Design method of large-diameter concrete filled steel tubular column with built-in prefabricated core column

Abstract

The invention belongs to the technical field of steel pipe concrete, and discloses a design method of a large-diameter steel pipe concrete column with a built-in prefabricated core column, the large-diameter steel pipe concrete column comprises a steel pipe and a core column which are coaxial, the core column is a prefabricated concrete column, and a filling layer is located between the steel pipe and the core column; the reasonable contribution of the core column in the overall bearing capacity of the large-diameter concrete filled steel tubular column is ensured by designing prefabrication ratio checking calculation, then the rigidity performance of a component is verified from the overall level of a building through equivalent rigidity checking calculation, the supporting capacity of the component is ensured, all internal forces are output, and finally, all the internal forces are checked calculation, so that the overall bearing capacity of the large-diameter concrete filled steel tubular column is ensured. And a closed-loop iterative optimization mechanism of parameters of the core column, the steel pipe and the filling layer is formed, so that the core column, the steel pipe and the filling layer can be integrally matched and stably stressed, and the reliability and safety of components are guaranteed. The core column adopts the precast concrete column, so that the construction period can be shortened compared with a scheme of casting the core column on site, and the cost can be saved compared with a scheme of using a solid steel column.

Description

Technical Field

[0001] This invention belongs to the field of steel-concrete composite technology, specifically relating to a design method for large-diameter steel-concrete composite columns with built-in precast core columns. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Concrete-filled steel tubular (CFST) columns are widely used in long-span or super high-rise buildings due to their excellent load-bearing performance. In super high-rise buildings, CFST columns can reach heights of 40–60 m (without intermediate beams or slabs for connection) and diameters exceeding 3 m. To address the technical challenge of concrete shrinkage within circular CFST columns with diameters greater than 2 m, existing technologies compress the shrinkage space of the cast-in-place concrete within the column by first constructing a core column or installing a solid steel column inside the circular CFST column.

[0004] Due to the considerable height of concrete-filled steel tubular (CFST) columns in super high-rise buildings, construction must be carried out in sections. Constructing the core column first, followed by the CFST column, leads to extended construction time and difficulties in positioning and connecting the longitudinal reinforcement of the core column's steel cage. Conversely, using solid steel columns results in high material costs because steel is more expensive than concrete. Furthermore, since the core column and CFST column are not cast integrally, their stress distribution differs. Therefore, designing and verifying the parameters of both the core column and CFST column to ensure overall structural stability is a critical technical challenge that needs to be addressed. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a design method for large-diameter steel-concrete composite columns with built-in precast core columns. By using built-in precast core columns, the technical problems of long construction period and high cost in the prior art are solved. At the same time, by verifying the precast ratio, equivalent stiffness, compressive bearing capacity, shear bearing capacity, local compressive bearing capacity, and axial compression ratio, the parameters of the core column and the steel-concrete composite column are designed to ensure that the two can be stably matched.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A design method for a large-diameter steel tube concrete column with an embedded precast core column is provided. The large-diameter steel tube concrete column includes a coaxial steel tube and a core column, the core column being a precast concrete column, and the filling layer being located between the steel tube and the core column. The design methodology includes the following steps: S1. Pre-set the steel grade and wall thickness of the steel pipe, the concrete grade of the filling layer and the core column; and set the cross-sectional area of ​​the core column. and the cross-sectional area of ​​the filling layer ; Verification of prefabrication ratio ; ; ; The value range is 0.2-0.4; In the formula: The compressive bearing capacity of the core column concrete; The concrete compressive bearing capacity of the component; This is the design value of the concrete compressive strength of the core column; This refers to the design value of the concrete compressive strength of the infill layer; S2. If the prefabrication ratio calculation result is within the range, then perform the equivalent stiffness calculation. S3. Input the equivalent stiffness calculation results and the parameters of the steel pipe, filling layer, and core column determined in S1 into the overall building model where the component is located to calculate the axial pressure of the component. and axial tensile force Bending moment lateral shear force Localized compressive load ; S4. Verify the data obtained in S3. The verification includes verification of compressive bearing capacity, shear bearing capacity, local compressive bearing capacity, and axial compression ratio. If a calculation fails, return to S1 to adjust the relevant parameters, such as the concrete grade of the filling layer or core column, the cross-sectional area of ​​the core column, the steel grade of the steel pipe, and the wall thickness of the steel pipe.

