Analysis For Durability And Residual Service Life Of Prestressed Concrete Bridge Structure

Because of good performance characteristics and superior spanning capacity, modern prestressed concrete bridge structure are being used at a large-scale in the highway and railway construction areas. Under the influence of natural factors such as climate, environment, the material in prestressed concrete deteriorated gradually. And the structure damage caused by increasing overloading make its mechanical properties has constantly attenuated. High stress state of the high strength prestressed steel aggravates the risk of brittle fracture after stress corrosion. Therefore, through the study for the durability and service life prediction of the prestressed bridge, the PC (prestressed concrete)bridge reliability in the real corrosion environment can be known, the laws of time-dependent reliability can be disclosed. It can present theoretical basis and practice reference for the safty use and durability design, evaluation of the PC bridges.Considering the characteristics of using environment, mechanics properties and the structure features, some efforts have been made for the durability analysis and life prediction of PC bridge structure based on reliability. The major contents are presents as follows:1. After comparative study of the common time-dependent reliability methods such as the time comprehensive method, time discrete method and first excursion probability method,it presents the first excursion probability method basing on the time discrete to analysis the time-dependent structure reliability.and a clear solution approach for it is also be given.2. Presents the concept of the prestressed concrete covering layer system,then taking into consideration of the effect of stress level in concrete diffusion process, the carbonization reaction and diffusion process in the complete carbonated zone and the half-carbonated one under multi factor is analyzed. The carbonization loss-blunt length solving equation is presented frist, and the durability limit state equation for prestressed concrete structures under carbonization condition is proposed, which can determine the depth of the covering layer system for prestressed concrete structures. Then the paper proposes a method for determining covering layer system depth, and the depth of the covering layer system in some representative cities is given. Furthermore considering the effect of stress level in concrete and the non-prestressed reinforcement, it also presents a chloride ingress corrosion model. The durability limit state equation for prestressed concrete structures is established, which can determine the depth of the covering layer system for prestressed concrete structures. The paper then proposes a method for determining covering layer system depth, and the depth of the covering layer system for some representative coastal city in the chloride corrosion environment is even be given.3. basing on the problem about loss-blunt of the prestressed steel and the corrosion crack caused by steel rust of the common non-prestressed reinforcement structure, it studies the time of the loss-blunt of the prestressed steel and the corrosion crack of non-prestressed steel in the main two kinds of the corrosion environment (carbonization and the chloride ingress) by the method of the durability service life analysis. Therefore the durable life of the prestressed steel and the corrosion cracking span-life of common steel are established and the variation law of the two kinds of service life are obtained, which effected by the corrosion environment, time and position. In the carbonization circumstances, the durable life of the prestressed steel is less than the corrosion cracking span-life of common steel in the north of China, and the law will be in a reversal of phenomenon in the south of China. In the chloride ingress environment, chlorine ion ingressed rapidly, and the both kind of service life is less than common. The corrosion cracking span-life of common steel is less than the service life of prestressed steel, and its durability appearance check assessment can be used as a durability assessment for PC bridge.4. Using the method of the extreme state design as the durability design of the PC bridge, the durability limit state and service life standards of the PC bridge structure are divided into three categories, the PC bridge beginning rust extreme state of prestressed steel, the PC bridge corrosion cracking limit states of common steel and the load cracking limit states of the PC bridge. Then the three life criterions correspond to the limit states are proposed. Therefore the extreme state equation expression is deduced and the target reliable index values for the three durability of limit state are suggested.5. After studying the huge geographical differences of the PC bridge disease, it presents the environment zonation of the depth of the covering layer system as the key content of durability environment division. After sensitivity analysis of the effect factors in the environment sensitive factors in different environment is suggested as the index of the environment zonation. Basing on the environment sensitive factors analysis in the carbonization and the chloride ingress environment, the the division regions for the PC bridge covering layer system depth of the different region in China is proposed.6. After analysis about the variation rule of PC bridge load and time-dependent resistance, the durability service reference period and the assessment reference period of the PC bridge is proposed. The variation rules of the load in different reference period are studied, which are the general run load state and Intensive run load state of the the present standard load in the bridge code and the fitting load state on the basis of statistical analysis load test data on site.The resistance attenuation pattern of the PC bridge cracking extreme state in different environment is analysed and the time-dependent durability for the service life of PC bridge basing on the the load cracking limit states are finally proposed. Through analysis for a30m standard T beam of PC bridge, the variation rule of service life in different environment obtained, and the results show that the overload and the corrsiong condition is the real reason of the bridge durability accident of the rapidly decreased service life. Therefore the computing method of the bridge durability service life is proved to be effective...