Method for calculating axial bearing capacity of concrete filled steel tubular column with double defects after being impacted

Abstract

The invention relates to the technical field of calculation of axial bearing capacity of concrete-filled steel tubular columns, in particular to a method for calculating axial bearing capacity of a double-defect concrete-filled steel tubular column after impact. The method comprises the following steps: firstly, obtaining structural design parameters, an annular void rate, a corrosion rate and residual deflection of the concrete-filled steel tubular column with double defects; then, calculating the axial bearing capacity of the concrete-filled steel tube column only having the annular void after being subjected to the vertical impact and the axial bearing capacity of the concrete-filled steel tube column only having the surface corrosion of the steel tube after being subjected to the vertical impact in the corrosion area; the residual axial bearing capacity coefficient of the steel pipe concrete column with the double defects after the corrosion area is subjected to vertical impact is obtained; and finally, multiplying the axial bearing capacity by the residual axial bearing capacity coefficient to accurately calculate the axial bearing capacity of the double-defect concrete-filled steel tubular column after vertical impact on the corrosion area on the surface of the steel tube of the double-defect concrete-filled steel tubular column.

Description

Technical Field

[0001] The invention relates to the technical field of calculation of the axial bearing capacity of a steel tube concrete column, in particular to a method for calculating the axial bearing capacity of a steel tube concrete column containing double defects after being impacted. Background Art

[0002] Steel tube concrete is widely used in marine structures such as water-borne bridges and offshore platforms due to its excellent load-bearing properties, simple construction methods, and high material utilization rate. However, during long-term service, such structures face severe environmental and working condition challenges: the humidity and corrosiveness of the marine environment will inevitably lead to corrosion on the surface of the steel tube, resulting in thinning of the steel tube wall thickness and degradation of mechanical properties; at the same time, due to factors such as concrete material quality defects, concrete shrinkage, and temperature changes, gaps of varying degrees are likely to appear between the steel tube and the core concrete, forming annular void defects. The superposition of the dual defects of surface corrosion and annular voids will significantly reduce the mechanical properties of steel tube concrete columns, such as peak load, initial stiffness, and ductility, and have an adverse effect on their axial bearing capacity.

[0003] Especially when double-defective concrete-filled steel tube columns are subjected to brief vertical impacts from objects such as vehicles and ships, the attenuation of their axial bearing capacity is even more complex. However, existing methods for calculating the axial bearing capacity of concrete-filled steel tube columns have significant shortcomings: they only provide design values ​​for impact equivalents based on macroscopic parameters such as the tonnage of the impacting object, without considering the reduction in structural bearing capacity caused by double defects such as surface corrosion and annular voids. Existing research has primarily focused on calculating the axial bearing capacity of concrete-filled steel tube columns with no defects or a single defect (surface corrosion or annular voids only), without incorporating the coupled effects of double defects into the calculation model, nor considering the effect of residual deformation after impact on the remaining axial bearing capacity.

[0004] The limitations of the above-mentioned calculation method make it unable to accurately reflect the true axial bearing capacity of steel tube concrete columns with dual defects of surface corrosion and annular voids after impact under actual service conditions. The calculation results are poorly accurate and have large deviations, making it difficult to quantitatively assess the safety of the structure. This may not only lead to overdesign and waste of resources, but may also cause serious engineering accidents due to underestimation of bearing capacity attenuation, resulting in immeasurable economic losses and safety risks. Therefore, there is an urgent need for an axial bearing capacity calculation method that can accurately account for the dual defects of corrosion and annular voids, as well as the residual deformation after impact, to address the shortcomings of existing technologies. Summary of the Invention

[0005] In order to avoid and overcome the technical problems existing in the prior art, the present invention provides a method for calculating the axial bearing capacity of a double-defect concrete-filled steel tube column after impact. The present invention can more accurately calculate the axial bearing capacity of a double-defect concrete-filled steel tube column after impact.

