A method and system for evaluating the bearing performance of a hollow steel tube concrete intersecting joint

Abstract

The present application relates to a kind of hollow steel pipe concrete intersecting node bearing performance evaluation method and system, comprising: obtaining the geometric parameter, material parameter and interface hollow defect parameter of target steel pipe concrete K type node, the hollow rate and steel ratio under different hollow shape j are calculated;Based on hollow shape j, call pre-trained bearing capacity reduction coefficient model, input hollow rate and steel ratio, the overall bearing capacity reduction coefficient is obtained by calculation;Obtain the reference ultimate bearing capacity of target node in the state without hollow defect;According to formula, the finite element ultimate bearing capacity of the node with hollow defect is calculated, and the bearing capacity evaluation is completed;The existing evaluation method based on steel pipe-concrete interface complete contact assumption does not consider the difference of spherical cap type and crescent type hollow shape and the coupling influence of steel ratio, leading to the problem that the bearing capacity evaluation result of steel pipe concrete K type node with hollow defect is dangerous.

Description

Technical Field

[0001] This invention belongs to the field of structural engineering in civil engineering, and relates to a method and system for evaluating the load-bearing performance of intersecting joints of hollow steel tube concrete. Background Technology

[0002] Concrete-steel tubular (CFST) structures combine the circumferential restraint of the steel tube on the core concrete with the compressive strength of the concrete, resulting in high load-bearing capacity, excellent ductility, and overall stability. They are widely used in lattice-type load-bearing systems in engineering fields such as CFST arch bridges, long-span truss bridges, and wind turbine towers. In CFST structures, K-joints bear the load transfer function between the web members and the chord members, and their local mechanical response directly determines the overall safety of the structure. Existing research shows that when the interface between the steel tube and the core concrete maintains effective contact, the core concrete can provide radial support to the chord tube walls, alleviate stress concentration in the intersection area, significantly improve the ultimate bearing capacity of the joint, and improve its failure mode.

[0003] However, in actual engineering, due to factors such as concrete shrinkage and creep, insufficient pouring and vibration, bleeding settlement, temperature difference deformation between steel pipe and concrete, and long-term service deterioration, interface voids are easily formed between the inner wall of the steel pipe and the core concrete. For horizontal or near-horizontal chord members, gravity settlement and bleeding can easily form spherical (SC) voids at the top of the chord members; while eccentric shrinkage, uneven local contact, and complex stress states may induce circumferential crescent (CR) voids distributed along the circumference of the chord members. Existing studies on ordinary CFST members have confirmed that interface voids weaken the combined effect of the steel pipe and the core concrete, leading to a decrease in the load-bearing capacity, stiffness, and energy dissipation capacity of the member. However, the above conclusions cannot be directly extrapolated to the K-type nodes of CFST: under the combined action of tension and compression web members, the intersecting area of ​​the K-type node is in a complex three-dimensional stress state, and its ultimate bearing capacity and failure mode are jointly controlled by the local plasticity of the chord members, the deformation at the root of the web members, and the radial support provided by the core concrete. Interface voids not only weaken radial support stiffness but also alter the force transmission path in the critical failure zone, causing a shift in the dominant failure mode between chord shear failure, web member controlled failure, and combined failure. For example, a spherical void located directly on the main force transmission path in the web member loading zone has a significantly stronger reduction effect on bearing capacity than a crescent-shaped void distributed circumferentially. While increasing the steel content of the chord can enhance the circumferential stiffness of the pipe wall, under high void ratios, an abnormal phenomenon may still occur where thick-walled chord nodes transition from web member controlled failure to chord shear failure.

[0004] Currently, there is no dedicated bearing capacity assessment method for K-type nodes in CFST bridges with interface voids, both domestically and internationally. In engineering practice, directly applying existing code formulas based on the assumption of no voids will overestimate the radial support effect of the core concrete, thus significantly overestimating the actual safety margin of the node. While some studies have attempted to analyze the impact of voids through finite element simulation, they generally suffer from two limitations: first, they fail to systematically distinguish the differentiated impact mechanisms of void morphologies (spherical / crescent-shaped), using only the void rate to characterize the degree of defect, leading to significant deviations between the assessment results and the actual stress state; second, they lack a quantitative reduction model coupling void morphology, void rate, and chord steel ratio, making it difficult to meet the needs of rapid and accurate on-site assessment. Therefore, there is an urgent need for a bearing capacity assessment method and system for CFST K-type nodes that comprehensively considers differences in void morphology, the influence of steel ratio, and the law of failure mode transfer, providing technical support for the safe operation and maintenance of defective nodes in in-service CFST bridges and lattice-type load-bearing structures. Summary of the Invention

