Method for calculating axial bearing capacity of double-defect-containing steel pipe concrete column after impact

Abstract

The present application relates to the technical field of steel pipe concrete column axial bearing capacity calculation, in particular to a kind of steel pipe concrete column axial bearing capacity calculation method after containing double defect steel pipe concrete column is impacted. First, the structural design parameters of the steel pipe concrete column with double defects, annular void ratio, corrosion rate and residual deflection are obtained;Then, the axial bearing capacity of the steel pipe concrete column with only annular void after being vertically impacted, the axial bearing capacity of the steel pipe concrete column with only steel pipe surface corrosion after being vertically impacted in the corrosion area, and the residual axial bearing capacity coefficient of the steel pipe concrete column with double defects after being vertically impacted in the corrosion area are calculated;Finally, the axial bearing capacity and the residual axial bearing capacity coefficient are multiplied, and the axial bearing capacity of the steel pipe concrete column with double defects after being vertically impacted in the steel pipe surface corrosion area can be calculated more accurately.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel tube concrete column axial bearing capacity calculation, in particular to a method for calculating the axial bearing capacity of a steel tube concrete column with double defects after impact. BACKGROUND

[0002] Steel tube concrete is widely used in marine structures such as water bridges and offshore platforms due to its excellent mechanical properties, simple construction method and high material utilization rate. However, during long-term service, such structures face severe environmental and working condition challenges: the moisture and corrosion of the marine environment will inevitably cause corrosion on the surface of the steel tube, resulting in a reduction in the wall thickness of the steel tube and degradation of its mechanical properties. At the same time, due to factors such as concrete material quality defects, concrete shrinkage and temperature changes, gaps of varying degrees between the steel tube and the core concrete are prone to occur, forming annular void defects. The superposition of surface corrosion and annular void double defects can significantly reduce the mechanical properties of steel tube concrete columns, such as peak load, initial stiffness and ductility, and adversely affect their axial bearing capacity.

[0003] In particular, when a steel tube concrete column with double defects is subjected to a short vertical impact from a vehicle, ship or other object, the attenuation of its axial bearing capacity is more complex. However, the existing technology for calculating the axial bearing capacity of steel tube concrete columns has obvious shortcomings: only the design value of the impact equivalent force is given based on the tonnage and other macro parameters of the impacting object, without considering the reduction of the structure's bearing capacity due to the double defects of surface corrosion and annular void. Existing research has mostly focused on the calculation of the axial bearing capacity of steel tube concrete columns with no defects or single defects (only surface corrosion or only annular void), without considering the coupling effect of double defects, and even less considering the impact of residual deformation after impact on the remaining axial bearing capacity.

[0004] The limitations of the above calculation methods make it difficult to accurately reflect the true axial bearing capacity of a steel tube concrete column with surface corrosion and annular void double defects after impact under actual service conditions. The calculation results have poor precision and large deviations, making it difficult to quantitatively evaluate the safety of the structure. This not only may lead to overdesign and waste of resources, but also may cause serious engineering accidents due to underestimation of the bearing capacity attenuation, resulting in immeasurable economic losses and safety risks. Therefore, there is an urgent need for a method for calculating the axial bearing capacity that accurately considers the effects of corrosion, annular void double defects and residual deformation after impact to address the shortcomings of existing technology. SUMMARY

[0005] To avoid and overcome the technical problems existing in the prior art, the present application provides a method for calculating the axial bearing capacity of a steel tube concrete column with double defects after impact. The present application can more accurately calculate the axial bearing capacity of a steel tube concrete column with double defects after impact.

[0006] To achieve the above object, the present application provides the following technical solutions.