[0006] To achieve the above object, the present invention provides the following technical solutions: A method for calculating the axial bearing capacity of a double-defect concrete-filled steel tube column after impact, comprising the following calculation steps: S1. Obtain the structural design parameters, annular void ratio, corrosion ratio, and residual deflection of a double-defective concrete-filled steel tube column after vertical impact on the corroded area of ​​the steel tube surface; S2. Based on the obtained structural design parameters, annular void ratio, and corrosion rate, calculate the axial bearing capacity of a concrete-filled steel tube column with only a single defect of annular void or steel tube surface corrosion after being subjected to a vertical impact; S3. Based on the obtained annular void ratio, corrosion ratio, and residual deflection, calculate the residual axial bearing capacity coefficient of the double-defective concrete-filled steel tube column after being subjected to a vertical impact in the corrosion area on the steel tube surface; S4. Multiply the axial bearing capacity calculated in steps S2 to S3 by the residual axial bearing capacity coefficient to obtain the axial bearing capacity of the double-defective concrete-filled steel tube column after the corrosion area on the steel tube surface is subjected to a vertical impact.

[0007] As a further solution of the present invention: the sub-steps of step S1 are as follows: S11. Obtain the structural design parameters of the concrete-filled steel tube column by consulting the current design data, including the outer diameter of the steel tube. , steel pipe thickness , steel pipe yield strength , cross-sectional area of ​​steel pipe , length of concrete-filled steel tube column , concrete cross-sectional area and standard value of concrete axial compressive strength ; S12. Measure the cross-sectional area of ​​the void at the geometric center of the vertical impact area. The ratio of the cross-sectional area of ​​the void to the cross-sectional area of ​​the concrete at the geometric center is the annular void ratio at the vertical impact area. ; S13. Measure the initial weight and the weight after corrosion of the steel pipe. The ratio between the two weights is the surface corrosion rate of the steel pipe. ; S14. Perform vertical impact on the vertical impact area of ​​the steel tube concrete column and measure the residual deflection of the steel tube concrete column after the vertical impact.

[0008] As a further solution of the present invention, the axial bearing capacity of a concrete-filled steel tube column with only an annular void defect after being subjected to a vertical impact is calculated using the following formula: ; ; ; ; Where, It represents the axial bearing capacity of a concrete-filled steel tube column with only annular void defect after being subjected to vertical impact; represents the force component coefficient; It represents the axial peak stress when the concrete strength reaches its peak after being confined by the steel pipe; Indicates the hoop tensile stress of the steel pipe; Indicates the inner diameter of the steel pipe.

[0009] As a further solution of the present invention, the axial bearing capacity of a concrete-filled steel tube column with only a single defect of steel tube surface corrosion after being subjected to a vertical impact is calculated using the following formula: ; Where, It indicates the axial bearing capacity of a concrete-filled steel tube column with only a single defect of steel tube surface corrosion after being subjected to a vertical impact in the corrosion area.

[0010] As a further solution of the present invention, the residual axial load-bearing capacity coefficient is calculated by the following formula: ; Where, It indicates the residual axial bearing capacity coefficient of the double-defective concrete-filled steel tube column after the corrosion area on the steel tube surface is subjected to vertical impact; It indicates the residual deflection of a double-defective concrete-filled steel tube column after being subjected to a vertical impact on the corrosion area of ​​the steel tube surface; Indicates the length of the concrete-filled steel tube column.

[0011] As a further solution of the present invention, the axial bearing capacity in step S4 is calculated by the following formula: ; Where, It represents the axial bearing capacity of a double-defective concrete-filled steel tube column after being subjected to vertical impact in the corrosion area on the steel tube surface.

[0012] As a further solution of the present invention: axial bearing capacity The expression is obtained as follows: First, concrete-filled steel tube column specimens containing only surface corrosion defects were prepared, and multiple groups of different steel tube surface corrosion rate gradients were set. A drop weight impact tester was used to vertically impact the corrosion area, and the axial bearing capacity of each specimen after impact was measured and recorded. Using the axial bearing capacity of non-corroded specimens after the same vertical impact as a benchmark, the measured axial bearing capacity coefficient at different corrosion rates was calculated, that is, the ratio of the axial bearing capacity after corrosion to the axial bearing capacity without corrosion. Then, according to the data change trend, the least square method is selected as the fitting tool to solve the linear model by minimizing the sum of squares of the errors between the measured axial bearing capacity coefficient and the fitting value. The slope and intercept ; Finally, the data of “steel pipe surface corrosion-measured axial bearing capacity coefficient” is substituted into the linear model to calculate 、 , Finalize the linear fitting formula .

[0013] As a further solution of the present invention, a drop hammer impact tester is used to perform vertical impact on the steel tube concrete column, and in the same set of vertical impact tests, the momentum of the hammer when it falls and contacts the steel tube concrete column is the same each time.

[0014] As a further solution of the present invention: in the vertical impact test, the momentum of the weight is controlled by adjusting the mass of the weight or the falling height of the weight.