[0005] In view of this, in order to solve the problem that the existing evaluation methods based on the assumption of complete contact at the steel-concrete interface do not consider the differences between the spherical and crescent-shaped void morphologies and the coupling effect of the steel content, resulting in dangerously biased evaluation results of the bearing capacity of steel-concrete K-type joints with void defects, the present invention provides a method and system for evaluating the bearing performance of intersecting steel-concrete joints with void defects.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for evaluating the load-bearing capacity of a hollow steel-concrete intersecting joint includes the following steps:

[0008] S1. Obtain the geometric parameters, material parameters, and interface void defect parameters of the target steel-concrete composite K-type node; among which, the geometric parameters include at least the chord outer diameter D and the chord wall thickness T; the material parameters are used to calculate the steel content of the chord. The interface void defect parameters should include at least the void morphology j and the void rate. Calculate the chord diameter-to-thickness ratio based on the chord wall thickness T and the chord outer diameter D. =D / 2T, and based on the cross-sectional area of ​​the chord steel tube With core concrete cross-sectional area Ratio calculation of steel content ;

[0009] S2. Based on the vacancy morphology j in step S1, call the pre-trained bearing capacity reduction coefficient model and input the vacancy rate. and steel content The overall bearing capacity reduction factor was calculated. ;

[0010] Among them, the pre-trained bearing capacity reduction coefficient model assumes the following when it is constructed. Voiding rate Increase the steel content of the chord members Improving the load-bearing capacity reduction has the opposite effect; therefore, the following method is adopted. The reduction factor for the overall bearing capacity induced by voiding is given by the formula, where j represents the voiding morphology and is taken as SC and CR respectively. Enter the empty rate as a decimal. Enter as a decimal. , and Let be the coefficients to be determined, where Characterizing the voiding rate Impact on bearing capacity degradation Characterizing steel content Enhances the inhibitory effect on desiccation sensitivity. Reflects the emptying rate Increased size leads to weakened local support. Reflecting the chord wall thickness T and steel content The increased inhibition of desiccation sensitivity. Overall bearing capacity reduction factor .

[0011] Based on the finite element parametric analysis results, the bearing capacity reduction coefficients for different voiding morphologies were obtained by fitting using the nonlinear least squares method: when the voiding morphology j is a spherical cap type SC... When the vacuolation morphology j is a circumferential crescent-shaped CR, ;in, and All values ​​are expressed in decimal form. The fitting results show that the reduction term for SC debonding increases faster with the debonding rate, indicating that it more directly weakens the local supports near the main force transmission path; the reduction term for CR debonding... More sensitive, indicating that with the increase of chord wall thickness, the circumferential contact disturbance caused by CR void can be significantly weakened by the chord's own stiffness. When the void shape cannot be reliably identified, one can take... As a conservative estimate.

[0012] S3. Obtain the benchmark ultimate bearing capacity of the target node under the condition of no void defects. Reference ultimate bearing capacity Obtain the reference ultimate bearing capacity P by any of the following methods: 1) Conduct a full-scale loading test on the reference node without voids to obtain the reference ultimate bearing capacity P. u0 Alternatively, load tests can be conducted on scaled-down models that meet geometric, material, and load similarity conditions, and the test results can be converted into the reference ultimate bearing capacity P based on the similarity relationship. u0 ;2) The ultimate bearing capacity P of the non-void node was calculated using an experimentally verified nonlinear finite element model.u0 3) The initial reference bearing capacity is obtained by using a pre-set bearing capacity calculation model that is applicable to the node form, geometry, and stress state of the reference node without voids in the current design code. The correction coefficient is determined based on the loading test of the reference node without voids or the nonlinear finite element calculation results verified by the test. The reference ultimate bearing capacity P is then obtained after correction. u0 .

