Open Access

Failure analysis plays an important role in engineering procedures to enhance railway safety. Five railway accidents in Germany and the practical work to investigate the root cause are presented. In all cases, fatigue fracture was the failure mechanism caused by material defects or unforeseen overload. In all cases improved inspection techniques could have prevented the accident.

Departure from Cologne, Central Station, Germany, due to fatigue failure of one of the driving axles. The train was emergency stopped immediately and, due to low travel speed at this point, no serious injuries occurred to passengers. Referring to public interest, the public attorney’s office solicited the German Federal Institute for Materials Research and Testing (BAM) for the analysis of the root cause. No deviations from specification were found in the geometries of the basic parts of the bogie or the wheelset assembly. Inspection of the axle fragments using standard acoustic non-destructive testing (NDT) techniques revealed no additional cracks and no indications of oversized discontinuities. Metallographic and chemical inspection of the axle material and its microstructure revealed all parameters to be acceptable except for an elevated impurity level. The fracture surfaces of the axle fragments were heavily damaged due to some continued travel after final breakage on the high speed line before Cologne Central Station. Extensive visual inspection of the remaining beachmarks was carried out to find the origin of the fatigue crack. The region of the crack origin was located near the axle surface but could not be analysed in detail due to secondary damage. Fatigue was identified as the mechanism of crack growth until final fracture, but the reasons for crack initiation initially remained unclear. Neither standard NDT techniques nor metallography according to the relevant axle specifications were able to identify inclusions in the material that could have served as crack initiation sites. However, discontinuities were detected near the crack origin in micro computer tomography and ultrasonic immersion testing. Subsequent metallographic sample preparation was targeted to specific areas based on the location coordinates of the flaws identified by these NDT techniques. These revealed non-metallic inclusions that were much larger than admissible for the relevant specifications. It is likely that the fatigue crack in the highly loaded axle volume initiated at those non-metallic inclusions.

In this paper, we use distributed fiber optic sensing (DFOS) for traffic load monitoring on a newly constructed bridge instrumented with a network of embedded optical fibers. Specifically, the optical fibers are embedded longitudinally in all bridge girders at two depths, forming a looped sensing configuration that enables the measurement of different stress states when a vehicle passes. The measurements presented here were conducted before the bridge was opened to traffic, using a mobile crane weighing approximately 36 metric tons, with the load distributed evenly across three axles. We show that our DFOS system can effectively capture the bridge structural response to the moving mobile crane and provide estimates of axle weight distribution and spacing. Finally, the results indicate that, although the fibers located in the girders beneath the loaded lane are strongly affected by the traffic, the fibers beneath the unloaded lane show only a negligible response, highlighting the ability to separate the effects of vehicles traveling in neighboring lanes.

Das Messfeld auf der A9 im Zusammenhang mit dem Projekt "SensoJointField" wird vorgestellt. Es erfolgt zunächst eine Einordnung in den angestrebten Paradigmenwechsel innerhalb des technischen Regelwerkes. Erste Messergebnisse infilge quasi-statischer saisonaler Fugenbewegungen sowie infolge verkehrsinduzierter Fugenbewegungen werden den Streckenbetreibern vorgestellt.

The events of September 11, 2024, will remain etched in the collective memory of Germany’s bridge engineering community. The sudden and unannounced partial collapse of a prestressed concrete bridge rightfully reverberated across society at large. The structure in question was the Carola Bridge in Dresden. This architecturally refined and exceptionally slender bridge is, with good reason, regarded by professionals as an icon of its time's structural engineering. Even by today’s standards, its design and construction would pose a considerable challenge. This paper presents the main findings from investigations undertaken to determine the cause of the collapse and attempts to reconstruct the failure process. Additionally, the acoustic monitoring system implemented to safeguard the remaining superstructures is also presented.