[0007] Preferably, the equivalent stiffness calculation includes the overall axial compression stiffness. Overall bending stiffness Overall shear stiffness Verification is performed, and the verification formula is as follows: ; ; ; In the formula: These are the elastic moduli of the steel pipe, core column concrete, and filling layer concrete, respectively. These are the shear moduli of the steel pipe, core column concrete, and filling layer concrete, respectively. These are the moments of inertia of the sections of the steel pipe, core concrete, and filling concrete, respectively.

[0008] Preferably, the compressive bearing capacity verification is divided into the bearing capacity verification of compression-bending members and the bearing capacity verification of tension-bending members. The bearing capacity verification of compression-bending members is performed under long-term and short-term design conditions. ; during earthquake design conditions ; in, ; + ; or ; In the formula: N is the design value of axial compressive bearing capacity; N0 is the design value of compressive bearing capacity of the axially compressed short column; This refers to the seismic adjustment coefficient for the bearing capacity of structural members. The bearing capacity reduction factor is used to account for the effect of slenderness ratio; The bearing capacity reduction factor is used to account for the effect of eccentricity; For the hoop specifications; A coefficient related to the concrete strength grade; The core strength reduction factor can be taken as 0.9~1.0; This refers to the design strength value of the reinforcing steel bars inside the core column; This represents the cross-sectional area of ​​the steel reinforcement inside the core column.

[0009] Preferred, hoop index In the formula: This is the design strength value for the steel pipe; when , + ; when , .

[0010] Preferably, the load-bearing capacity verification of tension-bending members should meet the following requirements: ; ; ; In the formula: This is the design value of the flexural bearing capacity of the component; This is the design value of the axial tensile bearing capacity of the component; The radius of the concrete cross-section inside the steel pipe.

[0011] Preferably, shear capacity verification is performed under long-term and short-term design conditions. ; during earthquake design conditions ; in, ; ; In the formula: This is the design value for transverse shear capacity; Shear span, which is the distance from the point of application of the lateral concentrated load to the edge of the support or node; The outer diameter of the steel-concrete composite column; To be compatible with transverse shear force The corresponding design value for axial pressure is zero when it is tensile.

[0012] Preferably, the local compressive bearing capacity verification satisfies: ; There are three calculation scenarios, namely: ≤ or ≤ ≤ or ≥ ; in, This represents the design value for local compressive bearing capacity. The base area is calculated for localized compression. This refers to the localized area of ​​the concrete subjected to pressure. The total cross-sectional area of ​​the concrete portion of the component is, i.e. The total value.

[0013] Preferred, ≤ : when , ; when , ; ≥ : ; when .

[0014] Preferred, ≤ ≤ It still exists at that time or The working conditions when

[0015] ; ; : ; ; Preferably, axial compression ratio The verification should be performed using the following formula: ; ≤[ ]; In the formula: [ [This refers to the standard limit.]

[0016] Compared with the prior art, the advantages and positive effects of this invention are: The core column of this invention uses a precast concrete column, which saves construction time compared to the on-site casting method and reduces costs compared to the use of solid steel columns. The design method of this invention ensures the reasonable contribution of the core column to the overall load-bearing capacity of the component through precast ratio calculation. Then, it verifies the stiffness performance of the component from the overall building level through equivalent stiffness calculation, ensuring its supporting capacity and outputting various internal forces. Finally, by calculating these internal forces and using a closed-loop iterative optimization mechanism for the parameters of the core column, steel pipe, and infill layer, it ensures that the three components can work together stably under stress, guaranteeing the reliability and safety of the component. Attached Figure Description

