An externally reinforced concrete-filled steel tube column and its peak bearing capacity calculation method

Abstract

The present invention relates to the field of construction, specifically an externally reinforced steel tube concrete column and a method for calculating the peak bearing capacity. The steel tube concrete column includes a steel tube and a core concrete located inside the steel tube; a UHPC layer is cast on the outer ring of the steel tube, the outer ring cross-section of the UHPC layer is square, and the center line of the UHPC layer coincides with the axis of the steel tube; stirrups located on the outer ring of the steel tube are pre-embedded in the UHPC layer, and longitudinal steel bars are arranged on the inner ring of the stirrups along the vertical direction. The present invention provides an externally reinforced steel tube concrete column. The present invention can reinforce steel tube concrete with an annular void area so that its actual bearing capacity exceeds the original design value level. The present invention also provides a method for calculating the peak bearing capacity of an externally reinforced steel tube concrete column, which can quantitatively evaluate the peak bearing capacity of the reinforced steel tube concrete, providing a theoretical basis for the subsequent use and maintenance of the steel tube concrete.

Description

Technical Field

[0001] The present invention relates to the field of construction, and in particular to an externally reinforced steel tube concrete column and a peak bearing capacity calculation method. Background Art

[0002] Because it fully utilizes the mechanical properties of two different construction materials, steel tube concrete (CFST) boasts convenient construction, strong load-bearing capacity, and strong seismic resistance. It is widely used in large-scale projects such as ultra-high, large-span, and heavy-load projects. However, due to poor concrete material quality, concrete shrinkage, and temperature fluctuations, CFST components that have been used for a long time will develop varying degrees of void defects between the concrete and the steel tube, causing the concrete and steel tube to debond, forming an annular void zone. This significantly reduces mechanical properties such as peak load, initial stiffness, and ductility, affecting the load-bearing performance of the CFST composite structure.

[0003] To ensure the smooth operation of steel tube concrete-filled components with void defects, it is necessary to reinforce them after voids are created between the concrete and the steel tube. Currently, secondary grouting is often used to repair the annular void area inside the steel tube concrete. However, the current method of repairing steel tube concrete through secondary grouting still has the following problems: 1. The void area has a complex shape (such as irregular, narrow, or with air pockets), and the secondary grouting may not be able to completely fill the void area, resulting in local residual voids and affecting the overall density; and if the thermal expansion coefficient and elastic modulus of the secondary grouting material differ significantly from those of the original concrete or steel tube, interfacial stress may be generated due to temperature changes or loads, causing secondary voids or cracking; during secondary grouting, the original interface of the void area may contain oil, rust, or loose particles. If it is not thoroughly cleaned, the bonding strength of the grouting layer and the original structure will be significantly reduced. 2. After secondary grouting repairs, the peak bearing capacity of the repaired concrete-filled steel tube cannot be fully restored to the original design value, and it is impossible to quantitatively evaluate the peak bearing capacity of the repaired concrete-filled steel tube. This leads to the risk of sudden failure of the structure under extreme loads (such as earthquakes and typhoons). Therefore, the above problems need to be solved urgently. Summary of the Invention

[0004] To avoid and overcome the technical problems existing in the prior art, the present invention provides an externally reinforced concrete-filled steel tube column. This method can reinforce concrete-filled steel tubes with annular voids, increasing their actual bearing capacity to exceed the original design value. The present invention also provides a method for calculating the peak bearing capacity of externally reinforced concrete-filled steel tube columns, enabling quantitative assessment of the peak bearing capacity of reinforced concrete-filled steel tubes, providing a theoretical basis for the subsequent use and maintenance of concrete-filled steel tubes.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] An externally reinforced concrete-filled steel tube column comprises a steel tube and a core concrete located within the steel tube; a UHPC layer is cast around the outer ring of the steel tube, the outer ring of the UHPC layer has a square cross-section, and the centerline of the UHPC layer coincides with the axis of the steel tube; stirrups are pre-embedded within the UHPC layer and are located around the outer ring of the steel tube, and longitudinal steel bars are arranged along the inner ring of the stirrups in the vertical direction.