[0013] S4. The overall bearing capacity reduction factor calculated based on step S2. and the benchmark ultimate bearing capacity obtained in step S3 According to the formula The finite element ultimate bearing capacity of nodes with void defects was calculated. Complete the load-bearing capacity assessment;

[0014] S5. Based on the obtained chord diameter-to-thickness ratio D / T and void ratio Referring to the preset failure mode mapping relationship, the potential failure modes of the target node, including chord shear failure and web member failure, are predicted. The preset failure mode mapping relationship is: when 71.15 < D / T ≤ 122.0 and 0% ≤ When ≤8%, both the spherical cap-shaped void node and the circumferential crescent-shaped void node are predicted to be chordal punching shear failure; when 54.90<D / T≤71.15 and 0%≤ When the percentage is ≤8%, the spherical cap-shaped void joint is predicted to be a chord member punching shear failure; for the circumferential crescent-shaped void joint, when 0%≤ When the percentage is <6%, it is presumed to be web member failure; when 6% ≤ When ≤8%, it is presumed to be chord shear failure; when 44.75<D / T≤54.90, for the spherical cap-shaped void joint, when 0%≤ When the percentage is <4%, it is presumed to be web member failure; when 4% ≤ When the failure rate is ≤8%, it is predicted to be chord shear failure; the circumferential crescent-shaped void node is at 0%≤ When ≤8%, it is presumed to be web member failure; when 40.7≤D / T≤44.75, for a spherical cap-shaped voided node, when 0%≤ When the percentage is <6%, it is presumed to be web member failure; when 6% ≤ When the failure rate is ≤8%, it is predicted to be chord shear failure; the circumferential crescent-shaped void node is at 0%≤ When the failure rate is ≤8%, it is presumed to be a failure of the web member.

[0015] The evaluation system based on the above-mentioned method for evaluating the bearing capacity of intersecting concrete-filled steel tube joints includes:

[0016] The data acquisition module is used to obtain the geometric parameters, material parameters, and interface void defect parameters of the target steel-concrete composite K-type node, and to calculate the chord diameter-to-thickness ratio D / T and steel content. ;

[0017] The reduction factor calculation module has a built-in pre-trained bearing capacity reduction factor model, which is used to receive the input void shape j and void rate. and steel content Output the corresponding overall bearing capacity reduction factor. ;

[0018] The benchmark bearing capacity acquisition module is used to acquire the benchmark ultimate bearing capacity of the target node in the state without voids. ;

[0019] The bearing capacity assessment module is connected to both the reduction factor calculation module and the benchmark bearing capacity acquisition module, based on the formula. The finite element ultimate bearing capacity of nodes with void defects was calculated. ;

[0020] Failure Mode Prediction Module; Pre-stores the aforementioned failure mode mapping relationships, used for prediction based on chord diameter-to-thickness ratio (D / T) and steel content. Voiding rate And output the j-parameter of the detachment morphology for early warning of potential damage modes;

[0021] The storage module stores the baseline bearing capacity database for nodes of different specifications and the corresponding reduction factor calculation results;

[0022] The display module visually shows the node structure, location of void defects, early warning information on failure modes, and the final load-bearing capacity assessment information.

[0023] The beneficial effects of this invention are as follows:

[0024] 1. The bearing capacity evaluation method for intersecting steel-concrete composite joints with voids disclosed in this invention breaks through the limitations of traditional specifications based on the ideal assumption of "complete interface contact," and for the first time considers the differentiated impact of spherical and crescent-shaped voids on the joint bearing capacity. Compared with the problem of easily overestimating the bearing capacity by directly applying the formulas of specifications without voids, this invention can quantify the real reduction effect caused by defects.

[0025] 2. The load-bearing performance evaluation method for intersecting steel-concrete composite joints disclosed in this invention introduces a coupling mechanism between steel content and void ratio, enabling the differentiation between "thick-walled safety" and "thin-walled danger" conditions. For joints with high steel content and large wall thickness, this invention can accurately determine their low sensitivity to void defects, avoiding excessive maintenance; while for voids in thin-walled or critical load-bearing areas, it can accurately issue early warnings. This refined graded evaluation strategy avoids a "one-size-fits-all" reinforcement approach, significantly reducing the operation and maintenance costs of in-service bridges and towers.

