Method and system for analyzing mechanical properties of hogging moment area of UHPC thin-layer reinforced steel-concrete composite beam

Abstract

The invention discloses a method and system for analyzing the mechanical property of a hogging moment area of a UHPC thin-layer reinforced steel-concrete composite beam, 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 the non-uniform rusted steel bar according to a steel constitutive model and mechanical property test data of the rusted steel bar; according to the UHPC constitutive model, comparing the ultimate load with the unloaded proportion and the ultimate load with the preloaded proportion under the same chlorine salt corrosion damage degree to obtain a concrete damage coefficient; a residual flexural capacity model of the UHPC reinforced steel-concrete composite beam after the load-corrosion effect is obtained according to a geometric mechanical property reduction model of the non-uniform corrosion steel bar and a composite beam force balance equation, and a long-term bending calculation model of the UHPC reinforced steel-concrete composite beam after the load-corrosion effect is obtained by introducing a correction coefficient; and the bearing capacity performance analysis accuracy of the steel-UHPC composite beam in the hogging moment area under the load-corrosion coupling action is improved.

Description

Technical Field

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

[0002] The analysis of the mechanical properties of the negative moment zone of composite beams is one of the key issues in the research of steel-concrete composite structures, mainly focusing on the complex stress states where the concrete slab is in tension and the steel beam is in compression in structures such as bridges and building floors that bear alternating loads. The research background stems from the requirements of modern engineering for structural lightweight, high load-bearing capacity, and economy. However, problems such as concrete cracking, steel bar yielding, local buckling of steel beams, and interface slip are prone to occur in the negative moment zone, directly affecting the structural stiffness, durability, and ultimate load-bearing capacity.

[0003] Current code documents and existing literature have defined the calculation of the flexural bearing capacity of steel-concrete composite beams in the negative moment zone and composite members with UHPC (Ultra-High Performance Concrete) thin layers. In the calculation of the flexural bearing capacity of composite beams in the negative moment zone, each country's code assumes that the concrete is cracked and ignores its flexural contribution, only considering the tension provided by steel bars and steel beams. On this basis, the academic community has considered the contribution of UHPC to the flexural performance of composite beams, established a calculation formula for the flexural bearing capacity of steel-UHPC composite beams, and also proposed a calculation method that initially covers the flexural bearing capacity of UHPC composite members. In recent years, the research results have gradually deepened, involving the calculation method of the long-term flexural bearing capacity of UHPC-reinforced members. For example, Mei Kuihua et al. and Yu Jian et al. have deduced the calculation method for the flexural bearing capacity of corroded UHPC-reinforced concrete members. However, during the long-term service of bridges, the action of loads cannot be ignored. Under the coupled action of loads and corrosion, the loads will cause cracks to appear in the negative moment zone of the bridge, and the corrosive medium will penetrate along the cracks, making it easier to corrode the steel bars inside the structure. As the corrosion further deepens, the corrosive substances will expand the cracks and cause further damage to the steel-UHPC composite beam. The existing technology still lacks research on the long-term performance of this kind of structure, especially the calculation method for the bearing capacity of steel-UHPC composite beams in the negative moment zone under the coupled action of loads and corrosion still has a theoretical gap. Summary of the Invention

[0004] The present invention provides a method and system for analyzing the mechanical properties of the negative moment zone of UHPC thin-layer reinforced steel-concrete composite beams to solve at least one of the technical problems mentioned in the background art.

[0005] The present invention provides a method for analyzing the mechanical properties of the negative moment region of a UHPC thin-layer reinforced steel-concrete composite beam, comprising the following steps: obtaining a geometric and mechanical property reduction model of non-uniformly corroded steel bars according to the steel constitutive model and the mechanical property test data of corroded steel bars, wherein the steel includes steel bars and steel beams; obtaining a concrete damage coefficient according to the UHPC constitutive model by comparing the ultimate loads without loading and with a preloading ratio under the same chloride corrosion damage degree, and the preloading ratio of the ultimate load is 0.4; obtaining a remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action according to the concrete damage coefficient, the geometric and mechanical property reduction model of non-uniformly corroded steel bars, and the force balance equation of the composite beam; introducing a correction coefficient into the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action to obtain a long-term flexural calculation model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action.

[0006] The present invention also provides a system applying the method for analyzing the mechanical properties of the negative moment region of a UHPC thin-layer reinforced steel-concrete composite beam, comprising: a steel analysis module, a UHPC analysis module, a bearing capacity analysis module, a composite beam verification module, and a mechanical property analysis database; wherein, the steel analysis module is used to obtain a geometric and mechanical property reduction model of non-uniformly corroded steel bars according to the steel constitutive model and the mechanical property test data of corroded steel bars, and the steel includes steel bars and steel beams; the UHPC analysis module is used to obtain a concrete damage coefficient according to the UHPC constitutive model by comparing the ultimate loads without loading and with a preloading ratio under the same chloride corrosion damage degree; the bearing capacity analysis module is used to obtain a remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action according to the concrete damage coefficient, the geometric and mechanical property reduction model of non-uniformly corroded steel bars, and the force balance equation of the composite beam; the composite beam verification module is used to introduce a correction coefficient into the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action to obtain a long-term flexural calculation model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action.

[0007] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages: 1. By providing the method and system for analyzing the mechanical properties of the negative moment region of a UHPC thin-layer reinforced steel-concrete composite beam, the present invention can effectively evaluate the contact characteristics between steel bars and concrete and the influence on the bearing capacity calculation of the composite beam under the load-corrosion coupling action, thereby realizing the dynamic correction of the load value and the strain value, and improving the calculation accuracy of the bearing capacity of the steel-UHPC composite beam in the negative moment region under the load-corrosion coupling action.

[0008] 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 judging whether to perform dynamic correction of the strain value according to the contact characteristic evaluation result, and then realizing the optimization of the strain value on the contact surface between the steel bar and the concrete, reducing the influence caused by poor contact, and improving the stability and reliability of the composite beam structure.

[0009] 3. The present invention compares the corrosion strain parameter reflecting the expansion degree of the steel bar corrosion product with a preset corrosion strain threshold, thereby dynamically correcting the load value and the strain value to reduce the influence of corrosion on the performance of the composite beam, and then realizing the accurate evaluation and intervention of the influence of steel bar corrosion, effectively ensuring the accuracy and reliability of the mechanical property parameters in the negative moment area of the composite beam, and thus improving the accuracy of the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action. Description of the Drawings

[0010] Figure 1 It is a flowchart of the mechanical property analysis method for the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam provided by the embodiment of the present application.

[0011] Figure 2 It is a mind map of the contact influence correction module provided by the embodiment of the present application.

[0012] Figure 3 It is a mind map of the corrosion influence correction module provided by the embodiment of the present application.

[0013] Figure 4 It is a constitutive model diagram of the steel bar in tension and compression provided by the embodiment of the present application.

[0014] Figure 5 It is a constitutive model diagram of the UHPC in tension provided by the embodiment of the present application.

[0015] Figure 6 It is a calculation diagram of the corroded composite beam provided by the embodiment of the present application.

[0016] Figure 7 It is a fitting curve diagram of the correction coefficient provided by the embodiment of the present application.