[0007] As a further solution of the present invention: the stirrups are square stirrups, the center lines of the stirrups coincide with the axis of the steel pipe, each corner point and each straight section of the stirrups are tied and fixed with longitudinal steel bars, and the adjacent longitudinal steel bars on the stirrups are arranged at equal spacing.

[0008] A method for calculating the peak bearing capacity of externally reinforced concrete-filled steel tube columns. After reinforcement, the peak bearing capacity of the concrete-filled steel tube columns is :

[0009] ;

[0010] in: represents the peak bearing capacity of the UHPC layer;

[0011] represents the peak bearing capacity of the steel tube concrete column;

[0012] represents the cross-sectional area of ​​the longitudinal reinforcement;

[0013] Indicates the yield strength of the longitudinal reinforcement;

[0014] as well as are fitting coefficients.

[0015] As a further solution of the present invention: the hollowing rate of the steel tube concrete column, the thickness of the UHPC layer and the diameter of the steel tube concrete column are used as design variables, and the fitting calculation is performed. as well as :

[0016] ;

[0017] ;

[0018] in: is the ratio of the thickness of the UHPC layer to the diameter of the concrete-filled steel tube;

[0019] is the void ratio of the concrete-filled steel tube column.

[0020] As a further solution of the present invention:

[0021] ;

[0022] in, is the compressive strength of concrete confined by stirrups;

[0023] is the cross-sectional area of ​​the UHPC layer.

[0024] As a further solution of the present invention:

[0025] ;

[0026] in, is the reduction factor;

[0027] is the cross-sectional area of ​​the steel pipe;

[0028] is the yield strength of the steel pipe;

[0029] is the cross-sectional area of ​​the core concrete;

[0030] is the compressive strength of the core concrete.

[0031] As a further solution of the present invention:

[0032] ;

[0033] ;

[0034] in, is the contact stress between the steel tube and the core concrete;

[0035] is the standard value of the axial compressive strength of the core concrete;

[0036] is the yield strength of the steel pipe;

[0037] is the thickness of the steel pipe;

[0038] is the inner diameter of the steel pipe.

[0039] As a further solution of the present invention: hour, =0.75; when hour, =1.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] 1. The present invention enhances the confinement effect by providing a UHPC layer outside the CFST, and deploys stirrups and longitudinal reinforcement within the UHPC layer. The UHPC layer and the steel tube jointly confine the core concrete, providing stable external confinement even if there are voids inside the steel tube. Compared to the secondary pouring method, external reinforcement of the CFST enables its actual bearing capacity to exceed the original design value, significantly improving the overall stiffness and peak bearing capacity of the CFST column.

[0042] 2. The present invention forms a spatial reinforcement skeleton within the UHPC layer through the coordination of longitudinal reinforcement and stirrups, significantly enhancing the bending and shear resistance of steel tube concrete columns; the outer cross-section of the UHPC layer is square, which is convenient for connection with existing beam-column nodes and is suitable for rapid reinforcement of building and bridge structures.

[0043] 3. Compared with the traditional technical solution of secondary grouting that cannot completely fill the voids, the present invention uses outsourcing UHPC for reinforcement, which is more reliable, avoids repeated repairs, and effectively improves material utilization. At the same time, the high density and impermeability of UHPC can protect the steel pipe from corrosion and extend the service life of the structure. By adjusting the thickness of the UHPC layer and the amount of reinforcement, it can flexibly deal with different degrees of voids in steel tube concrete.

[0044] 4. This invention develops a method for calculating the peak bearing capacity of reinforced concrete-filled steel tube columns. By integrating variables such as void ratio and UHPC layer thickness, this method allows for a precise assessment of the peak bearing capacity of reinforced concrete-filled steel tube columns. This addresses the difficulty in calculating the ultimate bearing capacity of concrete-filled steel tube columns repaired with traditional secondary grouting. During the calculation process, a reduction factor is adjusted based on the void ratio, ensuring reliable and secure results. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a structural schematic diagram of the present invention.

[0046] Figures 2 to 7 Schematic diagram comparing the load-displacement curve of a specimen calculated using the model of the present invention with the load-displacement curve obtained from actual tests on a group of identical specimens.