[0007] A method for calculating the axial bearing capacity of a double-defect-containing steel pipe concrete column after impact, comprising the following calculation steps:

[0008] S1, obtaining the structural design parameters, annular void ratio, corrosion rate of the steel pipe concrete column with double defects, and the residual deflection after the vertical impact on the corrosion area of the steel pipe surface thereof;

[0009] S2, based on the obtained structural design parameters, annular void ratio and corrosion rate, calculating the axial bearing capacity of the steel pipe concrete column with only annular void or single defect of the steel pipe surface corrosion after vertical impact;

[0010] S3, based on the obtained annular void ratio, corrosion rate and residual deflection, calculating the residual axial bearing capacity coefficient of the steel pipe concrete column with double defects after vertical impact on the corrosion area of the steel pipe surface thereof;

[0011] S4, multiplying the axial bearing capacity and the residual axial bearing capacity coefficient calculated in steps S2 to S3, so as to obtain the axial bearing capacity of the steel pipe concrete column with double defects after vertical impact on the corrosion area of the steel pipe surface thereof.

[0012] As a further scheme of the present application, the sub-steps of step S1 are as follows:

[0013] S11, obtaining the structural design parameters of the steel pipe concrete column by consulting the design data of the current steel pipe concrete column, including the steel pipe outer diameter , steel pipe thickness , steel pipe yield strength , steel pipe cross-sectional area , steel pipe concrete column length , concrete cross-sectional area , and concrete axial compressive strength standard value ;

[0014] S12, measuring the void cross-sectional area at the geometric center of the vertical impact area, and the ratio between the void cross-sectional area and the concrete cross-sectional area at the geometric center point is the annular void ratio at the vertical impact area;

[0015] S13, measuring the initial weight and the weight after corrosion of the steel pipe, and the ratio between the two weights is the steel pipe surface corrosion rate ;

[0016] S14, vertically impacting the vertical impact area on the steel pipe concrete column, and measuring the residual deflection of the steel pipe concrete column after vertical impact.

[0017] As a further scheme of the present application: the axial bearing capacity of the steel pipe concrete column with only annular void single defect after being subjected to vertical impact is calculated by the following formula:

[0018] ;

[0019] ;

[0020] ;

[0021] ;

[0022] In the formula, represents the axial bearing capacity of the steel pipe concrete column with only annular void single defect after being subjected to vertical impact; represents the component force coefficient; represents the axial peak stress when the concrete strength reaches the peak value after being constrained by the steel pipe; represents the hoop tensile stress of the steel pipe; represents the inner diameter of the steel pipe.

[0023] As a further scheme of the present application: the axial bearing capacity of the steel pipe concrete column with only steel pipe surface corrosion single defect after being subjected to vertical impact is calculated by the following formula:

[0024] ;

[0025] In the formula, represents the axial bearing capacity of the steel pipe concrete column with only steel pipe surface corrosion single defect after being subjected to vertical impact in the corrosion area.

[0026] As a further scheme of the present application: the residual axial bearing capacity coefficient is calculated by the following formula:

[0027] ;

[0028] In the formula, represents the residual axial bearing capacity coefficient of the steel pipe concrete column with double defects after being subjected to vertical impact in the steel pipe surface corrosion area; represents the residual deflection of the steel pipe concrete column with double defects after being subjected to vertical impact in the steel pipe surface corrosion area; represents the length of the steel pipe concrete column.

[0029] As a further scheme of the present application: the axial bearing capacity in step S4 is calculated by the following formula:

[0030] ;

[0031] In the formula, This indicates the axial bearing capacity of a double-defect concrete-filled steel tube column after it is subjected to a vertical impact in the corroded area on the surface of its steel tube.

[0032] As a further aspect of the present invention: axial bearing capacity The process of obtaining the expression is as follows:

[0033] First, steel-concrete composite column specimens containing only corrosion defects on the steel pipe surface were prepared, and multiple sets of different corrosion rate gradients on the steel pipe surface were set up. The corroded area was vertically impacted by a drop hammer impact tester, and the axial bearing capacity of each specimen after impact was tested and recorded. Based on the axial bearing capacity of the uncorroded specimen after the same vertical impact, the measured axial bearing capacity coefficient under different corrosion rates was calculated, which is the ratio of the axial bearing capacity after corrosion to the axial bearing capacity without corrosion.

[0034] Next, based on the data trend, the least squares method was selected as the fitting tool. By minimizing the sum of squared errors between the measured axial bearing capacity coefficient and the fitted value, the linear model was solved. slope and intercept ;

[0035] Finally, the data of "steel pipe surface corrosion - measured axial bearing capacity coefficient" were substituted into the linear model to calculate the result. , ,

[0036] The final linear fitting formula was determined. .

