Within the study described here, a riveted plate girder bridge was considered. The structure was erected in the early 1930s. Even though the structure is generally in a good condition, few local cracks were identified by visual inspections. One of these cracks is located in a gusset plate. This observation was the starting point for further investigations which are described in this contribution.

First a finite element model of the superstructure was created. To verify that the model represents the global structural behaviour of the bridge with sufficient accuracy an experimental modal analysis was performed. Based on the measured data several natural frequencies and mode shapes were identified.

In the next step the expected remaining lifetime of the main structural elements was estimated based on a standard approach. The results propose a remaining lifetime of several decades. From numerical simulations of a train passage the cracked gusset plate was identified as a hot spot with the highest stress concentrations in the structure. This was the reason for further investigations that concentrate on this structural detail. An assessment of this critical structural detail according to a standard method gave the result that the nominal lifetime of this local structural element has already expired.

Further investigations include a structural health monitoring system that controls both the actual loads by passing trains and the resulting strains in the considered gusset plate. Based on the monitored loads the assumptions for the calculations can be improved. Furthermore the calculated stresses can be validated by comparison with measured data. The two latter questions are subject of ongoing research.

Additionally to standard fatigue analyses laboratory fatigue tests of the specific detail are performed. These tests are still in progress. It is expected that the existing knowledge about the fatigue behaviour of respective details, for which it is difficult to select an appropriate notch case from codes, can be improved by fatigue tests.

1

EN1993-1-9, "Eurocode 3: Design of Steel Structures, Part 1-9: Fatigue", CEN: Brussels, Belgium, 2004.

2

Richtlinie 805, "Tragsicherheit bestehender Bauwerke", Deutschen Bahn AG, Germany, 2002.

3

SIA 269, "Grundlagen der Erhaltung von Tragwerken", Swiss Society of Engineers and Architects, 2011.

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