[0047] Figures 8 to 10 Schematic diagram comparing the load-displacement curve of the specimen calculated by the model of the present invention with the load-displacement curves obtained from actual tests of two groups of identical specimens.

[0048] In the figure: 1. UHPC layer; 2. Stirrups; 3. Longitudinal reinforcement; 4. Steel pipe; 5. Annular void area; 6. Core concrete. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0050] See also Figure 1 In an embodiment of the present invention, an externally reinforced concrete-filled steel tube column and a peak bearing capacity calculation method are provided. The concrete-filled steel tube column includes a steel tube 4 and a core concrete 6 cast within the steel tube 4. After an annular void space 5 is formed between the steel tube 4 and the core concrete 6, the concrete-filled steel tube column is externally reinforced. During external reinforcement of the concrete-filled steel tube column, a UHPC layer 1 is cast around the outer periphery of the steel tube 4. The UHPC layer 1 has a regular quadrangular prism structure, and the centerline of the UHPC layer 1 coincides with the axis of the steel tube 4.

[0051] During pouring, UHPC layer 1 is interspersed with square stirrups 2 at intervals along its height. Longitudinal reinforcement bars 3 are evenly spaced within the inner ring of stirrups 2 and are secured to the stirrups 2 before pouring. In this embodiment, a set of longitudinal reinforcement bars 3 is provided at each of the four corners of the stirrups 2, and a set of longitudinal reinforcement bars 3 is placed in the middle of each of the four straight sections of the stirrups 2, for a total of eight sets of longitudinal reinforcement bars 3, with equal spacing between adjacent sets.

[0052] The peak bearing capacity of the concrete-filled steel tube column is :

[0053] ;

[0054] ;

[0055] ;

[0056] ;

[0057] ;

[0058] ;

[0059] in: represents the peak bearing capacity of the UHPC layer;

[0060] represents the peak bearing capacity of the steel tube concrete column; based on the Poisson's ratio and strain relationship between concrete and steel tube, the critical void ratio is derived as 0.2%. Assuming that the contact stress of the steel tube on the concrete changes linearly with the increase of the void ratio, the peak bearing capacity of the steel tube concrete column is calculated;

[0061] represents the cross-sectional area of ​​the longitudinal reinforcement;

[0062] Indicates the yield strength of the longitudinal reinforcement;

[0063] as well as All are fitting coefficients;

[0064] is the ratio of the thickness of UHPC layer 1 to the diameter of the CFST column;

[0065] is the void ratio of the concrete-filled steel tube column;

[0066] is the compressive strength of concrete confined by stirrup 2;

[0067] is the cross-sectional area of ​​UHPC layer 1;

[0068] is the reduction factor, which is affected by the void ratio;

[0069] when hour, The value is 0.75; when hour, The value is 1;

[0070] is the cross-sectional area of ​​the steel pipe 4;

[0071] is the yield strength of the steel pipe 4, measured in a field test or obtained according to the reference specification;

[0072] is the standard value of the axial compressive strength of the core concrete 6, measured in a field test or obtained according to the reference specification;

[0073] is the cross-sectional area of ​​the core concrete 6;

[0074] is the compressive strength of the steel tube concrete confined by the steel tube 4;

[0075] is the contact stress between the steel tube 4 and the core concrete 6;

[0076] is the thickness of the steel pipe 4;

[0077] is the inner diameter of the steel pipe 4.

[0078] When building the peak bearing capacity calculation formula, first build a finite element model of the steel tube concrete column reinforced with UHPC layer 1;

[0079] When the void ratio of the steel tube concrete material model is less than or equal to 0.2%, the steel tube confined concrete model is used. When the void ratio is greater than 0.2, the unconfined concrete stress-strain curve model is used.

[0080] To verify the model, three types of experiments were conducted: axial compression test on UHPC columns, axial compression test on concrete-filled steel tube columns with void defects, and test on concrete-filled steel tube columns reinforced with UHPC.

[0081] like Figures 2 to 10 As shown in Figure 1, nine specimens of different specifications were selected, and the load-displacement curves of the specimens obtained from the actual test and the model calculation were compared. When the load reaches the peak value, it means that the bearing capacity of the specimen has reached the peak value.

