Mechanical performance analysis method and system for negative moment zone of UHPC thin-layer reinforced steel-concrete composite beams

Abstract

The present invention discloses a method and system for analyzing the mechanical properties of a UHPC thin-layer reinforced steel-concrete composite beam in the negative bending moment zone, and belongs to the technical field of composite beam performance analysis data processing. The method comprises the following steps: obtaining a geometric mechanical property reduction model of non-uniformly corroded steel bars based on a steel constitutive model and test data on the mechanical properties of corroded steel bars; obtaining a concrete damage coefficient by comparing the ultimate loads of unloaded and preloaded ratios under the same chloride corrosion damage degree based on the UHPC constitutive model; and obtaining a residual bending bearing capacity model of the UHPC reinforced steel-concrete composite beam after load-corrosion using the geometric mechanical property reduction model of the non-uniformly corroded steel bars and the composite beam force balance equation; introducing a correction coefficient to obtain a long-term bending calculation model of the UHPC reinforced steel-concrete composite beam after load-corrosion, thereby improving the accuracy of the bearing capacity performance analysis of the steel-UHPC composite beam in the negative bending moment zone under load-corrosion coupling.

Description

Technical Field

[0001] The present invention relates to the technical field of composite beam performance data analysis and processing, and in particular to a method and system for analyzing the mechanical properties of a UHPC thin-layer reinforced steel-concrete composite beam in a negative moment zone. Background Art

[0002] The analysis of the mechanical properties of composite beams in the negative bending zone is a key issue in the study of steel-concrete composite structures. This research focuses on the complex stress conditions in structures subjected to alternating loads, such as bridges and building floors, where the concrete slab is in tension and the steel beam is in compression. This research stems from the demand for lightweight, high-capacity, and economical structures in modern engineering. However, negative bending zones are prone to problems such as concrete cracking, steel yielding, localized steel beam instability, and interfacial slip, which directly impact structural stiffness, durability, and ultimate bearing capacity.

[0003] Current codes and existing literature define the calculation of the flexural capacity of steel-concrete composite beams in the negative moment region and composite members using thin layers of UHPC (Ultra-High Performance Concrete). When calculating the flexural capacity of composite beams in the negative moment region, national codes assume concrete cracking and ignore its flexural contribution, considering only the tensile forces provided by the reinforcement and steel beam. Based on this, researchers have considered the contribution of UHPC to the flexural performance of composite beams, established a calculation formula for the flexural capacity of steel-UHPC composite beams, and proposed a preliminary calculation method for the flexural capacity of UHPC composite members. In recent years, research has progressed, including methods for calculating the long-term flexural capacity of UHPC-reinforced members. For example, Mei Kuihua et al. and Yu Jian et al. have derived calculation methods for the flexural capacity of corroded UHPC-reinforced concrete members. However, the role of loads in the long-term service life of bridges cannot be ignored. The coupled effects of load and corrosion can cause cracks in the negative moment region of bridges. Corrosive media can penetrate through these cracks and easily corrode the structural reinforcement. As corrosion progresses, corrosive substances will expand cracks and further damage the steel-UHPC composite beams. Existing research on the long-term performance of this type of structure remains insufficient, especially in the theoretical calculation method for the bearing capacity of steel-UHPC composite beams in the negative bending moment zone under load-corrosion coupling. Summary of the Invention

[0004] The present invention solves at least one of the technical problems mentioned in the background technology by providing a method and system for analyzing the mechanical properties of a UHPC thin-layer reinforced steel-concrete composite beam in a negative bending moment zone.

[0005] The present invention provides a method for analyzing the mechanical properties of a UHPC thin-layer reinforced steel-concrete composite beam in a negative moment zone, comprising the following steps: obtaining a geometric mechanical property reduction model of non-uniformly corroded steel bars based on a steel constitutive model and test data on the mechanical properties of corroded steel bars, wherein the steel includes steel bars and steel beams; obtaining a concrete damage coefficient by comparing ultimate loads with no load and ultimate loads with preload ratios under the same chloride corrosion damage degree based on the UHPC constitutive model, wherein the preload ratio of the ultimate load is 0.4; obtaining a residual bending bearing capacity model of the UHPC reinforced steel-concrete composite beam after load-corrosion based on the concrete damage coefficient, the geometric mechanical property reduction model of the non-uniformly corroded steel bars, and a composite beam force equilibrium equation; and introducing a correction coefficient into the residual bending bearing capacity model of the UHPC reinforced steel-concrete composite beam after load-corrosion to obtain a long-term bending calculation model of the UHPC reinforced steel-concrete composite beam after load-corrosion.

[0006] The present invention also provides a system for applying a method for analyzing the mechanical properties of a UHPC thin-layer reinforced steel-concrete composite beam in a negative moment zone, comprising: a steel analysis module, a UHPC analysis module, a bearing capacity analysis module, a composite beam verification module, and a mechanical properties analysis database; wherein the steel analysis module is used to obtain a geometric mechanical property reduction model of non-uniformly corroded steel bars based on a steel constitutive model and test data on the mechanical properties of corroded steel bars, wherein the steel includes steel bars and steel beams; the UHPC analysis module is used to obtain a concrete damage coefficient by comparing the ultimate loads of unloaded and preloaded ratios under the same chloride salt corrosion damage degree based on the UHPC constitutive model; the bearing capacity analysis module is used to obtain a residual bending bearing capacity model of the UHPC reinforced steel-concrete composite beam after load-corrosion based on the concrete damage coefficient, the geometric mechanical property reduction model of the non-uniformly corroded steel bars, and the composite beam force equilibrium equation; and the composite beam verification module is used to introduce a correction coefficient into the residual bending bearing capacity model of the UHPC reinforced steel-concrete composite beam after load-corrosion to obtain a long-term bending calculation model of the UHPC reinforced steel-concrete composite beam after load-corrosion.

[0007] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0008] 1. The present invention provides a method and system for analyzing the mechanical properties of UHPC thin-layer reinforced steel-concrete composite beams in the negative moment zone, thereby effectively evaluating the contact characteristics between steel and concrete and the impact of load-corrosion coupling on the bearing capacity calculation of the composite beam. This allows for dynamic correction of load and strain values, thereby improving the accuracy of calculating the bearing capacity of steel-UHPC composite beams in the negative moment zone under load-corrosion coupling.

[0009] 2. The present invention compares the contact characteristic index obtained based on the contact characteristic parameters on the contact surface between the steel bar and the concrete with a preset contact characteristic threshold, thereby determining whether to perform dynamic correction of the strain value based on the contact characteristic evaluation result, thereby optimizing the strain value of the contact surface between the steel bar and the concrete, reducing the impact of poor contact, and improving the stability and reliability of the hybrid beam structure.

[0010] 3. The present invention compares the corrosion strain parameter reflecting the expansion degree of steel corrosion products with a preset corrosion strain threshold, thereby dynamically correcting the load and strain values ​​to reduce the impact of corrosion on the performance of the composite beam. This enables accurate assessment and intervention of the impact of steel corrosion, effectively ensuring the accuracy and reliability of the mechanical performance parameters in the negative bending moment zone of the composite beam, thereby improving the accuracy of the residual bending bearing capacity model of UHPC-reinforced steel-concrete composite beams after load-corrosion effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Flowchart of the method for analyzing the mechanical properties of the negative moment zone of UHPC thin-layer reinforced steel-concrete composite beams provided in the embodiments of the present application.

[0012] Figure 2 A mind map of the contact impact correction module provided in an embodiment of the present application.

[0013] Figure 3 A mind map of the corrosion impact correction module provided in an embodiment of the present application.

[0014] Figure 4 This is a diagram of the tensile and compressive constitutive model of steel provided in the embodiments of this application.

[0015] Figure 5 This is a diagram of the UHPC tensile constitutive model provided in the examples of this application.

[0016] Figure 6 Calculation diagram of the corroded composite beam provided in the embodiment of the present application.

[0017] Figure 7 This is a correction coefficient fitting curve diagram provided in the embodiment of the present application.