[0037] As a further aspect of the present invention: a drop hammer impact tester is used to conduct vertical impacts on the steel-concrete composite column, and in the same set of vertical impact tests, the momentum of the hammer is the same each time it falls and contacts the steel-concrete composite column.

[0038] As a further aspect of the present invention: in a vertical impact test, the momentum of the hammer is controlled by adjusting the mass of the hammer or the height at which the hammer falls.

[0039] As a further scheme of the present application: the corrosion area and the annular void position of the surface of the prepared steel pipe concrete column specimen are both located in the middle of the column; during the vertical impact test, the impact positions of each group of tests remain consistent. The unity of the positions can minimize the interference of irrelevant variables, ensure the stable correspondence between the key features such as corrosion and annular void and the action points of the impact effect, make the test results determined only by the target variables, and improve the reliability and comparability of the data. At the same time, the fixed position setting facilitates focusing on the mechanical response law of a specific area, reduces the result deviation caused by the dispersion of positions, and can more accurately capture the stress failure characteristics of the middle of the column (i.e. the key defect concentration area) under impact load, providing clear and effective data support for subsequent analysis of the impact of defects on the structure, and enhancing the persuasiveness of the test conclusion.

[0040] Compared with the prior art, the present application has the following advantages:

[0041] The present application quantifies the axial bearing capacity when there is only annular void single defect and only steel pipe surface corrosion single defect respectively by step-by-step calculation, and then introduces the annular void rate, corrosion rate and residual deflection to calculate the residual axial bearing capacity coefficient under double defects, and finally obtains the result by multiplication integration. The influence mechanism of single defect and double defect is clearly distinguished, the independent effects of the two defects on the axial bearing capacity are considered, and the comprehensive effects of double defects and residual deformation after impact are coupled through the residual bearing capacity coefficient, so that the calculation process is logical and the steps are operable, which can accurately quantify the axial bearing capacity of the steel pipe concrete column after impact under the superposition of double defects, effectively makes up for the deficiency that the existing technology is difficult to handle the influence of double defects of surface corrosion and annular void on the bearing capacity, provides a more reliable calculation path for evaluating the actual bearing performance of such components, and provides a precise theoretical basis for the use and maintenance in engineering. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The axial bearing capacity calculation flowchart of the present application. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0044] Please refer to Figure 1 The method of the present application includes the following contents:

[0045] I. Obtain test data

[0046] A batch of steel pipe concrete columns with double defects of annular void and surface corrosion at the middle position were selected as test specimens for systematic testing by drop hammer impact testing machine. Before testing, the key parameters of the specimen need to be preprocessed and recorded: the geometric parameters such as the outer diameter of the steel pipe , the thickness of the steel pipe , the length of the steel pipe concrete column are measured by precision measuring tools; the yield strength of the steel pipe and the standard value of the axial compressive strength of concrete are obtained by material mechanics performance testing method; the cross-sectional area of the steel pipe and the cross-sectional area of the concrete are calculated; the annular void rate is determined by ultrasonic testing technology or infrared imaging method , and the surface corrosion rate of the steel pipe is measured by weight loss method or electromagnetic induction method , to ensure the accuracy and integrity of the initial parameters.