[0017] Figure 8a It is a structural diagram of the steel-NC-UHPC composite beam (unit: mm) provided by the embodiment of the present application, Figure 8b It is an elevation structural diagram of the steel-NC-UHPC composite beam specimen (unit: mm) provided by the embodiment of the present application, Figure 8c It is a cross-sectional structural diagram of the steel-NC-UHPC composite beam specimen (unit: mm) provided by the embodiment of the present application.

[0018] Figure 9 It is a loading device diagram provided by the embodiment of the present application.

[0019] Figure 10 This is the layout diagram of the measuring points of the steel-NC-UHPC composite beam provided by the embodiment of the present application.

[0020] Figure 11 This is the device diagram of the comprehensive tester.

[0021] Figure 12 This is the structural schematic diagram of the mechanical property analysis system for the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam provided by the embodiment of the present application. Specific implementation manners

[0022] In the embodiment of the present application, by providing a method and system for analyzing the mechanical properties of the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam, the following problem is solved: during the long-term service process of the bridge, under the coupled action of load and corrosion, the load will cause cracks in the negative moment area of the bridge. The corrosive medium penetrates along the cracks, and it is easier to corrode the steel bars in the structure. As the corrosion further deepens, the corrosive substances will expand the cracks and cause further damage to the steel-UHPC composite beam. There may be expansion and extrusion of the rust products around the surrounding concrete, generating additional strain, resulting in low accuracy of the load value and strain value measured by the comprehensive tester, thus leading to low accuracy in the analysis of the bearing capacity performance of the steel-UHPC composite beam in the negative moment area under the coupled action of load and corrosion. According to the steel constitutive model and the test data of the mechanical properties of corroded steel bars, a geometric and mechanical property reduction model for non-uniformly corroded steel bars is obtained, and the steel includes steel bars and steel beams; according to the UHPC constitutive model, by comparing the ultimate loads of unloaded and preloaded ratios under the same chloride salt corrosion damage degree, the concrete damage coefficient is obtained, and the preloading ratio of the ultimate load is 0.4; according to the concrete damage coefficient, the geometric and mechanical property reduction model of non-uniformly corroded steel bars and the composite beam force balance equation, a remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action is obtained; by introducing a correction coefficient into the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action, a long-term flexural calculation model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action is obtained, realizing an improvement in the accuracy of the bearing capacity performance analysis of the steel-UHPC composite beam in the negative moment area under the coupled action of load and corrosion.

[0023] The technical solution in the embodiment of the present application is to solve the following problem: during the long-term service of a bridge, under the coupled action of load and corrosion, the load will cause cracks in the negative moment area of the bridge. The corrosive medium penetrates along the cracks, which will more easily corrode the steel bars in the structure. As the corrosion further deepens, the corrosive substances will expand the cracks and cause further damage to the steel-UHPC composite beam. There may be expansion and extrusion of rust products around the concrete, generating additional strain, resulting in low accuracy of the load value and strain value measured by the comprehensive tester, and thus low accuracy in the analysis of the bearing capacity performance of the steel-UHPC composite beam in the negative moment area under the coupled action of load and corrosion. The general idea is as follows: According to the steel constitutive model and the mechanical property test data of corroded steel bars, a geometric and mechanical property reduction model of non-uniformly corroded steel bars is obtained. By comparing the ultimate loads of specimens without loading and specimens with a preloading ratio under the same chloride corrosion damage degree, the concrete damage coefficient is obtained. Based on the concrete damage coefficient, the geometric and mechanical property reduction model of non-uniformly corroded steel bars, and the force balance equation of the composite beam, a remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after the action of load and corrosion is obtained. By introducing a correction factor into the above model, a long-term flexural calculation model of the UHPC-reinforced steel-concrete composite beam after the action of load and corrosion is obtained, achieving an improvement in the accuracy of the analysis of the bearing capacity performance of the steel-UHPC composite beam in the negative moment area under the coupled action of load and corrosion.

[0024] To better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings of the specification and specific implementation manners.

[0025] As Figure 1As shown in the figure, it is a flowchart of the mechanical property analysis method for the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam provided by the embodiment of the present application. This method includes the following steps: According to the steel constitutive model and the mechanical property test data of corroded steel bars, a geometric and mechanical property reduction model of non-uniformly corroded steel bars is obtained. The steel includes steel bars and steel beams; According to the UHPC constitutive model, by comparing the ultimate loads of specimens without loading and with a preloading ratio under the same chloride corrosion damage degree, the concrete damage coefficient is obtained. The preloading ratio of the ultimate load is 0.4; According to the concrete damage coefficient, the geometric and mechanical property reduction model of non-uniformly corroded steel bars, and the force balance equation of the composite beam, a remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action is obtained; A correction coefficient is introduced into the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action to obtain a long-term flexural calculation model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action. The parameters in the negative moment area of the composite beam include the internal force of the UHPC matrix, the internal force of the longitudinal bars in the UHPC layer, the internal force of the longitudinal bars in the NC layer, the moments of the tension and compression zones of the steel beam on the plastic neutral axis of the composite beam, and the distances from 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, and the compression zone of the steel beam web to the plastic neutral axis of the composite beam. The remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action is used to reduce the effects of the non-uniform corrosion of the tension longitudinal bars in the UHPC thin layer and the degradation of the mechanical properties of the steel bars caused by the corrosion action, as well as the reduction of the bending resistance of the UHPC layer caused by interface debonding on the mechanical property analysis of the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam.

[0026] In this embodiment, the present invention respectively corrects the strain values and load values on the contact surface between the steel bar and the concrete according to the contact characteristic parameters and the corrosion strain parameters, reducing the influence of poor contact between the steel bar and the concrete surface and the expansion of the steel bar corrosion products on the strain values and load values. And based on the corrected strain values and load values and the parameters in the negative moment area of the composite beam, a remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action is generated, avoiding the deficiencies of the prior art and providing a bearing capacity calculation method for the long-term mechanical properties of the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam. This bearing capacity calculation method for the long-term mechanical properties of the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam can effectively calculate the flexural bearing capacity of the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam after the load-corrosion coupling action. At the same time, this calculation method considers the non-uniform corrosion of the tension longitudinal bars in the UHPC thin layer and the degradation of the mechanical properties of the steel bars caused by the corrosion action. The present invention also innovatively introduces a correction coefficient to characterize the reduction effect of the bending resistance of the UHPC layer caused by interface debonding.

[0027] In addition, the mechanical property analysis database is used to store relevant data on the mechanical property analysis method of the negative moment zone of the UHPC thin-layer reinforced steel-concrete composite beam, including: critical strain transfer efficiency, critical contact resistance, strain correction values corresponding to the range of each contact characteristic deviation index, the first contact characteristic threshold, the second contact characteristic threshold, etc. The data in the mechanical property analysis database can be directly queried from public databases such as transportation industry databases and science and technology resource sharing service platforms, or obtained through cooperation with departments such as construction enterprises, UHPC material production enterprises, relevant universities, and scientific research institutions.