[0018] Figure 8a The structural diagram of the steel-NC-UHPC composite beam provided in the embodiment of this application (unit: mm) Figure 8b The vertical structure diagram of the steel-NC-UHPC composite beam specimen provided in the embodiment of this application (unit: mm), Figure 8c Cross-sectional structural diagram of the steel-NC-UHPC composite beam specimen provided in the examples of this application (unit: mm).

[0019] Figure 9 A diagram of the loading device provided in an embodiment of the present application.

[0020] Figure 10 This is a diagram of the measurement point layout of the steel-NC-UHPC composite beam provided in the embodiment of this application.

[0021] Figure 11 This is the diagram of the integrated tester installation.

[0022] Figure 12 Schematic diagram of the structure of the negative moment zone mechanical performance analysis system for UHPC thin-layer reinforced steel-concrete composite beams provided in an embodiment of the present application. DETAILED DESCRIPTION

[0023] The embodiment of the present application provides a method and system for analyzing the mechanical properties of the negative bending zone of a UHPC thin-layer reinforced steel-concrete composite beam, thereby solving the problem that during the long-term service of the bridge, under the coupling of load and corrosion, the load will cause cracks to form in the negative bending zone of the bridge, and the corrosive medium will penetrate along the cracks, which will more easily corrode the steel bars in the structure. As the corrosion deepens, the corrosive substances will expand the cracks and cause further damage to the steel-UHPC composite beam. There may be expansion of corrosion products and backlog of surrounding concrete, generating additional strain, resulting in low accuracy of the load and strain values ​​measured by the comprehensive tester, thereby resulting in low accuracy of the bearing capacity performance analysis of the steel-UHPC composite beam in the negative bending zone under the load-corrosion coupling. According to the steel constitutive model and the test data of the mechanical properties of the corroded steel bars, the geometric mechanical properties of the non-uniformly corroded steel bars are obtained. Performance reduction model, steel includes steel bars and steel beams; according to the UHPC constitutive model, the ultimate load without loading and the ultimate load with preload ratio under the same chloride corrosion damage degree are compared to obtain the concrete damage coefficient, and the preload ratio of the ultimate load is 0.4; based on the concrete damage coefficient, the geometric mechanical performance reduction model of non-uniformly corroded steel bars, and the composite beam force equilibrium equation, the residual bending bearing capacity model of UHPC reinforced steel-concrete composite beams after load-corrosion is obtained; the correction coefficient is introduced into the residual bending bearing capacity model of UHPC reinforced steel-concrete composite beams after load-corrosion to obtain the long-term bending calculation model of UHPC reinforced steel-concrete composite beams after load-corrosion, which improves the accuracy of the bearing capacity performance analysis of steel-UHPC composite beams in the negative bending moment zone under load-corrosion coupling.

[0024] The technical solution in the embodiments of the present application is to solve the problem that during the long-term service of the bridge, under the coupled action of load and corrosion, the load will cause cracks in the negative bending moment area of ​​the bridge. The corrosive medium will penetrate along the cracks and will more easily corrode the steel bars in the structure. As the corrosion deepens, the corrosive substances will expand the cracks and cause further damage to the steel-UHPC composite beam. There may be expansion of rust products and backlog of surrounding concrete, generating additional strain, resulting in low accuracy of the load and strain values ​​measured by the comprehensive tester, thereby resulting in low accuracy of the bearing capacity performance analysis of the steel-UHPC composite beam in the negative bending moment area under the load-corrosion coupling. The overall concept is as follows:

[0025] Based on the steel constitutive model and test data on the mechanical properties of corroded steel bars, a geometric mechanical property reduction model for non-uniformly corroded steel bars was derived. The concrete damage coefficient was obtained by comparing the ultimate loads of unloaded and preloaded loads at the same chloride corrosion damage level. A residual bending capacity model for UHPC-reinforced steel-concrete composite beams after load-corrosion was derived based on the concrete damage coefficient, the geometric mechanical property reduction model for non-uniformly corroded steel bars, and the composite beam force equilibrium equation. A correction factor was introduced into the above model to obtain a long-term bending calculation model for UHPC-reinforced steel-concrete composite beams after load-corrosion, improving the accuracy of the bearing capacity performance analysis of steel-UHPC composite beams in the negative bending moment zone under load-corrosion coupling.

[0026] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0027] like Figure 1As shown, it is a flow chart of the mechanical property analysis method of the negative moment zone of the UHPC thin-layer reinforced steel-concrete composite beam provided in an embodiment of the present application, the method comprising the following steps: according to the steel constitutive model and the mechanical property test data of the corroded steel bars, a geometric mechanical property reduction model of the non-uniformly corroded steel bars is obtained, where the steel includes steel bars and steel beams; according to the UHPC constitutive model, the ultimate load without loading and the ultimate load with preload ratio under the same chloride corrosion damage degree are compared to obtain the concrete damage coefficient, where the preload ratio of the ultimate load is 0.4; according to the concrete damage coefficient, the geometric mechanical property reduction model of the non-uniformly corroded steel bars and the composite beam force equilibrium equation, a residual bending bearing capacity model of the UHPC reinforced steel-concrete composite beam after load-corrosion is obtained; and a correction coefficient is introduced into the UHPC reinforced steel-concrete composite beam after load-corrosion. In the residual flexural capacity model of concrete composite beams, a long-term flexural calculation model for UHPC-reinforced steel-concrete composite beams after load-corrosion action is obtained. The parameters of the negative moment zone of the composite beam include the internal forces of the UHPC matrix, the internal forces of the UHPC layer longitudinal reinforcement, the internal forces of the NC layer longitudinal reinforcement, the bending moments of the tensile and compressive zones of the steel beam relative to the plastic neutral axis of the composite beam, and the distances between the centroids of the upper flange of the steel beam, the tensile zone of the steel beam web, the lower flange of the steel beam, and the compressive zone of the steel beam web and the plastic neutral axis of the composite beam. The residual flexural capacity model of UHPC-reinforced steel-concrete composite beams after load-corrosion action is used to reduce the uneven corrosion of the tensile longitudinal reinforcement in the UHPC thin layer and the degradation of the steel reinforcement mechanical properties caused by corrosion, as well as the influence of the UHPC layer flexural reduction effect caused by interface debonding on the mechanical performance analysis of the negative moment zone of the UHPC thin layer reinforced steel-concrete composite beam.

[0028] In this embodiment, the present invention corrects the strain and load values ​​at the contact surface between the steel bar and concrete based on contact characteristic parameters and corrosion strain parameters, respectively, reducing the effects of poor contact between the steel bar and concrete surface and expansion of steel bar corrosion products on the strain and load values. A residual flexural capacity model for UHPC-reinforced steel-concrete composite beams after load-corrosion is generated based on the corrected strain and load values ​​and the negative moment zone parameters of the composite beam. This method avoids the shortcomings of the prior art and provides a bearing capacity calculation method for the long-term mechanical properties of the negative moment zone of UHPC thin-layer reinforced steel-concrete composite beams. This bearing capacity calculation method for the long-term mechanical properties of the negative moment zone of UHPC thin-layer reinforced steel-concrete composite beams can effectively calculate the flexural capacity of the negative moment zone of UHPC thin-layer reinforced steel-concrete composite beams after load-corrosion coupling. The calculation method also takes into account the uneven corrosion of the tensile longitudinal bars within the UHPC thin layer and the degradation of the steel bar mechanical properties caused by corrosion. The present invention also innovatively introduces a correction factor to characterize the flexural reduction effect of the UHPC layer caused by interface debonding.

[0029] In addition, the mechanical properties analysis database is used to store relevant data on the mechanical properties analysis method of the negative bending moment zone of UHPC thin-layer reinforced steel-concrete composite beams, including: critical strain transfer efficiency, critical contact resistance, strain correction value corresponding to each contact characteristic deviation index range, first threshold value of contact characteristics, and second threshold value of contact characteristics. The data in the mechanical properties analysis database can be directly queried through public databases such as the transportation industry database and the scientific and technological resource sharing service platform, or obtained through cooperation with construction companies, UHPC material manufacturers, or relevant universities, research institutions and other departments.