[0015] As a further solution of the present invention, the corrosion area and annular voids on the steel tube surface of the prepared concrete-filled steel tube column specimens are both located in the middle of the column; during the vertical impact test, the impact position of each test group remains consistent. This uniform position minimizes interference from irrelevant variables, ensuring a stable correspondence between key characteristics such as corrosion and annular voids and the point of impact, allowing the test results to be determined solely by the target variable, thereby improving the reliability and comparability of the data. At the same time, the fixed position setting facilitates focusing on the mechanical response laws of a specific area, reducing the result deviation caused by position dispersion, and more accurately capturing the stress-damage characteristics of the middle of the column (i.e., the key defect concentration area) under impact loads. This provides clear and effective data support for subsequent analysis of the impact of defects on the structural impact performance, enhancing the persuasiveness of the test conclusions.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses a step-by-step calculation method to first quantify the axial bearing capacity when only a single defect of annular void exists and when only a single defect of steel pipe surface corrosion exists, and then specifically introduces the annular void rate, corrosion rate and residual deflection to calculate the residual axial bearing capacity coefficient under dual defects, and finally obtains the result through product integration. It clearly distinguishes the influence mechanism of single defects and dual defects, taking into account the independent effects of the two defects on the axial bearing capacity, and couples the comprehensive influence of dual defects and residual deformation after impact through the residual bearing capacity coefficient, so that the calculation process is logically clear and the steps are operable. It can accurately quantify the axial bearing capacity of steel tube concrete columns after impact under the superposition of dual defects, effectively making up for the deficiency of the existing technology that it is difficult to simultaneously deal with the influence of dual defects of surface corrosion and annular void on bearing capacity, providing a more reliable calculation path for evaluating the actual bearing performance of such components, and also providing an accurate theoretical basis for use and maintenance in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart of the axial bearing capacity calculation of the present invention. DETAILED DESCRIPTION

[0018] 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.

[0019] See also Figure 1 , the method of the present invention includes the following contents: 1. Obtaining test data A batch of steel tube concrete columns with double defects of annular voids and steel tube surface corrosion in the middle position were selected as test pieces, and systematic tests were carried out using a drop hammer impact tester. Before the test, the key parameters of the specimens need to be pre-processed and recorded: the outer diameter of the steel tube is measured using precision measuring tools. , steel pipe thickness , length of concrete-filled steel tube column Other geometric parameters; use material mechanical properties test method to obtain the yield strength of steel pipe , Standard value of concrete axial compressive strength , calculate the cross-sectional area of ​​the steel pipe and concrete cross-sectional area ;Use ultrasonic testing technology or infrared imaging to determine the annular void rate , the steel pipe surface corrosion rate is measured by weight loss method or electromagnetic induction method , ensuring the accuracy and completeness of the initial parameters.

[0020] During the test, the steel tube concrete column was supported at both ends using fixed hinged supports, with the center of the column suspended and maintained strictly horizontal. The impact point was ensured to be located at the center of a pre-defined corrosion zone on the steel tube surface. Before specimen installation, the axial midpoint of the steel tube retarded concrete column was determined using measuring tools (such as a tape measure or vernier caliper) and marked on the column surface. Simultaneously, based on the extent of the corrosion zone and the annular void area, a vertical impact zone was defined at the center of the corrosion zone, commensurate with the size of the weight. The geometric center of the vertical impact zone and the axial midpoint of the steel tube retarded concrete column were coextensive in cross-section. During the test, the drop weight control system adjusted the weight's trajectory so that its central axis coincided with the "geometric center of the vertical impact zone" marked on the specimen surface. The impact test was then initiated. The core of the vertical impact zone consisted of the steel tube surface corrosion zone and the annular void area, both located in the center of the column. Therefore, the impact point of the hammer is made to completely coincide with the geometric center to ensure that the parameters such as "gap cross-sectional area" and "residual deflection" measured later correspond to the core area of ​​the impact. In order to accurately control the impact load conditions, the control system of the drop hammer impact tester needs to achieve constant hammer momentum: in the same set of tests, the weight of the hammer is fixed (such as selecting gradient values ​​such as 50kg and 100kg) and the impact speed is controlled by adjusting the drop height to ensure that the momentum of the hammer impact on all specimens in each group is completely consistent (the momentum calculation formula is p = mv ,in m is the mass of the hammer, v Each test was repeated at least three times, and the average value of the axial bearing capacity was taken as the valid data under the momentum condition to reduce the influence of accidental errors.