[0028] As Figure 2 shown, it is the mind map of the contact influence correction module provided by the embodiment of the present application. It includes: real-time monitoring of contact influence parameters, and obtaining the contact influence index through analysis of the contact influence parameters, 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, the corresponding contact characteristic evaluation result is recorded as the first contact characteristic result, and no additional processing is performed. If the contact characteristic index is greater than the first contact influence threshold and less than the second contact influence threshold, the corresponding contact characteristic evaluation result is recorded as the second contact characteristic result, and the strain value of the contact surface between the steel bar and the concrete is corrected according to the contact influence index. If the contact characteristic index is greater than or equal to the second contact influence threshold, the corresponding contact characteristic evaluation result is recorded as the third contact characteristic result, and manual intervention is notified to process the contact surface until the contact characteristic index is less than or equal to the second contact influence threshold.

[0029] Specifically, the steps of dynamically correcting the strain value between the steel bar and the concrete according to the contact characteristic parameters include: obtaining the contact characteristic index through analysis of the contact characteristic parameters, where the contact characteristic parameters include strain transfer efficiency and contact resistance, and the contact characteristic index represents the quantitative data of the combined influence degree of strain transfer efficiency and contact resistance on the contact performance between the steel bar and the concrete; obtaining the first contact characteristic threshold and the second contact characteristic threshold from the 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, a contact abnormality prompt is issued to notify the 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, the difference between the second contact characteristic threshold and the contact characteristic index is recorded as the contact characteristic deviation index, and the contact characteristic deviation index is matched with the strain correction values corresponding to the preset ranges of each contact characteristic deviation index in the mechanical property analysis database to obtain the strain correction value, and the strain value on the contact surface between the steel bar and the concrete is corrected according to the strain correction value to obtain the corrected strain value; if the contact characteristic index is greater than or equal to the second contact characteristic threshold, no additional processing is performed.

[0030] The steps for analyzing the contact characteristic parameters to obtain the contact characteristic index include: obtaining the reference data of the contact characteristic parameters from a preset mechanical property analysis database, specifically including: the critical strain transfer efficiency and the critical contact resistance; performing a ratio approach operation on the strain transfer efficiency and the critical contact resistance with the critical strain transfer efficiency and the contact resistance respectively, and then coupling and processing the results of the ratio approach operation by weighting them respectively using the contact characteristic contribution parameters, where the contact characteristic contribution parameters include the strain transfer efficiency contribution and the contact resistance contribution.

[0031] The method for obtaining the contact characteristic index is as follows: ; In the formula, represents the contact characteristic index of the contact surface between the steel bar and the concrete. The contact characteristic index represents the quantitative data of the influence degree of the strain transfer efficiency and the contact resistance on the contact performance between the steel bar and the concrete. represents the strain transfer efficiency contribution. represents the contact resistance contribution. represents the strain transfer efficiency of the contact surface between the steel bar and the concrete. The strain transfer efficiency refers to the effectiveness of the strain transfer from the steel bar to the concrete. The strain transfer efficiency can be obtained by placing strain gauges at different positions on the contact surface between the steel bar and the concrete, and the value obtained by performing a ratio operation on the difference between the average value of the strain values on the steel bar surface and the average value of the strain values on the concrete surface and the average value of the strain values on the steel bar surface is the strain transfer efficiency. If the strain transfer efficiency of the steel bar and the concrete is higher, the contact characteristic index is higher. represents the critical strain transfer efficiency. represents the contact resistance between the contact surfaces of the steel bar and the concrete. The contact resistance refers to the average resistance between the contact surfaces of the steel bar and the concrete. It directly affects the strain transfer efficiency because the existence of the resistance is related to the bonding force on the contact surface and the ease of current conduction. The contact resistance can be measured by applying a known current at different positions on the contact surface using the resistance test method, measuring the voltage change, and then calculating and taking the average value through Ohm's law. The smaller the contact resistance, the better the contact between the steel bar and the concrete, and the larger the contact characteristic index. represents the critical contact resistance.

[0032] and are respectively the preset strain transfer efficiency and the contribution degree corresponding to the contact resistance in the mechanical property analysis database. These contribution degrees are numerical indexes for measuring 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 the contact resistance. The table records each possible parameter value and its corresponding contribution degree, and these mapping relationships can be one-to-one or many-to-one. For example, in practical applications, when it is necessary to evaluate the contact characteristic index, the measured strain transfer efficiency and contact resistance can be respectively input into their corresponding mapping relationship tables, and the contribution degrees corresponding to these values can be quickly found, where the value range of the contribution degree is between 0 and 1.

[0033] It should be noted that in this algorithm, the strain transfer efficiency and the contact resistance are interrelated. When the contact resistance increases, it indicates that the contact quality between the steel bar and the concrete is poor, the bonding force is weak, and the strain transfer efficiency decreases. On the contrary, when the contact resistance is low, the bonding force between the steel bar and the concrete is good, and the strain transfer efficiency is high. The comprehensively analyzed contact characteristic index can reflect the overall bonding performance between the steel bar and the concrete. Through the contact characteristic index, the influence of the poor surface contact between the steel bar and the concrete on the strain value can be reduced, so as to predict the influence of factors such as corrosion and aging on the mechanical property analysis of the negative moment area of the composite beam.

[0034] As Figure 3 shown, it is the mind map of the rust influence correction module provided by the embodiment of the present application. It includes: real-time monitoring of the rust strain parameter, and analyzing the rust strain index according to the rust strain parameter. Comparing the rust strain parameter with the first rust strain threshold and the second rust strain threshold respectively. If the rust strain index is less than or equal to the first rust strain threshold, the corresponding expansion degree evaluation result is recorded as the first expansion degree result, and no additional processing is performed; if the rust strain index is greater than the first rust strain threshold and less than the second rust strain threshold, the corresponding expansion degree evaluation result is recorded as the second expansion degree result, and the rust influence parameter is obtained, and the load value and strain value of the expansion interference of the steel bar rust product are corrected according to the rust influence parameter; if the rust strain index is greater than or equal to the second rust strain threshold, the corresponding expansion degree evaluation result is recorded as the third expansion degree result, and an abnormal steel bar alarm is issued.

[0035] Specifically, the steps for dynamically correcting the load and strain values of steel bars according to the corrosion strain parameters include: analyzing the corrosion strain index based on the corrosion strain parameters. The corrosion strain parameters include the steel bar volume expansion rate, corrosion current density, and concrete expansion stress. The corrosion strain index represents the quantitative data of the combined influence degree of the corrosion strain parameters on the corrosion strain degree; obtaining the first corrosion strain threshold and the second corrosion strain threshold from the 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, obtain the corrosion influence contribution degree parameters from the preset mechanical property analysis database. The corrosion influence contribution degree parameters include the load value corrosion influence contribution degree parameter and the strain value corrosion influence contribution degree parameter. Correct the load value according to the load value corrosion influence index obtained from the corrosion influence parameter, corrosion strain index, and load value corrosion influence contribution degree parameter, and correct the strain value according to the strain value corrosion influence index obtained from the corrosion influence parameter, corrosion strain index, and strain value corrosion influence contribution degree parameter; if the corrosion strain index is greater than or equal to the second corrosion strain threshold, issue a steel bar anomaly prompt; the load value corrosion influence index represents the quantitative data of the combined influence degree 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 degree parameters include the load value corrosion depth contribution degree, load value corrosion current contribution degree, load value steel bar cross-sectional area contribution degree, and load value corrosion strain index contribution degree; the strain value corrosion influence contribution degree parameters include the strain value corrosion depth contribution degree, strain value corrosion current contribution degree, strain value steel bar cross-sectional area contribution degree, and strain value corrosion strain index contribution degree; the strain value corrosion influence index represents the quantitative data of the combined influence degree of the corrosion influence parameter and the corrosion strain index on the accuracy of the strain value disturbed by the expansion of corrosion products.