[0030] like Figure 2 The figure shows a mind map of the contact influence correction module provided in an embodiment of the present application. The method includes: monitoring the contact influence parameters in real time, and obtaining a contact influence index based on the contact influence parameter analysis, comparing the contact influence index with the first contact influence threshold and the second contact influence threshold, respectively; if the contact influence index is less than or equal to the first contact influence threshold, then recording the corresponding contact characteristic evaluation result as the first contact characteristic result without additional processing; if the contact characteristic index is greater than the first contact characteristic threshold and less than the second contact characteristic threshold, then recording the corresponding contact characteristic evaluation result as the second contact characteristic result; correcting the strain value of the contact surface between the steel bar and the concrete according to the contact influence index; if the contact characteristic index is greater than or equal to the second contact characteristic threshold, then recording the corresponding contact characteristic evaluation result as the third contact characteristic result, and notifying manual intervention to process the contact surface until the contact characteristic index is less than or equal to the second contact characteristic threshold.

[0031] Specifically, the step of dynamically correcting the strain value between the steel bar and the concrete based on the contact characteristic parameters includes: obtaining a contact characteristic index based on the contact characteristic parameters, the contact characteristic parameters including strain transfer efficiency and contact resistance, the contact characteristic index representing quantitative data of the degree of influence of the strain transfer efficiency and contact resistance on the contact performance between the steel bar and the concrete; obtaining a first contact characteristic threshold and a second contact characteristic threshold from a preset mechanical property analysis database; comparing the contact characteristic index with the first contact characteristic threshold and the second contact characteristic threshold, respectively; if the contact characteristic index is less than or equal to the first contact characteristic threshold, issuing a contact abnormality prompt and notifying a preset personnel to process the contact surface between the steel bar and the concrete; if the contact characteristic index is greater than the first contact characteristic threshold and less than the second contact characteristic threshold, recording the difference between the second contact characteristic threshold and the contact characteristic index as a contact characteristic deviation index; matching the contact characteristic deviation index with strain correction values ​​corresponding to each contact characteristic deviation index range preset in the mechanical property analysis database to obtain a strain correction value; and correcting the strain value on the contact surface between the steel bar and the concrete based on the strain correction value to obtain a corrected strain value; and if the contact characteristic index is greater than or equal to the second contact characteristic threshold, no additional processing is performed.

[0032] The step of obtaining a contact characteristic index based on contact characteristic parameter analysis includes: obtaining contact characteristic parameter reference data from a preset mechanical performance analysis database, specifically including: critical strain transfer efficiency and critical contact resistance; performing a proportion approximation operation on the strain transfer efficiency and critical contact resistance respectively with the critical strain transfer efficiency and contact resistance, and then using contact characteristic contribution parameters to weight the proportion approximation operation results and then couple them to obtain a contact characteristic index, wherein the contact characteristic contribution parameters include strain transfer efficiency contribution and contact resistance contribution.

[0033] The contact characteristic index is obtained as follows:

[0034] ;

[0035] Where, The contact characteristic index represents the contact surface between steel and concrete. The contact characteristic index is a quantitative data indicating the influence of strain transfer efficiency and contact resistance on the contact performance between steel and concrete. represents the contribution of strain transfer efficiency, represents the contact resistance contribution, Indicates the strain transfer efficiency of the contact surface between steel and concrete. The strain transfer efficiency refers to the effectiveness of strain transfer from steel to concrete. The strain transfer efficiency can be calculated by placing strain gauges at different locations on the contact surface between steel and concrete. The difference between the average strain value on the steel surface and the average strain value on the concrete surface is calculated as the ratio of the average strain value on the steel surface to the average strain value on the steel surface. The higher the strain transfer efficiency between steel and concrete, the higher the contact characteristic index. represents the critical strain transfer efficiency, Represents the contact resistance between the steel bar and concrete. Contact resistance refers to the average resistance between the steel bar and concrete contact surfaces. It directly affects the strain transfer efficiency because the existence of resistance is related to the bonding strength on the contact surface and the ease of current conduction. Contact resistance can be obtained by applying a known current at different positions on the contact surface using the resistance test method, measuring the voltage change, and then calculating it using Ohm's law and taking the average value. The smaller the contact resistance, the better the contact between the steel bar and concrete, and the larger the contact characteristic index. represents the critical contact resistance.

[0036] and These are the contribution degrees corresponding to the strain transfer efficiency and contact resistance preset in the mechanical properties analysis database. These contribution degrees are numerical indicators that measure the influence of the above parameters on the contact characteristic index. Specifically, there is a mapping relationship table for each of the strain transfer efficiency and contact resistance, which records each possible parameter value and its corresponding contribution degree. These mapping relationships can be one-to-one or many-to-one. For example, in actual applications, when it is necessary to evaluate the contact characteristic index, the measured strain transfer efficiency and contact resistance can be entered into their respective corresponding mapping relationship tables, and the contribution degrees corresponding to these values ​​can be quickly found. The contribution degree ranges from 0 to 1.

[0037] It's important to note that in this algorithm, strain transfer efficiency and contact resistance are correlated. Increased contact resistance indicates poor contact quality and weak bond strength between the rebar and concrete, leading to reduced strain transfer efficiency. Conversely, lower contact resistance indicates better bond strength and higher strain transfer efficiency. The contact characteristic index, derived from comprehensive analysis, reflects the overall bond performance between rebar and concrete. This index can be used to mitigate the effects of poor contact between the rebar and concrete surface on strain values, thereby predicting the impact of factors like corrosion and aging on the mechanical performance analysis of the negative moment zone of composite beams.

[0038] like Figure 3 The figure shows a mind map of the corrosion impact correction module provided in an embodiment of the present application. The method includes: real-time monitoring of corrosion strain parameters, analyzing the corrosion strain parameters to obtain a corrosion strain index, comparing the corrosion strain parameters with a first corrosion strain threshold and a second corrosion strain threshold, respectively; if the corrosion strain index is less than or equal to the first corrosion strain threshold, recording the corresponding expansion degree assessment result as a first expansion degree result without additional processing; if the corrosion strain index is greater than the first corrosion strain threshold and less than the second corrosion strain threshold, recording the corresponding expansion degree assessment result as a second expansion degree result, obtaining corrosion impact parameters, and correcting the load and strain values ​​of the expansion interference of steel bar corrosion products according to the corrosion impact parameters; if the corrosion strain index is greater than or equal to the second corrosion strain threshold, recording the corresponding expansion degree assessment result as a third expansion degree result, and issuing a steel bar abnormality alarm.

[0039] Specifically, the step of dynamically correcting the load and strain values ​​of the steel bars according to the corrosion strain parameters includes: obtaining a corrosion strain index according to the corrosion strain parameter analysis, the corrosion strain parameters include the steel bar volume expansion rate, the corrosion current density and the concrete expansion stress, and the corrosion strain index represents the quantitative data of the degree of influence of the corrosion strain parameters on the corrosion strain degree; obtaining a first corrosion strain threshold and a second corrosion strain threshold from a preset mechanical property analysis database; comparing the corrosion strain index with the first corrosion strain threshold and the second corrosion strain threshold respectively, if the corrosion strain index is less than or equal to the first corrosion strain threshold, no additional processing is performed; if the corrosion strain index is greater than the first corrosion strain threshold and less than the second corrosion strain threshold, obtaining a corrosion influence contribution parameter from the preset mechanical property analysis database, the corrosion influence contribution parameter including a load value corrosion influence contribution parameter and a strain value corrosion influence contribution parameter, and calculating the corrosion influence parameter, the corrosion strain index and the load value corrosion influence contribution parameter according to the corrosion influence parameter, the corrosion strain index and the load value corrosion influence contribution parameter. The load value is corrected by the corrosion influence index of the load value obtained by the parameter, and the strain value is corrected by the corrosion influence index of the strain value obtained by the corrosion influence parameter, the corrosion strain index and the strain value corrosion influence contribution parameter; if the corrosion strain index is greater than or equal to the second threshold of the corrosion strain, a steel bar abnormality prompt is issued; the load value corrosion influence index represents the quantitative data of the degree of influence of the corrosion influence parameter and the corrosion strain index on the accuracy of the load value disturbed by the expansion of corrosion products; the load value corrosion influence contribution parameter includes the load value corrosion depth contribution, the load value corrosion current contribution, the load value steel bar cross-sectional area contribution and the load value corrosion strain index contribution; the strain value corrosion contribution parameter includes the strain value corrosion depth contribution, the strain value corrosion current contribution, the strain value steel bar cross-sectional area contribution and the strain value corrosion strain index contribution; the strain value corrosion influence index represents the quantitative data of the degree of influence of the corrosion influence parameter and the corrosion strain index on the accuracy of the strain value disturbed by the expansion of corrosion products.

