Some Problems Of Life Cycle For Long-span Prestressed Concrete Box Girder Bridge

The prestressed concrete box girder bridges have been widely applied due to their advantages in applicability, safety, economy and so on. However, there are many flaws in this kind of bridge, such as web diagonal cracks and durability due to traditional design concept.The main research work can be summarized as follows:(1)The paper firstly introduces the theory and calculation model of the life cycle cost. Then the framework of the life cycle cost optimal design is put forward. Lastly, the princeples and main contents of life cycle design are defined on the basis of the comparison between life cycle design and traditional concept.(2)Based on life cycle cost analysis method, this paper proposes risk assessment system of web diagonal cracks. The time-dependent reliability model of web diagonal cracks based on conventional vertical prestressed system and low-retracting prestressed system is used to calculate the occurrence probability of web diagonal cracks. Parameter sensitivity analysis is adopted to attain the most impotant factor for web diagonal cracks which are due to vertical prestress loss. Meanwhile, low-retracting prestressed system studies vertify the effectiveness of the technique from views of reliability and life-cycle economics.(3)The domestic and external carbonation depth models are summarized in this paper. The carbonation depth prediction model is improved by considering the time-varying CO2 concentrations. The probability of initiation of reinforcement corrosion, the cracks in protective layer, too large width cracks in protective layer and structure failure under time-varying CO2 concentrations and different corrosion conditions are obtained through carbonation analysis of prestressed concrete beam bridge piers. Carbonation corrosion analysis under condition of different crack width, differernt measures and tmperature is examined respectively in this paper. The probability of reinforcement corrosion and structure failure is calculated through time-varying reliability analysis considering the effect of chloride ion corrosion. Three protective methods are presented in this paper. The optimal solution under conditions of carbonation corrosion and chloride ion corrosion is determined through the life cycle cost analysis.