[0036] Among them, the steps for analyzing the corrosion strain index based on the corrosion strain parameters include: obtaining the corrosion strain parameter reference data from the preset mechanical property analysis database, specifically including: the critical steel bar volume expansion rate, critical corrosion current density, and critical concrete expansion stress; performing a ratio approximation operation on the corrosion strain parameters and the corresponding corrosion strain parameter reference data respectively, and then coupling and processing the ratio approximation operation results after weighting them respectively using the corrosion strain contribution degree parameters. The corrosion strain contribution degree parameters include the steel bar volume expansion rate contribution degree, corrosion current density contribution degree, and concrete expansion stress contribution degree.

[0037] The method for obtaining the corrosion strain index is as follows: ; In the formula, The corrosion strain index representing the influence of the expansion of steel corrosion products Represents the contribution degree of the steel bar volume expansion rate Represents the contribution degree of the corrosion current density Represents the contribution degree of the concrete expansion stress

[0038] Represents the volume expansion rate of the steel bar after corrosion, and the acquisition method is as follows: ; In the formula, Is the ratio of the volume of the steel bar after corrosion to the volume of the original steel bar, Is the reduction amount of the steel bar cross-sectional area, Is the cross-sectional area of the original steel bar. The larger the steel bar volume expansion rate, the larger the corrosion strain index Represents the critical steel bar volume expansion rate

[0039] Represents the corrosion current density of the steel bar after corrosion, which can be directly measured by electrochemical sensors such as the current method. The larger the corrosion current density, the larger the corrosion strain index Represents the critical corrosion current density

[0040] Represents the concrete expansion stress generated by the expansion of the corrosion products after corrosion, which is the radial stress generated by the corrosion products squeezing the concrete. The acquisition method is as follows: ; In the formula, Is the elastic modulus of the concrete, And Are the outer radius of the concrete cover and the radius of the steel bar respectively. The larger the concrete expansion stress, the larger the steel bar volume expansion rate Represents the critical concrete expansion stress

[0041] It should be noted that in this algorithm, the steel bar volume expansion rate, the corrosion current density, and the concrete expansion stress are interrelated with each other. For example, the corrosion current density directly determines the steel bar corrosion rate and affects the volume expansion speed of the corrosion products. The larger the current density, the faster the corrosion speed and the higher the corrosion volume expansion rate; the higher the steel bar volume expansion rate, the more significant the concrete expansion stress. Steel bar corrosion is one of the main inducements for the degradation of the durability of concrete structures. The expansion stress generated by it will have a systematic impact on the mechanical properties of the negative moment area of the composite beam. The corrosion strain index obtained through comprehensive analysis can reflect the severity of the concrete damage caused by corrosion. During the corrosion process, the internal pressure caused by the volume expansion of the steel bar generates stress on the concrete, which may lead to the formation or expansion of concrete cracks. Through the corrosion strain index, the expansion degree of the steel bar corrosion products can be quantitatively evaluated, so as to track and evaluate the influence of steel bar corrosion on the accuracy of the structural load value and the steel bar strain value

[0042] , and are the contribution degrees corresponding to the preset steel bar volume expansion rate, corrosion current density, and concrete expansion stress in the mechanical property analysis database respectively. These contribution degrees are numerical indicators for measuring the influence of the above parameters on the corrosion strain index. Specifically, there is a mapping relationship table for each of the steel bar volume expansion rate, corrosion current density, and concrete expansion stress. The table records the contribution degree corresponding to each possible corrosion strain parameter value. These mapping relationships can be one-to-one or many-to-one. For example, in practical 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 input into their respective mapping relationship tables respectively, and the contribution degrees corresponding to these values can be quickly found. The value range of the contribution degree is between 0 and 1.

[0043] As a further solution, the steps for correcting the load value according to the corrosion influence index of the load value obtained from the corrosion influence parameters, corrosion strain index, and load value corrosion influence contribution degree parameter include: the corrosion influence parameters include corrosion depth, corrosion current, and steel bar cross-sectional area; obtaining the critical corrosion influence index from the preset mechanical property analysis database; matching the corrosion influence index of the load value with the load value empirical coefficient corresponding to each preset load value corrosion influence index range in the mechanical property analysis database to obtain the load value empirical coefficient; correcting the load value according to the load value empirical coefficient, corrosion influence index of the load value, and critical corrosion influence index to obtain the corrected load value.

[0044] Among them, the specific steps for obtaining the corrosion influence index of the load value include: obtaining the corrosion influence parameter reference data from the preset mechanical property analysis database, specifically including: critical corrosion depth, critical corrosion current, critical steel bar cross-sectional area, and critical corrosion strain index; respectively performing the ratio approximation operation 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 coupling and processing the ratio approximation operation results by using the load value corrosion influence contribution degree parameter respectively to obtain the corrosion influence index of the load value.

[0045] The strain value is corrected according to the corrosion influence index of the strain value obtained from the corrosion influence parameters, corrosion strain index, and strain value corrosion influence contribution degree parameter. The corrosion influence parameter can directly reflect the influence of corrosion on the bearing capacity of the steel bar. Although the corrosion expansion strain affects the concrete, it does not directly affect the bearing capacity of the steel bar. Therefore, it is more suitable for correcting the load value and strain value.

[0046] The steps of correcting the strain value according to the strain value corrosion influence index obtained from the corrosion influence parameter, corrosion strain index and strain value corrosion influence contribution parameter include: matching the strain value corrosion influence index with the strain value empirical coefficient corresponding to each preset strain value corrosion influence index range in the mechanical property analysis database to obtain the strain value empirical coefficient; correcting the strain value according to the strain value empirical coefficient, strain value corrosion influence index and critical corrosion influence index to obtain the corrected strain value.

[0047] Specifically, the calculation formulas for the corrected load value and the corrected strain value are as follows: ; where, when j = 1, represents the corrected load value, represents the load value directly read by the comprehensive tester, represents the load value empirical coefficient, represents the load value corrosion influence index, when j = 2, represents the corrected strain value, represents the strain value directly measured by the comprehensive tester, represents the strain value correction empirical coefficient, is the strain value corrosion influence index, is the critical corrosion influence index.

[0048] The specific steps for obtaining the strain value corrosion influence index include: performing a ratio approximation operation 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; using the strain value corrosion influence contribution parameter to perform a weighted coupling process on the ratio approximation operation results respectively to obtain the strain value corrosion influence index.

