Residual service life assessment in steel railway bridges using the updated FE model of an existing bridge.

Promoting railways as a sustainable, innovative, interconnected and safe means of transport, of both passengers and goods, and strengthening its contribution to the economy, industry and trade are some of the priorities which have involved the whole world in the last decades. Nowadays, on Norwegian soil, approximately 50 to 90 per cent of the goods are transported on rails over the entire territory. Because of increasing service loads and train speeds, rail authorities are therefore paying attention to predict and possibly extend the remaining service life of railway infrastructures.???? Accordingly, the aim of this study is to estimate the condition of an existing historical steel railway bridge in order to define cost-effective maintenance strategies and avoid the sudden interruption of the regular service with considerable economic losses. Railway bridges are indeed subjected to repetitive high stress due to the live loads acting on them, so they have to be examined to point out a possible fatigue failure. Real time structural health monitoring, however, may not always be available for maintenance purposes and for reporting progressive damage conditions up to failure. In this regard, a simple finite element model of the bridge is developed and employed as a simulation tool for numerical analyses. Moreover, a more accurate model is also prepared in parallel. The Modal Assurance Criterion (MAC) for the evaluation of mode shapes is exploited with the purpose of validate the two models respect to each other. In the absence of monitoring data on the real structure, a comparison between the previously developed models and others coming from independent studies is also performed. From that, it has been shown that the quality and the level of detail of a numerical model are a function of engineer's sensitivity and background and that modelling discrepancies can affect the results. Furthermore, the Late Acceptance Hill Climbing (LAHC) model updating algorithm is implemented with the aim of minimizing the disparities in behaviour of the models, improving consequently the fatigue life assessment of the bridge. The effect of model uncertainties is investigated on the most stressed components. Afterwards, the updated model is employed to evaluate the capacity losses of the bridges during its service period. An influence line analysis is conducted in the most critical sections in terms of shape equivalence and stresses magnitude. Lastly, taking into account eight different trains, Miner's cumulative damage law and S-N curves are used to assess the most damaged components, the most damaging trains and the residual service life of the structure. Hence, it is proven that, by exploiting simulations conducted on an optimized numerical model and the theory of fatigue, the estimation of the health of the structure is achievable.