Effect of rheological parameter uncertainties on bridge design

Uncertainties in definition of mechanical and rheological properties of concrete may give rise to a significant influence on the serviceability behaviour of prestressed concrete bridges. In this paper, in particular, shrinkage and creep parameters are considered as stochastic variables, adopting, on the opposite, a deterministic value for relaxation, due to the severe quality control applied in prestressing steel production. Assuming a Gauss distribution for probability density of involved variables, an analytical expression for the evaluation of prestressing losses may be derived. It is then possible to reach an accurate prediction of probability density distribution of tensile stresses in concrete section extreme fiber. The proposed approach is then validated by means of a statistical simulation using the Montecarlo method. Finally comparing the probability distributions of tensile stress at the extreme fiber and the tensile strength in concrete, the probability to reach the crack formation may be evaluated.