Optimization Of Maintenance Cost Of Corroded Reinforced Concrete Structures Based On Life-cycle Reliability

In recent years,with the vigorous development of marine resources,the demand for large-scale infrastructure facilities?bridges,tunnels,ports,etc.?has continuously increased,and the durability of reinforced concrete structures has become increasingly prominent.The durability problems of these reinforced concrete structures have seriously affected the safety and normal use of engineering projects;they have caused serious economic losses and bad social and environmental impacts to countries around the world.For newly-built basic project facilities,the status quo of structural deterioration is still very common,even in the design that emphasizes long-term service life.Thus,it can be seen that how to make a reasonable and effective maintenance decision in the operation period of the project to ensure that the structure meets the requirements of the safety and normal use of the structure has become one of the most active and frontier research fields at domestic and overseas.Combined with relevant existing researches and supported by the National Natural Science Found Project“life cycle performance and its design theory of concrete structure based on reinforced corrosion related durability?51378241?”,using the combination of experimental research and theoretical analysis,the study of the flexural performance degradation of RC beams under loading and chlorine salt erosion was performed.Based on the reliability probability theory,the durability and bearing capacity of the structure were evaluated and predicted.On this basis,the use of analytic hierarchy process and life-time cost method to make in-depth analysis of the decision-making of maintenance activities,and finally the bridge component as an example to analyze the relationship between the structural performance and life-cycle cost in the service process,and the full structural components Lifetime maintenance costs are optimized.The main contents of this paper are as follows:1.The durability deterioration process of corroded concrete members under chloride corrosion is studied.In this study,the flexural bearing behavior tests of six corroded RC beams?one standard beam and five prefabricated crack beams?in a chloride environment were conducted.an experiment of NaCl solution drying-wetting cycles and natural corrosion was carried out on pre-cracked concrete specimens for nearly 4years.Some steel samples with significant localized corrosion pits and whole corrosion were obtained.Based on study of the pit depth measurement,tensile test and finite element analysis,the geometric features and degradation mechanism of corroded steel bars were discussed and the practicability of the mathematical model was also verified.Following conclusions can be obtained:By fitting,the nominal yield strength,nominal ultimate strength and elongation ratio of corroded steel can be regarded as linearly decline when?_avg is less than 6.0%The relevant research achievements could provide some references to the performance evaluation of corroded reinforced concrete structures.The deflection of the test beam,the strain change of the concrete in the midspan,and the damage pattern were compared and analyzed.The test results show that the standard reinforced concrete beams subjected to bending damage belong to the ductile failure of the tendons,but the RC beam breaks into a certain degree of brittleness due to corrosion of the steel bars due to the alternating dry and wet chlorine salt and load coupling.At the same time,the feasibility of the calculation model for the flexural capacity of structural members established in this paper was verified by experiments.2.Taking the bridge component as an example,Monte Carlo sampling simulation is carried out by using MATLAB software,and life prediction model of structural members with reliability level is established.Based on the analysis of the existing research results and the related durability test results,the probabilistic life model and the time-varying reliability analysis method for the structural members to meet the requirements of different durability are established with the main parameters of the component loading state and the chlorine salt erosion environment.The service life of the bridge members under different life criteria is t₁=9.6a,t₂=18.8a and t₃=23.8a respectively.Similar to the general study rules.The simulation results show that the established reliability model can predict the service life of structural members,and it can provide certain suggestions for the assessment and design of concrete structural durability.3.Considering the uncertain factors of structural durability and safety,a comprehensive evaluation model that can reflect the durability and safety of real bridge conditions was established.This paper evaluates the real-time bridge structure status of the bridge structure as an example,and makes correct maintenance decisions for the structure;and compares the simulation results with the actual bridge conditions to verify the feasibility of the method.4.Optimization of life cycle maintenance cost of concrete structures.The life cycle cost of project structure is divided,and reliability based structural maintenance cost calculation model is established by using reliability theory.Taking bridge components as an example,by comparing the life cycle cost of different design schemes,the relationship between initial structural design performance and post maintenance is analyzed.The simulation results show that the service life of the structure can be predicted through the study of the structural reliability model.When the discount rate is not considered,the original design of the example is 12.42%less than the initial cost of the optimization.However,the original design is better than the optimization 66.7%higher maintenance costs,the original design of the total life cycle cost than the optimization program life cycle cost 46.6%.In addition,through the comprehensive evaluation of indicators such as structural service life,structural performance,and economic cost,the expected maintenance costs of concrete structures at different extreme levels of durability are estimated.