Integrated Methodology for Fatigue Life Prediction of Existing Metallic Railway Bridges

Resumo

In general, bridges are large structures modelled at the global scale in order to avoid computational
limitations. The fatigue assessment of these structures using such a type of modelling is not possible based on local
mechanical quantities due to the inherent difference between the size of bridges and the local nature of fatigue
phenomena. Currently, the most important standards propose S-N relations for nominal stresses to overcome this
multiscale problem, requiring an inherent approximation between the local characteristics of the investigated detail
and those at the basis of a relatable S-N curve, which may be particularly conservative for complex connections
of bridges in service with ancient construction technologies. Aiming to reduce unnecessary safety margins, local
fatigue approaches based on submodeling techniques leveraged by modal superposition principles are proposed to
implement local methods using fatigue quantities evaluated considering the real response of the mechanism of
loading transference. A complementary relation can then be established between the global conservative normative
approaches, applied to identify the fatigue-critical details, and such local fatigue approaches, defined as advanced
calculations stages. Therefore, an integrated methodology for fatigue life prediction of existing metallic railway
bridges is proposed, suggesting different phases of analyses at multiple scales. A real case study is investigated to
demonstrate the added value of this multiphase calculation strategy.