[0047] During the test, the steel pipe concrete column is supported by fixed hinge support at both ends, the middle part of the column is suspended and strictly kept horizontal, and the impact point is located at the center of the pre-set corrosion area on the surface of the steel pipe. Before the specimen is installed, the axial midpoint of the steel pipe concrete column is determined by measuring tools (such as tape measure, vernier caliper), and marked on the surface of the column; at the same time, according to the range of the corrosion area and the annular void area, a region matching the size of the weight is marked as the vertical impact area at the center of the corrosion area, and the geometric center of the vertical impact area is in the same cross section as the axial midpoint of the steel pipe concrete column. In the test operation, the falling trajectory of the weight is adjusted by the control system of the drop hammer impact testing machine, so that the central axis of the weight coincides with the "geometric center of the vertical impact area" marked on the surface of the specimen, and then the impact test is started. The core of the vertical impact area is the corrosion area and the annular void area on the surface of the steel pipe, and both of them are located in the middle part of the column. Therefore, the impact point of the weight is completely coincided with the geometric center, to ensure that the subsequent measured parameters such as "void cross-sectional area" and "residual deflection" correspond to the core area of the impact action. In order to accurately control the impact load condition, the constant momentum of the weight is realized by the control system of the drop hammer impact testing machine: in the same group of tests, the weight quality is fixed (such as selecting 50kg, 100kg, etc. gradient value), and the impact speed is controlled by adjusting the falling height, to ensure that the momentum of the weight impact on all specimens in each group is completely consistent (the momentum calculation formula is p = mv , where m is the mass of the hammer, and v is the falling impact speed). Each test is repeated at least 3 times, and the average value of the axial bearing capacity is taken as the effective data under the momentum condition, to reduce the influence of accidental errors.

[0048] After the completion of the test under the same momentum condition, adjust the weight mass (such as replace 150 kg, 200 kg) or change the drop height to adjust the impact speed, carry out a new set of tests according to the same test process as above, and obtain the response data of the test piece under different momentum impacts in turn. Immediately after each impact, the residual deflection of the concrete-filled steel tube column span is measured by using the laser displacement sensor, and the real-time axial bearing capacity of the test piece after impact is synchronously collected (recorded by the force sensor in real time), and the corresponding relationship database of "impact momentum-residual deflection-axial bearing capacity" is established, which provides comprehensive and accurate parameter support for subsequent calculation.

[0049] Through the above operation, the test data obtained is shown in Table 1.

[0050] Table 1 Test data

[0051] ;

[0052] II. Calculate the axial bearing capacity

[0053] 1. Obtain the axial bearing capacity

[0054] First, prepare a concrete-filled steel tube column specimen containing only steel tube surface corrosion defects, and set multiple groups of different steel tube surface corrosion rate gradients; vertically impact the corrosion area by using a drop hammer impact testing machine, test and record the axial bearing capacity of each test piece after impact; take the axial bearing capacity of the non-corrosion test piece after the same vertical impact as the benchmark, calculate the measured axial bearing capacity coefficient under different corrosion rates, that is, the ratio of the axial bearing capacity after corrosion to the axial bearing capacity without corrosion, and the specific values are shown in Table 1.

[0055] Next, according to the data trend, select the least squares method as the fitting tool, minimize the error sum of squares of the measured axial bearing capacity coefficient and the fitted value, and solve the slope and intercept of the linear model .

[0056] Finally, substitute the "steel tube surface corrosion-measured axial bearing capacity coefficient" data into the linear model to calculate , , and finally determine the linear fitting formula:

[0057] (1);

[0058] 2. Calculate the axial bearing capacity

[0059] First, according to the superposition principle, the axial bearing capacity of the test piece after impact is calculated as follows: ​The composition of the steel tube and the concrete is divided into two parts, and the steel tube and the concrete have considerable lateral interaction force for the steel tube concrete column with annular void defects. When the steel tube concrete column with annular void defects is axially compressed, the lateral outward expansion of the concrete is , and the lateral outward expansion of the steel tube is , and the following conditions are met:

[0060] (2);

[0061] (3);

[0062] wherein , are the Poisson's ratios of the concrete and the steel tube respectively, , are the axial peak strains of the concrete and the steel tube respectively. Since the top end is closed during the service of the steel tube concrete column, ; represents the radius of the internal concrete.

[0063] When the concrete and the steel tube just have interaction when the concrete reaches the peak axial bearing capacity, the following condition needs to be met:

[0064] (4);

[0065] wherein is the spacing between the steel tube and the concrete caused by the annular void. Since is usually greater than in the embodiment, is 21.5 times of , and is much greater than , and the Poisson's ratios of the concrete and the steel tube are not much different in value, so the simplified algorithm ignores the term, that is, ;

[0066] At this time, the annular void rate is: ;

[0067] Since is of the order of magnitude of 10-4, it can be ignored, so at this time ;

[0068] Since , .