[0017] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] Figure 1 This is a top view of a large-diameter steel-tube concrete column with an embedded precast core column, according to an embodiment of the present invention. Figure 2 When the core post in an embodiment of the present invention is a circular post, ≤ ≤ and Top view; Figure 3 When the core pillar of this embodiment of the invention is a rectangular pillar, ≤ ≤ and Top view; In the picture: 1. Steel pipe; 2. Core column; 21. Shear groove; 3. Filling layer. Detailed Implementation

[0019] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0020] The present invention will now be described in detail with reference to the accompanying drawings. This embodiment discloses a design method for a large-diameter steel-concrete composite column with an embedded precast core column, such as... Figure 1 As shown, the large-diameter steel-concrete composite column (hereinafter referred to as the "component") includes a coaxial steel pipe 1 and a core column 2. The core column 2 is a precast concrete column, and the infill layer 3 is located between the steel pipe 1 and the core column 2. The core columns are precast concrete columns, and the core columns are connected by inserting core column reinforcing bars into sleeves and then welding end plates. This method saves construction time compared to casting core columns on-site and saves costs compared to using solid steel columns. In this embodiment, as... Figure 2 , Figure 3 As shown, the cross-sectional shape of the core column 2 can be circular or rectangular.

[0021] The design method for large-diameter steel-concrete composite columns (i.e., structural members) specifically includes the following steps: S1. Determine the parameter information of steel pipe 1, core column 2, and filling layer 3; The grade and wall thickness of steel pipe 1, the grade of concrete for infill layer 3, and the grade of concrete for core column 2 are pre-set; due to the cross-sectional area of ​​the components... The area of ​​the core column 2 is fixed (i.e., the area of ​​steel pipe 1), so the cross-sectional area of ​​the core column 2 is set. Based on the wall thickness of steel pipe 1 and the cross-sectional area of ​​core column 2 The cross-sectional area of ​​filling layer 3 can be calculated. ; Next, the prefabrication ratio n is verified: ; ; ; In the formula: The prefabrication ratio ranges from 0.2 to 0.4. The concrete compressive bearing capacity of core column 2; The concrete compressive bearing capacity of the component; The design value of the concrete compressive strength of core column 2 is determined based on the selected concrete grade of core column 2; The design value of the concrete compressive strength of fill layer 3 is determined based on the selected concrete grade of fill layer 3.

[0022] It should be noted that, in order to enhance the shear resistance of the core pillar 2 and the filler layer 3, such as... Figure 1 As shown, a plurality of shear-resistant grooves 21 are evenly arranged around the core post 2. In this embodiment, the cross-sectional area of ​​the core post 2 is... Take the area at the minimum cross section of the shear groove 21 of the core column 2.

[0023] It should be noted that in this embodiment, the prefabrication ratio n is used to measure the load-bearing contribution of the core column 2 in the overall structure of the component, and to ensure a reasonable mix ratio between the core column 2 and the infill layer 3 concrete to achieve synergistic work. The grade and wall thickness of the steel pipe 1, the grade of the infill layer 3 concrete, and the grade of the core column 2 concrete all meet the specifications. In addition, when determining the parameter information of the core column 2 in S1, the reinforcement parameters of the core column 2 are also determined.

[0024] S2. If the calculated result of n in S1 is within the range of 0.2-0.4, then perform the equivalent stiffness calculation.

[0025] S3. Input the equivalent stiffness calculation results from S2, along with the parameter information for steel pipe 1, core column 2, and filling layer 3 determined in S1, into the overall building model containing the component. Simulate the overall stress and calculate the axial pressure of the large-diameter steel-concrete composite column. and axial tensile force Bending moment lateral shear force Localized compressive load .

[0026] In this embodiment, axial pressure and axial tensile force Bending moment lateral shear force Localized compressive load These are the main internal forces acting on the components. These internal forces are calculated through the overall building model and are an important basis for subsequent load-bearing capacity verification and stability analysis.

[0027] S4. Verify the data obtained in S3. The verification includes verification of compressive bearing capacity, shear bearing capacity, local compressive bearing capacity, and axial compression ratio. If any one of the verifications fails, return to S1 to adjust the relevant parameters, such as the concrete grade of the filling layer 3 or core column 2, the cross-sectional area of ​​core column 2, and the steel grade or wall thickness of the steel pipe.