[0026] 3. The method for evaluating the load-bearing capacity of intersecting steel-concrete composite joints disclosed in this invention addresses the difficulty in accurately defining the void morphology during on-site testing by providing a simple and conservative handling mechanism: when it is impossible to distinguish between spherical and crescent-shaped voids, simply take the smaller value of the calculation results for the two morphologies as the final reduction coefficient. This design eliminates the need for complex morphology reconstruction, simplifies the operation process, and strictly adheres to the "safety first" principle of engineering structural design, making it particularly suitable for evaluating aging in-service structures where testing conditions are limited.

[0027] 4. The method for evaluating the load-bearing capacity of intersecting steel-concrete composite joints disclosed in this invention establishes a reduction factor model covering commonly used engineering parameters such as diameter-to-thickness ratio of 40.7~122.0, steel content of 3.36%~10.61%, and void ratio of 0%~8%, encompassing the vast majority of K-type joint application scenarios in steel-concrete composite truss structures and arch bridges. Whether for defect acceptance of newly constructed structures or health monitoring of in-service structures, this method can be directly used for rapid evaluation, demonstrating extremely high engineering practical value.

[0028] 5. The method for evaluating the bearing capacity of intersecting joints of hollow steel-concrete composite tubes disclosed in this invention, after obtaining evaluation parameters such as the steel content of the chord, the interface void ratio, and the void morphology, can obtain the bearing capacity reduction coefficient through explicit calculation formulas, and determine the bearing capacity of the joint with interface void defects by combining the benchmark bearing capacity of the corresponding joint without voids. Within the applicable parameter range, it is not necessary to re-perform complex nonlinear finite element modeling and iterative calculations for each joint to be evaluated. This method has a clear input, calculation, and output process, which is easy to integrate into mobile applications, portable testing equipment, or BIM operation and maintenance systems. It can reduce the workload of calculation, improve the efficiency of bearing capacity evaluation, and provide technical support for engineering design review, construction quality assessment, and operation and maintenance of existing structures.

[0029] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0031] Figure 1 This is a finite element model diagram of the CFST K-type node with chord detachment defect according to the present invention;

[0032] Figure 2 The bearing capacity reduction factor under different voiding parameters of this invention The distribution and discreteness of, among which Figure 2 (a) is a graph showing the distribution of Ψ as a function of the de-voiding rate ρ under SC de-voiding. Figure 2 (b) is a distribution diagram of Ψ as a function of the devotion rate ρ under CR devotion. Figure 2 (c) Different emptying rates Below The discrete amplitude variation graph;

[0033] Figure 3 This is a comparison chart of the predicted reduction factor value and the finite element value of the present invention. Detailed Implementation

[0034] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0035] Single physical tests are limited by the number of specimens and the range of operating conditions, making it difficult to systematically evaluate the impact of interface voids on the failure mode and bearing capacity of CFST K-type joints. Therefore, based on the validated finite element model shown in Figure 1, multivariate parametric analysis was conducted. Referring to the design recommendations for pipe joints in CIDECT, ISO 14346, and GB 50936-2014, a parametric design matrix containing 45 operating conditions was established (see Table 1). In all models, the angle between the axes of the two web members and the chord member was 45°. The chord member dimensions were D×L=244mm×1500mm, and the web member dimensions were... =122mm×740mm, node structure, steel is Q355, core concrete is C60.

[0036] The parameter design is based on the principle of controlling the main variables. (Steel content) By adjusting the chord wall thickness, with a wall thickness of T = 2–6 mm, the corresponding diameter-to-thickness ratio is controlled. The value decreased from 61.0 to 20.3, covering a wider range of diameter-to-thickness ratios, and was used to analyze the influence of chord radial stiffness on the voiding effect and nodal mechanical properties. The degree of voiding was expressed as a dimensionless voiding rate. The void shape is characterized by the ratio of the void area volume to the corresponding core concrete reference volume. For a cross-section-controlled void model, this ratio can be equivalently reflected as the area ratio of the void section to the core concrete section, with a value ranging from 0% to 8%, to facilitate a unified comparison of different defect morphologies. The void shape j is divided into two types: spherical crown (SC) and circumferential crescent (CR). Spherical crown voids are controlled by adjusting the void height ds. The circumferential crescent-shaped void is used to characterize localized interfacial debonding caused by concrete segregation and shrinkage. Its maximum radial void depth dc is fixed at 5 mm, and the circumferential wrap angle is varied. control This parameter design, while maintaining the interpretability of defect geometry, helps to distinguish the effects of void morphology, void ratio, and chord diameter-to-thickness ratio on nodal response.

