11 and solving, we get:[[]] Substitute formula 14 into formula 6 to obtain the limit stress circle envelope equation based on F:[[]] In the formula:[[]] Let , and solve to get .

[0076] When , , , which indicates that and Intersect, that is, the actual ultimate stress circle envelope is and The broken line surrounded by the envelope.

[0077] When At that time, , , which indicates that the actual ultimate stress circle envelope is .

[0078] For general concrete, , so the ultimate stress circle envelope of the concrete punching surface is , there is: After sorting out, we can get: Step 3: Based on the punching angle Calculated by the formula of the ultimate bearing capacity of concrete.

[0079] The area increment of the circumferential fracture surface caused by punching is: According to the plastic upper bound theory and the related flow rule, the equality of the internal force work and the external force work gives: As Figure 6 Shown, for the punching strength under the axisymmetry of the circular load, its circumferential strain can be approximately considered , the cohesion of the concrete can be expressed as , Is the tensile stress of the concrete; Is the shear force, Is the diameter of the branch pipe 2, Is the thickness of the concrete slab after unfolding, x Is the displacement along the punching direction.

[0080] Further sorting out gives the calculation formula for the ultimate bearing capacity of concrete: Step 4: Calculation of the ultimate bearing capacity of the steel pipe. In this embodiment, no specific steel pipe structure is limited, as long as the cross-section of the main pipe 1 is circular and there is concrete inside it, and the branch pipe 2 is arranged on the main pipe 1 and is in a T shape.

[0081] Specifically, in this embodiment, taking the double-sided stiffened steel pipe T-joint as an example, the calculation is carried out according to the formula for the compression of the stiffening rib 3. As Figure 5 Shown, it includes a circular main pipe 1, a branch pipe 2 and a stiffening rib 3. The main pipe 1 and the branch pipe 2 are designed in a T shape. The setting direction of the stiffening rib 3 is the same as that of the branch pipe 2 and is used to fix the main pipe 1 and the branch pipe 2. In this embodiment, a total of 4 identical stiffening ribs 3 are set, and the four-direction stiffening ribs 3 surround the outer circumference of the branch pipe 2 in a circle.

[0082] Based on the above structure, the calculation formula for the first ultimate bearing capacity is: Among them, is the discrimination coefficient, as shown in (a), (b), and (c) in Figure 5 , C is the width of the stiffener 3, D is the outer diameter of the main pipe 1, is the radius of the main pipe 1, is the wall thickness of the main pipe 1, is the thickness of the stiffener 3, R is the height of the main pipe 1, is the yield strength of the steel pipe; is the effective amplitude of the stiffener 3 obtained according to the Thurlimann calculation theory formula.

[0083] When the said discrimination coefficient , then:

[0084] The second ultimate bearing capacity is expressed as: When the discrimination coefficient , then Among them, is the yield strength of the stiffener 3, and the ultimate bearing capacity of the steel pipe is the first ultimate bearing capacity and the second ultimate bearing capacity is the smaller of them. In this embodiment, the first ultimate bearing capacity is the bearing capacity under the failure of the wall of the main pipe 1, and the second ultimate bearing capacity is the bearing capacity under the failure of the stiffener 3. Step 5: Combine the formulas in Step 3 and Step 4 to obtain the ultimate bearing capacity of the concrete-filled steel tube hollow node: In the formula, is determined according to the ratio of the cross-sectional area of the stiffener 3 to the area of the branch pipe 2. For concrete-filled steel tubes without stiffeners, it is taken as 1, and for concrete-filled steel tubes with stiffeners, that is, in this embodiment, it is taken as 1.2.

[0085] On the other hand, the present invention also provides a bearing capacity calculation system for a circular steel tube thin-walled hollow concrete T-joint, and this system includes:

[0086] A model construction system for constructing a concrete punching model corresponding to the failure of a concrete-filled hollow steel tubular joint; the concrete punching model satisfies the following basic conditions: it is assumed that the main pipe of a circular steel tube thin-walled hollow concrete member is a structural system composed of two elements, namely, steel tube and concrete; when suffering punching failure, it is assumed that the failure results in the longitudinal and circumferential directions of the concrete occur simultaneously; it is assumed that the punching surface formed after the concrete-filled hollow steel tube is damaged by lateral bearing capacity is a smooth surface; it is assumed that the concrete cone formed by punching is circular at the top and elliptical at the bottom.

