This master thesis was written in the course of a research project to evaluate the reliability of reinforced concrete structures, both through experiments and calculation. The main part of the present thesis deals with a case study about Neumarktbrücke, a prestressed three span overpass over the Brenner highway in South Tyrol. Due to the high chloride feed parts of the structure had been heavily damaged through corrosion and as a consequence the bridge was demolished in 2008. Thereby data were collected for a follow-up performance assessment. The present case study evaluates the performance of a bridge structure which suffers from corrosion of the existing pre-stressing strands. It also investigates the effects of this degradation on the bending and the tensions within the bridge structure. The impact of this progressive corrosion of the pre-stressing steel on the reaction of the bridge was simulated with the help of nonlinear finite elements methods. Subsequently, the results of the models in various states of corrosion were compared. This reliability evaluation of existing bridge structures serves to estimate the current safety level and the life cycle performance and is meant to optimize maintenance intervals and to provide support in the decision to repair or to replace the structure. After an introduction into the topic the basics of reliability based performance methods, the development of performance indicators for system safety and the current practice are pointed out. In a further step nonlinear calculation method, the basic forms of non-linearity, the discretisation of static systems and the elastic load capacity behaviour of structures are illustrated. These theoretical basics serve to highlight processes of modern finite element methods running in the background of the calculations.