Research And Analysis On Durability And Numerical Test Of Modern Prestressed Structure

Modern prestressed concrete structures are popularly appliedto civil engineering, hydraulic engineering and communication engineering, due to their good behaviors. Like other structures, prestressed concrete structures may occur durability failure under long-term action of aggressive environments. However, up to now there are not many researches on their durability and the durability design method all over the world, and fewer studies on numerical test with the help of computers. So, under the supports of National Science Foundation of China and Jiangsu Province, a series of researches on the durability and numerical test of prestressed concrete have been done in this paper.First of all, the durability failure characteristics of prestressed concretes are analyzed. A general curvey of studies on durability of concrete structures at home and abroad are introduced. The importance on durability research of prestressed concretes is explained. The relevant conceptions and regulations about durability of concrete strucutre are showed. And finally the main researches in this paper are outlined.In the atmosphere environment, carbonation of concrete is the primary factor to cause steel bars to lose passivation and to begin corrosion. With the latest research achievements, a predicting model on carbonation depth considering the effect of stress level in concrete is built on the basis of our done experiment results, and this model is suitable to prictical projects. Based on the characteristics of durability failure of prestressed concrete structures, the attribute to durability limit state in the carbonation environment is put forward. And with the help of structural reliability theory, some reliability analysises and life prediction of prestressed structure are done. At same time, some simulation experiments on concrete carbonation depths in stress states are made with the help of artificial neural network, considering its complexity of carbonation process. Then three network models of BP, RBF and GRNN are built and their numerical experiments including train, simulation and prediction are done in the neural network toolbox of MATLAB. And the results show that neural network is an effective method in analyzing and predicting carbonation depth.To the prestressed concrete structures that are in marine or de-icing environments, chloride ion attack is the main reason to initiate corrosion of steel bars. With the latest research achievements, a predicting model on chloride ion transportation considering the effect of stress level in concrete is built on the basis of our done frog aggressive experiment results. Based on the characteristics of stress corrosion cracking of prestressing steel in prestressed structures, the attribute to durability limit state in the chloride attack environment is put forward. And with the help of structural reliability theory, some reliability analysises and life prediction of prestressed structure are done. On the other hand, the program of Diffusion in FEMLAB software is adopted to simulate the diffusion processes of chloride ion in concrete, which can consider below two factors that surface chloride concentration of element and chloride diffusion velocity aren't constants and will change with time. And this way will be a new method to predict the concentration distribution of chloride in concrete.The ultimate purpose to research the durability of prestressed structure is to durability design of new prestressed structures and to durability evaluation of service prestressed structures. With the new achievements on durability, the main contents about durability design of prestressed structures are outlined in this paper on the basis of knowing the surrounding action grade and design service life of structure or structural element. And a method of durability design of prestressed structures, which depends on structural durability performance and reliability theory, is given. Our method is similar to the current method of bearing capacity design and adopts subentry coefficients (or safty coefficients) to reflect reliability index. At last, some measures to improve durability of prestressed structure or structural elements and the main ways to meliorate structural whole durability are introduced.