Fatigue cracks in railway bridge hangers due to wind induced vibrations – Failure analysis, measures and remaining service life estimation

• Unexpected vibrations of bridge hangers were identified to be wind-induced.
• The unexpected vibrations reduced fatigue life of hangers significantly.
• One of the hangers suffered a long fatigue crack through 80% of the cross section.
• For restoration the surface of the hangers was grinded.
• The hanger butt welds were tested by NDE and exchanged if indications exceed a threshold value.

Unexpected wind-induced vibrations of the hangers have caused an early fatigue crack on specific steel components and joints of a railway bridge over the Elbe River at Lutherstadt Wittenberg, Germany. During regular periodic inspection a fatigue crack of approximately 240 mm length was found near a butt weld of the longest hanger. The hanger was immediately secured by welded butt straps across the crack. Based on experimental investigations of hanger vibrations additional bracings were added between the hangers to avoid wind-induced vibrations. The weld heat influence zone which was affected by high cyclic stresses was replaced by new material.Nevertheless it was impossible to determine sufficient remaining service life for those remaining bridge components that were exposed to extreme high real load cycles. The grinding of the affected steel surfaces was the key element of the remedial actions. Furthermore, additional fracture mechanic calculations were carried out in order to assess the remaining service life of the welded joints. In this respect, the calculation approach used by Deutsche Bahn AG was compared to further procedures from the mechanical engineering field. These investigations showed that the studied, repaired components have both, bearing and fatigue capacities within the validity of standards.