Development of Deterioration Models for Bridge Decks Using System Reliability Analysis

Generally, in the existing Bridge Management Systems(BMS) deterioration is modeled based on the visual inspections where the corresponding condition states are assigned to individual elements. In this case, the limited attention is given to the correlation between bridge elements from structural perspective. In this process, the impact of the history of deterioration on the reliability of a structure is disregarded which may lead to inappropriate conclusions. The Improved estimate of service life of a bridge deck may help decision makers enhance the intervention planning and optimize the bridge life cycle costs. A reliability-based deterioration model can potentially be an appropriate replacement for the existing procedures. The objective of this thesis is to evaluate the system reliability of conventional bridges designed based on the existing codes. According to the methodology developed in this thesis, the predicted element-level structural conditions for different time intervals are applied in the non-linear Finite Element model of a bridge superstructure and the system reliability indices are estimated for different time intervals. The resulting degradation curve could be calibrated and updated based on the outcomes of the visual inspections. Also, the reliability of innovative bridges that use non-conventional materials or structural forms such as Steel-Free Deck System has been evaluated by applying the newly developed method. The available deterioration models for conventional superstructuresare not applicable for the innovative bridge systems. Since there is no established deterioration model available for these innovative structures, it is difficult to predict the reliability of such bridges at different time intervals. The method developedhere adopts the reliability theory and establishes deterioration models for conventional and innovative bridges based on their failure mechanisms. This method has been applied in simply-supported traditional reinforced-concrete bridge superstructures designed according to the Canadian Highway Bridge Design Code (CHBDC-S6), and in an innovative structure with a Steel-Free Deck System, namely the Crowchild Bridge, in Calgary, Canada, as case studies. As an example to show the application of such developed deterioration curve, the developed model has been adopted in an old superstructure in Montreal. The results obtained from the newly developed model and bridge engineering groups’ estimations are found to be in accordance. Based on the reliability estimates, the conventional bridges designed based on the new code are found to be in a good condition during the initial stages of their service life,but their condition degrades faster once corrosion in steel reinforcements is initiated and spalling of concrete becomes evident. In case of the Steel-Free Deck, there is a low probability of failure at the end of the 75 years of its service life. It is found that the element-level assessment of a concrete deck is a conservative approach, since the interaction between the structural elements results in considerably higher reliability index and lower probability of failure. This thesis demonstrates how the proposed system reliability-based evaluation method can be adopted in determining the structural condition of a bridge which represents an important step forward in Bridge Management Systems. The system reliability deterioration model can be easily integrated to the existing Bridge Management Systems (BMS) by replacing the existing condition index by the reliability index or adding it to the assessing process as an additional parameter.