[0040] Among them, the step of obtaining the corrosion strain index based on the corrosion strain parameter analysis includes: obtaining corrosion strain parameter reference data from a preset mechanical property analysis database, specifically including: critical steel bar volume expansion rate, critical corrosion current density and critical concrete expansion stress; performing a proportion approximation operation on the corrosion strain parameters and the corresponding corrosion strain parameter reference data, and then weighting the proportion approximation operation results using the corrosion strain contribution parameters and then coupling processing to obtain the corrosion strain index, where the corrosion strain contribution parameters include the steel bar volume expansion rate contribution, the corrosion current density contribution and the concrete expansion stress contribution.

[0041] The corrosion strain index is obtained as follows:

[0042] ;

[0043] Where, The corrosion strain index represents the effect of expansion of steel corrosion products. Represents the contribution of steel bar volume expansion rate, represents the contribution of corrosion current density, Indicates the contribution of concrete expansion stress.

[0044] Indicates the volume expansion rate of steel bars after corrosion, which can be obtained as follows: Where, is the ratio of the volume of the corroded steel bar to the volume of the original steel bar, is the reduction in cross-sectional area of ​​the steel bar, is the original steel bar cross-sectional area. The greater the steel bar volume expansion rate, the greater the corrosion strain index. Represents the critical steel bar volume expansion rate.

[0045] It indicates the corrosion current density of the steel bar after corrosion. It can be directly measured by electrochemical sensors such as the current method. The greater the corrosion current density, the greater the corrosion strain index. represents the critical corrosion current density.

[0046] The expansion stress of concrete caused by the expansion of corrosion products after corrosion is the radial stress caused by the corrosion products squeezing the concrete. The method of obtaining it is as follows: Where, is the elastic modulus of concrete, and are the outer radius of the concrete cover and the radius of the steel bar respectively. The greater the concrete expansion stress, the greater the steel bar volume expansion rate. represents the critical concrete expansion stress.

[0047] It is important to note that the three factors in this algorithm—the rebar volume expansion rate, the corrosion current density, and the concrete expansion stress—are interrelated. For example, the corrosion current density directly determines the rebar corrosion rate and affects the volume expansion rate of corrosion products. The higher the current density, the faster the corrosion rate and the higher the corrosion volume expansion rate. The higher the rebar volume expansion rate, the more significant the concrete expansion stress. Rebar corrosion is a major factor in the durability degradation of concrete structures. The resulting expansion stress can systematically affect the mechanical properties of the negative moment zone of composite beams. The corrosion strain index, derived from a comprehensive analysis, can reflect the severity of concrete damage caused by corrosion. During the corrosion process, the internal pressure caused by the volume expansion of the rebar exerts stress on the concrete, potentially leading to the formation or expansion of concrete cracks. The corrosion strain index can quantitatively assess the expansion of rebar corrosion products, thereby tracking and evaluating the impact of rebar corrosion on the accuracy of structural load values ​​and rebar strain values.

[0048] 、 and These are the contributions corresponding to the steel bar volume expansion rate, corrosion current density, and concrete expansion stress preset in the mechanical properties analysis database. These contributions are numerical indicators that measure the influence of the above parameters on the corrosion strain index. Specifically, there is a mapping relationship table for each steel bar volume expansion rate, corrosion current density, and concrete expansion stress. The table records each possible corrosion strain parameter value and its corresponding contribution. These mapping relationships can be one-to-one or many-to-one. For example, in actual applications, when it is necessary to evaluate the corrosion strain index, the measured steel bar volume expansion rate, corrosion current density, and concrete expansion stress can be entered into their respective corresponding mapping relationship tables, and the contributions corresponding to these values ​​can be quickly found. The contribution values ​​range from 0 to 1.

[0049] As a further solution, the step of correcting the load value according to the load value corrosion influence index obtained from the corrosion influence parameter, the corrosion strain index and the load value corrosion influence contribution parameter includes: the corrosion influence parameters include corrosion depth, corrosion current and steel cross-sectional area; obtaining the critical corrosion influence index from a preset mechanical property analysis database; matching the load value corrosion influence index with the load value empirical coefficient corresponding to each load value corrosion influence index range preset in the mechanical property analysis database to obtain the load value empirical coefficient; correcting the load value according to the load value empirical coefficient, the load value corrosion influence index and the critical corrosion influence index to obtain the corrected load value.

[0050] Among them, the specific steps for obtaining the load value corrosion influence index include: obtaining reference data of corrosion influence parameters from a preset mechanical property analysis database, specifically including: critical corrosion depth, critical corrosion current, critical steel bar cross-sectional area and critical corrosion strain index; performing proportion approximation calculation on the corrosion depth, corrosion current, critical steel bar cross-sectional area and corrosion strain index with the critical corrosion depth, critical corrosion current, steel bar cross-sectional area and critical corrosion strain index respectively, and then using the load value corrosion influence contribution parameter to weight the proportion approximation calculation results and couple them to obtain the load value corrosion influence index.

[0051] The strain value is corrected by the corrosion influence index obtained based on the corrosion influence parameter, the corrosion strain index, and the strain value corrosion contribution parameter. The corrosion influence parameter can directly reflect the impact of corrosion on the bearing capacity of steel bars. Although the corrosion expansion strain affects concrete, it does not directly affect the bearing capacity of steel bars. Therefore, it is more suitable for correcting load and strain values.

[0052] The step of correcting the strain value according to the strain value corrosion influence index obtained from the corrosion influence parameter, the corrosion strain index, and the strain value corrosion influence contribution parameter includes: matching the strain value corrosion influence index with the strain value empirical coefficient corresponding to each strain value corrosion influence index range preset in the mechanical property analysis database to obtain the strain value empirical coefficient; and correcting the strain value according to the strain value empirical coefficient, the strain value corrosion influence index, and the critical corrosion influence index to obtain a corrected strain value.

[0053] Specifically, the calculation formulas for the corrected load value and the corrected strain value are as follows:

[0054] ; In the formula, when j=1, represents the corrected load value, Indicates the load value directly read by the comprehensive tester. Indicates the empirical coefficient of load value, Indicates the load value corrosion impact index, when j=2, represents the corrected strain value, Indicates the strain value directly measured by the comprehensive tester, Indicates the empirical coefficient for strain value correction, is the strain value corrosion influence index, is the critical corrosion impact index.

[0055] The specific steps for obtaining the strain value corrosion influence index include: performing a proportion approximation calculation on the corrosion depth, corrosion current, critical steel bar cross-sectional area, and corrosion strain index with the critical corrosion depth, critical corrosion current, steel bar cross-sectional area, and critical corrosion strain index, respectively; and weighting and coupling the proportion approximation calculation results using the strain value corrosion influence contribution parameter to obtain the strain value corrosion influence index.

[0056] Specifically, the load value corrosion impact index and strain value corrosion impact index are obtained as follows:

[0057] ;

[0058] Where j = 1 or 2, and the load value corrosion impact index is obtained as follows:

[0059] ;

[0060] The strain value corrosion impact index is obtained as follows:

[0061] ;

[0062] In the formula, when j=1, Indicates the load value corrosion impact index, Indicates the contribution of load value to corrosion depth, Indicates the contribution of load value to corrosion current density, Indicates the contribution of the steel bar cross-sectional area to the load value, Indicates the contribution of load value to corrosion strain index. When j=2, Indicates the strain value corrosion impact index, Indicates the contribution of strain value to corrosion depth, Indicates the contribution of strain value to corrosion current density, Indicates the contribution of the cross-sectional area of ​​the steel bar to the strain value, Indicates the contribution of the strain value to the corrosion strain index, Indicates the depth of corrosion, which can be obtained through electrochemical tests such as linear polarization method or actual measurement of the thickness of the corrosion layer. It reflects the geometric damage degree of steel bar corrosion. The greater the corrosion depth, the greater the corrosion impact index. Indicates the critical corrosion depth, Indicates the corrosion current density. The greater the current density, the greater the corrosion impact index. represents the critical corrosion current density, It represents the cross-sectional area of ​​the steel bar, which can be obtained by subtracting the corrosion loss area from the original steel bar cross-sectional area. The larger the cross-sectional area of ​​the steel bar, the smaller the corrosion impact index. represents the critical steel bar cross-sectional area, It represents the corrosion strain index. The larger the corrosion strain index is, the greater the corrosion impact index is. Represents the critical corrosion strain index.