[0028] It should be noted that the calculation of compressive bearing capacity, shear bearing capacity, local compressive bearing capacity, and axial compression ratio is used to evaluate the safety performance of the component under various loads, and to ensure that the column can meet the stress requirements under complex stress conditions such as axial pressure, shear force, and local compression.

[0029] It should also be noted that if the S4 verification fails, steps S1 to S4 will be repeated until all verifications pass. This iterative optimization process ensures that the core column 2, steel pipe 1, and filling layer 3 can work closely together to share the load and guarantee the stress stability and safety of the overall structure.

[0030] In step S2, the equivalent stiffness calculation includes the combined axial compression stiffness of the components. Calculate and combine bending stiffness Calculate and combine shear stiffness The specific calculation formula is as follows: ; ; ; In the formula: , , These are the combined axial compression stiffness, combined bending stiffness, and combined shear stiffness of the components, respectively. These are the elastic moduli of steel pipe 1, core column 2 concrete, and filling layer 3 concrete, respectively. These are the shear moduli of steel pipe 1, core column 2 concrete, and filling layer 3 concrete, respectively. Let be the moment of inertia of the sections of steel pipe 1, core column 2 concrete, and filling layer 3 concrete.

[0031] It should be noted that the elastic modulus and shear modulus are inherent properties of the material, primarily depending on the material's composition and strength grade (steel pipe or concrete). When determining the grade of steel pipe 1, the concrete grade of core column 2, and the concrete grade of infill layer 3 in S1, the elastic modulus and shear modulus of these components can be directly obtained. The moment of inertia is a geometric property of the cross-section, describing its ability to resist bending deformation. It depends only on the shape and size of the cross-section and is obtained based on the cross-sectional dimensions of steel pipe 1, core column 2, and infill layer 3 as defined in S1. After inputting the equivalent stiffness calculation results into the model, the deformation results of the component under simulated loads can be obtained.

[0032] Overall axial compression stiffness It measures a component's ability to resist axial deformation under axial pressure, reflecting the component's compressive deformation characteristics under axial load. The calculation involves superimposing the axial stiffness (elastic modulus multiplied by cross-sectional area) of the steel pipe 1, the core column 2 concrete, and the infill layer 3 concrete. Overall bending stiffness. It measures a structural member's ability to resist bending deformation under bending moment, reflecting its bending deformation resistance characteristics under bending load. The calculation involves superimposing the bending stiffness (elastic modulus multiplied by the moment of inertia of the section) of the steel pipe 1, the core column 2 concrete, and the infill layer 3 concrete. Overall shear stiffness. It measures the ability of a component to resist shear deformation under shear force, reflecting the shear deformation resistance characteristics of the component under shear load. The calculation is to superimpose the shear stiffness (shear modulus multiplied by cross-sectional area) of the steel pipe, core column concrete and filling layer concrete.

[0033] In step S4, the compressive bearing capacity verification is divided into two situations: the bearing capacity of compression-bending members and the bearing capacity of tension-bending members. The bearing capacity of compression-bending members is calculated under long-term and short-term design conditions. ; during earthquake design conditions ; in, ; + ; or ; In the formula: This is the design value for axial compressive bearing capacity; This represents the design value of the compressive bearing capacity of an axially compressed short column; The seismic adjustment coefficient for the bearing capacity of the component is taken according to the "Technical Specification for Concrete-Concrete Composite Steel Tube Structures"; The bearing capacity reduction factor, which takes into account the effect of slenderness ratio, is taken according to the "Technical Specification for Concrete-Concrete Composite Steel Tube Structures"; The bearing capacity reduction factor, which takes into account the effect of eccentricity, is taken according to the "Technical Specification for Concrete-Concrete Composite Steel Tube Structures"; The hoop specifications for the component; The coefficient is related to the concrete strength grade and is taken according to the "Technical Specification for Concrete-Concrete Composite Structures". The strength reduction factor for core post 2 can be taken as 0.9~1.0; This refers to the design strength value of the reinforcing steel bars inside the core column; The cross-sectional area of ​​the steel reinforcement in core column 2.

