Reliability-based Durability Design And Quality Control Of Reinforced Concrete Structures In Marine Environment

Surface deterioration due to chloride ingress is one of the major challenges in design and construction of reinforced concrete(RC)structures in marine environment.How to conduct the durability design and performance control of major marine concrete structures is one of the main issues that both designing and construction parts need to deal with.The reliability-based and quantitative design approach is a scientific mean to solve the problem and had been implemented in the durability design of the Hong KongZhuhai-Macao Sea-link Project.The approach was firstly mentioned in the amendment of Code for Durability Design of Concrete Structures(GB/T 50476-2019)in 2019.However,it needs to be supplemented and improved in several aspects,including considering only the limit state of depassivation of steel reinforcements,ignoring the spatial variability of durability parameters and lacking the corresponding theory of conformity control for productions.The dissertation aims at developing a durability design framework for marine concrete structures under chloride attack,and proposing the corresponding conformity control method for durability parameters,on the basis of the existing reliability-based durability quantitative design approach.The main works are as follows:1.The existing findings in prediction and calculation of concrete structures' surface deteriorations were summarized.To characterize the spatial variability of durability parameters,the random field theory as well as its discretization and constructing method were induced.The “batch effect” in members' production was considered.The 2-dimensional random simulation approach for surface deterioration of RC members under chloride-attack in marine environment was established based on Monte Carlo Simulation method.2.Statistic analysis of in-situ data for durability parameters of an immersed tube tunnel in an offshore construction project in south China was performed.The “batch effect”proposed by this dissertation was proved,and the statistic characteristics of durability parameters were calculated.2-dimensional simulation for surface deterioration of immersed tube tunnel in this project was conducted,and durability performance of the project was examined.It's found that obvious surface deterioration will not occur during the design service life of 120 years,and the actual durability performance is much better than the design expectation.3.The basic framework of durability design approach on member level was established,by performing the surface deterioration simulation and then the iterative optimization of the scheme,on the basis of the existing durability quantitative design approach.Three critical deterioration states for structural maintenance during service life were proposed.The durability performances including deterioration risks,maintenance demands,etc.were compared under various durability design levels,combinations of durability parameters and maintenance plans.4.The conformity control scheme for chloride diffusion coefficient of the offshore construction project in south China was reviewed,amended,and improved.The general method for designing a conformity control scheme for chloride diffusion coefficients in similar engineering projects was developed.By mean of Monte Carlo Simulation method,it was found that the conformity control scheme will improve the durability performance of the production lots with different efficiency,depending on the construction qualities of the lots.The bivariate conformity control scheme for chloride diffusion coefficient was established to consider the actual concrete cover depths.