Time-dependent reliability models for steel girder bridges

This research is focused on evaluating the structural reliability of a bridge as a function of time. The objective of this study is to develop time varying reliability profiles relating component and system reliability index to various rates of deterioration.; Deterioration (corrosion) model for steel girder bridges is developed. Corrosion rate curves are developed to account for the behavior of actual bridge conditions for long time exposure to corrosion. Deterioration model for bridge system was developed by idealizing corrosion patterns. The system model provides a lower bound for evaluation of bridge system.; Reliability analysis is performed on representative bridges. Selected bridges include structures designed according to AASHTO LRFD (1994) and existing typical bridges. Reliability analysis is performed for bridge component (girder) and for bridge system. The reliability index is calculated as a function of time. Reliability profiles of bridge components for moment and shear limit states indicate that in general, corrosion affects shear more than moment. Also, shear buckling is the critical failure mode for steel girders at maximum life time of the bridge. The results indicate that there exists correlation between corrosion effect and initial web thickness at design. Results from evaluation of reliability on existing structures indicate that in general, bridges are over designed in comparison to the requirement by the current design code.; Reliability analysis of bridge system was performed on the selected bridges. Comparison of reliability index for component and for system indicates that in general, system reliability index is higher than component reliability index. By considering the whole bridge system rather than a girder, the system approach can take into account combination of different failure modes. The reliability profiles of bridge systems indicate that there is additional safety reserve available in the structure to what is determined by component analysis. Thus the system approach provides better information for reliability evaluation of structures.; Developed reliability profiles as functions of time (for component and system) are useful for planning long term planning and management of bridges. The developed procedure can serve as a basis for making optimum decision regarding repair, rehabilitation or replacement based on the whole life performance.