Time-Dependent Reliability Assessment And Life Prediction Of Continuous Concrete Girder Bridges

The reliability of existing reinforced concrete bridges is one of the world-wide concerned problems in the field of the structure engineering. The reliability assessment and the service life prediction for the existing reinforced concrete structures can reveal the potential risk and make rational decisions to repair or demolition; moreover, it can also be directly applied in structural design. Therefore, it is not only important in theory to study the reliability assessment methods for existing bridges, but it also has the wide prospects of application as well as great economic and social benefits. In this thesis, with respect to the basic characteristics of existing highway reinforced concrete bridges, some important topics of reliability assessment and life prediction of existing bridges are systematically and thoroughly studied. The major contents are summarized as follows:Firstly, considering the charactreristics of the resistance degradation with time of continuous concrete girder bridges, the resistance degradation model during different phases in service life is built up based on the existing durability testing results of concrete carbonization and rebar corrosion.Secondly, three computation methods of time-dependent reliability are studied in detail, which include time-integrated approach, time-discretized approach and first-passage probability approach. By analyzing two practical examples, the computational accuracy and shortcomings of the three methods are compared carefully.Thirdly, the time-dependent reliability for the safety based on ultimate limit state and the serviceability based on crack width and deflection limit states are analyzed. The time-dependent reliabilities both in safety and serviceability are assessed according to the target reliability index.Fourthly, the continuous concrete girder bridge is simplified as a series system. The system time-dependent reliability of the bridge is analyzed, and the influence of the dependence between components, the degradation functions as well as the initial resistance on the system failure probability is analyzed in detail. Lastly, on the basis of the time-dependent reliability theory, the prediction of safety service life, serviceability service life and durability service life are studied according to different life criterion. Taking a practical bridge as an example, the remained service life of capacity-carrying, crack width, deflection, carbonization and corrosion of the bridge are predicted.It is shown in this study that analyzing and assessing the safety, serviceability and durability of existing bridges by virtue of time-dependent reliability theory can help engineers forecast the condition and the remained service life of the bridges; moreover, it can also help the government departments develop the Bridge Management System (BMS) to monitor the health state of the bridges in real time.