Time-variant finite element reliability analysis - application to the durability of cooling towers

Durability of natural-draught cooling towers is investigated using finite element reliability analysis. A response surface of the linear finite element model is first derived from mechanical considerations. This surface is explicit and exact under certain conditions and requires a single multi-load finite element analysis. This leads to an analytical formulation of the reliability problem. The influence of concrete carbonation and the induced rebars corrosion is then studied in the framework of time-variant reliability analysis. It is shown that the problem reduces to a sequence of time-invariant problems that can be solved using the first-order reliability method (FORM). The evolution in time of the probability of failure in a single point is computed as well as sensitivity factors. Finally, an attempt to introducing space-variant reliability is made. The great difference between the numerical results obtained in the first and in the second approach is emphasized.