The long-term assessment of large civil infrastructures such as prestressed concrete bridges is a challenging task. The real time history related to the phased construction, the influence of the adopted constructive method, the characterization of the employed concrete and the environmental conditions are crucial aspects for accurate predictions based on Finite Element Models. Data from long-term monitoring systems have been used to improve the quality of those predictions, namely to validate the design assumptions, to calibrate the structural model, and to update the safety coefficients. The new bridge over the Tagus River in Portugal, the Lezíria Bridge, comprehends a 1700. m long viaduct, which was erected using a movable scaffolding system. A long-term monitoring system was implemented and measurements were taken since the start of the construction. Based on these measurements, this work presents the analysis strategy adopted to compute the long-term behaviour based on a Finite Element Model. A detailed scanning of all information with relevance for the viaduct behaviour was performed. A full discussion concerning the real long-term behaviour is made, focusing the differences between the measurements and the results obtained with the numerical model, namely the trends due to shrinkage and creep and the variations due to the temperature. Finally, concerning to the viaduct lifetime, the predicted values for the measured parameters are updated, since the predictions based on the European standard rules presents significant bias to be used as reference values regarding the viaduct surveillance.