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

对于在役焊接钢构件在循环载荷作用下的评估，目前还没有基于断裂力学的概率验证概念。然而，为了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声明，这是必不可少的。这是确保具有相应关键结构细节的结构的经济和安全运行的唯一途径。现有的基于名义应力概念的验证通常不足以满足这一目的。对于桥梁，输入参数中的各种不确定性，如荷载历史或材料，导致结果不准确。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有效的方法，通过裂纹扩展模拟来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状况和输入参数的散射带。应区分确定剩余使用寿命所需的安全级别和与安全相关的运行时间间隔。要开发的方法应该是简单和容易应用的，而不需要耗时的裂纹扩展计算。它以断裂力学分析为基础，并以概率安全验证概念为特征。在项目范围内，将示范开发用于铁路桥梁。但是，它也适用于大量其他疲劳荷载作用下的钢结构。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。这些因素包括合适的初始裂纹尺寸和裂纹扩展方向、经过验证的材料参数以及包括可能的残余应力在内的载荷的影响。此外，必须将相关的设计细节转换为理想的断裂力学参考模型。在此基础上，将提出较老钢结构的一般概念。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移到相应的安全检查间隔中。为了验证这一概念，将进行蒙特卡洛模拟，并对安全水平和目标安全水平进行密集的科学工作。该研究项目的目的是开发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.