[0034] It should be noted that compression bending involves the simultaneous application of pressure and bending moment, while tension bending involves the simultaneous application of tension and bending moment. It is a basic criterion for verifying bearing capacity, representing the axial pressure borne by a component. It should not exceed its design axial compressive bearing capacity. To ensure sufficient safety reserves. This refers to earthquake design conditions, for Apply an additional adjustment factor This is to reflect the special nature of seismic action and the higher requirements for structural performance.

[0035] In this embodiment, The two calculation formulas take into account the synergistic effect of steel pipe 1, infill layer 3 concrete, core column 2 concrete, and their internal reinforcement, and use the hoop index. This reflects the restraining effect of steel pipe 1 on the concrete.

[0036] In this embodiment, the clamp index In the formula: This is the design strength value for steel pipe 1, which is related to the grade and thickness of steel pipe 1.

[0037] Hoop Index It is a key parameter for measuring the strength of the confinement effect of steel pipe 1 on the internal concrete (including the core column 2 concrete and the filling layer 3 concrete), and it comprehensively reflects the design strength value of steel pipe 1. steel pipe cross-sectional area Design value of compressive strength of core column 2 concrete Core cross-sectional area and the design value of the compressive strength of the 3rd layer concrete. , cross-sectional area of ​​the filling layer The relative relationship between them.

[0038] when , + This formula applies when the confinement effect of the steel pipe 1 on the internal concrete is relatively weak. In this case, the confinement effect of the steel pipe 1 is mainly reflected by increasing the compressive strength of the concrete, and this increase is related to the confinement index. The relationship is linear or approximately linear. This calculation method considers the bearing capacity of the infill layer 3 concrete and the bearing capacity of the core column 2 concrete (it also considers the potential strength loss due to the prefabrication of the core column 2, hence the use of a strength reduction factor). The bearing capacity of the reinforcing bars inside the core column 2 and the concrete strength gain brought about by the hoop effect of the steel pipe 1.

[0039] when , This formula applies to situations where the steel pipe exerts a strong constraint on the internal concrete. In such cases, once the confinement effect reaches a certain level, its strengthening effect on the concrete strength may no longer be a simple linear relationship, but rather exhibit a more significant nonlinear strengthening. This calculation method also considers the bearing capacity of the infill layer 3 concrete, the core column 2 concrete, and the reinforcing steel within the core column 2, but it does not account for the confinement effect. Different expressions were used to describe the enhancing effect of concrete under strong constraints, in order to more accurately reflect the concrete performance under strong constraints.

[0040] In this embodiment, when designing large-diameter steel-concrete composite columns (i.e., components), the constriction effect of the steel tube 1 on the internal concrete can be considered. By comparing the results, the design value of the compressive bearing capacity of the axially compressed short column can be dynamically selected. The calculation formula makes... The calculation is no longer a single, universal formula, but can accurately reflect the actual stress performance of components under different hoop effects.

[0041] In this embodiment, the load-bearing capacity calculation of the tension-bending member should meet the following requirements: In the formula: This is the design value of the flexural bearing capacity of the component; This represents the design value of the axial tensile bearing capacity of the member. This inequality is the core criterion for verifying the bearing capacity of tension-bending members, indicating the member's bearing capacity under axial tensile force. and bending moment The combined effect of the combined action should not exceed its ultimate bearing capacity.

[0042] In this embodiment This formula is used to calculate the design value of the axial bearing capacity of a component, where, Let be the cross-sectional area of ​​the steel pipe. This is the design strength value for the steel pipe; Let be the cross-sectional area of ​​the reinforcing bars inside core column 2. This represents the design strength value of the reinforcing steel bars inside core column 2. The axial tensile bearing capacity is mainly provided by the steel pipe 1 and the reinforcing steel bars inside core column 2.

[0043] In this embodiment In the formula: The radius of the cross-section of the concrete inside steel pipe 1 (i.e., the concrete of the infill layer and the core column); This is the design value of the compressive bearing capacity of a short column under axial compression. This formula is used to calculate the design value of the flexural bearing capacity of a large-diameter concrete-filled steel tube column.

