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

由于旧桥的大量存在以及交通荷载的增加，特别是公路桥梁的作用，对既有结构的评估变得更加重要。现有结构的特点是可以获得有关实际应力及其承载能力的附加信息。因此，结构测量(如果进行较长时间的监测)正越来越多地被用来以更现实的方式评估现有桥梁的状况。同时，利用结构测量或监测的可能性是多种多样的，并给出了安全实施的技术条件。然而，仍然需要澄清的是，在结构安全概念中应在多大程度上考虑通过结构测量和监测获得的额外信息。该研究方案旨在发展结构可靠性的基本原理，以便将关于实际应力的更详细的、基于测量的信息整合到既有桥梁评估的安全概念中。为此，将发展广义理论可靠性方法来评估使用极限状态函数的既有结构。此外，在对典型桥梁结构的这些决定性极限状态函数进行系统评估的基础上，将介绍推导基于量测的结构评估安全系数的一般方法。这涉及到记录极值的极限极限状态和记录载荷谱的疲劳极限状态。此外，还将开发一些方法来确定几种时间相关载荷的基于测量的安全系数。这些系统的研究将利用桥梁的例子来进行，因为首先，所发展的方法可以转移到一般结构工程的问题(通常是通过较少的工作量确定应力的方法)。其次，可以为解决当前桥梁现实评估的社会相关问题提供理论基础的直接贡献。

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.