[0069] According to the existing literature "Daniel C, Patrick P. Stress-strain model for confined high-strength concrete. J Struct Eng 1995; 121(3): 468-77.", when the concrete reaches the peak axial bearing capacity = 0.5, according to the specification "GB / T50010-2010", the axial peak strain of concrete is generally taken as 0.002, so we can get 0.002, which meets the condition that there is an interaction force between the steel tube and the concrete.

[0070] At the same time, referring to the research on FRP confined steel pipe concrete "Park JW, Hong YK, Hong GS, Kim JH, Choi SM. Design formulas of concrete filled circular steel tubes reinforced by carbon fiber reinforced plastic sheets. The twelfth East Asia-Pacific conference on structural engineering and construction, Procedia Engineering", the steel pipe confined steel pipe concrete with similar properties is defined as , where the hoop tensile stress coefficient A is 2 by combining the existing test data.

[0071] Finally, since the steel tube needs to meet the MISES yield criterion when it yields, at this time, due to the small contact stress between the steel tube and the concrete, it can be ignored, and the simplified form of MISES stress is adopted:

[0072] (5) ;

[0073] where, is the longitudinal stress, is the hoop stress, , is the yield stress of the steel tube, i.e. ;

[0074] Therefore, we use , that is, only need to get , then the remaining axial bearing capacity can be obtained in the subsequent calculation process. According to the existing test results, for the steel pipe concrete column with ring-shaped void defects, its Related to the annular void ratio, and satisfies:

[0075] (6);

[0076] Thus, by the above derivation can be obtained:

[0077] (7);

[0078] (8);

[0079] (9);

[0080] 3. Calculate the residual axial bearing capacity coefficient

[0081] Based on the data in Table 1, combined with , the corresponding residual axial bearing capacity coefficient of each test piece is obtained.

[0082] Observing the calculated residual axial bearing capacity coefficient, it is found that there is a relationship between it and , and : when the three increase, the residual axial bearing capacity coefficient decays nonlinearly, so a multivariate quadratic function is assumed:

[0083] (10);

[0084] In the formula, are all fitting coefficients.

[0085] Next, input the multiple sets of data containing Table 1 into formula (10), form a characteristic equation, and then minimize the "sum of squared errors of predicted and measured values" by the least squares method to obtain the specific value of each fitting parameter, and finally obtain formula (11):

[0086] (11);

[0087] 4. Calculate the axial bearing capacity

[0088] Based on Table 1 and the data calculated from Table 1, the axial bearing capacity of the corresponding test piece is calculated by formula (12), and the calculation results are shown in Table 2:

[0089] (12);

[0090] Table 2 Axial bearing capacity

[0091] .

[0092] III. Data Analysis

[0093] Based on the data in Table 2, the specific analysis is as follows:

[0094] 1. Influence of different defect types on bearing capacity

[0095] (1) No defect comparison only with corrosion defect

[0096] The calculated axial bearing capacity of the non-defective specimen 1 is 1074.931 kN, and the test axial bearing capacity is 1064.1 kN, which is the highest among all specimens.

[0097] When there is only a corrosion defect (specimen 2 and specimen 3), as the steel pipe surface corrosion rate increases from 0.03 to 0.05, the calculated axial bearing capacity decreases from 999.739 kN to 961.526 kN, with a decrease of about 3.8%; the test axial bearing capacity decreases from 946.6 kN to 884.2 kN, with a decrease of about 6.6%.

[0098] It can be seen that corrosion defects reduce the axial bearing capacity by weakening the steel pipe wall thickness and mechanical properties, and the higher the corrosion rate, the more obvious the decrease. Both the calculation model and the test capture this trend, verifying the reasonableness of the single corrosion defect quantification.

[0099] (2) No defect comparison only with ring void defect

[0100] Specimen 4 with only ring void defect compared with non-defective specimen 1: the calculated axial bearing capacity decreases from 1074.931 kN to 558.205 kN, with a decrease of about 48.1%; the test axial bearing capacity decreases from 1064.1 kN to 570.3 kN, with a decrease of about 46.4%.