[0044] If the verification results do not meet the inequality, it indicates that the component has a safety hazard under combined tension and bending. It is necessary to return to design step S1 to adjust the parameters of steel pipe 1, infill layer 3, or core column 2. For example, this could involve increasing the steel pipe wall thickness, increasing the reinforcement ratio, or adjusting the cross-sectional area of ​​the core column to improve the component's load-bearing capacity until the design requirements are met. This iterative design process ensures the structural safety and reliability of large-diameter steel-concrete composite columns with built-in precast core columns under complex load conditions.

[0045] In this embodiment, when performing shear capacity verification, two working conditions must be considered: long-term and short-term design conditions. ; during earthquake design conditions ; in, ; ; In the formula: This is the design value for transverse shear capacity; For shear spans, the distance (mm) from the point of application of the lateral concentrated load to the edge of the support or node; The outer diameter (mm) of the concrete-filled steel tube column; This is the design value of the axial compressive force corresponding to the transverse shear force V; it is zero when it is a tensile force.

[0046] It should be noted that the shear capacity verification is an assessment of the member's ability to resist shear failure. After the axial pressure N, bending moment M, and transverse shear force V of the member are calculated in step S3, the material strength of the core column 2 concrete and the infill layer 3 concrete is considered. ), geometric dimensions ( , , , ) and hoop specifications Calculate the design value of the transverse shear capacity of the member. The transverse shear force calculated by S3 and (or The calculation is compared to determine whether the shear capacity of the component meets the design requirements. If the calculation fails, the process returns to step S1 to adjust the concrete grade of the infill layer 3 or core column 2, or the cross-sectional area of ​​core column 2, or the steel grade and wall thickness of the steel pipe, thereby optimizing the shear performance of the column. This iterative design process ensures that the component has sufficient safety reserve when subjected to transverse shear force, avoiding structural failure due to shear failure.

[0047] In this embodiment, the local compressive bearing capacity verification is used to evaluate the ability of a large-diameter concrete-filled steel tube column to resist crushing in a localized area when subjected to concentrated loads. This verification is performed by comparing localized compressive loads. Design value of local compressive bearing capacity The local compressive bearing capacity verification must meet the following requirements: .

[0048] It should be noted that, since the cross-sectional dimensions of large-diameter steel-concrete composite columns are usually much larger than the local compressive area of ​​the load, performing local compressive strength calculations according to the "Technical Specification for Steel-Concrete Composite Structures" would result in distorted results and pose certain safety hazards. Therefore, based on the principle of local compressive bearing capacity calculation, the design value of the local compressive bearing capacity of the large-diameter steel-concrete composite column with embedded precast core column 2 is... Multiple calculation scenarios need to be considered.

[0049] like Figure 2 , Figure 3 As shown, the base area for localized compression calculation is... This refers to the actual contact area of ​​the load acting on the surface of a large-diameter steel-concrete composite column, which can be determined according to the "Code for Design of Concrete Structures"; the local compressive area of ​​the concrete is... This refers to the effective area of ​​concrete that actually participates in resisting pressure under load. It may be larger than this due to load diffusion effects. This may also vary depending on the limitations of the steel tube or core column. The total cross-sectional area of ​​the concrete portion of a large-diameter steel-tube concrete column is... ,Right now The total value represents the total effective bearing area of ​​all concrete inside the column.

[0050] In this embodiment, The design values ​​are calculated in three ways: ≤ or ≤ ≤ or ≥ .

[0051] Understandably, when When the smaller amount mainly acts on the core post 2 region, The calculations will focus on the strength and local load-bearing capacity of the core column; when When the core pillar 2 and the filling layer 3 are relatively large, The calculations will consider the synergistic effect of both and the load diffusion effect. This case-by-case calculation ensures... The value of can accurately reflect the actual local stress state and material response.

[0052] The base area calculated under localized pressure ≤ At that time, the local pressure mainly acts on the core column 2, and the restraining effect of the steel pipe 1 on the internal concrete is considered simultaneously. The results obtained in the previous calculation steps are as follows. , ;when , .

