Methods for assessment existing structures based on measured stresses with a focus on analysis of load combinations, model uncertainties and expansion at the level of the load-bearing system

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Due to the large number of old bridges as well as the increase of traffic loads, especially by road bridges, the realistic assessment of existing structures becomes more important. Existing structures are characterized by the possibility of obtaining additional information about actual stresses and their load capacity. Therefore, structural measurements are (or monitoring if performed over a longer period) being used increasingly to assess the condition of existing bridges in a more realistic way. Meanwhile, the possibilities of using structural measurements or monitoring are versatile and the technical conditions for a safe implementation are given. However, it still has to be clarified, to which extent the additional information obtained by structural measurements and monitoring are to be taken into account within the structural safety concept. This research proposal aims to develop the fundamentals of structural reliability in order to integrate more detailed, measurement-based information about actual stresses into the safety concept of assessment of existing bridges. For this purpose, generalized theoretical reliability methods will be developed for assessing existing structures using limit state functions. Furthermore, based on systematical evaluation of these decisive limit state functions for typical bridge structures, generalized approaches to deriving the safety factors for measurement-based structural assessment will be introduced. This concerns ultimate limit state with recording extreme values as well as fatigue limit state with recording loading spectrums. Moreover methods will be developed to determine measurement-based safety factors for several time-dependent loads. These systematical investigations will be done using the example of bridges because firstly, the developed methods are transferrable to the problems of the general structural engineering (by means of stresses determined with less effort usually). Secondly, a direct contribution to the theoretical fundamentals can be given for solving the current and socially relevant problem of the realistic assessment of bridges.