[0087] A punching angle calculation module for equivalenting the concrete cone formed by punching into a frustum of a cone, and at the same time unfolding the circumferential concrete into a concrete slab for calculation, and calculating the equivalent angle between the concrete crack caused by punching and the branch pipe according to the double-shear stress three-parameter criterion, that is, the punching angle.

[0088] A concrete ultimate bearing capacity calculation module for calculating the punching strength under axisymmetric circular load according to the obtained punching angle, so as to represent the concrete ultimate bearing capacity.

[0089] A concrete-filled hollow steel tubular T-joint ultimate bearing capacity calculation module for obtaining the ultimate bearing capacity of the concrete-filled hollow steel tubular T-joint according to the obtained ultimate bearing capacity of the steel tube corresponding to the concrete-filled hollow steel tubular T-joint, in combination with the concrete ultimate bearing capacity. The concrete-filled hollow steel tubular T-joint includes a main pipe and a branch pipe. The cross-section of the main pipe is circular, and concrete is arranged therein. The branch pipe is arranged on the main pipe and is in a T shape.

[0090] Furthermore, it includes:

[0091] The punching angle calculation module includes:

[0092] A punching strength analysis unit: The punching failure mode of the concrete slab is close to ideal rigid-plastic failure, and the bending effect in the structure is ignored. The punching strength of the concrete is analyzed according to the double-shear stress three-parameter criterion.

[0093] A relationship obtaining unit: The punching strength that conforms to the double-shear stress three-parameter criterion is regarded as the material being damaged, so as to obtain the relationship between the coefficient related to the material strength in the double-shear stress three-parameter criterion and the effective uniaxial tensile strength, uniaxial compressive strength and biaxial equal-compression strength.

[0094] A punching angle calculation unit: When the failure cone is symmetric about the axis of the branch pipe, the corresponding representation form of the double-shear stress three-parameter criterion is obtained, and the ultimate stress circle envelope is obtained according to the circumferential stress in the double-shear stress three-parameter criterion, so as to determine the punching angle.

[0095] Other technical features of the bearing capacity calculation system of a circular steel tube thin-walled hollow concrete T-joint described in this embodiment are similar to the corresponding bearing capacity calculation method of the circular steel tube thin-walled hollow concrete T-joint, and will not be elaborated here.

[0096] Those skilled in the art should understand that the embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0097] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0098] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present invention without departing from the spirit and scope of the embodiments of the present invention. Thus, if these modifications and variations of the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A method for calculating the bearing capacity of a circular steel tube thin-wall hollow concrete T-joint, characterized in that: The method includes: A concrete punching shear model corresponding to the destruction of hollow steel tube concrete T-type node is constructed; the concrete punching shear model meets the following conditions: it is assumed that the main pipe of the circular steel tube thin-wall hollow concrete T-type node is a structural system composed of two elements: steel tube and concrete; when subjected to shear destruction, it is assumed that the longitudinal and circumferential destruction of the concrete occurs simultaneously; it is assumed that the punching surface formed after the hollow steel tube concrete is destroyed by the lateral bearing force is a smooth curved surface; it is assumed that the concrete cone formed by the punching is round at the top and elliptical at the bottom; The concrete cone formed by the punching is equivalent to a truncated cone, and the circumferential concrete is expanded into a concrete flat plate, and the equivalent angle between the concrete crack caused by the punching and the branch pipe, that is, the punching angle, is calculated according to the three-parameter criterion of double shear stress; The punching shear strength under the axial symmetry of the circular load is calculated according to the obtained punching shear angle, thus indicating the ultimate bearing capacity of concrete; According to the obtained ultimate bearing capacity of the steel tube corresponding to the hollow steel tube concrete T-node, the ultimate bearing capacity of the hollow steel tube concrete T-node is obtained in combination with the ultimate bearing capacity of the concrete. The hollow steel tube concrete T-node includes a main pipe, a branch pipe and a stiffening rib. The cross-section of the main pipe is circular, the branch pipe and the main pipe are fixed in a T shape, and the stiffening rib is used to strengthen the connection between the main pipe and the branch pipe.