[0053] The base area in the localized compression calculation ≥ At this time, the local pressure covers the entire concrete cross-section of the column, and it is necessary to determine the appropriate action based on the situation. Does it exceed the cross-sectional area of ​​core column 2? Design values ​​of compressive bearing capacity of axially compressed short columns, respectively The design value of local compressive bearing capacity is calculated by combining the strength contribution ratio of the core column 2 and the filling layer 3 concrete. . Specifically, ;when .

[0054] This case-by-case calculation method allows for the selection of the most suitable calculation model based on the actual stress area and material properties when verifying the local compressive bearing capacity of large-diameter steel-concrete composite columns, thereby ensuring the accuracy and reliability of the verification results.

[0055] And in ≤ ≤ This means that the localized load area partially covers the core column 2 and partially covers the filling layer 3. In this case, it is necessary to accurately distinguish the localized pressure area. Cross-sectional area of ​​core column 2 The relationship, that is, in ≤ ≤ At that time, it still existed or The operating conditions.

[0056] when , indicating the localized area under pressure The concrete of core column 2 is located entirely inside core column 2 or coincides with the boundary of core column 2. The contribution is primary, but the infill concrete... exist Contributions within the scope should also be considered.

[0057] ; ; , indicating the localized area under pressure It extends beyond the core column 2 and into the filling layer 3, at which point the combined effect of the core column 2 concrete and the filling layer 3 concrete becomes more significant.

[0058] ; .

[0059] These formulas can fully consider the different contributions and interactions of the core column 2 concrete and the filling layer 3 concrete in the local compression area, as well as the constraint effect of the steel tube 1 on the internal concrete, so that the local compressive bearing capacity verification can more realistically reflect the actual stress state of the large-diameter steel tube concrete column.

[0060] In this embodiment, axial compression ratio The axial compression ratio is an important means of evaluating the stability and load-bearing capacity of a component under axial pressure. It primarily determines whether the cross-section of the component can safely resist the axial pressure N, and ensures that the component will not become unstable or fail due to excessive axial pressure. The verification should be performed using the following formula: ; ≤[ ]; In the formula: [ [The value is a standard limit and is taken according to the "Technical Specification for Concrete-Concrete Composite Steel Tube Structures".]

[0061] It is understandable that N is the axial pressure borne by the large-diameter steel-concrete composite column. This axial pressure N is calculated by inputting the parameters of the steel pipe, filling layer and core column determined in S1 into the overall building model where the large-diameter steel-concrete composite column is located. It is the maximum axial pressure borne by the component determined according to the load combination.

[0062] This formula calculates the ratio of the axial pressure N borne by a large-diameter steel-concrete composite column to the compressive bearing capacity contributions of the steel tube, the infill concrete, and the combined compressive bearing capacity contributions of the core concrete and the reinforcing steel within the core column. It not only considers the direct load-bearing effects of the steel tube and the infill concrete but also corrects for the combined load-bearing capacity of the core concrete and reinforcing steel through a reduction factor of 0.9.

[0063] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A design method of a large-diameter concrete-filled steel tubular column with a built-in precast core column, characterized by, The large-diameter steel pipe concrete column comprises a steel pipe and a core column coaxially arranged, the core column is a prefabricated concrete column, and a filling layer is arranged between the steel pipe and the core column; The design method comprises the following steps: S1, presetting the steel grade, wall thickness of the steel pipe, the filling layer and the concrete grade of the core column; and setting the cross-sectional area of the core column and calculating the cross-sectional area of the filling layer ; Check the precast ratio ; ; ; The value range is 0.2-0.4; In the formulae: is the compressive load bearing capacity of the core column; is the compressive load bearing capacity of the component; is the design value of the compressive strength of the concrete of the core column; is the design value of the compressive strength of the concrete of the filling layer; S2, if the prefabricated ratio calculation result meets the value range, equivalent stiffness calculation is performed; S3, input the equivalent stiffness calculation results and the parameters of the steel pipe, filling layer and core column determined in S1 into the overall building model where the component is located to calculate the axial compression of the component and axial tension , bending moment , lateral shear force , local compression load ; S4, checking calculation is performed on the data obtained in S3, and the checking calculation comprises checking calculation of compression bearing capacity, checking calculation of shear bearing capacity, checking calculation of local compression bearing capacity and checking calculation of axial compression ratio; If one checking calculation fails, the relevant parameters are adjusted, such as the concrete mark of the filling layer or the core column, the sectional area of the core column, the steel grade of the steel pipe and the wall thickness of the steel pipe.

