Probabilistic Prediction And Fuzzy Assessment On Durability Behavior Of Concrete Structures

In this thesis,an improved and more realistic approach for durability assessment of existing reinforced concrete(RC) structure has been developed on the base of probability statistic and fuzzy mathematics method on material,component and system layer from uncertain point of view.Based on Bayesian updating and spatial variation, path probability method(PPM) and hierarchy analysis model are developed for durability assessment of existing RC structure,taking into account those effect of carbonation,chloride ingression induced reinforcement corrosion and frost damage as the major reasons of degradation of concrete structure.The research contents for durability assessment are as follows:1.An empirical method is developed to determine input parameters of diffusion model, which related to altitude,season,material and service time in wet-dry cycling zone of harbor RC structures.Surface chloride level and apparent diffusion coefficient indicating chloride ingression state can be predicted according to weather information of sea area,and also the relationship between seriously damaged area and design tidal level is suggested for design reference,maintenance and power sampling of harbor concrete structure.2.A dynamic way for service life prediction is established using multi-environmental time similarity(METS) and Bayesian updating technique.Inspection of third reference structure and indoor accelerated test are performed to find the similarity relationship between natural and artificially simulated climate environment.Prior information is acquired and updated by field test with several samples to realize the behavior and life evaluation of RC structure.3.A path probability model(PPM) is proposed to predict the stochastic corrosion-crack and load capability degradation process of RC structures with time. The time-dependent probability distribution of reinforcement corrosion ratio,crack width and reduced load capability of RC concrete in carbonation,chloride penetration or coupling-effect environment can be calculated effectively by computer program.Therefore it enable the simulation of the whole process from harmful mediums erosion,corrosion initiation of reinforcement,corrosion induced concrete crack,corrosion and crack propagation to load capability reduction.The result has been proved reasonable in engineering assessment cases.4.Based on previous similarity experiments and engineering investigation,a multi-effect modified probabilistic model is present to be utilized in quantitative design of frost resistance and assessment of concrete structure in durability environmental zonation design point of view.5.An improved multiple-layer fuzzy assessment model is proposed to evaluate the durability condition of existing reinforced concrete bridges.Taking advantages of optimal interval based membership function,extended fuzzy operation and fuzzy weighted average technique,a multi-attributive decision making approach with eigenvector/weight is adopted to give a more realistic representation of components and bridge condition rating by corresponding computer program.Furthermore,the degraded durability behavior of substructure in future is predicted with the help of corrosion-crack path based PPM method.The present methodology will help decision makers and bridge engineers to arrive at a systematic judgment and methodical steps toward maintenance or repair.6.The spatial variation of model parameters is introduced as a supplement to current reliability analysis method in evaluating components or structures.The improved approach can produce not only the probability of failure but also the useful information as the proportion of surface area with initiation of rebar corrosion, cracking and spalling,etc.during the whole period of time that facilitates the repair or maintenance strategies for concrete structure from economical point of view.This research was supported by the project of National Natural Science Fund "Fundamental Research on Durability Design and Assessment of Concrete Structures in Chloride Erosive Environment"(50538070),863 program of National Hi-Tech Research Development "Durability Test Method and Assessment Technology of Important Coastal bridges"(2006AA04Z422),the West Traffic Construction Project of National Traffic Ministry "Study on Durability Index System,Test Methodology and Assessment Standard of Concrete Bridges"(200631822302-06),the science and technology project of Zhejiang Province "Key Anti-corrosion Techniques of Harbor and Costal Engineering and Development and Application of Supporting Facilities" (2006C13090),the agreement project of Chinese and Japanese(NSFC/JSPS) "Durability design theory of concrete structure based on Life-Cycle Cost Management Technique".Their support is gratefully acknowledged.