Research On The Reliability And Optimization Of Inspection And Maintenance Cost During The Service Life Of Subway Station Main Structure

In recent years,China's urban rail transit has developed rapidly.At of the end of 2017,the operation and construction mileage of domestic urban rail transit both exceeded 5,000 kilometers.As an important part of urban rail transit projects,metro stations generally adopt reinforced concrete structures,the design and service period of which are 100 years.At present,most of the subway lines in China has been put into service for less than 20 years.Due to the durability degradation problem as concrete strucuture ages,there is a possibility that the maintenance and repair work of the metro station structure in China will become increasingly pronounced in the future.Therefore,to accurately assess the service status of reinforced concrete structures of subway stations,and to ensure structural safety,a reasonable inspection and maintenance program is formulated to minimize costs and expenditures.This will provide important support for the long-term operation of subway lines and is of great practical significance and application value.Based on the theory of structural reliability,this paper takes the subway underground station as the research object,analyzing the reliability development law of the station main structure under the effect of durability degradation.The relationship between inspection and maintenance is also derived in a probabilistic way to establish the cost model of the subway station structure in service life,based on which the optimal detection period of subway stations and maintenance programs are determined under the aim of minimum cost.The main work of this article is as follows:(1)Taking an underground subway station in the Beijing Subway as an example,a finite element model of the main structure was constructed using the RFEM software,the distributions of internal forces in the floor,side walls,beams and columns were analyzed to simulate the time-dependent load distribution during the subway construction period.The maximum internal forces of the standard cross-section in beam and column structure of the station under different load conditions are obtained;Monte Carlo method was adopted to design an algorithm program to obtain the initial reliability index and failure probability of the major components:the reliability index of the lower structure column is 4.265,which is the lowest of all components,with failure probability to be 9.985×10-6;(2)Three factors that affect the durability of the subway station structure were selected i.e.carbonization,corrosion of steel bars,and stray current,the influencing mechanism of which on the durability of the structure was illustrated,and the function of the bearing capacity of the beam and column structure over time and the reliability of the beam structure was obtained.It is derived from the curve of degradation index of the reliability index that,during the service period of the subway station,only the beam structure needs to be repaired and reinforced;(3)By the event tree theory,the cost model for the service life of the subway station beam structure is established considering the possibility of post-detection maintenance,the durability degradation of the structure,the improvement in maintenance reliability of the structure and the time value of money,and the cost of each part is calculated based on the actual project.The cost-optimized detection scheme is obtained by adjusting the inspection scheme as follows:The testing was carried out at 45,60,75 and 90 years when the beam structure was commissioned.Under this condition,the estimated cost of testing and maintenance was 975,000 yuan,which was 69.2%lower than the original 5-year cycle testing program.On the premise of satisfying safety requirements,the optimal maintainence scheme is to apply CFRP plate to beams with different width at the 55,45,60 years.In an ideal state,the maintenance cost can be reduced to 248,800 yuan,93%lower than the standard maintenance plan.