STABLE AND DIVERGING TIME DEPENDENT BEHAVIOURS IN SOME TYPES OF BRIDGE STRUCTURES

ABSTRACT The behaviour of pre-stressed and cable stayed concrete bridges may be strongly affected by the time dependent response due to creep and shrinkage of concrete. Same experiences showed us that, even after accurate design assessments, some unsatisfactory service behaviour can arise, due to some level of uncertainty in the reference data. In this paper the role of the uncertainties has been investigated. As sources of uncertainty, the pretensioning forces in the cables, the relative humidity and the concrete strength have been considered. For a given set of data, the creep effects have been handled by means of a step by step computation of the stress history. The effects of the uncertainties have been simulated through a Monte Carlo approach. Two topical cases have been studied. The first set is exemplified by cable stayed bridges. In these structures, the role of uncertainties does not influence the time dependent behaviour sensibly and the system seems to be self-stabilizing over time. The second set is represented by prestressed cantilever-built bridges, for whom the effects of uncertainties cause a significant variance of the tip deflections. Finally, some suggestions to govern such type of delayed behaviours are proposed.