[0021] After completing the test under the same momentum conditions, adjust the weight of the hammer (such as changing to 150kg, 200kg) or change the drop height to adjust the impact speed, and conduct a new set of tests according to the same test process as above, and obtain the specimen response data under different momentum impacts in turn. After each impact, immediately use the laser displacement sensor to measure the residual deflection of the steel tube concrete column span, and simultaneously collect the real-time axial bearing capacity of the specimen after the impact (Real-time recording via force sensors) establishes a database of the corresponding relationship between "impact momentum-residual deflection-axial bearing capacity" to provide comprehensive and accurate parameter support for subsequent calculations.

[0022] Through the above operations, the experimental data obtained are shown in Table 1.

[0023] Table 1 Test data ; 2. Calculation of axial bearing capacity 1. Obtain axial bearing capacity

[0024] First, concrete-filled steel tube column specimens containing only surface corrosion defects of the steel tube were prepared, and multiple groups of different steel tube surface corrosion rate gradients were set. The corrosion area was subjected to vertical impact using a drop weight impact tester, and the axial bearing capacity of each specimen after impact was tested and recorded. The axial bearing capacity of the non-corroded specimen after the same vertical impact was used as a benchmark to calculate the measured axial bearing capacity coefficient at different corrosion rates. That is, the ratio of the axial bearing capacity after corrosion to the axial bearing capacity without corrosion. The specific values ​​are shown in Table 1.

[0025] Then, according to the data change trend, the least square method is selected as the fitting tool to solve the linear model by minimizing the sum of squares of the errors between the measured axial bearing capacity coefficient and the fitting value. The slope and intercept .

[0026] Finally, the data of “steel pipe surface corrosion-measured axial bearing capacity coefficient” is substituted into the linear model to calculate 、 , and finally determine the linear fitting formula: (1); 2. Calculate the axial bearing capacity

[0027] First, according to the superposition principle, The composition of the steel tube concrete column is divided into two parts: steel tube and concrete. For the steel tube concrete column with annular void defect, there is a considerable lateral interaction force between the steel tube and the concrete. When the steel tube concrete column with annular void defect is axially compressed, it will produce lateral outward expansion. Assuming that the lateral outward expansion of the concrete is , the lateral outward expansion of the steel pipe is ,but: (2); (3); in, 、 are the Poisson's ratios of concrete and steel pipe, 、 are the axial peak strains of concrete and steel tube respectively. ; Indicates the radius of the inner concrete.

[0028] When the concrete needs to reach its peak axial bearing capacity, the concrete and the steel pipe need to interact with each other, and the following conditions must be met: (4); in, is the distance between the steel pipe and the concrete caused by the annular void. Usually greater than In this embodiment for 21.5 times, it can be seen Much greater than , and the Poisson's ratio of concrete and steel pipe is not much different in value, so a simplified algorithm is used to ignore Item, that is ; At this time, the annular void rate is: ; Here due to The magnitude is too small and can be ignored. ; because ,therefore .

[0029] 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 standard "GB / T50010-2010", the peak axial strain of concrete The general value is 0.002, so we can get 0.002, there is an interaction force between the steel pipe and concrete that meets this condition.

[0030] At the same time, referring to the research on FRP-confined steel tube concrete, "Park JW, Hong YK, Hong GS, Kim JH, Choi SM. Design formulas of concrete filled circular steel tubes reinforcedby carbon fiber reinforced plastic sheets. The twelfth East Asia-Pacific conference on structural engineering and construction, procedia engineering", the improvement of concrete strength by steel tube-confined steel tube concrete with similar properties is defined as , where the hoop tensile stress coefficient is A The value of is obtained as 2 by combining the existing test data.

[0031] Finally, since the steel pipe must meet the MISES yield criterion when yielding, the contact stress between the steel pipe and concrete is too small and can be ignored. The simplified form of MISES stress is used: (5); in, is the longitudinal stress, is the hoop stress, , is the yield stress of the steel pipe ; For this purpose, , that is, only require The residual axial bearing capacity can be obtained in the subsequent calculation process. According to the existing test results, for steel tube concrete columns with annular void defects, It is related to the annular void ratio and satisfies: (6); Therefore, through the above deduction, we can get: (7); (8); (9); 3. Calculate the residual axial bearing capacity coefficient Based on the data in Table 1, combined with , obtain the corresponding residual axial bearing capacity coefficient of each specimen .