2. The method for calculating the bearing capacity of a circular steel tube thin-wall hollow concrete T-node according to claim 1 is characterized in that: The calculation of the equivalent angle between the concrete crack and the branch pipe caused by punching, i.e., the punching angle, according to the three-parameter criterion of double shear stress includes: The punching shear failure mode of concrete slab is equivalent to the ideal rigid-plastic failure mode, and the punching shear strength of concrete is analyzed according to the double shear stress three-parameter criterion. If the punching strength meets the double shear stress three-parameter criterion, the material is considered to be destroyed, thus obtaining the relationship between the coefficient related to the material strength in the double shear stress three-parameter criterion and the effective uniaxial tensile strength, uniaxial compressive strength and biaxial isostatic strength; When the destruction cone is symmetrical about the branch axis, the corresponding double shear stress three-parameter criterion expression is obtained, and the ultimate stress circle envelope is obtained according to the annular stress in the double shear stress three-parameter criterion, thereby determining the punching angle.

3. The method for calculating the bearing capacity of a circular steel tube thin-wall hollow concrete T-node according to claim 2 is characterized in that: The relationship between the coefficient related to material strength and the effective uniaxial tensile strength, uniaxial compressive strength and biaxial isostatic strength in the three-parameter criterion of double shear stress is obtained, including: When different normal stress influence coefficients are taken, the double shear stress three-parameter criterion can be obtained: In the formula, , , It is a coefficient related to material strength and is determined by material property tests; If one of the formulas 1 and 2 is satisfied, it means that the steel pipe and concrete materials are damaged; Assuming that concrete is an ideal rigid-plastic material, its effective uniaxial tensile strength, uniaxial compressive strength and biaxial isostatic strength are , and , according to Kupfer test data: ,make ,but: The cohesion of concrete is obtained from the punching strength under the axisymmetric condition of circular load, and then the ultimate bearing capacity of concrete is obtained.

4. The method for calculating the bearing capacity of a circular steel tube thin-wall hollow concrete T-node according to claim 3 is characterized in that: When the destruction cone is symmetrical about the branch pipe axis, the corresponding double shear stress three-parameter criterion expression is obtained, including: When the destruction cone is symmetrical about the branch axis, the hoop stress is , since the displacement field is axisymmetric, that is ; Assuming that the plastic deformation is small and the concrete volume is incompressible, the following is obtained from the plastic deformation theory: Substituting Formula 3 into Formula 1 and Formula 2, we obtain the three-parameter criterion for double shear stress in the axisymmetric case: in: .

5. The method for calculating the bearing capacity of a circular steel tube thin-wall hollow concrete T-node according to claim 4 is characterized in that: The method of obtaining the limit stress circle envelope according to the hoop stress in the double shear stress three-parameter criterion, thereby determining the punching angle, includes: A point M is set on the punching surface, which is a point on the limit stress circle equation G. The normal stress and shear stress of point M on the punching surface are recorded as and ; Then when The limit stress circle equation G is: Because the equation F and equation G is tangent at point M, equation and equation G are tangent at point M, then equation F is tangent to equation G and The same as equation G at point M ; where equation F refers to equation 1; equation Refers to Formula 2; From formula 4, formula 5, and formula 6, we get: Combining Formula 7 and Formula 9, we can get: Combining Formula 8 and Formula 9, we can get: Combining Formula 4 and Formula 10, we can get: Substituting Equation 12 into Equation 6, we obtain the equation for the ultimate stress circle envelope based on Equation F: in: Combining Formula 5 and Formula 11, we can get: Substituting Equation 14 into Equation 6, we obtain the equation of the ultimate stress circle envelope based on F: in: make When ;when hour, , which shows and Intersect, that is, the actual limit stress circle envelope is and The enclosing polyline; when hour, , , which means that the actual limit stress circle envelope is ; When the ultimate stress circle envelope of the concrete punching surface is Sometimes: Then, according to formula 17, the corresponding punching angle is obtained: .