[0037] Table 1. Parametric Model Numbers and Dimensions

[0038]

[0039] Current pipe joint design methods typically establish bearing capacity expressions based on controlled failure modes, mainly covering typical mechanisms such as chord surface plasticity, chord punching shear, and web member failure. The bearing capacity formulas for CHS K-type joints in IIW and CIDECT primarily target hollow circular steel pipe joints; GB 50017-2017 also does not include explicit bearing capacity reduction terms for CFST K-type joints with voids. For CFST K-type joints without voids, existing models often borrow the functional form of IIW / CIDECT to establish chord punching shear bearing capacity formulas and perform regression verification using chord punching shear or combined failure samples. However, these models assume that the core concrete can provide continuous and effective radial support to the chord wall, and cannot directly reflect the interface support degradation and bearing capacity reduction effects caused by local voids. Void defects change these assumptions. After the local contact between the chord wall and the core concrete is weakened, the radial deformation of the chord, the plastic expansion of the intersection zone, and the additional bending moment at the root of the web members may all change. The degree of influence depends on whether the defect is located near the main force transmission path and whether the chord wall thickness can compensate for the local support loss. If the punching shear formula for chords without voids is directly used to evaluate members with voids, it is equivalent to assuming a void reduction factor of 1.0, which cannot reflect the differentiated degradation caused by voids in SC and CR. The finite element results of this embodiment show that, under an 8% void ratio, the P of the T2-T6 series in the SC condition... u / P u0 The values ​​are 0.524, 0.561, 0.618, 0.722, and 0.849, respectively, while the corresponding values ​​in the CR condition are 0.636, 0.766, 0.972, 0.995, and 0.998. This difference indicates that the voiding effect must simultaneously consider the chord diameter-to-thickness ratio, voiding shape, and voiding rate.

[0040] A reduction coefficient database was established based on 40 finite element models containing voids. The samples cover wall thicknesses from T2 to T6, two void types (SC and CR), and void rates ranging from 2% to 8%. To reflect the coupled effects of wall thickness, void type, and void rate, all samples containing voids were included in the subsequent fitting. Figure 2It can be seen that under SC voiding, Ψ generally decreases with increasing voiding ratio ρ, and the decrease is greater in thin-walled chords; CR voiding still causes a reduction in bearing capacity in thin-walled chords, but with increasing chord wall thickness, Ψ approaches 1.0 in most working conditions. To quantify the differences caused by different wall thicknesses and voiding morphologies under the same voiding ratio, Figure 2 The range of values ​​for Ψ and their dispersion amplitude for each ρ level are also given. As ρ increases from 2% to 8%, the range of Ψ expands from 0.910-1.000 to 0.524-0.998, and the corresponding dispersion amplitude increases from 0.090 to 0.474. This result indicates that the void ratio ρ only reflects the magnitude of the defect and cannot characterize the degree of bearing capacity degradation alone; the reduction factor Ψ should simultaneously consider the influence of the void morphology and the chord diameter-to-thickness ratio or steel content.

[0041] To verify the accuracy of the newly added reduction factor, the formula will be used. Japanese style Calculated With finite element normalization result Ψ FE = P u,gap / P u0 A comparison was made. The comparison results are shown below. Figure 3 The statistical indicators are shown in Table 2.

[0042] Table 2 Statistical Indicators for Model Validation of Reduction Factor

[0043]

