Accumulation of damage in the assessment of historic riveted steel bridges

• Applicant: Professor Dr.-Ing. Martin Mensinger
• Subject Area: Structural Engineering, Building Informatics and Construction Operation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 571853242

With the expansion of the railway network in the 19th century, a large number of steel railway bridges were constructed in Germany. Today, around 10,000 of these bridges are still in use, with about 5,000 dating back to before 1920. These older structures primarily use riveted joints and have now exceeded 100 years of service, approaching or surpassing their original design life. This raises a critical question for infrastructure safety: should these bridges be replaced, or can their operation be safely continued under certain restrictions? A central aspect in making this decision is the assessment of the remaining service life of these bridges. This has typically been calculated using the nominal stress approach combined with the theory of linear cumulative damage — a methodology long embedded in German and European standards and also called Palmgren-Miner rule. It assumes that fatigue damage accumulates linearly with each load cycle, independent of the sequence or interaction of loads. However, this simplification introduces significant variability in cumulative damage predictions, especially when stress amplitudes vary or fall near the endurance limit. Since riveted bridges often operate under such conditions, current estimates may not accurately reflect actual fatigue behavior. This research project aims to improve damage assessment methods by focusing on the fatigue performance of riveted joints, particularly under low stress amplitudes close to or below the endurance limit. It will quantify the impact of rivet-specific factors such as clamping force, bearing pressure, and hole geometry, and develop suitable S-N (stress-life) curves tailored to riveted joints. This effort addresses the limitations of existing, often overly conservative, design assumptions. To account for material and load variability, the project proposes using probabilistic S-N curves. These better reflect the inherent scatter in fatigue strength and the changing load spectra of rail traffic over the past century. For realistic modeling, fatigue tests and crack propagation analyses will be conducted using actual riveted joints. This approach allows for a more accurate evaluation of fatigue life before crack initiation and the progression of cracks in real bridge components. Comparative analysis with prior studies will help clarify the limitations of previous methodologies. Moreover, the project will use finite element methods (FEM) to simulate the complex stress conditions around rivet holes, including the effects of clamping, bearing, and friction forces. These simulations will contribute to a more precise understanding of stress distribution and fatigue behavior in riveted connections. Overall, this research is essential to ensure the safe, cost-effective management of aging railway infrastructure. By improving assessment accuracy, it helps avoid unnecessary bridge replacements while supporting the continued use of historically and economically valuable structures.

• DFG Programme: Research Grants