Study On Performance Degaration And Remaining Useful Life Prediction For R.C. Bridge Near Coastal Areas

Steel bars of coastal highway bridge are easy to be corroded due to chloride ion erosion and many other environmental factors, which will lead to the degradation of structure performance and even structural collapse. Because of those problems, a lot of money needs to be paid to repair, reinforce or to rebuild the bridges, which will cause large economic losses and bad social impact.This paper is supported by National Science Foundation of "Analysis theory and test study on time-variant bearing capacity of in-service concrete box-girder bridge", and the project of "Taizhou coastal concrete bridge degradation and disaster mechanism research".In order to predict the durability life, carrying capacity and remaining service life of the existing concrete bridges, and to suggest the best bridge maintenance strategies, the research on degradation mechanism of coastal concrete bridge service performance was conducted by using Life-cycle Theory. Specific studies are as follows:1. The models for predicting the remaining service life of concrete structures were summarized, and their study scope and deficiencies were pointed out from the aspects of durability, reliability and life-cycle concept. Disease positions of340concrete bridges in Taizhou were statistical analyzed. For the purpose of assessing the safety of bridges, the durability and reliability of substructures were mainly focused on.2. Considering the characteristics of concrete carbonation, chloride diffusion and steel corrosion of coastal concrete bridges in Taizhou, the parameter of water-cement ratio was introduced into the calculation model for carbonation depth. The dynamic reliability of concrete carbonation and steel rust expansion was calculated and discussed from the component level. Finally, the durability life of an existing bridge was predicted using the modified model.3. A modified chloride diffusion model was proposed by considering two factors of load impact and chloride iron combining capacity. Compared to traditional chloride iron diffusion model, the modified model could be more reasonable and close to the reality of existing concrete bridges. Also, based on the factors of load impact and chloride iron combining capacity, a corrosion model of steel bar was further put forward, which could provide theoretical basis for predicting the remaining life of concrete bridges4. Time-varying reliability and failure probability of the background project were calculated by using the above chloride iron diffusion model and reinforcement corrosion model, in which only the effect of reinforcement corrosion on the structural resistance was considered. The remaining useful life was also predicted.5. Based on the life distribution function in reliability assessment of system components, the system security and maintenance strategies of coastal highway bridges were analyzed. The beast maintenance strategy steps were given by the life-cycle function, which was also verified by practical engineering.6. The deterioration of highway bridges in coastal areas is characterized by the degradation of reliability index and state index. A deteriorated model of reliability index and state index was established. The effect of loads and environment was considered in the proposed model. At the same time, a life-cycle maintenance strategy optimization model was also developed, and the genetic algorithm (GA) was used as solution method. Finally, the life-cycle economic benefits and optimal maintenance strategy of a practical bridge were evaluated as an example.