[0063] 、 、 and These are the contribution degrees corresponding to the corrosion depth, corrosion current, steel cross-sectional area and corrosion strain index preset in the mechanical properties analysis database. These contribution degrees are numerical indicators that measure the influence of the above parameters on the corrosion impact index. Specifically, there is a mapping relationship table for each of the corrosion depth, corrosion current, steel cross-sectional area and corrosion strain index. The table records each possible parameter value and its corresponding contribution degree. These mapping relationships can be one-to-one or many-to-one. For example, in actual applications, when it is necessary to evaluate the corrosion impact index, the measured corrosion depth, corrosion current, steel cross-sectional area and corrosion strain index can be input into their respective corresponding mapping relationship tables, and the contribution degrees corresponding to these values ​​can be quickly found. The contribution degree ranges from 0 to 1.

[0064] It's important to note that the corrosion depth, corrosion current density, steel cross-sectional area, and corrosion strain index in this algorithm are interrelated. For example, current density determines the corrosion rate; a greater corrosion rate within a given time period leads to a greater corrosion depth. Increased corrosion depth reduces the effective cross-sectional area of ​​the steel bar. A larger corrosion strain index increases the risk of concrete cracking and makes the composite beam's protective layer more susceptible to cracking. The corrosion impact index, derived from a comprehensive analysis, accurately reflects the combined impact of corrosion product expansion interference on load and strain values. Correcting load and strain values ​​based on the corrosion impact index more realistically reflects the impact of steel corrosion on the bearing capacity of concrete structures, making structural durability analysis more scientific.

[0065] Furthermore, based on the corrected load and strain values, the unloaded and preloaded load values ​​under the same chloride corrosion damage degree are compared to obtain the concrete damage coefficient as follows:

[0066] like Figure 4 The figure shows the tensile and compressive constitutive model diagram of steel provided in the embodiment of this application. For uncorroded steel bars and steel beams, the tensile and compressive constitutive models of the steel bars and steel beams are described using a simplified bifold line model. The tensile and compressive constitutive relationships of the steel bars and steel beams are as follows: ;in, is the tensile stress, is the elastic modulus; , are yield strength and ultimate strength respectively; 、 、 are strain value, yield strain, and ultimate strain, respectively.

[0067] Regarding the reduction in material properties of corroded steel bars, the present invention introduces the degradation effect of the steel bar mechanical properties caused by corrosion on the basis of the short-term bending calculation model. The geometric and mechanical property reduction model of non-uniformly corroded steel bars is as follows: ; ; Where, Represents the effective cross-sectional area of ​​the corroded steel bars, is the corrosion rate, The cross-sectional area of ​​the steel bar is the nominal cross-sectional area of ​​the steel bar used, which can be found in the national standard. In order to consider the steel bar yield strength reduction due to corrosion, The tensile strength of steel bars is reduced taking into account corrosion.

[0068] like Figure 5 As shown in FIG, the UHPC tensile and compressive constitutive model diagrams provided in the embodiment of the present application are shown, and the constitutive relationship of UHPC is expressed as follows: Where, is the elastic modulus of UHPC; is the ultimate tensile stress of UHPC; is the cracking strain of UHPC; is the peak tensile strain of UHPC.

[0069] At the same degree of chloride corrosion damage, the ultimate load of the undamaged specimen is 123kN, and the ultimate load of the damaged specimen is 121kN. The concrete damage coefficient is the ratio of the ultimate load of the damaged specimen to the ultimate load of the undamaged specimen, and the concrete damage coefficient is 0.984.

[0070] Furthermore, the composite beam includes: UHPC layer matrix, NC layer, UHPC steel bar, NC layer steel bar, steel beam upper flange, steel beam lower flange, and steel beam web. Figure 6 The force balance equations for the composite beam load analysis are as follows: Where, 、 、 、 、 、 、 They represent the resultant forces of the UHPC layer matrix, the UHPC layer tensile longitudinal reinforcement, the NC layer tensile longitudinal reinforcement, the upper flange of the steel beam, the lower flange of the steel beam, the tensile part of the steel beam web, and the compressive part of the steel beam web. Where, represents the concrete corrosion damage coefficient; is the steel fiber crack bridging coefficient, ; is the plasticity parameter, which is set as 0.35 in the Code for Design of Ultra-High Performance Concrete Structures (T / CCPA 35-2022); is the volume ratio of steel fiber; is the length and diameter of the steel fiber; is the ultimate tensile stress of UHPC, is the elastic modulus of UHPC; , represents the ultimate tensile strain of UHPC; , represents the positive cross-sectional area of ​​the UHPC layer, Represent the width and thickness of UHPC layer respectively. Where, is the ultimate tensile strength of the steel bar; Represents the total area of ​​longitudinal reinforcement in the UHPC layer. Where, is the ultimate tensile strain of the steel bar; is the elastic modulus of the steel bar, ; Represents the total area of ​​longitudinal reinforcement in the NC layer. ; Where, 、 They represent the internal forces of the upper flange of the steel beam and the internal forces of the web of the steel beam above the neutral axis respectively; , They represent the strain on the flange of the steel beam and the strain at the centroid of the steel beam web above the neutral axis, respectively. Y is the distance between the neutral axis of the composite beam and the highest point of the composite beam. is the thickness of the NC layer; It represents the elastic modulus of the steel beam and can be obtained through the performance test of the steel beam parent material; 、 Respectively represent the width of the upper flange of the steel beam and the width of the web of the steel beam; Indicates the thickness of the upper flange of the steel beam. ; Where, 、 They represent the internal forces of the lower flange of the steel beam and the internal forces of the web of the steel beam below the neutral axis respectively; , They represent the strain of the lower flange of the steel beam and the strain of the web of the steel beam below the neutral axis respectively; 、 Respectively represent the width and thickness of the lower flange of the steel beam; is the total height of the composite beam.

[0071] The commonly used calculation method for the design and calculation of steel-concrete composite beams is usually to adopt simplified plasticity theory, which simplifies the stress diagram of the composite beam into an equivalent rectangular stress diagram. According to the specimen section design calculation of the present invention, it is found that the neutral axis of the composite beam section is located at the upper flange of the steel beam (the side flange connected to the bridge deck). As the composite beam enters the plastic state, the neutral axis gradually moves toward the middle of the steel beam web. In the calculation framework of the short-term bending performance of the composite beam set by the present invention, the shear force of the composite beam is fully connected, and the influence of interlayer slip is not considered. The top surface of the UHPC cracks first. When the UHPC layer cracks, the plastic neutral axis of the composite beam moves to the web of the steel beam. When the limit is reached, the corresponding stress-strain distribution of the composite beam is as follows: Figure 6 The calculation diagram of the corroded composite beam is shown in the figure.

[0072] When the composite beam reaches its ultimate bearing capacity under the coupled load-corrosion effect, the tensile reinforcement in the UHPC layer exceeds the ultimate strain, and the tensile reinforcement in the NC (normal concrete) layer generally exceeds the yield strain. In some specimens, the NC layer reinforcement even reaches the ultimate strain. The strain at a specific point in the composite beam cross section is obtained as follows: Where, is the strain at the i-th height in the composite beam section; is the bending curvature of the composite beam section; is the distance from the i-th height in the composite beam section to the neutral axis of the section; It represents the yield tensile strain of the longitudinal reinforcement in the NC layer, which can be directly obtained by querying the corresponding reinforcement specifications; is the distance from the top surface of UHPC to the neutral axis of the cross section; is the distance between the longitudinal reinforcement of the NC layer and the top surface of the UHPC, i is the number of each height point in the composite beam section, i=1,2,3,...,N, N is the total number of height points in the composite beam section.