6. The method for calculating the bearing capacity of a circular steel tube thin-wall hollow concrete T-node according to claim 5 is characterized in that: The punching shear strength under the axial symmetry of the circular load is calculated according to the obtained punching shear angle, thereby indicating the ultimate bearing capacity of concrete, including: The area increment of the annular fracture surface caused by punching is: According to the plastic upper limit theory and related flow laws, the internal work and external work are equal and we get: Where, for the punching strength under the axisymmetric circular load, the cohesion of concrete is expressed as , After further arrangement, the ultimate bearing capacity of concrete is obtained: in, is the tensile stress of concrete; is the shear force, is the concrete diameter at the branch pipe, is the thickness of the concrete slab after unfolding, x is the displacement along the punching direction.

7. The method for calculating the bearing capacity of a circular steel tube thin-wall hollow concrete T-joint according to claim 6, characterized in that: The method of obtaining the ultimate bearing capacity of the hollow steel tube concrete T-node based on the obtained ultimate bearing capacity of the steel tube corresponding to the hollow steel tube T-node and combining it with the ultimate bearing capacity of the concrete includes: The ultimate bearing capacity of the hollow steel tube concrete T-node is calculated by the ultimate bearing capacity of the steel tube corresponding to the hollow steel tube T-node. and the ultimate bearing capacity of concrete Specifically: in, It is determined according to the ratio of the cross-sectional area of ​​the stiffening rib on the hollow steel pipe T-node to the branch pipe area.

8. A bearing capacity calculation system for circular steel tube thin-wall hollow concrete T-joints, characterized in that: The system includes: a model building system for building a concrete punching model corresponding to the destruction of a hollow steel tube concrete T-type node; the concrete punching model meets the following conditions: it is assumed that the main pipe of the circular steel tube thin-wall hollow concrete T-type node is a structural system composed of two elements, steel tube and concrete; when subjected to punching destruction, it is assumed that the destruction results of the concrete in the longitudinal direction and the circumferential direction occur simultaneously; it is assumed that the punching surface formed after the hollow steel tube concrete is destroyed by the lateral bearing force is a smooth curved surface; it is assumed that the concrete cone formed by the punching is round at the top and elliptical at the bottom; The punching angle calculation module is used to convert the concrete cone formed by the punching into a truncated cone, and at the same time, expand the annular concrete into a concrete flat plate for calculation, and calculate the equivalent angle between the concrete crack caused by the punching and the branch pipe according to the double shear stress three-parameter criterion, that is, the punching angle; The concrete ultimate bearing capacity calculation module is used to calculate the shear strength under the axial symmetry of the circular load according to the obtained shear angle, thereby indicating the ultimate bearing capacity of the concrete; The ultimate bearing capacity calculation module of the hollow steel tube concrete T-node is used to obtain the ultimate bearing capacity of the hollow steel tube concrete T-node according to the ultimate bearing capacity of the steel tube corresponding to the hollow steel tube concrete T-node and the ultimate bearing capacity of the concrete. The hollow steel tube concrete T-node includes a main pipe, a branch pipe and a stiffening rib. The cross-section of the main pipe is circular, the branch pipe and the main pipe are fixed in a T shape, and the stiffening rib is used to strengthen the connection between the main pipe and the branch pipe.

9. The bearing capacity calculation system of circular steel tube thin-wall hollow concrete T-node according to claim 8 is characterized in that: The punching angle calculation module includes: Punching shear strength analysis unit, used to convert the punching shear failure mode of concrete slab into an ideal rigid-plastic failure mode, and analyze the punching shear strength of concrete according to the double shear stress three-parameter criterion; A relationship obtaining unit is used to determine that when the punching strength meets the double shear stress three-parameter criterion, the material is regarded as being destroyed, thereby obtaining the relationship between the coefficient related to the material strength in the double shear stress three-parameter criterion and the effective uniaxial tensile strength, uniaxial compressive strength and biaxial isostatic strength; The punching angle calculation unit is used to obtain the corresponding double shear stress three-parameter criterion representation when the destruction cone is symmetrical about the branch axis, and obtain the ultimate stress circle envelope according to the annular stress in the double shear stress three-parameter criterion, so as to determine the punching angle.

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