[0032] Observe the calculated residual axial load coefficient and find that it is 、 and There is a relationship between the three: when the three increase, the residual axial bearing capacity coefficient decays nonlinearly, so it is assumed that the multivariate quadratic function: (10); Where, are coefficients to be fitted.

[0033] Next, multiple sets of data including Table 1 are input into formula (10) to form the characteristic equation. Then, the least squares method is used to minimize the sum of squares of the errors between the predicted values ​​and the measured values. This is used to solve the specific values ​​of the parameters to be fitted, and finally formula (11) is obtained: (11); 4. Calculate axial bearing capacity

[0034] Based on Table 1 and the data that can be calculated from Table 1, the axial bearing capacity of the corresponding specimen is calculated using formula (12): , the calculation results are shown in Table 2: (12); Table 2 Axial bearing capacity .

[0035] 3. Data Analysis Based on the data in Table 2, the specific analysis is as follows: 1. The influence of different defect types on bearing capacity (1) No defects vs. only corrosion defects The calculated axial bearing capacity of the defect-free specimen 1 is 1074.931 kN, and the tested axial bearing capacity is 1064.1 kN, which is the highest value among all specimens.

[0036] When only corrosion defects exist (Specimens 2 and 3), as the surface corrosion rate of the steel pipe increases from 0.03 to 0.05, the calculated axial bearing capacity decreases from 999.739 kN to 961.526 kN, a decrease of about 3.8%; the tested axial bearing capacity decreases from 946.6 kN to 884.2 kN, a decrease of about 6.6%.

[0037] This indicates 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 significant the reduction. Both the computational model and the test capture this trend, validating the rationality of quantifying a single corrosion defect.

[0038] (2) No defect vs. only annular void defect Comparing specimen 4 with only annular void defects with specimen 1 without defects: the calculated axial bearing capacity dropped from 1074.931 kN to 558.205 kN, a decrease of about 48.1%; the tested axial bearing capacity dropped from 1064.1 kN to 570.3 kN, a decrease of about 46.4%.

[0039] This indicates that the annular void disrupts the steel tube's restraint on the core concrete, resulting in a significant decrease in axial bearing capacity. The computational model accurately quantifies the weakening effect of the annular void, with the magnitude of the reduction generally consistent with the experimental results.

[0040] (3) Single defect vs. double defect Double-defect specimens 5 and 6 had both annular voids and corrosion. Compared with specimen 4, which only had annular voids, the calculated axial bearing capacity of specimen 5 dropped from 558.205 kN to 530.391 kN, a decrease of about 5%. The calculated axial bearing capacity of specimen 6 further dropped to 507.058 kN, a decrease of about 9.2%. The experimental axial bearing capacity also decreased simultaneously, with decreases of 6.1% and 9.2%, respectively.

[0041] It can be seen that the double defect leads to a lower bearing capacity than a single defect through the coupling effect of "voids weakening constraints + corrosion weakening steel pipe strength". The calculation model accurately reflects this superimposed weakening effect.

[0042] 2. Verification of deviation between calculated value and test value From the data in Table 2, we can see that the ratio of the two axial load capacities ranges from [0.979, 1.087], which is specifically expressed as follows: Defect-free specimen 1: ratio 1.010, deviation +1.0%; Specimens 2 and 3 with surface corrosion only: ratios 1.056 and 1.087, with deviations of +5.6% and +8.7%; Specimen 4 with only annular voids: ratio 0.979, deviation -2.1%; Double defect specimens 5 and 6: ratios are 0.990 and 0.979, with deviations of -1.0% and -2.1%.

[0043] It can be seen that the deviations are all controlled within ±10%, and the deviations of the double-defect specimens (-2.1% to -1.0%) are smaller than those of the specimens with only corrosion, indicating that the present invention can more accurately quantify the coupling effect of double defects, verifying the scientific nature of the step-by-step calculation logic, and showing that the calculation formula of the present invention can more accurately calculate the axial bearing capacity of steel tube concrete columns with double defects and residual deformation after impact.