2. A design method of a large-diameter concrete-filled steel tubular column with a built-in precast core column according to claim 1, characterized in that, The equivalent stiffness calculation includes overall axial compression stiffness , overall bending stiffness , overall shear stiffness The calculation formula is as follows: ； ； ； In the formula: E1, E2, E3 respectively are the elastic modulus of the steel pipe, the core column concrete, and the filling layer concrete; G1, G2, G3 respectively are the shear deformation modulus of the steel pipe, the core column concrete, and the filling layer concrete; I1, I2, I3 respectively are the cross-sectional moment of inertia of the steel pipe, the core column concrete, and the filling layer concrete.

3. A design method of a large-diameter concrete-filled steel tubular column with a built-in precast core column according to claim 1, characterized in that, The compression bearing capacity checking is divided into compression-bending member bearing capacity checking and tension-bending member bearing capacity checking, the compression-bending member bearing capacity checking is under the permanent and transient design condition ; under the earthquake design condition ; wherein ; + ; or ; In the formula: is the design value of axial compression bearing capacity; is the design value of compression bearing capacity of the axial compression short column; is the seismic adjustment coefficient of the bearing capacity of the component; is the bearing capacity reduction coefficient considering the influence of slenderness ratio; is the bearing capacity reduction coefficient considering the influence of eccentricity ratio; is the sleeve index; is the coefficient related to the strength grade of concrete; is the strength reduction coefficient of the core column, which can be taken as 0.9-1.0; is the design value of the strength of the steel bars in the core column; is the sectional area of the reinforcement of the steel bars in the core column.

4. A method of designing a large diameter concrete filled steel tubular column with a built-in precast core column as claimed in claim 3, wherein The cuff indicator ; in which: is the steel pipe strength design value; When , + ; When , .

5. A method of designing a large diameter concrete filled steel tubular column with a built-in precast core column as claimed in claim 3, wherein, The tension-bending member bearing capacity checking shall meet: ; ; ; In the formula: is the design value of flexural capacity of the member; is the design value of axial tensile capacity of the member; is the radius of the concrete cross section in the steel tube.

6. A method of designing a large diameter concrete filled steel tubular column with a built-in precast core column as claimed in claim 1, wherein, The shear capacity check is performed in the permanent, short-term design situation ; in the seismic design situation ; wherein ; ; wherein: is the design value of the transverse shear capacity; is the shear span, i.e. the distance from the point of application of the transverse concentrated load to the edge of the support or node; is the outer diameter of the concrete filled steel tube column; is the design value of the transverse shear force is the corresponding axial compressive force design value, which is taken as zero when it is a tensile force.

7. A method of designing a large diameter concrete filled steel tubular column with a built-in precast core column as claimed in claim 1, wherein The local compression bearing capacity checking satisfies: ; There are three calculation cases, respectively ≤ or ≤ ≤ or ≥ ; wherein, is the local compressive load bearing design value, is the base area for local compressive calculation; is the local compressive area of concrete; is the total sectional area of the concrete part of the member, i.e. is the total value.

8. A method of designing a large diameter concrete filled steel tubular column with a built-in precast core column as claimed in claim 7, wherein, The ≤ : When , ; When , ; The ≥ : ； When .

9. A method of designing a large diameter concrete filled steel tubular column with a built-in precast core column as claimed in claim 7, wherein, The ≤ ≤ There are also Or working conditions, When ； ； ： ； 。 10. The method of designing a large diameter concrete filled steel tubular column with a built-in precast core column as claimed in claim 1, wherein, The shaft pressure ratio The calculation is performed according to the following formula: ； ≤[ ]； In the formula: ] is the specification limit.

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