[0073] Substituting the internal forces of each key load-bearing component into the moment balance equation, the residual bending bearing capacity of the UHPC reinforced steel-concrete composite beam after load-corrosion can be calculated. As shown below: ; Where, It represents the bending moment of the tensile and compressive zones of the steel beam about the plastic neutral axis of the composite beam; 、 、 、 They represent the distances between the centroids of the upper flange of the steel beam, the tension zone of the steel beam web, the lower flange of the steel beam, the compression zone of the steel beam web and the plastic neutral axis of the composite beam respectively; 、 、 are the distances from the centroid to the plastic neutral axis of the UHPC layer, the longitudinal reinforcement in the UHPC layer, and the longitudinal reinforcement in the NC layer, respectively.

[0074] According to the results of long-term bending tests, the degree of debonding at the UHPC-NC interface is closely related to the degree of corrosion. It can be regarded as a function of the degree of corrosion, that is, The bending test results of the test beam were used to Perform nonlinear fitting to obtain the correction coefficient ( ) is as follows: ;like Figure 7 As shown in the figure, it is the correction coefficient fitting curve provided in the embodiment of the present application. =0.9410 indicates that the characteristic points and the curve fitting effect are good. Long-term bending calculation model of UHPC reinforced steel-concrete composite beams As shown below: ;

[0075] Furthermore, the residual bending capacity model of UHPC reinforced steel-concrete composite beams after load-corrosion was verified, e.g. Figure 8a 、 Figure 8b and Figure 8c As shown, Figure 8a This is the structural diagram of the steel-NC-UHPC composite beam (unit: mm). Figure 8bThis is the elevation structure diagram of the steel-NC-UHPC composite beam specimen (unit: mm). Figure 8c Figure 2 is the cross-sectional structural diagram of the steel-NC-UHPC composite beam specimen (unit: mm).

[0076] like Figure 9 The figure shows the loading device provided in the embodiment of this application. First, adjust the spacing of the supports on the distribution beam supporting the servo press and hoist the specimen and the loading distribution beam, ensuring a pure bending section of 830 mm for the steel-NC-UHPC composite beam and 800 mm for the UHPC-NC composite plate. Simultaneously arrange the strain gauges and LVDT displacement sensors and connect them to the data acquisition tool to prepare for the test. ① Preloading: Load to 20 kN using force control mode (5 kN / s). Maintain the load level for 3 minutes to eliminate contact gap and verify the stability of the strain gauge and displacement sensor data. ② Loading: From 0 to 0.7 Pu (Pu is the ultimate load), use force control mode (5 kN / s); from 0.7 Pu to Pu, switch to displacement control mode (0.2 mm / min); cease loading when the load exceeds Pu and drops to 0.7 Pu. ③ Unloading: After cessation of loading, unload to 0 kN at a rate of -5 kN / s using force control mode. The test data is then saved and photographed to record the specimen's status.

[0077] like Figure 10 The figure shows the measurement point layout for the steel-NC-UHPC composite beam provided in the embodiment of this application. ① Displacement gauges: Vertical displacement gauges were placed at the midspan and L / 4 section to obtain load-deflection curves; orthogonal displacement gauge groups were set at the slab ends to calculate section rotation angles; displacement gauges were placed horizontally at the supports, L / 4 section, and steel beam ends (composite beams) using angle steel to quantify UHPC-NC interlayer slip. ② Strain gauges: Concrete strain gauges were placed along the height of the specimen's midspan section to verify the flat section assumption; longitudinal strain gauges were placed along the slab on both sides of the interface at the supports and L / 4 section to examine interface coordination; strain gauges were placed along the longitudinal reinforcement at the midspan of the UHPC slab to monitor reinforcement strain. ③ Embedded chord strain gauges (load-corrosion coupling test): Embedded strain gauges were placed at the midspan and L / 4 points of the longitudinal reinforcement in the NC slab to read the reinforcement strain in real time. During the loading process, the HC-F600 comprehensive crack tester was used to synchronously observe and record the development of cracks in the specimens, and all deflection and strain data were automatically collected using a static acquisition instrument.

[0078] Based on the aforementioned benchmark specimen test results, this study conducted crack width control pre-cracking experiments on four sets of steel-NC-UHPC composite beam specimens (SNU-C-0 / 05 / 15 / 20). A 1000kN long-column hydraulic servo press (loading rate 2kN / s) was used for staged loading, with target residual crack widths of 0, 0.05, 0.15, and 0.20mm (accuracy ±0.02mm), respectively.

[0079] In addition, the present invention breaks through the limitations of single-factor testing through the self-balancing reaction frame-electrochemical accelerated corrosion device. The modular framework supports independent control of load-corrosion parameters, has a short assembly and disassembly cycle, and can achieve environmental simulation of electrochemical accelerated corrosion under sustained load. The device consists of two parts: a mechanical loading module and an electrochemical corrosion module. ① Mechanical loading module: A constant load is applied by a hand-cranked jack, and two groups of specimens are locked synchronously to simulate a long-term service stress state. At the same time, the load level and the strain value of the embedded string strain gauge in the specimen can be read in real time through a comprehensive tester. ② Electrochemical corrosion module: In a 5% NaCl solution environment, a direct current drives the cathode of the stainless steel mesh and the anode of the steel bar to be corroded to form a closed loop. The constant current mode is used to accelerate corrosion, and the monitoring potential is regulated in real time.

[0080] like Figure 11 The figure shows the load-corrosion coupling test process provided by an embodiment of the present application. The steps are as follows: ① Test apparatus installation: Build the load-corrosion coupling test apparatus. The specimens are stacked symmetrically within the loading frame, ensuring that the negative moment area is subjected to bending (the UHPC layer is subjected to tension) during loading. The specimens are then leveled and aligned using a spirit level. ② Using the ultimate load (Pu) measured in the bending test of the reference specimen as a reference, a holding load of 0.4Pu is applied to the specimen using a hand-cranked jack to simulate the long-term load level under normal bridge operation. After loading is complete, the oil pump is locked, and the holding load stability is monitored in real time using a comprehensive tester. ③ Prepare a 5% NaCl solution using analytical grade NaCl reagent. The amount of solution injected into the tank is sufficient to completely submerge the specimen. ④ Connect the specimen's reserved power conductors and stainless steel mesh to the positive and negative terminals of a DC power supply, respectively. Apply a constant current at a preset current density to ensure that holding load and energized corrosion proceed simultaneously. During the power-on process, the circuit status is monitored in real time using an ammeter and voltmeter.

[0081] After the load-corrosion coupling test, four sets of steel-NC-UHPC composite beams were subjected to four-point bending loading tests. The composite beam specimens that completed the four-point bending failure test were dismantled by a crusher and the corroded steel bars were extracted using a standard sampling process to quantify the extent of steel bar corrosion damage. Figure 12As shown, it is an operation flow chart for extracting rusted steel bars provided in an embodiment of the present application. Specifically, there are five core steps: (1) Steel bar sampling: Use a crusher to dismantle the composite beam specimens that have completed the four-point bending test to expose the internal steel skeleton, use an angle grinder to cut the longitudinal steel bars at equal intervals (300mm), and collect the interface shear steel bars at the same time; (2) Steel bar grouping: For the obtained shear stirrups, load-bearing longitudinal bars and other components, group and number each type of steel bar according to "specimen number-steel bar type-sampling location"; (3) Pickling and rust removal: Soak the steel bars in dilute hydrochloric acid for 10 to 15 minutes until the rust products are dissolved, and use a brush to wipe off the surface attachments of the steel bars; (4) Neutralization treatment: Neutralize the residual acid solution with saturated Ca(OH)2 solution, soak for 5 minutes, remove it, and use pH test paper to detect the surface pH value to neutral (7.0±0.5); (5) Drying and weighing: Place the steel bars in an electric constant temperature drying oven, dry them at 105℃ for 2 hours, cool them to room temperature, and weigh them using an electronic balance (accuracy 0.01g) to record the mass data.