[0101] It can be seen that the ring void destroys the restraint effect of the steel pipe on the core concrete, resulting in a significant decrease in the axial bearing capacity. The calculation model accurately quantifies the weakening effect of the ring void, and the decrease is basically consistent with the test.

[0102] (3) Single defect comparison with double defects

[0103] Double defect specimens 5 and 6 have both ring void and corrosion, compared with specimen 4 with only ring void, specimen 5 has a calculated axial bearing capacity of 530.391 kN, a decrease of about 5% from 558.205 kN; specimen 6 further decreases to 507.058 kN, a decrease of about 9.2%; the test axial bearing capacity decreases synchronously, with a decrease of 6.1% and 9.2%, respectively.

[0104] Therefore, the double defects cause the bearing capacity to be lower than the single defect through the coupling effect of "void weakening constraint + corrosion weakening strength of the steel pipe", and the calculation model accurately reflects the superimposed weakening effect.

[0105] 2. Deviation verification of calculated value and test value

[0106] From the data in Table 2, the ratio of the two axial bearing forces ranges from 0.979 to 1.087, and the specific performance is as follows:

[0107] Defect-free test piece 1: ratio 1.010, deviation +1.0%;

[0108] Only surface corrosion test pieces 2 and 3: ratio 1.056, 1.087, deviation +5.6%, +8.7%;

[0109] Only annular void test piece 4: ratio 0.979, deviation -2.1%;

[0110] Double defect test pieces 5 and 6: ratio 0.990, 0.979, deviation -1.0%, -2.1%.

[0111] Therefore, the deviation is controlled within ±10%, and the deviation of the double defect test piece (-2.1% to -1.0%) is smaller than that of the test piece with only corrosion, which shows that the coupling effect of the double defects is more accurate, verifies the scientificity of the step-by-step calculation logic, and shows that the calculation formula of the application can more accurately calculate the axial bearing capacity of the steel pipe concrete column with double defects and the influence of residual deformation after impact.

[0112] The above is only a preferred specific embodiment of the application, but the protection scope of the application is not limited thereto, and any person skilled in the art can make equivalent replacement or change according to the technical solution and the inventive concept of the application within the technical range disclosed by the application, which should be covered within the protection scope of the application.

Claims

1. A method for calculating the axial load capacity of a double-defective steel tube reinforced concrete column after impact, characterized by, The method comprises the following calculation steps: S1, obtaining the structural design parameters, annular void ratio, corrosion rate of the steel pipe concrete column with double defects, and the residual deflection of the steel pipe concrete column after the corrosion area of the steel pipe surface is subjected to vertical impact; S2, calculating the axial bearing capacity of the steel pipe concrete column with only annular void or single defect of the steel pipe surface corrosion after being subjected to vertical impact based on the obtained structural design parameters, annular void ratio and corrosion rate; S3, calculating the residual axial bearing capacity coefficient of the steel pipe concrete column with double defects after the corrosion area of the steel pipe surface is subjected to vertical impact based on the obtained annular void ratio, corrosion rate and residual deflection; S4, coupling the axial bearing capacity and the residual axial bearing capacity coefficient calculated in steps S2 to S3 to obtain the axial bearing capacity of the steel pipe concrete column with double defects after the corrosion area of the steel pipe surface is subjected to vertical impact.

2. The method for calculating the axial load capacity of a double-defective steel tube reinforced concrete column after impact according to claim 1, characterized in that, The sub-steps of step S1 are as follows: S11, by consulting the current design data of the steel pipe concrete column, obtaining the structural design parameters, including the steel pipe outer diameter , steel pipe thickness , steel pipe yield strength , steel pipe cross-sectional area , steel pipe concrete column length , concrete cross-sectional area and the standard value of the concrete axial compressive strength ; S12, measure the void cross-sectional area at the geometric center of the vertical impact area, and the ratio between the void cross-sectional area and the concrete cross-sectional area at the geometric center point is the annular void rate at the vertical impact area ; S13, measure the initial weight of the steel pipe and the weight after corrosion, the ratio of the two weights is the corrosion rate of the steel pipe surface ; S14, vertically impacting the vertical impact area on the steel pipe concrete column and measuring the residual deflection of the steel pipe concrete column after vertical impact.

