Method for assessing residual use and determination of safe operating time intervals of existing welded steel bridges

对于循环载荷下现有焊接钢构件的评估，迄今为止还没有基于断裂力学的概率验证验证概念。然而，这是必不可少的，以便能够对大量历史钢结构的剩余使用寿命和安全检查间隔做出可靠的说明。这是确保具有相应关键结构细节的结构的经济和安全操作的唯一方法。基于名义应力概念的现有验证通常不足以达到此目的。在桥梁的情况下，输入参数（如荷载历史或材料）中的各种不确定性会导致不准确的结果。此外，结构的当前状况不包括在验证中。因此，计划项目的目的是开发一种经过验证的方法，通过裂纹扩展模拟确定安全运行时间间隔和剩余使用寿命。在这种情况下，也要考虑结构的当前条件和输入参数的散射带。确定剩余使用寿命所需的安全水平与安全相关的操作时间间隔之间应加以区分。要开发的方法应该简单且易于应用，不需要耗时的裂纹扩展计算。它是基于断裂力学分析，其特点是概率安全验证概念。在项目范围内，它将作为铁路桥梁的典范。然而，它也适用于大量的其他疲劳加载钢结构。作为项目的一部分，应定义具有相关统计分布函数的适当输入参数。这些包括适当的初始裂纹尺寸和裂纹扩展方向，验证的材料参数和负载的影响，包括可能的残余应力。此外，相关的设计细节必须转换成理想化的断裂力学参考模型。在此基础上，将开发旧钢结构的一般概念。为此，计划进行断裂力学模拟，其结果随后可以通过回归分析和概率考虑转换为相应的安全检查间隔。为了验证这一概念，将进行蒙特卡罗模拟，并就安全水平和目标安全水平开展密集的科学工作。该研究项目的目的是开发一种基于断裂力学的可靠性理论验证概念，通过该概念可以安全地评估现有钢结构的进一步使用。

For the assessment of existing welded steel components under cyclic loading, no probabilistically validated verification concept based on fracture mechanics exists so far. However, this is essential in order to be able to make reliable statements on the remaining service life and safe inspection intervals for the large number of historic steel structures. This is the only way to ensure the economic and safe operation of structures with correspondingly critical structural details. The existing verification based on the nominal stress concept is usually not sufficient for this purpose. In the case of bridges, various uncertainties in the input parameters such as the load history or material lead to inaccurate results. In addition, the current condition of the structure is not included in the verification. Therefore, the aim of the planned project is to develop a validated method for the determination of safe operation time intervals and remaining service life by means of crack propagation simulations. In this context, the current condition of the structure and the scatter bands of the input parameters are also to be considered. A distinction is to be made between the required safety level for the determination of the remaining service life and the safety-relevant operating time intervals. The methodology to be developed should be simple and easy to apply without the need for time-consuming crack propagation calculations. It is based on fracture mechanical analyses and is characterized by a probabilistically secured verification concept. Within the scope of the project, it will be developed exemplarily for railroad bridges. However, it is also applicable to a large number of other fatigue-loaded steel structures. Appropriate input parameters with associated statistical distribution functions are to be defined as part of the project. These include appropriate initial crack sizes and crack propagation directions, validated material parameters and the influence of loading including possible residual stresses. In addition, relevant design details have to be transferred into idealized fracture mechanical reference models. On this basis, a general concept for older steel structures will be developed. For this purpose, fracture mechanical simulations are planned, the results of which can subsequently be transferred into correspondingly safe inspection intervals via regression analyses and probabilistic considerations. In order to validate the concept, Monte Carlo simulations will be conducted and intensive scientific work will be carried out on the safety levels and targeted level of safety. The aim of the research project is to develop a reliability-theoretical verification concept based on fracture mechanics, through which further use of existing steel structures can safely be assessed.