[0082] like Figure 12 As shown, it is a structural schematic diagram of the mechanical performance analysis system of the negative bending zone of the UHPC thin-layer reinforced steel-concrete composite beam provided in an embodiment of the present application. The mechanical performance analysis system of the negative bending zone of the UHPC thin-layer reinforced steel-concrete composite beam provided in an embodiment of the present application includes: a steel analysis module, a UHPC analysis module, a bearing capacity analysis module, a composite beam verification module and a mechanical performance analysis database; wherein the steel analysis module is used to obtain a geometric mechanical performance reduction model of non-uniformly corroded steel bars based on the steel constitutive model and the mechanical performance test data of the corroded steel bars, and the steel includes steel bars and steel beams; the UHPC analysis module is used to obtain a geometric mechanical performance reduction model of non-uniformly corroded steel bars based on the UHPC constitutive model and the mechanical performance test data of the corroded steel bars; The model uses the ultimate load of no loading and the ultimate load of applied preloading ratio under the same chloride corrosion damage degree to obtain the concrete damage coefficient. The bearing capacity analysis module is used to obtain the residual bending bearing capacity model of UHPC reinforced steel-concrete composite beams after load-corrosion based on the concrete damage coefficient, the geometric mechanical property reduction model of non-uniformly corroded steel bars, and the composite beam force equilibrium equation. The composite beam verification module is used to introduce the correction factor into the residual bending bearing capacity model of UHPC reinforced steel-concrete composite beams after load-corrosion to obtain the long-term bending calculation model of UHPC reinforced steel-concrete composite beams after load-corrosion.

[0083] In summary, the embodiments of the present application obtain a geometric mechanical property reduction model of non-uniformly corroded steel bars based on the steel constitutive model and the mechanical property test data of corroded steel bars, where the steel includes steel bars and steel beams; according to the UHPC constitutive model, the ultimate loads without loading and with preload ratios under the same chloride corrosion damage degree are compared to obtain the concrete damage coefficient, and the preload ratio of the ultimate load is 0.4; according to the concrete damage coefficient, the geometric mechanical property reduction model of non-uniformly corroded steel bars, and the composite beam force equilibrium equation, a residual bending bearing capacity model of the UHPC reinforced steel-concrete composite beam after load-corrosion is obtained; a correction coefficient is introduced into the residual bending bearing capacity model of the UHPC reinforced steel-concrete composite beam after load-corrosion to obtain a long-term bending calculation model of the UHPC reinforced steel-concrete composite beam after load-corrosion, thereby improving the accuracy of the bearing capacity performance analysis of the steel-UHPC composite beam in the negative bending moment zone under load-corrosion coupling.

[0084] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0085] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0086] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0087] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0088] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0089] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. The mechanical performance analysis method of the negative bending moment zone of UHPC thin layer reinforced steel-concrete composite beam is characterized by: The following steps are involved: According to the steel constitutive model and the mechanical property test data of the corroded steel bars, a geometric mechanical property reduction model of the non-uniformly corroded steel bars is obtained, wherein the steel bars include steel bars and steel beams; According to the UHPC constitutive model, the concrete damage coefficient is obtained by comparing the ultimate load of no loading and the ultimate load of preloading ratio under the same chloride corrosion damage degree. The residual bending capacity model of UHPC reinforced steel-concrete composite beams after load-corrosion was obtained based on the concrete damage coefficient, the geometric mechanical property reduction model of non-uniformly corroded steel bars, and the composite beam force equilibrium equation. The correction coefficient is introduced into the residual bending capacity model of UHPC reinforced steel-concrete composite beams after load-corrosion, and the long-term bending calculation model of UHPC reinforced steel-concrete composite beams after load-corrosion is obtained. The method of obtaining the residual bending capacity model of the UHPC reinforced steel-concrete composite beam after load-corrosion based on the concrete damage coefficient, the geometric mechanical property reduction model of the non-uniformly corroded steel bars, and the composite beam force equilibrium equation comprises the following specific steps: Obtain composite beam strain data, UHPC layer size data, steel beam size data, NC layer size data, the distance between the composite beam neutral axis and the highest point of the composite beam, and the total height of the composite beam; Obtain the elastic modulus and ultimate tensile strain of UHPC from the UHPC constitutive model; obtaining the internal force of the UHPC matrix according to the internal force related parameters of the UHPC matrix, wherein the internal force related parameters of the UHPC matrix include a concrete damage coefficient, a steel fiber crack bridging coefficient, an elastic modulus of the UHPC, an ultimate tensile strain of the UHPC, a UHPC layer width, and a UHPC layer thickness; The ultimate tensile strength of steel bars and the effective cross-sectional area of ​​corroded steel bars were extracted from the geometric mechanical property reduction model of non-uniformly corroded steel bars. The internal force of the longitudinal reinforcement in the UHPC layer is obtained based on the corrosion rate, ultimate tensile strength of the reinforcement and the effective cross-sectional area of ​​the corroded reinforcement; Obtain the elastic modulus and ultimate tensile strain of the steel bar from the steel constitutive model; The internal force of the longitudinal reinforcement in the NC layer is obtained based on the elastic modulus of the reinforcement, the ultimate tensile strain of the reinforcement and the total area of ​​the longitudinal reinforcement in the NC layer; The internal force of the upper flange of the steel beam is obtained according to the strain of the upper flange of the steel beam, the elastic modulus of the steel bar, the width of the upper flange of the steel beam and the thickness of the upper flange of the steel beam; The internal force of the web of the steel beam above the neutral axis is obtained according to the parameters related to the internal force of the web of the steel beam above the neutral axis, wherein the parameters related to the internal force of the web of the steel beam above the neutral axis include the strain at the web of the steel beam above the neutral axis, the elastic modulus of the steel bar, the width of the web of the steel beam, the distance between the neutral axis of the composite beam and the highest point of the composite beam, the thickness of the UHPC layer, the thickness of the NC layer, and the thickness of the upper flange of the steel beam; The internal force of the lower flange of the steel beam is obtained according to the strain of the lower flange of the steel beam, the elastic modulus of the steel beam, the width of the lower flange of the steel beam and the thickness of the lower flange of the steel beam; Obtaining the internal force of the web of the steel beam below the neutral axis based on the data related to the internal force of the web of the steel beam below the neutral axis, wherein the data related to the internal force of the web of the steel beam below the neutral axis includes the strain at the web of the steel beam below the neutral axis, the elastic modulus of the steel beam, the width of the web of the steel beam, the total height of the composite beam, the distance between the neutral axis of the composite beam and the highest point of the composite beam, and the thickness of the lower flange of the steel beam; The residual flexural capacity of the UHPC reinforced steel-concrete composite beam after load-corrosion is obtained according to the parameters related to the residual flexural capacity of the composite beam, wherein the parameters related to the residual flexural capacity of the composite beam include bending moment related parameters and bearing capacity related parameters.

2. The method for analyzing the mechanical properties of UHPC thin-layer reinforced steel-concrete composite beams in the negative bending moment zone according to claim 1 is characterized by: The composite beam force equilibrium equation specifically includes: the internal force of the UHPC matrix, the internal force of the UHPC layer longitudinal reinforcement, the internal force of the NC layer longitudinal reinforcement, the internal force of the upper flange of the steel beam, the internal force of the lower flange of the steel beam, the internal force of the web of the steel beam above the neutral axis, and the internal force of the web of the steel beam below the neutral axis.