3. The method for calculating the axial load capacity of a double-defective steel tube reinforced concrete column after impact according to claim 2, characterized in that, The axial bearing capacity of the steel pipe concrete column with only annular void after being subjected to vertical impact is calculated by the following formula: ； ； ； ； wherein denotes the axial load-carrying capacity of a steel tube concrete column with only annular void after subjected to a vertical impact; denotes the component force coefficient; denotes the axial peak stress of concrete when the strength of concrete reaches the peak value after being constrained by the steel tube; denotes the hoop tensile stress of the steel tube; denotes the inner diameter of the steel tube.

4. The method for calculating the axial load capacity of a double-defective steel tube reinforced concrete column after impact according to claim 3, characterized in that, The axial bearing capacity of the steel pipe concrete column with only steel pipe surface corrosion after being subjected to vertical impact is calculated by the following formula: ； In the formula, The axial load capacity of the steel tube concrete column with only surface corrosion of the steel tube after vertical impact in the corrosion zone is represented.

5. The method for calculating the axial load capacity of a double- imperfection-containing concrete-filled steel tubular column after impact according to claim 4, characterized in that, The residual axial bearing capacity coefficient is calculated by the following formula: ； In the formula, represents the residual axial bearing capacity coefficient of a steel pipe concrete column with double defects after a vertical impact on the steel pipe surface corrosion zone thereof; represents the residual deflection of a steel pipe concrete column with double defects after a vertical impact on the steel pipe surface corrosion zone thereof; represents the length of the steel pipe concrete column.

6. The method for calculating the axial load capacity of a double- imperfection-containing concrete-filled steel tubular column after impact according to claim 5, characterized in that, The axial bearing capacity in step S4 is calculated by the following formula: ； In the formula, The axial load capacity of a double-defective steel tube concrete column subjected to vertical impact at the corrosion zone on the surface of the steel tube is represented.

7. The method for calculating the axial load capacity of a double- imperfection-containing concrete-filled steel tubular column after impact according to claim 6, characterized in that, Axial load capacity The expression acquisition process is as follows: First, prepare the steel pipe concrete column specimen with only steel pipe surface corrosion defect, set multiple groups of different steel pipe surface corrosion rate gradients; vertically impact the corrosion area by a drop hammer impact testing machine, test and record the axial bearing capacity of each steel pipe concrete column specimen after impact; take the axial bearing capacity of the non-corrosion specimen after the same vertical impact as the benchmark, calculate the measured axial bearing capacity coefficient under different corrosion rates, that is, the ratio of the axial bearing capacity after corrosion to the axial bearing capacity without corrosion; Then, according to the data variation trend, the least square method is selected as the fitting tool, and the error sum of squares of the measured axial bearing capacity coefficient and the fitting value is minimized to solve the slope and the intercept k of the linear model b ; Finally, the data of "corrosion of steel pipe surface - measured axial bearing capacity coefficient" is substituted into the linear model, and the calculation result is , Finalize linear fit formula .

8. The method for calculating the axial load capacity of a double- imperfection-containing concrete-filled steel tubular column after impact according to claim 7, characterized in that, The drop hammer impact testing machine is used to vertically impact the steel pipe concrete column, and in the same group of vertical impact tests, the momentum of the falling hammer is the same when it contacts the steel pipe concrete column.

9. The method for calculating the axial load capacity of a double- imperfection-containing concrete-filled steel tubular column after impact according to claim 8, characterized in that, In the vertical impact test, the momentum of the hammer is controlled by adjusting the mass of the hammer or the falling height of the hammer.

10. The method for calculating the axial load capacity of a double- imperfection-containing concrete-filled steel tubular column after impact according to claim 9, characterized in that, The prepared steel pipe concrete column specimen has the corrosion area and annular void position on the steel pipe surface located in the middle of the column; during the vertical impact test, the impact position of each group of tests remains consistent.

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