[0049] Specifically, the obtaining methods of the load value corrosion influence index and the strain value corrosion influence index are as follows: ; where, j = 1 or 2, and the obtaining method of the load value corrosion influence index is: ; The obtaining method of the strain value corrosion influence index is: ; where, when j = 1, represents the load value corrosion influence index, represents the load value corrosion depth contribution degree, represents the load value corrosion current density contribution degree, represents the load value steel bar cross-sectional area contribution degree, Indicates the contribution degree of the load value to the corrosion strain index. When j = 2, Indicates the corrosion influence index of the strain value, Indicates the contribution degree of the strain value to the corrosion depth, Indicates the contribution degree of the strain value to the corrosion current density, Indicates the contribution degree of the strain value to the cross-sectional area of the steel bar, Indicates the contribution degree of the strain value to the corrosion strain index, Indicates the corrosion depth, which can be obtained through electrochemical tests such as the linear polarization method or by measuring the actual corrosion layer thickness, reflecting the geometric damage degree of steel bar corrosion. The greater the corrosion depth, the greater the corrosion influence index. Indicates the critical corrosion depth, Indicates the corrosion current density. The greater the current density, the greater the corrosion influence index. Indicates the critical corrosion current density, Indicates the cross-sectional area of the steel bar, which can be obtained by subtracting the corrosion loss area from the original cross-sectional area of the steel bar. The greater the cross-sectional area of the steel bar, the smaller the corrosion influence index. Indicates the critical cross-sectional area of the steel bar, Indicates the corrosion strain index. The greater the corrosion strain index, the greater the corrosion influence index. Indicates the critical corrosion strain index.

[0050] 、 、 and are respectively the contribution degrees corresponding to the corrosion depth, corrosion current, cross-sectional area of the steel bar, and corrosion strain index preset in the mechanical property analysis database. These contribution degrees are numerical indicators for measuring the influence of the above parameters on the corrosion influence index. Specifically, there is a mapping relationship table for each of the corrosion depth, corrosion current, cross-sectional area of the steel bar, and corrosion strain index. The table records the contribution degree corresponding to each possible parameter value, and these mapping relationships can be one-to-one or many-to-one. For example, in practical applications, when it is necessary to evaluate the corrosion influence index, the measured corrosion depth, corrosion current, cross-sectional area of the steel bar, and corrosion strain index can be respectively input into their corresponding mapping relationship tables, and the contribution degrees corresponding to these values can be quickly found. The value range of the contribution degree is from 0 to 1.

[0051] It should be noted that in this algorithm, the corrosion depth, corrosion current density, cross-sectional area of the steel bar, and corrosion strain index are interrelated. For example, the current density determines the corrosion rate, and the greater the corrosion rate within the same time, the greater the corrosion depth; the increase in corrosion depth will lead to a decrease in the effective cross-sectional area of the steel bar; the greater the corrosion strain index, the greater the risk of concrete cracking, and the more likely the cover of the composite beam is to crack. The corrosion influence index obtained through comprehensive analysis can accurately reflect the comprehensive influence of the expansion interference of corrosion products on the load value and strain value. By correcting the load value and strain value according to the corrosion influence index, the influence of steel bar corrosion on the bearing capacity of concrete structures can be more realistically reflected, making the analysis of structural durability more scientific.

[0052] Furthermore, based on the corrected load value and strain value, the method for obtaining the concrete damage coefficient by comparing the unloaded and preloaded load values under the same chloride salt corrosion damage degree is as follows: As Figure 4 shown, it is the tension and compression constitutive model diagram of steel provided by the embodiment of the present application. For the uncorroded steel bar and steel beam materials: the tension and compression constitutives of the steel bar and steel beam are both described by a simplified double-line model. The tension and compression constitutive relationships of the steel bar and steel beam are as follows: ; where is the tensile stress, is the elastic modulus; , are the yield strength and ultimate strength respectively; , , are the strain value, yield strain, and ultimate strain respectively.

[0053] Regarding the reduction of the material properties of corroded steel bars, based on the short-term bending calculation model, the present invention introduces the degradation effect of the mechanical properties of steel bars caused by corrosion. The geometric and mechanical property reduction models of non-uniformly corroded steel bars are as follows: ; ; ; In the formula, represents the effective cross-sectional area of the corroded steel bar, is the corrosion rate, is the cross-sectional area of the steel bar, which is the nominal cross-sectional area of the used steel bar and can be obtained from the national standard specification, [[ID= forty]] is the tensile strength of the steel bar considering corrosion reduction.

[0054] As Figure 5 shown, it is the tension and compression constitutive model diagram of UHPC provided by the embodiment of the present application. The UHPC constitutive relationship is expressed as follows: ; In the formula, ​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.

[0055] Under the same degree of chloride corrosion damage, the ultimate load of the undamaged specimen is 123 kN, and the ultimate load of the damaged specimen is 121 kN. 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.

[0056] Furthermore, the composite beam includes: UHPC layer matrix, NC layer, UHPC steel bars, NC layer steel bars, upper flange of steel beam, lower flange of steel beam, and web of steel beam. According to Figure 6 the force balance equations are listed based on the force analysis of the composite beam shown as follows: ; In the formula, , , , , , , respectively represent the resultant forces of the UHPC layer matrix, tensile longitudinal bars of the UHPC layer, tensile longitudinal bars of the NC layer, upper flange of the steel beam, lower flange of the steel beam, tensile part of the web of the steel beam, and compressive part of the web of the steel beam. Among them, ; In the formula, represents the concrete corrosion damage coefficient; is the steel fiber crack bridging coefficient, ; is the plastic parameter, which is taken as 0.35 from the "Design Code for Ultra-High Performance Concrete Structures" (T / CCPA 35-2022); is the volume ratio of steel fibers; is the length and diameter of steel fibers; is the ultimate tensile stress of UHPC, is the elastic modulus of UHPC; , represents the ultimate tensile strain of UHPC; , represents the cross-sectional area of the UHPC layer, respectively represent the width and thickness of the UHPC layer. ; In the formula, is the ultimate tensile strength of the steel bar; represents the total cross-sectional area of the longitudinal bars in the UHPC layer. ; In the formula, 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.

[0057] 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.

[0058] 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; represents the yield tensile strain of the longitudinal reinforcement in the NC layer, which can be directly obtained by referring to the corresponding steel bar specifications; is the distance from the top surface of the UHPC to the neutral axis of the section; is the distance from the longitudinal reinforcement in the NC layer to the top surface of the UHPC. i is the number of each height in the composite beam section, i = 1, 2, 3,..., N, and N is the total number of heights in the composite beam section.

[0059] Substitute the internal forces of each key stressed component into the moment equilibrium equation, and the remaining flexural bearing capacity of the UHPC-reinforced steel-concrete composite beam after load-corrosion can be calculated as follows: ; ; In the formula, represents the moment of the tensile and compressive zones of the steel beam about the plastic neutral axis of the composite beam; , , , respectively represent the distances from the centroid 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 to the plastic neutral axis of the composite beam; , ,: are the distances from the centroids of the UHPC layer, the longitudinal reinforcement in the UHPC layer, and the longitudinal reinforcement in the NC layer to the plastic neutral axis respectively.