3. The method for analyzing the mechanical properties of UHPC thin-layer reinforced steel-concrete composite beams in the negative bending moment region according to claim 1 is characterized by: The composite beam strain data includes the strain at each height of the composite beam cross section under the composite beam bearing limit state, the strain of the upper flange of the steel beam, the strain of the web of the steel beam above the neutral axis, the strain of the lower flange of the steel beam, and the strain of the web of the steel beam below the neutral axis; The UHPC layer dimension data includes the UHPC layer width, the UHPC layer thickness, the total area of ​​the UHPC layer longitudinal reinforcement, the distance from the center of mass of the UHPC layer to the plastic neutral axis, and the distance from the center of mass of the longitudinal reinforcement in the UHPC layer to the plastic neutral axis; The steel beam dimension data includes the width of the steel beam web, the width of the steel beam upper flange, the thickness of the steel beam upper flange, the width of the steel beam lower flange, the thickness of the steel beam lower flange, the distance between the centroid of the steel beam upper flange and the plastic neutral axis of the composite beam, the distance between the centroid of the steel beam web tension zone and the plastic neutral axis of the composite beam, the distance between the centroid of the steel beam lower flange and the plastic neutral axis of the composite beam, and the distance between the centroid of the steel beam web compression zone and the plastic neutral axis of the composite beam; The NC layer dimension data includes the total area of ​​the longitudinal reinforcement in the NC layer, the thickness of the NC layer, and the distance from the centroid of the longitudinal reinforcement in the NC layer to the plastic neutral axis.

4. The method for analyzing the mechanical properties of UHPC thin-layer reinforced steel-concrete composite beams in the negative bending moment region according to claim 1, characterized in that: The step of obtaining the residual flexural bearing capacity of the UHPC reinforced steel-concrete composite beam after load-corrosion based on parameters related to the residual flexural bearing capacity of the composite beam comprises: The bending moments of the tension zone and the compression zone of the steel beam relative to the plastic neutral axis of the composite beam are obtained according to the bending moment related parameters, wherein the bending moment related parameters include the internal force of the upper flange of the steel beam, the distance between the center of mass of the upper flange of the steel beam and the plastic neutral axis of the composite beam, the internal force of the web of the steel beam above the neutral axis, the distance between the center of mass of the tension zone of the web of the steel beam and the plastic neutral axis of the composite beam, the internal force of the lower flange of the steel beam, the distance between the center of mass of the lower flange of the steel beam and the plastic neutral axis of the composite beam, the internal force of the web of the steel beam below the neutral axis, and the distance between the center of mass of the compression zone of the web of the steel beam and the plastic neutral axis of the composite beam; The residual flexural capacity of the UHPC-reinforced steel-concrete composite beam after load-corrosion was obtained based on capacity-related parameters. The capacity-related parameters include the bending moments of the tensile and compressive zones of the steel beam relative to the plastic neutral axis of the composite beam, the internal forces of the UHPC matrix, the distance from the centroid of the UHPC layer to the plastic neutral axis, the internal forces of the longitudinal reinforcement of the UHPC layer, the distance from the centroid of the longitudinal reinforcement of the UHPC layer to the plastic neutral axis, the internal forces of the longitudinal reinforcement of the NC layer, and the distance from the centroid of the longitudinal reinforcement of the NC layer to the plastic neutral axis.

5. The method for analyzing the mechanical properties of UHPC thin-layer reinforced steel-concrete composite beams in the negative bending moment region according to claim 1, characterized in that: The rust rate is obtained as follows: Get the initial steel bar mass; The ultimate load was obtained through bending tests on composite beam benchmark specimens. Based on the bending test results of composite beam benchmark specimens, crack width control pre-cracking experiments were carried out on four groups of steel-NC-UHPC composite beam specimens. The four groups of steel-NC-UHPC composite beam specimens were subjected to ultimate loads in proportion to the preload ratio; A load-coupling experiment was conducted on four groups of steel-NC-UHPC composite beam specimens after applying an ultimate load corresponding to the composite beam preload ratio, to obtain composite beams after the load-coupling experiment. The composite beams after the load-coupling experiment were obtained by injecting a load-coupling experimental reagent into a solution tank, connecting the reserved power conductors and stainless steel mesh of the four groups of steel-NC-UHPC composite beam specimens to the positive and negative electrodes of a DC power supply, respectively, and applying a constant current at a preset current density. The composite beam bending test was carried out on four groups of steel-NC-UHPC composite beam specimens after the load-coupling test to obtain the composite beams after the bending test; After the bending test, the four groups of steel-NC-UHPC composite beam specimens were dismantled to expose the internal steel skeleton. The longitudinal steel bars were cut at equal intervals using an angle grinder, and the interface shear reinforcement was collected. Group and number the obtained shear reinforcement and longitudinal reinforcement; The corrosion rate is obtained based on the initial steel bar mass and the steel bar mass after corrosion. The steel bar mass after corrosion is obtained by soaking the steel bar until the corrosion products are dissolved, wiping off the attachments on the steel bar surface, neutralizing the residual acid solution until the pH value of the steel bar surface is neutral, and drying and weighing the neutralized steel bar.

6. The method for analyzing the mechanical properties of UHPC thin-layer reinforced steel-concrete composite beams in the negative bending moment region according to claim 5, characterized in that: The steps of the bending test include: Performing preloading for the bending test, which includes adjusting the spacing of the supports on the distribution beam supporting the servo press, hoisting the test specimen and loading the distribution beam, synchronously arranging strain gauges and displacement meters and connecting them to the acquisition tool, loading the force control mode to a preset force value, maintaining the load level to eliminate contact gap, and verifying the stability of the strain gauge and displacement sensor data; When the load is less than the preset ratio of the ultimate load, the force control mode is used. When the load exceeds the preset ratio of the ultimate load but does not reach the ultimate load of the finite element simulation, the mode is switched to the displacement control mode. When the load exceeds the ultimate load, the load is reduced to the preset ratio of the ultimate load of the finite element simulation and the loading is stopped. After stopping loading, the load was unloaded to 0 using the force control mode and the experimental data were saved.

7. The method for analyzing the mechanical properties of UHPC thin-layer reinforced steel-concrete composite beams in the negative bending moment region according to claim 5, characterized in that: The steps of conducting crack width control pre-cracking treatment experiments on four groups of steel-NC-UHPC composite beam specimens based on the bending test results of the composite beam benchmark specimens include: The key results of the pre-cracking treatment of composite beam specimens were obtained by applying graded loading according to the target residual crack width. The key results of the pre-cracking treatment of the composite beam specimens include Pcr, crack width, pre-cracking load, residual deflection and Ks, where Pcr represents the initial crack load of each specimen, the pre-cracking degree represents the target value of the controlled crack width of each specimen, the pre-cracking load refers to the load corresponding to when the target value of the controlled crack width is reached, the residual deflection refers to the residual deflection in the mid-span of each specimen after unloading, and Ks refers to the elastic bending stiffness of each specimen.

8. The method for analyzing the mechanical properties of UHPC thin-layer reinforced steel-concrete composite beams in the negative bending moment region according to claim 5, characterized in that: The long-term bending calculation model of the UHPC reinforced steel-concrete composite beam after load-corrosion is the product of the correction factor and the residual bending bearing capacity model of the UHPC reinforced steel-concrete composite beam after load-corrosion; The correction coefficient is obtained by performing nonlinear fitting on the corrosion rate using the bending test results of four groups of steel-NC-UHPC composite beam specimens.

9. The negative moment zone mechanical performance analysis system for UHPC thin-layer reinforced steel-concrete composite beams is characterized by: The system is used to execute the mechanical property analysis method of the negative bending moment zone of the UHPC thin-layer reinforced steel-concrete composite beam according to any one of claims 1 to 8, and the system specifically comprises: a steel analysis module, a UHPC analysis module, a bearing capacity analysis module, a composite beam verification module, and a mechanical property analysis database; The steel material analysis module is used to obtain a geometric mechanical property reduction model of non-uniformly corroded steel bars based on the steel material constitutive model and mechanical property test data of corroded steel bars, wherein the steel materials include steel bars and steel beams; The UHPC analysis module is used to obtain the concrete damage coefficient by comparing the ultimate load of no loading and the ultimate load of preloading ratio under the same chloride corrosion damage degree according to the UHPC constitutive model; The bearing capacity analysis module is used to obtain the residual bending bearing capacity model of the UHPC reinforced steel-concrete composite beam after load-corrosion based on the concrete damage coefficient, the geometric mechanical property reduction model of the non-uniformly corroded steel bars, and the composite beam force balance equation; The composite beam verification module is used to introduce the correction coefficient into the residual bending bearing capacity model of the UHPC reinforced steel-concrete composite beam after load-corrosion action, so as to obtain the long-term bending calculation model of the UHPC reinforced steel-concrete composite beam after load-corrosion action.

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