| System reliability can be used as an important tool for an efficient evaluation of existing bridge structures. The traditional element-based approach to bridge design and evaluation does not allow for consideration of interaction between the components that form a structural system and, therefore, it can be conservative. Safety of the structural system also depends on the degree of redundancy (load sharing) and ductility. As a result, it has been observed that the load carrying capacity of the whole structure can be much larger than what is determined by the design of individual components. Therefore, this dissertation is focused on the analysis of behavior of a bridge structure treated as a system. The objective is to develop system reliability models for evaluation of steel girder bridges subjected to aging (corrosion). To do so, the load and resistance parameters are identified and a system reliability analysis procedure for the whole bridge as a structural system is developed. The limit state functions are formulated based on the available models. Special models are considered for partially deteriorated structures and components. The basic load combination considered in this study includes dead load, live load and dynamic load. The three limit states identified are defined as member failure, which is a check of individual member safety using elastic and member capacity as defined in current specifications, ultimate limit state, which is defined as the ultimate capacity of the bridge system or the formation of a collapse mechanism, and functionality limit state, which is defined as the capacity of the structure to resist a live load displacement in a main longitudinal member equal to 0.75% of span length. The analysis is performed for different values of span length, truck position, number of vehicles on the bridge, girder spacings, and stiffness of structural members. For each combination of these parameters, the bridge resistance is determined in terms of the gross vehicle weight (GVW) of two side-by-side trucks. The reliabilities are also calculated for individual components (girders) and compared to system reliabilities of the bridge. The resulting system reliability can serve as a basis for the development of a rational bridge design and evaluation procedure. |