[0044] Depend on Figure 3 As shown in Table 2, the empty samples of SC The average value is 0.9959, R0 2 The mean value of CR for empty samples was 0.9173, the mean value of COV was 0.0641, the mean value of RMSE was 0.0453, and the maximum absolute error was 0.0925; the mean value of CR for empty samples was 0.9948, and the mean value of R was 0.9948. 2 The coefficient of performance (COP) is 0.9298, the coefficient of variation (COV) is 0.0358, the RMSE is 0.0297, and the maximum absolute error is 0.0757. The predicted points are generally distributed around the 1:1 line, and no systematic error monotonically deviates with the void ratio or chord diameter-to-thickness ratio. This result indicates that the formula... Japanese style This can reasonably describe the difference in overall bearing capacity reduction caused by the detachment of SC and CR within the parameter range of this paper. According to the formula... The finite element ultimate bearing capacity of nodes with void defects was calculated. Complete the bearing capacity assessment, and establish its The model is a void-induced overall bearing capacity reduction model, which examines the bearing capacity degradation of nodes with voids relative to nodes without voids under the same geometric and loading conditions. Using nodes without voids in the same series as a benchmark, this model can characterize the coupling effect of chord diameter-to-thickness ratio, void morphology, and void ratio on the overall bearing capacity reduction. Its applicable boundaries differ from the single chord punching shear strength formula and are consistent with the observed failure mode transfer laws. The above processing provides a clear parameter basis and applicable scope for subsequent establishment of design-type bearing capacity models based on larger databases.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for evaluating the load-bearing capacity of a hollow steel-concrete intersecting joint, characterized in that, Includes the following steps: S1. Obtain the geometric parameters, material parameters, and interface void defect parameters of the target steel-concrete composite K-type node; among which, the geometric parameters include at least the chord outer diameter D and the chord wall thickness T; the material parameters are used to calculate the steel content of the chord. The interface void defect parameters should include at least the void morphology j and the void rate. Calculate the chord diameter-to-thickness ratio based on the chord wall thickness T and the chord outer diameter D. =D / 2T, and based on the cross-sectional area of ​​the chord steel tube With core concrete cross-sectional area Ratio calculation of steel content ; S2. Based on the vacancy morphology j in step S1, call the pre-trained bearing capacity reduction coefficient model and input the vacancy rate. and steel content The overall bearing capacity reduction factor was calculated. The pre-trained load-bearing capacity reduction coefficient model assumes the following when it is constructed. , adopting the formula The reduction factor for the overall bearing capacity induced by voiding is given by the formula, where j represents the voiding morphology and is taken as SC and CR respectively. Enter the empty rate as a decimal. Enter as a decimal. , and Let be the coefficients to be determined, where Characterizing the voiding rate Impact on bearing capacity degradation Characterizing steel content Enhances the inhibitory effect on desiccation sensitivity. Reflects the emptying rate Increased size leads to weakened local support. Reflecting the chord wall thickness T and steel content The inhibitory effect on the sensitivity to void removal after enhancement; S3. Obtain the benchmark ultimate bearing capacity of the target node under the condition of no void defects. ; S4. The overall bearing capacity reduction factor calculated based on step S2. and the benchmark ultimate bearing capacity obtained in step S3 According to the formula The finite element ultimate bearing capacity of nodes with void defects was calculated. Complete the load-bearing capacity assessment.

2. The method for evaluating the bearing capacity of the intersecting joint of hollow steel tube concrete as described in claim 1, characterized in that, In step S1, the diameter-to-thickness ratio of the chord is... Satisfy: 20.3≤ ≤61.0; chord steel content Satisfy: 3.36% ≤ ≤10.61%; Void removal rate Satisfy: 0%≤ ≤8%.

3. The method for evaluating the bearing capacity of the intersecting joint of hollow steel tube concrete as described in claim 1, characterized in that, In step S1, the vacuolation morphology j is obtained through non-destructive testing equipment; vacuolation rate Defined as the percentage of the volume of the voided area to the reference volume of the core concrete, or equivalently, through cross-sectional measurement, as the percentage of the cross-sectional area of ​​the voided area to the cross-sectional area of ​​the core concrete.

4. The method for evaluating the bearing capacity of the intersecting joint of hollow steel tube concrete as described in claim 1, characterized in that, In step S2, the bearing capacity reduction coefficients for different voiding morphologies are obtained by fitting using the nonlinear least squares method: when the voiding morphology j is a spherical cap type SC, ; When the empty morphology j is a circumferential crescent-shaped CR ;in, and All values ​​are in decimal form. When the empty form cannot be reliably identified, take the decimal form. As a conservative estimate.