[0060] According to the long-term flexural test results, it can be seen that the degree of debonding at the UHPC-NC interface is closely related to the degree of corrosion. Therefore can be regarded as a function of the degree of corrosion, that is . Use the flexural test results of the test beam to perform non-linear fitting on , and the expression of the correction coefficient ( ) is as follows: ; As Figure 7 shown, it is the fitting curve of the correction coefficient provided by the embodiment of the present application. In the figure = 0.9410 indicates that the characteristic points fit well with the curve. The long-term flexural calculation model of the UHPC-reinforced steel-concrete composite beam is as follows: ; Furthermore, verify the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion. As Figure 8a , Figure 8b and Figure 8c shown, where Figure 8a is the structural drawing of the steel-NC-UHPC composite beam (unit: mm),[[ID=]] Figure 8b is the elevation structural drawing of the steel-NC-UHPC composite beam specimen (unit: mm).Figure 8c It is the cross-sectional structure diagram of the steel-NC-UHPC composite beam specimen (unit: mm).

[0061] As Figure 9 shown, it is the loading device diagram provided by the embodiment of the present application. First, adjust the spacing of the upper supports on the distribution beam supporting the servo press and hoist the specimen and the loading distribution beam to ensure that the pure bending section of the steel-NC-UHPC composite beam is 830 mm and the pure bending section of the UHPC-NC composite slab is 800 mm. Synchronously arrange strain gauges and LVDT displacement gauges and connect them to the acquisition tool to prepare for the test. ①Preloading: Load to 20 kN in the force control mode (5 kN / s), and maintain the load level for 3 minutes to eliminate the contact gap and verify the data stability of the strain gauges and displacement sensors. ②Formal loading: From 0 to 0.7Pu (Pu is the ultimate load), adopt the force control mode (5 kN / s); from 0.7Pu to Pu, switch to the displacement control mode (0.2 mm / min); when the load exceeds Pu and drops to 0.7Pu, stop loading. ③Unloading: After stopping loading, adopt the force control mode and unload to 0 kN at a speed of -5 kN / s, and then save the test data and take pictures to record the state of the specimen.

[0062] As Figure 10 shown, it is the measuring point layout diagram of the steel-NC-UHPC composite beam provided by the embodiment of the present application. ①Displacement gauges: Vertically arranged displacement gauges at the mid-span and L / 4 sections to obtain the load-deflection curve; an orthogonal displacement gauge group is set at the plate end to calculate the section rotation angle; displacement gauges are horizontally arranged at the supports, L / 4 sections, and the ends of the steel beams (composite beams) using angle steels to quantify the interlayer slip of the UHPC-NC layer. ②Strain gauges: Concrete strain gauges are arranged along the height direction of the mid-span section of the specimen to verify the plane section assumption; longitudinal strain gauges along the plate are arranged on both sides of the interface at the supports and L / 4 sections to investigate the interface coordination performance; strain gauges along the bar direction are arranged at the mid-span of the longitudinal bars in the UHPC slab to master the steel bar strain situation. ③Embedded chord strain gauges (load-corrosion coupling test): Embedded strain gauges are arranged at the mid-span and L / 4 of the longitudinal bars in the NC slab to read the steel bar strain values in the slab in real time. During the loading process, the development of cracks in the specimen is synchronously observed and recorded using an HC-F600 crack comprehensive tester, and all deflection and strain data are automatically collected using a static data collector.

[0063] Based on the test results of the above benchmark specimens, pre-cracking treatment tests for crack width control were carried out on four groups of steel-NC-UHPC composite beam specimens (SNU-C-0 / 05 / 15 / 20). A 1000 kN long-column hydraulic servo press (loading rate 2 kN / s) was used to implement hierarchical loading, and the target residual crack widths were 0, 0.05, 0.15, and 0.20 mm (accuracy ±0.02 mm) respectively.

[0064] In addition, the present invention breaks through the limitations of single-factor tests through a self-balancing reaction frame-electrochemical accelerated corrosion device. The modular framework supports independent regulation of load-corrosion parameters, has a short disassembly and assembly cycle, and can simulate the environment of electrochemical accelerated corrosion under the load-bearing state. The device consists of two parts: a mechanical loading module and an electrochemical corrosion module. ① Mechanical loading module: Apply a constant load through a hand-operated jack, synchronously lock two groups of specimens, simulate the long-term service stress state, and at the same time, the load level and the strain value of the embedded vibrating wire 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 a stainless steel mesh cathode and a steel bar to be corroded anode to form a closed circuit, and the constant current mode is used to accelerate corrosion, and the potential is monitored and regulated in real time.

[0065] As Figure 11 shown, it is a process diagram of the load-corrosion coupling action test provided by the embodiment of the present application. The steps are as follows: ① Test device installation: Build a load-corrosion coupling action test device. Stack the specimens symmetrically in the loading frame to ensure that the negative moment area is bent (the UHPC layer is in tension) during loading, and level and align the specimen positions through a level. ② Based on the ultimate load (Pu) measured in the flexural test of the reference specimen, apply a holding load of 0.4Pu to the specimen through a hand-operated jack to simulate the long-term load level under the normal use state of the bridge. After the loading is completed, lock the oil pump, and the holding stability is monitored in real time through a comprehensive tester. ③ Configure a 5% concentration NaCl solution using analytical pure NaCl reagent, and the injection volume in the solution pool should be sufficient to completely immerse the specimen. ④ Connect the reserved energized wires of the specimen and the stainless steel mesh to the positive and negative poles of the DC power supply respectively, and conduct constant current energization according to the preset current density to ensure that the holding load and the energized corrosion are carried out synchronously. During the energization process, the circuit state is monitored in real time through an ammeter and a voltmeter.

[0066] After the load-corrosion coupling test, a four-point bending loading test is carried out on four groups of steel-NC-UHPC composite beams. For the composite beam specimens that have completed the four-point bending failure test, the corroded steel bars need to be extracted through the disintegration of the crusher and the standard sampling process to quantify the degree of steel bar corrosion damage. As Figure 12As shown in the figure, it is the operation flow chart for extracting corroded steel bars provided by the embodiments of this application. Specifically, it includes the following five core steps: (1) Steel bar sampling: Use a crusher to disassemble the composite beam specimens that have completed the four-point bending test to expose the internal steel bar skeleton. Use an angle grinder to cut the longitudinal steel bars at equal intervals (300 mm), and at the same time collect the shear-resistant steel bars at the interface; (2) Steel bar grouping: For components such as shear-resistant stirrups and stress-bearing longitudinal steel bars obtained, group and number various steel bars according to "specimen number - steel bar type - sampling position"; (3) Pickling and rust removal: Immerse the steel bars in dilute hydrochloric acid for 10 to 15 minutes until the rust products dissolve, and use a brush to wipe off the attachments on the surface of the steel bars; (4) Neutralization treatment: Neutralize the residual acid solution with saturated Ca(OH)2 solution, take it out after soaking for 5 minutes, and use a 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 electrothermal constant temperature drying oven, dry them at 105°C for 2 hours, cool to room temperature, and then weigh them using an electronic balance (accuracy 0.01 g) to record the mass data.