[0082] Figures 2 to 10 Corresponding to the comparative analysis of specimens 1 to 9 respectively.

[0083] by Figure 2 For example, the model is used to build specimen 1 and calculate the load-displacement curve of specimen 1. At the same time, a group of specimens 1 with the same parameters as in the model are made, and actual tests are carried out on specimen 1 to record the load-displacement curve of specimen 1. After comparing the two load-displacement curves, we can get Figure 2 Schematic comparison diagram. Figures 3 to 7 Compare similarly.

[0084] Then Figure 8 For example, the model is used to build specimen 7 and calculate the load-displacement curve of specimen 7. At the same time, two groups of specimens 7 with the same parameters as in the model are made. Actual tests are carried out on the two groups of specimens 7, and the load-displacement curves of the two groups of specimens 7 are recorded. After comparing the three load-displacement curves, we can get Figure 8 Schematic comparison diagram. Figures 9 and 10 Compare similarly.

[0085] exist Figures 2 to 7 In the figure, the solid line represents the load-displacement curve of the specimen obtained by model calculation, and the dotted line represents the load-displacement curve of the specimen obtained by actual test. Figures 2 to 7 In actual testing, only one set of specimens is used for each test.

[0086] exist Figures 8 to 10In the figure, the solid line represents the specimen load-displacement curve obtained by model calculation, and the dotted line and the dashed line represent the specimen load-displacement curves obtained by actual tests on two specimens of the same specifications. Figures 8 to 10 In actual tests, two groups of specimens with the same specifications are used for each test.

[0087] It can be seen that Figures 2 to 10 As shown in the figure, the load-displacement curve of the specimen obtained by the model calculation is highly consistent with the load-displacement curve obtained from the actual test in terms of line shape and peak value.

[0088] According to 7 parameters , compressive strength of core concrete 6 , UHPC concrete strength f co,core , void ratio of steel tube concrete , stirrup spacing S , stirrup diameter d , and the yield strength of the steel pipe , 28 different specimens were designed (the 28 specimens here are independent specimens, not Figures 2 to 10 The peak load capacity of these 28 specimens was calculated using the verified finite element model. , the calculation results are shown in Table 1 below:

[0089] Table 1

[0090] ;

[0091] Select the two most influential ones based on key parameters as well as Fit the correction coefficient and establish the peak bearing capacity calculation formula:

[0092] The designed void ratios are 0%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.6%, 0.8%, 1%, 1.5%, 2%, and 4%, respectively. Combined with the core concrete axial compressive strength of 40 MPa, 50 MPa, and 60 MPa, 36 sets of finite element models were built. Based on the calculation results of the 36 sets of finite element models, the peak bearing capacity of the UHPC was compared with the peak bearing capacity of the steel tube concrete column model with only the UHPC layer but no steel tube concrete column, and 36 sets of finite element models were obtained. Data, data fitting to obtain correction coefficient Calculation method.

[0093] Design void ratio is 0%, 0.1%, 0.2%, 0.6%, 1%, 1.5%, 2%, combined The values ​​are 0.4, 0.5, 0.6, 0.7, and 0.8 respectively. 35 finite element models are built. According to the calculation results of these 35 models, the bearing capacity of the steel tube concrete when the composite component reaches the peak bearing capacity is taken and compared with the bearing capacity of the steel tube concrete when it reaches the peak, and 35 Coefficient results, data fitting to obtain correction coefficients Calculation method.

[0094] Combining the superposition principle, the peak bearing capacity of the composite column structure is divided into UHPC, longitudinal reinforcement and steel tube concrete. The bearing capacity values ​​are calculated separately, and the peak bearing capacity calculation formula is obtained after superposition.

[0095] In order to verify the accuracy of the numerical calculation of this application, the experimental data described in the document "Behavior of ultra-high-performance concrete (UHPC) encased concrete-filled steel tubular (CFST) stubcolumns under axial compression" were selected for verification. The yield strength of the steel tube is 377.1MPa and the yield strength of the longitudinal reinforcement is 589MPa. The results are compared with the calculation results specified in the "TCECS188-2019 Technical Specification for Steel Tube Concrete Composite Column Structure" (hereinafter referred to as the "Specifications"), as shown in Table 2 below. As can be seen from Table 2, the average value of the calculation results / experimental values ​​of the present invention is 1.006, while the average value of the calculation results / experimental values ​​of the "Specifications" is 1.13, which obviously overestimates its bearing capacity. Therefore, the calculation results of the present invention can more accurately predict the peak bearing capacity of steel tube concrete composite columns reinforced with UHPC, providing a basis for engineering design.

