Assessment of the Safety Against Fatigue Failure of Riveted Railway Bridges Based on Fracture Mechanics

The fracture mechanics concept is becoming increasingly important in the assessment of the fatigue safety of historic railway bridges. Compared to the stress-life-concept, the main advantage is that only the current and future traffic loads must be considered. The crack model, fracture-mechanical material parameters and the size of suspected or actual fatigue cracks are other significant factors influencing the fracture-mechanical crack growth calculations. This paper focuses on the characterization of these input variables. Hot-driven rivets generate a clamping force due to shrinkage during cooling after manufacture. This has the effect of compression stress on the connected parts and has a positive influence on the fatigue behavior of the component. This article presents a crack model for determining the stress intensity factor of riveted components. The model can consider not only the component stress acting orthogonally to the crack plane but also the rivet clamping force acting orthogonally to the sheet metal plane. The material properties of steels from the first half of the 20th century differ significantly from those of modern structural steels. The results of the Paris-Parameters for crack growth on structural steel St 48 from 1925 are presented. The fracture mechanics assessment of cyclically loaded structures includes inspections as well as crack growth calculations. In riveted structures, fatigue cracks occur at the point of greatest notch stress, at the edge of the rivet hole. An inspection method has been developed for this area, hidden by the rivet head, which can be used to detect fatigue cracks at a very early stage. The influence of the three parameters mentioned – crack model, Paris-Parameter, and initial crack length – on the result of fracture mechanics crack growth calculations is presented using the example of the Elbe-Bridge in Meissen.