[0067] As Figure 12 shown in the figure, it is the structural schematic diagram of the mechanical property analysis system for the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam provided by the embodiments of this application. The mechanical property analysis system for the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam provided by the embodiments of this application includes: a steel material analysis module, a UHPC analysis module, a bearing capacity analysis module, a composite beam verification module, and a mechanical property analysis database; among them, the steel material analysis module is used to obtain the geometric and mechanical property reduction model of non-uniformly corroded steel bars according to the steel material constitutive model and the mechanical property test data of corroded steel bars. The steel materials include steel bars and steel beams; the UHPC analysis module is used to compare the ultimate loads of unloaded and preloaded ratios under the same chloride corrosion damage degree according to the UHPC constitutive model to obtain the concrete damage coefficient; the bearing capacity analysis module is used to obtain the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion according to the concrete damage coefficient, the geometric and mechanical property reduction model of non-uniformly corroded steel bars, and the composite beam force balance equation; the composite beam verification module is used to introduce a correction coefficient into the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion to obtain the long-term flexural calculation model of the UHPC-reinforced steel-concrete composite beam after load-corrosion.

[0068] In summary, according to the steel constitutive model and the mechanical property test data of corroded steel bars, the geometric and mechanical property reduction model of non-uniformly corroded steel bars is obtained, where the steel includes steel bars and steel beams; according to the UHPC constitutive model, the concrete damage coefficient is obtained by comparing the ultimate loads of specimens without preloading and with a preloading ratio of 0.4 under the same chloride corrosion damage degree; according to the concrete damage coefficient, the geometric and mechanical property reduction model of non-uniformly corroded steel bars, and the force balance equation of the composite beam, the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action is obtained; by introducing a correction coefficient into the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action, the long-term flexural calculation model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action is obtained, improving the accuracy of the bearing capacity performance analysis of the steel-UHPC composite beam in the negative moment area under the load-corrosion coupling action.

[0069] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0070] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows 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 the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices produce means for implementing the functions specified in Figure 1 one or more of the processes or multiple processes and / or blocks Figure 1 one or more of the blocks or multiple blocks.

[0071] These computer program instructions can 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, such that the instructions stored in the computer-readable memory produce a manufactured article including instruction means that implement the functions specified in Figure 1 one or more of the processes or multiple processes and / or blocks Figure 1 one or more of the blocks or multiple blocks.

[0072] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus, so that a series of operational steps are performed on the computer or other programmable apparatus to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable apparatus provide steps for implementing the functions specified in one process or a plurality of processes and / or blocks Figure 1 in one block or a plurality of blocks Figure 1 specified in one block or a plurality of blocks.

[0073] Although the preferred embodiments of the present invention have been described, additional changes and modifications can be made by those skilled in the art once they learn of the basic inventive concept. Therefore, the appended claims are intended to be construed to cover the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0074] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. Mechanical property analysis method for negative moment zone of UHPC thin layer reinforced steel-concrete composite beam, characterized in that, It includes the following steps: According to the steel constitutive model and the mechanical property test data of corroded steel bars, a geometric and mechanical property reduction model of non-uniformly corroded steel bars is obtained, where the steel includes steel bars and steel beams; According to the UHPC constitutive model, by comparing the ultimate loads of specimens without loading and specimens with a preloading ratio under the same chloride corrosion damage degree, a concrete damage coefficient is obtained; According to the concrete damage coefficient, the geometric and mechanical property reduction model of non-uniformly corroded steel bars, and the force balance equation of the composite beam, a remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action is obtained; A correction coefficient is introduced into the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action to obtain a long-term flexural calculation model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action.

2. The mechanical property analysis method for the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam according to claim 1, wherein: The force balance equation of the composite beam specifically includes: the internal force of the UHPC matrix, the internal force of the longitudinal bars in the UHPC layer, the internal force of the longitudinal bars in the NC layer, 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 steel beam web above the neutral axis, and the internal force of the steel beam web below the neutral axis.

3. The mechanical property analysis method for the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam according to claim 2, wherein: The specific steps for obtaining the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action according to the concrete damage coefficient, the geometric and mechanical property reduction model of non-uniformly corroded steel bars, and the force balance equation of the composite beam are as follows: Obtain the strain data of the composite beam, the dimension data of the UHPC layer, the dimension data of the steel beam, the dimension data of the NC layer, the distance from the neutral axis of the composite beam to the highest point of the composite beam, and the total height of the composite beam; Obtain the elastic modulus of UHPC and the ultimate tensile strain of UHPC from the UHPC constitutive model; Obtain the internal force of the UHPC matrix according to the relevant parameters of the internal force of the UHPC matrix, where the relevant parameters of the internal force of the UHPC matrix include the concrete damage coefficient, the steel fiber crack bridging coefficient, the elastic modulus of UHPC, the ultimate tensile strain of UHPC, the width of the UHPC layer, and the thickness of the UHPC layer; Extract the ultimate tensile strength of the steel bar and the effective cross-sectional area of the corroded steel bar from the geometric and mechanical property reduction model of non-uniformly corroded steel bars; Obtain the internal force of the longitudinal bars in the UHPC layer according to the corrosion rate, the ultimate tensile strength of the steel bar, and the effective cross-sectional area of the corroded steel bar; Obtain the elastic modulus of the steel bar and the ultimate tensile strain of the steel bar from the steel constitutive model; Obtain the internal force of the longitudinal bars in the NC layer according to the elastic modulus of the steel bar, the ultimate tensile strain of the steel bar, and the total cross-sectional area of the longitudinal bars in the NC layer; Obtain the internal force of the upper flange of the steel beam 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; Obtain the internal force of the steel beam web above the neutral axis according to the relevant parameters of the internal force of the steel beam web above the neutral axis, where the relevant parameters of the internal force of the steel beam web above the neutral axis include the strain at the steel beam web above the neutral axis, the elastic modulus of the steel bar, the width of the steel beam web, the distance from the neutral axis of the composite beam to 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; Obtain the internal force of the lower flange of the steel beam 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; The internal force of the steel beam web below the neutral axis is obtained based on the relevant data of the internal force of the steel beam web below the neutral axis. The relevant data of the internal force of the steel beam web below the neutral axis include the strain at the steel beam web below the neutral axis, the elastic modulus of the steel beam, the width of the steel beam web, the total height of the composite beam, the distance from the neutral axis of the composite beam to the highest point of the composite beam, and the thickness of the lower flange of the steel beam. The remaining flexural capacity of the UHPC-reinforced steel-concrete composite beam after load-corrosion is obtained based on the relevant parameters of the remaining flexural capacity of the composite beam. The relevant parameters of the remaining flexural capacity of the composite beam include the moment-related parameters and the bearing capacity-related parameters.

4. The mechanical property analysis method for the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam according to claim 3, characterized in that: The strain data of the composite beam include the strain at each height of the composite beam section under the ultimate bearing state of the composite beam, the strain of the upper flange of the steel beam, the strain at the steel beam web above the neutral axis, the strain of the lower flange of the steel beam, and the strain at the steel beam web below the neutral axis. The size data of the UHPC layer include the width of the UHPC layer, the thickness of the UHPC layer, the total cross-sectional area of the longitudinal reinforcement in the UHPC layer, the distance from the centroid of the UHPC layer to the plastic neutral axis, and the distance from the centroid of the longitudinal reinforcement in the UHPC layer to the plastic neutral axis. The size data of the steel beam include the width of the steel beam web, the width of the upper flange of the steel beam, the thickness of the upper flange of the steel beam, the width of the lower flange of the steel beam, the thickness of the lower flange of the steel beam, the distance from the centroid of the upper flange of the steel beam to the plastic neutral axis of the composite beam, the distance from the centroid of the tension zone of the steel beam web to the plastic neutral axis of the composite beam, the distance from the centroid of the lower flange of the steel beam to the plastic neutral axis of the composite beam, and the distance from the centroid of the compression zone of the steel beam web to the plastic neutral axis of the composite beam. The size data of the NC layer include the total cross-sectional 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.

