Time dependent behaviour of an elementary bridge model in presence of uncertainties

During the last decades the excessive deflections of many long span bridges received wide attention both in the research and maintenance fields. The faults of the original previsions can be attributed to (a) lacks in the models adopted for the structural assessment, (b) weak reliability of some shrinkage and creep formulations used for the analyses and (c) differences between the phases of the actual erection techniques and those planned during the design tasks. In this paper the role of the uncertainty affecting quantities and parameters governing the whole attitude of these structures is outlined. With reference to simple but significant examples, it will be shown how some types of bridges possess low sensitivity to the uncertainties, while others result greatly affected by them, exhibiting divergent behaviors over time.