[0096] Table 2

[0097] ;

[0098] The basic principles of the present application have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in this application are merely illustrative and not restrictive, and it should not be assumed that these advantages, strengths, and effects are required of each embodiment of this application. In addition, the specific details disclosed above are merely illustrative and facilitating understanding, and are not restrictive. The above details do not limit this application to necessarily being implemented using the above specific details.

[0099] The block diagrams of the devices, devices, equipment, and systems involved in this application are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As will be appreciated by those skilled in the art, these devices, devices, equipment, and systems can be connected, arranged, or configured in any manner. Words such as "include," "comprise," "have," and the like are open-ended words, meaning "including but not limited to," and can be used interchangeably therewith. The words "or" and "and" used herein refer to the words "and / or" and can be used interchangeably therewith, unless the context clearly indicates otherwise. The word "such as" used herein refers to the phrase "such as but not limited to," and can be used interchangeably therewith.

Claims

1. A method for calculating the peak bearing capacity of an externally reinforced concrete-filled steel tube column, characterized in that: The steel tube concrete column comprises a steel tube (4) and a core concrete (6) located in the steel tube (4); a UHPC layer (1) is cast on the outer ring of the steel tube (4); the outer ring cross section of the UHPC layer (1) is square, and the center line of the UHPC layer (1) coincides with the axis of the steel tube (4); stirrups (2) located on the outer ring of the steel tube (4) are pre-embedded in the UHPC layer (1), and longitudinal steel bars (3) are arranged on the inner ring of the stirrups (2) along the vertical direction; After reinforcement, the peak bearing capacity of the steel tube concrete column is : in: represents the peak bearing capacity of the UHPC layer (1); represents the peak bearing capacity of the steel tube concrete column; represents the cross-sectional area of ​​the longitudinal reinforcement (3); represents the yield strength of the longitudinal reinforcement (3); as well as All are fitting coefficients; The void ratio of the CFST column, the thickness of the UHPC layer (1) and the diameter of the CFST column are used as design variables to calculate the fitting as well as : in: is the ratio of the thickness of the UHPC layer (1) to the diameter of the CFST column; is the void ratio of the concrete-filled steel tube column.

2. The method for calculating the peak bearing capacity of an externally reinforced concrete-filled steel tube column according to claim 1, characterized in that: The stirrups (2) are square stirrups, the center line of the stirrups (2) coincides with the axis of the steel pipe (4), each corner point and each straight section of the stirrups (2) are tied and fixed with longitudinal steel bars (3), and the adjacent longitudinal steel bars (3) on the stirrups (2) are arranged at equal spacing.

3. The method for calculating the peak bearing capacity of an externally reinforced concrete-filled steel tube column according to claim 1, characterized in that: in, is the compressive strength of concrete confined by stirrups (2); is the cross-sectional area of ​​the UHPC layer (1).

4. The method for calculating the peak bearing capacity of an externally reinforced concrete-filled steel tube column according to claim 1, wherein: in, is the reduction factor; is the cross-sectional area of ​​the steel pipe (4); is the yield strength of the steel pipe (4); is the cross-sectional area of ​​the core concrete (6); is the compressive strength of the core concrete (6).

5. The method for calculating the peak bearing capacity of an externally reinforced concrete-filled steel tube column according to claim 4, characterized in that: in, is the contact stress between the steel tube (4) and the core concrete (6); is the standard value of the axial compressive strength of the core concrete (6); is the yield strength of the steel pipe (4); is the thickness of the steel pipe (4); is the inner diameter of the steel pipe (4).

6. The method for calculating the peak bearing capacity of an externally reinforced concrete-filled steel tube column according to claim 4, characterized in that: when hour, =0.75; when hour, =1.

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