5. The mechanical property analysis method for the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam according to claim 3, characterized in that: The steps of obtaining the remaining flexural capacity of the UHPC-reinforced steel-concrete composite beam after load-corrosion according to the relevant parameters of the remaining flexural capacity of the composite beam include: Obtaining the moments of the tension and compression zones of the steel beam about the plastic neutral axis of the composite beam according to the moment-related parameters. The moment-related parameters include the internal force of the upper flange of the steel beam, the distance from the centroid of the upper flange of the steel beam to the plastic neutral axis of the composite beam, the internal force of the steel beam web above the neutral axis, the distance from the centroid of the tension zone of the steel beam web to the plastic neutral axis of the composite beam, the internal force of the lower flange of the steel beam, the distance from the centroid of the lower flange of the steel beam to the plastic neutral axis of the composite beam, the internal force of the steel beam web below the neutral axis, and the distance from the centroid of the compression zone of the steel beam web to the plastic neutral axis of the composite beam. Obtaining the remaining flexural capacity of the UHPC-reinforced steel-concrete composite beam after load-corrosion according to the bearing capacity-related parameters. The bearing capacity-related parameters include the moments of the tension and compression zones of the steel beam about the plastic neutral axis of the composite beam, the internal force of the UHPC matrix, the distance from the centroid of the UHPC layer to the plastic neutral axis, the internal force of the longitudinal reinforcement in the UHPC layer, the distance from the centroid of the longitudinal reinforcement in the UHPC layer to the plastic neutral axis, the internal force of the longitudinal reinforcement in the NC layer, and the distance from the centroid of the longitudinal reinforcement in the NC layer to the plastic neutral axis.

6. The mechanical property analysis method for the negative moment area of the UHPC thin layer reinforced steel-concrete composite beam according to claim 3, characterized in that: The method for obtaining the corrosion rate is as follows: Obtaining the initial mass of the steel bars; The ultimate load is obtained through the flexural test of the composite beam reference specimen. Based on the results of the flexural test of the composite beam reference specimen, pre-cracking treatment experiments for crack width control are carried out on four groups of steel-NC-UHPC composite beam specimens; Apply the ultimate load at the preloading ratio to the four groups of steel-NC-UHPC composite beam specimens; Perform a load-coupling experiment on the four groups of steel-NC-UHPC composite beam specimens after applying the ultimate load at the preloading ratio of the composite beam to obtain the composite beam after the load-coupling experiment. The composite beam after the load-coupling experiment is obtained by injecting a load-coupling experiment reagent into the solution pool, connecting the reserved energized wires and the stainless steel mesh of the four groups of steel-NC-UHPC composite beam specimens to the positive and negative poles of a DC power supply respectively, and performing constant current conduction at a preset current density; Perform a flexural test on the four groups of steel-NC-UHPC composite beam specimens after the load-coupling experiment to obtain the composite beam after the flexural test; Disassemble the four groups of steel-NC-UHPC composite beam specimens after the flexural test respectively to expose the internal steel bar skeletons, cut the longitudinal steel bars equidistantly using an angle grinder, and collect the interface shear steel bars at the same time; Group and number the obtained shear steel bars and stress-bearing longitudinal steel bars; Obtain the corrosion rate based on the initial steel bar mass and the mass of the corroded steel bar. The mass of the corroded steel bar is obtained by soaking the steel bar until the corrosion products dissolve, wiping off the attachments on the surface of the steel bar, then neutralizing the residual acid solution until the pH value of the steel bar surface is neutral, and drying and weighing the neutralized steel bar.

7. The mechanical property analysis method for the negative moment zone of the UHPC thin layer reinforced steel-concrete composite beam according to claim 6, characterized in that: The steps of the flexural test include: Conduct preloading for the flexural test. The preloading for the flexural test includes adjusting the spacing of the upper supports on the distribution beam supporting the servo press, hoisting the specimen and the loading distribution beam, synchronously arranging strain gauges and displacement gauges and connecting them to the acquisition tool, loading in the force control mode to a preset force value, maintaining the load level to eliminate the contact gap, and verifying the data stability of the strain gauges and displacement sensors; When the load is less than the preset ratio of the ultimate load, use the force control mode. When the load exceeds the preset ratio of the ultimate load and does not reach the ultimate load of the finite element simulation, switch the mode to the displacement control mode. When the load exceeds the ultimate load, reduce the load to the preset ratio of the ultimate load of the finite element simulation and stop loading; After stopping loading, unload the load to 0 in the force control mode and save the experimental data.

8. The mechanical property analysis method for the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam according to claim 6, characterized in that: The steps of carrying out pre-cracking treatment experiments for crack width control on the four groups of steel-NC-UHPC composite beam specimens based on the results of the flexural test of the composite beam reference specimen include: Implement hierarchical loading according to the target residual crack width to obtain the key results of the pre-cracking treatment of the composite beam specimens; The key results of the pre-cracking treatment of the composite beam specimens include Pcr, crack width, pre-cracking load, residual deflection, and Ks. Among them, Pcr represents the initial cracking 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 reaching the target value of the controlled crack width, the residual deflection refers to the residual deflection at the mid-span of each specimen after unloading, and Ks refers to the elastic flexural stiffness of each specimen.

9. The mechanical property analysis method for the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam according to claim 1, characterized in that: The long-term flexural calculation model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action is the product of the correction coefficient and the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action; The correction coefficient is obtained by non-linearly fitting the corrosion rate using the flexural test results of four groups of steel-NC-UHPC composite beam specimens.

10. Mechanical property analysis system for negative moment area of UHPC thin layer reinforced steel-concrete composite beam, characterized in that: The system is used to execute the mechanical property analysis method for the negative moment area of the UHPC thin-layer reinforced steel-concrete composite beam described in any one of claims 1-9. The system specifically includes: a steel analysis module, a UHPC analysis module, a bearing capacity analysis module, a composite beam verification module, and a mechanical property analysis database; Among them, the steel analysis module is used to obtain the geometric and mechanical property reduction model of non-uniformly corroded steel bars according to the steel constitutive model and the mechanical property test data of corroded steel bars. The steel includes steel bars and steel beams; The UHPC analysis module is used to obtain the concrete damage coefficient by comparing the ultimate loads of unloaded and pre-loaded ratios under the same chloride salt corrosion damage degree according to the UHPC constitutive model; The bearing capacity analysis module is used to obtain the remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action according to the concrete damage coefficient, the geometric and mechanical property reduction model of 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 remaining flexural bearing capacity model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action to obtain the long-term flexural calculation model of the UHPC-reinforced steel-concrete composite beam after load-corrosion action.

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