PSI - Issue 22

Stéphane Sire et al. / Procedia Structural Integrity 22 (2019) 64–69 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction The French railway network includes over 30 000 km of railway tracks and more than 5000 metallic bridges. Since some of these bridges were built during the second half of the nineteenth century, they have been in service for over a century. Forty five percent of these structures are hot riveted bridges. Considering their service life, they need adapted measures for their maintenance. Indeed, due to the increase of rolling speed and axle load, fatigue is one of the main phenomena to take into account in order to extend the safe service life of metallic bridges. The fatigue pathologies are revealed by the deconsolidation of connections followed by cracks that can be observed during the structure surveillance. But since it is difficult to apprehend the exact fatigue damage by theoretical calculations, bridge residual service life estimation is inaccurate. Besides, fatigue problems are not specific to the French railway network, similar observations had been made by other research teams all over Europe, as shown by Al- Emrani (2002) for Sweden’s railway network, De Jesus et al. (2015) for Portuguese structures, Pipinato et al. (2009) in Italy and Helmerich (2012) in Germany. This phenomenon of fatigue, studied experimentally during the 19th century (mainly by Wöhler), made it possible to set up design regulations for metallic bridges that took into account variable loads. Indeed, these loads were mentioned for large spans bridges from the 1891 regulation in France. In addition, during the same period, materials and train capacities (loads and speed) have evolved. Advances in metallurgy and strength of materials have indeed led to the progressive replacement of wrought iron by steel in the construction of metal bridges. Directly placed under the rails, the stringers are the most sensitive structural elements to fatigue; they sustain indeed a much higher number of stress cycles than other elements. This paper aims to compare the mechanical strength of the stringers (beam calculation model) with an acceptable fatigue range resulting from an analysis of the fatigue curves, see references Afnor (2005), Taras and Greiner (2010), and SIA (2011). 2. Evolution of regulations in France In parallel with the development of the French rail network (Fig. 1), regulations in the construction of metal bridges have followed one another since the 1858 regulation to the current Eurocodes standards, see Gallegos Mayorga et al. (2017).

Fig. 1. Evolution of the French railway network and the construction regulations in France.

In order to standardize the calculations for the construction of metallic bridges and to relate their strength to the overloads that are expected to travel on the French railway network, a standard train has been adopted, see Ministère des travaux publics (1891). The successive regulations thereby take into account the evolution of axle loads and their spacing as shown in Fig. 2 with the composition of the standard trains as mentioned in the 1891, 1915 and 1927 regulations. For instance, the 1891 type train included two locomotives with tender (for charcoal) of 56 and 24