Durability Assessment And Service Life Prediction Of Concrete Structure Under Fuzziness And Randomness

Concrete (RC/PC) structure is one of the most widely used structure types in civil engineering. Recently the durability failure of RC structure has become an important problem in the field of civil engineering. Durability deficiency of RC structures caused by chloride ions penetration happens widely and causes a huge loss. Durability assessment and service life prediction of structures under marine environment attach increasingly weight to engineers. This paper, which is supported by the National Natural Science Foundation (50878098), analyzed a hydro-structure; then assessed the durability and predicted the service life of the structure using fuzzy mathematics and stochastic simulation. The main contents and achievements are as follows:1. Durability of a hydro-structure in Lianyunguang wharf was studied. The service condition, durability situation and requirement of durability inspection of Lianyunguang wharf have been introduced; and the durability investigation results of the wharf and the major structures have been statistically analysed, including empty drum and bare bar, concrete strength, cover thickness, concrete carbonation depth, steel bar section corrosion loss and chlorine ion in concrete etc. The durability state of this wharf has been evaluated, and some maintenance concepts were proposed. These analyses have provided engineering reference data for the durability assessment and service-life prediction in the follow-up three chapters.2. Durability of a hydro-structure was assessed using fuzzy mathematics theory. The samples were analyses of clustering integrated application of dynamic equivalence relation clustering method and fuzzy c-means clustering method; and the durability of marine structures was assessed using fuzzy toolbox of MATLAB. The uncertain descriptions were established for each sample dynamically, and avoid the impact of subjective factors on the results of assessment. This is a reasonable reflection of the durability of the structure and the method is feasible. The results indicate that the new method avoids the unreasonable of durability assessment due to hard division, and more objective. This method which is based on soft division and fuzzy c-means clustering, can been done to number of samples and evaluation indicators. The membership of each sample belong to the clustering center were given. This method was easy programming and has some practical significance.3. The durability service life of concrete structures under chloride ion erosion was studied. According to the function of a seaport berth wharf and approach bridge, appearing the most acceptable appearance of injury in concrete surface was to be assessed as the durability limit state. The methodology for marine structures durability service life assessment use field investigation data was presented. Influencing factors of durability service life of concrete structure in marine environment were analyzed. Field investigation dates were used to calculate the durability parameters(chloride concentration of concrete surface, chloride concentration at steel-concrete interface, chloride diffusion coefficient). The durability service life assessment results show good agreement with that of field investigation. The concrete cover thickness, chloride concentration in concrete cover, strength of concrete, chloride concentration at steel-concrete interface, chloride concentration of concrete surface and critical chloride concentration are the key elements to the durability service life assessment.4. Durability assessment and service life prediction of concrete structure based on fuzzy reliability method and Monte Carlo principal was studied. Considering the uncertain factors of durability service life prediction and taking the influencing factors as random variable, the random distribution of every parameter was confirmed and probabilistic durability service life prediction model was established based on the structure durability parameters which were calculated from the on-site measured data. The awaiting assessment structural members were stochastic simulation based on Monte Carlo principal using CrystalBall software. The uncertainty predicting results which are based on random probability were got, and the predicted service life was established on basis of failure probability and reliability. This accords with the actual engineering, and has some practical value. The probability distribution, statistical distributed parameters and its sensitivity, relevance etc. of hypothetical parameters and predicting parameters which were produced by stochastic simulation have been analyzed. The influence of predicting results which were caused by the change of hypothetical parameters in service life prediction was got. The major influencing factor of durability service life is the concrete cover thickness, so the probability distribution of cover thickness is extremely important in durability assessment and service life prediction. The chloride concentration of concrete surface, critical chloride concentration, and chloride diffusion coefficient etc. which are characterizations of chloride concentration under marine environment are also very important factors in hydro-structure durability assessment and service life prediction.This paper has assessed the durability service life of concrete structure under chloride ion erosion environment systematically, practically, roundly and effectively. The influencing factors of durability have been analyzed. Scientific strengthening and maintenance tactics can be made by durability assessment and service life prediction of the existing marine structures; and the durability level and construction quality of planed building structures can be improved by analyzing influencing factors of durability life. Durability assessment and service life prediction of chloride erosion concrete structures can both service the existing structure and guide the durability design of planed building structures.