5. The method for evaluating the bearing capacity of the intersecting joint of hollow steel tube concrete as described in claim 3, characterized in that, The reference ultimate bearing capacity in step S3 Obtain the reference ultimate bearing capacity P by any of the following methods: 1) Conduct a full-scale loading test on the reference node without voids to obtain the reference ultimate bearing capacity P. u0 Alternatively, load tests can be conducted on scaled-down models that meet geometric, material, and load similarity conditions, and the test results can be converted into the reference ultimate bearing capacity P based on the similarity relationship. u0 ;2) The ultimate bearing capacity P of the non-void node was calculated using an experimentally verified nonlinear finite element model. u0 3) The initial reference bearing capacity is obtained by using a pre-set bearing capacity calculation model that is applicable to the node form, geometry, and stress state of the reference node without voids in the current design code. The correction coefficient is determined based on the loading test of the reference node without voids or the nonlinear finite element calculation results verified by the test. The reference ultimate bearing capacity P is then obtained after correction. u0 .

6. The method for evaluating the bearing capacity of the intersecting joint of hollow steel tube concrete as described in claim 1, characterized in that, It also includes a failure mode prediction step: based on the obtained chord diameter-to-thickness ratio D / T and void ratio. Referring to the preset failure mode mapping relationship, the potential failure modes of the target node, including chord shear failure and web member failure, are predicted. The preset failure mode mapping relationship is: when 71.15 < D / T ≤ 122.0 and 0% ≤ When ≤8%, both the spherical cap-shaped void node and the circumferential crescent-shaped void node are predicted to be chordal punching shear failure; when 54.90<D / T≤71.15 and 0%≤ When the percentage is ≤8%, the spherical cap-shaped void joint is predicted to be a chord member punching shear failure; for the circumferential crescent-shaped void joint, when 0%≤ When the percentage is <6%, it is presumed to be web member failure; when 6% ≤ When ≤8%, it is presumed to be chord shear failure; when 44.75<D / T≤54.90, for the spherical cap-shaped void joint, when 0%≤ When the percentage is <4%, it is presumed to be web member failure; when 4% ≤ When the failure rate is ≤8%, it is predicted to be chord shear failure; the circumferential crescent-shaped void node is at 0%≤ When ≤8%, it is presumed to be web member failure; when 40.7≤D / T≤44.75, for a spherical cap-shaped voided node, when 0%≤ When the percentage is <6%, it is presumed to be web member failure; when 6% ≤ When the failure rate is ≤8%, it is predicted to be chord shear failure; the circumferential crescent-shaped void node is at 0%≤ When the failure rate is ≤8%, it is presumed to be a failure of the web member.

7. An evaluation system based on the method for evaluating the bearing capacity of intersecting concrete-filled hollow steel tube joints according to any one of claims 1 to 6, characterized in that, include: The data acquisition module is used to obtain the geometric parameters, material parameters, and interface void defect parameters of the target steel-concrete composite K-type node, and to calculate the chord diameter-to-thickness ratio D / T and steel content. ; The reduction factor calculation module has a built-in pre-trained bearing capacity reduction factor model as described in claim 1, used to receive the input voiding morphology j and voiding rate. and steel content Output the corresponding overall bearing capacity reduction factor. ; The benchmark bearing capacity acquisition module is used to acquire the benchmark ultimate bearing capacity of the target node in the state without voids. ; The bearing capacity assessment module is connected to both the reduction factor calculation module and the benchmark bearing capacity acquisition module, and is based on the formula... The finite element ultimate bearing capacity of nodes with void defects was calculated. .

8. The evaluation system as described in claim 7, characterized in that, The data acquisition module includes one or more combinations of an ultrasonic flaw detector, an industrial endoscope, or a 3D laser scanner, used to detect the internal void morphology and quantify the void rate of the chord members. .

9. The evaluation system as described in claim 7, characterized in that, The system also includes a failure mode prediction module, which pre-stores the failure mode mapping relationship as described in claim 6, for use based on the chord diameter-to-thickness ratio D / T and steel content. Voiding rate And output the j-parameter of the detachment morphology to provide early warning of potential damage modes.

10. The evaluation system as described in claim 9, characterized in that, The system also includes a storage module and a display module; the storage module is used to store the benchmark bearing capacity database of nodes of different specifications and the corresponding reduction factor calculation results; the display module is used to visually display the node structure, the location of void defects, the early warning information of failure modes, and the final bearing capacity assessment information.

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