[0044] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for calculating the axial bearing capacity of a double-defect concrete-filled steel tube column after impact, characterized in that: The calculation steps include: S1. Obtain the structural design parameters, annular void ratio, corrosion ratio, and residual deflection of a double-defective concrete-filled steel tube column after vertical impact on the corroded area of ​​the steel tube surface; S2. Based on the obtained structural design parameters, annular void ratio, and corrosion rate, calculate the axial bearing capacity of a concrete-filled steel tube column with only a single defect of annular void or steel tube surface corrosion after being subjected to a vertical impact; S3. Based on the obtained annular void ratio, corrosion ratio, and residual deflection, calculate the residual axial bearing capacity coefficient of the double-defective concrete-filled steel tube column after being subjected to a vertical impact in the corrosion area on the steel tube surface; S4. Couple step S2 to step S3 to calculate and obtain the axial bearing capacity and the residual axial bearing capacity coefficient, and obtain the axial bearing capacity of the double-defective concrete-filled steel tube column after the corrosion area on the steel tube surface is subjected to a vertical impact.

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

3. The method for calculating the axial bearing capacity of a double-defect concrete-filled steel tube column after impact according to claim 2, characterized in that: The axial bearing capacity of a concrete-filled steel tube column with only annular voids after vertical impact is calculated using the following formula: ； ； ； ； Where, It represents the axial bearing capacity of the steel tube concrete column with only annular voids after being subjected to vertical impact; represents the force component coefficient; It represents the axial peak stress when the concrete strength reaches its peak after being confined by the steel pipe; Indicates the hoop tensile stress of the steel pipe; Indicates the inner diameter of the steel pipe.

4. The method for calculating the axial bearing capacity of a double-defect concrete-filled steel tube column after impact according to claim 3, characterized in that: The axial bearing capacity of a concrete-filled steel tube column with only surface corrosion of the steel tube after being subjected to vertical impact is calculated using the following formula: ； Where, It indicates the axial bearing capacity of the steel tube concrete column with only steel tube surface corrosion after being subjected to vertical impact in the corrosion area.

5. The method for calculating the axial bearing capacity of a double-defect concrete-filled steel tube column after impact according to claim 4, characterized in that: The residual axial load factor is calculated using the following formula: ； Where, It indicates the residual axial bearing capacity coefficient of the double-defective concrete-filled steel tube column after the corrosion area on the steel tube surface is subjected to vertical impact; It indicates the residual deflection of a double-defective concrete-filled steel tube column after being subjected to a vertical impact on the corrosion area of ​​the steel tube surface; Indicates the length of the concrete-filled steel tube column.

6. The method for calculating the axial bearing capacity of a double-defect concrete-filled steel tube column after impact according to claim 5, characterized in that: The axial load capacity in step S4 is calculated using the following formula: ； Where, It represents the axial bearing capacity of a double-defective concrete-filled steel tube column after being subjected to vertical impact in the corrosion area of ​​its steel tube surface.

7. The method for calculating the axial bearing capacity of a double-defect concrete-filled steel tube column after impact according to claim 6, characterized in that: Axial bearing capacity The expression is obtained as follows: First, concrete-filled steel tube column specimens containing only surface corrosion defects were prepared, and multiple groups of different steel tube surface corrosion rate gradients were set. A drop weight impact tester was used to subject the corrosion zone to vertical impacts, and the axial bearing capacity of each concrete-filled steel tube column specimen after impact was measured and recorded. Using the axial bearing capacity of the uncorroded specimen after the same vertical impact as a benchmark, the measured axial bearing capacity coefficient at different corrosion rates was calculated, i.e., the ratio of the axial bearing capacity after corrosion to the axial bearing capacity without corrosion. Then, according to the data change trend, the least square method is selected as the fitting tool to solve the linear model by minimizing the sum of squares of the errors between the measured axial bearing capacity coefficient and the fitting value. The slope k and intercept b ; Finally, the "steel pipe surface corrosion-measured axial bearing capacity coefficient" data is substituted into the linear model to calculate , Finalize the linear fitting formula .

8. The method for calculating the axial bearing capacity of a double-defect concrete-filled steel tube column after impact according to claim 7, characterized in that: A drop hammer impact tester is used to perform vertical impact on the steel tube concrete column. In the same set of vertical impact tests, the momentum of the hammer is the same each time it falls and contacts the steel tube concrete column.

9. The method for calculating the axial bearing capacity of a double-defect concrete-filled steel tube 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 height from which it is dropped.

10. The method for calculating the axial bearing capacity of a double-defect concrete-filled steel tube column after impact according to claim 9, characterized in that: In the prepared steel tube concrete column specimens, the corrosion area on the steel tube surface and the annular void position are both 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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