Study On The Method Of Service Life And Sensitivity Analysis For Concrete Structure In Chloride Environment

The main reason for the destruction of concrete structures in chloride environment is due to corrosion of chloride ions penetration caused by diffusion,diffusion model of chloride ions in concrete of chloride ion is the key to analyze and predict the durability of marine concrete structure and service life.The actual structure is affected by the environment of chloride.The concrete structure often suffers from durability failure such as steel bar corrosion and concrete cracking when it is far less than the design life.The reason is due to the randomness of structural geometry,material properties and environmental conditions,which exacerbates the complexity of durability analysis and design of concrete structures.So,through the establishment of this format is more simple,with stochastic boundary element method to promote the full time domain initial higher computational efficiency,considering the thickness of concrete protective structure,boundary conditions and characteristics of random factors of concrete material properties,reliability analysis of concrete under chloride environment service life.In order to analyze the influence of the random parameters on the reliability,the reliability sensitivity coefficient based on the total differential is established.Furthermore,the service life sensitivity coefficient of concrete structures is established,and the direct quantitative relationship is established for the first time with the sensitivity of the random parameters to the service life.The main research work and conclusions in this paper are as follows:(1)A full-time initial value propulsion boundary element method for chloride ion diffusion analysis in concrete has been established.Compared with the time-phased stepwise advancing boundary element method,the full-time initial value advancing boundary element method can eliminate the integral term in the chloride ion diffusion domain.Avoiding the intra-domain dispersion not only simplifies the calculation format,but also improves the stability of the iterative process and the accuracy of the calculation results,reducing the time-consuming calculation.(2)Considering the randomness of the parameters,the durability of the concrete structure under chloride erosion is analyzed by the stochastic boundary element method.Considering the spatial variability of parameters,a nonlinear stochastic boundary element method is established to overcome the computational error caused by the "ignoring and then introducing" random parameters in the traditional stochastic boundary element method.(3)Based on the reliability index definition of the first reliability method,the analytical expressions of service life of concrete structures under chloride erosion are deduced.Based on the principle of simplifying the calculation points,a practical calculation expression for service life of concrete structures is obtained.(4)Based on the full differential,the sensitivity coefficient to the parameter mean and variability is established.The sensitivity coefficient reflects the influence of the relative change of the mean and standard deviation of the random variable on the relative change of the reliability index,and has a clear physical meaning.And it is a dimensionless parameter,which overcomes the incompatibility of the sensitivity coefficient of each parameter caused by the inconsistent dimension of the traditional sensitivity coefficient.(5)The sensitivity coefficient of service life to parameter mean and variability was established,and the direct connection between service life and parameter sensitivity was established for the first time.This sensitivity coefficient also overcomes the defect that the traditional sensitivity coefficient cannot compare the sensitivity of the deterministic parameter and the random parameter sensitivity.(6)The proportional relationship between reliability and random parameters is established based on the linear limit state equation.The proportional relationship can directly calculate the influence of the variation of the mean or variability of multiple random variables on the reliability.